Effects of female cowbird removal on reproductive success of hooded warblers

  • Published source details Stutchbury B.J.M. (1997) Effects of female cowbird removal on reproductive success of hooded warblers. The Wilson Bulletin, 109, 74-81.


This study is summarised as evidence for the following.

Action Category

Remove/control adult brood parasites

Action Link
Bird Conservation
  1. Remove/control adult brood parasites

    A replicated, controlled before-and-after study between 1984 and 1995 at three 50-100 ha (2 experimental and 1 control) hardwood forest sites in Pennsylvania, USA (Stutchbury 1997) found that the proportion of hooded warbler Wilsonia citrina nests parasitised by brown-headed cowbirds Molothrus ater was significantly lower during years when cowbirds were removed (11% of 241 nests parasitised in 1991-5 vs. 64% of 28 nests parasitised in 1984-90). When comparing sites, parasitism rates were lower on sites with cowbird removal (0-11% of 280 nests parasitised at removal sites vs. 38-58% of 32 nests at controls). However, there were no changes in warbler nesting success between sites with low (?5%) and high (>30%) levels of parasitism (average of 1.7 fledglings/nest in sites with low parasitism vs. 1.6 fledglings/nest in sites with high parasitism). The authors suggest that nesting success may be more determined by high rates (22-52%) of predation, than by parasitism. An average of 11-20 female and 7.5-17 male cowbirds were removed each year.


Output references
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 19

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Butterfly Conservation People trust for endangered species Vincet Wildlife Trust