Pond A16 (Summer)
Terns and Black Skimmers
by Eve Meier and Steve Finney
Summer is a fun time to visit Pond A16 at Don Edwards San Francisco Bay National Wildlife Refuge in Alviso. Noisy and active terns and skimmers have arrived to nest on the man-made islands in the salt pond. Come back often to see the birds in different breeding stages, from courtship to nesting to feeding their young.
Trip Covers: June - September
Key Birds: Black-necked Stilt, American Avocet, Caspian Tern, Forster’s Tern, Black Skimmer
How to Bird
Don Edwards San Francisco Bay National Wildlife Refuge in Alviso consists of the Environmental Education Center (EEC), New Chicago Marsh, scrub habitat, a native garden and salt ponds that were once owned by Cargill. As part of the South Bay Salt Pond Restoration Project, many of the old salt ponds with their man-made islands are being restored back to tidal marsh habitat. But, to maintain breeding habitat for the terns and skimmers that feed on salt water fish and use the islands for nesting, some of the ponds have been left intact and new islands have been constructed. This guide covers the 1.6-mile round trip walk out to the Pond A16 observation deck where you will see the man-made islands and the breeding birds that use them. The hard-packed dirt trail is wide and uncrowded making social distancing a breeze.
Pond A16 with man-made islands. Eve Meier
Starting from the main parking lot, pass through the gate to the right of the EEC and butterfly garden (trailhead on interactive map). Continue on this short section of paved road until you reach the first pond. This is Pond A16. Turn right on the hard-packed dirt Mallard Slough Trail (#1 on interactive map) so that Pond A16 will be on your left and the marshy Mallard Slough will be on your right. You will continue along this trail until you reach the observation deck.
Along your walk, look for American White Pelicans, Double-crested Cormorants and Greater Yellowlegs in the salt pond. Savannah Sparrows can be seen on the ground along the edges of the pond while Barn Swallows can be observed feeding over the water. Mallard Slough will be noisy with Marsh Wrens, Common Yellowthroats and Song Sparrows.
Savannah Sparrow by Deanne Tucker
In 0.2 miles, you’ll pass a floating dock on your right (#2 on map). Walk down the ramp to scan up and down Mallard Slough. I like to have a seat and really take my time here. This time of year, you may see Cinnamon Teals nestled against the edges of the reeds, Common Gallinules swimming in the water or Snowy Egrets standing in the shallow waters. (In the fall, this is a good location to look for Sora and Virginia Rail.)
Floating dock along the Mallard Slough Trail. Eve Meier
When you are done birding from the floating dock, continue along the trail for another 0.6 miles to reach the observation deck (#3 on map) where you will see many man-made islands of different sizes and shapes in the salt pond. Different species of birds prefer different islands. The Forster’s Terns are nesting on the smaller, muddy islands while the Caspian Terns prefer the large barren gravel islands. Both these species migrate to this area to breed about April and will remain through September. There can be hundreds of terns out there and they make a lot of noise. Come back throughout the season to watch the various breeding stages from courtship displays early in the season through the feeding of recently fledged young. But beware! The Forster’s Terns can be territorial and may swoop at your head! To learn more about these birds and the restoration work, watch the SFBBO Webinar Return of the Terns! Using Social Attraction to Establish Tern Nesting Colonies in South San Francisco Bay.
Salt Pond A16 Observation Deck. Eve Meier
Caspian Terns are the largest terns in the world. Notice the bright red-orange bill. These birds winter in coastal areas but breed along ocean coastlines, barrier islands, lakes and rivers. Elizabeth Steward
Forster’s Terns are much smaller than Caspian Terns. Note the bird’s forked tail. These birds winter along ocean coasts and in the inland Southeast and nest in large inland wetlands and in saltwater marshes. Carter Gasiorowski
In addition to the terns, a small group of Black Skimmers may be present. Like the terns, these coastal birds migrate here to breed. The skimmers prefer to nest on the larger, barren gravel islands. See if you can spot resting skimmers - they often put their entire bodies, including their head and bill, on the sand. And when the flock flies in unison, it’s a beautiful sight. To learn more about identifying terns and skimmers, watch Ask BirdGuy 17: The Terns of Summer.
Black Skimmers have uneven bills; the top mandible is very short in comparison with the long lower mandible. When the bird flies close to the water, the lower mandible plows the surface of the water. Brooke Miller
Black-necked Stilts and American Avocets, both year-round residents, also breed here and can be viewed from the observation deck. These birds start nesting in April and by June, you may see their young on the edges of the small muddy islands. The young birds are able to feed themselves almost immediately (precocial) and blend in well with their environment.
Black-necked Stilt Chick. Tom Grey
Juvenile Black-necked Stilt with parent. Males appear to accompany older chicks more often than females. Audry Nicklin
At this point you can either continue your counterclockwise circle around Salt Pond A16 using the Mallard Slough Trail (3.3 mile long loop) for a longer walk with similar habitat or return the way you came.
Ready for More?
A little farther past the observation deck is the 0.5 mile Mallard Slough Spur Trail. This trail is nice for better views of shorebirds on the mudflats of Pond A17 if the tide is low, and also for views of Coyote Creek and of the ghost town of Drawbridge.
To see even more nesting stilts and avocets, check out the spring self-guided field trip to New Chicago Marsh.
Interactive Map
Driving Directions: From CA-237 exit north onto Zanker Rd. Continue on Zanker Rd for about 2.5 miles (Zanker Rd becomes Los Esteros Rd). Make a sharp right turn onto Grand Blvd. The small dirt parking lot is on your left in ½ mile. If the main gate is open, continue another ¼ mile past the dirt lot into the main parking lot Latitude/Longitude: 37.439150, -121.959655). Note: do not leave your valuables in the car.
Parking: Large paved parking lot is open from 7 am - 5 pm daily. There is a small dirt parking lot just outside the main gate.
Fees: None
Public Transportation: None available
Hours: The trails are open sunrise to sunset. NEW HOURS! The main parking lot is open daily from 7am - 5pm.
Facilities: Even though the Environmental Education Center is closed, the porta-potty in the main parking area is open. Cell phone signal typically strong.
Trip Miles: 1.5 miles round trip
Trail Conditions: Hard-packed dirt
Accessibility: This route is not wheelchair accessible due to a large gate across the trail entrance.
Bikes: This is a great trip to do by bike.
Dogs: Dogs are not allowed
More Information
Alviso Don Edwards San Francisco Bay National Wildlife Refuge Trail Map
Mallard Slough Trail map
Don Edwards San Francisco Bay National Wildlife Refuge Website
eBird hotspot: Don Edwards NWR--Pond A16
BirdGuy with SCVAS Executive Director Matthew Dodder Video 17: Terns of Summer
SFBBO Webinar Return of the Terns! Using Social Attraction to Establish Tern Nesting Colonies in South San Francisco Bay
For more information on the ghost town of Drawbridge watch California Gold
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, birding identification resources, and more.
Read “What to Look for Now” by SCVAS Executive Director Matthew Dodder.
Banner Photo Credit: Forster’s Tern by Carter Gasiorowski
Last Updated: 03/13/2022
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