Bruce Calkins and I drove up to the San Dieguito River valley east of Del Mar today to scout out my area for this coming Thursday’s Rancho Santa Fe Christmas bird count. Because of the virtual lack of rain so far this winter the seasonal wetlands that are productive when wet are now completely dry, requiring me to come up with a new strategy. In the now horseless horse pastures along San Dieguito Road there were about 325 Canada Geese (many fewer than in the past) divided into two flocks. The flock in the NE corner of the pastures had one Snow Goose with it. The other flock was along the far west side of the pastures, requiring us to walk around the south end of the pastures and north halfway up the west side to study them closely. With this larger flock we had one Aleutian Canada Goose with a moderately well developed white neck ring.
At the square pond just east of the right-angle bend in Via de la Valle it looked more like summer than winter: besides one female Bufflehead, the only birds swimming were coots, Ruddy Ducks (including a male in breeding plumage), and Pied-billed Grebes—including two downy chicks (recalling Paul Lehman’s observation of Pied-billed Grebe chicks in Loma Alta Creek during last Saturday’s Oceanside CBC). Also far more typical of summer than of winter was one female or immature Least Bittern that allowed fairly good views by scope—something to look for again this Thursday.
We also walked along the new trail along the north side of the San Dieguito River estuary. About halfway between Interstate 5 and Jimmy Durante Blvd., between the two Osprey platforms (to both of which the Ospreys were bringing new sticks), we saw a pair of California Gnatcatchers and a hybrid Eurasian × American Wigeon. On the wigeon, the sides were grayer than in the American, and the rear of the head was quite rufous, but the front of the head looked much more like the American with a strong green patch through the eye, little rufous on the face, and the crown more cream color than yellow.
Back on the subject of the Cackling Goose…. Last Monday, courtesy of navy biologist Tiffany Shepherd, we received at the San Diego Natural History Museum a fourth specimen of the Cackling Goose this fall/winter. The latest one was from North Island Naval Air Station—shot as an aircraft-strike hazard after repeated attempts at hazing away from the runway failed. On Wednesday Lea Squires skinned it—another beautifully made specimen. Unlike the first three that we had received through Project Wildlife, this one was a female, immature as specified by the lack of development of the ova in the ovary. It was the same size as the three previous specimens and very similar in plumage with only the barest hint of a white neck ring. Like the first three, this specimen has the bill tapered laterally, a shape found only in the Aleutian and the Cackling Goose proper (Branta hutchinsii minima). All the other subspecies have a more straight-sided, spatulate bill; this includes B. h. taverneri, as Jean Delacour specified in his original description of that subspecies. Therefore our specimens are not taverneri or the Lesser Canada Goose (Branta canadensis parvipes) as I suspected initially. I have Dick Erickson to thank for steering me to the right literature that addresses the variation of the Aleutian Cackling Goose explicitly: the recent book “Waterfowl of North America, Europe, and Asia” by French ornithologist Sébastien Reeber (see review in Western Birds 48:65-67, 2017; https://www.westernfieldornithologists.org/archive/V48/48(1)-p065-p067.pdf). According to this source, in the Aleutian Cackling Goose the characteristic white neck ring is lacking in the juvenile plumage; it appears only during a bird’s first winter as the juvenile plumage is replaced. It makes sense that most of the Cackling Geese reaching San Diego County, far south of their usual winter range, are juveniles. All four specimens that we have received this year have been juveniles—as demonstrated by the narrower rectrices and more rounded (rather than nearly square) tips to many of the body feathers. So that explains why the specimens are perfect in size and bill shape for the Aleutian but lacked the characteristic color pattern. The Aleutian seems to be the subspecies of the Cackling or Canada Geese in which the juvenile plumage differs most conspicuously from later plumages.