Hutton’s shearwater count – Population estimation

In 2002, an estimate of the population of Hutton’s shearwater was made by Graeme Taylor (Department of Conservation) and Paul Scofield (Canterbury Museum) using mark-recapture techniques.  A team visited the Kowhai River colony where 2000 birds were spray painted red or yellow underneath.  After the marking was finished, sightings were made from boats at sea or from the beach, of the ratio of coloured/non-coloured birds from which the estimates of the number of breeding birds were made. It had been 12 years since that work took place and the Trust repeated the exercise again in September 2014.

Four boats were used on the water, each with two teams consisting of an observer and a recorder. Each team made observations from a different side of the boat, to ensure birds were not counted twice as the boat moved slowly through the rafts of shearwaters sitting on the water.  The count involved counting the number of birds sighted with red paint and the number of birds without paint.