Birds aren’t lost, they’re adapting to human-driven changes

The bird has strayed thousands of miles from its native range in East Asia over the last two years, roving from the Denali Highway in Alaska down to a potential sighting South Texas before moving eastward and back north to Canada and New England. Its cartoonish yellow beak and distinctive wing coloration recently attracted crowds of rapt birders to Maine before turning up on April Fools’ Day in Nova Scotia.

“We live in a world of very little surprise,” said Nick Lund, the outreach manager for Maine Audubon and creator of The Birdist blog. Catching a glimpse of a far-flung bird in one’s backyard, he said, “is like the purest form of joy.”

But the rogue Steller’s sea eagle isn’t just a lost bird: It is an avian vagrant, a term that describes birds that wing their way well beyond their species’s normal range of movement. Humans have long marvelled at such exotic stragglers — which experts also refer to as waifs, rarities, extralimitals, casuals and accidentals — and what they suggest about the biological importance of wandering. “The ‘accidentals’ are the exceptional individuals that go farthest away from the metropolis of the species; they do not belong to the ordinary mob,” Joseph Grinnell, a field biologist in California, noted in 1922. “They constitute sort of sensitive tentacles, by which the species keeps aware of the possibilities of aerial expansion.”

The peripatetic sea eagle wasn’t 2021’s only extralimital. Other fan favourites strayed from the parts of Central and South America where they are typically found: an Inca tern spotted in Hawaii; a small-billed elaenia captured in a net in Quebec; a heron-like limpkin recorded in Texas for the first time; and, a gray-breasted Martin observed in Prospect Park in Brooklyn.

“Each time there’s a vagrant it’s its own exciting story,” Mr. Lund said. “It has this treasure hunter’s charm.” A new book, “Vagrancy in Birds,” extends this century-old notion — arguing that vagrancy does not always represent a tale of navigational avian misfortune, but can be one of the first visible signs of bird species adapting to human-driven alterations to Earth’s waters, lands and skies.

“We’re destroying and creating habitats,” said Alexander Lees, a co-author of the book and a senior biodiversity lecturer at Manchester Metropolitan University in England. “We’d expect wildlife to adapt to that.” Migratory birds are equipped with tools to navigate what Heinrich Gätke, a German ornithologist, described in 1895 as “the whole vault of heaven.” Some rely on potentially inherited “mental maps” refined during the first journeys of life. Many employ an internal clock for measuring elapsed time. They may also have an internal compass for determining orientation that they calibrate using the sun, stars, patterns of polarized light and the Earth’s magnetic field.

Most will successfully migrate entire lifetimes without a hitch. But the avian navigation system is not error-proof.

For one, unusual weather patterns can rechart a bird’s regularly scheduled flight path. In 1927, for example, a cold spell combined with an “exceptionally high easterly wind” pushed a spray of Lapwings across the Atlantic Ocean to Newfoundland. More recently, extreme droughts have sent marsh-loving glossy ibises from the Mediterranean as far north as the British Isles.

Renault is a reporter with NYT©2022

The New York Times