Joseph Burant, Roxan Chicalo, Emily J Williams, Laura Phillips, Matthew Fuirst, D. Ryan Norris

Our understanding of avian incubation behaviour is primarily derived from species that nest in the temperate conditions of spring and summer. This leaves uncertainties about strategies employed by a relatively small number of species adapted to breed under sub-zero, winter-like conditions. We used in-nest temperature loggers (iButtons) to monitor incubation behaviours of Canada Jays, cache-reliant, year-round residents of boreal and sub-alpine environments that breed in the late winter/early spring and have female-only incubation. Females had high levels of daytime nest attentiveness (92 ± 3% of daytime spent on the nest; ± SD), taking an average of only 5.5 (± 0.1) off-bouts per day with a mean duration of 13.3 (± 0.2) min. per bout. Variation in nest attentiveness was primarily driven by off-bout duration, suggesting that the number of off-bouts per day may be limited to reduce nest activity around the nest and avoid attracting nest predators. In contrast to expectations, weather conditions (mean daily temperature and total daily rainfall) were not associated with variation in either the number or duration of off-bouts. Our results suggest that incubation strategies of Canada Jays are likely not shaped by prevailing weather conditions but instead by predation threat and availability of cached food, the latter of which reduces foraging opportunity costs by allowing females to reliably acquire sufficient food during the few times they leave the nest each day.