Showing papers by "Royal Society for the Protection of Birds published in 2006"

Why do we still use stepwise modelling in ecology and behaviour

Abstract: 1. The biases and shortcomings of stepwise multiple regression are well established within the statistical literature. However, an examination of papers published in 2004 by three leading ecological and behavioural journals suggested that the use of this technique remains widespread: of 65 papers in which a multiple regression approach was used, 57% of studies used a stepwise procedure. 2. The principal drawbacks of stepwise multiple regression include bias in parameter estimation, inconsistencies among model selection algorithms, an inherent (but often overlooked) problem of multiple hypothesis testing, and an inappropriate focus or reliance on a single best model. We discuss each of these issues with examples. 3. We use a worked example of data on yellowhammer distribution collected over 4 years to highlight the pitfalls of stepwise regression. We show that stepwise regression allows models containing significant predictors to be obtained from each year's data. In spite of the significance of the selected models, they vary substantially between years and suggest patterns that are at odds with those determined by analysing the full, 4-year data set. 4. An information theoretic (IT) analysis of the yellowhammer data set illustrates why the varying outcomes of stepwise analyses arise. In particular, the IT approach identifies large numbers of competing models that could describe the data equally well, showing that no one model should be relied upon for inference.

Assessing the impacts of wind farms on birds

Abstract: The potential effects of the proposed increase in wind energy developments on birds are explored using information from studies of existing wind farms. Evidence of the four main effects, collision, displacement due to disturbance, barrier effects and habitat loss, is presented and discussed. The consequences of such effects may be direct mortality or more subtle changes to condition and breeding success. The requirements for assessing the impact of future developments are summarized, including relevant environmental legislation and appropriate methods for undertaking baseline surveys and post-construction monitoring, with particular emphasis on the rapidly developing area of offshore wind farm assessments. Mitigation measures which have the potential to minimize impacts are also summarized. Finally, recent developments in the monitoring and research of wind energy impacts on birds are outlined and some areas for future work are described.

Predicting the global spread of H5N1 avian influenza.

Abstract: The spread of highly pathogenic H5N1 avian influenza into Asia, Europe, and Africa has resulted in enormous impacts on the poultry industry and presents an important threat to human health. The pathways by which the virus has and will spread between countries have been debated extensively, but have yet to be analyzed comprehensively and quantitatively. We integrated data on phylogenetic relationships of virus isolates, migratory bird movements, and trade in poultry and wild birds to determine the pathway for 52 individual introduction events into countries and predict future spread. We show that 9 of 21 of H5N1 introductions to countries in Asia were most likely through poultry, and 3 of 21 were most likely through migrating birds. In contrast, spread to most (20/23) countries in Europe was most likely through migratory birds. Spread in Africa was likely partly by poultry (2/8 introductions) and partly by migrating birds (3/8). Our analyses predict that H5N1 is more likely to be introduced into the Western Hemisphere through infected poultry and into the mainland United States by subsequent movement of migrating birds from neighboring countries, rather than from eastern Siberia. These results highlight the potential synergism between trade and wild animal movement in the emergence and pandemic spread of pathogens and demonstrate the value of predictive models for disease control.

Habitat connectivity and matrix restoration: the wider implications of agri-environment schemes

