BREEDING BIOLOGY OF ACADIAN FLYCATCHERS IN A BOTTOMLAND HARDWOOD FOREST

From 1993-1995, we located and monitored 601 Acadian Flycatcher (Empid onax virescens) nests in a large contiguous tract of bottomland hardwo od forest on the White River National Wildlife Refuge, Arkansas. Annua l reproductive success was significantly different among years; rangin g from 10-25% (Mayfield estimate) over the three years of the study. T here was no significant difference in nest success among study plots, with nesting success showing a trend of increasing late in the breedin g season. Clutch size for nonparasitized nests averaged 2.9 +/- 0.02 ( SE) eggs with a mode of 3. Rates of Brown-headed Cowbird (Molothrus at er) parasitism were low (21%), accounting for 7% of all nest failures. However, parasitism by cowbirds resulted in a reduction of clutch siz e for nests initiated early (i.e., first nests and replacements) in th e breeding season. Predation was the leading cause of nest failures, a ccounting for 75% of all failures. Snakes and avian predators were tho ught to be the leading cause of nest failures. Although additional fac tors must be investigated, preliminary results indicate that nest pred ation is a major influence on this population, despite the size of the forest tract.