With a length of up to 22 inches and a wingspan of five feet or more, Swainson's hawks (Buteo swainsoni) can rightly be called majestic. In dramatic courtship and territorial displays, Swainson's become aerial acrobats, with male hawks making lengthy free dives, and the males and females circling and interlinking talons, followed by tumbling. Additionally, this fascinating bird is dependable, forming long-term monogamous pairs and returning year after year to the same nest.

Tetra Tech biologists Jeanette Weisman and David Munro have been conducting surveys of Swainson's hawks in California's Central Valley. The hawks' population declined sharply in the twentieth century, due to a loss of breeding and wintering habitat and from ingesting pesticide-ladened insects. Consequently, California lists the hawks as threatened, and the US lists them as a species of concern protected by the Migratory Bird Treaty Act.

Jeanette and David had previously confirmed Swainson's hawk territories in the survey area, as well as an active Swainson's hawk nest. The area had undergone some reductions in riparian vegetation as part of a levee reconstruction project. Our surveys began before the hawks returned to the area, but we observed many other Central Valley wildlife, including sandhill cranes (Grus Canadensis) and western bluebirds (Sialia mexicana). Also, an assortment of local hawks and owls was getting a head start on nesting in the mature and full-canopied California sycamores (Plantanus racemosa) and oaks (Quercus spp.).

Due to their large size, Swainson's hawks are conspicuous when soaring or perching on a high branch, but they can be surprisingly well concealed when nesting. In May, Jeanette observed a nesting pair, and in early July she saw two nestlings at this nest. Both the male and female Swainson's watched closely as the nestlings flapped their wings in preparation for their first flight. For this pair of Swainson's, this amounts to a successful breeding season so far, as the average clutch size of the hawks is just two to three eggs. Jeanette will continue to observe these newest Swainson's hawks until they and their parents migrate to their wintering grounds in South America.