Picture of intertidal habitat in Chichester Harbour


Many wild birds have developed a migration strategy in response to changes in their environment that affect the availability of food, water and a sheltered place to nest and breed.

Environmental factors are key to a bird's survival. The changing seasons can transform a comfortable environment into a hostile one; the food and water supply may dwindle or disappear, plant cover may vanish, and competition with other animals may increase. Wild animals face the problem of living in a habitat that is only suitable for a portion of the year, and so nature has provided methods for coping with the situation. While some animals resort to hibernation, many wild birds turn to migration using the powers of flight to adapt to seasonal changes by moving to locations with more food and more favourable environmental conditions.

Before the bird embarks on its migration, it must prepare for the journey by storing fat as fuel. It needs to choose the correct time of year and weather conditions for departure, and must stick to a compass course throughout its flight. On long journeys, the bird will need to stop to refuel, using a site it may not have visited before, with unfamiliar food (if it is a young bird). Along the way, it may be blown off course by strong winds and storms. There is a risk of running out of fuel over the sea, or of finding a fuelling site is no longer available. As if these challenges weren't enough, there is a chance of attack by a bird of prey, being shot or trapped by hunters, or suffering from a pollution incident. The migratory routes that birds follow today are the result of natural selection in an ever-changing world, and despite the hazards, wild birds continue to maintain their evolved migratory behaviour.

Greenshanks are familiar migrants throughout Britain and Ireland, sighted widely along coastal and inland waters in spring and autumn. Several hundred Greenshanks over-winter in the UK, mainly in the West and Ireland. Breeding Greenshanks are found in the uplands of north and west Scotland, using the poorly drained, boulder-strewn peat soils of the Highlands where the landscape is more open. 1500 pairs breed in Scotland, some of which winter in the UK and Ireland. During passage and whilst over-wintering, Greenshank use a wide variety of feeding habitats. Inland these are likely to be lakes, reservoirs and sewage-farms. On the coast, Greenshanks are mostly found on estuaries, but also on saltmarsh, lagoons and muddy shores.

Other Greenshank populations breed throughout much of Scandinavia and eat to Siberia. These birds inhabit the taiga and forest zones of the Palearctic, including forest marshes, forest clearings and areas of scrub with lakes and bogs. Eastern Greenshank populations winter further south, through sub-Saharan Africa, southern Asia and even as far as Australia.

Chichester and Langstone Harbours form part of a network of coastal (and inland) wetlands used for migrating and wintering shorebirds. These sites are inter-connected to form the east Atlantic flyway, and each stepping stone or staging site is vital in the success of migration strategies. The loss or damage of one site in this chain can have severe consequences for the birds that use this route, potentially causing the dramatic declines and changes in populations of our shorebirds.

For more information about migration see details for the Migration Atlas (by Wernham et al 2002) in Contacts and Information.