A rare northern visitor in winter

Bill Chaisson
Of a Feather
In open country through the winter, when you spot a flock of snow buntings, look for some darker birds among them. These will perhaps be Lapland longspurs. A few may also be found among flocks of horned larks. According to The Birds of New Hampshire, the longspur is a “regular fall migrant, a scarce winter resident, and a spring migrant in small numbers primarily along the coast.”

These birds have a compactness to them that distinguishes them from sparrows and their devotion to grasslands and any other form of treeless expanse exceeds that of any sparrow. The Lapland longspur (Calcarius lapponicus) has a “small acutely conical bill, which is deeper at the base than it is wide; exposed nostrils; long, pointed wings … and a slender and nearly straight hind claw about the length of the toe.” (Nelson Nichols in Birds of America)

The males are striking birds in their breeding plumage. The upper chest, throat, sides and top of the head are black with a broad white stripe that ascends the neck from the shoulder and then angles toward the bill over the eye. The nape is marked by a patch of chestnut and the lower chest and belly are white. The back and wings are streaked with chestnut, black, and white. The females lack the bold black area and aside from being paler overall are otherwise similar.

In the winter, when we in the United States get to see them, the males resemble the females. During the fall molt the males acquire brown or buff tips to their new feathers, which obscures their contrasting pattern. In the spring, these tips wear away and you may see the breeding plumage on some late migrants.

In North America, C. lapponicus breeds in Alaska and along the Arctic Ocean coast through the Canadian archipelago to the coast of Greenland. In Eurasia it is found from the mountains of Norway to the eastern tip of Siberia on the Bering Sea. In other words, it has a classic Holarctic distribution. It is regarded as a “short-distance migrant” because in the winter it only drops down to the northern United States in the New World and to a broad swath between Ukraine and northern China in the Old World.

Regionally, you are most likely to see them in January and February over on the sea coast, foraging in cut-over or fallow agricultural land, wind-blown salt marshes, dune areas, and even airports and golf courses. They prefer anywhere where the vegetation is short and the seeds are plentiful. If the wind is not strong enough to blow the snow away to expose the ground, the longspurs will move on.

This species is in a small family called the Calcariidae, which also includes three genera, the closely related Calcarius species (Smith’s and chestnut-collared longspurs), the less closely related thick-billed (formerly McCown’s) longspur, and the snow buntings (two species). All these birds share the very long hind claw that arcs up from the hind toe and is unlike anything possessed by other finches, but is shared with larks and some pipits. The pipits (Motacillidae) and larks (Alaudidae) are entirely unrelated to the longspurs. The evolution of the same adaptive hind claw is an example of convergent evolution: features develop due to similar environmental pressures rather than shared heritage. (I wrote columns about pipits in a September 21, 2019 and horned larks in January 9, 2021.)

But just what is that shared environmental pressure? All these groups include birds that live almost entirely on the ground and rarely perch on branches. The long hallux (hind claw) stabilizes the bird on the ground and allows it to forage in high winds. Longspurs are often observed crouching so low that their legs are not visible as they feed. On the other hand, a very long hallux is completely in the way when the bird attempts to grip a tree branch or twig.

It is a good example of the compromises that result from natural selection. Back in the 1980s, when the “intelligent design” crowd surged into the limelight as a “counter-argument” to natural selection, evolutionary biologists like Stephen Jay Gould were at pains to point out just how clunky some of the outcomes of organic evolution can be. Among birds, we can see, for example, the plight of the diving ducks, grebes and loons. Their legs are set very far back on their bodies, which allows them to swim underwater beautifully, but they are unable to walk on dry land.

Specifically, the long hallux in longspurs, pipits, and larks seems to be an adaptation to walking on ground covered with soft vegetation, like the type associated with tundra and grasslands. In a charmingly titled paper in the Journal of Zoology (“How the longspur won its spurs: A study of claw and toe length in ground-dwelling passerine birds”), Rhys Green of Cambridge University and others found that even among the same species, birds that lived in grassier, more vegetated habitats versus bare ground substrate had significantly longer rear claws and overall larger feet. Not all pipits are open-ground dwellers and among them the hind-claw length varies accordingly from species to species.

Within Calcarius, the Lapland longspur is the most widespread and genetically the “root” species. The similar chestnut-collared breeds in a smaller range in the upper Great Plains, as if it got left behind after the last Ice Age. The quite different looking Smith’s longspur has a breeding range that overlaps with C. lapponicus but it is more limited in extent and confined to North America. Molecular genetic analysis (John Klicka and others at University of Nevada, Las Vegas) showed in 2003 that the thick-billed longspur is more closely related to the snow buntings. To the surprise of many, the calcariids are not at all related to the emberizine group (sparrows). Their resemblance to one another is just one more example of convergent evolution.

— Bill Chaisson has been a birdwatcher for more than 50 years. His columns are collected at shinhollow.wordpress.com.