Interactive effects of body mass changes and species-specific morphology
on flight behaviour of chick-rearing Antarctic fulmarine petrels under
diurnal wind patterns
Abstract
For procellariiform seabirds, wind and body morphology are crucial
determinants of flight costs and flight speeds. During chick-rearing,
parental seabirds commute frequently to provision their chicks, and
their body mass changes between outbound and return legs. In Antarctica,
the typical diurnal katabatic winds which blow stronger in the mornings,
form al natural experiment to investigate flight behaviours in response
to wind conditions. We GPS-tracked three closely related species of
sympatrically breeding Antarctic fulmarine petrels which differ in wing
loading and aspect ratio and investigated their flight behaviour in
response to wind and changes in body mass. All three species reached
higher flight speeds under stronger tailwinds, especially on return legs
from foraging, when wing loading was increased since birds carried food
for their chicks. Flight speeds decreased under stronger headwinds.
Antarctic petrels (Thalassoica antarctica; intermediate body mass,
highest wind loading and aspect ratio) responded stronger to changes in
wind speed and direction than cape petrels (Daption capense; lowest body
mass, wing loading and aspect ratio) or southern fulmars (Fulmarus
glacialoides; highest body mass, intermediate wing loading and aspect
ratio). Birds did not adjust their flight direction in relation to wind
direction nor maximum distance to nest when they encountered strong
headwinds on their outbound commutes. However, birds appeared to adjust
the timing of commutes to those hours of the day when headwinds were
weakest and they were more likely to encounter favourable tail- and
crosswinds. Despite these adaptations to the predictable diurnal wind
conditions, birds frequently encountered unfavourably strong headwinds,
possibly as a result of weather systems disrupting the katabatics
coupled with the need to feed. How the predicted decrease in Antarctic
near-coastal wind speeds over the remainder of the century will affect
flight costs and breeding success which ultimately drives population
trajectories remains to be seen.