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Field Sparrow Reproductive Success and Nesting Ecology

1978; Oxford University Press; Volume: 95; Issue: 1 Linguagem: Inglês

10.2307/4085491

1938-4254

Louis B. Best,

Fire effects on ecosystems

Field Sparrow reproductive success and nesting ecology were studied in central Illinois on a tract composed of grassland, shrub-grassland, and shrub-woodland. Egg and nest successes were 11.2% and 10.2% respectively. Major causes of nest failure included: predation, primarily by snakes (76% of all active nests), nest desertion following brood parasitism by the Brown-headed Cowbird (7%), and nest desertion from unknown causes (7%). Eleven percent of the nests were parasitized; most (63%) were deserted as a result. Nests with young received heavier predation than nests with eggs. Early nests were placed predominantly in standing grass litter, but as the breeding season advanced forbs, trees, and shrubs became the most frequently used nesting substrates. Mean nest height increased as the season advanced. The frequency of desertion (from unknown causes), cowbird parasitism, snake predation, and successful fledging was not significantly different among nests placed in the major vegetation types, although mammalian predation did differ significantly. Nest height did not influence nesting outcome significantly. Nest vulnerability to snake predation was independent of relative nest concealment. Desertion (nonparasitized nests) and snake predation were distributed uniformly among nests throughout the study area, but nests preyed upon by mammals were somewhat clumped, and cowbirds parasitized nests within or near the shrub-woodland. The occurrence of snake predation was proportional to the number of nests. Predation intensity was not related to brood size. Nesting success increased slightly as the season advanced. The incidence of snake predation was negatively correlated with maximum daily relative humidity, but unrelated to other weather measurements.