Recreational trails, human activity, and nest predation in lowland riparian areas

Abstract

In areas of human settlement, greenways and open-space land are often intended to serve recreational purposes as well as provide wildlife habitat, but the compatibility of these goals is uncertain. We examined the effect of recreational trails on the risk of nest predation and nest predator activity at four lowland riparian sites along the Front Range of Colorado. At one site on each of two streams, we placed a transect of artificial nests near a recreational trail and another transect on the opposite side of the stream. We also placed another transect of nests at a second site on each stream that was not associated with a recreational trail. In 1995, nests were baited with quail eggs; in 1996 a clay egg was also added to nests to aid us in nest predator identification. Artificial nests are not perfect surrogates for natural nests, but are useful in generating hypotheses about causes of nest failure and for detecting changes in predator assemblages. Overall, predation rates were high (94%). There were significant differences in vulnerability to predation on the different transect types, with a tendency for predation rates to increase with distance from trails. There was a significant effect of time with a greater risk of predation in 1996. In 1996, 83% of the clay eggs that were recovered showed signs of predation. House Wrens destroyed 11% of the clay eggs; impressions from Black-billed Magpies, Blue Jays, and Common Grackles were found on 69%; mice preyed on 25%; and squirrels on 12% of the eggs. Birds attacked more nests near trails than away from trails, whereas mammals appeared to avoid nests near trails to some extent. These results support the contention that recreational trails and human activity may affect nesting success for some species, and suggest that patterns of nest predation reflect the unique, and sometimes, counter-intuitive responses of individual predator species. Rather than relying on simplistic assumptions about the compatibility of recreation and wildlife, it is important to consider how individual species respond to the habitat alteration and human activity associated with trails when deciding where trails should be located and in developing overall conservation strategies in human-dominated areas.