Date: 2/22/21 2:16 pm From: Feldstein, Steven B <sbf1...> Subject: More Fox Sparrow excitement
I am continuing to have lots of fun with Fox Sparrows. I hope that this post will be interesting, as it deals with my attempt to try to learn something about the sex (male vs female), behavior and migration of the Fox Sparrows I've been seeing.
This morning I saw two Red Fox Sparrows side-by-side this under my neighbor's feeder. When I saw the two birds together, I was hoping that one would look something like a Red/Slate-colored Fox Sparrow intergrade, but that wasn't the case. The plumage of both birds was just about the same, with one individual perhaps being just slightly darker. It's probably the first time that I have ever seen two Red Fox Sparrows together. The "darker" individual was very aggressive, chasing every other bird, including several Dark-eyed Juncos, a larger Northern Cardinal, and the other Red Fox Sparrow under my neighbor's feeder. In the three weeks that the Red Fox Sparrow has been here, I never saw it chase away other birds.
I noticed that tail feathers on the "darker" Red Fox Sparrows were markedly longer than that of the other Red Fox Sparrow. So, I looked up the length of tail feathers in Peter Pyle's "Identification Guide to North American Birds". For iliaca, he indicates a tail length of 63-70mm for females and 67-75mm for males. For zaboria, it is 65-73mm and 68-77mm, respectively. Since the difference in tail length between these two Red Fox Sparrows was obvious to my eyes, and these birds were probably of the same subspecies, my guess is that the bird with the shorter tail is a female, even though for most bird species there are more males than females at the northern edge of their range in winter. Therefore, I am guessing that the Red Fox Sparrow that's been here for at least three weeks (the bird that I first thought may be an intergrade) and probably wintering in State College, is a female. In contrast, for the Red Fox Sparrow with the longer tail, my guess based on the tail length, aggressive behavior, and timing, is that it is a male. With regard to timing, Nick and Greg's Birds of Central Pennsylvania indicates that early migrant Fox Sparrows can arrive in late February. This provides further support for this individual being a male, since males tend to migrate earlier in spring in most bird species. Since the winds were southerly and strong last night, perhaps the "darker" individual arrived last night. That would explain its voracious eating behavior and its aggressiveness to all other birds, as it needed to replenish its lost energy reserves.
I've put together different factors to try to learn some interesting points about these two Red Fox Sparrows. I'd be curious to hear any comments in support of or in disagreement with my picture.