Philopatry

Philopatry is the tendency of an animal to remain in or return to the area of its birth to breed. With time, philopatry has also begun to mean an animal returning to the same place to breed even if it was not born in that location. Some birds and some mammals exhibit philopatry.

An advantage of philopatry is that over time the animal accumulates knowledge about the immediate environment – food and water sources, competitors and threats from predators. It is a definite advantage to not need to assess and acquire new defensive and foraging skills each year.

Philopatry creates a situation where the population grows in one area resulting in less resources per capita which eventually might lead to reduced fecundity and survival, an undesirable situation. Another disadvantage is that philopatry can also result in inbreeding.

In most mammals it is the female that returns to the same location and the males are more likely to  disperse (not return to the natal site). With most birds it is the opposite, the females disperse and the males return to their birth location. Of course, there are exceptions to every generalization. Paul Greenwood in a 1980 article discussed the reasons why different sexes typically disperse. He attributed the differences in part to mating strategies.

One of the exceptions to the “bird rule” is the snow goose (Chen caerulescens). The females exhibit philopatry while the males disperse. Snow geese usually form long-term pair bonds while on the wintering grounds or during the spring migration during their second year and begin to breed in the third year. The female snow goose returns to her birth colony and the male follows her regardless of where he was born.

Greenwood believes that since male snow geese do not arrive on the breeding grounds alone without their mates, the males do not need to find and defend a territory. The male also assumes extensive parental duties, including helping to care for the young and defense of the family. Since the male remains with the female snow goose in a monogamous relationship and helps with raising the chicks and without the need to establish a nesting territory, the male can remain with the female as she returns to her birth colony.

These snow geese were photographed in a neighbor’s alfalfa field along County Road 91 near Lookout CA (Modoc County).

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