Ecology and Management of Shiny Cowbirds (Molothrus bonariensis) and Endangered Yellow-Shouldered Blackbirds (Agelaius xanthomus) in Puerto Rico

Abstract

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Brood parasitism leads to zero recruitment in the globally endangered Yellow CardinalGubernatrix cristata

“…Hence, evaluating Shiny Cowbird densities and eventually controlling Shiny Cowbird populations might be considered in future conservation plans for Yellow Cardinals. Control strategies on brood parasites have improved the reproductive success of threatened species in the past (Cruz et al 2005, Krabbe et al 2011, Hartmann et al 2017. These studies have shown that trapping cowbirds near host nesting areas and cowbird feeding areas, as well as shooting cowbirds, resulted in marked population increases of the threatened host species.…”

“…Hence, evaluating Shiny Cowbird densities and eventually controlling Shiny Cowbird populations might be considered in future conservation plans for Yellow Cardinals. Control strategies on brood parasites have improved the reproductive success of threatened species in the past (Cruz et al 2005, Krabbe et al 2011, Hartmann et al . 2017).…”

Invasive birds: global trends and impacts

“…Brood parasitism by Shiny Cowbirds reduces the breeding success of their hosts in several ways. First, parasite females peck and puncture host eggs during parasitic and non-parasitic visits, reducing clutch size and increasing the probability of nest abandonment (Post and Wiley, 1977b;Cruz and Andrews, 1997;Kattan, 1998;Reboreda, 1998, 2002;Mermoz and Reboreda, 1999;Sackmann and Reboreda, 2003;Cruz et al, 2005;Astié and Reboreda, 2009;Dominguez et al, 2015). Second, parasite eggs may interfere with host incubation lowering the hatching success of the remaining host eggs (Wiley, 1985;Woodworth, 1997;Reboreda, 2006, Tuero et al, 2007).…”

“…In the Antilles, three endemic species, the Bahamas Oriole (Icterus northropi; Price et al, 2011), the Yellowshouldered Blackbird (Cruz et al, 2005) and the Puerto Rican Vireo (Woodworth, 1997) suffer the joint pressure of anthropogenic habitat loss and brood parasitism by the Shiny Cowbird. Two of these species are threatened globally: the Bahamas Oriole (critically endangered) and Yellow-shouldered Blackbird (endangered) (IUCN, 2018).…”

“…Shiny Cowbird trapping was established from 1985 to 2003 in south-western Puerto Rico, near the breeding areas of the globally endangered Yellow-shouldered Blackbird, which in 1982 had a population of approximately 300 individuals (Wiley et al, 1991). During that period, 29,981 Shiny Cowbirds were captured, and parasitism on Yellow-shouldered Blackbird nests dropped from 95% (pre-trapping period, 1973-1983) to less than 10% (trapping period, 1985-2003) (Cruz et al, 2005). Since 1985, control of Shiny Cowbirds through adult trapping and egg and chick removal in nests built in artificial structures has been implemented without interruption.…”