thumb |upright=1.3 |Reverse migration
Reverse migration, also called reverse misorientation, is a phenomenon whereby a bird migrates in the opposite direction to that typical of its species during the spring or autumn. that birds from east of Lake Baikal in Siberia (circled) could not occur in western Europe because their migration routes were too north–south. Most of these lost young birds perish in unsuitable wintering grounds, but there is some evidence that a few survive, and either re-orient in successive winters, or even return to the same area.
As migration is most often genetically programmed before birth, there can be rare variations and defects that change the migration programming. These variations will account for some but not all reverse migration cases. Birds that have changed their migration path, if they survive, may breed with others who also follow this different migration route. Their offspring and subsequent generations may now follow the new, genetically programmed migration route.
Genetic variations may be triggered by a range of factors, including mutations in the genes responsible for the sensing of environmental cues such as photoperiod (day length) or geomagnetic fields, which birds use for navigation. Other factors, such as changes in habitat availability, food sources, or climate conditions, may also contribute to changes in migration patterns. These genetic and environmental influences can lead to the rare but intriguing phenomenon.
thumb |188x188px |A station like this can be used to track transmitters on birds.
Methods of tracking migration
Tracking radar
A single bird can be tracked using a manually operated tracking radar to understand the target's position and trajectory and to predict where it will arrive. As the bird flaps its wings, the echo can be recorded and compared to patterns to understand flight patterns and changes in flight patterns. Tracking radar was primarily used to monitor specific individuals during nocturnal migration.
thumb |A yellow-breasted bunting, considered less likely to be a pseudo-vagrancy migrant
However, an article in British Birds by James Gilroy and Alexander Lees notes that while misorientation primarily occurs in the approximately opposite direction, it can also occur in random directions. These random directions could be partly the result of genetic variations or abnormalities. Birds that adopt and continue to migrate in this atypical direction have been called pseudo-vagrancy migrators. Some species are more prone to pseudo-vagrancy migration: yellow-breasted bunting, for example, is considered to be less prone to pseudo-vagrancy than, say, yellow-browed warbler. rather than to the north in birds that normally migrate south. By only examining species that migrate solitarily during the night, they eliminated the possibly of group migration, where birds could be influenced by the behaviour of others.
Reverse migration to avoid flying over large expanses of water
Reverse migration is occasionally observed in Door County, Wisconsin. When broad-winged hawks traveling north reach the tip of the Door Peninsula and the islands beyond, the long stretches of water sometimes unnerve them. Instead of crossing over to the Garden Peninsula, they turn around and fly back down the peninsula.
See also
- Drift migration