Predator activity and nest success of willow flycatchers and yellow warblers Academic Article uri icon


  • Willow flycatchers (Empidonax traillii) and yellow warblers (Dendroica petechia) are riparian-dependent species that have declined throughout much of their former range in California, USA. These declines have been primarily associated with the loss of riparian breeding habitat, increases in brood parasitism, and increases in nest predation. We (1) identified potential nest predators using inactive yellow warbler nests; (2) determined the relationship of meadow wetness, meadow size, and amount of edge to predator activity; (3) determined the association between potential nest predator activity and nest success; and (4) determined how proximity to forest edge and isolated trees was related to nest success. We used automatic cameras to monitor inactive yellow warbler nests baited with zebra finch (Taeniopygia guttata) eggs to identify nest predators. We used track plates (mammalian), point counts (avian), and time-constrained searches (reptilian) to assess the activity of potential nest predators. We photographed short-tailed weasel (Mustela erminea), Douglas squirrel (Tamiasciurus douglasii), lodgepole chipmunk (Tamias speciosus), deer mouse (Peromyscus maniculatus), and unidentified chipmunks (Tamias spp.) depredating yellow warbler nests baited with finch eggs. The amount of meadow covered with water was negatively associated with the activity of chipmunks and Douglas squirrels. Meadow size was negatively associated with Douglas squirrel activity. The amount of edge was positively associated with the activity of Douglas squirrels, chipmunks, Steller's jays (Cyanocitta stellen), and brown-headed cowbirds (Molothrus ater). Nest predation was the major cause of nest failure in our study. However, only short-tailed weasels, Douglas squirrels, Clark's nutcrackers (Nucifraga columbiana), Steller's jays, Cooper's hawks (Accipiter cooperii), and brown-headed cowbirds had activity indices that were negatively associated with nest success of either species. The distance to isolated trees was associated with willow flycatcher nest success, whereas the distance to both isolated trees and to the forest edge was associated with yellow warbler nest success - nests located closer to isolated trees and the forest edge were more likely to be parasitized and/or depredated. Our results suggest that flooding portions of meadows may restrict meadow access to forest-edge-associated nest predators.

published proceedings

  • Journal of Wildlife Management

author list (cited authors)

  • Cain, J. W., Morrison, M. L., & Bombay, H. L.

complete list of authors

  • Cain, JW||Morrison, ML||Bombay, HL

publication date

  • July 2003