Spatial ecology of endangered roseate terns and foraging habitat suitability around a colony in the western North Atlantic

Abstract

Predicting habitat suitability and understanding habitat utilization are important to inform and orient conservation and management decisions for the recovery of endangered species. In North America, the roseate tern Sterna dougallii is listed as endangered in both the northeastern USA and Canada, where little is known about the foraging spatial ecology of the species. We equipped breeding roseate terns with miniature GPS tracking devices during incubation at North Brother Island, the main Canadian colony. Our aim was to characterize the spatial foraging ecology of the species, identify marine zones of importance, and develop a habitat suitability model around the colony. Our results provide novel, high resolution information on individual foraging trips, notably showing that individuals restricted their range around the colony (15.4 km) while performing multiple foraging trips: up to 11 daytime trips and a maximum total of 152.9 km travelled per day. Roseate terns concentrated their foraging effort around the colony and further south along the coast to the Cockerwit Passage. Using distance from colony, sea surface temperature, distance from land, bathymetry, and subtidal substrate type as covariates in a habitat suitability model, a high proportion of the deviance was explained (72.4%); the model also predicted high occurrence of foraging near the colony, in Cockerwit Passage, and at additional sites to which the birds were not tracked. Along with the description of important marine areas for roseate terns nesting on North Brother Island, this habitat suitability model provides a relevant and essential context for understanding roseate tern habitat use in a broad sense, but with a focus on habitat requirements during incubation.

Variation in isotopic niche partitioning between adult roseate and common terns in the Northwest Atlantic

“…Previous studies tracking roseate terns have found that adults restrict their foraging range to within 15 km of the colony during the incubation and early chickrearing periods of their lifecycles (Pratte et al 2021), but foraging range during the pre-breeding period is not known. After the adult terns have reached the breeding colonies post-migration, they forage in the vicinity of colonies to replenish energy reserves, engage in courtship, and build nests, but may be less spatially constrained during this time period (Cabot & Nisbet 2013).…”

“…Radio-telemetry studies of roseate and common terns (e.g. Loring et al 2019, Pratte et al 2021) could inform spatial partitioning or overlap of foraging locations, how foraging range changes from the pre-breeding period to chick rearing, and how partitioning changes with shifting environmental and social conditions. Finally, prey availability can also shift throughout the breeding season (Safina & Burger 1985, Safina et al 1988.…”

“…Roseate terns in the NWA nest almost exclusively on coastal islands and almost always in association with colonies of the more abundant common tern S. hirundo (Cabot & Nisbet 2013). During the breeding season, terns are central-place foragers, restricting their range to within 15 km around the colony as they maintain their nests and provision their young (Jessopp et al 2020, Pratte et al 2021. Previous studies on the foraging strategies of roseate and common terns in this region have largely focused on the chick-provisioning period, where the prey that adults deliver to chicks is directly viewed by observers stationed at the colonies (Richards & Schew 1989, Safina 1990a, Safina et al 1990, Goyert 2015, Yakola et al 2022.…”

Predicting Seabird Foraging Habitat for Conservation Planning in Atlantic Canada: Integrating Telemetry and Survey Data Across Thousands of Colonies

“…At the time, this included all known telemetry studies using devices enabling geographic positions of breeding seabirds in Atlantic Canada, plus additional data from common eiders from two colonies in Maine, USA, and from Leach's storm-petrel from one colony in France (Saint Pierre and Miquelon). These included unpublished data (Black, 2006;Symons, 2018;and other unpublished sources) as well as reassessment of previously published data on terns (Rock et al, 2007a;Rock et al, 2007b;Pratte et al, 2021), gulls (Maynard & Ronconi, 2018;Anderson et al, 2019;Shlepr et al, 2021), alcids (Regular et al, 2013Pratte et al, 2017;Gulka et al, 2019), northern gannet (Garthe et al, 2007;Garthe et al, 2011;Montevecchi et al, 2012), Leach's storm-petrel (Pollet et al, 2014;Hedd et al, 2018), and common eider (Mallory et al, 2020).…”

“…VHF data were obtained from studies of common and Arctic terns (Black, 2006;Rock et al, 2007a) which rely on aerial surveys to obtain location estimates, thus providing limited, but the only, tracking data available for these species. Roseate terns were tracked by VHF tags at Country Island (Rock et al, 2007b) and GPS at North Brother Island (Pratte et al, 2021). All tags were deployed on breeding adults.…”