Interspecific and intraspecific foraging differentiation of neighbouring tropical seabirds

R E Austin,S C Votier,J A Green,J Harvey,J Newton,J Haakonsson,G Ebanks-Petrie,F De Pascalis,J P Y Arnould

doi:10.1186/s40462-021-00251-z

Abstract

BackgroundSocial interactions, reproductive demands and intrinsic constraints all influence foraging decisions in animals. Understanding the relative importance of these factors in shaping the way that coexisting species within communities use and partition resources is central to knowledge of ecological and evolutionary processes. However, in marine environments, our understanding of the mechanisms that lead to and allow coexistence is limited, particularly in the tropics.MethodsUsing simultaneous data from a suite of animal-borne data loggers (GPS, depth recorders, immersion and video), dietary samples and stable isotopes, we investigated interspecific and intraspecific differences in foraging of two closely-related seabird species (the red-footed booby and brown booby) from neighbouring colonies on the Cayman Islands in the Caribbean.ResultsThe two species employed notably different foraging strategies, with marked spatial segregation, but limited evidence of interspecific dietary partitioning. The larger-bodied brown booby foraged within neritic waters, with the smaller-bodied red-footed booby travelling further offshore. Almost no sex differences were detected in foraging behaviour of red-footed boobies, while male and female brown boobies differed in their habitat use, foraging characteristics and dietary contributions. We suggest that these behavioural differences may relate to size dimorphism and competition: In the small brown booby population (n < 200 individuals), larger females showed a higher propensity to remain in coastal waters where they experienced kleptoparasitic attacks from magnificent frigatebirds, while smaller males that were never kleptoparasitised travelled further offshore, presumably into habitats with lower kleptoparasitic pressure. In weakly dimorphic red-footed boobies, these differences are less pronounced. Instead, density-dependent pressures on their large population (n > 2000 individuals) and avoidance of kleptoparasitism may be more prevalent in driving movements for both sexes.ConclusionsOur results reveal how, in an environment where opportunities for prey diversification are limited, neighbouring seabird species segregate at-sea, while exhibiting differing degrees of sexual differentiation. While the mechanisms underlying observed patterns remain unclear, our data are consistent with the idea that multiple factors involving both conspecifics and heterospecifics, as well as reproductive pressures, may combine to influence foraging differences in these neighbouring tropical species.

Highlights

Social interactions, reproductive demands and intrinsic constraints all influence foraging decisions in animals
While the mechanisms underlying observed patterns remain unclear, our data are consistent with the idea that multiple factors involving both conspecifics and heterospecifics, as well as reproductive pressures, may combine to influence foraging differences in these neighbouring tropical species
Where multiple species with similar morphologies coexist, this can manifest as resource partitioning in space, time and/or diet, resulting in divergent ecological niches [1, 8,9,10,11]. Such pressures and outcomes operate within species, and intraspecific segregation in resource use based on sex, life stage and even at the individual level is common within the animal kingdom [12,13,14]. Such resource partitioning has been widely associated with factors linked to body size differences [15, 16], and in communities with large populations may be driven by density dependence [17, 18]

Summary

Introduction

Reproductive demands and intrinsic constraints all influence foraging decisions in animals. Where multiple species with similar morphologies coexist, this can manifest as resource partitioning in space, time and/or diet, resulting in divergent ecological niches [1, 8,9,10,11] Such pressures and outcomes operate within species, and intraspecific segregation in resource use based on sex, life stage and even at the individual level is common within the animal kingdom [12,13,14]. Such resource partitioning has been widely associated with factors linked to body size differences [15, 16], and in communities with large populations may be driven by density dependence [17, 18]. While competitive pressures offer one potential explanation for interspecific and intraspecific differentiation in foraging, many other factors such as differing nutritional or physiological requirements [19], predation risk [4, 20], or sociality (e.g. avoidance of mating attempts: [21, 22]) have been proposed as causal factors, a limited consensus exists between studies and systems

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