Writing for Audubon.org in 2017, Kenn Kaufman looked at the boggling mating strategies of the white-throated sparrow (Zonotrichia albicollis), which comes in two morphs: one with black-and-white head stripes, the other with brown-and-tan stripes. “Within each gender, white-striped birds are more aggressive while tan-striped birds are more nurturing. […] Nesting pairs consist of one bird from each morph more than 95 percent of the time, but it’s especially interesting to consider what happens on those occasions when two birds of the same morph pair up. In short, it’s likely to be a bad idea.” The next time I see one—they do turn up around here—I’ll have to look more closely.