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Dependence of the endangered black-capped vireo on sustained cowbird management
Wilsey, C., J. Lawler, D. Cimprich, AND N. Schumaker. Dependence of the endangered black-capped vireo on sustained cowbird management. CONSERVATION BIOLOGY. Blackwell Publishing, Malden, MA, 28(2):561-571, (2014).
The US military owns much of the habitat remaining for the endangered Black-capped Vireo. Habitat loss and fragmentation, have heavily impacted vireo populations over the past century. and climate change will have an increasing effect on their viability into the future. But the Black-capped Vireo also suffers from intense nest parasitization from the Brov.n-headed Cowbird. The US military has been controlling cowbird populations at great effort and expense. This paper examines the extent to which the military must continue to control cowbirds into the future in order to ensure vireo population viability.
Conservation-reliant species depend on active management for sustained protection from persistent threats. For species that are listed as threatened or endangered under the U.S. Endangered Species Act, being conservation-reliant means that they require continued management even after abundances have surpassed recovery goals. Required management may include control of another species, habitat maintenance, or artificial recruitment. In some cases, it may be difficult to determine if persistence requires sustained management. Here, we use a spatially explicit population modeling platform, HexSim, to simulate the management of a brood parasite, the Brown-headed Cowbird (Moluthrus ater), on a population of the endangered Black capped Vireo (Vireo atricapilla). The two-species simulation model includes common life history events (e.g. immigration/emigration, dispersal, reproduction, and survival) as well as impacts of cowbird population management and brood parasitism. Our model is constructed from data on vireos and cowbirds collected on the Fort Hood Military Reservation, Texas, U.S.A. It includes observed responses to cowbird trapping and shooting over the past 15 years as well as responses to a broad-scale experimental cessation of cowbird trapping on Fort Hood from 2006-2010. Our simulations under potential future conditions show that in the absence of cowbird control, vireo populations will likely fall below the minimum population recovery target. In general, lowering the frequency of cowbird control activities results in a declining vireo population, but limiting cowbird control to a portion of Fort Hood, or limiting base-wide actions to alternating years both resulted in smaller (11-48% declines) but stable vireo populations. Our simulations suggest that vireos are a conservation-reliant species that will depend on cowbird control actions as long as cowbird densities remain high.