San Diego Management & Monitoring Program


Swainson's hawk
Buteo swainsoni

Vertebrata

Vertebrata
Kingdom Phylum Subphylum Class Order Suborder Family

Current distribution rangewide

Distribution occurs from western North America throughout the Great Plains of the U.S., into Central America, migrating as far south as Argentina [1].


Known Populations in San Diego County

A rare migrant of San Diego County. Sightings have occurred in Borrego Valley, Lakeside, Warner Springs, and El Centro [1].


List status

CESA- Threatened [2].


Habitat affinities

Generally found in plains, dry grasslands, and open woodlands [3]. Forages in open grasslands, small open woodlands, and sparse shrublands [3].Nesting occurs in shrublands, grasslands, riparian areas, and agricultural landscapes [4].


Taxonomy and genetics

There are no recognized subspecies [5].


Seasonal activity

Migration is diurnal [4]. Nearly the entire population migrates between breeding grounds in western North America to wintering grounds in the lowlands of Argentina. Overall migration can take up to 2 months (20,000km) [4]. Flocks will begin to disperse from Argentina in late February to mid-March and migrate back late August into September [6].


Life history/ reproduction

Arrival to breeding grounds begin around March or April [7]. Nest will be constructed 7-15 days after arrival and takes one or two weeks to complete [7]. Nests are typically built in trees, shrubs, or a small group of trees along a stream [8]. Young are altricial and inactive for the first 8-10 days, but able to stand at about 13-17 days. Young can feed themselves at about 23-26 days, but the female may still feed them for up to 32 days. Juveniles first attempt to fly at 29-33 days and fly at around 38-46 days [7].


Diet and foraging

Young are fed rodents, rabbits, and reptiles [9]. However, when not breeding, adults feed almost exclusively on insects, primarily grasshoppers [9].


Threats

Pesticides are a large cause of mortality for Swainson's Hawks. Illegal shooting is also a threat to Swainson's Hawk populations [10].


Swainson's hawk sources