Pond A4 (Winter/Early Spring):
A Wintertime South Bay Birding Sampler
by Adam Burnett
Walk or bike around Pond A4 in Sunnyvale for a broad birding sample of southern San Francisco Bay in winter. Diving ducks blanket the pond, terns and pelicans fly overhead, marsh birds lurk in the surrounding channels, raptors perch on utility towers, and—as a reminder of the human footprint on the landscape—crows and blackbirds scavenge around the adjacent landfill. This convergence of habitats provides a great opportunity to look for rarities, rack up a big species list, and simply enjoy the wide variety of birds this area has to offer.
Key Birds: Greater Scaup, Red-breasted Merganser, Common Loon, Golden Eagle, Great-tailed Grackle
Trip Covers: October - April
How to Bird
This self-guided trip describes a 3.7-mile route that loops around Pond A4, located along the San Francisco Bay shoreline in Sunnyvale and San José. The loop around the pond is 2.9 miles, and the trail from the parking area to the pond is 0.4 miles each way. Though the full loop makes for an enjoyable outing, many birds on the pond are visible from the south edge, where the trail enters from the parking area, so even an abbreviated trip here can be rewarding.
The trailhead starts on West Caribbean Drive next to the parking area (shown on interactive map below). Moffett Channel will be on your right. In 400 feet, make a right turn to cross over Moffett Channel. Then make a left turn, and take the trail that leads northeast through a gate in a chain-link fence. Keeping the treatment plant buildings on your right and the channel on your left, continue to follow this trail. After about 400 feet, the trail makes a right-angle turn and heads east-southeast toward Pond A4. The trail reaches Pond A4 after 0.4 miles.
The trailhead for the Bay Trail at the parking area on Carl Road. The trail leading to Pond A4 passes through the open gate on the right.
Ahead lies the pond, which is typically full of hundreds if not thousands of ducks during the winter months. Plenty of birds will be apparent to the naked eye, while others will be more distant, toward the center of the pond. Birding here with only binoculars is worthwhile, but a scope will facilitate better views of the more distant birds. The most common waterfowl on the pond include Greater Scaup, Lesser Scaup, and Ruddy Ducks. Greater tends to be the more numerous scaup species on this pond, but both are usually present.
Greater Scaup Pair by Raminder Bajwa
Greater Scaup by Gena Zolotar
Other diving ducks that may be around in smaller numbers include Canvasback, Redhead, Bufflehead, and Common Goldeneye. Pond A4 is also one of the best places in the county to see the Red-breasted Merganser, a fish-eating duck with a spiky crest and a thin, serrated bill. Two Common Loons have been seen here from October 31, 2020 through the end of December, and will be worth watching for as the winter continues. This majestic bird of northern ponds and lakes is a fairly common winterer along the coast, but is rare in the South Bay. Watch for them from the north and northeast sides of the pond, as they may be too distant to see clearly from the pond’s south edge.
Red-breasted Merganser Pair by Tom Grey
Red-breasted Merganser by Chuq Von Rospach
In addition to birds on the water, some interesting fish-eating birds can be found flying overhead. Large numbers of Brown Pelicans appeared in the South Bay in the summer and fall of 2020, and some of them likely will linger through the winter. Look for them fishing on the pond or flying overhead in ragged V-formation. Along the south shore of the pond, listen for the clamorous rattling call of a Belted Kingfisher, and watch for it hovering above the water while picking out a fish to target. Also worth mentioning is the Elegant Tern, a larger cousin of the more familiar Forster’s Tern. The Elegant Tern breeds mostly in Mexico and Southern California, then migrates northward in late summer before heading south again for the winter. Though they have left for the season, this pond is a great place to see them from August through October.
At the southwest corner of the pond, narrow strip-shaped islands serve as resting places for a variety of birds. Shorebirds such as Greater Yellowlegs, Black-necked Stilts, and Short-billed and Long-billed Dowitchers roost here while taking a break from foraging. Snowy and Great Egrets, Black-crowned Night-Herons, and the occasional Great Blue Heron also hang out here regularly. Two Brandt’s Cormorants spent a few months on these islands with Double-crested Cormorants in fall 2020.
The strip islands at the southwest corner of the pond can host a variety of birds, as evidenced by the Great Blue Heron near the bottom right corner of this photo.
In addition to the pond and islands, also pay attention to the other habitats surrounding you. The shrubs and fennel along the trail host songbirds including Common Yellowthroat and White-crowned, Golden-crowned, and Lincoln’s Sparrows.
To the southeast of your vantage point lies the business end of the SMaRT Station, where a conveyor belt spews garbage into waiting trucks, attended by omnivorous birds including American Crows, European Starlings, and various blackbirds. The starlings and blackbirds also spend time roosting in the marsh vegetation in the channels bordering the south edge of the pond. Among the Red-winged and Brewer’s Blackbirds, look for scarcer species such as Tricolored and Yellow-headed Blackbird.