Abstract: Summary 1 The spread and intensification of agriculture are recognized as two of the most important global threats to wildlife. There are clear links between agricultural change and declines in biodiversity across a wide range of agricultural systems, and convincing evidence that reversing these changes leads to a recovery in wildlife populations. 2 Nearly 4 billion euros are now paid annually through agri-environment schemes (AES) to farmers in Europe and North America to make environmental improvements to their land. Where appropriately designed and targeted, these schemes have proved successful in reversing declines in farmland wildlife populations. 3 We argue that insights gained from island biogeography and metapopulation theory, and from theoretical and empirical assessments of landscape connectivity suggest that AES may carry substantial wider benefits, which so far have not been considered in the design and deployment of such schemes. ‘Softening’ agricultural land could offset some of the negative impacts on biodiversity of the loss and fragmentation of non-agricultural habitats; could allow species to adapt to climate change; could slow the spread of alien and invasive species; and could contribute positively to the coherence of key biodiversity and protected area networks. Indeed, AES might represent the only viable way to counter these threats. 4 We outline a number of ways in which these wider benefits could be taken account of in the design of AES and suggest a number of characteristics of the species most likely to benefit from them. 5 Synthesis and applications. Agri-environment schemes might bring significant environmental benefits to habitats other than farmland by restoring the agricultural matrix that separates them. Theoretical and empirical research suggests that matrix restoration improves a number of ecosystem functions. Where they are available, AES might therefore represent a viable mechanism for addressing a range of pandemic environmental problems such as global climate change. Little consideration has so far been given to these wider conservation applications in the design, deployment and monitoring of AES.

Census error and the detection of density dependence.

Abstract: 1. Studies aiming to identify the prevalence and nature of density dependence in ecological populations have often used statistical analysis of ecological time-series of population counts. Such time-series are also being used increasingly to parameterize models that may be used in population management. 2. If time-series contain measurement errors, tests that rely on detecting a negative relationship between log population change and population size are biased and prone to spuriously detecting density dependence (Type I error). This is because the measurement error in density for a given year appears in the corresponding change in population density, with equal magnitude but opposite sign. 3. This effect introduces bias that may invalidate comparisons of ecological data with density-independent time-series. Unless census error can be accounted for, time-series may appear to show strongly density-dependent dynamics, even though the density-dependent signal may in reality be weak or absent. 4. We distinguish two forms of census error, both of which have serious consequences for detecting density dependence. 5. First, estimates of population density are based rarely on exact counts, but on samples. Hence there exists sampling error, with the level of error depending on the method employed and the number of replicates on which the population estimate is based. 6. Secondly, the group of organisms measured is often not a truly self-contained population, but part of a wider ecological population, defined in terms of location or behaviour. Consequently, the subpopulation studied may effectively be a sample of the population and spurious density dependence may be detected in the dynamics of a single subpopulation. In this case, density dependence is detected erroneously, even if numbers within the subpopulation are censused without sampling error. 7. In order to illustrate how process variation and measurement error may be distinguished we review data sets (counts of numbers of birds by single observers) for which both census error and long-term variance in population density can be estimated. 8. Tests for density dependence need to obviate the problem that measured population sizes are typically estimates rather than exact counts. It is possible that in some cases it may be possible to test for density dependence in the presence of unknown levels of census error, for example by uncovering nonlinearities in the density response. However, it seems likely that these may lack power compared with analyses that are able to explicitly include census error and we review some recently developed methods.

Changes in bird communities following conversion of lowland forest to oil palm and rubber plantations in southern Thailand

Abstract: This paper describes changes in bird communities following the conversion of lowland forest to commercial oil palm and rubber plantations. Conversion of forest to plantations resulted in a reduction in species richness of at least 60%, with insectivores and frugivores suffering greater losses than more omnivorous species. Of the 128 species recorded across all habitats, 84% were recorded in forest, and 60% were recorded only in that habitat. Of the 16 Globally Threatened or Near-Threatened species recorded in the study, 15 were recorded only in forest. Species occurring in plantations were significantly more widespread in Thailand than species recorded only in forests and had a tendency towards smaller body size. Species richness in plantations was unaffected by plantation age or distance from nearest forest edge, but was significantly greater where undergrowth was allowed to regenerate beneath the crop trees. Bird communities in oil palm and rubber plantations were extremely similar, and there was a strong positive correlation across species in their relative abundance in each plantation type. The results indicate that a high proportion of species formerly present in the region are unable to adapt to conversion of forest to oil palm and rubber plantations, resulting in large losses of bird species and family richness and the replacement of species with restricted ranges and high conservation status by those with extensive ranges and low conservation status. Initiatives that reduce pressure to clear new land for plantations, for example by increasing productivity in existing plantations and improving protected area networks, are likely to be more effective in conserving threatened forest birds than initiatives to improve conditions within plantations, though both should be encouraged.

