The ecology and conservation of Great Crested Grebes (Podiceps cristatus) at Lough Neagh, Northern Ireland

Abstract

During a study carried out between 1995-99, Lough Neagh (Northern Ireland) was established as the most important breeding site of Great Crested Grebes in Britain and Ireland, and one of the most significant in Western Europe.

The population of grebes on Lough Neagh, which numbered at least 4,286 individuals in 1999, was found to contain resident and partial-migratory elements. A study was made of abundance, spatial distribution, breeding biology, post-breeding dispersion and conservation issues. Activity time budgets were monitored in 1998 using radiotelemetry. Four adult birds that were tagged moved from Lough Neagh to overwinter on Belfast Lough, a traditional coastal site where the grebe population peaked at 2,300 birds between 1997-99.

The summer population at Lough Neagh increased by a mean annual growth rate of 13% over five years, with the present population exceeding the 1 % qualifying threshold for Wetland Birds of International Importance (1,500 grebes). However, long term changes were confused as national counts in 1965 and 1975 underestimated the breeding population, and summer counts in the mid 1980's resulted in low estimates of less than 1,500 birds.

The size of the wintering population was also underestimated in official WeBS monthly wildfowl counts undertaken from the shore. This was shown through periodic diurnal and nocturnal sampling of grebes by boat over two winters and from eight locations. Grebes were found to associate with diving ducks (viz, Scaup, Tufted Duck, and Pochard) up to 5 km from the shore. Based on these observations an estimate of between 1-2,000 grebes was extrapolated for the whole lake.

Habitat surveys were unde1taken on Lough Neagh and related to breeding densities, breeding success rates and habitat preferences. Results showed that the largest numbers of grebes nested in reeds, but bulrush attracted the highest densities of breeding birds. Comparisons were made with grebe populations in other areas. Detailed studies at three island and six marginal breeding sites examined causes of low breeding success over five years. Experimental habitat improvements were tested at three unmanaged reedbed sites in 1997-1998, and these showed that birds successfully adapt to changes in the environment.

Methods were tested and developed to trap grebes under license using mist nets over water. Individuals caught were colour marked and ringed. Diet was analysed using stomach-flushing procedures, and fish distribution and abundance was sampled over four months using gill nets. Migratory and seasonal habitat switching trends were found to relate to variations in food supply and poor weather.

This study suggests that urgent action is needed to protect the future of this vulnerable population, and strong recommendations have been prepared for Government attention. At Lough Neagh, relevant measures include action to reduce mink, reduction of waterfowl m01tality due to gill nets, lessening of human disturbance, erection of groynes to protect nests from wave damage, and habitat management. At Belfast Lough contingency plans are needed to counter potential accidental oil spillage, and recommendations are made for legislative amendments to extend SPA designations into the sea-lough to include all important roost sites.

Date of Award	Apr 2000
Original language	English