Humanassisted Vagrancy

Not all apparent transoceanic vagrants have travelled unaided, for some types of birds hitch rides on ships. One documented incident involved the ship 'Mauritania' as it began its seven-day transatlantic journey from New York to Southampton (England) on 7 October 1962 (Durand 1963). On the morning of the second day, when the ship was 400-500 km out from New York and under heavily overcast skies, more than 130 birds of at least 34 species appeared on deck, mainly passerines but also woodpeckers. The crew provided fruit and other types of food, which some of the birds ate. As the days passed, these birds gradually disappeared, and others were added, but by 12 October nine birds were still present as the ship passed the Fastnet Lighthouse off southwest Ireland. At this point a Yellow-shafted Flicker Colaptes auratus flew ashore. When the ship docked at Southampton on 15 October, four birds were still present, including two White-throated Sparrows Zonotrichia albicollis, one Song Sparrow Melospiza melodia and a Slate-coloured Junco Junco hyemalis. The next day, a White-throated Sparrow was seen in a nearby park. The author mentioned similar incidents from other journeys.

Most records of birds alighting on ships refer to passerines which stay for a few days or so, but occasionally for longer if they are fed. At least one species, the House Crow Corvus splendens from southern Asia, has apparently moved around the world entirely on ships, and has established itself in a number of widely separated port towns. Some other ship-assisted visitors are surprising, such as the Double-crested Cormorant Phalacrocorax auritus which travelled undetected in the hold of a cargo ship from Newfoundland to Scotland (Cottridge & Vinicombe 1996). Incidents such as these raise the possibility that almost any migratory passerine could cross the Atlantic on a ship or by using different ships as stepping stones. But this does not mean that no passerine vagrants have crossed the Atlantic naturally, and it is inconceivable that shorebirds and other types of transoceanic vagrants have travelled in this way. In any case they could not take the types of food provided on ships.

0 0

Post a comment