The Great-tailed Grackle also frequents this area. Our largest blackbird, this species has extended its range into the western United States from its home base in Mexico and Central America. Another rapidly expanding species, the introduced Eurasian Collared-Dove, is found here regularly as well. Look for them perched on buildings and poles around the SMaRT Station, and around the Twin Creeks playing fields to the southeast of the pond. Listen for their “coo-coo-cook” song, with a similar quality but a different cadence compared to the more familiar song of the Mourning Dove.
Female Great-tailed Grackle by Bobbi Goodman
Male Great-tailed Grackle by Becky Ewens
Looking southeast across the pond from its north edge.
Once you have finished scanning the southwest corner of Pond A4, you can explore further by traveling clockwise around the pond, keeping Pond A4 on your right. The west side of the pond is bordered by Moffett Channel, which also hosts waterfowl and marsh birds. Rarer marsh species to search for include Swamp Sparrow (rare) and American Bittern (uncommon).
Along the north edge of the pond, a large expanse of marshland opens to your left.
As you reach the segment of trail along the north edge of the pond, an expansive tidal marsh area appears on your left. Open pools of water in these marshes can attract impressive concentrations of egrets and Greater Yellowlegs. This less-traveled stretch of trail offers a peaceful experience, particularly when the vocalizations of singing Western Meadowlarks and calling Soras waft over the marshlands. During hunting season (Oct - Jan on Wednesday, Saturday, and Sunday), there may be duck hunters in these marshes; the experience is marginally less peaceful if punctuated by distant gunshots.
Sora by Luis Villablanca
When you reach the east side of the pond, look across Guadalupe Slough for distant views of Salt Pond A8 to the east. Like the other salt ponds, this large pond often hosts excellent birds, but its shoreline is closed to the public, so this stretch of trail is one of the best places from which to scan it. Though the viewing is distant, it is still possible to find interesting birds on A8 from this vantage point, as attested by a Black Oystercatcher seen here repeatedly in early 2016.
A pumping station near the southeast corner of the pond.
Returning to your starting point along the southern edge of the pond, look up at the utility towers along the south side of the trail. They provide favorite perches for raptors, including Red-tailed Hawk, Peregrine Falcon, Bald Eagle, and particularly Golden Eagle. Two Golden Eagles seem to frequent one of these towers in particular, and have been seen here regularly throughout 2020. The ditch on the south side of the pond often holds lots of dabbling ducks, such as Mallard and Northern Shoveler, plus the odd Green Heron or Common Gallinule.
Ready for More? The same trailhead also provides access to the other trails at the Sunnyvale WPCP, including the East Pond, the West Pond, and the landfill hills to the west, which offer sweeping views out over the ponds. The San Francisco Bay Trail links this location to other destinations along the bay.
Interactive Map
Directions: From CA-237 in Sunnyvale, exit Lawrence Expy/Caribbean Dr. Continue onto Caribbean Dr. In 1.2 miles park along E Caribbean Dr (just past Borregas Ave). Access the Bay Trail from here (shown on the interactive map). Latitude/Longitude: 37.417672, -122.019018
Parking: paved parking, ADA compliant spots available in both parking locations
Fees: None
Public Transportation: The Borregas Light Rail Station and the bus stop at the intersection of Java Drive and Borregas Avenue are each 0.6 mile from the trailhead on West Caribbean Drive next to the parking area.
Trail Hours: Sunrise to sunset
Facilities: There is a portable restroom at the end of Carl Road. It is often not very pleasant.
Trip Mileage: 0.4 miles one way to the southwest corner of pond, 2.9 mile optional loop around the pond
Trail Conditions and Accessibility: The trail around Pond A4 is flat, hard-packed sand and dirt. It becomes muddy when wet, then forms hard ruts when it dries, particularly along the south edge of the pond. This segment of trail, which coincides with the Bay Trail, is wide and frequently traveled by bicyclists, joggers, and walkers, whereas the other segments of trail are narrower and less traveled. The segment of trail along the northeast side of the pond is particularly narrow and bordered by bulging clumps of grass and fennel. The trail around the pond has no benches and is exposed to the elements, with no sources of shade or shelter.
Bikes: This is a great trip to do by bike.
Dogs: Allowed on 6-ft leash
More Information
City of Sunnyvale Trail Information
eBird hotspot: Sunnyvale WPCP--Pond A4
More Resources
For more trips like this one, visit Self-Guided Field Trips.
Visit the SCVAS Birding Resources page for more information on where to bird, our birding community, bird identification resources and more.
Read “What to Look for Now” by SCVAS Executive Director Matthew Dodder.
Banner Photo Credit: Red-breasted Merganser by Tom Grey
Last Updated: 5/02/2022
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