Chapter Index


Survey and field research methods: detection and identification of lorises and pottos in the wild, some literature about methods and sympatric species

Compiled by Helga Schulze with data by (in alphabetic order) Prof. Dr. Eberhard Curio, Bernhard Meier, Anna Nekaris, Ulrike Streicher (Endangered Primate Rescue Center), Frank Wiens and Annette Zitzmann.

Detection of lorises in the field. Eyeshine, sympatric species, search stretegies
    Sources of light recommended for field use
    Visible behaviour: movements helpful for identification of species; protective behaviour (flight, camouflage)
Indiviadual identification, recognition marking
Survey/census methods

Detection of lorises in the field

Relative size and distance of eyes  
Some Asian species:
Loris tardigradus (individual differences see identification key for subspecies)
Nycticebus sp.
Paradoxurus hermaphroditus, common palm civet
Felis chaus, jungle cat
Martes sp., marten
Herpestes sp., mongooses (basically terrestrial)
Some African species:
Arctocebus and Perodicticus
Galagos: .
  Euoticus sp.
  Galagoides demidoff
  In darkness with a torchlight, head lamp or other light. When the source of light is held close to the eyes of the observer, the tapetum lucidum in the eyes of the animals (reflecting layer of cells behind the retina) causes a reflection well visible as long as the animal is looking towards the light. The tapetum causes light rays to cross the retina twice and probably shifts ultra-violet light into visible wavelength for better vision in darkness. It occurs in many nocturnal and some diurnal and crepuscular species (see below); differences in the colour and strength of the eye-shine, the size and distance of eyes provide some information about identity of species. Even light of rather low intensity causes a visible eye-shine in Loris; the bright reflexion of N. coucang eyes is well visible from a distance of 200 m in the wild (B. Meier, unpublished; Petter, Hladik 1970; Barrett, 1984; F. Wiens and A. Zitzmann, pers. comm.).
Change of pupil size and shape with diminishing light intensity. 
Left: cat. Right: Loris

Sources of light used or recommended:

Use of red or infrared light (see below, technical equipment) has a number of advantages: it is not strongly reflected by surrounding vegetation, and at least some nocturnal animal species are unable or less able to see these wavelengths. Barrett (1984) confirmed this effect for Nycticebus. The animals are therefore less aware of observation, show a more normal behaviour and a diminished tendency to retreat or hide their faces for camouflage. Disadvantages of red light: it does not allow proper judgement of the colour of eyeshine, and its diminished intensity may be still sufficient in more open vegetation; in tropical rainforest, loss of light by canopy may make use of the stronger white light necessary (Southern 1955; Barrett 1984).

Lamps used by several authors: Barrett (1984): headlamp powered by a 6 v motor-cycle accumulator battery which delivered a steady current for 24-30 hours. Charles-Dominique (1971): strong white head-lamp with a light angle wider than the field of vision and two nickel cadmium accumulators fixed to a girdle. B. Meier (unpublished): strong pivoted spot-light (white) on top of a Landrover.

Southern (1955) tried infrared light and visible red light for observation; since military infrared "sniperscopes" provided an insufficient resolution and the high-pitched whine emitted by the transformer disturbed the animals, he preferred use of normal binoculars in combination with an automobile headlamp screened like a darkroom lamp to give visible red light.

Headlamps can for instance be obtained from the following sources:

Petzl Distribution Sport: Zone Industrielle, 38920 Crolles, France. Phone: x33-476 92 09 20; FAX: x33-476 08 82 04; petzl@dial.oleane.com; http://www.petzl.com: accumulator / battery headlamps including one which allows choice between bright halogen light with shorter duration and more dim "standard" light for longer observation with one set of batteries. This type of lamp, when equipped with an additional red filter in front of one lamp, might provide further possibilities to observe lorises.

CEAG Licht- und Stromversorgungstechnik, Postfach 305, Dortmund, Germany (accumulator lamps, including strong headlamps, for minery and other purposes)

Characteristics of eye reflection and other features helpful for detection and identification:

A tapetum is present in all prosimians with the exception of few diurnal and crepuscular Lemur species, but absent in tarsiers and in simian primates; Aotus lacks an eyeshine in spite of being nocturnal and having a kind of tapetum (Martin 1990, Rowe 1996). A conspicuous eyeshine is, for instance, also found in many nocturnal carnivores, particularly in cats, in some marsupials, rodents and fruit-bats (e. g. Pteropus) and in some birds (Boeckh, 1975; Grzimek, 1967; Martin, 1990)

Eyeshine characteristics:

In prosimian primates in general: golden-yellow or yellow-red (Martin, 1990)

In Loris: eye reflexion strong; when the eyes of the animal are directed towards the source of light, two large round orange spots, set very close to each other (see figure above), become visible. According to Singh et al. (2000) eye reflection in L. t. lydekkerianus in the fiels was orange from any direction whereas in other nocturnal mammals, for instance civets, eye colour varied with eye movements; civet eyes in addition were smaller. Typical way to glance for a moment at intervals, see also below: behavioural characteristics. Eye characteristics cannot be mistaken for those of sympatric other species in Sri Lanka; no such statement for India found. (B. Meier, pers. comm.; Petter, Hladik 1970; Nekaris 1997)

In Nycticebus pygmaeus: as in N. coucang

In Nycticebus coucang: strong orange or orange-red reflexion (Barrett 1984; F. Wiens, pers. comm.); because of similarity with other sympatric species (see below) characteristics of eye-shine alone are not sufficient for species identification, consideration of characteristic movement and eye-blinking patterns may be helpful (F. Wiens, pers. comm.)

In Arctocebus: ?

In Perodicticus: ?

Examples of sympatric species in Asia which might be mistaken for lorises because of eye-shine:

Carnivores: in general: eyeshine greenish-blue (Martin, 1990) or yellow (see below). Arboreal nocturnal carnivores in Sri Lanka: yellow-green reflexion (B. Meier, pers. comm.; Petter, Hladik 1970). Viverrids in Malaysia: some species with an eye-shine similar to that of N. coucang, but different movements and eye-blinking patterns (F. Wiens, pers. comm.). Palm civets, particularly Paradoxurus hermaphroditus, in Malaysia: yellow to orange, somewhat similar to N. coucang (F. Wiens, pers. comm.). (Barrett, 1984, mentions white or lemon-yellow reflexion). Cats: yellowish eyeshine (Boeckh, 1975: no information whether referring to all cat species or domestic cats only).

Rodents: flying squirrels, for instance Petaurista petaurista, in Malaysia: yellow to orange (F. Wiens, pers. comm.). (Barrett, 1984: white or lemon-yellow reflexion, somewhat similar to N. coucang)

Fruit-bats (e. g. Pteropus): tapetum present, no information about colour of eyeshine (Martin 1990)

Ungulates (hoofed mammals): greenish-blue eyeshine (Martin 1990)

Birds: Long-tailed night-jars (Caprimulgus macrurus) have a colour of eye-shine similar to that of N. coucang, but usually only one eye is visible, and the animals are found sitting in characteristic places, on lookouts such as masts (F. Wiens, pers. comm.)

Sympatric species in Africa with reflecting eye background:

Galagos (Galagoides allenii,Galagoides demidoff, Euoticus elegantulus): orange to whitish eyeshine? (Colour seen in G. moholi in Bochum and on photos of several species in Rowe, 1996; Martin 1990); galagos can be identified by their characteristic calls (Charles-Dominique; 1971; Bearder et al., 1995, Ambrose, Bearder, 1995). Usual time, frequency of calling?

Viverrids: for instance African linsang or Oyan, Poiana Richardsoni (arboreal, nocturnal); African palm civet, Nandinia binotata (arboreal, nocturnal and black-legged mongoose, Bdeogale nigripes (usually terrestrial, nocturnal, predominantly insectivorous) (Charles-Dominique, 1971, Charles-Dominique 1977, Nowak 1991)

Rodents? Martin, 1990, mentions greenish-blue eyeshine in Pedetes, a terrestrial species of dryer areas.

