Showing papers by "Royal Society for the Protection of Birds published in 1999"

The second Silent Spring

Abstract: The drive to squeeze ever more food from the land has sent Europe's farmland wildlife into a precipitous decline. How can agricultural policy be reformed so that we have fewer grain mountains and more skylarks?

Breeding success and causes of breeding failure of curlew Numenius arquata in Northern Ireland

Abstract: 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.

A study of the restoration of heathland on successional sites: changes in vegetation and soil chemical properties

Abstract: Summary 1. Lowland heaths are high-profile ecosystems for conservation action in Britain, but many areas have been invaded by Betula spp., Pinus sylvestris, Pteridium aquilinum and Rhododendron ponticum. As succession occurs on heaths, changes occur in both the vegetation and the soil chemical properties of the site. 2. Nine heathland sites in the Poole Basin area of Dorset were studied, where management of successional sites to restore heathland had occurred. The efficacy of heathland restoration in terms of both the vegetation and the soil chemical properties was assessed. 3. The management had allowed many heathland species to establish and the majority of sites to start to become similar to the neighbouring heathland. The reversion of increased soil nutrients was found to be more problematic, with levels of ammonium–nitrogen, phosphorus, pH, calcium and magnesium remaining greater than those of the heathland soils. 4. The vegetation and soil data were analysed using canoco (canonical correspondence analysis) and were then used to test four hypothetical models that related changes in biotic factors (vegetation) and abiotic variables (soil nutrients) following management to the success of the restoration of heathland on successional sites. 5. A second canoco analysis was carried out in which the managed sites were treated as passive samples. This model was used to measure the distances between the heath, successional and managed sites. These distances provided measures of management success and the resilience of the treated late-successional ecosystem. 6. The successional species present before management affected the success of reversion; management of Pinus sylvestris sites was generally more successful than management of others sites, especially those invaded by Betula. The most significant effect of different management techniques resulted from litter-stripping, which reduced the nutrients available and improved and accelerated the success of reversion.

Status of the volcanically threatened Montserrat Oriole Icterus oberi and other forest birds in Montserrat, West Indies

Abstract: Summary The Montserrat Oriole Icterus oberi is endemic to the Caribbean island of Montserrat where, prior to 1995, it was widely distributed across the island's three main interior mountain ranges: the Centre, Soufriere and South Soufriere Hills. In July 1995, a long-dormant volcano on Chances Peak in the Soufriere Hills began to erupt. Since then the forest habitat of the oriole on the Soufriere and South Soufriere Hills has been devastated by pyroclastic flows and surges, heavy ash eruptions and rock falls. The Montserrat Oriole populations that inhabited these two mountain ranges have probably been lost. In December 1997, a census of the remaining Centre Hills population was undertaken to assess its status in the face of the heavy ash fall that occurred earlier the same year. To do this, a systematic grid of 140 sample points was overlaid on an area of 1,437.5 na encompassing the Centre Hills, and a 10-minute count of all bird species was undertaken at 137 of these points during an eight-day survey period. The distance from the point to each oriole detected was measured and records of all other species were allocated to one of five distance bands radiating out from the point. Distance sampling was used to model densities, and thus to estimate population sizes, of eight bird species in the study area. It was estimated that 4,000 (95% CIs 1,500-7,800) Montserrat Orioles remain in the Centre Hills and thus the world. Although the probability of pyroclastic flows and surges overrunning the Centre Hills is considered rerrtote, it is recommended that the Montserrat Oriole be classified as Globally Threatened (Endangered) under the revised IUCN threat categories because of its loss of breeding habitat since 1995.

