Anyone who writes a list of bird sightings at local wildlife refuges in the winter months would be well advised to bring more than a single sheet of paper on which to write and a spare pencil or two, as well.
A study, published three years ago in Ornithological Applications, shows that tens of millions of migratory birds depend on the California’s Central Valley and the Colorado River Delta river and wetland habitats on their seasonal journeys through a largely arid landscape.
Visitors to the San Luis NWR during the just-past month of December reported seeing a whopping 115 species of birds while visiting the refuge. While it may seem counter-intuitive, the diversity of life on the wildlife refuges of the San Luis NWR Complex – measured by the number of species – increases during the (relatively) cold, damp, gray days of winter, thanks to birds.
The wildlife refuge is home to a host of year-round resident bird species like red-tailed hawks, great blue herons, and western meadowlarks. In the summer they are joined by species like the Swainson’s hawk, western kingbird, and ash-throated flycatcher that breed and nest here. These are species that spend their winters in locations to the south like Mexico, Central America, and South America and when the summer breeding season is finished, they return to tropical habitats for the winter.
However, while so many summer species head south, dozens of other bird species that breed in the far northern boreal forests of Alaska and Canada fly in to take their place. In addition, some bird species return to the valley floor in winter from their breeding grounds at higher elevations like the Sierra Nevada. Still other birds, like the American white pelican fly just a state or two away to breed and return to the San Joaquin Valley for the winter.
During the winter the wildlife refuges are home to dozens of species of ducks, geese, and shorebirds – species that have no counterparts here during the summer. Included in this group would be the iconic sandhill crane. Another group that sees a huge diversity surge during the winter is the raptors (birds of prey). During the summer, six species of raptors (Northern Harrier, Red-shouldered Hawk, Red-tailed Hawk, American Kestrel, White-tailed Kite) can be found throughout the refuge complex including one summer breeding species that leaves for the winter – the Swainson’s hawk.
During the winter, however, as many as 15 species of raptors can be found – and increase of 150 percent! The winter resident raptors list adds Osprey, Bald Eagle, Golden Eagle, Sharp-shinned Hawk, Cooper’s Hawk, Ferruginous Hawk, Rough-legged Hawk, Merlin, Peregrine Falcon, Prairie Falcon. Of course, one might not see all these species every time they go out, nor every year, for that matter.
Other periods of peak diversity for birds on the wildlife refuges are the shoulder seasons of spring and fall migration. During those times, dozens of migrating songbirds travel the Pacific Flyway from their southern wintering grounds to their northern breeding grounds and back again.
The springtime migrants pass through on their way north while many of the winter species are still here and the fall migrants move through on their way south as the migratory waterfowl and shorebirds are arriving to spend the winter.
Bundle up, grab the binoculars and spotting scope, and get out to any wildland to enjoy the diversity winter has offered.
The Merced National Wildlife Refuge (located at 7430 West Sandy Mush Road), the San Luis National Wildlife Refuge and the San Joaquin River National Wildlife Refuge comprise the San Luis National Wildlife Refuge Complex. Its headquarters and visitor center are located just north of Los Banos off Highway 165 at 7376 South Wolfsen Road.
The refuges are open to visitors daily from one half-hour before sunrise to one half-hour after sunset. The visitor center is open Monday through Friday except federal holidays from 8 a.m. to 4:30 p.m. For more information, call the refuge visitor center at 209-826-3508, ext. 127 or check out the upcoming events on the website at fws.gov/refuge/san-luis.
