The Coastal Plain of northern Alaska is an important nesting area for a variety of avian species, where the productivity of ground-nesting species can be strongly influenced by nest predators. Recently, the density of red foxes (Vulpes vulpes) has increased in many areas of the Arctic, likely because of climate warming as well as the availability of anthropogenic food sources during winter. In areas where they occur sympatrically, red foxes can outcompete and kill the smaller Arctic fox (Vulpes lagopus). There is considerable dietary overlap between the fox species, but if the red fox is a more successful nest predator, this ongoing shift in canid species could have important implications for ground-nesting species like the Yellow-billed Loon (Gavia adamsii). We examined time-lapse photographs from 186 nests of Yellow-billed Loons in northern Alaska during the years 2008 – 15 and 2019 for the presence of foxes and other nest predators and quantified nest predation by species. Although both Arctic and red foxes were photographed near nests, we found that all successful predation of Yellow-billed Loon nests by foxes was attributable to red foxes, which were the second most frequent predator of Yellow-billed Loon nests after Glaucous Gulls (Larus hyperboreus). Arctic foxes photographed at Yellow-billed Loon nests were unsuccessful at displacing incubating loons. Several data sources suggest that the prevalence of red foxes has increased in Arctic Alaska over the last three decades, a change that is likely to have negative impacts on the nesting success of Yellow-billed Loons and possibly other large waterbirds.

The Coastal Plain of northern Alaska is an important nesting area for a variety of avian species, where the productivity of ground-nesting species can be strongly influenced by nest predators. Recently, the density of red foxes (Vulpes vulpes) has increased in many areas of the Arctic, likely because of climate warming as well as the availability of anthropogenic food sources during winter. In areas where they occur sympatrically, red foxes can outcompete and kill the smaller Arctic fox (Vulpes lagopus). There is considerable dietary overlap between the fox species, but if the red fox is a more successful nest predator, this ongoing shift in canid species could have important implications for ground-nesting species like the Yellow-billed Loon (Gavia adamsii). We examined time-lapse photographs from 186 nests of Yellow-billed Loons in northern Alaska during the years 2008 – 15 and 2019 for the presence of foxes and other nest predators and quantified nest predation by species. Although both Arctic and red foxes were photographed near nests, we found that all successful predation of Yellow-billed Loon nests by foxes was attributable to red foxes, which were the second most frequent predator of Yellow-billed Loon nests after Glaucous Gulls (Larus hyperboreus). Arctic foxes photographed at Yellow-billed Loon nests were unsuccessful at displacing incubating loons. Several data sources suggest that the prevalence of red foxes has increased in Arctic Alaska over the last three decades, a change that is likely to have negative impacts on the nesting success of Yellow-billed Loons and possibly other large waterbirds.

Reductions in nest attendance can increase predation risk and, therefore, reduce nesting success of ground‐nesting birds. We recorded the incubation behavior, nest predators, and nesting success of yellow‐billed loons (Gavia adamsii) at 2 adjacent study areas with differing amounts of industrial activity on the Arctic Coastal Plain of Alaska, USA, during 2008–2015 and 2019. Successful pairs had higher incubation constancies (97.3 ± 1.7% [SE], n = 96 nests) than failed pairs (91.6 ± 3.1%, n = 79 nests) and took fewer and shorter recesses than failed pairs. The intrusion of conspecifics into territories significantly lowered the daily incubation constancy of nesting pairs. Daily incubation constancy also declined as the daily maximum temperature increased, especially during periods with little wind. Both conditions contributed to nest failure. Predation was the primary cause of nest failure, with glaucous gulls (Larus hyperboreus) and parasitic jaegers (Stercorarius parasiticus) accounting for 41% of the nest failures. These avian predators took advantage of unattended nests, underscoring the consequence of disrupting incubation behavior. In both study areas, nest survival decreased as recess frequency increased. In the Colville Delta study area, loons with territories composed of separate nesting and brood‐rearing lakes had lower nest survival than loons that used 1 lake for both activities. In the National Petroleum Reserve‐Alaska study area (NPR‐A), loons nesting on shorelines and peninsulas had lower nest survival than those nesting on islands and nest survival decreased as the proportion of days with intruders increased. The overall probability of a nest hatching ≥1 egg in the Colville Delta study area was 0.40 (95% CI = 0.26–0.54) and was 0.68 (95% CI = 0.40–0.91) in the NPR‐A study area. Our results demonstrate the importance of nest attendance by yellow‐billed loons in warding off nest predators on the Arctic Coastal Plain of Alaska and provide a mechanism that shows how a warming Arctic climate could negatively affect yellow‐billed loons.