How often do chimpanzees and bonobos living in the wild have an estrus?

Hi and thanks for your question,

"estrus: "The period of heat, or maximum sexual receptivity, in the
female." (Wilson, 1975).
Most of the primates mate when they are fertile usually within a short
period around ovulation; this is with the exception of humans and
bonobos.

Chimpanzees:
'In females, the first swellings of the sex skin occur between the
ages of 7 ½ and 8 ½ (years), and gradually increase in size until the
female chimpanzee is about 10 or 11 and begins to be mated by males,
which constitutes her first estrus.'

Female chimps have an estrus cycle of around 34-35 days:
'When a female chimpanzee comes into heat - or into estrus, as a
scientist would say - the sex skin of her genital area becomes
swollen....A swelling usually persists for about ten days before
becoming flabby and wrinkled and then shrinking away to nothing again.
Normally it occurs at a point midway between menstrual periods, which
in the female chimp occur about every thirty-five days.'
(Chimpanzee Behaviour:
http://www.lessonsforhope.org/abc/show_description.asp?abc_id=27)

'The female has a 35-day menstrual cycle, is receptive to mating for
6.5 days out of each cycle, and can breed at any time of the year'
(http://www.safariforless.com/chimpanzee.htm)

Chimps come into estrus every 36 days  have obvious estrus swellings
for around 8-12 days.

Bonobos:
Bonobos differ to chimps and are more similar to humans (they don't
only have sex to reproduce) -
'Instead of a few days out of her cycle, the female bonobo is almost
continuously sexually attractive and active.'
(http://www.dhushara.com/book/socio/bonobo/bonobo.htm)

'The tumescent phase of the female's genitals, resulting in a pink
swelling that signals willingness to mate, covers a much longer part
of estrus in bonobos than in chimpanzees. Instead of a few days out of
her cycle, the female bonobo is almost continuously sexually
attractive and active.'
(Bonobo Sex and Society: http://www.brembs.net/bonobos.html)

'Whereas the chimpanzee has a menstrual cycle of approximately
thirty-five days, the bonobo's is closer to forty-five days, and the
period of swelling covers a greater portion of the cycle (75% compared
to 50% in the chimpanzee).'
(Bonobo: Bibliographical Excerpts:
http://www.serpentfd.org/a/dewall1997.html)

Bonobos have 'Obvious estrus swellings for about 20/35 days.'
(http://www.missouri.edu/~mmm9f9/anth60/facts/bonobo.html)

'Menstrual bleeding occurs, as in humans, and lasts 3-4 days'
(http://medicine.ucsd.edu/cpa/bono.html)


Search Strategy:
I used the following terms at ://www.google.com to help answer
this question:
bonobo estrus: ://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=bonobo+estrus&btnG=Google+Search
chimpanzee estrus: ://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=chimpanzee+estrus
primates estrus: ://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=primates+estrus
estrus cycle primates:
://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=estrus+cycle+primates

I hope that answers your question, please advise if you need any
clarification.

Kind regards,
Ali

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Clarification of Answer by england_ali-ga on 23 Oct 2002 02:10 PDT

Thanks for the rating Kathy. :o)

I found this response to be complete and left me with a clear answer
to my question.  My question involved two speices and both were
addressed.  I am very pleased with the answer, it's timeliness and the
service oveall.  Thanks, Kathy