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The Center for Native Grasslands Management

Title: Influence of trees in the landscape on parasitism rates of grassland passerine nests in southeastern North Dakota
Year: 2009
Author(s): Pietz, P. J., Buhl, D. A., Shaffer, J. A., Winter, M., Johnson, D. H.
Source Title: Condor
Source Type: Journal
pages: 36-42
Original Publication: http://  
Abstract: Woody vegetation has been linked to increased rates of Brown-headed Cowbird (Molothrus ater) parasitism for some grassland hosts. In northern North Dakota, however, studies reported that parasitism of grassland passerine nests was lower in landscapes with trees than in those without trees. We looked for evidence of this pattern elsewhere, using data from two studies conducted on the Sheyenne National Grassland in southeastern North Dakota. Specifically, we examined the probability of parasitism relative to percent tree cover within 2 km of a nest. We found a negative relationship for grassland passerine nests of all species tested. Our results support the suggestion that cowbirds are less likely to parasitize nests of grassland passerines where tree cover on the landscape is greater. This pattern could be explained by cowbirds switching to alternative hosts in woodlands, but this hypothesis needs further testing.