Interspecific and intraspecific foraging differentiation of neighbouring tropical seabirds

Abstract

Background Social 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. Methods Using 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. Results The 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. Conclusions Our 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.

Relative effects of static and dynamic abiotic conditions on foraging behaviour in breeding Sandwich terns

“…2), as observed in many other seabirds (e.g. González-Solís et al 2000, Wakefield et al 2013, Robertson et al 2014, Austin et al 2021.…”

Variations in inter‐specific and sex‐related niche partitioning in pelagic boobies during their annual cycle

“…First, the degree of sexual size dimorphism in boobies is colony‐specific (Nelson, 1978; Van Oordt et al., 2018), and greater size dimorphism might facilitate competitive exclusion and niche specialization. For example, red‐footed booby females were 5% heavier than males and had a 0.4% larger culmen in the current study (Table 3), whereas females in the Cayman Islands were 15% heavier and had a 3.9% larger culmen than males (Austin et al., 2021) and females at Europa Island were 14% heavier and had a 3.5% larger culmen (Weimerskirch et al., 2006). Second, the occurrence of differences in some but not other booby colonies might due to an effect of environmental conditions on local prey distribution and availability.…”

“…On Europa Island, chick-rearing females had similar δ 15 N values but higher δ 13 C values than males (Cherel et al, 2008), and in the Cayman Islands, incubating and chick-rearing females had higher δ 15 N and δ 13 C values than males (Austin et al, 2021).…”

“…The contrasting results within species and colonies may be associated with the distribution of their prey, with the study period, or with the size of the colonies. For example, foraging segregation might be more common in heterogeneous (Castillo‐Guerrero et al., 2016 ) than in homogeneous environments (Lerma, Serratosa, et al., 2020 ), during breeding (when birds are limited to foraging close to their colonies) compared with non‐breeding periods (Phillips et al., 2017 ; Roy et al., 2021 ), and in larger colonies compared to smaller ones (Austin et al., 2021 ; Petalas et al., 2024 ; Soanes et al., 2016 ; Wakefield et al., 2017 ).…”

Habitat selection and foraging segregation between two geographically proximate tropical seabird colonies

“…Foraging areas may also vary depending on season and breeding stage; seabirds typically travel further during incubation, however large sample sizes are required to understand these variables (Soanes et al 2015). Whilst previous studies have highlighted how foraging strategies vary for the species within colonies (Weimerskirch et al 2009;Miller et al 2018;Austin et al 2021) and when compared with colonies in different oceans (Soanes et al 2015(Soanes et al , 2016Correia et al 2021), there is a lack of evidence for foraging variability among colonies within in the same archipelago or atoll. Understanding inter-colony variations in the same geographic areas can be used to better address the establishment and assess the effectiveness of MPAs and IBAs.…”