Fruit bats (Charles-Dominique, 1971)

Ungulates (hoofed mammals): greenish-blue eyeshine (Martin 1990)

Birds: owls, night jars (Charles-Dominique, 1971)

Sympatric species in the different regions of distribution area which can be mistaken for slender lorises because of size, appearance, similar vocalizations or movements? (Viverrids, martens, arboreal cats, other arboreal species? Birds? Similarity of lorises with small owls?) See under references: literature about sympatric species.

Behavioural aspects:

Visible behaviour: movements helpful for identification of species; protective behaviour (flight, camouflage)
Hiding of the face or hiding are typical behaviours in lorises when disturbed (see figure).

The manner in which slender lorises glance at and look away from the light is helpful for identification in connection with eye reflektion (B. Meier, unpublished; Nekaris 1997). According to Petter and Hladik (1970), Loris eye reflection in the wild was seldom visible for more than a second whereas nocturnal Malagasy lemurs looked towards the light for rather long periods. Barrett (1984) mentioned that observation with red light does not cause the eye-blinking pattern otherwise characteristic for lorises. In the captive Loris tardigradus nordicus at Ruhr-University, hiding of the face / turning the face away from an observer is regularly shown as a sign of stress when shy animals are approached by a human. In spite of their usual curiosity, shy animals may freeze for longer periods in a posture in which they cannot see the approaching human. This is probably a camouflage behaviour (hiding of the conspicuous facial markings). Kingdon (1997) confirms for Arctocebus c. calabarensis in the wild that normal census methods with use of torchlights are unsuccessful because the animals hide their heads and eyes at the least disturbance. Slender lorises habituated to observation may look into a torchlight for somewhat longer periods when curious, but they may also look aside as though they dislike the light shining into their eyes. In captivity, slender lorises are cautious when perceiving something unfamiliar, but they may become well habituated to a wide variety of regularly-occurring stimuli. Considerable difference in the reactions towards stimuli have therefore been observed. In the wild, too, different local habituation of animals, for instance to cars or people, might lead to different survey results; and adaptation of survey methods to local conditions might improve the results.

Freezing for camouflage apparently is a behaviour typical for all Lorisinae / Loridae; it is common in captive Loris and is also reported for Arctocebus and Perodicticus in the wild (Charles-Dominique, 1971). Inconspicuous, silent flight, particularly upwards, and hiding behind foliage or other cover are typical protective behaviour of the captive L. t. nordicus of Ruhr-University when being disturbed and are as well described for Loris from the wild (B. Meier, unpublished; Petter, Hladik 1970). According to Charles-Dominique (1977), pottos in the wild, noticing an observer in fairly close proximity (about 20 m) in all cases became immobile. When approach continued, they fled; when the observer remained immobile for 1-2 minutes, they very slow moved away, moving limbs one-by-one, immediate freezing at the slightest movement of the observer. This reaction in addition was dependant on the quality of environment: the animals fled rapidly if hiding in the proximity was possible; where environment provided no opportunity to escape, for instance in isolated trees, freezing was more frequent. In N. coucang, F. Wiens (pers. comm.) observed similar behaviour.

On the other hand, in Loris, captive observation showed that cautious approach and exploration of sources of unfamiliar stimuli is a very characteristic behaviour, apparently vital for the animals´ safety (Schulze, Meier 1995). Balance between curiosity and caution was found to be dependant on individual differences and experience of animals and on the kind and size of stimuli: small visible objects were approached quicker and more readily than otherwise equal large objects (T. Milinski and S. Frank, unpublished), noise of rattling of breaking twigs clearly caused flight or hiding. During search for Loris in Sri Lanka with a head-lamp or car spot-light, the following strategy worked well: switching off the light at intervals and remaining completely silent and motionless for at least 1-2 minutes, lying motionless on the ground or car top, avoiding conspicuous eye movement or glintering of teeth (captive lorises show a fine perception of slightest movements). The lorises then apparently tried to find out where the origin of the disturbance had vanished, climbed an outlook or even approached the observer, and suddenly switching on the light again and quickly trying to scan the forest showed their eye-shine (B. Meier, unpublished). F. Wiens mentions for N. coucang that animals habituated to observation often did not look towards the observer. In such cases, waving with the torch-light often helped. (See also above: red light). MacKinnon and Phillips (1993) mention "pishing" (making sibilant, squeaking or rasping sounds) to make certain bird species approach and investigate the source of the sound.

Places / altitude where the species have been found in earlier studies:

Loris: occurrence reported higher in large trees (L. t. grandis in rainforest near Kandy) to low altidude in bushes; occasionally walks on the ground.

N. coucang: as in Loris

Arctocebus: prefer lower altitude; detection therefore less difficult than in pottos. Prefer substrate with small diameters, particularly vertical lianes (Charles-Dominique, 1971).

In Perodicticus: higher in the trees, detection very difficult (Charles-Dominique, 1971).

Search strategies:

During search for Loris in Sri Lanka in 1979 and 1980 (B. Meier, unpublished, duration: 12 weeks), a pivoted spot-light on top of a Landrover was used to spot the occurrence of Loris eye-reflection at a speed of 10-15 km/h. To test the method, the same road was repeatedly searched on 10 different days, and 15 of 20 times lorises were seen in the same areas.

MacKinnon and Phillips (1993) mention that the speed of movement of an observer through the forest has a considerable influence on the result of surveys: an observer moving slowly in order not to miss anything will see lots of individuals but will be likely to miss the species which silently move away and hide when noticing him. Quick, silent moving or quiet sitting for a while may lead to observation of animals never seen otherwise. MacKinnon and Phillips recommend a combination of all three methods by turns for survey, with observers being silent and dressed in drab, never white clothes.

Activity peaks may also play a role in the probability to detect animals (MacKinnon and Phillips, 1993). For lorises and pottos, studies indicate activity throughout the night with or without some increase of activity in the beginning and end of the night (Seitz 1967; Durrell 1949, quoted by Seitz; Baudenon 1949, quoted by Seitz, data from Ruhr-University). In the captive lorises at Ruhr-University, activity regularly decreased after consumption of larger amounts of food.

Strong wind may make detection and observation easier because the animals climb down to lower altitudes (Streicher, pers. comm.).

Gill et al. (1997) mention use of portable thermal imaging for estimating deer population density in forests with varying visibility, "clearly revealing warm-bodied animals even if partly obscured by vegetation", animals in this study could be detected at so long distances that disturbance was minimized or prevented; lorises, however, are much smaller, usually living in a rather warm environment and keep at least their distal parts cool in order to save energy; so it seems doubtful whether infrared wave detection can also help to detect them

Charles-Dominique and Bearder (1979) used traps in addition to searching for rainforest lorisids and caught several pottos in an area in which a survey had been unsuccessful. In the course of a field study on slender lorises, a total of 1150 hours of trap nights in the areas where animals were sighted, with sixteen Tomahawk and four Havahart live traps baited with honey -banana bait of Tomahawk Trap Company, ripe fruits and crickets, remained without any success, animals were then obtained by climbing trees and catching them by hand (Kar Gupta 1995; Kar Gupta 2001: pers. comm). Detailed information about mark-recapture and other trapping for surveys is provided in Skalski and Robson (1992) and Sutherland (1996 a). In the paper on hand, no recommendations how to catch lorisids with traps are included in order to avoid use of such information for other than conservation purposes. Some captive slender lorises at Ruhr-University showed behavioural changes for 1-2 years after traumatic events (catching, transfer to unfamiliar environment), apparently trying to avoid certain stimuli reminding them of the stressful situation. In house mice, individual reaction to traps ("trap-proneness" and "trap-shyness") were found to be similar in parents and offspring and apparently independent of experience in traps (Crowcroft and Jeffers, 1961).

