The typical image of migration is of northern landbirds such as swallows and birds of prey making long flights to the tropics. Many northern-breeding ducks, geese and swans are also long-distance migrants, but need only to move from their arctic breeding grounds far enough south to escape frozen waters.
The Lesser Striped Swallow is a partial migrant within Africa
This means that most wildfowl remain in the Northern hemisphere, but in milder countries. For example, the Pink-footed Goose migrates from Iceland to Britain and neighbouring countries. Usually wintering grounds are traditional and learned by the young when they migrate with their parents.
Some ducks, such as the Garganey, do move completely or partially into the tropics.
A similar situation occurs with waders (called "shorebirds" in North America). Many species, such as Dunlin and Western Sandpiper, undertake long movements from their arctic breeding grounds to warmer locations in the same hemisphere, but others such as Semipalmated Sandpiper travel huge distances to the tropics.
Dunlin (Calidris alpina)
Most of the wildfowl are large and powerful, and even the waders are strong fliers. This means that birds wintering in temperate regions have the capacity to make further shorter movements in the event of particularly inclement weather.
The same considerations about barriers and detours that apply to long-distance land-bird migration apply to water birds, but in reverse: a large area of land without bodies of water that offer feeding sites is a barrier to a water bird. Open sea may also be a barrier to a bird that feeds in coastal waters. Detours avoiding such barriers are observed: for example, Brent Geese migrating from the Taymyr Peninsula to the Wadden Sea travel via the White Sea coast and the Baltic Sea rather than directly across the Arctic Ocean and northern Scandinavia.
For some species of waders, migration success depends on the availability of certain key food resources at stopover points along the migration route. This gives the migrants an opportunity to "refuel" for the next leg of the voyage. Some examples of important stopover locations are the Bay of Fundy and Delaware Bay.
Some Alaskan Bar-tailed Godwits have the longest non-stop flight of any migrant, flying 11,000 km to their New Zealand wintering grounds (BTO News 258: 3, 2005). Prior to migration, 55% of their bodyweight is stored fat to fuel this uninterrupted journey.
This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.
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