Bird

Many - see section below.

Mating systems and parental care

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Sources for this section include:

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• Gowaty, Patricia Adair: Male Parental Care and Apparent Monogamy among Eastern Bluebirds (Sialia Sialis). The American Naturalist 121(2): 149-160 (1983).
• Ketterson, Ellen D. and Nolan, Val: Male Parental Behavior in Birds. Annual Review of Ecology and Systematics 25: 601-28 (1994).
• Zeveloff, Samuel and Boyce, Mark: Parental Investment and Mating Systems in Mammals. Evolution 34(5): 973-982 (1980).

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The three predominant mating systems are polyandry, polygyny, and monogamy. Monogamy is seen in approximately 91% of all bird species. Polygyny constitutes 2% of all birds and polyandry is seen in less than 1%. Monogamous species of males and females pair for the breeding season. In some cases, the individuals may pair for life. Sexual selection theory and the relatively low typical parental investment that males make in offspring would suggest that polygynous mating systems should predominate in the animal kingdom. The real puzzle then is why do males become monogamous at all, especially so often in bird species.

Related Topics:
Monogamy - Polygyny - Polyandry

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In most groups of animals, male parental care is rare, but in birds it is quite common; it is more extensive in birds than in any other vertebrate class. One reason for this large percentage of monogamy with birds is due to the fact that male birds are just as adept at parental care as females. In fact, male care can be seen as important or essential to female fitness. "In one form of monogamy such as with obligate monogamy a female cannot rear a litter without the aid of a male" (Gowaty, 1983). It is assumed that when such male care is necessary, monogamy will evolve directly with this. It seems strange then that a male?s ability to defend mates and resources relies on his ability to separate himself from parental care.

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The parental behavior most associated with monogamy was male incubation. This is very interesting, because male incubation is the most confining male parental behavior. It not only consumes time, but also may require physiological changes that interfere with usual mating. With the extreme loss of mating opportunities, there is a reduction in the reproductive success among males. "This information then suggests that sexual selection may be less intense in taxa where males incubate, hypothetically because males allocate more effort to parental care and less to mating" (Ketterson and Nolan, 1994). It is understood then that the females associated with these males base their choice of mate on parental behaviors rather than physical appearance.

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It is surprising that with the amount of time and energy needed, that paternal care is selected for at all. Evolution suggests that a female should choose mates that confer maximum fitness. Therefore, if males contribute to the care of the offspring both male and female fitness may be maximized. "High paternal care has been seen among many species of monogamous mammals and several authors suggest that male investment is one of the primary advantages of monogamous mating (Zeveloff and Boyce, 1980). This suggests then that this mating system whether costly or not must be advantageous in some way or these females would not be selecting males with this behavior.

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It seems likely that fitness is increased in some way by this behavior of male parental care, but not so extreme that it is adopted by most other species. Surprisingly, there appears to be a lot of research to show that monogamy and paternal behavior are actually maladaptive due to its cost to fitness. However, is this due to the use of male care in this mating system? While the answer may be yes, it also seems to prevail in bird populations for some reason. What this reason is though may never be pin pointed to an exact answer. Some observations are thrown out by a couple of researchers but with no conclusive data or results. The only thing concluded seems to be that it is unnecessary. For now, until more research is done, we must instead be content to just know it persists.

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