April 16, 2012
Hunting Birds Favor Uniquely Colored Birds, Study Indicates
Goshawks tend to focus in on pigeons with unique colors when the birds are travelling in large flocks -- a phenomenon known as the "oddity effect," according to a new study published last Thursday in the journal Current Biology.
The study, which was authored by Christian Rutz of Oxford University's Department of Zoology, looked at goshawks as they preyed on feral pigeons in Hamburg, Germany, the institute reported on their website Friday.
His goal was to determine whether or not the strategy of focusing on individuals with appearances that stand out of the crowd -- which allegedly made it easier for the predator to zero-in on a lone target in an otherwise "confusing, moving mass" -- would actually result in a more successful hunt.
"Pigeons flock together particularly when being attacked, which makes it harder for hawks to single out an individual," Rutz told BBC Nature News Reporter Anna-Louise Taylor. "There is evidence that goshawks selectively target feral pigeons as a means to overcome confusion effects and carry out more successful attacks."
According to Taylor, pigeons are predominantly grey-blue in color, but they also come in various different hues, including the rare white variety. For the purpose of his research, Rutz split the birds into two different categories -- white or non-white -- then gathered feathers from pigeon remains in 35 different goshawk nests. While he says that only 1.6% of the birds are white in color, more than one-fifth of the feathers recovered from the nests were white.
Furthermore, he suggests that it establishes a link between the "oddity effect" as a hunting strategy and the reproductive success of the goshawks. This is because male goshawks only prey on pigeons and other small birds once per year, during the reproductive season, Taylor said.
Once they catch one, they "return to their nests to pluck it and feed it to their young," and the high percentage of white feathers discovered in the nest suggests that hawks "which master the selective attack strategy are the best breeders."
"Male goshawks apparently hone their hunting skills over their first few years of life. As they get older, they become not only better pigeon hunters in general, but they also get increasingly selective for odd-colored individuals," Ruiz said in a statement. "An efficient hunter can provide a lot of food to their offspring“¦ In goshawks, the most selective pigeon hunters initiate their clutches very early in the season and raise young of excellent body condition."