It is pretty general knowledge that many species of birds migrate as the weather starts to get cold. But the details about which species migrate, when they migrate, where they go, and which populations stay as year-round residents are best answered through long-term research projects such as bird banding. Although there are a variety of methods employed by researchers to capture birds for banding, the most common method is mist netting. Mist nets are made of practically invisible thin nylon or polyester mesh suspended between two poles, resembling a volleyball net. When birds unknowing fly into the nets, they are caught in the “pockets” that form from baggy portions of the net, and are held there until carefully extracted by trained researchers. Birds are then carefully identified, measured, sexed, and weighed, and are fitted with a uniquely coded band. If a captured bird already has a band (a “recapture”), the information from its previous capture can be compared with current data to learn where that individual has been, how it has grown, and some approximation of its age. When this is done over many years, mist netting and banding becomes an important mechanism for monitoring species diversity, relative abundance, and population size.

Saturday I was able to participate in Mass Audubon’s seasonal bird banding research at the Wellfleet Bay Wildlife Sanctuary. Similar ornithological research has been carried out at this site since Oliver L. Austin and his son, Oliver L. Austin Jr. established a bird banding station there in the 1930s. The father son pair managed the Austin Ornithological Research Center until the land was sold to the Massachusetts Audubon Society in 1952. Although there have been lapses in data collection over time, Mass Audubon continues this research today, with seasonal bird banding during both the spring (April to June) and fall (September to November) migrations. Three of the species we observed during the Saturday morning banding were the black-capped chickadee (Poecile atricapillus), the American goldfinch (Spinus tristis), and the tufted titmouse (Baeolophus bicolor).

Black-capped Chickadees are year-round residents on Cape Cod. Instead of migrating, chickadees congregate into flocks of approximately 10-12 individuals for the winter. These winter flocks of chickadees contain both mated chickadee pairs and nonbreeders, although first year birds are generally “kicked out of the nest” and must find a new flock of their own (away from their parents). Although primarily composed of chickadees, these winter flocks often contain other species as well, including nuthatches, woodpeckers, kinglets, creepers, warblers and vireos.

The tufted titmouse is also a year-round resident. Unlike chickadees, however, tufted titmouse pairs do not gather into larger flocks for the winter. Instead, a pair will generally remain on its territory together, and they are frequently accompanied by one of their young from that year. The tufted titmouse pictured below was a juvenile born this year, as evidenced by the mix of adult and juvenile feathers visible on its wings.

Unlike chickadees and titmouses, American goldfinches do migrate for the winter. Although due to their range, we may still see them all year. The birds that breed on Cape Cod will migrate south, but the American goldfinches that bred in more northern areas may winter here. Most people picture American goldfinch adult males as strikingly bright yellow with a black forehead, black wings and white markings, however, these colors are much duller in winter, when males are a drab, unstreaked yellowish-brown, with blackish wings and two pale wingbars. The individual pictured below is clearly a male, but his vibrant yellow colors have already started to fade for the winter.