female ornament size
Matteo Griggio, Giuliano Matessi & Andrea Pilastro
Ethology 109(8): 659-670
August 2003
Abstract
We investigated the relationship between male nest defence and female
breast patch size in an alpine population of rock sparrow (Petronia
petronia) in northern Italy. We presented a mounted weasel (Mustela
nivalis), a common nest predator, to 28 pairs breeding in nest boxes,
with 12-13-d-old nestlings, and measured the intensity of male and
female defence reaction. We measured the frequency of attack flights,
intensity of alarm calling and total time spent in view, and then
combined these for each individual, in a single defence factor by
principal component analysis. All the females arrived to defend the
nest while only 21 males arrived, and females defended the nest more
intensely than males. We analysed, by stepwise regression, the
relationship of male defence factor to female behaviour and phenotype
(breast patch size, a measure of quality) and brood properties (size,
mass, phenology). Male defence factor was significantly related only
to female breast patch size. We argue that male rock sparrows
apparently make parental investment decisions according to their
mate's quality, and examine possible alternative hypotheses.
|