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Guernsey Wader Counts


Methods


On a designated day each month the teams of observers visit all ten sectors at, or around, high tide and counts the birds present. The observer also notes any causes of disturbance (e.g. walkers, dogs, aircraft, vehicles etc - the list is endless!) and also the impact of that event in terms of the severity of the impact on the birds. These data are collated and sent to the BTO.


Fig 1. Each month these sectors are counted at, or around, high tide and the numbers of waterbirds are recorded.

 

Standard methods are used to work out an 'index' of abundance for each species in each winter where there is enough data. In essence this is really the same as working out the average number of birds using a site over a winter and scaling is accordingly. In the analysis carried out here we present the data for the winter period (defined here as October to March inclusive) and the graphs etc are based on the average number of birds counted each month within that period. Where missing counts occur we 'impute' an estimate of the numbers present. This is based on the normal count for that site in that month and it is scaled appropriately according to whether there has been a general increase/decrease at other sites. See here for further details of methodology and statistical analysis.

The 'Alerts' system used in the UK to classify species into RED (declines of more than 50%), AMBER (declines between 25% and 50%) and GREEN (increasing or small declines of less than 25%). The abundance indices are smoothed and change calculated over 5, 10 and 20 years to give short, medium and long-term changes. This traffic light system shows the current status of each species.



 
   
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