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Predator removal may not increase nesting success

You may have experienced the disappointment that accompanies a nest failure, whether due to bad weather, nest parasitism, or predators. When a predator raids a nest that you monitor, it is common to wonder if there is anything that you can do to eliminate this threat. But before you blame that snake or raccoon, please consider that every animal has a role to play in its environment and birds have always experienced such losses to some degree. Also, eliminating specific nest predators from an area may have little impact on the overall survival of bird populations.

Scientists recently observed nests of Northern Bobwhite with cameras to learn if predator removal would increase bobwhite nesting success. (This species nests on the ground and typically has low nesting success.) They found that the removal of common predators, like raccoons, opossums, and armadillos, did make these species less abundant within the area, but it did not increase the bobwhites’ nesting success. When these predators were removed, other less common predators, such as snakes, rodents, and fire ants, preyed on nests instead. This effect is known as compensatory mortality, and it applies to fledglings and adult birds, too. Although it’s upsetting to witness the consequences of a predator visiting a nest, keep in mind that it’s impossible to completely eradicate all predators and removing one primary predator from an area can actually make matters worse by allowing other nest predators, which were formerly kept in check by the primary predator, to thrive. Take heart, though, because a good number of young birds do fledge–many of them, no doubt, thanks to the favorable habitat and predator guards provided by many nest monitors. For tips on safeguarding nests, read our article on Dealing with Predators and our Code of Conduct.

Reference: Ellis-Felege, S. N., M. J. Conroy, W. E. Palmer, and J. P. Carroll. 2012. Predator reduction results in compensatory shifts in losses of avian ground nests. Journal of Applied Ecology 49(3):661-669.

Cornell Lab of Ornithology

Cornell Lab of Ornithology