Marcia Bonta

Snowbirds

"Peekaboo," by Scott M Duncan in NE Ohio (Creative Commons BY-NC-SA license)

It was a fine early December day — 18 degrees with partial sunshine and a howling wind.  A new half-inch of snow covered the ground.  I counted the birds at my feeders because it was a Project FeederWatch day.  For over 20 years, two days a week from November until early April, I’ve been counting birds for this Cornell University Laboratory of Ornithology program.  On that day, I recorded a record 16 species of birds — 24 house finches, two American tree sparrows, a song sparrow, two white-throated sparrows, a swamp sparrow, 25 American goldfinches, 19 mourning doves, a pair of white-breasted nuthatches, a pine siskin, four tufted titmice, two black-capped chickadees, a male downy woodpecker, two red-bellied woodpeckers, a purple finch, and 50 dark-eyed juncos.

Fifty dark-eyed juncos!  It was a challenge to count them as they swarmed over the ground and back steps beneath the feeders, looking like giant black and white ants, and pushed the other ground feeders to the periphery.  I had hit an all time high junco count and the Project FeederWatch website questioned my number when I entered my results.  That’s because over half of FeederWatch participants report six juncos or less.  Last winter my average junco group was 40.2.  The other bird species averaged .5 to 3 except for pine siskins (17.8) and American goldfinches (17.2).  Furthermore, when we conducted our Christmas Bird Count on foot over our mountaintop property, we tallied 208 species.  And, by January, sixty juncos were visiting my feeders.

According to most sources, winter junco flocks consist of 15 to 30 birds and settle on 10-acre territories.  During the day, they go from food source to food source, looking for a variety of wild seed sources to sustain them through the winter. The millet, milo, and cracked corn they prefer at feeders merely supplement the 5000 seeds they must consume every day from wild sources such as lamb’s quarters, thistles, broom sedge, ragweed, foxtail, and chickweed.  Our unshorn First and Far fields and home grounds provide a wealth of such seeds.

Junco tracks in Plummer's Hollow (photo by Dave)

Then, as the day darkens, several juncos seek shelter in our juniper tree near the feeders, but most head for our three-acre Norway spruce grove at the top of First Field.  One of my winter pleasures is sitting at dusk on Alan’s Bench, which is enclosed by spruces, and watching the juncos stream in from all directions.  At first they “zeet, zeet” to protest my presence, but they soon settle down beneath the sheltering boughs.

We aren’t far from the nearest breeding area for dark-eyed juncos — the Allegheny High Plateau — so I suspect that’s where our juncos, at least the earliest arrivals in late September, come from.  But as their numbers increase, many may be migrating from as far north as the boreal forests of Canada.  Traveling from 30 to 200 miles a night, how far juncos migrate depends on the weather, the lateness of the season, and the amount of body fat they have stored.  In Pennsylvania female juncos move southward ahead of males and adult females before young females.  In fact, adult juncos winter farther south than youngsters and those young migrate later than the adults do.  But we have plenty of the spiffy, dark gray to black males as well as the duller gray females and young, all of which have snowy white bellies.

When I first studied birds, our juncos were called slate-colored juncos.  But in the 1970s, ornithologists lumped five species of juncos into one and renamed them dark-eyed juncos.  However, the ornithologists designated those former five species — slate-colored, white-winged, Oregon, gray-headed and Guadalupe — as groups.  Our slate-colored junco is by far the widest distributed of the groups, breeding from Alaska to Newfoundland, as far south as Texas and along the Appalachians to North Carolina and northern Georgia.  Within the slate-colored hyemalis group are three subspecies— Junco hyemalis hyemalis, J.h.carolinensis, and J.h.cismontanus.  Here in Pennsylvania we have both J.h.hyemalis and J.h.carolinensis, the former in the northern glaciated and high plateau areas, the latter in the more southern portions of the state, especially in the mountains of Westmoreland County at the Powdermill Nature Reserve, where they have carried out field and banding studies of juncos since 1983. Of course, for mere amateurs like me, telling these subspecies apart in the field is impossible.

Because our juncos reminded European taxonomists of their reed bunting, they named them Junco, which means “reeds” in Latin.  Hyemalis is Latin for “winter.” But many folks still know dark-eyed juncos as “snowbirds.”  Other popular names include “black snowbird,” “common snowbird,” and “eastern junco.”  Henry David Thoreau, writing his journals in the mid-nineteenth century, referred to them as “blue snowbirds,” “slate-colored snowbirds,” and “slate-colored sparrows.” John James Audubon wrote in 1831 that “there is not an individual in the Union who does not know the little Snow-bird.”  Probably they were called snowbirds because most people only saw them in winter when the birds left the forests for parks, rural roadsides, farms, and today for backyard birdfeeders.

Dark-eyed junco by Tom Davis in Wilmington, Delaware (Creative Commons BY-NC-SA)

Not only do juncos visit more feeders across the continent than any other species, but also they are incredibly abundant — an estimated 630 million strong.  Because they flock together during the winter, their winter social behavior has been a popular subject for researchers.  In these flocks, males dominate females, and within each sex, adults dominate youngsters.  You can observe this at feeders when birds lunge at other birds and flick their tails, exposing their white outer tail feathers.  Those males with the most white in their tails are the most dominant.  Usually, this behavior occurs in early morning or late afternoon when they are feeding more heavily, especially when it is very cold or snowy.  Those dominant birds feed in the middle of the food area, and it’s up to the subordinates to look out for predators.  They also get less to eat, which is a problem if food is scarce, but if food is abundant, both subordinates and dominants thrive.

