Boy howdy, that Fox Sparrow sure has a big bill and we actually caught two on Sunday, both with roughly similar measurements.

There are, according to most authorities, 17 or so different subspecies of Fox Sparrow. These are generally broken up into 4 broad (possibly species level) groups. One group, collectively bundled as megarhyncha, has a pretty big bill. Could this be a vagrant from that group?
No, believe it or not, its bill isn’t big enough. There are two measurements that we make on Fox Sparrows. One along the upper ridge of the bill tells us the length. The other, taken from the place outboard of the holes in the nose down to the flat part at the base of the bill tells us the thickness. The bill of our bird in hand is plenty long enough, but it’s not deep enough to be a megarhyncha.
But there are other “big billed” Fox Sparrows and they fall into the Sooty Group. We only seem to catch them in the early fall and late spring, presumably because they winter farther south than our “average” Sooties. We put them in a pile we call unalaschensis/ridgewayi, because that’s (approximately) where they land on the graph.
I’ve been catching and measuring Fox Sparrows for quite a while. It took me a couple of seasons before I realized I could not sort individual Sooty Fox Sparrows reliably into these finer subspecific categories. I can say with some confidence that we catch all Sooty-type subspecies, because when I can take all the measurements we make, put them on a scatter plot, they the cover continuum of sizes and shapes from the largish, deep-billed sinuosa to the smallish, tiny-billed fuliginosa (in fact, most of the birds we catch seem to match fuliginosa). But the key here is continuum. There are no clean boundaries.

A handy map made by Robert Zink was publish a few years back in Birding Magazine (December 1999) which lays out the breeding ranges for most of the forms.

As can be seen, it’s kind of unlikely that any of the Fox Sparrow types other than Sooty are going to turn up in a net on the North Coast of Oregon, especially megarhyncha. Of the Slate-colored forms only olivacea seems likely and it’s a “small-billed” type.
So, assuming I’ve made the proper diagnosis and our bird genuinely belongs in the unalaschensis/ridgewayi pile, our quiz bird is headed to Kodiak or the Aleutians.
For those of you who want to play along at home, the measurements of the two birds caught Sunday were:
|
Bird one |
Bird two |
| Wing |
81mm |
75mm |
| Tail |
65mm |
70mm |
| Exposed culmen |
12.2mm |
12.1mm |
| Bill depth |
7.3mm |
6.9mm |
Bird one is the bird in the photographs.
And just for closure…
The other quiz bird was, as most of you correctly surmised, a female MacGillivray’s Warbler. We rarely catch this species. They don’t seem to come down to the coastal riparia, preferring the clearcuts up higher in the Coast Range.