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Signs of estrus in lorises and pottos
See also determination of sex

Estrus in lorises and pottos can usually be recognized by increased opening of the vagina; parts of the genital region becoming slightly turgid and reddish. Captive females can be trained to allow regular control with a torchlight while clinging to wiremesh getting some titbits.

Besides visible changes of female genitalia, behaviour of the male clearly indicates estrus: in Loris, frequent appeasing "krik" vocalisation, pursuit of the female, attempts to sniff her genital region and attempts to mount can be observed. During pre-estrus, defensive chitter of the female often is the first behaviour noticed by keepers.

Slender loris (L. tardigradus, L. lydekkerianus) female

Signs of anestrus in a L. t. nordicus female. The vaginal cleft is more or less closed, the rims look normal and yellowish In pre-estrus, the vaginal cleft begins to open more widely, the surrounding tissue is still looking normal. Sexual interest of males increases (sniffing, krik calls, pursuit) Signs of estrus: the vagina is open, the rims and parts of the clitoris look turgid and reddened. Sealed vagina in a small red slender loris female, probably tardigradus or an intermediate tardigradus-grandis form. A sealed vagina is closed with no apparent cleft visible and may lead to erroneous sexing of the animal as a male. The condition may occur during anestrus or pregnancy; it has been observed in the red loris forms and in Nycticebus, but not in the captive L. t. nordicus in the facility of Ruhr-University.
Estrus signs are not always clearly distinguished as shown above; the degree of opening of the vaginal cleft may in addition vary with movement, distinction is possible on the average only. Reddening of the vaginal rims and apparent sexual interest of males are clearer signs.
After copulation, a vaginal plug may be visible in the vagina. It forms by hardening of a liquid apparently produced by the male; its purpose may be prevention of loss of sperm, prevention of copulation of the female with other males or possibly both. Observation showed unsuccessful attempts of a male to copulate once more with a female whose vagina was already closed by a plug from an earlier copulation. Size and shape of plugs may vary, here some examples. In L. t. nordicus the plugs are white to whitish-translucient. The female removes the plug with the teeth after some time, usually next day it is gone.

Slender loris male

Signs of sexual activity in slender loris males rather seem to be behavioural than morphological ones (pursuit, sniffing of the female genitalia, following, appeasing "krik" calls, attempts to mount). In captive L. t. nordicus at Ruhr-University, external visibility of testes of adult males varies, they may be partly inguinal, with flat and inconspicuous scrotum, or move into the scrotum, making it more prominent. In addition, the size of scrotum with testes inside may vary, see figures in the page about determination of sex. Which part of genitalia cause the enlargement is still unknown. At Ruhr-University enlargement of testes were observed when ambient temperatures were high, testes apparently helping to emit heat; no correlation with sexual activity was observed. Osman Hill confirmed that a captive slender loris male has sired offspring while his testes were inguinal and inconspicuous. 

Lesser slow loris (Nycticebus pygmaeus) female

Female external genitalia of a N. pygmaeus female during anestrus During estrus, the surroundings of the vagina are partly turgid. .Sealed vagina

Slow loris (N. coucang, N. bengalensis, N. (c.) javanicus) female

Anestrus Estrus .Sealed vagina

Potto (P. potto) female

Anestrus Estrus

Sources: Loris tardigradus: data from Ruhr-University and Osman Hill 1953; animals belonging to the red subspecies obtained from Frankfurt Zoo. Nycticebus pygmaeus: drawings based on photos by Helena Fitch-Snyder, Rüdiger Lippe, Bernhard Meier, Helga Schulze and live animals in the care of R. Lippe. Nycticebus coucang: drawings based on photos by Frank Wiens and Annette Zitzmann (wild N. c. coucang, Malaysia), Helena Fitch-Snyder and Karen Weisenseel and estrus sign description by Manley 1966. Perodicticus potto: based on Osman Hill 1953, Sanderson 1940, Charles-Dominique 1966 and 1977, Manley 1966 and 1976


Charles-Dominique, P., 1966: Glandes préclitoridiennes de Perodicticus potto. Biol. Gabon. 2: 355-359

Charles-Dominique, P., 1977: Ecology and Behavior of Nocturnal Primates. Prosimians of Equatorial West Africa, Duckworth, London.

Osman Hill, W. C., 1953: Primates: Comparative anatomy and taxonomy. Vol. I, Strepsirhini. Edinburgh University Press, Edinburgh.

Sanderson, I. T., 1940: The mammals of the north Cameroon forest area. Transactions of the Zoological Society of London 14: 623-725

Manley, G. H., 1966: Reproduction in lorisoid primates. Symposia of the Zoological Society of London 15: 439-509

Manley, G. H., 1976: Functions of the external genital glands of Perodicticus and Arctocebus. Pp. 313-329 in: Prosimian Behaviour, Martin, R.D.; Doyle, G. A.; Walker, A. C. (eds.), Duckworth, London.

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Lorises and pottos: species, subspecies, local populations
Last amendment: 28 March 2004
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