Foraging behaviour and habitat-use drives niche segregation in sibling seabird species

Abstract

To mediate competition, similar sympatric species are assumed to use different resources, or the same but geographically separated resources. The two giant petrels ( Macronectes spp.) are intriguing in that they are morphologically similar seabirds with overlapping diets and distributions. To better understand the mechanisms allowing their coexistence, we investigated intra- and interspecific niche segregation at Marion Island (Southern Indian Ocean), one of the few localities where they breed in sympatry. We used GPS tracks from 94 individuals and remote-sensed environmental data to quantify habitat use, combined with blood carbon and nitrogen stable isotope ratios from 90 individuals to characterize their foraging habitat and trophic ecology. Females of both species made distant at-sea foraging trips and fed at a similar trophic level. However, they used distinct pelagic habitats. By contrast, males of both species mainly foraged on or near land, resulting in significant sexual segregation, but high interspecific habitat and diet overlap. However, some males showed flexible behavioural strategies, also making distant, pelagic foraging trips. Using contemporaneous tracking, environmental and stable isotope data we provide a clear example of how sympatric sibling species can be segregated along different foraging behaviour dimensions.

Spatial segregation in a sexually dimorphic central place forager: Competitive exclusion or niche divergence?

“…A good example of where the first hypothesis (H1) has been used to explain sexual segregation is in the dimorphic, scavenging giant petrels Macronectes spp. The larger, dominant males have been observed to directly exclude females from seal and penguin carcasses on land, forcing females to primarily forage at‐sea (Gonzalez‐Solis et al., 2000; but see discussions in Granroth‐Wilding & Phillips, 2019 and Reisinger et al., 2020 that demonstrated more behavioural flexibility than previously thought for these species). Social dominance and competitive exclusion have also been suggested to explain sexual segregation in polygynous species.…”

“…The two main hypotheses commonly used to explain sexual segregation in central place foragers are (H1) competitive exclusion (through direct competition) or (H2) niche divergence (through indirect competition, Phillips et al, 2004).A good example of where the first hypothesis (H1) has been used to explain sexual segregation is in the dimorphic, scavenging giant petrels Macronectes spp. The larger, dominant males have been observed to directly exclude females from seal and penguin carcasses on land, forcing females to primarily forage at-sea(Gonzalez-Solis et al, 2000; but see discussions in Granroth-Wilding &Phillips, 2019 andReisinger et al, 2020 that demonstrated more behavioural flexibility than previously thought for these species).…”

The role of allochrony in influencing interspecific differences in foraging distribution during the non-breeding season between two congeneric crested penguin species

“…Marine predators, such as seabirds, face different constraints during the breeding and non-breeding seasons. Most seabirds breed in colonies and foraging is confined to a restricted radius around this central place owing to the need to return to the nest to care for offspring, which may lead to high intra- and interspecific competition between individuals and species [ 20 , 21 ]. Once breeding is over and central place constraints are relaxed one would expect sympatric species with similar resource requirements to disperse into the wider environment at low densities and intermix as resource limitation and competition will be reduced.…”

The foraging behavior of nonbreeding Adélie penguins in the western Antarctic Peninsula during the breeding season

“…The null hypothesis was rejected if the overlap calculated from the observed data was significantly different from the overlap calculated from a simulated dataset (1000 permutations) in which breeding state (breeder and nonbreeder) was randomly assigned to individuals during each breeding stage. Significance ( p values) was estimated as the proportion of permuted overlap scores that were smaller than the observed overlap (e.g., Botha & Pistorius, 2018; Reisinger et al, 2020). The p values calculated from Monte Carlo permutations are approximations and are thus given with 95% confidence intervals.…”