Contribution of urban-suburban tree care practices to reduced habitat for cavity nesting birds

Cavity nesting birds are among the bird species most strongly impacted by urbanization, due in part to reduced abundance of a key resource, snags or standing dead trees. However, many cavity nesters also nest in dead portions of live trees, and less is known about the distribution and management of this resource. A candidate mechanism affecting this resource is arboricultural tree care, a practice which typically removes hazardous deadwood from places that impact people or property. Using standardized hazard ratings by certified arborists, we assessed the degree of overlap between tree hazards and bird habitat in 3 locations spanning a wildland-urban gradient. We conducted vegetation sampling, bird counts, and hazard ratings along 100m transects. We conducted nest monitoring in the wildland site, an area of abandoned town sites in western Massachusetts with relatively unmanaged, open-grown trees and an intact cavity nesting bird community. Trees used by cavity nesting birds exhibited higher hazard ratings than nearby randomly chosen trees of the same size and species, particularly in the category of “probability of failure” (probability of falling). In addition, the wildlands location had proportionally greater numbers of trees with both high hazard ratings and suitable nesting habitat than trees in suburban and urban residential plots. The relationship between probability of failure and presence of suitable nesting habitat is nonlinear. Thus, while tree care practices likely constitute an important factor in loss of habitat for cavity nesting birds, it may be possible to reduce these impacts without increasing hazards to people and property.