Now we see them, now we don’t. Call them a mystery gull, as if just identifying gulls were not mystery enough in the first place.
But Bonaparte’s Gulls – “Bonys” for short – can be a lovely addition to a winter birding trip. Small and delicate, they are at least two sizes down from the common Herring or Black-backed Gulls.
In the field, birders sort gulls first by size. Bonys are tiny, almost tern-like. Next come details: the dark “earmuffs” which are all that remain of the dark hoods they wear in summer, fine black lines edging the wing-tips or marking the tail. Juveniles show a dark “M” pattern across the back, while adults are a subtle gray. They have a dark bill and pinkish legs.
Identification can be tricky, which is why birders either love gulls or hate them. And Bonys are usually absent from most of our popular beaches in summer, making them an almost exclusively winter treat, or penance, with a sharp wind. There can be a few stragglers in the summer, but it is easy for them to disappear among the large raucous birds most people just lump together under the name “seagulls.” But here off Nantucket Bonys really do spend a lot of time at sea.
They are definitely not your average dumpdwelling, garbage-picking, parking-lot French-fry-eating gull. In fact, they are notably, uniquely absent from garbage dumps. Dainty and graceful, we usually find them by the ocean, where they may head well offshore in search of food. In some years we can count them by the hundreds or even thousands. But sometimes there is only a single Bony on the beach, if indeed any can be found at all.
They are dainty in their habits as well as in their appearance. A bird feeding in the floating wrack close to shore darts quickly but delicately at plankton, small fish or amphipods, tiny shrimp-like crustaceans caught up among the seaweed. They make a meal of what would hardly be an appetizer for a larger bird.
Sitting on the water or swimming in circles, they pick, pick, pick, turning their heads from side to side. They can plunge or make a shallow dive, sometimes just dipping with their bill. A flock in flight makes a lovely sight, like an animated Escher print, or a snowstorm wheeling in an unseen wind. They glide, they hover, they skim, they dance over the waves, sometimes just stirring the surface with a foot, like a skater or ballet dancer.
They are endemic to North America, meaning they depend on this continent to reproduce, even though they are sometimes found elsewhere. They make spring and fall migrations across much of the United States. Many spend the winter, or at least part of it, on the Great Lakes as long as they remain ice-free. Some spend the time in the interior of the Southeast, but the remainder seek out coastlines east and west. In the east they can be found from Maine to the West Indies, in the west from Washington to Mexico. Some go as far south as Cuba or lounge in the Gulf of Mexico.
In summer they fly north for the short season of long days. On the map their breeding territory forms a rough triangle. Its blunt northwestern point covers about two-thirds of the Alaskan interior. British Columbia fills its southwestern corner. The eastern point of the triangle is in southern Ontario, and the connecting northern line skirts James Bay, Hudson Bay and stretches across the Yukon Territory to Alaska.
Sometimes feeding over pools in the tundra or at the foot of a glacier, they scatter in low densities over the wide, remote areas of the taiga. As inland inhabitants they typically eat many insects in summer: grasshoppers, beetles, locusts, ants, even bees.
And here they show another unique trait. Most gulls plop down on the ground and lay their eggs in a wrack-lined scrape. But Bonys build a proper nest of twigs and moss or lichens lined with grass, up in the branches of coniferous trees. Widely dispersed, they nest in single-pair homesteads or in small groups of perhaps a dozen pairs, more spread-out village than colony. That makes them difficult to study in the breeding season, and much about them is still unknown.
They are named Bonaparte’s Gulls not for their imperious traits or in honor of the French
emperor Napoleon, but after his nephew, Charles Lucien Bonaparte, an ornithologist who moved to Philadelphia with his wife in 1822. As a member of the Academy of Natural Sciences of Philadelphia, he updated Alexander Wilson’s early book “American Ornithology,” naming several species after the earlier author.
But it was considered very bad form to name a species after oneself, and Bonaparte apparently followed the tradition. His gull was first described by George Ord, who originally called it sterna Philadelphia. Subsequent ornithologists moved it into the genus Larus with other gulls. But recent analysis now puts it in a separate group with other hooded gulls.
Historically Bonaparte’s Gulls were not always a feature of Nantucket’s avifauna. When a local bird guide was written in the 1940s they were considered rare vagrants of unpredictable appearance. It is worth reading the records if only for their brevity: “1875, four shot November 8 and sent to Brewster.” This refers to William Brewster, a famous ornithologist of the day, meaning that it was such an unusual bag as to be of recognized scientific interest.
The record goes on: “1890, March 20, two birds; 1892, six birds May 10-29; 1896, immature shot on Muskeget, June 26.”
Then the records are presumably of single individuals: “1912, January 10; 1938, August 7; 1940, May 29; 1944, August 20; 1946, March 4, one found dead obviously for some time.”
It is also of interest that the dates drift all over the calendar.
Contrast this to some records from the heydays around the millennium: 1,000 in Nantucket Harbor in 1998, 50 at Wauwinet on Jan. 1, 1999, 700 at Low Beach on Jan. 1, 2000, 3,000 there on Dec. 28, 2010.
Low Beach, where under certain conditions of wind and tide all the goodies of the ocean swirl in close, can be a hot spot for sea birds. From the deep waters offshore, floating masses of seaweed and all the life sheltered within come ashore to make a smorgasbord of plankton, tiny shrimp and little fish. With as many as seven different species of gull feeding as if on a conveyer belt from Codfish Park to Low Beach, it is no wonder birders call the phenomenon “gull soup.”
But the feast is movable, and recently has become more irregular and unpredictable. The numbers of Bonys have shrunk, too: 250 in 2016, 200 in 2017. Their locations move as well. A few hundred were seen in the fall last year at the west end, off Tuckernuck or in Madaket Harbor. Will they be back or will they stay offshore? Will they gather in mainland harbors or head further south? We never know from year to year.
Still, it is always worth a look, scanning the other gulls for a tiny, elegant, mysterious Bony. ///
Virginia Andrews writes the weekly “Island Bird Sightings” column for The Inquirer and Mirror, Nantucket’s newspaper since 1821, and is a regular writer for Nantucket Today.
