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Blackburnian Warbler, Scilly – Ornithology

Hundreds of birdwatchers from all over England and even mainland Europe recently descended on the tiny island of Bryher on the Isles of Scilly (pronounced si-lee) southwest of Cornwall, England, to catch a glimpse of a tiny bird from the U.S. which has rarely been seen in the U.K. In Mid-October, 2022, “twitchers” arrived in great numbers to see the bird. (The British term twitcher, often used as a synonym for an avid birder, is applied to those who travel long distances to see a rare bird. The term apparently originated in the 1950s, when it was used to describe the nervous behavior of Howard Medhurst, a British birdwatcher.)

The Blackburnian Warbler is endemic to North America where it breeds in pine forests and winters in South America in open forests and coffee plantations. This wandering insectivorous bird is the first sighting in England and only the fourth in the UK.

Immature Blackburnian Warbler, photo from BBC

Now how does a bird that weighs about 1/3 of an ounce (9 grams) cross 3000 miles (4800 km) of ocean? A radio story about this warbler supposed that the bird was helped by the jet stream. Considering that the jet stream, high speed west to east winds, are 6 to 9 miles (9-14 km) above the earth, it is highly unlikely that the warbler could make use of these winds. The highest flying bird in the world, the Griffon Vulture, can go as high as 7 miles and a few other large birds (cranes, swans, geese) can also reach the edges of the jet stream, but not the warbler, which is an inefficient flyer compared to larger birds.

The Blackburnian Warbler crosses expanses of ocean twice each year from North America to South America, but there are islands along the way where they can rest and refuel. And stragglers have been found way out of their normal range on the west coast of the U.S. and northwestern Canada, crossing large land areas. But there are only a few sightings across the sea, in Iceland and Great Britain.

So how does a small bird like the Blackburnian Warbler make it across the ocean?

Well, they simply cannot fly non-stop because they can’t carry the needed energy sources and their constant flapping flight uses a lot of energy. The solution? They find a ship going their way.

I’ve been on many cruises and a few research ships and I’ve seen at least a dozen instances of land birds landing on ships to rest – herons, egrets, Egyptian Nightjar, Short-eared Owl, Belted Kingfisher, swallows, and an American Kestrel. I don’t know how long some were on the ship but I remember the owl being a passenger for at least three days.

On the ship the birds can get fresh water, either from the washing of the deck, the pool, rain, or dew condensing on the infrastructure. The bigger birds can last a few days without feeding but the smaller birds cannot; but it is common for ships, lighted at night, to attract insects that smaller birds can feed on.

I have no proof that the Blackburnian Warbler was a stowaway on a cruise ship, but I can’t imagine any other way for this bird to have reached the Scilly Isles.

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