Potential impacts of climatic change upon geographical distributions of birds

Abstract: Potential climatic changes of the near future have important characteristics that differentiate them from the largest magnitude and most rapid of climatic changes of the Quaternary. These potential climatic changes are thus a cause for considerable concern in terms of their possible impacts upon biodiversity. Birds, in common with other terrestrial organisms, are expected to exhibit one of two general responses to climatic change: they may adapt to the changed conditions without shifting location, or they may show a spatial response, adjusting their geographical distribution in response to the changing climate. The Quaternary geological record provides examples of organisms that responded to the climatic fluctuations of that period in each of these ways, but also indicates that the two are not alternative responses but components of the same overall predominantly spatial response. Species unable to achieve a sufficient response by either or both of these mechanisms will be at risk of extinction; the Quaternary record documents examples of such extinctions. Relationships between the geographical distributions of birds and present climate have been modelled for species breeding in both Europe and Africa. The resulting models have very high goodness-of-fit and provide a basis for assessing the potential impacts of anthropogenic climatic changes upon avian species richness in the two continents. Simulations made for a range of general circulation model projections of late 21st century climate lead to the conclusion that the impacts upon birds are likely to be substantial. The boundaries of many species’ potential geographical distributions are likely to be shifted 1000 km. There is likely to be a general decline in avian species richness, with the mean extent of species’ potential geographical distributions likely to decrease. Species with restricted distributions and specialized species of particular biomes are likely to suffer the greatest impacts. Migrant species are likely to suffer especially large impacts as climatic change alters both their breeding and wintering areas, as well as critical stopover sites, and also potentially increases the distances they must migrate seasonally. Without implementation of new conservation measures, these impacts will be severe and are likely to be exacerbated by land-use change and associated habitat fragmentation. Unless strenuous efforts are made to address the root causes of anthropogenic climatic change, much current effort to conserve biodiversity will be in vain.

Removing the Threat of Diclofenac to Critically Endangered Asian Vultures

Abstract: Veterinary use of the nonsteroidal anti-inflammatory (NSAID) drug diclofenac in South Asia has resulted in the collapse of populations of three vulture species of the genusGyps to the most severe category of global extinction risk. Vultures are exposed to diclofenac when scavenging on livestock treated with the drug shortly before death. Diclofenac causes kidney damage, increased serum uric acid concentrations, visceral gout, and death. Concern about this issue led the Indian Government to announce its intention to ban the veterinary use of diclofenac by September 2005. Implementation of a ban is still in progress late in 2005, and to facilitate this we sought potential alternative NSAIDs by obtaining information from captive bird collections worldwide. We found that the NSAID meloxicam had been administered to 35 captiveGyps vultures with no apparent ill effects. We then undertook a phased programme of safety testing of meloxicam on the African white-backed vultureGyps africanus, which we had previously established to be as susceptible to diclofenac poisoning as the endangered AsianGyps vultures. We estimated the likely maximum level of exposure (MLE) of wild vultures and dosed birds by gavage (oral administration) with increasing quantities of the drug until the likely MLE was exceeded in a sample of 40G. africanus. Subsequently, sixG. africanus were fed tissues from cattle which had been treated with a higher than standard veterinary course of meloxicam prior to death. In the final phase, ten Asian vultures of two of the endangered species(Gyps bengalensis,Gyps indicus) were dosed with meloxicam by gavage; five of them at more than the likely MLE dosage. All meloxicam-treated birds survived all treatments, and none suffered any obvious clinical effects. Serum uric acid concentrations remained within the normal limits throughout, and were significantly lower than those from birds treated with diclofenac in other studies. We conclude that meloxicam is of low toxicity toGyps vultures and that its use in place of diclofenac would reduce vulture mortality substantially in the Indian subcontinent. Meloxicam is already available for veterinary use in India.

