As November approaches, we are on the cusp of the season in which our local bird populations, both species and numbers, become much less predictable. During the summer nesting season, our local species are virtually the same from year to year. Permanent residents like chickadees and nuthatches are supplemented in summer by migratory species, whose individuals usually return to the precise locations where they nested the previous year. Densities are determined by each species characteristic territorial behavior.
Autumn struck quickly here. On the heels of last week's unusually cool temperatures, a number of songbird species typical of early fall migration began showing up: ruby- and golden-crowned kinglets, brown creepers and yellow-rumped warblers. The latter is always the last of the warbler species to depart, and you can expect them to become abundant in the first half of October.
Cool breezes and colorful foliage of autumn are taking hold now as summer 2018 fades into the background. In thinking back over the summer, there are several things that struck me about the seasons' birds that may also be of interest to you. For one thing, ruby-throated hummingbirds persisted for at least a week longer than I expected. I was still seeing several at our flowers and feeders on Sept. 15, though they became suddenly scarce after that, once the heat broke and colder days arrived.
This is the time to be looking for common nighthawks migrating south, especially in the couple of hours before dusk. Nighthawks are one of my favorite species because of their aerial grace and agility and their habit of flying in loose groups, enabling one to see dozens or more at once. In flight, they superficially resemble small gulls in shape, but they are dark, fast-flying and show a conspicuous white bar on the flight feathers perpendicular to the wing.
In this very quiet time of summer, most young song sparrows, black-capped chickadees, red-eyed vireos and others have left their nests and are moving about locally, still dependent to some degree on their parents for food and protection.
No matter how much we may be tempted to interpret bird behavior in human terms, birds are little more than feathered machines powered by hard-wired brain circuits. Except for a few species with more advanced brain development, like crows and ravens, learning plays only a very small role. Most everything they do is purely instinctive, including their "decisions" on nest type and location. The consequences of nest placement over millions of years of bird evolution are quite profound and have influenced other aspects of birds' reproductive biology in interesting ways.
This is the time to expect a big increase of ruby-throated hummingbirds attending your nectar feeders. Like seed-eating species, hummingbirds also switch to insect-feeding when feeding their young. By now the young are out of the nest and beginning to show up at your feeders and flowering plants in numbers, ready for doses of nectar. They will increase through August and taper off quickly toward the end of the month, as they wing their way south to Mexico for the winter.
During the past week I was struck with the recognition that bird song, so palpable during the past couple of months, was tapering off rapidly. It's hard to believe that most species of songbirds have already raised their young and will soon be going into a post-breeding molt phase that precedes migration back south. It is indeed a short nesting season here in the northwoods. I want to take advantage of this lull in bird song to reflect on the importance of song in the lives of breeding songbirds.
This is the time of year when most birds are either sitting on eggs or tending their young. The timing of the hatch tends to coincide with peaks of abundance of the foods that are most important for development of the young. In my last column, I spoke about how many species switch from a vegetarian diet to a high-protein insect diet when their young are in the early developmental stage.
Those of you from my generation (betrayed by my picture) surely recall the Beach Boys' classic surfing song that is the title of this column. Many years ago, I gave up surfing for birding, a sport in which I'm actually capable of catching the wave.