Charles-Dominique and Bearder (1979) tried to minimize traumatic effects of capture by regular inspection of traps during night to avoid animals being kept prisoner for a longer time; in animals caught with insufficient care, re-catching turned out to be very unlikely. Harcourt (1987) set traps (for Microcebus) for a few hours only and avoided to set them in rainy nights. Kenward (1987) describes a possibility to control traps by magnet-operated radio transmitters (magnet pulled off the transmitter when the trap is operated).

Sutherland (1996 b) mentions hair collecting facilities which may help to determine occurrence of species without traumatic capture. Hair tubes ( for smaller mammals) are tubes of a width slightly larger than the study species with double-sided sticky tape stuck to the inside; hair catchers are facilities with wire-brush-like structures animals are encouraged to squeeze through. Such facilities, baited ore just attached where animals are likely to pass, are left in the field for 1-2 weeks. For a lynx study, a "perfume" containing pheromones was developed for use with hair catchers; the animals rub their head glands on the scent bait, trying to deposit their own marks (Karge, 1999). Hair catchers can be used in combination with a reference collection or identification key for hair of sympatric species or for DNA studies.


In Loris, territorial whistling, chittering and other vocalization occur (Schulze, Meier 1995). According to Petter and Hladik (1970), humans can hear Loris whistling over a distance of 100 m. Singh et al. (2000) used territorial whistles for detection during a survey. In Zimmermann (1995 a, b), oscillograms and sonagrams of whistle calls of Loris, Nycticebus coucang, N. pygmaeus and Perodicticus potto are published.
Further information about vocalization in our behaviour database.

Voice recognition? Sympatric species with vocalizations which can be mistaken for loris / potto vocalization? The ornithologist Bill Evans, Cornell University, Ithaca, developed a voice recognition software which compares vocalization with a "library" of sonagrams of species; it identifies calls more reliably than even human observers and can record the presence of species in the field without observers being present ("Nickerchen ...", 1995)

Differences in vocalization within genera, species / subspecies differences? Vocalizations of large grey and small brown or reddish Loris forms from Sri Lanka, kept at Ruhr-University, sounded similar; there was no evidence for vocalization differences helpful for distinguishing slender loris forms as described in galagos (Bearder et al., 1995, Ambrose, Bearder, 1995).

Voice archives: for instance:

National Sound Archive, Wildlife Section, 29 Exhibition Road, London SW7 2AS, GB, R. Ranft, Curator; website: http://www.bl.uk/collections/sound-archive/nsa.html, searchable catalogue: http://www.bl.uk/collections/sound-archive/cat.html

Tierstimmenarchiv (animal voice archive), Museum für Naturkunde, Humboldt-Universität, Institut für systematische Zoologie, Invalidenstr. 43, D-10115 Berlin, K.-H. Frommolt, Curator (Frommolt, 1993; Frommolt, pers. comm.). Website: http://www.biologie.hu-berlin.de/~tsarchiv/index.html, catalogue: http://audentify.iai.uni-bonn.de/contents/searchtext.php

Bird-watchers use playback of tape-recorded vocalization to cause a reaction; MacKinnon and Phillips (1993), however, mention that too frequent use particularly of tape recordings of territorial calls may disturb territorial behaviour and reduce the natural alarm responseds of the animals. In captive slender lorises, aggressive behaviour between formerly peaceful mates occurred as a consequence of territorial whistles by animals in neighbouring cages.


In N. coucang and N. pygmaeus, gnawing of branches may leave visible traces. Gnaw marks found in a tree species in Vietnam at an altitude of 8 m after observation of pygmy lorises had an average diameter of 2.5 cm and were encrusted by dried exudates, suggesting that lorises had supplemented their diet with gum or sap (no feeding behaviour was observed). Gnaw marks produced in captivity might be a sign of boredom (Tan 1994; Schweigert, pers. comm.; Streicher, pers. comm.; gum-feeding in N. coucang reported by Barrett 1984).

Nycticebus pygmaeus gauge hole. Photo: Ulrike Streicher, Endangered Primate Rescue Center, Vietnam Gauge marks of captive Nycticebus coucang (redrawn from a photo of branches in the collection of K.-H. Schweigert)


    Loris faeces
Faeces, smell: Loris faeces are small, firm and fall down where the animals are just active. Slender lorises do not fecally mark branches, and in the captive colony of Ruhr-University there were no places where conspicuous quantities of faeces were deposited. Territories are marked with small quantities of urine deposited on branches; such markings are optically inconspicuous, but easily watersoluble, some urine will probably be washed down by rain. During normal emission of urine, some drops to the ground. Detection of lorises, their faeces or urine with trained dogs might be a possibility to improve survey results. Zwickel (1980) gives a review of possibilities to use dogs in wildlife management and provides addresses where to obtain further unpublished information. He mentions that dogs may be useful in studies of marking behaviour, activity sites and refuge behaviour, that collection with dogs gives almost unbiased data on food habits of some species and less sex and age biased results than for instance catching of animals with traps. Particularly in animals located higher in trees behind foliage, dogs might be a valuable help.

Offering of food mixed with indigestible markers to animals might help to get information about range sizes. Kenward (1987) proposes coloured fibres; in tests with otters (Schulze, unpublished), small parts of coloured feathers and different small seeds worked well.

Individual recognition, marking of animals:
Numerical marking up to 15 by marking different limbs. Based on Renner, 1996. Dying of the fur or cutting ring-shaped gaps into the fur around the limbs might work in lorises (not yet tested).
  Nocturnal conditions (changed colours, general vision) in connection with the different altitude of animals in the trees make an individual identification and estimation of size difficult (F. Wiens, pers. comm.). Catching and marking wild animals may help to determine population density without counting individuals twice. But marking requires consideration of consequences for the animals, including for instance: susceptibility to traumatic effects of capture (capture shock in certain species leading to death by chilling or predation, see Kenward 1987, Ginsberg et al., 1995). Effects on study results caused by capture, handling and / or marking, danger of strangling or getting stuck, increased detectability of marked animals to predators, local laws, visibility of marks from the distance, their longevity and the number of animals supposed to be distinguished must be considered. Ryder (1978) describes possible traumatic effects of different kinds of immobilizing and other drugs on wild animals and discusses humane methods, including the use of "biodegradable" material, decaying after the period for which it is needed, for marking to minimize the need for recapture.

Handling of animals caught for marking and examination; use of drugs: see separate chapter, in preparation; some information can be found in our first aid chapter, the chapter about self-protection when handling these species which produce a toxin, and the chapter about anesthesia and tranquilizers.

A variety of numerical marking codes are in use, independant from the kind of marks used (examples: see figures on the next page; the ear marking code shown represents one of several systems in use, it makes a maximum of two marks per ear necessary). Combination of such codes with markings of different colours may allow individual marking of large numbers of animals. Rice and Kalk (1996) provide a review of standard marking methods, including addresses where to obtain necessary equipment. See also Stonehouse 1978.

