How increasing levels of private land enrollment in conservation agreements affect the population viability of grassland birds

There is a growing recognition that to effectively conserve biodiversity efforts have to extend into the realm of engaging private landowners. Agricultural lands have been particularly attractive targets for integrating conservation and production goals. Changes in hayfield management associated with agricultural intensification, including earlier and more frequent harvests, have a severe impact on grassland birds. Government-administered conservation incentive programs benefit grassland birds by delaying harvest dates on enrolled land to allow nesting pairs to successfully fledge at least one brood during the breeding season. In contrast, hayfields that are mowed during the breeding season support sink populations and may function as ecological traps. We examined the effect of increasing levels of hayfield enrollment on grasshopper sparrow population viability using a spatially-explicit, stage-structured, stochastic model of a grasshopper sparrow metapopulation in an urbanizing region of New Jersey. The probability of metapopulation extinction (POE) decreased as the proportion of enrolled hayfields increased and fell below 10% when about half of all available agricultural land was enrolled. POE also decreased with increasing numbers of enrolled hayfields most likely because hayfield enrollment removes a sink population from the landscape in addition to creating a source population. Our results are encouraging as they demonstrate that extinction risk for this grassland-dependent imperiled species can be reduced without having to protect or manage all remaining grassland habitat in the landscape.