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Marine heatwaves are increasing in frequency and can disrupt marine ecosystems non-linearly. In this study, we examined the effect of the North Pacific warming event of 2014, the largest long-term sea surface anomaly on record, on black-legged kittiwake Rissa tridactyla foraging trips before, during, and after the event. We assessed foraging trip characteristics (trip distance and duration), the dispersal of foraging locations, and the persistence of foraging areas within and among years. Foraging trip characteristics, foraging area size, and location varied from year to year. Kittiwake foraging was more dispersed, direct, and farther from the colony in years immediately after and during the warming event. A third of the foraging area used pre-heatwave (2012) was important in subsequent years, which indicates that this area was, and may still be, a perennial foraging hot spot. During the chick-rearing stage, black-legged kittiwakes increased their speed and reduced the proportion of resting compared to the incubation stage. We conclude that marine heatwaves may have a strong impact on seabird foraging, extending foraging ranges, and that those impacts may be nonlinear with a strong lag.

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In 1987, David Cairns proposed that a gradient of colony-based measures on seabirds could be used to assess food supply in the ocean. Measures closely tied to the ocean, such as foraging trip duration, would be sensitive to small declines in food supply while measures more closely tied with the nest site, such as reproductive success, would be sensitive to large declines in food supply. The continual refinement of tracking devices holds the potential to clearly link variables measured via seabirds to food supply, possibly extending Cairns' hypothesis. Here, we review the various tests of Cairns' hypothesis, and demonstrate that those tests have had variable success, partly because of the complex and nonlinear relationships between food supply and colony-based measures. We summarize the metrics available from biologgers and argue that such devices can provide a more direct proxy of food supply. We conclude that Cairns' hypothesis can be extended to biologger-derived parameters and that seabird behavior can be used as an early warning signal for declining food supply.

Biologging has revealed many of the mysteries surrounding seabird behavior far from land. However, tagging seabirds with biologgers may influence the very traits they are designed to observe. Such ‘tag effects’ are often argued to be minimal below a threshold of 3% of body mass. Nonetheless, few studies carefully separate handling from tagging effects, so the effect of tag size is often confounded with the effect of handling. Puffins, including rhinoceros auklets Cerorhinca monocerata, are notoriously difficult to work with due to high nest abandonment rates. To examine tagging and handling effects in rhinoceros auklets, we compared abandonment rates of individuals equipped with a GPS weighing ~2.3% of body mass with abandonment rates of birds handled but not equipped, and of birds not handled at all (controls). We used the egg flotation technique to estimate egg development and predict hatching date, thus allowing treatments to be applied at the appropriate time. Handling more than doubled abandonment rates compared to control birds, and tagging more than doubled abandonment rates compared to birds that were handled but not tagged. Abandonment rates decreased as incubation progressed and were lowest during chick-rearing. We conclude that both handling and tagging of auklets increase abandonment, and that effects are lowest during chick-rearing.