Contra Costa county 8/6/2018
After an extended hiatus I finally made it back to Contra Costa county. I spent the day with Ethan Monk and, for part, with Dominik Mosur working from Richmond to East county. Migration was well under way but somewhat hard to detect as conditions at shorebird spots were moderate and passerine migrants were rather quiet after 8am.
We started at Point San Pablo, which appears to be the most lucrative migrant trap on the bayside. We started by the Marina and the adjacent oaks, picking through flocks and covering as much of the area as possible. Between 6:30 and 8:00am, we found nearly 40 passerine migrants in this part of the peninsula. Most interesting was seeing a cohort of 5 warblers (including at least 2 yellows and an orange-crown) pick up at the tip of the point and head to Marin. This may indicate that this place is not just an exceptional "trap" but actually a genuine spot for a sort of Morning flight. I have noticed over about a dozen August visits here that the site is extremely productive starting at sunrise for about two hours, and then seriously slows down. If you wish to visit this site, I would strongly recommend early morning for maximum success. Later in the season, this could be one of the best places to find vagrants in the county. For reference, the entire rest of the day we saw less than 5 other passerine migrants.
Highlights/migrants here included:
Spotted Sandpiper-6 together
Pacific-slope Flycatcher-3 in oaks/canyons
Empidonax sp-1 that appeared extremely gray did not appear to be a Pac-slope but seen very briefly. May have heard a "whit" note at this time as well
Warbling Vireo-1 in oaks/canyons
Blue-gray Gnatcatcher-4 was a very good count for this peninsula, all in the in oaks/canyons
Orange-crowned Wabler-3 in in oaks/canyons
Yellow Warbler-9 was the first major push of this relatively late migrant I have heard of from the area. All in oaks/canyons
Black-throated Gray Warbler-2 in oaks/canyons
Wilson's Warbler-8, all but 2 in oaks/canyons
Warbler sp-3 in oaks/canyons
Western Tanager-1 in oaks/canyons
Black-headed Grosbeak-1 in oaks/canyons
Lazuli Bunting-1 flying west high overhead at point
Hooded Oriole-4 in oaks/canyons
Bullock's Oriole-3 in oaks/canyons
Full eBird checklist here: https://ebird.org/view/checklist/S47690204
From there we proceeded to the West county WTP, meeting up with Dominik Mosur and hoping the slack and receding high tide would still have pushed a few birds there from Wildcat marsh. Unfortunately the only migrant shorebird were a couple of Semipalmated Plovers. It is likely one needs at least a 5' high tide for this spot to be truly productive.
Full eBird checklist here: https://ebird.org/view/checklist/S47690059
From there we split to Canal Boulevard. Brooks Island was, incredibly, devoid of all but a couple individual terns, but there was a nice showing of Pelicans and gulls.
Full eBird checklist here: https://ebird.org/view/checklist/S47691097
From there we headed to Miller/Knox hoping for migrants in the trees or activity on the bay, we unfortunately found neither save a calling Black-headed Grosbeak in the willows at Miller/Knox.
Full eBird checklist here: https://ebird.org/view/checklist/S47692111
We then headed to San Pablo Reservoir. It was perhaps the most dull I have ever seen the place, with almost no calling passerines on the way up. Nonetheless, teh reservoir hosted:
Caspian Tern-2 including juv
After a brief and unproductive stop at Waterbird Regional Preserve, we headed to Waterbird Way Pond, which was loaded with shorebirds. It seems like a good place over the next month to check for Stilt Sandpiper or Ruff. Highlights and shorebirds here included:
Hooded Oriole-1 appeared to be a migrant
We then headed to the Deer Ridge Golf Course area to test our luck with Roadrunner, but came up dry. According to homeowners it is still alive and well but sporadic as always.
We then headed to the Byron WTP which hosted a number of shorebird migrants. Highlights here included:
Full eBird checklist here: https://ebird.org/view/checklist/S47696609
Heading to Clifton Court, we found the reservoir mostly vacant, but still with a few interesting birds:
Pied-billed Grebe-22 was not an exceptional count, as this species migrates at this season
WHIMBREL-1 was a very rare bird for east county in Fall
Full eBird checklist here: https://ebird.org/view/checklist/S47697176
We headed north to Discovery Bay and were not disappointed. Around the golf course we found:
BALD EAGLE-1 was a very good bird for East county, and my first
VIOLET-GREEN SWALLOW-4 were quite unexpected as this species is relatively rare in East county. It is nearly unrecorded in the Bethel Bradford area, but in the Southeast part of the county they appear to be more regular, at least at this season
Western Bluebird-2 were part of the isolated population at this location
Full eBird checklists here: https://ebird.org/view/checklist/S47698079
From there we headed north to the Holland Tract with a primary focus on the Central Tract marshes. While water levels seemed great, few shorebirds were present, but still we found:
Blue-winged Teal-1 was a rare bird for East county
Bank Swallow-2 is a now expected species in the region
Blue-gray Gnatcatcher-1 was a migrant
YELLOW-HEADED BLACKBIRD-4 fed into the pattern of late summer occurrence of this species at this site. I previously suspected breeding, but after a May visit turned up none I believe these could alternatively be post-breeding dispersants from elsewhere in the valley
Tricolored Blackbird-1 follows the same pattern as Yellow-headed
Full eBird checklist here: https://ebird.org/view/checklist/S47700398
From there we hit Piper Slough hoping for Dusk Flight and Ibis. Unfortunately no ibis and the only things moving were larids, but we still found:
Pied-billed Grebe-53 were migrants
American Coot-350 were likely the first "fall" migrants here
We ended the day with 109 species, about average or perhaps a bit below for this time of Year. Was a nice way to finish my Summer stay in California.