Big Flight at Mitchell Canyon 4/17
I had the great fortune of going to Mitchell Canyon today, as there turned out to be an absolutely spectacular flight. I was not optimistic about conditions given strong winds and fog, but apparently the winds helped instigate the flight on this day.
Around 7am up White Canyon I ran into John Toldi, and we spent the vast majority of the day together. The first 20 minutes we spent locating the ideal place in the canyon to watch migrants pour northwest up-canyon, which we eventually decided to be around here (37.9051286, -121.9571243). Over the ensuing four hours we found over 500 Warblers along with assorted other migrants pouring Northwest along White Canyon. The vast majority of these were Orange-crowned Warblers but there were also good showings of Black-throated Gray, Townsend's and Nashville Warblers and smaller showings of Tanagers, Grosbeaks, and Hermit Warblers. During our flight watch the following numbers of migrants were recorded moving up White Canyon:
Golden-crowned Kinglet-1 was late
Ruby-crowned Kinglet-29 was a good count for this day
Orange-crowned Warbler-301 likely represents the County high count
Black-throated Gray Warbler-51
From there (starting at 11AM) we worked down White Canyon and up the main canyon about a mile before turning back towards the visitor center. Migrant numbers in the main canyon region were still quite high despite the time of day. In addition to the migrants listed above, some stuff found either not-moving at White Canyon or in the Main Canyon were:
Hammond's Flycatcher-17 was interestingly the exact same number found here by Derek and John yesterday
Hermit Thrush-12 seemed high for this date
Lawrence's Goldfinch-1 at Visitor Center was a good bird for this location (and just my second up the canyon)
Orange-crowned Warbler-28 was in stark contrast to the 100s streaming by White Canyon
MacGillivray's Warbler-3 was a good count for mitchell
Black-throated Gray Warbler-14
To reach this area I parked in the neighborhoods along Mitchell Canyon Road and biked i. Near those Neighborhoods there was a single Red-breasted Nuthatch, presumably a leftover from last Winter's irruption.
The kinglet push seemed late to me, with early April seeming to be the peak normally. By this date we normally only have a few stragglers, but this was far from a normal day.
Given the mass of this movement there's a lot of questions to be answered. Perhaps the biggest is what conditions cause such a mass movement. Observers in Napa and Solano county have often correlated large ridgeline flights in those respective counties with clear skies and strong NW winds. The winds were certainly present today, at least in White Canyon, but the overall region seemed more Southwest, and there was quite a bit of fog/overcast nearby.
Full eBird checklist here: https://ebird.org/checklist/S67382750
San Francisco, CA