September is a month of change. Cooler temperatures most often catch our attention, but it's September's progressively shorter days that trigger the transitions from summer to fall.
Overhead, flocks of geese honk loudly as they wing their way south. Adult male ruby-throated hummingbirds began leaving a month ago, and most adult females and their young have also departed by now. But my feeders stay busy with birds from farther north that will continue to filter through for another month. So keep nectar feeders filled until you see no hummers for at least a week.
At backyard feeding stations, change is also evident. Cardinal and blue jay numbers vary unpredictably as juveniles disperse and fall flocks form. In the meantime, especially on chilly mornings, chickadees, titmice, nuthatches, and woodpeckers will begin visiting feeders more frequently. These birds are more sedentary, and as they make the switch from a summer diet of invertebrates to a fall diet of seeds, they become more conspicuous at feeders.
Meanwhile, goldfinches are becoming less conspicuous. The fall molt is underway. Males replace their brilliant golden mantle with a dull olive-brown plumage. Only their black wings marked with pale wing bars and buffy or yellowish shoulders remind us of their summer form. Many casual birders don't even recognize goldfinches in nonbreeding plumage. But in April, their brilliant colors will return.
And expect your goldfinch population to swell between now and Thanksgiving. Northern breeders migrate south to more temperate areas. This is one reason we usually see many more goldfinches at feeders during the fall and winter than we do in mid-summer.
The appearance of trees also changes in September. Along country roads, fall webworms encase the outer branches of cherry and walnut trees in unsightly silky tents. And throughout the woods the chemical pigments that make leaves green during the growing season begin to fade, and other pigments -- shades of gold, crimson, and chestnut -- reveal themselves to the delight of leaf peepers everywhere.
Deep inside hollow trees, late summer broods of all four species of tree squirrels mature. If the weather cooperates, they will emerge in time to fatten up for the winter. If winter strikes earlier, most will die young.
Migrating song birds forage feverishly in the tree tops for food to fuel their southbound migration. Though some such as towhees and flickers may travel only a few hundred miles, others such as red-eyed vireos and Canada warblers travel all the way to South America. If you see one of these neotropical migrants this month, take a moment to marvel at how creatures weighing barely one-third of an ounce routinely make three or four such round trips in a lifetime.
In abandoned fields, amidst an almost unbroken sea of goldenrod, thousands of immature orange and black milkweed bugs emerge from maturing milkweed pods. Unlike butterflies, which undergo a complete metamorphosis, adult-like larva hatch from the eggs of these true bugs. After a series of simple molts, adults emerge. Sometimes, unnerving numbers of milkweed bugs gather on the walls of houses and garages in the fall.
And speaking of unnerving numbers of insects, if fall's upon us, can another invasion of lady bird beetles be far behind? Make sure your vacuum cleaner's in tip-top shape.
September's shorter days also bring longer, cooler nights. After dark, extended families of flying squirrels compete with deer for leftover sunflower seeds.
The familiar evening chorus of katydids and tree crickets fades, while pairs of hooting great horned owls reestablish their pair bonds. And screech owls whinny from dusk til dawn.
Finally, each fall those of us who feed backyard birds worry about the price of bird food. This year's news is not good. Thanks to drought conditions throughout the Great Plains, the sunflower crop is poor, so supplies will be limited and prices will probably increase.
Furthermore, the millet crop in Colorado, where most millet is grown, is down more than 75 percent. So beware of cheap filler seeds such as milo, wheat, and oats finding their way into bird food mixes. These seeds may keep seed mix prices down, but birds won't eat them.