Even so, these small raptors
expend a constant amount of energy per foraging trip
Date: June 7, 2017
Source: PLOS
Kestrels adapt their flight and
hunting strategies to weather conditions, including solar radiation, wind
speed, and air temperature, according to a study published June 7, 2017 in the
open-access journal PLOS ONE by Jesús Hernández-Pliego from Estación Biológica
de Doñana, Spain, and colleagues.
Theory predicts that to maximize
fitness, foraging animals should gain the most energy for the least cost of
time and energy. Hernández-Pliego and colleagues tested this theory in
kestrels, small insectivorous falcons that return to their nest to feed their
chicks after a foraging trip. Kestrels have the options of commuting via
time-saving flapping flights or energy-saving soaring-gliding flights, and of
capturing prey via time-saving active hovering flights or energy-saving
perch-hunting.
To explore whether the birds'
behavioral decisions reflect trade-offs during the commuting and searching
parts of foraging trips, the researchers tracked lesser kestrels with GPS and
tri-axial accelerometers, which provide data on energy and time budgets in wild
animals. The study included six kestrels (four males and two females) from two
breeding colonies with in the Guadalquivir river basin of southwestern Spain.
The researchers found that
kestrels' behavioral decisions varied with weather conditions. When solar
radiation increased -- which strengthens thermal updrafts -- commuting birds
replaced flapping with soaring-gliding. When wind speed increased -- which
provides a stronger lift -- searching birds replaced perch-hunting with
hovering. But kestrels also hovered more when air temperature increased
possibly as warmer weather boosts the activity of large grasshoppers, the birds'
preferred prey. While flight and hunting strategies varied dramatically with
the weather, the researchers also found that the energy expended per foraging
trip remained constant. This suggests that the birds have a fixed energy budget
per foraging trip and adjust their behavior accordingly when environmental
conditions vary.
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