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Providing evidence to improve practice

Individual study: Removing brown-headed cowbirds Molothrus ater temporarily reduces parasitism on Bell’s vireos Vireo bellii and increases productivity of both vireos and cowbirds at five tall-grass prairie sites in Kansas, USA

Published source details

Kosciuch K.L. & Sandercock B.K. (2008) Cowbird removals unexpectedly increase productivity of a brood parasite and the songbird host. Ecological Applications, 18, 537-548


This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Remove/control adult brood parasites Bird Conservation

A controlled before-and-after cross-over study between 2003 and 2005 at five tall-grass prairie sites (24-83 ha) in Kansas, USA (9) found that brood parasitism by brown-headed cowbirds Molothrus ater on Bell’s vireos Vireo bellii was significantly lower at sites where a total of 980 cowbirds (171 adult females, 724 adult males and 85 juveniles) were removed in 2004-5, compared to before removals (47 and 58% parasitism in 130 nests in removal plots in 2004 and 2005 respectively  vs. 64-81% parasitism in 130 nests in 2003). There was no corresponding decrease in areas when cowbirds were not removed (77-85% parasitism in 278 nests in non-removal plots in 2004-5). Vireo productivity was higher at removal plots (2.6 compared to 1.2 vireo fledglings/pair) and nest success was higher for non-parasitised nests (64% of nests producing at least one chick vs. 51% of parasitised nests). However, cowbird productivity was also higher for removal plots than control plots (0.3 compared to 0.1 cowbird chicks/vireo pair).