This post is written by Olivia Schouten, one of our Hubbard Conservation Fellows. Olivia hails from Pella, Iowa, and has strong experience in prairie ecology. Look for more posts from her, as well as our other Fellow, Alex Brechbill, in coming months.
One of my favorite things about the change from winter to spring is the return of migratory birds. While the rest of spring has been reluctant to arrive, I am still reminded of the inevitable change in season as more and more birds arrive in the area. What started with sandhill cranes back in February just continues as killdeer, turkey vultures, and swallows, among others, seem to appear overnight when a favorable wind blows from the south.
Among the new arrivals are northern flickers, a woodpecker that despite its name, tends to feed on the ground. This migratory bird arrived here on the Platte River quite suddenly over Easter weekend, and they’ve been everywhere ever since! While common across North America, if you’ve spent any time travelling and recognize this bird, you may have noticed something interesting: birds in the eastern half of the continent are not the same color as those in the west.
In fact, there are two color variants of northern flickers. Eastern birds are called yellow-shafted flickers, and those in the west are red-shafted. The ‘yellow/red-shafted’ designation refers to the unusual coloration on the shafts of the wing and tail feathers of this bird. Where most birds’ feathers either have white, brown, or black shafts, northern flickers’ are bright yellow or salmon-red, depending on the variant. The undersides of these feathers also display the same color, resulting in bright flashes of color when the birds fly, turning a somewhat drab bird into something spectacular.
There are some other differences between the eastern and western variants. Yellow-shafted birds have a red crescent on the nape of their neck, and while all males have a ‘mustache’ patch of feathers extending down their cheek, it is black in yellow-shafted males, and red in red-shafted males. These differences are so clear, that for many years the two variants were considered different species.
However, what complicated that classification was the presence of hybrids of the two variants in a large zone stretching from Texas to Alaska, cutting right through the heart of the Great Plains, including central Nebraska. These hybrids, called intergrades, display combinations of facial traits found in the red- and yellow-shafted variants. In my home state of Iowa all you will see are yellow-shafted flickers. However, here in Nebraska I see flickers with their wings flashing everything from yellow to dark salmon red, and all colors in between.
Now considered one species, northern flickers are just one example of a common trend seen among North American birds. If you flip through a bird field guide and study the range maps, you will often find pairs of similar species where one occurs in the east, and one in the west, with the transition between the two occurring right down the middle of the continent. Eastern screech-owls and western screech-owls, ruby-throated hummingbirds and black-chinned hummingbirds, eastern and western wood-pewees, eastern and western meadowlarks, vireos, bluebirds, warblers, and on and on and on, you can’t escape the pattern. For many, it’s as if there was an invisible wall through Oklahoma, Nebraska, South Dakota, and upward keeping these species from spreading any further.
Clearly, something is going on in the middle of the continent when it comes to birds, and this hybridization sometimes makes it difficult for ornithologists to determine where species begin and end, or whether they should even be considered different species at all. One of the leading hypotheses is that climactic changes during past ice ages created unsuitable habitat in the center of the continent that separated previously connected populations. Time allowed for the divergence of these now separate populations, and when they reconnected as the ice retreated, enough differences had accumulated that they were no longer the same species.
Of course, this divergence was carried to varying degrees of completion depending on the bird. While some of these species pairs, like flickers, hybridize quite readily, and in fact never quite diverged enough to be different species at all, others, such as meadowlarks, while nearly identical in appearance, developed different enough songs that their separation was maintained.
So pay attention to the flickers around you here in Nebraska and elsewhere along the hybrid zone, and see if you have can spot the different variants!