Birds build homes in which to raise their young just as humans do, although their site selections are more varied and often in obscure, hidden places. It is common to think of nests being in tree branches. But some birds build nests on the ground, in bushes and cavities; some build on the sides and eaves of houses, as well as on other man-made structures. Birds use natural substances and materials to construct: mud, saliva, spider webs, caterpillar silk, leaf mold, twigs, grasses, and certain other plant fibers. The nest protects the bird’s eggs from windy and wet weather and predators, and keeps eggs and nestlings warm.
Over 180 Species Nest in the Bay Area
What comes to mind when most people think about city birds are pigeons, crows, sparrows, and gulls. Yet these birds are only a small portion of the more than 120 species that reside in Alameda, Contra Costa and San Francisco Counties year round.
Annual migration brings in additional species to the area, including more than 60 other breeding species (such as orioles and kingbirds). In total, over 350 species live, nest, or pass through the San Francisco Bay Area during the year. Most birds rely on trees, shrubs, and brush for food, cover, nesting, and rest.
Many birds nest during the spring and summer. Unfortunately this is also the time of year that people tend to trim trees, prune shrubs, and clear brush. Severely cutting, trimming, and topping trees, bushes, reeds, and other greenery in the spring and summer can destroy nests and eliminate valuable nest sites.
There are laws that protect birds, their nests, eggs, and young from being removed, destroyed or harassed. Violating any of these laws may result in fines and imprisonment.
Many species nest between March 1 and August 31. The California Department of Fish and Wildlife often requires surveys for raptor (bird of prey) nests from January 15 to September 15.
Several species court and nest outside this time frame, such as some herons and egrets, many raptors, and most hummingbirds. Depending on the species, nesting birds may be found at any time of year.
Consult an independent qualified biologist for safe trimming times upon discovering any large nest.
Certain species such as hawks, owls, herons, egrets, crows, and ravens often re-use nests. If you find a large nest made of twigs — even if it’s unoccupied — assume that it belongs to one of these birds and do not disturb it.
Planning Your Tree Project
Plan your project for the months outside of nesting season — generally September through January. Hire an arborist who is ISA (International Society of Arborists) certified, a licensed landscaper, or a qualified tree trimmer who knows and cares about a tree’s health. Avoid hiring “bargain‟ tree trimmers or handymen, as they are generally inexperienced and may cause more harm than good to the trees.