Skip to Main Content
Density and Reproductive Success of California TowheesAuthor(s): Kathryn L. Purcell; Jared Verner
Source: Conservation Biology 12(2). Pp. 442-450
Publication Series: Miscellaneous Publication
PDF: Download Publication (0 B)
DescriptionModels of habitat selection commonly asume that higher-quality source habitats will be occupied at higher densities than sink habitats. We examined an apparent sink habitat for California Towhees (Pipilo crissalis) in which densities are greater than in nearby source habitats. We estimated territory density using spot-mapping and monitored nests of towhees in grazed and ungrazed oak-pine woodland habitat. Breeding density of California Towhees was higher in ungrazed oak-pine woodlands than in grazed areas, yet birds in the ungrazed site experienced lower reproductive success. Predation during the nestling period was primarily responsible for the lower nest success. Clutch size and the number of youngfledged were also lower in the ungrazed site. Towhees selected nest sites with high foliage density and cover of live oaks (Quercus wislizenii) in the understory. Grazed sites had greater cover of live oak than ungrazed sites, and successful nests were more often built in live oak than in otherphnt species. This pattern could not be explained by dominant birds settling in grazed sites and excluding subdominant individuals because a large proportion of adults continued to settle in the ungrazed area. Towhees may have perceived the dense foliage of the ungrazed area as suitable due to abundant nest sites, cover, and food, resulting in an "ecological trap." The resulting high density of birds there may have contributed to density-dependent predation. Alternatively, towhees are not ideally adapted to their habitats because of their sedentary habits and site tenacity that is not affected by persistent nest loss. We stress the need to examine the reproductive success and productivity of individual species within specific habitat types.
- You may send email to firstname.lastname@example.org to request a hard copy of this publication.
- (Please specify exactly which publication you are requesting and your mailing address.)
- We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
- This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
CitationPurcell, Kathryn L.; Verner, Jared. 1998. Density and Reproductive Success of California Towhees. Conservation Biology 12(2). Pp. 442-450
- Thinning interior live oak in California's Southern Sierra Nevada
- Habitat relationships of amphibians and reptiles in California oak woodlands
- Population diversity and evidence of introgression among the black oaks of California
XML: View XML