Structure of Social Networks in a Passerine Bird: Consequences for Sexual Selection and the Evolution of Mating Strategies

By Kevin P. Oh and Alexander V. Badyaev

The American Naturalist, Volume 176, Issue 3
DOI: 10.1086/655216

Social networks in birds: the benefit of having not so fine-feathered friends?

The extravagant displays and colorful plumages of male birds are essential components of courtship for many species. But a new study of social behaviors in finches shows that in the competition to attract females, success depends not only on a male's appearance, but also the company he keeps.

Previous research has shown that when choosing a mate, a female will tend to prefer the most elaborate and colorful male she encounters. However, females must often choose from a limited sample of males, suggesting that potential suitors might improve their lot by joining social circles where they will stand out compared to rivals.

To test this hypothesis, evolutionary biologists Kevin Oh and Alexander Badyaev from the University of Arizona carried out a three-year study of a wild population of house finches, a highly gregarious songbird native to the North American southwest desert. Male house finches have colorful feather patches that vary among individuals from dull yellow to dark red, with the latter generally more attractive to females. In the present study, published in the September issue of The American Naturalist, the researchers examined social encounters between birds using network analysis, which is particularly well-suited for elucidating patterns of social behavior in such a complex system with hundreds of interacting individuals.

They found that house finch social networks are characterized by distinct groups of closely interacting birds. Further, these groups are important for mating decisions, as female finches tend to choose partners from within their same social group. In a closer examination of individual male behavior, Oh and Badyaev discovered that male house finches commonly move between different social groups during the winter, especially the relatively unattractive yellow males that presumably have the most to gain. Indeed, by the beginning of the spring mating season, males that frequently switched social settings were able to essentially increase their own attractiveness by interacting with comparatively less attractive (i.e., yellower) competitors—and this paid off in terms of mating success: "surprisingly, by associating with particular social groups, normally drab males had nearly the same success in attracting females as did the most colorful males," said lead author Oh, now a postdoctoral research associate at Cornell University.

The results of this study show that such "social networking" can profoundly influence the relationship between male attractiveness and mating success, which has important insight for understanding how flashy traits like the peacock's tail evolve and are maintained. Furthermore, it suggests that competition to attract females will favor particular suites of social behaviors for males of differing attractiveness.