California Department of Fish and Wildlife

What's Going on at Grizzly Island Wildlife Area During the Year

Public Use Schedule Note: These are all general time frames - Call (707) 425-3828 for exact dates.
February - July Open for Hiking, Fishing, Nature Viewing (Dog Training allowed only in February and July)
August - September Area Closed to All General Public Use during Special Tule Elk Hunts
Late September Area Opens for last 1-2 weeks in Sept. for hiking, nature viewing, fishing, and dog training
October - January Area Closed to All General Public Use during Waterfowl Hunting Season (NO fishing access)


Fall is announced by the tremulous bugling of the tule elk. No fences contain these wild elk. The bulls easily weigh 600 to 800 pounds, thanks to the benevolent environment. They have grown splendid new antlers and are in the rut. Fights between bulls are a noisy, magnificent spectacle of calling, jousting and sparring. The sight of two males charging and the violent clacking of their antlers is something to be remembered and experienced from a safe distance.

Small groups of northern pintail are bellwethers of the fall migration, finding Grizzly Island's ponds and waterways in early August. By the end of September, the marsh abounds with this distinctive duck.

There are green-winged teal and American widgeon by September, when the first small flocks of tule geese are spotted. In groups of 30 to 50, their annual arrival is reason enough to celebrate: Grizzly Island is one of just three significant wintering areas for the entire world's tule goose population! Slightly larger than the greater white-fronted goose, it is also marked with darker, dusky plumage.

As you drive or hike between the ponds, you're apt to see wading egrets and great blue herons. There are several rookeries in the marsh. Since they are very vulnerable to disturbance, most are not accessible. One rookery can be viewed from the Crescent Unit.

The smaller snowy egret and black-crowned night herons prefer the cover provided by tules, lining many of the ponds and ditches, as do yellowthroats, marsh wrens and the Suisun song sparrow. Keep an eye out for plush river otters in the ditches or sloughs: Grizzly Island has one of California's largest populations of these playful mammals. The same areas may also hide a few of the rare, fall-blooming Suisun aster. Some have been spotted at Hill Slough.

During August and September, V-shaped formations of American white pelicans glide into the marsh for a predictable but brief stay. Like so many ducks and wading birds, they will find their fill of fish in the shallow marshes and ponds. Most will be gone by November, except for a few non-breeding residents.

The fields and upland areas draw a rich variety of raptors. Migratory rough-legged, ferruginous and sharp-shinned hawks are attracted by a large resident rodent population. Black shouldered kites and red-tailed hawks are lured to these fields all year long. You may even catch a glimpse of an occasional prairie falcon or an endangered peregrine falcon. Thanks to the hardworking California Waterfowl Association, a great deal has been learned about the area's northern harrier, short-eared owl - and waterfowl - as a result of studies they've conducted for CDFW.


The opportunity to view waterfowl is at its peak during the winter months. As many as 250,000 ducks color the marshes with their vivid nuptial plumage and courtship displays. While other areas may attract greater total numbers, Grizzly Island's fertile marshes yield one of the greatest densities of nesting mallards in all of North America. During late January and February, pairs can be seen scouting the upland fields for nesting areas.

Shallow tidal and diked areas are dotted with shorebirds that winter each year at Grizzly Island. The least sandpiper, dunlin and yellowlegs probe the mudflats for food and fill the marsh with their special songs. The slough banks are often lined with determined anglers, anxious to land sturgeon known to exceed 70 inches.

The tule elk bulls and pregnant cows are in separate groups now. The rut is over and, by March, they will drop their magnificent antlers, as they do each year.

This is an excellent time to visit Hill Slough - a 1,750-acre gem at the entrance to the complex. A year round sanctuary, additional flooding attracts about 30,000 waterfowl - mallard, northern pintail, American widgeon, gadwall. The native grasses in the upland areas are a haven for ring-necked pheasant and support a year-round population. Unload your canoe here and drift along the winding waterway for several miles. Ripples on the water may be river otters, muskrat, even beaver. Large flocks of long-billed curlew can be seen feeding in the hills just south of the slough.

The bright orange pickleweed lining the slough and ponds is critical habitat for the diminutive, endangered salt marsh harvest mouse. This unusual rodent is found only at Bay Area salt marshes, which have dwindled dramatically because of bayside development.

This is no ordinary mouse! It builds a nest of grass high in the pickleweed and even clings to the swaying plants during the changing tide. It has thoroughly adapted to the seasonal and tidal cycles of the salt marsh. Despite its incredible hardiness, this species is considered endangered because so much salt marsh habitat has been destroyed. The legal mandate to save the salt marsh harvest mouse has allowed habitat to be saved for it - and for countless other species.


The spring migration of the waterfowl is announced with noisy wingbeats and trumpeting calls while the birth of the season's first white-spotted tule elk calves is solitary and quiet. It is not unusual to see day-old calves near Parking Lots 3 or 4, still awkward and wobbly - and seemingly alone. Do not disturb or approach the calf; mother is nearby and will return to her young once you have departed. Within days, when her calf is strong, she rejoins the group; this offers both greater safety and other cows that willingly help with babysitting duties.

Golden-hued brass buttons carpet the pond bottoms. A huge nesting population of goldfinches can be spotted along the levees. Fields hiding heavy rodent and bird populations attract a variety of raptors. Watch for short-eared owls near Parking Lot 1. Especially high densities of ground nesting owls and northern harrier have also been found here; both are active in the early morning and evenings, although midday sightings are not uncommon.

The 70-acre brood pond recently constructed by Ducks Unlimited near Parking Lot 2 shelters broods of ducklings-first mallard and northern pintail, then cinnamon teal and gadwall later in the spring. Shorebirds like American avocet, killdeer and black-necked stilt, use this pond for nesting, as well. The female killdeer dramatically announces if you're too close to her nest; she'll try to distract you by flying as if her wing is injured.


Once again, the pickleweed is bright green and the resident mallard, gadwall, and cinnamon teal are drab in their muted summer plumage. Change and contrast are a permanent part of the marsh scenery.

Audubon cottontail and black-tailed jackrabbits scamper across the road, trying to dodge vehicle traffic and the sharp scrutiny of golden eagles soaring overhead. Adult birds are dark with golden hackles, an impressive silhouette against the cobalt blue sky.

Groups of immature American white pelicans bob on the brood pond across from Parking Lot 2. Be sure to stop long enough to watch their unusual cooperative fishing strategy. Unlike their diving cousin, the brown pelican, white pelicans work together to surround fish in shallow water, then scoop them into their ample pouches. Watch the pond edges for the first yellowlegs, curlews and dowitchers, beginning in mid-July. You may also see roosting great-horned owls in the eucalyptus trees to the northeast.

By midsummer, the tule elk cows, yearlings and calves have gathered in large groups. The mature bulls, separate now, are much preoccupied with the growth of their new antlers. In early summer, the antlers are still covered with a fine, velvety coat: this contains the blood supply that nourishes the growing tissue until August. Then, the antler finally hardens and long chards of dried velvet hang, in tatters, from the antlers. You can watch the bulls rub on just about anything upright, like trees, power poles or fence posts, to remove the dried velvet.

You may also see CDFWers working diligently to repair the usual elk damage and to flood additional ponds for resident waterfowl and shorebird broods. The sight of the first pintail in early August is a reminder that another cycle is about to begin anew.