Non-invasive temporary marking: Rice and Kalk (1996) mention dyes (Nyanzol), bleach, paint sticks and balls of paint shot with a gun, causing marks with a duration of usually less than a month. Longer-lasting marks might be achieved with certain human hair dye or hair-clipping in certain parts of the body. Markings with Nyanzol-D, a black hair dye which has been repeatedly used in animal studies, were visible for 7 months, until mold. The powder is mixed with water, for fixing this dye solution to the fur hydrogen peroxide solution is needed. The two solutions can be mixed together to facilitate the process. (Chihuahuan desert lab manual: Prairie dogs website). Megna (2001) for instance remommends a mix of 12 cc water, 12 cc over-the-counter hydrogen peroxide, 48 cc rubbing alcohol, and 1 heaping tablespoon of dye, stirred well, allowed to sit a while, stirred again and applied with a sponge-type paint/craft brush. More information see Laboratory Primate Newsletter 40 (3), July 2001: Marking Monkeys - Nyazol D. The former dye factory „Nyanza Chemical Company“ was closed in 1978; but Nyanzol might be available from Albinal Dyestuff Intl., www.albanildye.com (Giles 2000, F. Loureiro, pers. comm.). In animals with dark fur bleached marks may be better visible. Day, Schemnitz and Taber (1980) provide further information about different dyes and possibilities to apply them to animals, for instance with a paint pistol by the Nelson Paint Company, operated by CO2, which allows dying of animals with paint pellets at a distance of 15 m. They mention that for instance picric acid applied on rabbits was still well visible after seven months. F. Wiens (1995, unpublished) noted that on slow lorises dark colour spots were well visible from some distance; light marks were less well visible.

Permanent, invasive visible marking:

Tattoos are usually not well recognizable from the distance even if rather hairless parts are tattoed, and in some species tattoos are less permanent than in others (Rice and Kalk, 1996). Tattoing on the plantar side of feet or medial surface of the upper thigh has worked well in some lorises, but in other individuals, tattoos became unreadable or vanished. There is some evidence that too dense tattooing in Loris may lead to skin necroses and subsequent vanishing of the tattoos (observation at Ruhr-University). In small ears, ear tattoos may lead to extensive damage and atrophy of the ear (Rice and Kalk, 1996).

Ear-notching (cutting notches into the ear pinnae or using a special plier-punch) is commonly used in laboratory and zoo animals, but it is an amputation and not allowed everywhere. Ryder (1978) regards this marking method as not humane. Rice and Kalk (1996) mention excessive bleeding after ear-notching adult individuals. In slender lorises, blood-vessels leading along the ear rims probably play a role in the regulation of body temperature (see figure).

Laboratory animal marking by ear notching. Left: sites for numerical marking of the ear rim up to number 100. Based on Rice and Kalk, 1996. Example: 68 = 1 + 7 + 20 + 40. Right: marking method recommended by Renner, 1996. But see right figure for possible disadvantages of such an invasive marking method Enlarged bloodvessels in a Loris ear during high ambient temperatures

Ear tags

Ear tags are commercially available in numerous sizes, different colours or with numbers. Tagging means piercing of the ear pinna; plastic tags seem to be less likely to cause infections. Size and thickness of the ear, location of stiffer cartilage or large blood vessels ought to be considered when chosing place and weight of tags (see also Rice and Kalk, 1996). Ear tags are well visible, but they may be torn off or get lost.


is a permanent, well-visible marking method which has been used for animals of the size from neonatal mice to elephants; it is regarded as painless because the tissue is cooled down to numbness and nerves are believed to be inactivated for several weeks by freezing. But the method still needs development, the final well-visible marks appear with delay, and good results depend on correct marking: after cooling of the skin to such a degree that melanocytes in the hair follicles are permanently destroyed, the superficial epidermis and hair is shed within weeks, and the new hair growing after 1-3 months is white. Excessive freezing causes scars instead, insufficient freezing causes incomplete marks. Freeze-marking can for instance be done with a thick copper tool cooled down in a mixture of dry ice and 95% alcohol (Rice and Kalk, 1996).

Attaching of collars, leg bands, radio transmitters and other tags:

Kenward (1987) mentions the following possible consequences of radio tag attachment besides possibly traumatic effects of capture, handling and presence of tags: temporary increase in grooming on costs of other behaviour, desertion of offspring by tagged parents or parents rejecting tagged offspring, skin lesions or reduced insulation and increased energy expenditure by damaged fur / feathers because of badly-fitting tags, reduction of agility in low weight individuals. Kenward recommends initial longerlasting tests with captive individuals of the species in question, when possible, before attaching tags to wild individuals. Broad collars are well visible, but need regular control to ensure that they do not cause health problems (Rice and Kalk, 1996). In lesser slow lorises, collars might cause problems because of seasonal weight changes which may also alter neck circumference considerably (U. Streicher, Endangered Primate Rescue Center). Loss of weight in slow lorises might lead to loose collars increasing the danger that twigs stick fast between collar and neck; in fact broken twig remnants were found under a collar (F. Wiens, pers. comm.). Lightweight stainless metal bead chains (see figure) have been successfully used as collars in small mammals (E. Curio, Ruhr-University Bochum, pers. comm.; Luft, Curio 2001); such chains can for instance be obtained from PÖSAMO chain factory Pötz & Sand, Frohnstr. 44, 40789 Monheim, Germany, or via a czech PÖSAMO factory. Luft and Curio successfully used these chains for marking bats and for attaching radio transmitters to them because they are lightweight (less than 0.7 % of body weight of the bats marked) and have no sharp edges; no dirt can stay under the rotating balls, causing skin problems, and their length is easily adjustable. Luft and Curio closed the chains with stainless steel locks with four-digits numbers laser-engraved on them for individual marking. The locks can be secured against loss by filling them with some glue; Luft and Curio closed them and in addition reduced abrasion of fur through the lock by covering it with soft silicon tubing (which was semi-transparent to allow reading of the numbers on the locks). Marking of lorises with such chains around the wrists? Hidden under fur, such chain collars do not allow identification without handling; individual identification from the distance might be possible by attaching short coloured tassels to the chain (see figures below), but this method has not yet been tested.
In Loris, coloured plastic pigeon leg bands with an inner diameter of 8-9 mm, fixed around the wrists, turned out to be well visible even from some distance. The type of rings used (flat elastic tape rolled up) allows spreading of the rings and attaching them to the animals cautiously with the help of a second person. Captive animals carried such bands for years without any problems; only in two cases, lorises managed to get rid of their ring. In pygmy slow lorises at the Endangered Primate Rescue Center, Vietnam, no problems caused by the rings were observed, but in animals living in groups some arm rings were damaged by chewing or lost. Chewing was not observed, so it is unknown whether the animals themselves or conspecifics removed the rings (U. Streicher, unpublished). For slow lorises, at least the rather small pigeon rings cannot be recommended even though they are elastic and widen when spread; when such rings were tested on several confiscated slow lorises in Indonesia, one developed problems (swollen hand; after removal of the ring a wound was detected under it); the rings then were all removed (Femke den Haas, pers. comm.). F. Wiens (pers. comm.) made attempts with arm and leg bands on two wild slow lorises; both animals somehow managed to get rid of the ring.
Plastic bird rings might be secured by agglutination with acetone (B. Meier, pers. comm.)

Recognition marking with collars and bracelets

Stainless steel bead chain used for marking fruit bats. Redrawn from a photo by E. Curio, Philippine Endemic Species Conservation Project. This type of chain is lightweight, can be well adapted in length and no dirt can accumulate under it.  Coloured bird ring around the wrist of a pygmy loris. Photo: Ulrike Streicher, Endangered Primate Rescue Center. This type of ring is too narrow for use in larger slow lorises, and under the broad ring dirt  may accumulate and cause skin problems if it´s not loosely fitting. Loose bracelets on the other hand may increase the danger of getting caught in some cleft. (In captive slender lorises, however, this kind of bracelets was used for many years without causing problems)


Some more ideas for recognition marking with coloured tassels

Tassels made of coloured fibers, attached to a bead chain with loops. Photo taken in daylight. Three tassels, left: material for production of fly-fishing lures; middle, straigt fibers: dyed artificial hair from a barber´s shop. Right: two tassels made of stripes of metal-like reflecting plastic foil. The tassel bases were made as slender as possible to minimize the risk that the animal gets hooked in any cleft. This type of marking has not yet been practically tested.
The same tassels as in the photo left, seen with infrared night vision equipment (Sony Handycam digital video camera with night shot function). Colour differences are invisible, reflecting properties in infrared light apparently differ from reflexion in daylight. But differently reflecting tassels of varying structure and lenght should allow development of marks distinguishable with infrared night vision equipment.
Photos: H. Schulze
Tassel made with stainless steel loop and Stabilit epoxy glue.

