Showing papers by "Royal Society for the Protection of Birds published in 2002"

Economic Reasons for Conserving Wild Nature

Abstract: On the eve of the World Summit on Sustainable Development, it is timely to assess progress over the 10 years since its predecessor in Rio de Janeiro. Loss and degradation of remaining natural habitats has continued largely unabated. However, evidence has been accumulating that such systems generate marked economic benefits, which the available data suggest exceed those obtained from continued habitat conversion. We estimate that the overall benefit:cost ratio of an effective global program for the conservation of remaining wild nature is at least 100:1.

The selection of stubble fields by wintering granivorous birds reflects vegetation cover and food abundance

Abstract: Summary 1 Fields left fallow after harvest (i.e. stubble fields) support high wintering densities of many species of granivorous bird. We examined correlates of use by eight such species of different types of intensively managed wheat and barley stubble fields, organic wheat fields and set-aside fields on mixed lowland farmland in central England. Field occupancy was studied in relation to the physical characteristics of fields and seed abundance. 2 Higher seed abundance was associated with greater occupancy by linnet Carduelis cannabina, grey partridge Perdix perdix, chaffinch Fringilla coelebs, yellowhammer Emberiza citrinella, reed bunting Emberiza schoeniclus and corn bunting Miliaria calandra. Larger areas of bare earth within stubble fields were associated with greater occupancy by linnet, yellowhammer, reed bunting and corn bunting, but lower occupancy by woodpigeon Columba palumbus. 3 On conventional intensively farmed sites, seed abundance and area of bare earth were significantly greater on barley stubbles than on wheat stubbles. 4 Seed numbers fell throughout the winter in all stubble types, although reductions were greatest on intensive barley stubbles, intermediate on intensive wheat stubble and lowest on undersown organic wheat stubbles. 5 Within fields occupied by linnets, areas used for feeding had significantly greater quantities of seeds known to be important in their diet. Feeding areas also had a greater area of bare earth than randomly selected ‘non-feeding areas’. 6 Linnets and reed buntings were rarely found on fields where densities of weed seeds important in their diets fell below 250 seeds m−2. In autumn, yellowhammers and grey partridges rarely fed on fields where cereal grain density was below 50 m−2. However, in spring, both species fed on these fields irrespective of grain density, perhaps indicating a switch to other food sources. 7 We suggest that land managers wishing to maximize the value of overwinter stubble fields for granivorous birds locate such fields where there is a substantial natural regeneration of weed flora and where previous cropping (e.g. barley) is likely to offer a sparse stubble with substantial areas of bare ground.

Widespread local house-sparrow extinctions

Abstract: Agricultural intensification is blamed for the plummeting populations of these birds. House-sparrow populations have declined sharply in Western Europe in recent decades1,2, but the reasons for this decline have yet to be identified, despite intense public interest in the matter. Here we use a combination of field experimentation, genetic analysis and demographic data to show that a reduction in winter food supply caused by agricultural intensification is probably the principal explanation for the widespread local extinctions of rural house-sparrow populations in southern England. We show that farmland populations exhibit fine-level genetic structuring and that some populations are unable to sustain themselves (sinks), whereas others act as sources.

Survival rates, causes of failure and productivity of Skylark Alauda arvensis nests on lowland farmland

Abstract: This paper analyses data from 995 Skylark Alauda arvensis nests found on lowland farms in southern England from 1996 to 1998. The majority of recorded nest failures were caused by predation except in agricultural grass, where trampling and agricultural operations were equally important. Nest survival rates varied between crop types, nests in cereals being around twice as likely to succeed as nests in grass or set-aside. In cereals, nest survival rates increased with increasing distance from the nearest tramline and declined over the course of the breeding season. Predator control also had a significant independent effect on nest survival rates. On one farm where many other factors were held constant, a highly significant increase in nest survival rates from 12.3% to 40.7% coincided with the introduction of intensive predator control, which also appeared to bring forward mean laying dates. Most environmental factors explaining significant variation in nest survival rates did so only at the chick stage. The mean number of chicks produced per nesting attempt was 1.26 in cereals, 0.78 in set-aside and 0.63 in grass, the differences being due primarily to variation in nest survival rates. Low densities of Skylark territories in cereal crops are not therefore the consequence of low breeding success at the scale of the individual nest and probably reflect limitations on the number of attempts made in a season. Measures taken to improve the attractiveness of cereal crops as a nesting habitat for Skylarks, and beneficial changes in grassland management, are likely to increase overall productivity.

