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Trends In Breeding Wader Populations In Northern Ireland between 1986 And 2000
Abstract
The 2000 breeding wader survey covered 38 sites within three of the key wader areas, Lough Neagh/Beg, Upper and Lower Lough Erne. The method of fieldwork and analysis generally followed those described in O’Brien and Smith (1992), with the exception of curlew which utilised Grant et al. (2000). Data from past surveys were re-examined for standardisation. This encompassed 334 site surveys from 129 sites within five of the ‘key wader areas’.
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Counts of individual Curlew and estimates of breeding pairs from ‘field-by-field’ surveys were highly correlated with the numbers of nesting pairs, as determined by intensive studies on 27 sites located on four grassland-dominated study areas. The mean count of individual Curlew over three standard survey visits to each site was used to estimate numbers of nesting pairs. This estimate exceeded the number of nesting pairs on all study areas (as assessed by intensive studies) by 12% but was more accurate than the maximum number of pairs estimated from the three survey visits on each site (the previous convention for estimating breeding pairs). Estimates of the number of pairs hatching chicks were assessed by recording alarm-calling Curlew during late survey visits. The maximum number of alarm-calling pairs was used to estimate the number of pairs hatching chicks, overestimating this by 54%. Three of the study sites were adjacent to extensive moorland which produced overestimates during surveys because moorland nesting birds fed and led broods onto these sites. Omitting these sites from consideration reduced the degree of overestimation to 1% for the number of pairs and 7% for the number of pairs hatching chicks.
A panel formed from the British Trust for Ornithology, the Wildfowl & Wetlands Trust, the Royal Society for the Protection of Birds, the Joint Nature Conservation Committee and the Game Conservancy Trust has identified the most recent reliable estimates of the breeding, wintering and passage populations of birds in Britain and in the United Kingdom. This paper summarises the most-up-to-date estimates in a single table with the intention of providing a useful resource for conservation. This is the first year that the Avian Population Estimates Panel (APEP) has published estimates, and it will aim to publish revisions every three years.
1. The present study investigated breeding success and causes of breeding failure of curlew, a species for which the UK holds internationally important breeding numbers. Studies were undertaken between 1993 and 1995 in two areas of Northern Ireland, where the species’ breeding range has recently contracted and breeding numbers are declining. Avian nest predators were abundant 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 islands.
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 than most estimates of productivity from other studies of breeding curlew. The differences between the recorded productivity levels and those estimated to be required to maintain a stable population are sufficient to account for the observed decline in Northern Ireland's breeding curlew population.
3. Predation was the main proximate cause of breeding failure, with nest predation being of most importance in reducing productivity. Only 3·6–19·0% of all nests hatched on each study area in each year, with nest predation accounting for 85–97% of failures. Survival of chicks from hatching to 31 days of age was 38·5% in Antrim and 19·1–29·2% on Lough Erne. Predation accounted for 74% of chick mortality.
4. Nest failure rates were not related to the vegetation height around nests nor to clutch laying date on either study area. They differed among the islands and one shoreside site on Lough Erne. Almost all nest predation on Lough Erne was attributable to avian predators, but in Antrim foxes probably accounted for most nest predation. The likelihood of predation on chicks was 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 predator control in Northern Ireland have declined but there have also been considerable changes in land‐use that could benefit generalist predator species or increase the vulnerability of curlew nests to predation. It is recommended that large‐scale trials of legalized predator control and land‐use manipulation should be undertaken to identify appropriate conservation management methods.
1. In the UK, Phase 1 survey is a standard method of habitat mapping that has been used widely for environmental assessment and management planning. In this paper we make the first rigorous test of the precision with which environmental consultants apply the technique.
2. Six ecologists surveyed independently the same upland site in northern England. In pairwise comparisons between maps, spatial agreement was found to average 25·6% (with a range of 17·3–38·8%) of the area of the study site. The numbers of land cover types that were identified ranged from 13 to 21. Four or more surveyors agreed on the classification of 19% of the study site, while the area of land upon which all six agreed was only 7·9% of the study site. Spatial errors in the positioning of habitat boundaries occurred, but were a relatively minor source of the differences between maps. The majority of differences between maps were due to classification errors. Land cover types with similar species compositions were most frequently confused.
3. Spatially referenced field ‘target notes’ giving additional information on the vegetation mapped in each survey varied in number between 18 and 56. The contents of target notes were inadequate to allow a retrospective assessment of mapping decisions. The total numbers of species listed in target notes varied between surveys from 25 to 145. Sorenson's similarity for species lists derived from pairs of surveys ranged from 18·8% to 63·7%, and was not related to spatial agreement between surveys.
4. Time spent at the field site was not a correlate of any aspect of the results or cost of the survey. Three surveys conducted by members of a professional institute for ecologists were the most expensive, and also recorded larger numbers of target notes and species than the other surveys. However, their maps were no more similar than other pairs of maps.
5. Analysis of the survey results and comparisons with other methods of vegetation mapping suggest that mapping precision could be increased by (i) placing a greater emphasis on use of aerial photographs and other extant map data prior to (and during) field work; (ii) making greater provision for mapping of mosaics and increasing the level of floristic information in habitat definitions; (iii) recording a greater number of more detailed target notes in the field; and (iv) providing office-based support to assist in the interpretation of aerial photographs, and the cross-checking of field surveyors’ preliminary classifications against the contents of target notes and habitat definitions. The current application of the Phase 1 approach by environmental consultants places too great a reliance on decision-making by the (frequently) unsupported lone surveyor whilst in the field.
Trends in breeding wader populations in Northern Ireland with related data on habitat composition and curlew breeding success
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