Idea how to insert a piece of biodegradable material in a bead chain: fine leather shoe string attached in two bead chain locks with knots. The string may be further attached by filling the locks with glue. Information about the time after which biodegradable materials fall off under different climatic conditions is still lacking.


Use of "biodegradable" material, decaying after the period for which it is needed, as proposed by Ryder (1978, see also above), would certainly be a good idea in field studies, but at present information about practical solutions is lacking. A recognition mark caused to fall of by a radio signal would allow removal after finishing a study, minimizing the risk for the animal (see Kenward, 1987)

Light-emitting markers may allow easier retrieval of marked animals in darkness. (Risk that such markings also help predators to locate the animal?). Beta lights are fluorescent markers which may operate 10-20 years and are visible at 400 m. They consist of sealed glass capsules internally coated with phosphorus and filled which tritium gas which emits low-energy beta particles causing the phosphorus to glow. They are available in different sizes and colours, for instance from Saunders-Roe Development Ltd., Millington Road, Haynes, Middlesex UB3 4NB, U. K.; beta light in connection with radio transmitters can be obtained from Biotrack, Stoborough Croft, Grange Road, Stoborough, Wareham, Dorset BH20 5AJ, U. K., phone: x44-1929 552992, e-mail: brian@biotrack.demon.co.uk or sean@biotrack.demon.co.uk. For use of Beta light a permission from radiation safety authorities such as the Nuclear Regulatory Commission in Washington is necessary (B. Meier, pers. comm.; Lehner 1979 and 1996; Kenward 1987; MacDonald, 1978; Wolcott, 1980, Day, Schemnitz and Taber, 1980). Lehner (1996) mentions other methods for luminescent marking. Buchler (1976) described production and use of a chemiluminescent tag weighing less than 0.5 g, filled with liquid from CYALUME chemical emergency light sticks, which gave light for several hours after mixing of the chemicals. Lemen and Freeman (1985) used a pigment powder, fluorescent under ultraviolet light, with low toxicity: small mammals were caught in traps, their fur saturated with the fine powder. After being released, the animals left traces of the powder during first night which persisted until next heavy rain.

So far, too little is known about the risks caused by attaching collars, bracelets or other marks to wild animalls over a longer period.
Hair clipping on one or several limbs is probably the least dangerous method for producing recognition marks visible from the distance

Survey / census methods:

Sampling is done for determination of species, of numbers of individuals in a given area or population, population dynamics and answers to many ecological questions. For development of a sampling program, one essential step is the comparison and evaluation of potential sampling techniques. Usually this is done by randomly locating sites in a habitat and collecting one sample unit by each sampling technique being considered; care should be taken that one technique does not interfere or bias another one (Pedigo, 1994; Buntin, 1994). Changes of habitat quality or behaviour of the species, for instance weather conditions, annualperiodic differences in density of foliage, changes of distribution / abundance of food, migration, occurrence of hibernation / torpor periods, increased or decreased caution in relation to breeding periods might influence results.

Standardized methods for determination of population density in general and of average population density in a larger area with uneven distribution or differences in detectability of speciemens: see literature about biological and geographic survey methods below, under references

Some terms concerning population survey methods:

Sample / sample population: part of a larger population examined
Sampling: basic quantitative collection of population data, for instance concerning density, dispersion, age structure or other properties of the population, from a part of a population, subsequently generalising from the sample to the whole population. Samples must be representative of the whole, otherwise generalisation to the whole will produce biased results (based on Greenwood, 1996, changed.
Random sampling: n possible samples with the same probability for each sample to be selected
Count / direct count: counting individuals for instance in a study population / area / herd
Census / true census: counting all individuals in a population (Pedigo, 1994)
Survey: usually an organized program with detailed, established protocols for monitoring animals (Higley, Peterson 1994)
Monitoring: studying the development of populations or their environment over a period of time, using the same techniques of monitoring each time or, if the decision is made to change techniques, with a time of overlap in which both methods are used to determine the relative efficiency of both for calibration of data (adapted from Greenwood, 1996); broad sense, often only qualitative sampling used to trigger more precise quantitative sampling programs, for instance in seasonally occurring species (Higley, L. G.; Peterson, R. K. D., 1994). (Greenwood, 1996, used the term "surveillance" for observation of changes over time).
Population index: measurement related to the actual total number of animals (ideally the ratio of index to number should be constant: I/N = K; I = population index, N = number of individuals, K = index ratio, K may be known or unknown). Examples of indices: number of animals seen while standing in a place during a certain period or while walking a certain distance or number of calls heard in a standard period. Indices can be compared to other indices (for instance of different places or times). Judgement of comparability, however, depends on knowledge of the examined species, because detectability, frequency of calls or other counted events may vary. Standardisation, for instance similar weather conditions,the same time of day or season and similar methods for data collection or multiple randomized observations are necessary. (Based on Greenwood, 1996, changed).

Some terms used for describing properties of populations: (based on Pedigo, 1993)

Absolute population density: total count or estimate of all individuals in a given area (Pedigo, 1994).
Absolute population estimates: actual numbers of individuals on a given surface-area unit (Pedigo, 1994).
Estimates of the total population: counting all individuals of a representative unit of the population (for instance in a certain area) (Pedigo, 1994)
Basic population estimates: number of individuals per standard unit of habitable space. The standard unit for a species / population, for instance ft² of branch surface, may be established formally by a group of researchers or informally through traditional practice (Pedigo, 1994).
Relative population estimates: no direct relationship to land surface area, but referenced to the sampling technique used (Pedigo, 1994)
Density: an expression of abundance of a species / population in an area
Dispersion: the spatial distribution of individuals of a species / population
Natality: birth rate
Mortality: death rate
Age structure: relative proportions of individuals in different age classes
Population growth (population growth form): shape of population growth curve

Population density of Lorisinae / Loridae: methods used in earlier studies and general considerations concerning lorises or pottos or their habitatsSingh et al. (1999) recommend "fixed point line transects" (Burnham et al. 1980) as the best method because, although males on occasions moved as far as 00 m durinng a single night´s activity, females seldom moved more than a few metresEstimation of number of animals remaining undetected, dependant on density of vegetation, altitude of trees, preferred altitude of stay? Charles-Dominique and Bearder (1979) recommend to note the distance of detected animals from survey pathways for every type of vegetation (with use of a surveyor´s tape or calibrated string, when necessary, because distances in the rainforest are easily overestimated) and to consider only the strips on either side of the path for population density estimates in which no reduction of the number of animals because of distance from the path was found. At Makokou, Gabon, the following distances for fairly good detection of animals were determined: Undergrowth of primary forest: 30m. Canopy of primary forest: 30m. Flooded primary forest: 20m. Secondary forest and tree-fall zones: 20m. River banks surveyed from a canoe: 10 m

Danger of wrong population density estimates because of patchy or uneven distribution of animals?

A 12-week search in Sri Lanka in 1979 and 1980 (Meier and Nieschalk, unpublished) showed that in most examined areas lorises appeared to be absent even when the habitat appeared to be suitable, whereas in several pockets of 50-100 km² high population densities were found for no evident reason. Data of densities only from locations which are chosen for surveys because of occurence of lorises at higher densities might therefore cause misleading population density estimates and underestimation of threat. Standardized methods for determination of population density in general and of average population density in a larger area with uneven distribution? See literature below.

