Last week, I wrote about the red-winged blackbird, which is one of the first migratory species to arrive in our area in the spring. I characterized the great flocks of red-wings as the vanguard of an approaching army, spreading out across the landscape and claiming it for themselves. Ownership of land and territories can be a curious thing. I feel like I own my property — at least for a little while — but the birds clearly see the same patch of land as their own. Apparently, multiple species simultaneously can own the same patch of Earth. As long as the species are not in direct conflict with one another, the sky is the limit.
The second most-likely species to arrive in our area in the springtime is the common grackle (Quiscalus quiscula). This particular bird is often lumped in with the “blackbirds,” but even the most casual glance at today’s photograph will reveal the error in this notion. Adult males are actually ensconced in a plumage that literally contains a rainbow of colors. However, the tricky thing about this is the fact that their feathers really are black. They just happen to contain tiny microscopic structures that are capable of refracting light.
On a bright, sunny day with a blue sky, an adult male common grackle would absolutely look black. But if the sun is at the correct angle these black feathers will glow with iridescent colors. The head is generally blue, the wings are purple, and the feathers of the back and belly can be a coppery yellow. Think of the astounding glowing green of a male Mallard’s head and you’ll have the picture. The feathers can appear to be glowing with an inner light.
On a cloudy day with just the right conditions, the birds can take on an entirely different look. A bright day with high clouds just thick enough to prevent any shadows from being cast will provide enough light for the male grackle’s feathers to show color all at the same time. The colors are a bit duller and more in the realm of pastels, but the effect may actually be more impressive than the stunning appearance of iridescence on a sunny day. The adult male in today’s photo illustrates this effect. Blues, violets, greens, yellows and copper-brown feathers are all visible. The only colors missing are reds and oranges, which are colors that are generally produced by pigments, rather than by refraction.
Adult female grackles are quite different in appearance. Their feathers are much less colorful and their bodies are much smaller. This is sexual dimorphism at its highest, but now that I’ve said that I can see that some of you might be thinking, “sexual what?” Well, the concept is simple enough once you learn the vocabulary, so here goes. The body’s shape is often referred to as “morphology,” the branch of biology that deals with the form of living organisms, and with relationships between their structures. Simply put, your morphology is your shape and appearance.
We all have a fairly good grasp on the term sexual, which basically refers to the difference between male and female organisms. The prefix “di-“ in the word “dimorphism” primarily derives from the Greek “dis,” which means “two.” Taken as a whole, the term “sexual dimorphism” means that the two sexes have two forms. We are all exquisitely familiar with this concept because humans also exhibit strong sexual dimorphism. Males tend to be larger than females and their body shapes are noticeably different. The same is true with grackles.
Males are larger and much more colorful than the females, which is a bit different from most other species. In most cases the males are more colorful, but are not larger. Canada Geese show the larger size in males, but their coloration is no different from the females. Then, in the hawks and owls, the females tend to be larger than the males, but again, they share the same coloration. This puts Common Grackles in a league of their own, at least on a local scale.
Once spring really arrives, the initial flocks of Common Grackles can be very impressive in size. Hundreds, and even thousands of birds will fly together in huge flocks as they move north and catching sight of such an assemblage can be quite a thrill. As with the Red-winged Blackbirds, there is a huge advantage to showing up early to claim the best territories, but this often comes with the risk of showing up just a tad too early. When this happens, backyard feeding stations can become overwhelmed with hungry grackles.
Before too long, however, the flocks will break up as the individual males start to claim this patch of land or that. They generally prefer to be near water, but they also need a territory that contains some rather large conifers, where the females will build their nests and generally fend for themselves once mating has occurred. The proximity to water is more important than the availability of conifers and after about two weeks of incubation, the 4-5 eggs will hatch. After another two weeks the baby grackles will finally fledge and they will follow their mothers, harassing them for food. These fledglings have gray feathers and dark eyes, unlike the eyes of adults, which are pale yellow.
With a winter like the one we’ve had this year it is entirely possible that Red-winged Blackbirds and Common Grackles will arrive at the same time. One can imagine a host of birds stuck in the south, impatiently waiting for the weather to clear so that they can surge northward. Common Grackles will happily travel in large mixed flocks with Red-winged Blackbirds, Brown-headed Cowbirds, and even European Starlings, so such flocks can be quite noisy and obvious when they first appear. All you have to do is turn off the TV, abandon your phone, and go outside with your eyes open. If they are around, you’ll know it.
Bill Danielson has been a professional writer and nature photographer for 28 years. He has worked for the National Park Service, the US Forest Service, the Nature Conservancy and the Massachusetts State Parks and he currently teaches high school biology and physics. For more information visit www.speakingofnature.com, Speaking of Nature on Facebook, or the Speaking of Nature Podcast.