Individual study: Effects of trapping brown-headed cowbirds Molothrus ater on the nesting success of dickcissel Spiza americana at Konza Prairie Biological Station, Kansas, USA
Sandercock B.K., Hewett E.L. & Kosciuch K.L. (2008) Effects of experimental cowbird removals on brood parasitism and nest predation in a grassland songbird. The Auk, 125, 820-830
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
A controlled cross-over experiment at four 24-36 ha tall-grass prairie sites in Kansas, USA (Sandercock et al. 2008) found that, in 2004, parasitism of dickcissel Spiza americana nests by brown-headed cowbirds Molothrus bonariensis was significantly lower in two plots where 346 cowbirds were removed (76 adult females, 231 adult males and 39 juveniles) than in two control plots (51% of 53 treatment nests and 85% of 27 control nests respectively). However, in 2005 when treatments were reversed and 634 cowbirds (95 adult females, 493 adult males and 46 juveniles) removed from the remaining two plots, there was no such difference (78% of 45 nests and 82% of 44 nests respectively). In neither year were there differences in dickcissel productivity between experimental and control plots (2004: 0.32 and 0.29 chicks/nest respectively; 2005: 0.06 and 0.04 chicks/nest respectively). The authors suggest that nest survival was very low (34% in 2004, 7% in 2005) due to predation and other causes, not because of parasitism.