Tuesday, July 27, 2021

A Gambel's White-crowned Sparrow Irruption

This blog isn’t dead yet – I’m still here and do have lots to share. I have much that I could have been blogging about these past three months – so much that the idea of catching up seems too overwhelming a task to even start on. But here I am, and I can’t let the amazing White-crowned Sparrow migration I witnessed in the yard this past spring go undocumented.

I’ll briefly review the subspecies of White-crowned Sparrows we have in Oregon and then share some photos from the phenomenal migration of Gambel’s White-crowned Sparrows that birders experienced in western Oregon in mid-April this year. It would be nice to at least to have a written record of what transpired on my blog, since it seems to have been a rather rare event, with essentially nothing published of this phenomenon, at least in the literature covering Oregon ornithology and in the available species accounts of White-crowned Sparrow.

In Oregon we have three distinct subspecies of White-crowned Sparrow.

1. Zonotrichia leucophrys pugetensis is the population that breeds in western Oregon, from just east of the Cascade crest to the coast, and much of the population is either sedentary or short-distance migrants. Presumably those that breed at the highest elevations migrate the farthest, and our resident birds are augmented by some wintering here from farther north. Apart from the voice, a pale yellow bill and dull blackish back stripes separated by buffy stripes are characteristic of this subspecies.
This pugetensis White-crowned Sparrow was at Cape Meares on the Oregon coast where a common breeder.

2. Zonotrichia leucophrys oriantha breeds in scattered brushy mountain meadows east of the Cascades. This entire population is migratory and winters mostly in northwestern Mexico, with occasional individuals in southeastern Arizona. The black lores and reddish bill are more like the nominate subspecies of eastern North America.
This oriantha White-crowned Sparrow was at Yellowstone National Park, where they breed.

3. Zonotrichia leucophrys gambelii is the widespread breeder in the high arctic regions of NW North America and is essentially entirely migratory, mostly wintering in eastern Washington and Oregon south to NW Mexico. It’s the abundant wintering subspecies in the SW United States. Its bill is an orangey yellow, and the dark back stripes have a reddish hue, with the pale stripes being grayish white.
A migrant gambelii White-crowned Sparrow where it is an expected migrant near Lakeview, Oregon.

Very much like the winter of 2019-2020, this past winter I had two or three White-crowned Sparrows of the locally and regionally breeding subspecies Z. l. pugetensis in the yard as part of the winter flock of passerines. They used the brush pile for cover and took advantage of my practice of scattering bird seed on the ground all around the yard. This species is not common nor unexpected in suburban Eugene, though if you go just outside town to slightly more rural areas, winter flocks will have dozens of them. These are essentially all Z. l. pugetensis, which also breeds throughout most of western Oregon (especially in brushy areas on the coast and in clearcuts in mountains), and there is some regional migratory movement that is little understood. If you go back just a couple blogs, you’ll see where I documented that a Canadian bird was passing through here at the end of March, presumably wintering somewhere not far south of here and heading back to breed in southwesternmost Canada.

These are photos of a first winter and an adult pugetensis that wintered in the yard.

Note the pale yellow bill and blackish back stripes.

Suddenly on April 13, there was a huge increase in White-crowned Sparrows at my brush pile, rising to 24 total birds on April 15 and 16, and continuing for a couple of weeks in decreasing numbers before the last ones departed by April 30. It turns out all these new birds were the high-arctic breeding subspecies Z. l. gambelii. I got many photos of them and recorded their distinctive songs several times. It’s worth noting here that a year ago, while I was paying very close attention to bird movements in the yard and neighborhood, there was no such influx of migrant White-crowned Sparrows. In any event, it was that song, instantly transporting me back to my back yard in Tucson, that clued me in.
The first five notes of George Lloyd's Symphony No. 5

The actual status of Z. l. gambelii in western Oregon is poorly known, though the references I checked  (albeit dizzyingly circular) simply state that it’s the common migrant east of the Cascades and less common west of the Cascades. It seems the only published evidence of their presence in western Oregon  is a mention of a late April specimen (“and at other dates”) from a collector Portland in the late 1920’s. Since then, it seems little has been done to document this subspecies. Recent eBird submissions do show that that they occur from time to time, but when exactly, how many, how often, and under what circumstances? Unfortunately, the lack of awareness and apathy from birders who can’t count it as a species on their lifelists has resulted in few attempts to document the status of what actually may be a perfectly legitimate species.
This gambelii White-crowned Sparrow in my yard shows the orangey bill, and the often brighter and broader white head stripes are apparent.

