Reduction in host use suggests host specificity in individual shiny cowbirds (Molothrus bonariensis)

Published source details López-Ortiz R., Ventosa-Febles E.A., Ramos-Álvarez K.R., Medina-Miranda R. & Cruz A. (2006) Reducción en el uso de hospedero sugiere especificidad de hospedero en individuos de Tordos Lustrosos (Molothrus bonariensis) . Ornitología Neotropical, 17, 259-269.
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This study is summarised as evidence for the following.

	Action	Category
	Remove brood parasite eggs from target species’ nests Action Link
	Remove/control adult brood parasites Action Link

Remove brood parasite eggs from target species’ nests

A controlled before-and-after study in mangrove forests on Puerto Rico in 2000, 2001 and 2003 (López-Ortiz et al. 2006) found that a significantly lower proportion of yellow-shouldered blackbird Agelaius xanthomus nests were parasitised by shiny cowbirds Molothrus bonariensis, compared to yellow warbler Dendroica petechia nests, following the removal of cowbird eggs and chicks from artificial nests used by blackbirds from 1991, and the control of adult cowbirds from 1983 (3% of 927 blackbird nests vs. 37% of 165 warbler nests). Prior to cowbird control, parasitism rates had been higher for blackbirds (91-95% of 202 blackbird nests in 1975-83 vs. 63% of warbler nests). Parasitism rates in areas without cowbird control were lower for blackbirds (44% of 32 nests) and higher for warblers (85% of 13 nests). The authors suggest that removing eggs and nestlings reduces the proportion of cowbirds that imprint on specific hosts, reducing future parasitism. The effect of adult cowbird removal is discussed in ‘Remove adult brood parasites’.
Remove/control adult brood parasites

A controlled before-and-after study in 2000, 2001 and 2003 in mangrove forests in Puerto Rico (López-Ortiz et al. 2006) found that a significantly lower proportion of yellow-shouldered blackbird Agelaius xanthomus and yellow warbler Dendroica petechia nests were parasitized by shiny cowbirds Molothrus bonariensis following the removal of adult cowbirds (from 1982 onwards), cowbird eggs and chicks from artificial nests used by blackbirds (from 1991 onwards) (blackbirds: 91-95% of 202 nests studied in 1975-83 vs. 3% of 927 nests in 2000, 2001 and 2003; warblers: 63% of nests in 1975-83 vs. 37% of 165 nests in 2000, 2001 and 2003). Decreases in areas without cowbird control were either smaller or non-existent (44% of 32 blackbird nests and 85% of 13 warbler nests in reference areas parasitised). The effect of egg and chick removal is discussed in ‘Remove brood parasite eggs from target species’ nests’.