The evolution of begging display may be influenced by gene–environment interaction, through the mechanisms that adjust begging behaviour to environmental conditions of offspring, including intensity of sibling competition within broods. We decomposed the complex begging display of yellow-legged gull, Larus michahellis, chicks into two different functional components: begging for food (pecks) and drawing the attention of parents (chatter calls). We examined these begging components in 2-day-old chicks that hatched and grew up in foster nests, by performing a begging test for each chick alone without the hindrance of its foster siblings. Male chicks and those with poorer body condition begged for food at higher rates than females and those with better body condition, respectively. Chicks from larger broods begged for food more frequently, but chicks from male-biased broods begged less frequently. If begging is costly, chicks may adjust their begging efforts to the intensity of sibling competition. Frequency of chatter calls varied with sex, chick order within broods and body condition: females, the third chicks and those with poorer condition produced chatter calls more frequently. Genetic origin had a significant effect on frequency of chatter calls but not on begging for food, while foster nest effect was null in both traits. Therefore, chatter calls (but not pecks) can be subject to evolution under directional selection. Different begging components may have evolved through different evolutionary pathways.
Diaz-Real, J., Kim, S.Y. & Velando, A., 2016. Hatching hierarchy but not egg-related effects governs behavioral phenotypes in gull chicks. Behavioral Ecology. doi: 10.1093/beheco/arw110
In many bird species that practice parental care, siblings often compete for resources and care provided by their parents, although their strategies differ according to hatching rank and condition. Differences in offspring strategies are generally attributed to hatching order and maternal effects, which are difficult to separate because these effects are often correlated. For example, third-hatched chicks of large gull species receive more egg testosterones and corticosterone, which influence early behavioral patterns. In this study, we carried out a cross-fostering experiment with first- and last-laid eggs of the yellow-legged gull (Larus michahellis) to test whether the within-brood variation in behavioral strategies for competing with siblings and coping with stress are due to maternal effects or to hatching order. Chicks hatched in the last position within the experimental brood emitted more chatter calls to attract parents’ attention, were less prone to respond to warning of danger, and had a lower breathing rate while restrained than first-hatched chicks. Egg laying order did not affect chick behaviors or breathing rate. Thus, we concluded that the different behavioral strategies of chicks were determined by their posthatching experience and not by the original egg position within the clutch. Last-laid eggs were smaller and chicks from those eggs grew slower than chicks from first-laid eggs. Independently of the original laying order, chicks that hatched first in the experimental brood grew faster than their siblings. Overall, our results indicate that behavioral strategies of chicks are plastic and influenced by their early social