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Intra-annual Shifts in Atlantic Puffin \u3ci\u3eFratercula arctica\u3c/i\u3e Depredation and Kleptoparasitism by \u3ci\u3eLarus\u3c/i\u3e Gulls at a Multi-species Seabird Colony
No full textGreat Black-backed Gulls Larus marinus and American Herring Gulls L. argentatus smithsonianus are considered dietary generalists at the population level: they consume a variety of prey types, including the adults and offspring of other seabirds, and they shift among prey types as availability varies. Atlantic Puffin Fratercula arctica adults, eggs, and chicks are often the target of depredation, and adults are also susceptible to kleptoparasitic attacks by large gulls during their summer breeding season in coastal Newfoundland, Canada. We investigated the depredation and kleptoparasitism of puffins by large gulls during July–August 2021/22 at a multi-species breeding colony on the northeast coast of Newfoundland. We hypothesized that both the inshore arrival of spawning Capelin Mallotus villosus, a key forage fish species in the region, and the onset of the puffin chick-rearing period, which typically coincide, influence puffin depredation and kleptoparasitism by large gulls. Shoreline transects on James Island revealed a decrease in new adult puffin carcasses during puffin chick rearing and Capelin spawning, with most adult puffin depredation occurring before the inshore arrival of spawning Capelin in both years. Behavioural observations (i.e., focal animal, behavioural sampling, and instantaneous scan sampling) revealed that Great Black-backed Gulls were more often present within puffin burrow areas and spent a higher proportion of time in these areas relative to American Herring Gulls, especially during Capelin spawning and puffin chick-rearing. Within puffin burrow areas, Great Black-backed Gulls depredated chicks and kleptoparasitized adults. As only ~30% of followed individuals of both gull species entered puffin burrow areas, it is possible that only a few Great Black-backed Gulls were responsible for puffin depredation and kleptoparasitism
Tracked Gulls Help Identify Potential Zones of Interaction between Whales and Shipping Traffic
No full textSeabird-vessel interactions are often studied through the lens of fisheries bycatch, but seabirds encounter many watercraft types. Western Gulls Larus occidentalis breeding on the Farallon Islands (California, USA) have a foraging domain that encompasses both shipping lanes and productive fishing grounds, resulting in ample opportunities for vessel encounters. Previous research showed that these Western Gulls can serve as ecosystem indicators because their foraging behavior is linked to ocean prey conditions, and because their foraging grounds overlap with that of Humpback Whales Megaptera novaeangliae, which can make prey accessible. Because ship strikes and entanglement in fishing gear are concerns for whales in this region, we investigated gull-vessel interactions as a proxy for identifying whale ship-strike risk by assessing the geographical overlap between GPS-tracked gulls and vessels using the Automatic Identification System. During 2014–2019, 40% of tracked gulls encountered a vessel, resulting in 85 encounters. Gulls mostly encountered cargo ships and tug/pilot boats, mainly within the shipping lanes (79%). Over 30% of these encounters co-occurred with gull foraging events, and most encounters were situated within shipping lanes (80%). Moreover, most gull foraging events began before the vessel encounters, which appeared to interrupt gull behavior. Interannual variability of encounters was mainly related to gull foraging locations: during years of high oceanic productivity, foraging more frequently occurred at sea rather than nearshore or on land, leading to more encounters with ships. This study builds on work that documented overlap between Humpback Whales and Western Gulls but did not test whether foraging gulls encountered vessels. We found that some vessel encounters coincided with gull foraging events; from that, we suggest that the real-time processing of seabird tracking data could provide additional information on whale distribution (which is more difficult to study) within regions of high ship-strike risk and could be included as another tool for dynamic ocean management
Marbled Murrelet \u3ci\u3eBrachyramphus marmoratus\u3c/i\u3e Use of a Freshwater Lake on Vancouver Island, British Columbia, 2018–2023
No full textMarbled Murrelets Brachyramphus marmoratus are small seabirds widely distributed in nearshore waters on the west coast of North America, from Alaska to central California. A 1986 review of anecdotal records revealed that Marbled Murrelets use coastal freshwater lakes during the breeding season, possibly to forage, and in winter, possibly while prospecting for nest sites in old-growth forest. Our weekly surveys and observations on Sproat Lake (central Vancouver Island, British Columbia, Canada) from November 2018 to March 2023, confirmed year round use by murrelets, with absences during the prealternate molt (beginning mid-March) and the prebasic molt (August and September), when the birds were probably at sea. Putative pairs predominated in all months, which suggests mated adults; single murrelets were recorded infrequently when pairs would have been separated during incubation. Murrelets were not observed holding prey, and fledglings were not recorded on the lake. The emerging importance of freshwater lakes and their watersheds as an aspect of Marbled Murrelet life history requires further research, particularly in light of this species’ possible sensitivity to human recreational and other disturbances when using lakes. Identification of recurring use of freshwater lakes, such as Sproat Lake, by Marbled Murrelets could inform conservation actions directed toward potential nesting habitat in nearby old-growth forests
