Data from: Hatching hierarchy but not egg-related effects governs behavioral phenotypes in gull chicks

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 experience.