Habitat attributes and chestnut-backed chickadee nest site selection in uncut and partial-cut forests

We examined the relationship between habitat attributes and nest-site selection by chestnut-backed chickadees ( Poecile rufescens (Townsend, 1837); hereinafter chickadees) in uncut and partial-cut forests in northwest British Columbia. We described the characteristics of uncut sites and compared them with structurally modified partial-cut sites (mature and old forests). We then compared the use and selection of habitat by chickadees at uncut and partial-cut sites at three spatial scales: (1) the stand (19–24 ha uncut or partial-cut stand), (2) the nest patch (a 0.031 ha patch centered on nest trees), and (3) the nest tree. At the stand scale, we found no correlation between the density of breeding chickadees and the characteristics of uncut and partial-cut sites. At the nest-patch scale, chickadees in uncut and old partial-cut sites selected nest patches with higher densities of broken-top trees compared with available habitat within territories. At the nest-tree scale, chickadees selected nest trees with boring insects and broken tops in uncut and mature partial-cut sites and large trees with boring insects in old partial-cut sites. Our results suggest that chickadees exhibited flexibility in resource selection but also selected resources with similar attributes at the nest-patch and nest-tree scales. Managed stands that maintain a range of tree species and conditions, including live trees with areas of disease, insect attack, and damage, will provide the specific structural attributes used for nesting by weak cavity excavators such as the chickadee.

Effects of Urban Sprawl on Snags and the Abundance and Productivity of Cavity-Nesting Birds

We investigated the occurrence of, and relationships among, snags and cavity-nesting birds in the rapidly urbanizing region around Seattle, Washington in 2001 and 2002. We measured the density of snags in 49 sites (1-km2 “suburban landscapes” that included built and forested portions), and determined the diameter, height, decay status, and species of individual snags. We spot-mapped territories and observed nests of cavity-nesting birds at a stratified, random subsample of 13 sites. Snags, especially red alder (Alnus rubra), were abundant in sites' forested portions, but rare in the built portions. Snag density was positively correlated with density of live trees. Snags in built versus forested portions were similar in all attributes except decay, which was more advanced in forested areas. In the oldest suburbs (60–80 years old), snags in forested portions were larger, more decayed, and more likely to have broken tops than those in younger suburbs (2–20 years old). Cavity-nesting bird species richness and equity of individuals per species was highest in suburban landscapes where remaining forest was not fragmented, but adjacent to highly intermixed urban and urban-forest land covers. Suburban landscapes with highly interspersed land covers had higher densities of Black-capped Chickadees (Poecile atricapillus), Red-breasted Nuthatches (Sitta canadensis), Northern Flickers (Colaptes auratus) and Downy Woodpeckers (Picoides pubescens); suburban landscapes with higher percentages of forest had higher densities of Brown Creepers (Certhia americana), Chestnut-backed Chickadees (Poecile rufescens), Pileated (Dryocopus pileatus) and Hairy Woodpeckers (Picoides villosus). Red-breasted Sapsucker (Sphyrapicus ruber) densities were positively correlated only with the density of snags. All study sites had low bird densities compared to wildlands, presumably due to the relative lack of live trees and snags. Cavity-nesting birds bred successfully in all landscapes; seven of the nine species produced fledglings in >50% of their nesting attempts. Snags important for nesting were larger in diameter, taller, and more decayed than expected based on availability. Snags with active nests also had evidence of previous use, fungal conks, broken tops, and substantial bark. Efectos de la Expansión Urbana sobre la Abundancia y la Productividad de Aves que Nidifican en Cavidades Resumen. Durante el 2001 y 2002, investigamos la presencia de, y la relación entre, troncos muertos y aves que nidifican en cavidades en los alrededores de Seattle (Washington), una región que está urbanizándose rápidamente. Medimos la densidad de troncos en 49 sitios (1-km2 de “paisajes suburbanos” que incluyeron ambientes edificados y bosques) y determinamos el diámetro, altura, estado de descomposición y especie de troncos individuales. Mapeamos los territorios mediante registros puntuales y observamos los nidos de aves que nidifican en cavidades en una sub-muestra estratificada y al azar de 13 sitios. Los troncos, especialmente de Alnus rubra, fueron abundantes en las áreas con bosque, pero raros en las áreas edificadas. La densidad de troncos se correlacionó positivamente con la densidad de árboles vivos. Los troncos de las áreas edificadas y de las áreas con bosque fueron similares en todos sus atributos excepto en su descomposición, que fue más avanzada en los sitios boscosos. En los suburbios más viejos (60–80 años), los troncos en las áreas con bosque fueron más grandes, estuvieron más descompuestos y presentaron mayor probabilidad de tener sus extremos rotos que aquellos presentes en los suburbios más nuevos (2–20 años). La riqueza de especies que nidifican en cavidades y la equitatividad de individuos por especie fueron mayores en los paisajes suburbanos donde el bosque remanente no estaba fragmentado, sino adyacente a coberturas con una gran mezcla de sitios urbanos y sitios en la transición bosque-ciudad. Los paisajes suburbanos con coberturas ampliamente entremezcladas presentaron mayores densidades de Poecile atricapillus, Sitta canadensis, Colaptes auratus y Picoides pubescens; los paisajes suburbanos con porcentajes más altos de bosque presentaron mayores densidades de Certhia americana, Poecile rufescens, Dryocopus pileatus y Picoides villosus. Las densidades de Sphyrapicus ruber sólo se correlacionaron positivamente con la densidad de troncos. Todos los sitios de estudio tuvieron bajas densidades de aves comparados con áreas silvestres, debido presumiblemente a la carencia relativa de árboles vivos y troncos. Las aves que nidifican en cavidades criaron con éxito en todos los paisajes; siete de las nueve especies produjeron volantones en >50% de sus intentos de nidificación. Los troncos importantes para nidificar fueron más grandes en diá metro y altura y estuvieron más descompuestos que lo esperado con relación a su disponibilidad. Los troncos con nidos activos también presentaron evidencias de uso previo, deformaciones producidas por hongos, copas rotas y bastante corteza.