Local annual survival of booming male Great Bittern Botaurus stellaris in Britain, in the period 1990–1999

Abstract: Male Great Bitterns Botaurus stellaris have individually distinctive boom vocalizations which have been used since 1990 to count the British population accurately. We used vocal individuality to identify birds between years and analyse the survival of the British booming population. We used six instances of Great Bitterns known to be the same birds (from radio tracking and re-sighting of darvic rings) in successive years to provide a means of identification independent from vocalizations. All of these birds remained in the same territory from one year to the next. Seven spectrogram measures were chosen as quantitative descriptors of Great Bittern booms. Boom similarity was expressed in terms of Euclidean 'acoustic' distance between descriptors of pairs of birds. Great Bitterns that were known to be the same birds had more similar booms across years than those known to be different. The acoustic distances and knowledge of site fidelity were used to construct parsimonious rules on which to base re-identification decisions and to build survival histories. Great Bittern local survival in Britain as a whole was estimated as 70% (± 5.1 se) with survival in north-west England (at Leighton Moss) higher (82.8%, ± 7.3 se) than that in East Anglian sites (65.2%, ± 5.4 se) (X 2 1 = 3.4, P = 0.07). Movements of males between years were apparent between sites within the Suffolk and Norfolk coastal regions but not on a large scale. Survival of adult males in East Anglia was positively related to winter rainfall, but there was no significant relationship with winter temperature. There was a positive relationship between the annual population change in East Anglia and the annual local adult survival rate.

The distribution and habitats of crossbills Loxia spp. in Britain, with special reference to the Scottish Crossbill Loxia scotica

Abstract: A study was carried out, primarily in northern Scotland, to relate bill and wing measurements to diagnostic calls of crossbill species, and thereby use the calls to describe the distributions and habitats of the different species Bill depth and wing length measurements from museum specimens and live-trapped birds were used to describe the size categories Almost all measurements of crossbills from England were similar to measurements of Common Crossbills from Fennoscandia Museum specimens showed that crossbills in northern Scotland between 1822 and 1990 were a combination of Common Crossbills, birds which were intermediate between Common and Parrot Crossbills (Scottish Crossbills), and perhaps a few Parrot Crossbills However, catches of crossbills between 1995 and 2000 showed that Parrot Crossbills (based on bill and wing measurements) were present at some sites in the Highlands Recordings of flight calls and excitement calls of birds of known bill sizes allowed a classification of crossbills according to call types Four different flight calls (referred to here as types 1–4) and five excitement calls (types A–E) were recognized A sample of small-billed birds, thereby identified as Common Crossbills, indicated that there were three groups of Common Crossbills: those giving type 1 flight calls and type A excitement calls (1A), type 2 flight calls and type B excitement calls (2B), and type 4 flight calls and type E excitement calls (4E) Large-billed birds identified as Parrot Crossbills gave mainly type 2 flight calls and type D excitement calls Birds with intermediate bill depths (Scottish Crossbills) gave type 3 flight calls and type C excitement calls Distributions based on calls showed that 1A Common Crossbills were widespread in Scotland but the other types of Common Crossbill were rare Parrot Crossbills were found in a few localities in the Highlands, and Scottish Crossbills (defined as those giving type 3 flight calls and type C excitement calls) were restricted to the northern and eastern Highlands Scottish Crossbills and 1A Common Crossbills had overlapping distributions, and overlapped greatly in the types of forests they used between January and March when the Scots Pine cones were still closed However, Scottish Crossbills were more frequently associated with stands containing Scots Pine compared with Common Crossbills

