A few long versus many short foraging trips: different foraging strategies of lesser kestrel sexes during breeding

Abstract

Background: In species with biparental care both members of the breeding pair cooperate to raise the offspring either by assisting each other in every reproductive task or by specializing in different ones. The latter case is known as reproductive role specialization. Raptors are considered one of the most role-specialized groups, but little is known about parental behavior away from the nest. Until the advent of biologgers, avian role specialization was traditionally studied with direct observations at the nest because of the difficulties of following and recording the behavior of free-ranging individuals. In this paper we analyze how the role specialization of the lesser kestrel (Falco naumanni) influences foraging movement patterns throughout the breeding season. We tracked 30 lesser kestrel breeders from two breeding colonies using high-frequency GPS-dataloggers during four consecutive breeding seasons.

Results: We found no differences between sexes in lesser kestrel foraging movements early in the breeding season before the formation of the breeding pair. However, we observed sexually distinct foraging movement strategies later in the breeding season once breeding pairs were formed. Lesser kestrel males performed a large number of short foraging trips while females made a few long ones. This maximized the provisioning rate by males to feed their mates and offspring. Meanwhile, lesser kestrel females spent more time at the colony than males in order to defend the nest, incubate the eggs and brood the nestlings. Females also helped their mates to provision the nestling once these had grown and required more food and less protection. Furthermore, lesser kestrels showed a sexual spatial segregation in foraging areas, with males foraging closer to the colony than females.

Conclusions: The lesser kestrel responds to changes in energy demand throughout the breeding season with its foraging movement strategy, but in a different way depending on parental sex. The sexual spatial segregation observed is likely to be the result of an adaptive foraging strategy based on role specialization to reduce prey depletion close to the colony and intersexual competition in order to improve breeding success.

Keywords: Biologging; Breeding ecology; Falco naumanni; Foraging behavior; GPS; Movement ecology; Role specialization; Spatial segregation.

Fig. 1

Effect of the interaction between sex and phenological period on lesser kestrel daily distance traveled (a), daily number of foraging trips (b), daily colony attendance (c), and foraging trip duration (d) as predicted by GLMMs. Colors indicate kestrel sex: female in red and male in blue. Significance of post-hoc comparison between sexes within phenological periods is indicated above the bar pairs. Significance of post-hoc comparison between phenological periods within sexes is indicated under the bars: values not sharing a common letter are significantly different, either uppercase letters for females or lowercase letters for males. P-values are indicated: < 0.5 (*), < 0.01 (**), and < 0.001 (***). Sample size = 244 complete days and 2171 foraging trips

Fig. 2

Effect of the interaction between sex and eldest chick age on lesser kestrel daily distance traveled (a), daily number of foraging trips (b), and daily colony attendance (c) during the nestling period predicted by GLMMs. Regression lines are depicted for females (red circles, red line) and for males (blue triangles, blue line). Sample size = 84 complete days

Fig. 3

GPS data sampled at 3-min frequency from a complete day of tracking of 4 random individual lesser kestrels in each phenological period: Establishment (a), courtship (b), incubation (c), and nestling (d). Colors indicate kestrel females (red and orange) and kestrel males (light and dark blue). The black star indicates the location of the breeding colony

Fig. 4

Lesser kestrel percentages of habitats used by each sex for foraging: female in red and male in blue. Sample size = 322 foraging locations

Fig. 5

Effect of the interaction between sex and phenological period on the probability of performing a perching bout (a) and the total perching time (b) during foraging trips predicted by GLMMs. Colors indicate kestrel sex: female in red and male in blue. Significance of post-hoc comparison between sexes within phenological periods is indicated above the bar pairs. Significance of post-hoc comparison between phenological periods within sexes is indicated under the bars: values not sharing a common letter are significantly different, either uppercase letters for females or lowercase letters for males. P-values are indicated: < 0.5 (*), < 0.01 (**), and < 0.001 (***). Sample size = 2171 foraging trips

Fig. 6

Partial effects of the day-of-year (best GAMM) and the interaction between sex and day-of-year (second best GAMM) on lesser kestrel body mass. A penalized smoothing spline with 7.52° of freedom was adjusted to day-of-year in the best GAMM fitted to lesser kestrel body mass (a). Penalized smoothing splines of 3.88 and 5.26° of freedom were adjusted to day-of-year for females (b) and males (c), respectively, resulted from the second best GAMM fitted to kestrel body mass. Grey shading represents the standard error of the mean effect. The dashed lines show the mean starting days of courtship, incubation and nestling periods. Sample size = 275 individual body masses