Corticosterone-implanted chicks transmit stress to parents and neighbors in a colonial seabird

In animals living in groups, stress-induced changes in behavior can be a
source of social information, and stressed individuals can potentially
become stressors for other social partners, with important consequences
for social and population dynamics. Here, we studied stress transmission
from experimentally stressed chicks to both their parents and neighbors in
the yellow-legged gull (Larus michahellis), a seabird that forms large
breeding colonies. To do this, we experimentally increased the level of a
stress hormone by corticosterone implant in the first-hatched chicks of
the brood and observed its effects on their parents and both adults and
chicks in the neighboring nests. Two days after the implant,
corticosterone-implanted chicks showed reduced basal corticosterone
levels, probably due to a physiological feedback response. Exogenous
corticosterone promoted behavioral changes in the corticosterone-implanted
chicks, showing faster responses to a potential predator attack than the
placebo-treated chicks. Eight days after implantation, not only the
corticosterone-implanted chicks but also the neighboring chicks showed
elevated corticosterone levels after a standardized handling stress
compared to the placebo-implanted chicks and their neighbors. The parents
and neighbor adults of the corticosterone-implanted chicks showed
increased mobbing behavior but reduced aggressive and resting behaviors in
comparison to the adult gulls living close to the placebo-implanted
chicks. Overall, our results suggest that individual physiological stress
in a colony may be socially transmitted within families and neighbors,
with potential consequences for colony dynamics.