Danger of wrong estimation of population density if survey pathways are leading along types of habitat different from average forest cover? For the Bornean rainforest, MacKinnon and Phillips (1993) mention that forest edges with light falling in sideways, for instance along roads, are very rich feeding zones with a rather dense bird population, better observation possibilities and particularly inhabited by "forest-edge species". Literature reports (Petter, Hladik 1970, Johnson 1984) indicate that slender lorises were detected close to roads or in forest rims close to water, but it is not quite clear whether this was due to use of roads or boats for searching or due to a preference of forest rims by the animals.

Is the distribution constant or does it change, for instance with seasons? Petter and Hladik (1970) mention L. t. nordicus which during nine nights in December / January were found close to a lake, whereas in May and October several animals were detected close to a road a few hundred meters further east, more distant from the shore of the lake. They concluded that in slender lorises the location of range / teritory may vary in the course of the year. So far, no reports about longer or regular migrations have been found. Slender and slow lorises may walk over the ground to reach distant trees (Petter, Hladik 1970; F. Wiens and A. Zitzmann, pers. comm.).

Some literature concerning collection of habitat data:

Basic methods for habitat analysis and description are described by Gysel and Lyon (1980) and Jones and Reynolds (1996). Korschgen (1980) provides a review of procedures for food-habits analyses, such as sampling and analysis of stomach contents and faeces; further information about methods for analysis of faeces are for instance provided in Dickmann and Huang (1988). Hutchins (1994) gives a review of techniques used for quantitative sampling of arthropods. Nagy and Haufler (1980) describe analysis methods for determination of forage nutritive quality.

Some literature references: planning conservation projects

Caldecott, J. O., 1996: Designing conservation projects: People and Biodiversity in Endangered Tropical Environments. Cambridge University Press, Cambridge. ISBN/ISSN 0-521-47328-4 (Hardcover).

Margoluis, R.; Salafsky, N.; Balla, A. (Illustrator), 1998: Measures of Success : Designing, Managing, and Monitoring Conservation and Development Projects. Island Press. ISBN: 1559636122  (Paperback, 363 pages)

Some literature references: field methods, biological and geographic survey methods

Feinsinger, P., 2001: Designing Field Studies for Biodiversity Conservation: The Nature Conservancy. Island Press. ISBN: 1559638788 (Paperback: 224 pages)

Barnett, A., 1995: Primates: Expedition Field Techniques. By Expedition Advisory Centre, Royal Geographical Society, London.

Boitai, L.; Fuller, T. K., 2000: Research techniques in animal ecology: controversies and consequences. Columbia University Press, New York.
ISBN: 0-231-1134-4 or ISBN 0-231-1134-2.

Giles, R. H. (ed.), 1972: Wildlife management techniques. 3rded., rev. The Wildlife Society, Washington, D. C. ISBN: 0-933564-08-2.
    Giles, R. H. (ed.), 1969: Wildlife management techniques. The Wildlife Society, Washington, D. C.

Hayek, Lee-Ann C.; Buzas, M. A., 1997: Surveying natural populations. Columbia University Press, New York. Hardback. ISBN: 0-231-10240-2.
= Hayek, Lee-Ann C.; Buzas, M. A., 1998: Surveying natural populations. Columbia University Press, New York. Paperback.
Content: statistical principles for quantitative population surveys.

Hill and Clayton, 1985: Wildlife after dark: a review of nocturnal observation techniques. Occasional paper no. 17, James Ford Bell museum of Natural History, University of Minnesota, Minneapolis. 23 pp. (Quoted in Lehner 1996)

Kenward, R., 1987: Wildlife radio tagging. Equipment, field techniques and data analysis. Academic Press, London.

Lehner, Philip N., 1996: Handbook of ethological methods, 2. ed. Cambridge Univ. Press, Cambridge. 672 pp. ISBN 0-521-55405-5
    Lehner, Philip N., 1979: Handbook of ethological methods. Garland STPM Press, New York, London. ISBN: 0-8240-7024-0.

Sutherland, William J., 1996 a: Ecological census techniques: a survey. Cambridge University Press, Cambridge. ISBN: 0-521-47244-x.
Content: survey methods; methods for estimation of population size in plants and animals; methods for measuring environmental variables such as weather, water chemistry and soil composition.

Skalski, John R.; Robson, D. S., 1992: Techniques for wildlife investigations. Design and analysis of capture data. Academic Press, San Diego (u. a.). ISBN: 0-12-647675-6
Content: capture - marking - recapture data: evaluation, incorporation into population investigations; quantification in changes of animal abundance, assessment of environmental impact.

Ritchie, William; Wood, M.; Wright, R.; Tait, D., 1988: Surveying and mapping for field scientists. Addison Wesley Longman ISBN: 0-582-30086-x.
Content: geographic surveying techniques; mapping.

Ritchie, William; Tait, D. A.; Wood, M.; Wright, R., 1977: Mapping for field scientists. A problem.solving approach. A. S. Barnes and Company, South Brunswick and New York. ISBN: 0-498-02036-3.
Content: ground, aerial, photogrammetric geographic surveying; reading maps, mapping: comprehensive practical introduction for field scientists with no surveying experience.

References quoted in the text:

Ambrose, L.; Bearder, S. K., 1995: Identifying primate species from their calls. Poster abstract, International Conference on the Biology and Conservation of Prosimians, Chester, 13-16 September 1995.
in press? in: Folia Primatologica 69 (Suppl. 1) (= Proceedings of the international conference on the biology and conservation of prosimians, Chester, 13-17 November 1995).

Barrett, E., 1984: The ecology of some nocturnal, arboreal mammals in the rainforests of peninsular Malaysia. Ph.D. Thesis, Cambridge University

Baudenon, P., 1949: Contribution à la connaissance du Potto de Bosman dans le Togo-Sud. Mammalia 13: 76-99.

Bearder, S. K.; Honess, P. E.; Ambrose, L., 1995: Species diversity among galagos with special reference to mate recognition. Pp. 331-352 in: Alterman, L.; Doyle, G. A.; Izard, M. K. (eds): Creatures of the Dark. The nocturnal prosimians. New York, Plenum Press.

Berry, R. J., 1970: Covert and overt variation, as exemplified by British mouse populations. Symp. zool. Soc. Lond. 26: 3-26.

Boeck, J., 1975: Nervensysteme ud Sinnesorgane der Tiere. Herder Verlag, Freiburg im Breisgau.

Buchler, E. R., 1976: Chemiluminescent tag for tracking bats and other small nocturnal animals. Journal of mammalogy 57: 173-176.

Buntin, G. D., 1994: Developing a primary sampling program. Pp. 99-115 in: Handbook of sampling methods for arthropods in agriculture. Pedigo, L. P.; Buntin, D. G. (eds.), CRC Press, Boca Raton.

Burnham, K. P.; Anderson, D. R.; Laake, J. L., 1980: Estimation of density from line-transect sampling of biological populations. Wildlife monographs 72: 1-202.

Charles-Dominique, P., 1971: Eco-ethologie des prosimiens du Gabon. Biol. Gabonica 7: 121-228.

Charles-Dominique, P.; Bearder, S. K., 1979: Field studies of lorisid behavior: methodological aspects. Pp. 567-629 in: Doyle, G. A.; Martin, R. D.: The Study of Prosimian Behavior. Academic Press, New York.

Chihuahuan desert lab manual: Prairie dogs website – Project 3. Study proposal / field protocol: Reintroduction and monitoring of prairie dog populations: a study proposal. http://www.nps.gov/cave/cdl/p3protocol.pdf. Seen on 29 June 2001.

Crowcroft, W. P.; Jeffers, J. N. R., 1961: Variability in the behaviour of wild house mice (Mus musculus L.) towards live traps. Proc. Zool. Soc. Lond. 137: 573-582.

