Birds and other wildlife depend on urban trees. How trees are cared for can greatly enhance or diminish the habitat value of those trees. While many tree care workers and managers appreciate wildlife, they have little information about how work can best be accomplished with minimal or no negative impact to wildlife. In the past two years, arborists, wildlife biologists, and many other professionals in California have worked together to develop Best Management Practices (BMPs) to guide tree care workers, property managers, and homeowners to care for trees AND wildlife. A tree care worker’s knowledge about the needs and nesting habits of wildlife can translate into protecting and enhancing habitat, but it also enables the arborist to offer clients the added service of good environmental stewardship. Wildlife provide uncountable ecological services which directly and indirectly benefit humans. Greater awareness offers new opportunities to the industry and those that hire them.
Tree care activities are handled by many people with various levels of training and responsibility. Many factors go into tree care decisions such as: plant health, branch structure, clearance requirements, aesthetics, risk, and climber safety. Tree care practices are outlined by the International Society for Arboriculture (http://www.isa-arbor.com/store/product.aspx?ProductID=58 ) based on decades of research and experience in managing urban forests.
Understand Impacts
Customary tree care practices sometimes have unintended consequences. Pruning removes potential habitat and nest sites and can reduce the tree’s other resources. Canopy thinning practices often remove too much of the tree canopy (more than 25%), exposing birds and nests to elements and predators. The removal all dead and dying trees and dead branches eliminates potential habitat and other resources for cavity nesters. Understory clearing, including the removal of leaf litter and organic matter, reduces coverage, habitat and foraging opportunities for wildlife. Noise associated with equipment and worker presence can cause early fledging and nest abandonment. Chemical fertilizers and pesticides can cause health problems, and even fatalities, for birds and other wildlife.
Bird regulations make time of year important
The primary laws and regulations protecting birds and other wildlife are the Migratory Bird Treaty Act (MBTA), Endangered Species Act, California Fish and Game Code, and California Environmental Quality Act. They protect birds especially during the breeding season, when most prepare for, have offspring, and care for these young until they are independent. Some species are legally protected all year. While it varies by region and species, February 1st to August 31st is typically considered the breeding season in California. September 1st to January 31st is the non-breeding season.
Landscapes have different habitat values.
Riparian areas are high value areas adjacent to rivers and streams (may or may not have water) and provide habitat for sensitive riparian birds and other special status species. Other high habitat value areas in urban forests include wildland areas, parks with many trees, and neighborhoods with tree-lined streets. Low habitat value areas may be city centers, sports fields or areas where hardscape dominates. Different tree care practices in these habitats are warranted.
Best Management Practices
In the BMPs three categories of work are recognized, based on the habitat value and whether the project is scheduled during the breeding season. In all categories workers are advised to be prepared with contact information for a bird biologist, local wildlife rehabilitator, and a wildlife trained arborist. These experts can be helpful in emergency situations or those which conflict with laws. (Training criteria for each specialist is defined in the BMPs. Training programs that meet the project’s criteria can be found on www.TreeCareForBirds.com)
A pre-work site visit is strongly recommended in Categories 2 and 3, regardless of the season. The purpose is to look for active nests, wildlife carrying food or showing signs of alarm. When active nests are found, delaying work until the young are independent of their parents is recommended to avoid disturbance and putting immature birds at risk of exposure to the elements and predators. When safety or other emergency circumstances require work to proceed, a wildlife biologist should be consulted and key considerations for working near active nests should include duration of work to be completed, the tools used (power or hand), the bird species involved (level of sensitivity to disturbance/special legal protection), distance of the work to the active nest (a no activity buffer), the status of the nest (condition and maturity of nestlings), location specifics (e.g. urban vs rural), and environmental conditions (temperature and wind).
Enhance Wildlife Habitat
Wildlife habitat is enhanced by keeping trees healthy through proper care, as well as increasing the number and types of trees and lower vegetation in the urban forest. This includes different age classes of trees, especially some that are dying and dead. Carefully selected dead trees and branches can be safely retained and monitored regularly to reduce risk. Keeping mature trees should be a priority as they provide more habitat than small, young trees. Increased brush and wood piles also provide prey and shelter. When treating pests and diseases, limit broad spectrum pesticides, never use anticoagulant rodenticides as wildlife eat insects and poisoned rodents. These good stewardship actions protect wildlife, ensure their ecological benefits, and improve human health, and enjoyment of nature. Please share them.