By March, junco males have joined our spring bird chorus, their trills making a “lovely tinkling chorus… as if a myriad of woodland sprites were shaking little bells in an intensive competition” Canadian naturalist-writer Louise de Kiriline Lawrence once wrote.  The males leave ahead of the females and by late April, our last junco is gone. By the time the females arrive on their breeding grounds, the males have established a two to three- acre territory.  At first, they chase returning females.  But if one stays on a male’s territory, he begins courtship by fanning his wings and tail, continual hopping, and picking up nesting materials.

Those males with the most white in their tails are most attractive to females.  They also have the highest testosterone levels.  But do they make the best mates?  According to researchers Ellen Ketterson and Joe McGothlin, that depends.  Those males with the highest testosterone levels attract older, more experienced females because their songs are sweeter.  They also produce more offspring.  However, they are not very good fathers, and their offspring are smaller when they hatch and die at higher rates.  The fathers are too busy displaying and chasing after other females to feed their mates or offspring as often as the less testosterone-charged males.

The dominant males also die sooner. Often, they are too busy showing off to be wary of predators. In addition, their elevated testosterone increases their stress, which leads to the production of a hormone called “corticosterone,” That hormone gives them quick energy even while it breaks down protein, leaving them with atrophied feathers, muscles, and organs.

Junco nest in Vermont, by Kent McFarland (Creative Commons BY-NC license)

Despite this dominant male junco angst, most pairs practice social monogamy and raise two families a year.  The female chooses the nest site and builds the nest.  Most sites are constructed on or near the ground in a bank or rock face, especially if grass or other vegetation overhangs it.  The nest we found in Little Pine State Park along the Lake Shore Trail last May was in a road bank under a bower of dried leaves caught in several small branches.  My husband Bruce, 13-year-old granddaughter Eva, and I saw a bird fly out of the bank.  Eva quickly found and photographed the nest woven of dried pine needles, twigs, and grasses, which contained four pale blue eggs strongly marked with brown squiggles and a brown blotch at the large end.  We stood quietly, waiting for its owner to return, and soon heard and then saw a scolding junco nearby.  The park, a forested gem with a small dammed lake in Lycoming County, provides excellent habitat for nesting juncos.

Cordelia Stanwood, an amateur ornithologist and photographer who lived in coastal Maine during the early twentieth century, wrote that “the nest site varies according to its situation.  I have seen juncos brooding amongst the roots of a growing clump of gray birches, partially under stumps and rocks, below a tuft of leaves, in a brush heap shaded by small evergreens, beneath bracken, and many within the side of a bank or knoll, the wall of a knoll covered with bird-wheat moss, or the side of a steep bank just under the overhanging sod [which] seems to be the most typical site for a junco nest.  A depression is made or enlarged in the side of the bank or knoll, and the moss or overhanging sod form a natural roof.”  Exactly, except that juncos also build unusual nests such as on a ledge beneath a house gable in Nova Scotia, in a half-pound tobacco can lying on its side in Saskatchewan, in a wind-vane bird feeder mounted on an eight-foot iron pipe in Olean, New York, and, for two years, in a hanging planter in Trucksville, Luzerne County, Pennsylvania.  The second year the female nested in April while Christmas greens were still in the planter and nested a second time, after the first nestlings fledged, in the planter when the greens were removed.

The female incubates the three to five eggs 12 to 13 days while the male warns of danger, keeps small birds from the nest, and tries to discourage eastern chipmunks, which are major nest predators.  Red and gray squirrels, deer mice, white-footed mice, jumping mice and weasels also threaten eggs and nestlings in some areas.

After the junco eggs hatch, usually within a few hours of each other, the nestlings quickly mature as both parents stuff them with mostly insects and spiders.  At 12 days of age, they leave the nest, although if they are disturbed, they can run off at nine days old.  Fourteen days later, they are able to fly well and feed themselves.

Then they are on their own and later join winter flocks.  It they are lucky they will evade a host of predators, including accipiters — especially sharp-shinned hawks — shrikes, owls, jays, feral and domestic cats particularly near bird feeders.  More than once in the winter I’ve watched a sharpie catch, kill, pluck, and eat a junco near our feeders.

But such occasional predation doesn’t seem to shrink our junco population.  Because they are such generalists in nesting habitat — breeding in coniferous or deciduous forests — and in winter habitat continent-wide, as well as in their food choices, dark-eyed juncos should remain a ubiquitous species for decades to come.

Dark-eyed Junco by Birdfreak.com, Rockford, Illinois (Creative Commons BY-SA license)

November 26, 2009 Posted by Marcia Bonta | Animal Behavior, Brush Mountain/ Plummer’s Hollow, Citizen Science, junco, Winter | Cordelia Stanwood, dark-eyed junco | 11 Comments