Hello again, Barry.
I've gathered some interesting material about animal monogamy. Recent
studies indicate that even in species that mate for life, a certain
amount of canoodling goes on. In the animal kingdom, as with
humankind, the fact that a male and a female may be bonded to each
other and raise offspring together does not necessarily preclude
sexual relationships with outsiders.
Below are excerpts from some online articles that I think you'll find
useful. You may want to read the articles in their entirety for more
"Q. I have read that Wolves, Eagles, and Swans mate for life. Are
there other species that do this?
A. There are many birds that form long term monogamous bonds. Because
both parents often cooperatively care for young, monogamy is practical
for those species. Once a good partner has been located, there is a
strong tendency to remain together, rather than expend energy each
season seeking and courting another mate. However, when biologists
look at the offspring of many so called monogamous species, there is
evidence that the female has mated with more than one male.
Upon close examination of species that supposedly mate for life, it
turns out that they are about as monogamous as humans; more than 50%
end up with a different partner. Wolves, like a few other social
mammals do indeed form long tern pair bonds, but they usually mate
with other individuals in the group."
The eNature Observer: Ask an Expert: Mated for Life?
"Is it true that wolves always mate for life?
Some wolves do, but some don't. A wolf will often stay with a chosen
mate for as long as he or she is available, and wolves often reject
mating attempts that are not by their own preferred mate. However, a
wolf may take a new mate if its former one passes away or is driven
from the pack. Serial monogamy, where a wolf has more than one mate
during its life span, but has only one mate at any given time, is not
uncommon. Polygyny is rare in wolves."
University of Alberta: Answers to Frequently Asked Questions About Wolves
"New research reveals a surprising risk factor for extinction:
monogamy. Large mammals that live in pairs or have small harems are
far more likely to die out than those with big harems in reserves in
Ghana....After accounting for the effect of reserve size, [Justin]
Brashares found that two of the factors studied correlated with local
extinctions in the Ghanian reserves. The first is population
isolation, which is not surprising because this was previously known
to be a risk factor for natural extinctions.
The second is harem size: mammals that are monogamous or have small
harems were more prone to extinction. For instance, several duiker
species, which are monogamous, died out an average of 10 years after
the reserves were established, while the African buffalo, which has
harems with about 15 females, is still living in all the reserves.
Similarly, several colobus monkey species, which have few mates, died
out an average of 18 years after the reserves were established, while
green monkeys and baboons, which have many mates, are still living in
all the reserves."
ScienceBlog: Monogamous animals may be more likely to die out
"Arginine vasopressin influences male reproductive and social
behaviours in several vertebrate taxa through its actions at the V1a
receptor in the brain. The neuroanatomical distribution of vasopressin
V1a receptors varies greatly between species with different forms of
social organization. Here we show that centrally administered arginine
vasopressin increases affiliative behaviour in the highly social,
monogamous prairie vole, but not in the relatively asocial,
promiscuous montane vole. Molecular analyses indicate that gene
duplication and/or changes in promoter structure of the prairie vole
receptor gene may contribute to the species differences in
vasopressin-receptor expression. We further show that mice that are
transgenic for the prairie vole receptor gene have a neuroanatomical
pattern of receptor binding that is similar to that of the prairie
vole, and exhibit increased affiliative behaviour after injection with
arginine vasopressin. These data indicate that the pattern of
V1a-receptor gene expression in the brain may be functionally
associated with species-typical social behaviours in male
PubMed: Increased affiliative response to vasopressin in mice
"Zoologist David Barash and his wife, psychiatrist Judith Lipton, have
studied monogamy in the animal kingdom. You may be surprised by how
little of it they found...
Monogamy in the animal kingdom is so rare that Barash and Lipton, the
authors of 'The Monogamy Myth,' say that those romantic Hallmark cards
with pictures of swans or other types of lovebirds should more
adequately feature the flatworm. Swans may mate for life, but they're
not necessarily faithful to their mate... The clue was DNA. They
looked at the offspring of birds and found that the mother bird's
offspring weren't necessarily the father bird's offspring. About 40
percent of the babies were sired by someone other than the mother's
And it is not just the male birds that are straying. Researchers
actually put little radio transmitters on the mother birds and found
out they were sneaking off in the morning to a neighboring nest for a
tryst and then slipping back home. It really shocked the scientists."