Day, G. I.; Schemnitz, S. D.; Taber, R. D., 1980: Capturing and marking wild animals. Pp. 61-88 in: Schemnitz, S. D. (ed.): Wildlife management techniques manual. The Wildlife Society, Washington, D. C.

Den Haas, Femke, quality controller animal care and paramedic, pers. comm., 2003: information from work at the Schmutzer Primate Center, Ragunan Zoo, Jakarta.

Dickman, C. R.; Huang, C., 1988: The reliability of fecal analysis as a method for determining the diet of insectivorous mammals. Journal of Mammology 69 (1): 108-113. ISSN: 0022-2372

Durrell, G. M., 1949: The angwantibo. Zoo life, London, 4: 29.

Giles, R. H., Jr., 2000 : The trevey. A total forest management plan and wildland management decision support system. Website: http://fwie.fw.vt.edu/rhgiles/Trevey/Deer.htm. Seen on 29 June 2001.

Gill, R. M. A.; Thomas, M. L.; Stocker, D., 1997: The use of portable thermal imaging for estimating deer population density in forest habitats. Journal of applied ecology 34 (5): 1273-1286.

Ginsberg, J. R.; Alexander, K. A.; Creel, S.; Kat, P. W.; McNutt, J. W.; Mills, M. G. L., 1995: Handling and survivorship of African wild dog (Lycaon pictus) in five ecosystems. Conservation Biology 9 (3): 665-674.

Greenwood, J. J. D., 1996: Basic techniques. Pp. 11-110 in: Sutherland, William J.: Ecological census techniques: a survey. Cambridge University Press, Cambridge.

Grzimek, B. (ed.), 1967: Grzimeks Tierleben, Vol. XII: Säugetiere 3. Kindler Verlag, Zürich. (German).

Gysel, L. W.; Lyon, J., 1980: Habitat analysis and evaluation. Pp. 305-326 in: Schemnitz, S. D. (ed.): Wildlife management techniques manual. The Wildlife Society, Washington, D. C.

Harcourt, C., 1987: Brief trap and retrap study of the Brown Mouse Lemur (Microcebus rufus). Folia Primatologica 49: 209-211

Higley, L. G.; Peterson, R. K. D., 1994: Initiating sampling programs. Pp. 119-136 in: Handbook of sampling methods for arthropods in agriculture. Pedigo, L. P.; Buntin, D. G. (eds.), CRC Press, Boca Raton.

Hladik, C. M.; Petter, J. J., 1970: Le loris tardigrade. Observations de terrains effectuées à Ceylan. Science et Nature 101.

Hutchins, S. H., 1994: Techniques for sampling arthropods in integrated pest management. Pp. 73-97 in: Handbook of sampling methods for arthropods in agriculture. Pedigo, L. P.; Buntin, D. G. (eds.), CRC Press, Boca Raton.

Johnson, J. M., 1984: Diurnal activities of the slender loris, Loris tardigradus, in the Mundanthurai Sanctuary, Tamil Nadu (India). Pp. 389-395 in: Current primate researches, M. L. Roonwal; S. M. Mohnot; N. S. Rathore (eds.), Jodhpur

Jones, J. C.; Reynolds, J. D., 1996: Environmental variables. Pp. 281-316 in: Sutherland, William J.: Ecological census techniques: a survey. Cambridge University Press, Cambridge.

Kar Gupta, K., 1995: Slender loris, Loris tardigradus, distribution and habitat use in Kalakad-Mundanthurai Tiger Reserve, India. Folia Primatologica 69 (suppl.): 401-402.

Kar-Gupta, K., in preparation: A study of distribution and habitat use by slender loris in Kalakad-Mundanthurai Tiger Reserve, India. Accepted with revision.

Karge, D., 1999: Verräterische Nagelkissen. Bild der Wissenschaft 10: 65.

Kenward, R., 1987: Wildlife radio tagging. Equipment, field techniques and data analysis. Academic Press, London.

Kingdon, J., 1997: The Kingdon field guide to African mammals. Academic Press, San Diego, London. ISBN: 0-12-408355-2

Korschgen, L. J., 1980: Procedures for food-habits analyses. Pp. 113-127 in: Schemnitz, S. D. (ed.): Wildlife management techniques manual. The Wildlife Society, Washington, D. C.

Lehner, Philip N., 1979: Handbook of ethological methods. Garland STPM Press, New York, London. ISBN: 0-8240-7024-0.

Lehner, Philip N., 1996: Handbook of ethological methods, 2nd edition. Cambridge University Press, Cambridge. ISBN 0-521-55405-5

Lemen, C. A.; Freeman, P. W., 1985: Tracking mammals with fluorescent pigments: a new technique. Journal of Mammalogy 66 (1): 134-136. ISSN: 0022-2372
Content: dye-maring, fluorescent pigments use in tracking; new technique, nocturnal activity

Luft, S.; Curio, E., , 2002: An improved necklace for marking fruit bats. Ecotropica 8: 249-251..

MacDonald, 1978: Radiotracking. Some applications and limitations. Pp. 192-204 in: Animal marking: recognition marking of animals in research, B. Stonehouse (ed.), MacMillan, London.

MacKinnon, J.; Phillips, K., 1993: The birds of Borneo, Sumatra, Java and Bali. Oxford University Press, Oxford. ISBN: 0-19-854035-3.

Martin, R. D., 1990: Primate origin and evolution. A phylogenetic reconstruction. Chapman and Hall, London

Megna, N. and others, 2001, in Marking Monkeys - Nyazol D. Laboratory Primate Newsletter 40 (3), July 2001, online edition in http://www.brown.edu/Research/Primate/lpn40-3.html#dye.

Nagorsen, David W.; Peterson, R. L., 1980: Mammal collector´s manual: A guide for collecting, documenting and preparing mammal specimens for scientific research. Life Sciences Miscellaneous Publications, Toronto: Royal Ontarion Museum. ISBN: 0-88854-255-0.

Nagy, J. G.; Haufler, J. B., 1980: Wildlife nutrition. Pp. 129-142 in: Schemnitz, S. D. (ed.): Wildlife management techniques manual. The Wildlife Society, Washington, D. C.

Nekaris, K. A.: Loris internet homepage: http://artsci.wustl.edu/~kabiela

Nekaris, K. A., 1997: A preliminary survey of the slender loris, Loris tardigradus, in South India. Sixty-sixth Annual Meeting of the American Association of Physical Anthropologists, St. Louis, Missouri, USA, April 1-5, 1997. American Journal of Physical Anthropology, 0 (SUPPL. 24). 176-177. ISSN: 0002-9483

"Nickerchen trotz Vogelzug", 1995 (no author mentioned); Illustrierte Wissenschaft (Norderstedt, Germany) 6: 25.

Pedigo, L. P., 1994: Introduction to sampling arthropod populations. Pp. 1-11 in: Handbook of sampling methods for arthropods in agriculture. Pedigo, L. P.; Buntin, D. G. (eds.), CRC Press, Boca Raton.

Petter, J. J.; Hladik, C. M., 1970: Observations sur le domaine vital et la densité de population de Loris tardigradus dans les forêts de Ceylan. Mammalia 34 (3): 394-409.

Renner, P., 1996: Aufgaben des Tierpflegers bei der Erstellung von transgenen Mäusen. Der Tierschutzbeauftragte 3: 213-218.

Rice, C. G.; Kalk, P., 1996: Identification and marking techniques. Pp. 56-66 in: Kleimann, D. G.; Allen, M. E.; Thompson, K. V.; Lumpkin, S.; Harris, H. (eds.): Wild mammals in captivity, Principles and techniques. The University of Chicago Press, Chicago.

Rowe, N. (ed.), 1996: The pictorial guide of living primates. Pogonias Press, New York.