A stable isotopic investigation into the causes of decline in a sub‐Antarctic predator, the rockhopper penguin Eudyptes chrysocome

Abstract: The rockhopper penguin (Eudyptes chrysocome) is a conspicuous apex marine predator that has experienced marked population declines throughout most of its circumpolar breeding distribution. The cause(s) for the declines remain elusive, but the relatively large spatio-temporal scale over which population decreases have occurred implies that ecosystem-scale, at-sea factors are likely to be involved. We employ stable isotope analyses of carbon ( 13 C/ 12 C, expressed as d 13 C) and nitrogen ( 15 N/ 14 N, d 15 N) in timeseries of rockhopper penguin feather samples, dating back to 1861, in order to reconstruct the species’ ecological history. Specifically, we examine whether rockhopper penguin population decline has been associated with a shift towards lower primary productivity in the ecosystem in which they feed, or with a shift to a diet of lower trophic status and lower quality, and we use long-term temperature records to evaluate whether shifts in isotope ratios are associated with annual variations in sea surface temperature. Having controlled temporally for the Suess Effect and for increases in CO2 concentrations in seawater, we found that overall, d 13 C signatures decreased significantly over time in rockhopper penguins from seven breeding sites, supporting the hypothesis that decreases in primary productivity, and hence, carrying capacity, for which d 13 C signature is a proxy, have been associated with the decline of penguin populations. There was some evidence of a long-term decline in d 15 N at some sites, and strong evidence that d 15 N signatures were negatively related to sea surface temperatures across sites, indicative of a shift in diet to prey of lower trophic status over time and in warm years. However, a siteby-site analysis revealed divergent isotopic trends among sites: five of seven sites exhibited significant temporal or temperature-related trends in isotope signatures. This study highlights the utility of stable isotope analyses when applied over relatively long timescales to apex predators.

Collapse of Asian vulture populations: risk of mortality from residues of the veterinary drug diclofenac in carcasses of treated cattle

Abstract: Summary 1. The populations of three species of South Asian vultures ( Gyps bengalensis , Gyps indicus and Gyps tenuirostris ) have declined rapidly within the last decade and all are now critically endangered. Veterinary use of the non-steroidal anti-inflammatory drug diclofenac appears to be a major cause of the declines. Vultures are likely to be exposed to the drug when they feed on carcasses of livestock that were treated with diclofenac before death. 2. We measured the concentration of diclofenac in the tissues of treated Indian humped and European cattle ( Bos indicus and Bos taurus ) in relation to the interval between dosing and death. We used a dose‐response model to assess the risk posed to wild vultures if they feed on carcasses of treated livestock. 3. Diclofenac concentrations in fat, intestine, kidney and liver were considerably higher than those in muscle, but concentrations in the first four tissues initially depleted more rapidly (half-life 6‐8 h) with time since the last injection of the drug, compared with muscle (halflife 15 h). Depletion rates became much slower in all tissues 25‐98 h after the last injection. 4. Diclofenac concentration, averaged across the carcass, was enough to cause appreciable mortality (> 10% of birds per meal) if oriental white-backed vultures G. bengalensis were to take a large meal from the carcass of an animal that was given its last dose of the drug within a day or two before death. Vultures that feed selectively on tissues with high concentrations of the drug, such as kidney, liver and intestine, would be exposed to a higher risk and for longer after dosing. 5. Synthesis and applications. The tissues of cattle treated with diclofenac are a hazard to wild vultures that feed on an animal that dies within a few days after treatment. Intestine, kidney and liver have the highest diclofenac concentrations, but the concentration averaged across all the edible tissues of the carcass is also hazardous. Withdrawal of diclofenac from veterinary use on animals whose carcasses may become available to scavenging vultures is recommended. In ex situ and in situ conservation projects, vultures should be fed on carcasses of animals that are known not to have been treated with diclofenac in the week before death.

