Song sparrows, top carnivores and nest predation: a test of the mesopredator release hypothesis

Abstract

Ground-nesting North American landbirds have declined in the longterm, including species with a variety of migratory strategies. The mesopredator release hypothesis explains declines by suggesting that the virtual elimination of top carnivores (large-bodied canids and felids) from much of North America has "released" populations of nest-destroying mesopredators (i.e., medium-sized terrestrial omnivores such as the raccoon Procyon lotor). The hypothesis predicts (1) higher nest success in the presence than in the absence of top carnivores, and (2) a positive relationship between mesopredator abundance and nest predation. Results from a 4-year "natural experiment" in the agricultural landscape of southern Michigan tended to support prediction 1. When coyotes (Canis latrans) were absent in 1993 and present in 1994, 1995 and 1996, Mayfield nest survival in song sparrows (Melospiza melodia), a ground-nesting landbird, increased significantly during the same 4-year interval. Relative frequency of nest predation, the most common cause of nest failure, declined significantly over the four years. Coyotes may have decreased nest predation in 1994-1996 by reducing the abundance of raccoons, apparently the main nest predator in the study area. In an experiment testing prediction 2, mesopredator abundance and predation rate on artificial nests were positively related, as predicted by the hypothesis. Although the present study is not wholly conclusive by itself, we cautiously suggest it contributes to a growing body of evidence derived from a number of studies supporting the mesopredator release hypothesis.

Initial colonization of Long Island, New York by the eastern coyote, Canis latrans (Carnivora, Canidae), including first record of breeding

“…In this case, we received numerous-albeit unconfirmed-reports that this pair of coyotes had lived and bred for several years in the original 7.64 ha woodlot and, we speculate, only became visible to officials and the larger community once their territory was developed and they were forced to move their 8 young pups out of the woodlot. Also, coyotes are one of the few predators that can thrive in developed environments and thus may fill a valuable ecological role (Rogers and Caro 1998, Henke and Bryant 1999, Crooks and Soule 1999, Cherry et al 2016). Managers and officials should thus implement management policies that focus on coexistence, public education, aversive conditioning, and conservation ethics rather than broad-scale lethal removal, although targeted lethal removal needs to remain an option for genuine problem animals.…”

Anthropogenic resource subsidies decouple predator–prey relationships

“…Indeed, predator-prey interactions have profoundly influenced the evolution of life history traits and breeding ecology of birds, as nest predation is the major source of avian reproductive failure in most systems (Ricklefs 1969, Martin 1988. The impact of predators on reproductive success generally increases with abundance and/or activity of nest predators (e.g., Andre´n 1992; Zanette andJenkins 2000, Weidinger 2002), though loss of apex predators also can reduce nest survival via mesopredator release (Rogers and Caro 1998, Crooks and Soule´1999, Terborgh et al 2001, Rayner et al 2007.…”

Could controlling mammalian carnivores lead to mesopredator release of carnivorous reptiles?

“…Competitive interactions can be complex and shifts in their dynamics have resulted in unpredictable and sometimes profound impacts on lower trophic levels [3,4]. Compelling examples are emerging describing the deleterious impacts that subordinate predators, or mesopredators, inflict on prey species after being released from competition with a dominant predator [5][6][7][8][9][10]. Some instances of mesopredator release have yielded counterintuitive outcomes; for example, the removal of cats from an island resulted in a decline rather than an increase in the resident seabird colony because rats were released from regulation by cats, resulting in an increase in rat numbers and egg predation rates [4].…”