9/4/2023 0 Comments Brown songbird![]() ![]() Overall, productivity increased during 1991–2010, with more pronounced increases associated with lower levels of landscape forest cover. The best predictor of nest survival was parasitism status, with parasitized nests surviving at lower rates than unparasitized nests. Nest survival increased insubstantially across time during laying and incubation, but not during the nestling stage. Declining parasitism rates were associated with increased fledging brood sizes, with more pronounced increases as landscape forest cover decreased. Fledging brood size and nest survival rates were positively associated with landscape forest cover, confirming the fragmentation hypothesis for Midwest forest birds. Parasitism rates and intensities declined substantially during 1991–2010. We evaluated whether there were concomitant changes in fledging brood size, nest survival, a combination of the two metrics (i.e., host young produced per nest attempt), and whether such changes were more substantial with decreasing landscape forest cover. We used 20 years of nest monitoring data from five sites in Missouri across a gradient of landscape forest cover to assess temporal trends in the rate and intensity of brood parasitism for Acadian Flycatchers ( Empidonax virescens), Indigo Buntings ( Passerina cyanea), and Northern Cardinals ( Cardinalis cardinalis). However, cowbirds are also experiencing long-term population declines, which should reduce parasitism pressure and thus increase productivity of host species. Many songbird species have experienced significant population declines, partly because of brood parasitism by the Brown-headed Cowbird ( Molothrus ater), which is positively associated with increasing landscape forest cover in the midwestern United States.
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