The Blackpoll Warbler, weighing only 12 grams, makes an annual round-trip flight of 10,000-14,000 miles from the Amazon in Brazil to its breeding grounds in New Hampshire, the Yukon and Alaska. It makes an 88-hour flight, lasting 3 days, from Maritime Canada and Maine directly over the ocean, a 2,200-mile non-stop flight, landing in Aruba and then moving on to the Amazon forests. Blackpoll warblers breed in the boreal forests. To make such a long flight they double their weight by eating insects and berries. Bird banders can observe yellow fat just below the skin before they depart. In humans, this would indicate high cholesterol. By the time they reach Aruba, the fat is burned up to provide needed energy.
Near Bermuda, flocks can reach 1,000 birds as they use Northeast Trade Winds. They increase their altitude to 15,000-21,000 feet high where air is calmer and no raptors to interrupt their journey.
These birds fly at night, like many warblers and thrushes, and can be observed with binoculars as they cross the full moon. The flight was discovered, not by radar, but by an ornithologist sitting poolside at Bermuda one evening. He recognized the bird’s distinctive call notes. This can be done right here in the Monadnock Region. Best times to observe and hear night migration are 10:00 PM – 1:00 AM in September.
Birds migrating at night use the stars and orient to Polaris and the Constellation of Orion. Birds migrating by day use their angle to the sun and the Earth’s magnetic field to assist with migration.
With modern technology, the Motus Project, uses tiny geolocator tracking devices to track migrating birds as well as monarch butterflies and dragonflies. The University of Massachusetts, Amherst, and the University of Guelph in Ontario have been leaders in the geolocator field.