Delayed timing as a strategy to avoid nest‐site competition: testing a model using data from starlings and flickers

Abstract

European starlings (Sturnus vulgaris) introduced to North America compete with native cavity‐nesting birds for nest sites. I examined whether natural selection could favour a strategy of delayed nesting in a population of northern flickers (Colaptes auratus), a native woodpecker, to reduce overlap in breeding phenology with starling competitors. I developed a mathematical model based on reproductive parameters for a population of flickers from central British Columbia, Canada. On average, 7% of flicker nests each year were usurped by starlings; daily probabilities of takeover declined through the season but were relatively low (1–2%). Flickers laid between 3 and 13 eggs and there was a negative correlation between clutch size and date. The probability of renesting after nest failure also declined during the season, but renesting intervals (2–19 days) were not associated with female age, or stage of nest loss. The model suggested that costs of delaying reproduction would outweigh benefits of an early start except when the probability of nest usurpation is very high (>75%) early in the season and declines rapidly through the summer. Thus, early laying dates should be favoured especially in northern latitudes where breeding seasons are short.