White-crowned Sparrow Males Unruffled by Younger Rivals
In the territorial world of nature, it’s not uncommon for older males to give way to the younger generation, albeit with a fight. Researchers have recently discovered that this is not necessarily the case with mature white-crowned sparrow males. In fact older males don’t even bother to get involved in any altercation, verbal or physical, and this is seen as evidence that they don’t view younger males as a threat.
In the study, which was carried out by Angelika Poesel and Douglas Nelson of the Ohio State University and funded by the National Science Foundation, it was noted that the older male would, however, become agitated and aggressive upon hearing a rival bird of the same age in his territory. It appears that the males of this species assess the fighting ability of their opponents based on age, and younger males simply don’t scare them.
The study observed a migratory population of white-crowned sparrows nesting in Bandon, Oregon, from 2008 to 2011. While plumage is an important indicator of maturity, the results of the study reveal that some birds use each other’s songs to determine age and threat level. As is the case with many bird species, male white-crowned sparrows use their songs to establish nesting territory and court a potential mate. Should a male sing in another’s territory, he can expect to be attacked and driven off if perceived to be a threat. With this particular bird species, second-year males do have plumage differences, but they also sing two or more versions of their species unique song before they choose one, and abandon the rest. This multiple version singing indicates to more mature males that the bird singing in his territory is a second-year male, and not a threat worth getting ruffled feathers about.
The research was carried out by playing various songs through loudspeakers within the established territories of mature males, and careful observation of the birds’ behavior. It was noted that second-year males that have established territory, did not tolerate other second-year males invading their space. It is thought that female birds are naturally more attracted to mature birds than to younger ones, and the older birds know this. Also, younger birds are disinclined to push their luck with a mature male which is likely to be stronger and more experienced.
Lead author of the study, Angelika Poesel, is curator of the Borrer Laboratory of Bioacoustics. Douglas Nelson is associate professor of evolution, ecology and organismal biology, and director of the University’s Borrer Laboratory.