Breeding success of the hen harrier Circus cyaneus in relation to the distribution of grouse moors and the red fox Vulpes vulpes

Abstract: Summary 1. A recent analysis showed that the survival and breeding success of female hen harriers were much lower on grouse moors than on other upland land management classes in Scotland, excluding the Orkney islands: a difference attributed to persecution of hen harriers by humans on grouse moors. However, this study did not look for possible beneficial effects on hen harrier breeding success of the control by moorland gamekeepers of other predators, particularly red foxes. 2. These and other recently published data were re-examined to see whether there was regional variation in hen harrier nest success associated with the presence or absence of foxes and the control of foxes and other predators by moorland gamekeepers. 3. The main finding of the previous analysis, that nest success was much lower on grouse moors than on moorland that was not managed for grouse or in young conifer forests, was even more striking when comparisons were made among land management classes within the same region. 4. The mean number of broods fledged per female hen harrier per year on two grouse moors at which gamekeepers prevented human interference with harrier nests and continued to control other predators was compared with the average for moorland in Scotland. Harrier productivity on these moors was much higher than the average for grouse moors, but similar to the average for moorland not managed for grouse shooting. 5. Nest success of hen harriers breeding on moorland not managed for grouse averaged 19% higher in regions where there were, on average, more grouse moors in the vicinity, but in young conifer forests success was 34% lower in regions with more grouse moors nearby. Neither of these differences was statistically significant. 6. Nest success within a particular land management class was not significantly different inside and outside the range of the red fox. 7. Even a generous assessment of the magnitude of a supposed beneficial effect of the control of foxes and other predators by moorland gamekeepers on hen harrier nest success indicated that its effect on the population trend of hen harriers would be small relative to the large negative effect of persecution of harriers on grouse moors.

Applications of large-scale studies of demographic rates to bird conservation

Abstract: Methods for diagnosing causes of bird population declines are described, paying special attention to methods that rely on comparisons among geographical regions and/or time periods with different population trends. Comparisons of breeding productivity and survival among regions or periods provide a valuable check on the diagnosis of external causes of a decline indicated by correlation with population trend. Ringing or tagging programmes can give information on population levels and are the main source of information on survival. Age ratios from counts or catches of juveniles and adults in standardized trapping programmes can provide data on breeding productivity. Nest recording schemes yield estimates of productivity if females make one breeding attempt per year or if the number of attempts per female can be estimated from supplementary data. Population models should be used to explore hypotheses about the external causes and demographic mechanisms of population declines. Models are described which have ...

Survival and dispersal of male Corncrakes Crex crex in a threatened population

Abstract: Survival and between-year movements of Corncrakes ringed as chicks and adult males were investigated in Scotland and Ireland. The probability of movement to sites at various distances from the ringing place was described by a modified random walk model. Most males returned to within a few kilometres of where they were ringed but there were indications that birds ringed as chicks dispersed further than adults. The dispersal model was combined with census data to estimate the probability of subsequent capture for each ringed individual and mean annual survival probabilities. First-year survival was estimated at 0.236, but with a wide confidence interval. Adult survival was estimated more precisely at 0.186. Independent data from studies of breeding success and population trends, taken with the estimated adult survival from recaptures, indicated a higher first-year survival rate (0.339), but the confidence intervals of the two estimates overlapped. Because adult survival was low, the rate of population growt...

The effect of parental age and experimentally manipulated brood size on the foraging effort and breeding performance of great skuas (Catharacta skua)

Abstract: We examined the effect of a brood-size manipulation on the foraging effort and chick rearing of known-age great skuas Catharacta skua . Young birds were expected to refrain from increasing reproductive effort and opt for a strategy of brood reduction, while old birds were expected to increase effort and rear more young. Increasing brood size led to an increase in foraging effort and brood neglect. Enlarged broods had a lower mean survival rate, but similar growth rates to one- and two-chick broods. Parents increased foraging effort to maintain chick growth rates at the expense of brood defence. This was associated with higher conspecific predation of enlarged broods. Foraging effort and chick feeding rate decreased with adult age. Younger adults increased foraging time in an attempt to satisfy the nutritional demands of the chicks, while older birds maintained a similar effort for all brood sizes. Younger adults achieved a lower fledging success despite their higher provisioning rates. Younger birds synchronized foraging and guarding duties less well, and so left the chicks unattended more often than older birds. As a consequence, their chicks suffered higher levels of conspecific predation. Defence of chicks through pair co-ordination and aggression was thus an important component of successful breeding for great skuas.