One of the 24 or so gambelii White-crowned Sparrows in my yard. In this light the reddish brown streaks on the back are very obvious.

I’m an ear birder with a notoriously poor visual memory, so my mental map of the various White-crowned Sparrow subspecies (and their dialects — maybe the subject of a later blog but perhaps too complicated…) is based on their songs. I grew up in western Oregon becoming very familiar with the classis pugetensis song of “Teeew, titit-ti-tieew, titititi,” with some variation on the ending. Then I spent some years (decades) living in Arizona where gambelii dominates as a migrant and winter bird, joined by birds of the interior breeding oriantha in migration and occasionally in winter. Birding Colorado, Utah, and SE Oregon in summers familiarized me with the visually distinctive oriantha birds, but it was always their distinctive song that struck me.

In Arizona, the abundant wintering White-crowned Sparrows, numbering into the 1000’s on a good day, were 99% gambelii. In the growing daylengths of the early year, the males would practice their song, and there was little variation. I’ve always likened it to the first five notes of George Lloyd’s Symphony No. 5. (It might be a relatively obscure piece of music, but it’s apparently his most famous work and worth knowing. I think of it as a mix of Gershwin’s Rhapsody in Blue with Holst’s The Planets, maybe with a bit of Bernstein’s West Side Story thrown in.) It was a common sound in my Tucson back yard.

I moved back to Oregon finally in September 2019, back into the land of our reliable resident, year-round pugetensis, and their song familiar from my youth. That’s all I saw here until I led my Oregon in Late Summer tour for WINGS in early September 2020, and we saw an abundance of southbound migrant gambelii as soon as we reached the central Oregon lava lands and Great Basin sagebrush steppe. I didn’t try to discern them using any possible field marks, going on the common knowledge that migrant White-crowned Sparrows east of the Cascade crest are all gambelii. And that’s still the apparent truth.

On October 24, 2020, while I was birding the Philomath Sewage Ponds about an hour north of where I live, I was watching the sparrows coming to a known seed drop, and I heard the obvious five notes of Lloyd’s Symphony No. 5, saw the bird, and took some photos, thinking maybe these will prove to be distinctive, should I ever try to find the time to tell the subspecies apart visually. In any event, that was the first time I had knowingly heard Gambel’s White-crowned Sparrow in western Oregon. This is my best photo of that bird. I can now see in the photos that the more orangey bill and reddish stripes to the back are quite noticeable. From looking at eBird submissions, it appears that this bird actually spent the winter here.

We had some very unusual weather here this spring (though there aren’t many on planet who couldn’t say the same thing these days). In early April just before these stray Gambel’s White-crowneds showed up, we had several days of persistent north and northeast winds and clear skies. Throughout the month we had drier weather (the driest April on record, in fact), colder nights, and warmer days than usual. It seems that these sparrows normally migrate only east of the mountains, and that makes sense considering that they’re coming from winter grounds in inland areas south and east of here and are returning to inland Arctic areas to breed. A route west of the Cascades would direct any northbound migrants along the coast and to Pacific forests of SW Canada and SE Alaska, not the interior Arctic. This is the route taken by our abundant migrant Russet-backed Swainson’s Thrushes and chryseola Wilson’s Warblers, for example.

So my guess is that this spring the unusual weather patterns, specifically the strong winds from the NE at the crucial altitude, led these sparrows to stray west of the Cascades. But if that is indeed the answer it only brings up more questions. If we were to have the exact same weather pattern next year, would we also see Gambel’s White-crowned on the west side? Or does it only happen in years with a bigger than normal winter population moving back north? How often does this happen? I’d love to keep track next year, but I’ll be leading my Jamaica tour in the middle of that same time frame. And I hope that a greater awareness will also result in more birders paying attention, documenting their sightings, and submitting their sightings to eBird.

This Cooper’s Hawk, one of our resident neighborhood pair, took note of the sudden influx of sparrows and spent several days in the yard, though it wasn’t very successful at catching any of them.