Rapid population declines of Egyptian vulture (Neophron percnopterus) and red‐headed vulture (Sarcogyps calvus) in India

Abstract: Since the early 1990s, large and rapid population declines of three species of vulture (Gyps spp.) endemic to south Asia have occurred on the Indian subcontinent and have led to these species being listed by IUCN as critically endangered. Evidence of rates of population decline, cause of death and toxicity is consistent with these declines being caused by poisoning of vultures through the ingestion of tissues from livestock treated with the anti-inflammatory drug diclofenac. In this paper, analysis of repeated surveys in and near protected areas widely spread across India shows that populations of two other vulture species, Egyptian vulture Neophron percnopterus and red-headed vulture Sarcogyps calvus, have also declined markedly and rapidly, but probably with a later onset than Gyps vultures in the same region. The declines continued at least up to 2003. It is recommended that these two species are considered for inclusion in the IUCN Red List and for urgent remedial conservation measures. Research is needed to determine whether or not the principal cause of these declines is diclofenac poisoning and to establish population trends in other scavenging birds in the Indian subcontinent.

The contribution of invertebrate taxa to moorland bird diets and the potential implications of land‐use management

Abstract: We reviewed the literature to determine the importance of invertebrates for moorland-breeding birds and considered our findings with respect to the conservation of such species in the UK. The diets of many moorland birds consist predominantly of invertebrates, with a wide range of taxa recorded in the diets of moorland birds during the breeding season. Relatively few taxa (Arachnida, Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera and Oligochaeta) were widely taken, with Diptera and Coleoptera being the most important. Among these latter two insect orders, Carabidae, Curculionidae, Elateridae and Tipulidae were the most important families. Comparisons of the diets of bird families, treated separately according to whether data were derived from adults or chicks, showed that waders take more interstitial invertebrates than passerines, which themselves take more foliage invertebrates. Although we lack detailed experimental data with which to demonstrate the direct effect of particular moorland management prescriptions on some of these key invertebrate taxa for breeding birds, available data suggest that management regimes that create a mosaic of habitats are likely to be most beneficial. In particular, heterogeneity in vegetation structure and species composition, and the presence of wet flushes associated with the synchronized spring emergence of adults of certain insect species, are likely to increase invertebrate food resources for birds.

Extinction Risk and Conservation Priorities

Abstract: Threatened species lists based on extinction risk are becoming increasingly influential for setting conservation priorities at regional, national, and local levels. Risk assessment, however, is a scientific endeavor, whereas priority setting is a societal process, and they should not be confounded

Weed seed resources for birds in fields with contrasting conventional and genetically modified herbicide-tolerant crops.

Abstract: The UK Farm Scale Evaluations (FSEs) have shown that the use of broad spectrum herbicides on genetically modified herbicide-tolerant (GMHT) crops can have dramatic effects on weed seed production compared to management of conventional varieties. Here, we use FSE data and information on bird diets to determine how GMHT cropping might change the food resources available to farmland birds. More than 60 fields of each of four crops, spring- and winter-sown oilseed rape, beet and maize, were split, one half being sown with a conventional variety, the other with a GMHT variety. Seed rain from weeds known to be important in the diets of 17 granivorous farmland bird species was measured under the two treatments. In beet and spring oilseed rape, rain of weed seeds important in the diets of 16 bird species was significantly reduced in GMHT compared to conventional halves; for no species did it increase. In winter oilseed rape, rain of weed seeds important in the diets of 10 species was significantly reduced in GMHT halves; for only one species did it increase significantly. By contrast, in maize, rain of weed seeds important in the diets of seven species was significantly greater in GMHT halves; for no species was it reduced. Treatment effects for the total weed seed energy available to each bird species were very similar to those for seed rain alone. Measuring the effects on individual bird species was outside the scope of this study. Despite this, these results suggest that should beet, spring and winter rape crops in the UK be largely replaced by GMHT varieties and managed as in the FSEs, this would markedly reduce important food resources for farmland birds, many of which declined during the last quarter of the twentieth century. By contrast, GMHT maize would be beneficial to farmland birds.

