Open corridors in a heavily forested landscape: Impact on shrubland and forest-interior birds

In eastern North America, remnant patches of forest surrounded by open habitat constitute unfavorable habitat for many species of migratory forest birds because of high rates of nest predation and cowbird parasitism. Although most evidence for this relationship comes from \u27forest islands\u27 surrounded by residential or agricultural land, even forest patches isolated from other forests by narrow open corridors such as roads and powerline rights-of-way seem to show this pattern. Productive habitat for migratory birds can be maintained by consolidating corridors and routing them along the periphery of forests to retain as much continuous forest as possible. Consolidation of open corridors provides another major advantage: the area along the corridor can provide a large area of suitable habitat for early successional birds, especially species that are shrubland or thicket specialists. Populations of many species of shrubland birds have declined in eastern North America as open habitats have been developed or have grown into forest. Rights-of-way and other areas subject to periodic artificial disturbance may become increasingly important to these species, which probably originally depended on habitat created by large-scale natural disturbances such as fires and windstorms. Relatively stable shrublands with a diversity of shrubland plants and birds can be maintained by selectively removing trees with basal applications of herbicide

Foraging ecology of temperate-zone and tropical woodpeckers

The foraging behavior of 11 species of woodpeckers in Guatemala, Maryland, and Minnesota was studied in order to test the seasonal stability hypothesis. This hypothesis predicts that specialization and species richness should be no greater for tropical wood-excavators than for those in the temperate zone because wood-excavators in both regions are buffered against seasonal change. Niche breadth values for six variables that describe foraging methods and perches were calculated by two methods. Unweighted niche breadth values were similar for tropical and temperate woodpeckers for all variables except foraging techniques; in this case the temperate species are more specialized. With weighted niche breadth values temperate species are more specialized for two variables and less specialized for two others. Thus there is no consistent tendency for tropical species to be more specialized. However, the excavating guild includes twice as many species in Guatemala as in either of the northern study sites. Two of the three additional species in Guatemala use a configuration of foraging methods and perches not used by northern woodpeckers. Hence the large number of tropical woodpecker species can be attributed partly to the greater range of resources available in the structurally complex rain forest

History of grassland birds in eastern North America

Until recently the severe decline in the populations of many species of grassland birds in eastern North America has aroused relatively little concern or conservation action. This response appears to be rooted in the perception that grassland birds invaded the East Coast from western grasslands after European settlers cleared the forest. Detailed historical accounts and analysis of pollen deposits, however, show that open grasslands existed on the East Coast of North America at the time of European settlement. Extensive grasslands resulted from burning and agricultural clearing by Native Americans. Natural disturbances, such as wildfire and beaver (Castor canadensis) activity, produced grasslands even before Native Americans cleared the forest. The presence of specialized grassland birds in Pleistocene deposits and in the earliest ornithological collections from eastern North America, and the existence of distinctive eastern populations of the Greater Prairie-Chicken (Tympanuchus cupido), Henslows Sparrow (Ammodramus henslowii), and Savannah Sparrow (Passerculus sandwichensis), indicate that grassland birds are an ancient component of biological diversity on the heavily forested East Coast of North America

Response of Bird Populations to Long-term Changes in Local Vegetation and Regional Forest Cover

We analyzed data from a woodland site for a 59-year period to determine whether changes in bird populations are related to changes in the diversity and relative abundance of woody plant species even when vegetation structure, degree of forest fragmentation in the surrounding landscape, and regional changes in bird populations are taken into account. Principal component analyses generated vegetation factors encompassing variables such as total basal area, shrub density, basal area of common tree species, and measures of tree and shrub species diversity. We also calculated a forest edge/ forest area index based on GIS analysis of the landscape within 2 km of the study site. Poisson regression models revealed relationships between these covariates and population changes for 19 bird species and for seven groups of species characterized by similar migration strategies or habitat requirements. All groups of habitat specialists showed a positive relationship with the first vegetation factor, which indicates that they declined as total basal area and dominance of oaks and maples increased and as tree and shrub diversity decreased. This suggests that floristic diversity may be important for determining habitat quality. Bird species associated with the shrub layer and with hemlock stands showed positive relationships with the second vegetation factor, suggesting that the recent decline in eastern hemlocks (Tsuga canadensis) because of hemlock woolly adelgid (Adelges tsugae) had an adverse impact on these species. Forest migrants, shrub-layer specialists, long-distance migrants and permanent residents showed negative relationships with the forest edge/forest interior index, indicating that conservation efforts to protect bird communities should take the wider landscape into account. The strongest relationship for most species and species groups was with the first vegetation factor, which suggests that species composition and diversity of trees and shrubs may be especially important in determining abundance of many forest bird species