Behavioral and trophic segregations help the Tahiti petrel to cope with the abundance of wedge-tailed shearwater when foraging in oligotrophic tropical waters

Abstract

Two species breeding in sympatry are more likely to coexist if their ecological niches are segregated either in time, space or in trophic habits. Here, we combined GPS-tracking, stable isotope analysis and DNA metabarcoding analysis to understand how the rare Tahiti petrel Pseudobulweria rostrata (TP) copes with the very abundant (i.e. 500,000 breeding pairs) wedge-tailed shearwater Ardenna pacifica (WTS) when breeding in sympatry in a tropical area. WTS foraged in restricted areas along their path, while TP predominantly foraged using extensive search behavior, suggesting a more opportunistic foraging strategy. Interspecific overlap of foraging areas was higher than intraspecific overlap. Breeding seasons largely overlap between species during the study, but TP seems to be asynchronous breeders. TP fed upon prey with higher δ15N values than WTS, and their diet was mainly composed of deep-sea organisms. TP could feed upon dead prey floating at the surface while WTS preyed mainly upon fish species that generally move in schools. Our study highlights several segregating mechanisms (temporal, behavioral and trophic) that could facilitate the coexistence of the two species despite the predominant number of WTS, and provides the very first information on the foraging and trophic ecology of the poorly-known TP.

Nest-site selection and its influence on breeding success in a poorly-known and declining seabird: The Tahiti petrel Pseudobulweria rostrata

“…Like many procellariid species, Tahiti petrels spend most of their time foraging at sea, except during their breeding period, when they depend on terrestrial environments to reproduce. New Caledonian populations breed asynchronously (i.e., breeding cycles extend throughout the year) [ 43 ], an atypical feature in Procellariidae [ 38 ]. Villard et al [ 39 ] estimated incubation and chick rearing periods to last 55 and 120 days, respectively [ 39 ].…”

Characterising the foraging ecology and mercury exposure of the Nationally Critical Whenua Hou diving petrel

“…The niche sizes of both species are decreasing over time, indicating increasingly specialised foraging behaviour (Bolnick et al, 2003). As there was significant isotopic niche overlap between the WHDPs and CDPs during the NBS, there is the potential for strong competitive pressure from the more abundant CDP population on the rare WHDPs (Ravache et al, 2020). However, since we do not know the non-breeding distribution of the CDP population on Whenua Hou, we cannot assume that their non-breeding grounds overlap for this competitive pressure to exist.…”

“…The WHDPs are shown to forage at a slightly higher trophic level than the CDPs, indicating they are targeting different prey during the breeding season Quillfeldt, McGill and Furness, 2005). This suggests that, during the breeding season, there is a low risk of interspecific competition from the CDP population compromising food availability for the WHDP population during the breeding season (Navarro et al, 2013;Ravache et al, 2020).…”

“…When one of the species is rare and understudied, it is important to characterise its feeding ecology and to investigate the degree of trophic overlap with surrounding species that could indicate competition over shared resources (Ravache et al, 2020).…”

“…Seabird communities are often comprised of dozens of species, densely populated, foraging in the areas surrounding their breeding colony (Navarro et al, 2013). If these species are not segregating their foraging habits temporally, spatially or trophically, it can result in more dominant species outcompeting and extirpating others (Ravache et al, 2020). however, it is assumed that they feed on a similar diet as SGDPs, primarily on euphausiids and copepods (Bocher, Cherel and Hobson, 2000).…”