Incubation is an energetically costly activity for birds, and may be particularly challenging in alpine environments where ambient temperatures are typically low but can fluctuate widely. Little is known about how incubating birds respond to cold temperatures such as those that occur in alpine environments. We measured incubation rhythms in horned larks (Eremophila alpestris) breeding in alpine tundra in British Columbia and found quadratic relationships between ambient temperature and the total time spent incubating, the frequency of recesses, and on-bout duration. Females spent less time on the nest as ambient temperature increased to 12-13°C; at higher temperatures the relationship was reversed. They adjusted the amount of time incubating by varying the frequency rather than duration of recesses. It appears that female horned larks in alpine environments modify their behaviour so as to minimize the cost of rewarming eggs and the risk of cooling the eggs. The ability of horned larks to maintain high levels of nest attentiveness at low ambient temperatures suggests that they are well adapted to the degree of environmental variation they currently experience in alpine environments and that they may compensate for the shorter breeding seasons and reduced re-nesting opportunities by increasing parental investment.