Thick-Billed Murres <i>Uria lomvia</i> at Cape Parry, Northwest Territories: Core-use Areas, Morphometrics and Chick Diets

Cape Parry is home to the only colony of Thick-billed Murres Uria lomvia in the western Canadian Arctic, but ecological information for this small, isolated population is lacking. To address this information gap, we investigated the spatial distribution, diving behaviour, diet, and morphometrics of male and female Cape Parry Thick-billed Murres during the breeding season. We tracked 23 chick-rearing adults (seven females and 16 males) using Global Positioning System (GPS) tags with depth sensors (2021) and collected chick diet data (2021, 2022) using observations and photos. Cape Parry murres foraged relatively close to the colony (4.5 ± 3.3 km) and mostly within the marine boundaries of the Anguniaqvia Niqiqyuam Marine Protected Area (ANMPA). Core-use foraging areas (50% utilization distribution [UD] of dive locations) and diving depths (up to 70 m) coincided with the relatively shallow waters near Cape Parry. There was no difference between sexes in foraging locations, but there was a clear difference between sexes in foraging times, as has been reported in other studies. Dive bouts at night, mostly performed by males, consisted of more frequent, shallower dives compared with daylight diving. Dive bout duration and calculation of murre diving efficacy suggest foraging effort (“time spent feeding”) was similar between day and night. Adults delivered fish up to 142 mm in length to their chicks, with a majority (81%‒90%) consisting of pelagic Arctic Cod Boreogadus saida, benthic Daubed Shanny Leptoclinus maculatus, and benthic Sandlance Ammodytes spp., with a higher proportion of Artic Cod delivered in 2022 compared to 2021. Morphometric measurements placed Cape Parry females closer to Atlantic than Pacific colonies, and Cape Parry males were positioned between the two geographic groups. In summary, this study provides the first spatial and foraging ecology data for the Cape Parry population of Thick-billed Murres, which is crucial for management and evaluating the adequacy of the ANMPA in supporting this species.