Many birds are sexually dimorphic — males are more colorful, the females are drab — but this isn’t true of white-throated sparrows.
White-throated sparrows come in two color morphs: white-striped shown above, tan-striped below. The crisp white-striped birds aren’t always male, the plain tan-striped birds aren’t always female. You can’t tell their sex by color.
Here they are side-by-side: white-striped on left, tan-striped on right. Notice that …
- Head stripes are black-and-white versus brown-and-tan
- Lores are bright yellow versus dull yellow
- Malar stripe is weak versus prominent
- Breast is gray versus brown-and-tan
- Breast is mostly clear versus very streaky
Not only do they look different but the white-striped birds are aggressive, philandering and don’t take much care of their kids while the tan-striped birds are gentle and very caring of their young.
You would think these differences would force one of the color morphs to disappear from the gene pool but it doesn’t. The reason is surprising.
When it comes to picking mates, these birds always mix it up. White-striped (aggressive) males mate with tan-striped (care-giving) females and the tan-striped (gentle) males mate with white-striped (philandering) females. Thus the color morphs and personalities persist.
Learn more about their amazing social behavior in this article by GrrlScientist in The Guardian, May 2011.
And when you see white-throated sparrows you’ll know you can’t tell their sex by their color but the drab ones are always good parents.
(photos: White morph white-throated sparrow from Wikimedia Commons, Creative Commons license. Tan morph by Henry McLin on Flickr, Creative Commons license. Click on each photo to see its original)
We had a small flock of about half a dozen of the white striped version eating from our ground feeder last year (they didn’t seem too aggressive). I didn’t notice any of the tan ones, but I’ll have to look more closely this year if they return. I look forward to our Winter visitors since they are different from our Summer birds. We usually have Tree Sparrows and Juncos, and occasionally we see Pine Siskins, White-Crowned Sparrows, and the White-Throated Sparrows. One year I saw a Hermit Thrush foraging at the edge of our woods.
Today, I think I saw a couple of immature snow geese at the reservoir on Waterdam Rd in Peter’s Township. Seems odd for them to be here this time of year, I would think it would be late for migration. I just caught a glimpse of them as I was driving in to work, so I’m not positive that’s what they were.