Unlocking Some Of The Untapped Value Associated With Our 20-Year Landbird Monitoring Database

Twenty years ago, numerous partners initiated a region-wide landbird monitoring program. I will provide a brief history, will describe the data we now have in hand, and will present a few results that have important management implications. Finally, I will discuss the niche modeling potential buried in the data that we have amassed, and will propose that the strategic placement of additional monitoring points carries the greatest chance of yielding useful results for wildlife biologists who work for land management and conservation organizations. We hope to pilot the new approach within a 3-forest region associated with the Southern Crown’s Collaborative Forest Landscape Restoration Partnership this year

Seasonal Variation in the Foraging Behavior of Some Migratory Western Wood Warblers

I observed the foraging behavior of four warbler species (Dendroica petechia, Oporornis tolmiei, Geothlypis trichas, and Wilsonia pusilla) in the summer in Wyoming and in the winter in Nayarit, Mexico. Of six variables (absolute foraging height, relative foraging height, vegetation density, horizontal foraging position, feeding method, and foraging substrate) believed to be potentially important in distinguishing the warbler species ecologically, the two foragingheight variables provided the greatest separation of the four species in both summer and winter. An analysis of the behavioral similarity of each species from summer to winter revealed that feeding method was the least changed behavior and that absolute foraging height involved the greatest behavioral flexibility. The behaviors that are most flexible are possibly the least well tied to the birds\u27 morphology and are also the ones that have been shown by other workers to reveal the effects of competitors through niche shifts. Therefore, ecological relationships among coexisting species (in terms of overlaps or positions in niche space) may never be fully derivable from morphological information alone

Seasonal-Changes in the Habitat Distribution of Transient Insectivorous Birds in Southeastern Arizona: Competition Mediated

The distribution and abundance of 26 migratory insectivorous bird species were recorded over an elevational habitat gradient in the Chiricahua Mountains, Arizona for the spring and fall migratory seasons. Most of the species used this area only during migratory passage, and 54% exhibited significant shifts in the habitats occupied from spring to fall. The majority (69%) of species also exhibited significant changes in density within habitats between seasons. Using pairwise correlations of bird densities from 7 habitat types and 2 seasons, I identified 5 groups that contained species whose seasonal distributional patterns were similar to one another but independent and distinct from members of the other 4 groups. Despite independence among groups in the seasonal patterns of habitat distribution, the combined density of all species was significantly positively correlated with a measure of food availability taken from each of the habitat types in each migratory season. Consequently, the spring-to-fall change in insect density within each habitat also was significantly correlated with the seasonal change in bird density over each of the habitat types. The hypotheses that best explain these correlations include that in which competitive adjustments among the migratory birds enable a close match to food resource availability and that whereby noncompetitive adjustments occur in response to the diversity (itself correlated with food abundance) of food types available

A Description of Mixed-Species Insectivorous Bird Flocks in Western Mexico

Insectivorous bird flocks were observed in all types of forested habitats during the nonbreeding season in western Mexico. The species composition of flocks changed markedly and predictably among five categories of habitat type. The average number of species per flock in lowland habitats was 4.7, while a mean of 18.6 species participated in highland flocks, ranking the latter among the most species-rich flocks in the world. The mean proportion of the local insectivorous species that participated in mixed-species flocks was significantly greater in the highlands (61.3%) than in the lowlands (24.6%). About half of the flock participants in both undisturbed lowland and highland habitats were north temperate migrants, ranking west Mexican flocks among the most migrant-rich in the world as well. In highland flocks, the maximum number of individuals per attendant species was generally two to three, but there were often six to twelve individuals belonging to each of several nuclear species. The lowland deciduous forest flocks seemed to lack nuclear species