On a warm, cloudy morning, at the far north end of the old field, a Blue Grosbeak was singing from the top of a chinaberry tree. The big silver, conical beak gleamed, the slightly peaked head was deep blue, and in pauses between songs, the Grosbeak switched its long tail energetically. But its plumage showed a lot of brown all over, with patches and shadings of blue, so it looked like a sub-adult Blue Grosbeak \u2013 a male from last season that has not yet acquired its full mature plumage \u2013 dark, rich blue all over, with striking rust-brown wingbars.<\/p>\n
I didn\u2019t have the best view, though, and the Grosbeak flew after only a minute or two, so I\u2019m not sure. Sunlight can do funny things to colors, and often a Blue Grosbeak looks more black or gray than blue from some angles. But \u2013 this one looked decidedly brown. It\u2019s puzzling because last summer the only Blue Grosbeak singing in the field all season appeared to be a sub-adult, and I wonder if that\u2019s going to be the case again this year.<\/p>\n
It\u2019s a small mystery, and I know I\u2019ll never know the full story because I\u2019ll only see the bird \u2013 if it stays around \u2013 once a day or so, at most. Maybe if I\u2019m lucky, I\u2019ll see a female, too, and on several occasions in past years I\u2019ve enjoyed catching glimpses of interesting Blue Grosbeak behavior. But there\u2019s so much more of its life that I\u2019ll never see. In general, there\u2019s a lot that is not known about the life and behavior of Blue Grosbeaks, and I think we\u2019re lucky to have them here. It always has seemed to me a signature species of this old field in summer.<\/p>\n
The species account in Birds of North America<\/em> notes: \u201cAlthough widespread throughout its breeding range, [the Blue Grosbeak] is generally scarce and virtually all aspects of its biology are poorly known, perhaps owing in part to its low numbers. . . . we still lack detailed information about Blue Grosbeak nesting ecology, courtship behavior, and song structure and learning, among other things.\u201d<\/p>\n The account goes on to note: \u201cNesting in shrubs or tangles of vines along forest edge or roadsides, Blue Grosbeaks commonly produce two broods per year. Limited data suggest that it is quite heavily parasitized by the Brown-headed Cowbird.\u201d*<\/p>\n Since I frequently see and hear Brown-headed Cowbirds in and around this old field, that seems a concern. More and more traffic on an already-busy highway just over the hill, and the replacement of fields, groves and wooded areas with subdivisions nearby have changed this habitat over the past decade or two, and each spring I watch and wonder if a Blue Grosbeak will return to nest here again.<\/p>\n So far the field itself remains large and wild, with a dense stand of full-grown pines as well as more open areas of thickets, vines and shrubs, and a power cut through the middle. So I\u2019m hopeful it can remain good enough habitat for the Grosbeaks \u2013 as well as Indigo Bunting, White-eyed Vireo, Gray Catbird and several other species.<\/p>\n