Costing eradications of alien mammals from islands

Abstract: The ability to estimate costs of alien species eradications is essential for a rigorous assessment of priorities for island restoration. Using a global data file from 41 islands, mostly gleaned from the ‘grey’ literature, we show that the cost of vertebrate eradications can be satisfactorily predicted if island area and species to be eradicated are known. About 72% of the variation in cost can be explained by island area, whereas, for a given area, rodent eradications are 1.7–3.0 times more expensive than ungulate eradications. Costs per hectare decrease with island size. Restricting the analysis to roughly half the data set, the relatively homogeneous half concerned with New Zealand islands, we identify two further influences on cost: date of eradication and distance to the main airport (an indicator of remoteness). For a given area, costs have declined over time but increase with island remoteness. This information therefore provides conservation planners with a robust, if preliminary, estimate of the cost of any proposed eradication programme.

The role of forest maturation in causing the decline of Black Grouse Tetrao tetrix

Abstract: Black Grouse Tetrao tetrix in Britain have declined through the 20th century, and most birds are now in Scotland. Many causes for this decline have been suggested, notably agricultural intensification, increased grazing levels and moorland afforestation. We examine habitat correlates of Black Grouse distribution and population change from a 700-km2 area in the core of the Scottish range, where the numbers of lekking male Black Grouse declined by an estimated 70% to 270 between 1990 and 2002. Habitat data were derived from satellite imagery, in combination with map and field-collected data. Lek occurrence, lek size and changes in lek size were all correlated with forest structure, either positively with the amount of pre-thicket forest cover, or negatively with closed canopy cover. Additional effects of the cover of grass moor and dry heath suggest that Black Grouse are most likely to occur where moorland comprises Heather Calluna vulgaris and grass mosaics. Analysis of the change in Black Grouse abundance within 1.5 km of discrete forest blocks suggests that forest maturation, which has been the dominant habitat change during the course of the study, alone accounts for 58–78% of the decline. Given the close association of Black Grouse and the occurrence of woodland (and particularly conifer plantation) throughout much of their British range, these findings can be used to inform the design of management schemes for the recovery of Black Grouse.

Mitigation of seabird mortality on factory trawlers: trials of three devices to reduce warp cable strikes

Abstract: Experimental trials were conducted onboard a stern trawler to identify the relative efficacy of three emerging mitigation measures (tori lines, warp scarer and Brady baffler) designed to reduce seabird mortality caused by warp cable strikes. The use of mitigation measures was clearly shown to substantially reduce seabird mortalities from collisions between seabirds and warp cables. Based on an established significant relationship between contact rate and seabird mortality, when using contact rate as an index of mortality there was a clear performance hierarchy of the three measures. Tori lines and the warp scarer were significantly more effective at reducing contacts than the Brady Baffler, whilst tori lines represent a smaller, but still significant, improvement on the warp scarer. While further testing would be required under local environmental and operational conditions, our findings are likely to have application for many trawl fisheries around the world.

Climate change may account for the decline in British ring ouzels Turdus torquatus.

Abstract: Summary 1Climate change is already affecting biodiversity, but the number of species for which reliable models relate weather and climate to demographic parameters is low. 2We modelled the effect of temperature and rainfall on the breeding success and territory occupancy of ring ouzels Turdus torquatus (L.) in northern Britain, using data from a range of study areas, including one where there was a long-term decline in ring ouzel abundance. 3Timing of breeding was significantly related to meteorological variables affecting birds in the early spring, though there was no evidence that laying dates had advanced. Breeding success was not significantly related to weather variables; instead, over 90% of annual variation in this parameter could be explained by density dependence. 4Annual change in territory occupancy was linked to rainfall and temperature the preceding summer, after the main breeding season and to rainfall in the wintering grounds 24 months previously, coincident with the period of juniper Juniperus sp. (L.) flowering. High temperature in late summer, intermediate levels of late summer rainfall, and high spring rainfall in Morocco 24 months previously all had negative impacts on territory occupancy the following year. 5All three weather variables have changed over recent decades, with a significant increase in summer temperature, a significant decrease in summer rainfall, and a nonsignificant decline in Moroccan spring rainfall. A model based on these trends alone predicted an annual decline in occupancy of 3·6% (compared with an observed decline of 1·2%), and suggested that increased summer temperatures may underlie declines in the British ring ouzel population. 6Changes in summer temperature after the main breeding period could affect the survival rates of adult and/or juvenile birds. An improved understanding of the post-breeding ecology of ring ouzels is required to elucidate the mechanisms and causes of this relationship. Such knowledge might allow management aimed at buffering the impacts of climate change on ring ouzels.

