Tropical montane and temperate hummingbirds incubate in small installments over long periods

Life-history strategies and development are shaped by climate and predation. We examined how temperature and nest survival drive incubation behavior in 104 nests of 34 hummingbird species across 2,939m of elevation in the Peruvian and Colombian Andes. At high elevations, cold temperatures led to more frequent, brief incubation bouts and extended incubation periods; survival modulated incubation behavior with no effect on development. Hummingbirds had the highest egg surface-area to volume ratios among all birds; in 147 species, incubation periods increased with decreasing ambient temperatures. We propose a new hypothesis to explain how in cold conditions, heat transfer to the embryo is fragmented into smaller increments and therefore extended over longer periods, underscoring the role of adult behavior in mediating embryonic temperature mismatches and life-history tradeoffs.