Sex and death: chd1z associated with high mortality in moorhens

Abstract: Sex ratios in clutches of moorhens (Gallinula chloropus) in Britain were measured on 83 chicks using the sex-linked CHD1 gene (Chromo-helicase/ATPase-DNA binding protein 1). Among birds, the female is the heterogametic sex (Z and W chromosomes), and the male is homogametic (two copies of the Z chromosome). We report variation among the PCR-amplified fragments of the CHD1Z, and the death of nearly all heterozygous male chicks (92%). In contrast, survivorship among females and homozygote males was 54-60%. Mortality in male heterozygotes was significantly higher than that of male homozygotes (P < 0.001). Chick and egg biometrics were not significantly different between these males. The CHD1Z was unlikely to be directly responsible but may have been hitchhiked by the causal gene(s). The observations appear to follow a classic underdominance (heterozygote inferiority) pattern, but raise the paradoxical question of why one form of the Z chromosome has not been fixed, as is expected from evolutionary theory. We discuss possible explanations and include a survey of British populations based on skin specimens.

Trends in Seabird Numbers on Aride Island Nature Reserve, Seychelles 1988-2000

Abstract: Count data for twelve species of seabird from Aride Island Nature Reserve, Seychelles were reviewed from 1988 to 2000. The numbers of six of the ten breeding species remained relatively stable during the period, while those of one species, the White-tailed Tropicbird (Phaethon lepturus) underwent a 60% decline. Roseate Tern (Sterna dougallii) numbers significantly declined between 1987 and 1993, followed by a significant increase between 1994 and 2000. Current count data for Audubon’s Shearwater (Puffinus l’herminieri) and the Wedge-tailed Shearwater (P. pacificus) are insufficient to establish trends. The maximum annual count of roosting non-breeding frigatebirds (Fregrata spp.) increased steadily throughout the period. The island has internationally important numbers of breeding seabirds (330,000-720,000 pairs per annum), including the largest known colony of Audubon’s Shearwater, the largest colony of the declining Roseate Tern in Seychelles, and the largest known colony of the nominate subspe...

Use of tracking strips and automatic cameras for detecting Critically Endangered Jerdon's coursers Rhinoptilus bitorquatus in scrub jungle in Andhra Pradesh, India

Abstract: Jerdon's courser Rhinoptilus bitorquatus is a nocturnal cursorial bird that is now only known from a small area of scrub jungle in Andhra Pradesh, India. Its population size, distribution and habitat requirements are poorly known because of its elusive habits. We conducted a trial of a survey method that involved deploying an array of 5 m long tracking strips consisting of smoothed fine soil, and checking them for footprints at regular intervals. We developed diagnostic methods for distinguishing the footprints of Jerdon's courser from those of other species. Tracks of Jerdon's courser were obtained on about one strip-night in 30 from areas where the species was known to be present. We suggest a procedure for using tracking strips to survey areas where Jerdon's courser has not yet been detected. The use of tracking strips carries a small risk of misidentification of footprints of other species, especially yellow-wattled lapwing Vanellus malarbaricus, as those of Jerdon's courser, but has the advantage that large areas can be surveyed without the use of expensive equipment or night-time fieldwork. We recommend the use of automatic camera traps to obtain confirmation of records of probable Jerdon's courser footprints.

Habitat associations of the Red-backed Shrike (Lanius collurio) in Carinthia, Austria

Abstract: In 1997 and 1998, we investigated the habitat use of Red-backed Shrikes breeding on farmland in Carinthia, southern Austria. We devised an objective census technique to obtain relative measures of shrike abundance and habitat coverage along 35 1 km transect belts, 60 m in width, positioned randomly throughout an area of 100 1 km squares. Shrike abundance was related to habitat variables by means of general linear models. Bivariate models suggested that Red-backed Shrikes were positively associated with grassland grazed by livestock, fence-lines and scattered trees and shrubs, but negatively associated with arable land and grassland that was not grazed. A model constructed with the help of forward selection indicated that shrike abundance was most strongly associated with a mixture of grazed grassland and scrub. Shrike abundance increased with grazed grassland cover. When the cover of grazed grassland was kept constant, shrike abundance increased with scrub cover up to between 10 % and 15 % cover, and declined thereafter. We tested the validity of the model using data from a further 20 transects, collected in 1998. The number of shrikes predicted under the model was significantly positively correlated with the number of shrikes recorded.

