Wetlands are the most important of life-supporting ecosystems that have sustained human lives and communities over the millennia. It facilitates the inclusion of a large gamut of habitats ranging from mangroves to peats and bogs. This diversity contributes to the enormous diversity of wetland organisms – making it a habitat of winged visitors from far and wide. Spread over 50 sq. km, the large Marsh, smaller satellite wetlands, large tracts of pasture land and patches of dry forests are locally known as Kazhiveli (a generic Tamil name for Marshes and swamps) – the Pallikaranai marsh attracts birds of different hues. The ‘class Aves’ coming from elsewhere are indeed a treat to watch.
Bird migration is the regular seasonal movement, often north and south along a flyway between breeding and wintering grounds, undertaken by many species of birds. Migration, which carries high costs in predation and mortality, including from hunting by humans, is driven primarily by availability of food. The Arctic Tern holds the long-distance migration record for birds, traveling between Arctic breeding grounds and the Antarctic each year. The timing of migration is controlled primarily by changes in day length. Migrating birds navigate using celestial cues from the sun and stars, the earth's magnetic field, and probably also mental maps.
Pallikaranai wetland, a freshwater swamp is perhaps the last of the surviving wetland is one of the 94 identified wetlands under National Wetland Conservation and Management Programme (NWCMP) operationalised by the Government of India. The topography of the swamp is such that it always retains some storage, thus forming an aquatic ecosystem. Indiscriminate dumping of toxic solid waste along the road, discharge of sewage, and construction of buildings, railway stations and a new road to connect Old Mahabhalipuram Road and Pallavaram have shrunk the wetland to a great extent.
In animal World there is something known as ‘dominance relationship’ – in stable groups the superior competitor should consistently win each contest and the inferior competitor should retreat. Dominance relationships can be measured by the result of fights in aggressive encounters among two individuals or the direction of threats or submissive gestures. It is not entirely about migration, there is something known as :
Philopatric (Adjective) - (of an animal or species) tending to return to or remain near a particular site or area.
Broadly, philopatry is the behavior of remaining in, or returning to, an individual's birthplace. More specifically, in ecology, philopatry is often associated with the behavior of elder offspring sharing the parental burden in the upbringing of their siblings or other younger kin, a classic example of kin selection. It derives from the Greek 'home-loving', although it can be applied to more than just the area that an animal was born in. Species that return to their birthplace in order to breed are said to exhibit natal philopatry or natal homing.
Species that return in consecutive years to the same breeding site or territory exhibit breeding philopatry or site fidelity. Migrating animals also exhibit philopatry to certain important areas on their route; staging areas, stop-overs, molting areas and wintering grounds. Philopatry is generally believed to help maintain the adaptation of a population to a very specific environment. The level of philopatry varies within migratory families and species.
So, there is much more to learn – simply by looking outside gazingly to the winged visitors around… how they move from place to place, what guides them to the lands more suited to them for breeding, how do they home in on their prey and more ……… are indeed amazing ~ and we think, homo sapiens are the ones possessed with great knowledge and thinking power.
With regards – S. Sampathkumar.