maandag, januari 25, 2010

Flying migrators over Haarlem - Bird migration - SMI 1.10

Hi Passengers !

Harlem.EN presents tonight this podcast about bird migration phenomenoms seen today in the skyline of Haarlem between 1.30 pm (beggining of the observation) and 5.30 (end of my observation). They have been thousands of flying migators coming from the west (the ocean) and going to the east (Germany).

They have flyed at a maximum of 500 meters above the ground due to an heavy weather full of clouds, snow is covering again the Netherlands since Saturday night and those birds must have certainly problems to migrate with this weather in the middle of January. I lived in Haarlem since 2001 and i have never seen that during the past Januaries in the North Holland skyline...
  • My questions are : Where they are coming from ? 
  • Where they are going and why now ? 
Feel free to let your answer in the ''BLABLA'' section in the endpost of this message !
I will be pleased to share some informations about this strange bird migration in the Dutch sky today (January 25/1/2010) with this animation made to understand what's happening upon our blue dot ?
Bird migration
is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. These however are usually irregular or in only one direction and are termed variously as nomadism, invasions, dispersal or irruptions. Migration is marked by its annual seasonality. In contrast, birds that are non-migratory are said to be resident or sedentary.

Historical views

The earliest recorded observations of bird migration were 3000 years ago, as noted by Hesiod, Homer, Herodotus, Aristotle and others. The Bible also notes migrations, as in the Book of Job (39:26), where the inquiry is made: "Doth the hawk fly by Thy wisdom and stretch her wings toward the south?" The author of Jeremiah (8:7) wrote: "The stork in the heavens knoweth her appointed time; and the turtledove, and the crane, and the swallow, observe the time of their coming."
Aristotle noted that cranes traveled from the steppes of Scythia to marshes at the headwaters of the Nile. Pliny the Elder, in his Historia Naturalis, repeats Aristotle's observations. Aristotle however suggested that swallows and other birds hibernated. This belief persisted as late as 1878, when Elliott Coues listed the titles of no less than 182 papers dealing with the hibernation of swallows. It was not until early in the nineteenth century that migration as an explanation for the winter disappearance of birds from northern climes was accepted.

The discovery in Germany of white storks embedded with African arrows provided early clues on migration. One of the oldest of these Pfeilstorch specimens was found in 1822 near the German village of Klütz, in the state of Mecklenburg-Vorpommern.

Threats and conservation

Human activities have threatened many migratory bird species.The distances involved in bird migration mean that they often cross political boundaries of countries and conservation measures require international cooperation. Several international treaties have been signed to protect migratory species including the Migratory Bird Treaty Act of 1918 of the US and the African-Eurasian Migratory Waterbird Agreement.

The concentration of birds during migration can put species at risk. Some spectacular migrants have already gone extinct, the most notable being the Passenger Pigeon (Ectopistes migratorius). During migration the flocks were a mile (1.6 km) wide and 300 miles (500 km) long, taking several days to pass and containing up to a billion birds.
Other significant areas include stop-over sites between the wintering and breeding territories. A capture-recapture study of passerine migrants with high fidelity for breeding and wintering sites did not show similar strict association with stop-over sites.
Hunting along the migratory route can also take a heavy toll. The populations of Siberian Cranes that wintered in India declined due to hunting along the route, particularly in Afghanistan and Central Asia. Birds were last seen in their favourite wintering grounds in Keoladeo National Park in 2002.

Structures such as power lines, wind farms and offshore oil-rigs have also been known to affect migratory birds. Habitat destruction by land use changes is however the biggest threat and shallow wetlands which are stopover and wintering sites for migratory birds are particularly threatened by draining and reclamation for human use.

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