A new study has shown that parental behavior of male blue tits is determined by female ornamentation, as previously predicted by the differential allocation hypothesis.
In choosing a mate both males and females rely on visual cues to determine which potential partner will supply the best genes, best nesting site, best territory, and best parenting skills.
The differential allocation hypothesis (DAH) makes the assumption that aesthetic traits indicate quality and arises from the needs of a parent’s current need to ensure current reproductive success and the reproductive success of their offspring. Ornamentation (ultraviolet coloration of the crown) and its maintenance is a cost which reduces energy available for reproduction, but without the ornamentation an individual may not be able to secure a mate. Ornamentation also plays a role in competition between males and between females, as well as signaling potential reproductive success.
But reproductive success does not only depend on the best genes and the best nest, it also depends on parenting skills.
Researchers at the Konrad Lorenz Institute of Ethology investigated the effect of female ornamentation on the chick-rearing behavior of their mates. Both males and female blue tits, Cyanistes caeruleus, have feathers on the top of their heads which reflect UV light. After their chicks had hatched, female blue tits were captured and their crowns smeared with either duck preen gland oil containing UV-blocking chemicals or the oil alone.
Although the UV-blocking chemicals did not alter the behavior of the females, their mates made fewer hunting trips to feed their brood. However the males made the same effort to protect their nest and defend their chicks as males with oil-only treated females.
“This is the first study to show that male blue tit behavior depends on female ornamentation,” explained Dr Matteo Griggio, a co-author of the study that will be published in the journal Frontiers in Zoology.
“Even though our experiment was minimally invasive to avoid partners not being able to recognize each other, the behavior of male blue tits in this study matched the DAH. The hypothesis also predicts that less attractive females should increase their parental investment but we found no compensatory female behavior.”
Bibliographic information: Mahr K, Griggio M, Granatiero M, Hoi H. 2012. Female attractiveness affects paternal investment: experimental evidence for male differential allocation in blue tits. Frontiers in Zoology. In press.