Point transect sampling with traps or lures

Abstract: Summary 1 The ability to monitor abundance of animal populations is becoming increasingly important, in light of growing concerns over the loss of biodiversity through anthropogenic changes. A widely used tool for such monitoring is distance sampling, in which distances of detected animals from a line or point are modelled, to estimate detectability and hence abundance. Nevertheless, many species still prove problematic to survey. We have developed two extensions to point transect sampling that potentially allow abundance to be estimated for a number of species from diverse taxa for which good survey methods have not previously been available. 2 For each method, the primary survey comprises a random sample of points, or more usually a systematic grid of points, through the region of interest. Animals are lured to a point, or trapped at a point, and the number of animals observed at each point is recorded. A separate study is conducted on a subset of animals, to record whether they respond to the lure or enter the trap, for a range of known distances from the point. These data are used to estimate the probability that an animal will respond to the lure or enter the trap, as a function of its initial distance from the point. This allows the counts to be converted to an estimate of abundance in the survey region. 3 We illustrated the methods using a lure survey of crossbills Loxia spp. in coniferous woodland in Scotland. 4 Synthesis and applications. Two extensions of point transect sampling that use the same statistical methodology, lure point transects and trapping point transects, have been developed. Lure point transects extend the applicability of distance sampling to species that can be lured to a point, while trapping point transects potentially allow abundance estimation of species that can be trapped, with fewer resources needed than trapping webs and conventional mark–recapture methods.

Genetic isolation and divergence in sexual traits: evidence for the northern rockhopper penguin Eudyptes moseleyi being a sibling species

Abstract: The taxonomic status of populations of rockhopper penguins (Eudyptes chrysocome) is still enigmatic. Northern populations differ from southern ones in breeding phenology, song characteristics and head ornaments used as mating signals. We conducted a molecular analysis using mitochondrial DNA sequencing to test if there is a gene flow barrier between northern (subtropical) populations and southern (subantarctic) populations in relation to the Subtropical Convergence, a major ecological boundary for marine organisms. Sequences of the control region and the ND2 gene were analysed in rockhopper penguins and in the macaroni penguin (Eudyptes chrysolophus), a closely related species. Genetic distances and phylogenetic analyses showed a clear split into three clades, two rockhopper clades and the macaroni penguin. Moreover, Theta(ST) and gene flow estimates also suggested genetic structuring within the northern rockhoppers. Our results add further support to the notion that the two rockhopper penguin taxa, often considered as two subspecies, can be recognized as two species E. chrysocome and E. moseleyi. The divergence in mating signals found between these two taxa seems to have occurred recently and relatively rapidly. Thus, the behavioural changes may have been enough to isolate these taxa without the need for morphological differentiation. The findings have important conservational implications, since E. moseleyi is far less abundant than E. chrysocome, but more populations may warrant an uplisting to endangered status if full species status should be recognized for more subpopulations.