Ryder, R. D., 1978: Postscript: towards humane methods of identification. Pp. 229-234 in: Stonehouse, B. (ed.): Animal marking: recognition marking of animals in research. University Park Press, Baltimore. 224 pp.

Schulze, H.; Meier, B., 1995: Behavior of captive Loris tardigradus nordicus: a qualitative description, including some information about morphological bases of behavior. Pp. 221-249 in: Creatures of the Dark, Alterman, L.; Doyle, G.; Izard, M. K. (eds.), Plenum Press, New York.

Seitz, E., 1967: Untersuchungen zur Aktivitätsrhythmik dunkelaktiver Halbaffen der Unterfamilie Lorisinae. Pp. 322-326 in: Neue Ergebnisse der Primatologie / Progress in primatology, 1st Congress of the International Primatological Society. Starck, D.; Schneider, R.; Kuhn, H.-J. (eds.), Gustav Fischer Verlag, Stuttgart.

Singh, M.; Lindburg, D. G.; Udhayan, A.; Anand Kumar, M.; Kumara, H. N., 1999: Status survey of slender loris Loris tardigradus lydekkerianus in Dindigul, Tamil Nadu, India. Oryx 33 (1): 31-37.   ISSN: 0030-6053

Singh, M.; Anand Kumar, M.; Kumara, H. N.; Mohnot, S. M., 2000: Distribution and conservation of slender lorises (Loris tardigradus lydekkerianus) in Southern Andhra Pradesh, South India. International Journal of Primatology 21 (4): 721-730.

Southern, N., 1955: Nocturnal animals. Scientific American 193 (4): 88-98.

Stonehouse, B. (ed.), 1978: Animal marking: recognition marking of animals in research. University Park Press, Baltimore. 224 pp.

Streicher, U., 2000-2004: unpublished data from work as a veterinarian at the Endangered Primate Rescue Center, Vietnam, including data from:
      Streicher, U., thesis in preparation.

Sutherland, William J., 1996 b: Mammals. Pp. 260-280 in: Ecological census techniques: a survey. Sutherland, W. J. (ed.). Cambridge University Press, Cambridge.

Tan, C. L., 1994: Survey of Nycticebus pygmaeus in southern Vietnam. 15th Congress of the International Primatological Society: 136. (Abstract)

Wolcott, T. G., 1980: Optical and radio-optical techniques for tracking nocturnal animals. Pp. 333-338 in: A handbook on biotelemetry and radio tracking, Amlaner, C. J.; Macdonald, D. W. (eds.), Pergamon Press, Oxford.

Zimmermann, E., 1995a: Acoustic communication in nocturnal prosimians. Pp. 311-330 in: Creatures of the Dark, Alterman, L.; Doyle, G.; Izard, M. K. (eds.), Plenum Press, New York.

Zimmermann, E., 1995b: Loud calls in nocturnal prosimians: structure, evolution and ontogeny. Pp. 47-72 in: Current topics in primate vocal communication, Zimmermann et al. (eds.), Plenum Press, New York.

Zwickel, F. C., 1980: Use of dogs in wildlife biology. Pp. 531-536 in: Schemnitz, S. D. (ed.): Wildlife management techniques manual. The Wildlife Society, Washington, D. C.

Some literature about species occurring in loris and potto habitats:


Ziegler, T., 2001: Die Amphibien und Reptilien eines Tieflandfeuchtwald-Schutzgebietes in Vietnam [Amphibians and reptiles of a lowland rain forest reserve in Vietnam]. NTV (Natur und Tier Verlag GmbH), Münster. 344 pp., 367 colour figures, 77 maps and diagrams. Information about 100 species, based on surveys in the region "Ky An - Ke Go", southern North Vietnam. ISBN: 3-931587-54-1  (German)


Bole, P. V.; Vaghani, Y., 1986: Field Guide to the Common Trees of India. Oxford University Press, Bombay, Delhi, Calcutta, Madras.

Champion, H. G.; Seth, S. K., 1969: A Revised Survey of the Forests Types of India. The Manager of Publication, New Delhi.

Gurung, K. K.; Sing, R., previously 1998: Field guide to the mammals of the Indian subcontinent: where to watch mammals in India, Nepal, Bhutan, Bangladesh, Sri Lanka and Pakistan. Academic Press.
Content: 106 species of larger mammals: identification in the field, habitat, range, status. Colour plates and figures of tracks.; review of national parks and protected areas.

Hutton, A. F., 1949: Notes on the snakes and mammals of the high wavy mountains, Madura district, South India. J. Bombay Nat. Hist. Soc. 48: 681-694

Prater, S. H. (ed.), 1965: The book of Indian animals. Bombay Natural History Society. First published 1948; reprinted with corrections 1980, several editions. Fourth impression: 1993. ISBN: 0 19 562169 7.

Sahni, K. C., 1998: The Book of Indian Trees. Oxford University Press, Mumbai.

Srivastata, A., 1999: Primates of Northeast India. Megadiversity Press, Bikaner, India. ISBN: 81-87585-00-5:
Content: Primates, their habitats, food plants, conservation.

Whistler, H., 1963: Popular handbook of Indian birds. Oliver and Boyd, Edinburgh.

Sri Lanka:

Eisenberg, J. F.; Lockhart, M., 1972: An ecological reconnaissance of Wilpattu National Park, Ceylon. Smithsonian Contributions to Zoology 101: 1 - 119. Smithsonian Press, Washington.

Eisenberg, J. F.; McKay, G. M., 1970: An annotated checklist of the recent mammals of Ceylon with keys to the species. Ceylon J. Sci. (Bio. Sci.) 8 (2): 69-99.

Henry, G. M., 1978: A guide to the birds of Ceylon. K. V. G. de Silva & Sons, Kandy, Sri Lanka.

Phillips, W. W. A., 1924: A guide to the mammals of Ceylon. Ceylon Journal of Science, Spolia Zeylanica XIII (1): 261-283.

Phillips, W. W. A., 1935: Manual of the mammals of Ceylon. Colombo Museum, Ceylon.

Slow loris distribution areas:

Duckworth, J. W.; Timmins, R. J.; Thewlis, R. C. M.; Evans, T. D.; Anderson, G. Q. A., 1994: Field observations of mammals in Laos, 1992-1993. Natural History Bulletin of the Siam Society, 42 (2): 177-205. ISSN: 0080-9462

Davison, G. W. H.; Fook, C. Y., 1998: A Photographic Guide to Birds of Peninsular Malaysia and Singapore. Chelsea Green Pub Co; Paperback: 144 pages; ISBN: 0883590360.

Francis, C. M., 2001: A Photographic Guide to Mammals of South-East Asia: Including Thailand, Malaysia, Singapore, Myanmar, Laos, Vietnam, Cambodia, Java, Sumatra, Bali Borneo. Ralph Curtis Pub. Paperback: 127 pages. ISBN: 0883590522.

King, B. F.; Dickinson, E. C., 1975: A field guide to the birds of south-east Asia. William Collins Sons & Co Ltd, London.

Madoc, G. C., 1956: An introduction to Malayan birds. Published by The Malayan Nature Society. Caxton Press Ltd., Kuala Lumpur, Federation of Malaya.

Webster, M.; Fook, C. Y., 1999: A Photographic Guide to Birds of Thailand. Paperback: 144 pages. Chelsea Green Pub Co; ISBN: 0883590417


Haltenorth, T.; Diller, H., 1977: BLV Bestimmungsbuch: Säugetiere Afrikas. BLV Verlagsgesellschaft, München.

Kingdon, J., 1997: The Kingdon field guide to African mammals. Academic Press, San Diego, London. ISBN: 0-12-408355-2

Williams, J. G., 1980: A field guide to the birds of Africa. William Collins Sons & Co Ltd., London.
In: Loris and potto conservation database, http://www.loris-conservation.org/database/
Last amendment: 3 April 2006

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