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Every September I’m reminded of that Brady Bunch episode when Bobby’s voice changes just as the Brady kids are about to record an album. They make the best of it by featuring his unreliably squeaky voice in a new song called “It’s time to change.”

I’m reminded of that because September is the beginning of a time of change in the natural world. We know it best from the changing fall foliage, when many of our maple leaves turn red, our oaks turn to orange, and our beeches and birches turn yellow. For many people, the changing foliage colors make autumn their favorite season – especially in northern New England where the tourist economy depends on it.

But foliage isn’t the only thing that changes colors in fall. Many birds do, too, as they transition from their bright breeding plumage into their drab winter plumage. And that makes it challenging to be a birdwatcher — or at least a bird identifier — when so many species look uncharacteristically dull.

For many years I avoided birdwatching in the fall, in part because the songbirds were more quiet and therefore harder to find. But I was also frustrated by the difficulties in identifying many of what one field guide has even referred to as the “confusing fall warblers.” But eventually I figured most of them out and now I enjoy the challenge of fall birding.

It was only recently, however, that I learned why some birds change colors and others don’t.

In part, it has to do with their behavior on their wintering grounds. Some birds defend a territory during the winter months, just as they do in spring and summer to protect their mate from unwanted attention. In winter, they may be defending an area with an abundance of food instead. And keeping their bright colors helps to draw attention to themselves while protecting their territory.

Other species flock together in the winter to make it easier to find productive foraging sites, and they no longer have a reason to defend a particular territory. Those birds are more likely to molt from their bright spring plumage into duller colors.

Birds that look rather drab during the breeding season, like sparrows, tend to remain drab all year. And most resident birds – those that stay here year-round without migrating – also keep the same plumage all year. Though not all.

It’s a confusing state of affairs, to be honest, but nature has a reason for everything, even though the scientific community hasn’t entirely figured out all the reasons for why things happen as they do.

Plenty of mammals also change colors in the fall and winter, though not many around Rhode Island. In northern New England, where snow cover is more common throughout the winter, animals like snowshoe hares and weasels exchange their brownish summer pelage for white fur to help camouflage themselves in the snow. Further north, it’s even more common as Arctic foxes, lemmings and other species do the same.

Around here, it’s mostly white-tailed deer that are a noticeably different color from season to season. In the fall, deer begin to molt their rusty summer coat into a faded brown or gray color. The transition into their darker winter fur, triggered by hormonal changes that occur each fall, helps them to absorb more of the sun’s heat to stay warm in winter.

Regardless of how or why they do it, these colorful changes play an important role in their life cycle. Now if only I could do something about my ghostly white legs.

Naturalist Todd McLeish has been writing about wildlife and the environment for more than 25 years. His newest book is called “Return of the Sea Otter.

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