Comments: BREEDING: Fields of dense grass. Open and partly open country (grassland, marsh, lightly grazed pasture, hayfields) in a wide variety of situations, often around human habitation (AOU 1983). Nests in buildings (church steeples, attics, platforms in silos and barns, wooden water tanks, duckblinds), caves, crevices on cliffs, burrows, and hollow trees, rarely in trees with dense foliage (AOU 1983). Caves, cliff crevices, and cut bank burrows are commonly used in the western U.S., rarely in the east. Uses nest boxes (Marti and Wagner 1985). Reproductive success generally is higher in a properly placed and maintained nest box than in a natural nest cavity.
FORAGING HABITAT: Dense grass fields are the chief foraging habitat, including saltmarsh, wet meadows, lightly grazed pastures, grass hayfields, and recently abandoned agricultural fields (Colvin 1980, 1984, 1985; Rosenburg 1986; Gubanyi 1989). Radiotelemetry studies indicate that these habitats are actively selected (Colvin 1984, Rosenburg 1986, Gubanyi 1989). Furthermore, the quantity and quality of dense grass habitats are significantly correlated with nest activity (Colvin and Hegdal 1988).
Other habitats occasionally used include alfalfa/grass (Colvin 1984), small grain (Ault 1971, Rosenburg 1986), fencelines, and roadsides (Ault 1971, Byrd 1982). In an intensively farmed area in eastern Virginia where grass availability was very low, foraged in small grain, a five-year-old clearcut, barnyards, and a pine (PINUS spp.) plantation used as a blackbird roost (Rosenburg 1986). Cultivated habitats in general are of little importance because of low prey populations and/or dense protective cover (Colvin 1984, Rosenburg 1986).
NESTING HABITAT: This is a cavity-nesting bird which uses natural as well as human-created cavities. Tree cavities are the principal nest site used in most areas of the Northeast (Colvin et al. 1984); those most frequently used are silver maple (ACER SACCHARINUM), American sycamore (PLATANUS OCCIDENTALIS), and white oak (QUERCUS ALBA) (Colvin et al. 1984, Byrd and Rosenburg 1986). Although cut bank burrows and cliff recesses are frequently used in the western U.S. (Otteni et al. 1972, Martin 1973, Rudolph 1978, Millsap and Millsap 1987, Gubanyi 1989), only a few cases of the use of such sites have been reported in the Northeast. R. Ferren (pers. comm.) described nest holes in the steep bluffs on the north and south ends of Block Island, Rhode Island. Recesses in a clay embankment along the Patuxent River in Maryland supported a breeding pair during the late 1980s (S. Smith, pers. comm.). Exposed barrels in a cut bank along the Rappahannock River of eastern Virginia supported approximately 15 nesting pairs in the late 1970s (S. Doggett, pers. comm.). A wide variety of human-made "cavities" are used as nest sites. Large platforms within barns and silos, tunnels dug into silage in roofed or topless silos, cavities among hay bales stored inside barns, barn cupola shelves, wooden water tanks, and offshore duckblinds are frequently used; feed bins, church steeples and belfries, platforms within commercial and industrial buildings (e.g., warehouses, grain elevators, mills, factories), attics of abandoned or occupied houses, ledges within chimneys, platforms beneath bridges, and World War II cement watch towers are occasionally used (Stotts 1958, Scott 1959, Reese 1972, Klaas et al. 1978, Soucy 1979, Bunn et al. 1982, Hegdal and Blaskiewicz 1984, Colvin 1984, Byrd and Rosenburg 1986, Matteson and Petersen 1988, Parker and Castrale 1990). In addition, nest boxes are readily used (Otteni et al. 1972, Marti et al. 1979, Soucy 1980, Ziesemer 1980, Colvin et al. 1984, Cook 1985, Schulz 1986, Byrd and Rosenburg 1986, Bendel and Therres 1988, Parker and Castrale 1990).
NON-BREEDING: In winter often roosts in dense conifers; also roosts in nest boxes if available (Marti and Wagner 1985).