Resilience to a severe marine heatwave at two Pacific seabird colonies

A severe marine heat wave (MHW) persisted in the California Current ecosystem from 2014 through 2016. The MHW featured record-high sea surface temperatures in 2015, with 2014 to 2016 being the warmest 3 yr period on record. Our decade-long (2010-2019) breeding and diet monitoring of the rhinoceros auklet Cerorhinca monocerata, a burrow-nesting seabird, at significant breeding colonies on Destruction Island (California Current) and Protection Island (Salish Sea) allowed us to compare reproductive and dietary responses to this MHW. Although the colonies are relatively close to each other, and their reproductive output is, on average, similar, the auklets’ responses to the MHW differed. At Destruction Island, burrow occupancy rates were lower during the MHW (0.54 ± 0.02 vs. 0.61 ± 0.02 [mean ± SE] in non-MHW years), suggesting that birds skipped breeding, but fledging success rates did not differ (0.85 ± 0.02 vs. 0.89 ± 0.03). At Protection Island, burrow occupancy remained at non-MHW levels (0.72 ± 0.02 vs. 0.69 ± 0.02), but reproductive success declined (0.71 ± 0.03 vs. 0.82 ± 0.02). Chick provisioning also showed different patterns. The energy (kJ) per bill load at Destruction Island showed no clear MHW effect, while at Protection Island, it was reduced. At the same time, bill-load prey item count rose at Protection Island, indicating increased foraging effort and/or a reduction in diet quality. Our results further suggest rhinoceros auklets may be more resilient than other seabird species to major climate perturbations. However, with MHWs predicted to become more frequent and severe, the auklets’ ability to maintain these levels of breeding success will be tested.