Hamilton Wetlands

The Plan: Brad Evans, PWA/ESA

Within these pages, we often praise Marin’s system of open space preserves. These areas are what we typically think of when we talk about bird habitat—natural plant and wildlife communities that have been preserved intact among the surrounding matrix of human development. The Hamilton Wetlands, in contrast, have not merely been preserved, but actually re-created. It is unusual—and therefore particularly gratifying—to encounter a huge, expensive, and ambitious feat of engineering whose beneficiaries include plovers and pintail as well as humans.

Working on land formerly occupied by the Hamilton Army Airfield, the restoration has required a huge effort over many years: planning began in 1996; the project was authorized by Congress in 1999; land was transferred, buildings removed, and preliminary decontamination of the site conducted in the early 2000s; millions of cubic yards of dredged material from other parts of the bay were pumped in over years to reverse decades of subsidence; and in 2014 the outer levee keeping out the waters of San Pablo Bay was finally breached. Tens of thousands of native plants have been planted and time will continue to shape the land as they become established, eventually creating a dense tidal marsh that will provide habitat for rails and other marsh birds while protecting against flooding and sea level rise.

Pickleweed - Jerry Kirkhart
Gumplant - sciencebabe on iNaturalist

In the meantime, there are birds now! The channels of bay water flood over onto tidal mudflats, which gradually give way to newly planted upland areas running adjacent to patches of native-ish woodland and suburban neighborhood. Public access is available on a 2.7 mile stretch of newly constructed Bay Trail which will eventually connect to Las Gallinas Ponds in San Rafael. While many of the birds in the 650 or so flooded acres may spend a good portion of their time at some distance from the trail (a spotting scope is certainly helpful), there are several areas along the trail where birds can be seen at closer quarters. The bird species seen and their proximity can also be affected by tidal conditions and winter rains, which will flood additional areas.

Tidal mudflats are home to some of our most spectacular and unique birds. The vivid plumage and lively feeding habits of American avocets and black-necked stilts make them easy to recognize and always entertaining to watch. The giant long-billed curlew is a wonderful demonstration of the odd extremes to which evolution can take a species, with its tremendous down-curved bill adapted to probing the burrows of crabs and other invertebrates. Our other notable down-curved-biller, the whimbrel, can also be seen here, particularly during August and September migration, with fewer remaining through the winter. The formidable marbled godwit and smaller dowitchers are similarly adept at mud-probing with their long, straightish bills. These probers can be contrasted with willets and yellowlegs, which walk and pick their prey primarily from the surface.

American Avocets - Gary Rosenfeld
Long-billed Curlew- Matthew Paulson
Least Sandpiper - Henry McLin
Semipalmated Sandpiper - Mick Thompson

Equally spectacular in their own way are the masses of hundreds or thousands of small flocking least and western sandpipers (“peeps”) and slightly larger dunlins. Least and western sandpipers can be seen in good numbers arriving from the north with other shorebirds as early as July, while dunlins are a later arrival, typically reaching the Bay Area around September, but then remaining common through the winter months. While small sandpipers may seem unspectacular and plain in their winter plumage, it is thrilling to watch one of these big flocks of hyperactive feeders suddenly take flight in an undulating mass of hundreds of twisting and turning birds, their calls filling the air

… like the vibrating crystal chiming sounds of a handful of pebbles thrown upon and bounding and glissading musically over a wide sheet of ice. 

– W.H. Hudson, Nature in Downland

Up a bit from the water and mud, upland vegetation provides a nice mix of cover and foraging areas for a variety of plover species. The common killdeers, with their loud, strident calls (from which their name derives), are joined by their endearingly miniature cousins, the single-breast-banded semipalmated plovers, who lurk in small groups among the plants, and the more or less unbanded snowy plover, an endangered coastal breeder that comes to Hamilton in small numbers in the winter. The larger black-bellied plover is inconspicuous in its winter plumage, but this is definitely the best place in Novato for broadening your circle of ploverine acquaintance. In the channels and submerged areas, look for all-year mallards and gadwalls to be joined from September on by more ducks such as northern shovelers, northern pintail, canvasbacks, American wigeon, buffleheads, ruddy ducks, and green-winged teal.

Northern Pintail - shell game on Flickr
Bufflehead - Doug Greenberg

Naturally, the focus at a massive wetlands restoration is on the waterbirds. But there are other groups of birds that thrive here as well. Both the marsh-in-progress and the surrounding uplands host plenty of prey for a variety of hawks: white-tailed kites hover-hunt for rodents, peregrine falcons cause havoc among the shorebirds in winter, and northern harriers cruise just above the covering vegetation as they search for both bird and mammal prey. The scrubby edges of the trail provide good sparrow habitat, from the winter-ubiquitous white-crowned and golden-crowned sparrows, to the crisply streaked savannah sparrow and the smudgy bumpkin of the marshes, our own special San Pablo subspecies of the song sparrow.

White-tailed Kite – Local photo by Don Bartling on Flickr

Practical Details

Bird Lists and Recent Sightings: See the eBird Hotspot page for the Hamilton Field Bay Trail.

Getting There: You can park either by a ramp near Hangar 6 and 7 or by the playground and ball fields at the end of Hangar Ave. You can find directions at the Hamilton Wetlands Restoration project website

Getting Around: The Hamilton Wetlands are bordered by a 2.7 mile stretch of the Bay Trail, with no real diverging paths to speak of. It is easy to cover as much or little of the trail as you like from either entrance. This stretch of nice, wide, level, recently constructed Bay Trail is also ideal for birding by bike: cruise easily through the dull stretches where birds are too far away and stop where things are more lively. To the south, the trail will connect officially to the Bay Trail segment at Las Gallinas Ponds. If you would like an abridged, printable pdf of this site profile, you can download one here

Rules & Access: The Bay Trail section at Hamilton is open from 30 minutes before sunrise to 30 minutes after sunset. Bikes and dogs on leash or under voice control are permitted. For additional rules, see the Hamilton Wetlands website

Header image: A flock of “peeps” (least or western sandpipers) takes flight, photo by Don McCullough on Flickr. I love watching those big undulating flocks – Hamilton is the place to see them around here.