Bird Communities of the Garry Oak Habitat in Southwestern British Columbia

Identifying the bird communities of a habitat could contribute to conservation efforts and provide benchmarks for ecosystem studies. Garry Oak (Quercus garryana) ecosystems in British Columbia are among the most endangered in Canada and warrant conservation. Four bird communities were determined by analyzing an extensive sample of Garry Oak habitat bird data. These communities were defined objectively by aggregations of the bird species themselves from across the various sites and areas. Characteristic species of these communities include American Goldfinch (Carduelis tristis), Spotted Towhee (Pipilo maculatus), Bewick’s Wren (Thryomanes bewickii), Rufous Hummingbird (Selasphorus rufus) and Chestnut-backed Chickadee (Poecile rufescens) in community 1; House Wren (Troglodytes aedon), Olive-sided Flycatcher (Contopus cooperi), Purple Finch (Carpodacus purpureus), White-crowned Sparrow (Zonotrichia leucophrys), and Pine Siskin (Carduelis pinus) in community 2; Western Tanager (Piranga ludoviciana),Yellow-rumped Warbler (Dendroica coronata), American Goldfinch, Pine Siskin, Pacific-slope Flycatcher (Empidonax difficilis), Cassin’s Vireo (Vireo cassinii) and Chipping Sparrow (Spizella passerina) in community 3; and Northwestern Crow (Corvus caurinus) and European Starling (Sturnus vulgaris) in community 4. Differences between the communities are suggested from the life history traits of the species, including a community consisting mostly of insectivores when on breeding territory (number 1), one with species foraging primarily in shrubs and trees (community 3), and another with tree-nesting ground gleaners (number 4). One community (number 3) had analogues in two widely disparate areas: oak-associated in north-central New Mexico, and aspen (Populus tremuloides)-related in northcentral British Columbia; otherwise communities reported in the literature were generally not directly comparable.