Combined bio-logging and stable isotopes reveal individual specialisations in a benthic coastal seabird, the Kerguelen shag

Abstract

Individual specialisations, which involve the repetition of specific behaviours or dietary choices over time, have been suggested to benefit animals by avoiding competition with conspecifics and increasing individual foraging efficiency. Among seabirds, resident and benthic species are thought to be good models to study inter-individual variation as they repetitively exploit the same environment. We investigated foraging behaviour, isotopic niche and diet in the Kerguelen shag Phalacrocorax verrucosus during both the incubation and chick-rearing periods for the same individuals to determine the effect of sex, breeding stage, body mass and morphometrics on mean foraging metrics and their consistency. There were large differences between individuals in foraging behaviour and consistency, with strong individual specialisations in dive depths and heading from the colony. Stable isotopes revealed specialisations in feeding strategies, across multiple temporal scales. Specifically, individuals showed medium term specialisations in feeding strategies during the breeding season, as well as long-term consistency. A clustering analysis revealed 4 different foraging strategies displaying significantly different δ15N values and body masses. There were no sex or stage biases to clusters and individuals in different clusters did not differ in their morphology. Importantly, the results suggest that the different strategies emphasized were related to individual prey preferences rather than intrinsic characteristics.

Intra- and inter-individual variation in the foraging ecology of a generalist subantarctic seabird, the gentoo penguin

“…This is consistent with other studies reporting that this species has high behavioural flexibility over its wide range (Wilson et al 1991, Robinson & Hindell 1996, Miller et al 2009, Kokubun et al 2010. Such flexible foraging habits likely provide a buffer against changes in prey availability and distribution in a limited, coastal environment (Lescroël & Bost 2005, Miller et al 2009), as shown in other inshore foragers (Hoskins et al 2008, Saraux et al 2011, Camprasse et al 2017.…”

“…We used complementary bio-logging and stable isotope analysis, coupled with morphometric measurements to: (1) describe their inter-individual variation in morphology, spatial use and dive behaviour; (2) quantify their intra-individual variation in foraging behaviour; (3) investigate the links between consistency in foraging behaviour, distances travelled and body condition; and (4) describe their interindividual variation in feeding ecology, and determine if dietary specialisations exist and are maintained outside of the breeding season. We predicted that: (1) individuals would differ greatly in foraging metrics, as gentoo penguin diet and behaviour are known to vary among colonies and between individuals of the same colonies, and that such variation would be attributed to differences in body mass, which influences dive depth (Lescroël et al 2004, Lescroël & Bost 2005, Cook et al 2013, Polito et al 2015, Camprasse et al 2017; (2) dietary and behavioural consistency would be detected, as populations usually considered generalists are increasingly shown to be composed of individual specialists (Woo et al 2008, Araújo et al 2011, Loxdale et al 2011, Layman & Allgeier 2012, Fodrie et al 2015; and (3) individuals displaying higher consistency in foraging behaviour would travel shorter distances and have higher body condition, as such consistency is thought to allow individuals to forage more efficiently (Bolnick et al 2003, Estes et al 2003.…”

Mate similarity in foraging Kerguelen shags: a combined bio-logging and stable isotope investigation

“…int-res.com/articles/suppl/ m578 p183_ supp. pdf) as shown in Camprasse et al (2017a). The difference in maximum depth between mates was lower than for nonmated birds (binomial GLMM: χ 2 = 68.34, df = 1, p < 0.0001); on average mates differed in depths by 17.1 ± 0.9 m, as opposed to 27.6 ± 0.5 m in nonmated birds.…”

“…Because Kerguelen shags tend to fly to their foraging grounds and dive predominantly at the most distal part of their trip (Camprasse et al 2017a), and because we wanted to know whether sexes or partners forage in the same locations, only core foraging area (50% home range) was calculated. Each trip for each male within each breeding stage was compared to each trip for each female sampled within the same stage by calculating the overlap in core foraging area between these 2 trips with the 'kerneloverlap' function in the adehabitatHR package using the Bhattacharyya's affinity (Fieberg & Kochanny 2005).…”

“…Individuals exhibit strong specialisation in such traits that can be maintained over the long-term, regardless of their sex, and therefore could be used by individuals to evaluate the quality of potential mates (Bearhop et al 2006, Cook et al 2006, Camprasse et al 2017a). They are long-lived, resident, and benthic foraging seabirds, and indi viduals repetitively exploit the same foraging areas (Camprasse et al 2017a). In addition, both parents often exhibit high nest fidelity, mate retention, and share incubation and chick-rearing duties (Aebischer et al 1995, Sapoznikow & Quintana 2008.…”