[All photographs copyright, Gary Nunn 2013] – Just before leaving Fort Rosecrans National Cemetery today I heard an unfamiliar, but quite pleasant, bird song just outside the east fence line south of the eucalyptus grove. I walked over and, from some distance, caught sight of the bird singing atop a bush behind the perimeter fence. But then it immediately hopped down out of sight! Viewed from behind the sparrow shaped bird had a large gray head, gray back, rich rufous wings, a long rufous tail, and, particularly noticeable, rufous upper tail coverts demarcated against the gray back. Hmmm, to be honest I was a bit puzzled!
I walked down to the fence and decided to give the “Universal Bird Attractor” (Wrentit chatter call!) a go. I waited a few minutes and was about to give up when, sure enough, out hopped the bird I had just seen. I was impressed to see it was a Fox Sparrow of the megarhynchus group of forms, more commonly known as “Thick-billed” Fox Sparrow! There were in fact two birds traveling together, one with a real honking grosbeak sized bill and the second a bit smaller billed.
It seems most likely both these birds are of the Passerella iliaca stephensi form found breeding in Southern California including just a handful found summering on the highest mountain tops in San Diego County. “Thick-billed” Fox Sparrows are only known to migrate a short distance moving to lower elevations in the winter near to their breeding range. So most likely these two birds originated nearby or from the southern Sierras.
I was confused by the bill color of these two individuals which both show some orange-yellow coloration on the lower mandible, and in one bird the upper mandible. What’s puzzling is that Thick-billed Fox Sparrows are illustrated in field guides with uniformly gray-colored bills. However after researching this point a bit further, including Jim Rising’s excellent The Sparrows of the United States and Canada illustrated by David Beadle, I discovered that outside the breeding season the bill can be more orange-yellow, and was in fact illustrated this way in older descriptions of these large-billed forms of Fox Sparrow. The Handbook of the Birds of the World, Vol. 16, already treats the four natural groups of Fox Sparrow as full species and also mentions the bill coloration being more orange-yellow outside the breeding season for the “Thick-billed Fox-sparrow” (note the logical new common name).
The Fox Sparrow complex is almost certainly headed towards a more progressive taxonomic treatment when it will be subdivided into its four natural groups – Red, Sooty, Slate-colored, and Thick-billed. This could prove interesting for San Diego County birders since all four have been found here in the county! I would recommend keeping a careful note of when and where you have seen these very different looking forms of Fox Sparrow.