How drought and cold hit disappearing water birds
STERLING field work by the British Trust for Ornithology volunteers throughout the country has revealed a marked decrease in the populations of some water birds, writes Michael Edwards.
The survey, conducted between 1995 and 1996 has revealed that drought conditions which persisted in many parts of the country for over two years have indicated that this unusual British phenomenon is affecting numbers of some wetland species.
Little grebe, mallard, mute swan and shelduck all showed decreases and several observers noted that some small ponds were completely dry by spring.
According to Andy Wilson of the BTOs census unit, that light-walking lily-trotter, the moorhen, also suffered, losing 4% on plots studied, possibly due a combination of low water table and cold winter weather.
Small birds were hit during the 1995-96 winter, the coldest for at least five years with particularly viscous cold snaps in December and late January.
Experience has told the BTO that such conditions increase over-winter mortality of certain species, especially small insectiverous birds such as wren and gold crest. Grey and pied wagtail numbers were down by a significant 19% on waterways while pied wagtail was down by 7% on farmland. Kingfisher and dipper also showed double figure decrease; the 10% fall in the latter taking the population to its lowest level for 13 years.
The grey (left) and pied wagtail populations dropped by 19%.