Scots pine growing on forested mires in Abernethy Forest, Strathspey, Scotland

Abstract: Summary A substantial proportion of the Abernethy Forest Reserve has Scots pine (Pinus sylvestris) growing on the surfaces of a variety of mires. The hydrology of the mires has been affected by drainage and peat cutting but this area is unusual in having had a long period of protection from grazing by domestic stock. There are three main types of pine populations found on these mires. Woodland bog comprises predominantly bog vegetation with abundant pine seedlings due to the heavy seed rain from the surrounding woodland. Only a few very small trees survive, which are stunted, heavily diseased and have very low seed production. Wooded bog also comprises predominately bog vegetation but there are scattered mature trees of a moderate height with an open canopy. The trees are fertile and can form uneven aged stands with regeneration. Bog woodland is a predominantly woodland vegetation with tall, dense tree cover on deep peat. The trees are well grown with a dense canopy. A few remnants of bog vegetation remai...

Between‐lake differences in the diet and provisioning behaviour of Black‐throated Divers Gavia arctica breeding in Scotland

Abstract: Surveys at 23 Black-throated Diver breeding lakes in Scotland showed large between-lake differences in the species and size range of potential prey. The study lakes were classified into four types according to the main size-taxa prey classes present. Type 1 lakes lacked small fish, Type 4 lacked salmonids < 300 mm and Types 2 and 3 both had all four of the main prey classes. Diver diet for 30 families at the study lakes was quantified from 7943 prey items seen fed to chicks, and 153 items seen eaten by adults, during 662 h of observations. At all lake types adults mostly ate salmonids of 120–240 mm in length, especially Brown Trout Salmo trutta, and European Eels Anguilla anguilla up to c. 350 mm. The prey eaten by chicks ranged widely, from c. 0.03 g to 300 g, with important implications for feeding behaviour. Young chicks (days 1–8) rejected items greater than 70 mm long. The diet of young chicks consisted mostly of small fish, either Three-spined Sticklebacks Gasterosteus aculeatus (Type 2 lakes) or Minnow Phoxinus phoxinus (Type 3 and Type 4 lakes). At other lakes (Type 1) it consisted mostly of mayfly larvae (Ephemeroptera); invertebrates were the only abundant potential small prey in these lakes. At all lakes the chick diet became more similar to that of adults as chicks grew. Adults provisioning chicks used two foraging strategies. In ‘excursion foraging’, adults hunted away from the chicks and carried prey back for them; in ‘attendance foraging’, the chicks accompanied the foraging adult(s). Excursion foraging was used mostly before day 4 and was strongly and positively correlated with the abundance of fish < 80 mm in length. This behaviour is probably adaptive, but is probably tenable only where small fish are relatively abundant. Young chicks fed mainly on small fish had higher survival rates than those fed on invertebrates.

A preliminary comparison of population estimation by tape response and mark/recapture methods for Storm Petrels Hydrobates pelagicus in two contrasting Scottish colonies

Abstract: The tape response method of population estimation was compared to mark/recapture methods for Storm Petrels Hydrobates pelagicus on two Scottish islands. On Priest Island the du Feu single‐session mark/recapture method gave an estimate not significantly different from the tape response method and was less demanding on personnel. On Eilean Hoan the Jolly‐Seber estimates made in 1998 and 1999 were similar to that obtained from the tape response method in 2001. Jolly‐Seber estimates made in 2000 and 2001 were similar to the du Feu estimate made in 2001, but different from the tape response method. The overall annual survival estimate of 0.87 on Eilean Hoan was identical to the previously published figure and almost the same as the 0.86 calculated from national ringing returns. These initial findings are used to identify problems with the mark/recapture methods and to suggest ways of solving them.

Silent fields: the decline of farmland birds in Europe.

Abstract: Populations of many farmland birds appear to have collapsed across much of Europe. Agricultural intensification is driving populations down over huge areas and represents probably the greatest single threat to the continent's birds. Understanding the problem, however, is only the first step to putting farmland birds back in the countryside. The plight of these once-widespread birds highlights the need for improved monitoring across Europe.