CNN: Instinct For Infidelity?
"Only about 10 percent of the birds and mammals that seem to mate for
life are actually faithful to their partners, according to studies
that suggest infidelity may be nature's way. Blame it on biology, say
New studies using genetic testing techniques show that even the most
apparently devoted of partners often mate around, visiting nearby
nests or dens or clans to enjoy the sexual company of strangers...
Some species, such as the eastern bluebird, gained reputations as
shining examples of devotion. Male and female partners work together
closely to build nests, incubate eggs, then feed and raise their
young. The truth is, bluebirds have a sex life that rivals a
television soap opera... 15 percent to 20 percent of chicks cared for
by a bonded pair of bluebirds were not fathered by the male."
SouthCoast Today: Animal monogamy rare, experts say
"Infidelity may be natural according to studies that show nine out of
10 mammals and birds that mate for life are unfaithful. Experts found
animals that fool around are only following the urges of biology.
New studies using genetic testing techniques show that even the most
apparently devoted of partners often go in search of the sexual
company of strangers.
Females stray to gather the best possible genes for their offspring,
while males are driven to father as many and as often as possible.
...There are two kinds of monogamy - social and genetic. In the first
kind partners bond and work together to raise their young. With
'genetic monogamy,' parents are faithful sex partners.
While social monogamy is relatively common, genetic monogamy is the
exception rather than the rule."
BBC News: Infidelity 'is natural'
"Social monogamy is relatively common among monogamous species, but
genetic monogamy is the exception. Overall, only ten percent of the
birds and mammals that seem to mate for life are actually faithful to
their partners... among primates, there are only two monkeys--the
marmoset and its South American cousin, the tamarin--that are
genetically monogamous. All other primates--monkeys, apes, and
humans--often mate outside their socially monogamous partnerships."
Emory University: Mating for Life?
"The traditional view of why more or less permanent monogamous bonds
are formed is changing, as interest has become focused on the
parentage of offspring reared by 'monogamous' pairs. Increasingly,
ornithologists and behavioral ecologists have come to view monogamy as
part of a 'mixed' reproductive strategy in which matings may occur
outside the primary pair bond, but both members of the pair still
contribute substantially only to the care and feeding of the young
from their own nest. Some species are viewed as facultatively
monogamous; that is, if released from certain environmental
constraints, they would typically exhibit some other form of mating
system such as polygyny (one male mating with more than one female) or
promiscuity (mating without forming pair bonds). According to this
view, for example, North American dabbling ducks are monogamous only
because males are unable to monopolize more than one female. These
ducks breed synchronously and their populations typically contain more
males than females... At the moment it is perhaps best simply to
consider monogamy as a social pattern in which one male and one female
associate during the breeding season, and not to make too many
assumptions about fidelity or parentage."
Birds of Stanford: Monogamy
"When it comes to mammals generally, monogamy has long been known as a
rarity. Out of 4,000 mammal species, no more than a few dozen form
reliable pair-bonds, although in many cases it is hard to characterize
them with certainty, because the social and sexual lives of mammals
tend to be more furtive than those of birds. Monogamous mammals are
most likely to be bats (a few species only), certain canids
(especially foxes), and a few primates, notably the tiny New World
monkeys known as marmosets and tamarins, a handful of mice and rats,
several odd-sounding South American rodents (agoutis, pacas, acouchis,
maras), the giant otter of South America, the northern beaver, a
handful of species of seals, and a couple of small African antelopes
(duikers, dik-diks, and klipspringers).
Even females in seemingly solitary species such as orangutans,
gibbons, and black bears have been found to copulate with more than
one male; hence, observations of social organization alone clearly can
be misleading . Until recently, lacking the appropriate genetic
techniques, we had little choice but to define monogamy by the social
relationships involved; only with the explosion of DNA fingerprinting
technology have we started to examine the genetic connections, those
most important to evolution. Thus, according to the highly-respected
book by David Lack, Ecological Adaptations for Breeding in Birds,
fully 92% of bird species are monogamous. Socially, this figure is
still accurate; sexually, it is way off."
W.H. Freeman: The Myth of Monogamy
Google search strategy:
Google Web Search: "monogamous species"
Google Web Search: "species OR animals" + "mate for life"
I hope this helps. If anything is unclear, or if a link does not
function, please request clarification.