Lifestyles

The migrants: here today, gone tomorrow

By BILL CHAISSON
Of a Feather
Over the past few days there has been a lone fox sparrow scratching at the bird seed that has collected beneath my now-absent feeder. You might think, “A sparrow? So what?” But the fox sparrow is one of those migrants that winters further south and breeds much further north, so we only get to see them in migration. The fox sparrow is a little different in that they often seem to be alone rather than in a flock. I was initially a little puzzled that there was only one bird out there, but when I looked it up they were consistently described as “solitary” or as traveling in small groups.

Fox sparrows are among the largest sparrows. Adults are 7 inches long, compared to song sparrows or juncos, which are little over 6 inches long. Like those two species, the fox sparrow has a continent-spanning range and includes many variant plumages that were once interpreted as separate species or subspecies. 

The geographic variant that we see here is called the “red” or “taiga” plumage. It is very much the most rufous of all the variations and explains the “fox” adjective. Taiga is the Russian word for “forest” and refers in the ecology parlance to coniferous forest, particularly the swathe of spruce and fir woodland that wraps around the northern temperate zone of this hemisphere in both North America and Eurasia.

The taiga is home to many birds that breed primarily up there and are either uncommon or absent elsewhere. Many of our so-called “winter finches,” like the pine grosbeak, the crossbills, and the redpolls meet this description. The ruby-crowned kinglet is another species, that like the fox sparrow, I have only seen passing through in migration. It winters in the Southeast as far north as Chesapeake Bay and breeds in the coniferous northern forests. Unlike the fox sparrow, its range includes the spruce and fir forests of northern New York and New England, so I may yet see them on their breeding grounds.

The ruby-crowned kinglet will not show up until April, which is before the wood warblers, but after the early migrants like the blackbirds and the fox sparrow. (I just received a phone call from someone telling me that there are robins at the Claremont airport, foraging in the snow. These may be taiga robins heading north.) The aforementioned winter finches usually stay in the taiga unless a food shortage or a population boom forces them to “irrupt” southward.

Ruby-crowned kinglets are tiny, just a little over 4 inches long, but they have an enormous song that begins with lisping si-si notes and builds in volume and richness to full sounding pudi-pudi notes. The males sing often during spring migration, which is usually what alerts me to their passage. They are small green and black birds with white wing bars that tend to forage high in the trees, so they are difficult to spot until they erupt into song. 

Unlike the fox sparrow, they migrate in flocks, so when one sings, it brings your attention to all the others. They look like least flycatchers, but they forage in the same busy way of a chickadee. Unlike flycatchers, their eyes appear to be enormous and are surrounded by a bright white ring. I have always been a little sad when they depart northward, as they seem like fun birds to have around.

Another species that we see only in migration is the rusty blackbird. They winter as far north as Connecticut and Rhode Island, but in small numbers. They are yet another bird of the taiga but like the kinglet they also deign to breed in the coniferous forest of northern New England and maritime Canada. Rusty blackbirds are only rusty in appearance during their fall migration and on their wintering grounds. Their scientific name is Euphagus carolinus, which suggests that they were first described on their wintering grounds in the southeast U.S. 

According to the North American Breeding Bird Survey, the rusty blackbird has “undergone one of the sharpest and most mystifying recent declines of any North American songbird.” Between 1966 and 2014 the species declined 4.4 percent per year, resulting in a cumulative decrease of the population by 89 percent. I have rarely seen the bird myself. Its remote breeding ground in the taiga contributes to the mystery as it is hard to study them in their preferred habitat of coniferous wetlands. 

The phenomenon is so severe that a Rusty Blackbird Working Group has been formed to look at the problem. The best guess for a cause is the loss of wooded bottomland on their wintering grounds to drainage and development (an estimated 80 percent loss through the 20th century). Many wood warblers are said to be declining for a similar reason: habitat loss on their wintering grounds in northern South America, where forests are cut down for logging and agriculture.

The blackbirds’ northern breeding grounds have not been immune to change either. Some of the clearest environmental changes associated with anthropogenic climate change have been seen at higher latitudes. According to rustyblackbird.org, the working group’s website, changes in temperature and precipitation patterns have had an impact on boreal wetlands that rusty blackbirds prefer. The species apparently depends on flooded woodlands to protect their nests during the breeding season. If the forests are too dry, predators can get to the eggs much more easily.

The international working group is explicitly asking for public input in the effort to collect data on this declining bird. The rustyblackbird.org site has a page where you can report sightings during migration, as not even their migration patterns are well understood.

The male rusty blackbirds are coal black in the spring, while the females are a cinnamon brown. They whitish-gold eyes like a grackle, but are set apart from grackles by their short tails. Red-wing blackbirds, in addition to their red and gold epaulets, have dark eyes. 

The most similar looking species is the Brewer’s blackbird, but that is a western bird rarely seen in the East, even in migration. The Brewer’s, moreover, has a longer tail than the rusty and its feathers are much glossier overall, with a green sheen on the back and purple on the chest and head.

With each passing migration season my initial excitement is tempered by the realization that with each successive event I am also another year older. I look forward to the coming spring waves of passers-through and know that the numbers of most species have declined greatly during my lifetime of birdwatching. I started paying attention to birds at age 11, so that is well over a half century of observation. Your average songbird, in contrast, lives only about three years, so most of them experience two or three migrations and then they’re done.

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