The arrival of Swainson’s Hawks
By Luke Matthews
Swainson’s Hawks have been arriving in the Sacramento Valley over the last month and I’ve finally started to notice large groups of them. These birds typically spend the spring and summer months here and migrate south, to warmer climates, for the winter. Swainson’s Hawks are often mistaken for Red-tailed Hawks, since they are roughly the same size and they have similar color patterns. However, Swainson’s typically have bright yellow bills with white forehead and throat patches, which makes it look like they have a brown hood. In flight, contrast on the wings between the dark colored edges and light colored interior feathers is another good way to identify a Swainson’s.
Swainson’s hawks prefer open habitat such as grasslands or agricultural fields. These hawks have become very well adapted to agriculture and now heavily rely on fields for hunting habitat. In fact, they are so accustomed to agriculture that they take advantage of agricultural practices that create disturbance in the fields and might expose prey. Agricultural activities such as irrigation (especially of crops such as alfalfa), mowing and chopping, baling or incorporation can attract very large groups of hungry Swainson’s Hawks. Although, Swainson’s Hawks are not the only birds that take advantage of this type of agricultural activity so they are often seen in mixed flocks of other birds such as Red-tailed Hawks, Rough-legged Hawks, Ravens, Crows, Herons and Egrets.
While Swainson’s Hawks rely on open habitats for hunting, they also require mature trees for nesting. These hawks prefer riparian areas with a variety of large tree to nest in; however, they will also use scattered trees in grasslands or on the edges of agricultural fields. Nests are typically built on a platform of sticks high up in a tree, where the female will incubate 2-3 eggs. During incubation the male’s job is to hunt and bring food to the female, but once the eggs have hatched, hunting for rodents, rabbits, and reptiles becomes a full time job for both parents. The parents have large home ranges and will travel up to 20 miles from the nest to hunt and bring prey back. Interestingly, once the nesting season is over and the young are able to feed themselves, adults switch back to their primary diet which is almost entirely made up of insects.
They next time you are driving past an agricultural field see a large group of birds stop and take a look because, this time of year, you are almost guaranteed to see a beautiful Swainson’s Hawk!
Luke Matthews is the Wildlife Programs Manager for the California Rice Commission