Challenges of quantifying direct heat stress effects of climate change on seabirds

The importance of heat stress as a consequence of climate climate change is often overlooked for seabirds. As endotherms, seabirds must actively thermoregulate at temperatures above their thermoneutral zone, or risk lethal hyperthermia. Although essential activities (e.g. foraging, breeding) may be traded off for thermoregulatory behaviors during periods of heat stress, a recent report by Olin et al. (2024; Mar Ecol Prog Ser 737:147–160 in this Theme Section) is one of very few that directly link this to demography. We argue that heat stress effects, which have strong theoretical support, are underreported directly because large-scale mortality events are rare, and small-scale events are hard to identify and easily obscured by indirect trophic effects. Quantifying heat stress effects on seabirds is necessary to understand fully the threats from climate change but requires prioritizing research in the following areas: developing methods to attribute heat mortality, determining baseline levels of heat mortality, elucidating ecological and organismal differences that underlie heat stress sensitivity, investigating the importance of possible sublethal mechanisms, and separating heat stress trade-offs from indirect effects of climate.