Missing from Westborough this winter are last year’s unusual bird visitors from the north – pine siskins, redpolls, and pine grosbeaks – but the juncos never disappoint us. They appear every winter so regularly and in such numbers that we may even be tempted to take them for granted.

Typically beginning in October, dark-eyed juncos (Junco hyemalis) show up like clockwork and tend to stick around through April. You might notice the first arrival around the same date every fall. These little winter birds stay so long – about half a year – that we often think of them as “our birds,” even though that group usually includes only year-round residents, such as chickadees and cardinals, and the many birds that come here for the spring-summer breeding season, such as robins, catbirds, pine warblers, and so many others. In May, we hardly notice that the juncos have left, because so many other birds are arriving as Westborough turns from wintering ground into breeding ground.

Some people know juncos as “snowbirds,” a name that sticks because the birds are here for the winter snows and because of their appearance – dark on top and contrasting snow-white below. Males and females look very similar, but males tend to be darker and grayer on top and females (like the one in our close-up photo) tend to be browner. Juncos’ bills are pink, sometimes with a dark tip. You may have noticed that juncos have white outer tail feathers that flash as they fly up from the ground, away from you. These flashing tail feathers are a good way to tell that you’ve just seen a junco.

Juncos are a kind of sparrow. Their habits are similar to those of other sparrows. They spend a lot of time on or near the ground. They search for food on the ground and low in shrubs and brush, where they take cover if danger looms. They hop around and peck at seeds, such as those from grasses and weeds such as ragweed. At your feeder, they prefer millet to larger seeds.

During the winter, juncos can be found in all of the lower 48 states. We’re used to seeing small flocks at bird feeders. You might also hear them twittering among themselves, much like flocks of chipping sparrows. But don’t be surprised if you take a walk in the woods and notice juncos there too, with their flashing white tail feathers. They’re familiar in suburbs, but juncos are actually forest birds because that’s where they go to breed. In late spring, they’ll move to the spruce and fir forests of Canada, Alaska, northern New England, and to mixed forests of conifers and hardwoods in the same areas. You’ll also find juncos nesting in western Massachusetts.

Why do the juncos leave wonderful Westborough and go to northern forests to breed, when so many other birds come here to nest and raise their young? What’s the big attraction of northern forests? You’ll know the answer if you’ve ever vacationed in these northern areas and noticed the hordes of insects. Not only do the northern forests offer seeds for juncos to eat, but the abundant insect populations also provide easy-to-catch animal protein for egg-laying females and growing chicks. The digestive systems of juncos and many other birds actually change and adjust every year to handle different diets in different seasons – seeds in the winter, and both insects and seeds in spring and summer.

But for now and several months to come, we’ll have flocks of juncos to watch at our feeders. You may have noticed that relations between flock members seem less than harmonious, with one junco taking a short run at another, or one quickly giving up its place at the feeder or on the ground to another. In reality, what you’re watching is a dominance hierarchy or “pecking order” in action. The birds look pretty much alike to us from a distance, so we don’t know who’s who in the flock, but the birds all know each other’s status – or who would win or lose in a real fight. As a result, there’s very little actual fighting. Yet we do witness some aggression as the birds remind each other who’s who in the pecking order.

Juncos are famous for their dominance hierarchies, which have been well studied in their winter flocks. The dominant birds have better access to food, cover, perches, and mates. In general, males are dominant to females, and adults dominate younger birds. Bigger birds are dominant to smaller ones (and males are typically 5 percent larger than females). The first birds to join a flock are usually dominant to birds that join later. (Junco flocks typically do not form around family groups, as happens with some other species, such as wild turkeys.)

Researchers studying junco migration have also found that males migrate shorter distances south than females do. Presumably the reason for this is so the males can quickly return to the northern breeding grounds in the spring and claim good territories that will attract females. As a result, winter flocks in northern areas tend to contain more males, and winter flocks in the south may contain more females.

What about flocks in Westborough? We can have fun looking out our windows at the juncos at our feeders to see if we can tell males from females and whether there is more of one sex than the other.

Speaking of watching birds at feeders, this month brings the opportunity to take part in the Great Backyard Bird Count, Feb. 14-17, sponsored by the National Audubon Society and the Cornell Lab of Ornithology. Find out more at http://www.birdsource.org/gbbc. You can contribute to this count even if you’ve already participated in Mass Audubon's Focus on Feeders backyard bird count, which was held Feb. 1-2. (The National Audubon Society and Mass Audubon are separate organizations, and these counts are separate events.)

How are juncos faring these days, according to bird counts? In Massachusetts, junco populations are considered stable, according to Mass Audubon’s “State of the Birds” report (available online). Yet national estimates from the North American Breeding Bird survey indicate that the overall numbers of juncos have been declining about 1.2 percent a year over 44 years (1966-2010). So let’s not take our winter juncos for granted. Support for land preservation is a sensible step we can take that benefits many species, as well as our own children and grandchildren.