Diagnosing the causes of bird population declines using comparative methods: The value of data from ringing

Abstract: Methods for diagnosing the causes of bird population declines are described. Special attention is paid to methods which rely on comparisons across geographical regions and/or time periods with different population trends. Comparisons of breeding success and survival across regions or periods provide a valuable check on the diagnosis of the causes of a decline determined by correlation of population trends with candidate causal external factors. Ringing can provide information on population levels and is the main source of information on survival. Age ratios of trapped birds and catches of juveniles and adults in standardised trapping programmes can provide data on breeding success. The latter information complements residts from nest recording because it reflects season‐long breeding success, rather than success per breeding attempt. Morphometric measurements of trapped birds also have potential uses for the assessment of breeding success. The computerisation of ringing information, as well as of recoveri...

Status of Raso Lark Alauda razae with notes on threats and foraging behaviour

Abstract: The Raso Lark Alauda razae is a globally endangered species that is endemic to the islet of Raso (16°93′ N, 24°38′ W) in the Cape Verde archipelago (Collar et al. 1994). Raso is a small (c.7 km 2 ) uninhabited islet with a plain averaging 25 m in elevation to the south and west and small boulder-strewn hills to the north and east rising up to 164 m (Figure 1). The islet comprises mostly rocky desert, with some extensive sandy patches on the western plain. Vegetation is sparse and confined to small patches on the plains and along dry river valleys.

Mortality incident in northern bald ibis Geronticus eremita in Morocco in May 1996

Abstract: In May 1996 there was an acute and dramatic mortality incident in the last remaining wild population of northern bald ibis Geronticus eremita. This species is Critically Endangered, comprising only about 250 wild individuals, which occur on the Atlantic coast of southern Morocco. Over a period of 10 days a total of 38 adult birds (aged 1 year or more) died or disappeared. Deaths, probably secondary to the loss of one or both parent birds, also occurred subsequently in six nestlings and one recent fledgling. The incident appeared to involve no other species. This paper describes the pattern of the incident, and pathological, microbiological and toxicological investigations and findings. Several features point to a toxic aetiology but the cause of the incident has not been established.

The scientific strategy of the BTO ringing scheme

Abstract: 1. This strategy aims to increase the contribution which ringing makes to conservation science and ornithological research, recognising that the primary outputs of the scheme are scientific publications based on data gathered by volunteer ringers. The strategy envisages a greater involvement of ringers in planned projects that are designed to provide specific types of information. Clear advice on priority species and categories of birds (eg age classes, seasons of ringing, breeding vs roosting) to be ringed and recaptured will be given to those ringing outside centrally organised projects. 2. The research programme will focus on two main topics, population dynamics and migration and movements. In addition research on life‐histories, moult and condition should be conducted when opportunities allow. 3. The Ringing Scheme makes a vital contribution to studies of population dynamics by providing data on survival rates and productivity, and sometimes also on numbers. Popidation dynamics models based on such da...

Sexing first year reed buntings emberiza schoeniclus using biometrics

Abstract: Currently ringers are unable to confidently sex some juvenile Reed Buntings due to the overlap in the biometric ranges of male and females, and possible difficulties in the interpretation of sexually dimorphic post‐juvenile head plumage. This study provides a method of correctly sexing most Reed Buntings in their first autumn on their wing measurements, or more accurately with both wing and weight combined. Biometrics of first year Reed Buntings sexed on plumage characteristics were taken at a site in south east Scotland over three years. There was a positive correlation between wing length and weight values, and sexual dimorphism was quantified. Discriminant analysis and logistic regression analysis were used to derive discriminant values and a formula which will differentiate between most males and females: if (‐1.33 x wing (mm)) ‐ (1.58 x weight (g)) +132.31 is positive, the sex is female, if negative, male. These criteria can be applied, by inference, to first year Reed Buntings of unknown sex.