MARTIN, K; University of British Columbia: Constraints on reproduction in arctic and alpine birds

Arctic and alpine birds live in extreme environments, with compressed breeding schedules and frequent delays or interruptions in breeding. Daily temperatures vary from below freezing to >45 degrees C, requiring both heating and cooling to maintain homeothermy. Timing of annual snow melt can vary by up to one month, and this strong seasonality determines clutch initiation dates and spring breeding condition, key parameters setting clutch size. However, realized annual fecundity is most strongly influenced by local predation regimes and renesting abilities after failure. Seasonal and daily stochasticity results in less time to conduct reproduction, higher or the same nesting failure and fewer broods/season than low latitude or low elevation species, but offspring quality may be higher. Arctic and alpine specialists have developed effective behavioural and physiological responses, good renesting abilities and improved survival. For ptarmigan, life histories shift along an r-K gradient with increasing severity of environmental conditions. Other bird species that breed along latitudinal or altitudinal gradients also employ behavioural and facultative stress responses to ameliorate their local conditions as the frequency and intensity of stochastic events increases. Fitness tradeoffs and the degree of life history differentiation for birds breeding along arctic and alpine gradients has received little study. Climate change with its anticipated increases in frequency and intensity of extreme weather events will likely have different impacts for arctic and alpine specialists than for birds breeding across habitat gradients.