When we think of bird migration we usually focus on those species that arrive here in the spring and then depart from here in the fall. These species are utilizing our rich, productive summers and avoiding our cold, food deprived winters. There is, though, a very interesting bird that arrives in our area in the mid- to late fall, thrives in our winters (often supported by our backyard bird feeders!), and then heads back into its northern breeding habitats in the spring. The bird is, of course, the slate-colored junco.
I saw my first slate-colored junco of the fall on October 30. He was poking around at the spilled sunflower seeds under my feeders and looked very much at home among the chickadees, titmice, cardinals and house finches.
The slate-colored junco is small, dark-colored sparrow with a long list of very descriptive common names including “snow bird,” and “winter finch.” It our the local version of the dark-eyed junco which is a very common bird at winter bird feeders across the United States and regularly one of the Top Ten birds in the annual Great Backyard Bird Count. The varieties of dark-eyed juncos over-winter in almost all of the lower forty-eight states (and down into northern Mexico) and have equally broad summer/breeding ranges across Canada and Alaska. Breeding may also occur in the mountains of the west, throughout New England, and down the Appalachian Mountains into northern Georgia. In Pennsylvania, in addition to winter populations of “bird feeder” slate-colored juncos, Deborah and I have observed dense, summer populations of this species in the mixed hardwood forests of the Allegheny National Forest in the northwest section of Pennsylvania.
The slate-colored junco is five to six and a half inches long and weighs between one half and nine tenths of an ounce. Males are slightly larger than females and are more darkly colored. They have gray hoods and backs, white bellies, and dark tails with distinctive white, lateral tail feathers. They also have short, triangular beaks and dark eyes. Juveniles are brown in color and have finely streaked, white breasts.
Like most sparrows, the slate-colored junco will eat a wide variety of foods. Their beaks are especially well adapted to cracking open even tough seeds (including sunflower seeds at bird feeders and an extensive number of wild plant (“weed”) seeds in their natural habitats). They also readily consume fruit (including wild blue berries, raspberries, and elderberries as they come into season) and many types of arthropods (including caterpillars, ants, flies, spiders, and beetles). They typically feed on the ground and move about both by walking and by hopping (a single hop can cover thirty centimeters). Natural ranges can be quite extensive (a single flock of juncos can feed in an area of ten to twelve acres), while human-modifications of their feeding ranges (i.e. bird feeding stations) can greatly reduce the size of the foraging range and overall rate of movement.
Flocks of fifteen to twenty individuals form in the autumn and winter. These flocks may include several of the junco sub-species and also several other species of sparrows and even bluebirds. These flocks gather together about thirty minutes before sunrise and disperse about forty-five minutes before sunset each day. Foraging success for each individual is significantly increased when they participate in one of the groups. An individual junco tends to stay in its foraging flock for the entire winter.
Males move into their summer breeding habitats in northern coniferous or mixed hardwood forests before females and mark off their individual breeding territories. A male will sing from the top of a tall tree to claim an area of two to three acres. They then attract the attention of the arriving females by dropping their wings and flaring their tails in order to show off their white, lateral tail feathers. Once a female accepts a male they become quite inseparable and within their territory seldom venture more the fifty feet away from each other.
The female builds the nest all on her own. The nest can be located on the ground or on low, horizontally oriented tree branches. Near human habitations juncos may also build their nests in the crawl spaces underneath buildings, inside the buildings themselves or on window ledges. The nest may be made of a variety of materials. Sometimes it is simply a gathering of pine needles and grass, sometimes it has a foundation of sticks on top of which softer materials are layered. Nests take three to seven days to build and they are seldom re-used.
Slate-colored juncos typically have two clutches of three to five eggs each breeding season although under optimal weather conditions, a third clutch is possible. The first clutch is laid in late spring (mid-April) and the second in mid-summer (mid-July). Eggs are incubated by the female for just under two weeks. Nestlings are actively fed by both parents and are able to fledge after another two weeks or so. Fledglings stay with and are dependent upon the parents for another three weeks. Males are very aggressively territorial during this reproductive period. Both male and female, though, will very vigorously defend their nest and nestlings.
The arrival of the juncos in Western Pennsylvania has both positive and negative implications: a handsome bird has returned to grace our lawns and fields, but now we have to deal with the cold, snowy months of winter!