Monogamy--the pairing of a single male with a single female--is common in birds but rare in most other animals. Monogamy usually requires that animals be able to recognize their mate as an individual, not a particularly easy cognitive task. In theory, a monogamous pairing insures that both of the mates will contribute to care of their offspring and to mutual defense. Monogamy may evolve when the cost of acquiring mates is very high, when females have the ability to restrict male behavior, or when offspring survival requires more intensive care than can be provided by a single animal.

The major cost of monogamy is that each individual makes their entire reproductive investment dependent on the fitness of their mate. This puts a real premium on choosing an appropriate mate. Choosing an inappopriate mate could have catastrophic fitness costs for an animal. Monogamous animals use two methods to "hedge their bets" on mate choice. First, they may actually engage in serial monogamy, bonding with a mate for one mating season, but choosing a different mate in a subsequent season. Second, many seemingly monogamous pairings are often subject to infidelities, or extrapair copulations. While over 90% of bird species appear to be monogamous, genetic studies show that in most populations at least a few offspring in each generation result from matings with partners other than a pair member. In some species extrapair copulations produce over half of the offspring.

A pair of wood ducks, Aix sponsa, resting. The bright coloration of the male suggests that females of this species use this characteristic to choose their mates. The female's drabber coloration makes her less conspicuous when she incubates eggs. In wood ducks removal of the male from the pair during breeding season does not affect the ability of the widowed female ot incubate the eggs, nor does it affect the survival of the eggs to hatching. However, the continued presence of the male makes production of a second brood more likely. This supports the hypothesis that the male may remain in the monogamous pairing because his chances of future reproduction are higher than if he leaves.


Manlove CA, Hepp GR 1998 Effects of mate removal on incubation behavior and reproductive success of female wood ducks CONDOR
100 (4): 688-693

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copyright ©2001 Michael D. Breed, all rights reserved