Breeding success and causes of breeding failure of curlew Numenius arquatain Northern Ireland

1. The present study investigated breeding success and causes of breeding f ailure of curlew, a species for which the UK holds internationally importan t breeding numbers. Studies were undertaken between 1993 and 1995 in two ar eas of Northern Ireland, where the species' breeding range has recently con tracted and breeding numbers are declining. Avian nest predators were abund ant in both areas, whereas foxes were abundant on the Antrim study area but generally were absent from the Lough Erne study area, which was mainly isl ands. 2. Productivity was estimated to be 0.14-0.26 fledglings per pair in Antrim and 0.20-0.47 fledglings per pair on Lough Erne, These figures are lower t han most estimates of productivity from other studies of breeding curlew. T he differences between the recorded productivity levels and those estimated to be required to maintain a stable population are sufficient to account f or the observed decline in Northern Ireland's breeding curlew population. 3. Predation was the main proximate cause of breeding failure, with nest pr edation being of most importance in reducing productivity. Only 3.6-19.0% o f all nests hatched on each study area in each year, with nest predation ac counting for 85-97% of failures. Survival of chicks from hatching to 31 day s of age was 38.5% in Antrim and 19.1-29.2% on Lough Erne. Predation accoun ted for 74% of chick mortality. 4. Nest failure rates were not related to the vegetation height around nest s nor to clutch laying date on either study area. They differed among the i slands and one shoreside site on Lough Erne, Almost all nest predation on L ough Erne was attributable to avian predators, but in Antrim foxes probably accounted for most nest predation. The likelihood of predation on chicks w as not related to their hatching date, hatching weight or body condition. 5. The results from this study Suggest that predation rates on curlew nests in Northern Ireland may have increased in recent decades. Levels of predat or control in Northern Ireland have declined but there have also been consi derable changes in land-use that could benefit generalist predator species or increase the vulnerability of curlew nests to predation. It is recommend ed that large-scale trials of legalized predator control and land-use manip ulation should be undertaken to identify appropriate conservation managemen t methods.