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Movements of wildlife species and associated colonization of habitats is often unpredictable. In the case of federally listed or at-risk species on military installations, this unpredictability can lead to ineffective management and/or interference with military training. Habitat restoration for wildlife management on military lands is a common, yet expensive, response to federal conservation (e.g. Endangered Species Act) and mitigation (e.g. Clean Water Act; Section 404) mandates, yet viable wildlife populations often fail to become established on restored habitat. As such, managers are tasked with encouraging animals to colonize restored habitat and methods for achieving this goal range from no active management (e.g. build it and they will come) to translocation of adults or eggs/young. These methods are often ineffective and/or expensive. Conspecific attraction, using the tendency for individuals of the same species to settle near one another, provides an alternative tool that can be a cost-effective means of attracting animals to newly created or restored habitats. The objectives of this project were to demonstrate the use of conspecific attraction as a cost-effective management tool for encouraging colonization of restored habitats by at-risk birds and amphibians and test the use of conspecific attraction to establish populations following cessation of the broadcast calls.
Prerecorded vocalizations of target species were broadcast from a playback system within focal areas, which consisted of a call box on a timer powered by a battery. Vocalizations were broadcast throughout the focal species’ breeding seasons from restored habitats, encouraging individuals to settle and breed near the playback system.
Conspecific attraction was relatively straight-forward to employ, but its effectiveness varied among species. The research team demonstrated clear success in attracting some bird and frog species into the target areas. In particular, northern bobwhite (Colinus virginianus) abundance increased dramatically on treatment plots and remained relatively high following cessation of calls. Abundance remained high or increased on treatment plots for grasshopper sparrows (Ammodramus savannarum). There was a trend for the proportion of treatment ponds colonized by wood frogs (Lithobates sylvaticus) to be higher (40% of ponds) than silent control ponds (10% of ponds). Similarly, eastern grey tree frogs (Hyla versicolor) colonized 30% of treatment ponds but no control ponds. However, many species showed a neutral response to conspecific playback, demonstrating the species-specific nature of this technique’s effectiveness.
Conspecific attraction presents an extremely cost-effective alternative to current management practices such as translocation or relying on passive colonization after habitat is created or restored. Only minimal equipment costs (<$300/broadcast station) and nominal man hours are required to set up the equipment, and total cost was ~$1,200 per demonstration plot annually. This approach costs approximately 0.1–10 percent of a comparable translocation, which can cost between $10,000 to well over $1,000,000 annually.
The primarily implementation issue encountered was the variation in effectiveness across the numerous species tested (25% of bird species and 50% of frog species). Species that are at low or moderate abundances tend to exhibit the highest responses to playback. Conspecific attraction may not be as effective for species occurring in relatively high abundances or that rely on more permanent breeding habitats.