Reproductive success of Water Pipits in an Alpine environment

To understand the evolution of avian reproductive strategies it is importan t to assess how differences in reproductive success are related to timing o f the breeding season, quality of nesting territories or breeders, or to a combination of these factors. Over three years, we studied the reproductive performance of female Water Pipits (Anthus spinoletta) in a temporally and spatially variable alpine environment. The study area covered two valley s lopes that differed in the probability of nest predation, food availability , and climate. Nest predation and harsh weather were the main proximate cau ses of differences in female reproductive success. Because these two enviro nmental factors were locally unpredictable, individual females could best o ptimize their seasonal reproductive success by choosing the "right" breedin g time. The average number of young fledged per season was inversely relate d to the date of initial breeding and increased from females with only firs t attempts, through females with replacement clutches, to females that rais ed two broods. Hence, the main advantage of early breeding lies in the chan ce of rearing a second brood after the first has fledged, or of producing a replacement clutch if the First fails due to predation or harsh weather.