89 The Wilson Journal of Ornithology 121(1):89–96, 2009 NEST NICHE PARTITIONING OF LEWIS’S AND RED-HEADED WOODPECKERS IN BURNED PINE FORESTS KERRI T. VIERLING, 1,6 DALE J. GENTRY, 2,4 AND AARON M. HAINES 3,5 ABSTRACT.—Lewis’s (Melanerpes lewis) and Red-headed Woodpecker (Melanerpes erythrocephalus) breed- ing ranges overlap slightly, but co-occurrence within habitats is thought to be rare because of niche similarity. Our objectives were to examine factors that allowed for co-existence in two burned pine (Pinus ponderosa) forests in the Black Hills, South Dakota. We monitored 53 Lewis’s and 38 Red-headed Woodpecker nests between 2002 and 2005, and compared clutch initiation dates and nest-site selection. Clutch initiation dates did not differ between species for 3 of 4 years. We compared multiple habitat factors surrounding nests of the two species, and only tree and snag densities differed between Red-headed Woodpecker nest sites (65.1  5.78 stems/ha) and those of Lewis’s Woodpeckers (48.5  6.06 stems/ha). These results are consistent with the foraging techniques used by the two species. We suggest that habitat partitioning is an important mechanism of coexistence for these two species, but also recommend further research on their foraging strategies. Received 3 December 2007. Accepted 2 June 2008. The coexistence of ecologically equivalent species is unlikely; mechanisms that allow for coexistence include habitat partitioning, use of resources during different times (i.e., temporal partitioning), and/or differential use of food (Schoener 1974, Anderson et al. 2002). Hab- itat partitioning between ecologically equiva- lent avian species is often evaluated using metrics such as nest site selection. For ex- ample, Martin and Martin (2001) examined the effect of Orange-crowned Warbler (Ver- mivora celata) removal on Virginia’s Warbler (V. virginiae) nest site selection and the effect of Virginia’s Warbler removal on Orange- crowned Warbler nest site selection. The re- sponses were asymmetric; Orange-crowned Warblers did not shift nest sites in response to Virginia’s Warbler removal but Virginia’s Warblers shifted nest sites in response to the removal of Orange-crowned Warblers (Martin and Martin 2001). These authors noted that a greater understanding of habitat partitioning is 1 Department of Fish and Wildlife, University of Idaho, P. O. Box 441136, Moscow, ID 83844, USA. 2 South Dakota School of Mines and Technology, 501 East Saint Joseph Street, Rapid City, SD 57701, USA. 3 Center for Research on Invasive Species and Small Populations, University of Idaho, P. O. Box 441141, Moscow, ID 83844, USA. 4 Current address: Teton Science Schools, 700 Coy- ote Canyon Road, Jackson, WY 83001, USA. 5 Current address: Upper Iowa University, Division of Science and Mathematics, P. O. Box 1857, 605 Washington Street, Fayette, IA 52142, USA. 6 Corresponding author; e-mail: kerriv@uidaho.edu important, particularly regarding the potential ecological consequences of coexistence be- tween ecologically similar species. Temporal partitioning of resources may also allow for coexistence of ecologically similar species. For example, differences in nesting phenologies by cavity nesters may decrease interspecific interactions and faciliate coexis- tence. Ingold (1989) studied the nesting phe- nologies of three co-occurring cavity nesters in Ohio. He found that Red-headed Wood- peckers (Melanerpes erythrocephalus) likely experienced little competition from European Starlings (Sturnus vulgaris) because of large differences in nesting phenologies, whereas Red-bellied Woodpeckers (M. carolinus) had a higher frequency of interactions with Euro- pean Starlings due to similarities in nesting phenologies of the two species. Lewis’s (M. lewis) and Red-headed wood- peckers have been hypothesized to be ecolog- ical equivalents (Bock et al. 1971) due to sim- ilarities in nest requirements, foraging activi- ties, and life history traits. Lewis’s Wood- peckers are aerial insectivores that require open forests in which to flycatch (e.g., Vier- ling 1997) and, additionally, require large snags in which to nest (Vierling 1997, Saab and Vierling 2001). Similarly, Red-headed Woodpeckers occur in open woodlands during the breeding season and use a diversity of for- aging habits including flycatching, gleaning, and excavating (Smith et al. 2000). Both spe- cies store mast (e.g., acorns, corn, nuts), which is a major food supply throughout the