Last week, from 17 to 21 September, our team from the San Diego Natural History Museum surveyed the riparian oasis in San Felipe Valley, about midway between the pass along Highway S2 and Scissors Crossing. The area became part of the San Felipe Wildlife Area several years ago, and our study was sponsored by the California Department of Fish and Wildlife. Last week’s visit followed one in July 2017 and another in March of this year.
On Wednesday 19 September, Lea Squires, Christine Beck, and I saw an adult Broad-winged Hawk. It flew out of the riparian woodland and circled over us for about a minute, showing a tail boldly banded with black and white, pale underwings with primaries and trailing edge sharply tipped with black, a head rather uniformly dark brown, breast mottled brown, sides barred brown, belly whitish, and upperparts gray. Then it headed down the valley.
The next day, I was with Marcus Hubbell and Stéphane Vernhet when we heard a high-pitched twittering from the opposite side of the creek, out of sight. I said, “if anything, that sounds like a Tropical Kingbird!” The bird kept calling but moving northwest up the valley—it was still calling when we met up with Lea Squires. I found a spot with a break in the trees where we could look across the creek to some mesquites on the opposite side. And there it was sitting atop one of the mesquites, a kingbird with a pale gray head, yellow belly, and dark but not black tail. At a distance of ~150 m the identification still relied more on the voice than on the plumage. Then the bird flew high into the air and headed out of sight to the northwest up the valley. The next morning, a bit farther upstream, I thought I heard the characteristic twittering call once in the distance. Then when I met up with Lori Hargrove a couple of hours later, she related that she had just seen the Tropical Kingbird very well right along Highway S2, noting the extensively bright yellow underparts, green back, large bill, etc. I don’t know of any previous records of the Tropical Kingbird far inland in San Diego County, but San Felipe Valley leads up to the lowest pass over the county’s mountains. So it’s a reasonable place to find a Tropical Kingbird as it makes the crossing that accounts for the species regularly reaching the coast. San Felipe Valley is well known as a corridor for spring migrants heading northwest, and seeing its use in fall was a reason for choosing a survey in mid-September. Several Vaux’s Swifts and Barn Swallows—as well as the Broad-winged Hawk—were following the route toward the southeast, but we hadn’t anticipated seeing it used as a corridor to the northwest in fall by the Tropical Kingbird.
Early fall arrivals were a Hermit Thrush on 18 Sep and a junco on 19 Sep. One Nashville Warbler had the throat white, the belly extensively white, and the back so gray it might have been mistaken for a Virginia’s Warbler, but the rump was the same green as in a Nashville. Wilson’s Warbler was by far the dominant species among the common migrants. An Acorn Woodpecker on 19 Sep was about two miles below the lowest oak trees. The Nuttall’s and Ladder-backed Woodpeckers meet here: there are several Nuttall’s in the riparian woodland along the creek, Ladder-backed in the scrub on the adjacent southwest-facing slope and occasionally crossing the creek.
The area has become an important site for breeding riparian birds—Lori counted up to 33 Bell’s Vireos along a mile and a quarter of creek on 25 July 2017—far greater than from 2003 to 2008 when she and Paul Jorgensen covered the area during our study of the effects of the fires. Last week, one Bell’s Vireo was still present and singing sporadically up until 20 September, and at least two Yellow-breasted Chats were still there on 21 September. Summer Tanagers were still present up until our departure on the 21st with a minimum of three individuals, one female and two adult males. On the morning of the 18th, one of the males was even singing. The museum’s early collections from the Colorado River attest to the population of the Summer Tanager there remaining into late September. But I don’t think any previous observations have confirmed that our recently established population in San Diego County remains similarly late. Also, the White-winged Dove is now resident in San Felipe Valley, as we saw it on all three visits, though no more than one bird per day last week.
Our mammal results include three species of bats—the western pipistrelle, California myotis, and Townsend’s big-eared bat—captured by Drew Stokes in two evenings of netting. Drew also saw a mountain lion!
The only downside to the week were the bug bites Lea and I got—possibly from two species of mites, including bites that look like chiggers. Lea got a bad case of chiggers in Camp Pendleton a couple of years ago. In my whole life I had never heard of chiggers in San Diego County. Is dealing with chiggers another price we must now pay for the warming climate?
Thanks to the California Department of Fish and Wildlife for sponsoring our study and Hans Sin for coordinating it.