Birds are generally unable to predict future changes in habitat condition when selecting nesting locations, and few studies have investigated the effect on birds of shifting habitat quality within nesting seasons. Anthropogenically influenced habitats such as agricultural landscapes are often associated with large shifts in quality that turn initially good habitat into poor habitat. We examined whether daily survival rates of Barn Owl (Tyto alba) nests in an agricultural landscape were influenced negatively by temporal instability in habitat conditions resulting from crop harvest. Although most nesting attempts by Barn Owls in our study area were initiated before the onset of harvest, fields adjacent to the majority of active nest boxes were harvested at some point during nesting attempts. Overall nest survivorship, as well as survivorship of individual nestlings within broods, was lower following harvest, likely because of associated declines in the abundance of rodents, the primary food source of Barn Owls. Nestlings in nests surrounded by harvested fields were generally lighter before fledging than young in nests surrounded by standing sugarcane and their associated dense rodent populations. Although instability of habitat quality in our study area was associated with reduced survivorship of individual Barn Owl nests, a population-level effect is unlikely given the overall fecundity of the population.
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Vol. 127 • No. 4