Yesterday morning I took my bird feeder down, in part because the Fish & Game recommends it if you want to avoid bear damage, but also because the melting of snow has revealed an enormous amount of bird seed on the ground. I sat down at my kitchen table to see what was what out there, and blackbird after blackbird began to alight on the ground outside and eat millet.
These blackbirds were right on time. According to the records sent to me by a reader last month, blackbirds are due back in Unity between early and mid March. Most of the ones on the ground outside my window were red-winged blackbirds. Most of these were adult males, although there were a few immature males sprinkled through this flock of 40 to 50 birds. The immature males were born last summer and retain some of the brown streaking that made them initially resemble their mothers, but they are now about half way to being replicas of their fathers.
The other blackbirds in the flock were common grackles. There were only five or six of these, but they were readily distinguished from the red-wings by their larger size, their long wedge-shaped tails, and their purplish iridescence (although that was hard to see on this overcast morning). If you look more closely you can also see that grackles have yellowish-white eyes, while those of redwings are dark.
There were no rusty blackbirds in this flock. They have been in steep decline for many years. We only see them in migration; they nest in Canada. Brewer's blackbirds are a more western species and are seen only rarely in migration here on the east coast. Both the rusty and the Brewer's have whitish eyes, but have shorter tails more like the red-winged blackbird.
I remember being fascinated by grackles when I first got interested in birding because at that time older books still separated the “bronzed” and “purple” grackles into separate species. There was a geographical separation, with the bronzed birds found north and west of the Appalachians and the purple birds were found in southern New England and east of the Appalachians all the way to Florida, according to eBird.org. Allaboutbirds.org separates the east coast populations into two different forms. In the southeast the iridescence is a greenish color on the back with purple on the bellies, while further up the coast the birds are more likely to be purple all over.
As I lived immediately north of the Hudson Highlands, which was the local ridge of the Appalachians, I thought I might be able to see both “species.” In fact, we had mostly purple grackles, with perhaps the occasional bird that could be called bronzed and a lot also seemed to have greenish backs. Given that I lived in the region where all the geographic forms overlapped, I guess that was about right. That they freely interbred was the primary reason they were eventually combined into one species. I might have been growing up looking at intermediate plumaged birds.
The iridescent colors are caused by refracting light through the structure of the feathers rather than by pigment. The feathers are infused with black pigment, but they flash yellowish-brown, green, or violet when the sun hits them at a particular angle. The consistent regional distribution suggests it is genetically controlled (not caused by nutrition) and one can easily imagine genetic variations in protein structures that would produce different angles of refraction and therefore different colors.
Most blue birds, including actual bluebirds, blue jays, and indigo buntings, are blue due to refraction rather than blue pigments. If you crush a blue jay feather with a mortar and pestle, it turns black. In contrast, the vibrant red of a cardinal is the actual color of the feather; it is still red if you crush it. Cardinals, in fact, seem suffused in red pigment (probably a carotenoid), as even their bills and legs have a reddish cast to them. Flamingos, on the other hand, are pink only if their diet includes crustaceans, which have carotenoids in their shells.
Common grackles, in theory, should winter as far north as southern New Hampshire and Vermont. That is what distribution maps in bird guides show, anyway. I have not seen any all winter. Many birds at the northern extreme of their range — winter or breeding — tend to stay in the valleys and lowlands because the mesoclimate is warmer there than in the surrounding uplands. Which is to say, in order to see winter grackles, you might have to hunt around in the Connecticut, Pemigewasset or Merrimack river valleys for them.
Unlike red-winged blackbirds, who are big eaters of invertebrates during the warmer months, common grackles are primarily seed eaters throughout the year. Only up to a quarter of their diet may be invertebrates in the warmer months. While they adore agricultural grains like corn and rice, they also eat sunflower seeds and the seeds of trees, even acorns. This focus on seeds helps them to winter as far north as they do, but a thick covering of snow would get in the way of their foraging.
When I got outside to walk the dog this morning, I was immediately bathed in the sound of the blackbird flock, which filled a couple of trees in my yard. The red-wings make their squeaks and chirring noises, but the grackles make a sound like a rusty gate abruptly moving an inch or two. They produce this sound with much apparent effort. They stiffen and then seem to gradually expand, their feather sticking out on end. Instead of exploding, which looks imminent every time, they emit their brief wheezing, grating “song.”
Like the rusty blackbird, the common grackle is declining in numbers. While they are still abundant and widespread, they have declined by 2 percent every year since 1966 (when data collection began) for a total loss of 58 percent of the population, according to the North American Breeding Bird Census. They are therefore classified as a “Common Bird in Steep Decline.”
On the other hand, the boat-tailed grackle is expanding its range northward. In my youth they were unheard of north of the mid-Atlantic states and now they are seen regularly in southern New England during the summer. When grackles fly, their long wedge-shaped tails become depressed in the middle and resemble the keel of a boat. The tails of boat-tailed grackles are even larger and relatively longer than those of common grackles and this southern species is larger overall. Common grackles are about a foot long and boat-tails are about 16 inches long. The iridescence of the boat-tailed grackles is consistently greenish-blue and they are also strictly tidewater birds. If they start showing up in the Connecticut Valley, then you'll know that climate change is proceeding even faster than we thought.