Winter Migration
Kolkata area

 

 
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Migration study in the Kolkata city area

 

 
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The Kolkata Metropolitan area at present plays host in winter to about 85 (120 historical) migrant species. Of these some are extremely rare and may not be observed every year. About 50 of these are regularly recorded by one or more observers.

Over the last 7 years, members of Bengalbird googlegroup have been tracking 1st arrivals of these 50 odd species in the Kolkata and West Bengal area. Migration data plays a critical role is assessing how birds adapt to change in environmental conditions. By and large, bird species have a regular migration cycle and finding a baseline enables us to observe and record variances. Such statistics are extremely scant in eastern India and this is our 1st effort in establishing such a baseline through community participation in which more than 70-80 birders participate actively over the years. From our data we have chosen 25 species for this presentation based on visibility, ease of identification, regularity and sequence of arrival.

The earliest species to arrive in our area are the Barn Swallows and Brown Shrikes, who may start arriving as early as in July. The waterfowl pick up the rear and start being observed around end October and early November. Members observing migrants report 1st arrivals which are posted to the group forum. Two different sightings are usually needed to confirm the 1st date of arrival (unless the 1st sighting was photographed).

The following charts highlight the range of arrival periods. They are based on 1st date of sighting of the species in our area over the period 2005 to 2010. The coloured areas indicate the possible arrival time.

Arrival trends are mirrored in the chart below. It is based on 1st arrival dates of different species over successive fortnights. The chart is not species specific, but arrival specific. For example, if a White Wagtail arrives in the 1st fortnight of September 2005 and September 2010, both records carry equal weight in the final output. 
In 2010, 12/25 species arrived in September which is an useful test for the trends shown.

Sumit Sen ©
Kolkata, India
Oct 2010.

 

   
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