How robust are Palearctic migrants to habitat loss and degradation in the Sahel

Abstract: The Sahel region of West Africa is an important wintering ground for Palearctic migrants. It is, however, undergoing significant anthropogenic degradation that is likely to reduce its value in this regard. Despite there being evidence that the populations of several Palearctic species may be determined by conditions on their Sahelian wintering grounds, there are almost no baseline data on their habitat use there and so the effects that habitat change might have on their future density and distribution cannot be determined. This study measured which habitat variables were associated with the presence of Common Whitethroat Sylvia communis, Lesser Whitethroat S. curruca and Subalpine Warbler S. cantillans by carrying out point counts and habitat measurements at 1861 points at 16 sites in northern Nigeria during the winters of 2001 and 2002. Common Whitethroats were most common at intermediate tree heights and densities of Salvadora persica (with this effect strongest in the pre-migratory period), and increased as Balanites aegyptiaca density increased initially, although this effect levelled off at higher Balanites densities. Subalpine Warblers were most common at intermediate tree heights and Balanites densities, increased as Acacia and Salvadora density increased, decreased with tree density and were least common at intermediate shrub densities. Lesser Whitethroats were most common at intermediate tree heights, Acacia and Salvadora densities, increased with Balanites density, and decreased with tree density and diversity. The shallow slopes of the significant relationships found between Palearctic warbler species and habitat parameters suggest that the group may be robust to habitat degradation, with densities remaining relatively constant across a wide range of habitat types. Common Whitethroats, in particular, appear to be able to survive in extremely degraded habitats, yet may be vulnerable to the disappearance of Salvadora, the fruit of which may allow pre-migratory fattening.

The effects of edge, fragment size and degree of isolation on avian species richness in highly fragmented forest in West Africa

Abstract: Almost nothing is known of the effects of forest fragmentation on bird diversity within the heavily degraded and fragmented forest remnants in West Africa. We examined the effects of edge, fragment size and isolation on bird species richness in southwestern Nigeria where forest fragmentation is pronounced. In total, 122 km of line transects were used to survey birds and vegetation within 45 forest patches between January 2000 and March 2002: 197 species were recorded. Avian species number and total counts in forest patches were unrelated to fragment area (within the observed range of 14–445 ha), but were negatively influenced by degree of isolation and increasing distance from the edge. As the total area of forested land within 15 km of a patch fell from 4 to 0%, so 21% of species were lost. In total, six and zero species (of 154 recorded more than once) were consistently recorded in the larger and smaller forest fragments, respectively, and four and two bird species were consistently recorded in unisolated and isolated forest fragments, respectively, suggesting that the addition of ‘edge’ species did not compensate for loss of species sensitive to fragmentation. Diversity index was not affected by either fragment area or degree of isolation, but decreased with distance from the edge. When individual species counts were considered, 68% of species (n = 62) showed no significant effect of distance to edge. Of those 20 species which showed an effect, 12 were less common close to the edge. Most species (65%) did not respond significantly to increasing isolation but of those 22 species that did, 20 were less common in more isolated fragments. Ninety-seven per cent of species showed no significant response to area. As avian diversity and species composition, but not species number, were apparently insensitive to forest fragmentation, our findings suggest that fragmentation reduces the probability of occurrence of a wide range of West African bird species, rather than a subset of fragmentation-sensitive species. The greater apparent sensitivity of present-day West African forest bird communities to fragmentation rather than patch size might reflect previous extinctions of area-sensitive species. Minimizing further forest fragmentation might be the most effective means of conserving avian diversity in current West African landscapes where most remaining forest patches are small (i.e. < 500 ha).

Using daily ration models and stable isotope analysis to predict biomass depletion by herbivores

Abstract: Summary 1 Food availability is one of the major factors governing the distribution of animals. Because animal numbers can in turn regulate the availability of food, the relationship between the two can be described in terms of resource depletion, which can be difficult to quantify. 2 We present a novel method utilizing multisource stable isotope mixing models and a daily ration approach to predict the depletion of seagrass (Zostera spp.) by grazing light-bellied Brent geese Branta bernicla hrota at Strangford Lough, Northern Ireland. 3 The model successfully predicted the depletion of Zostera spp. over the whole Lough compared with empirically derived estimates of biomass. Further, the model was able to predict biomass depletion over 2 years with different population sizes. 4 The predicted quantities of Zostera consumed were not in agreement with previous studies, being considerably higher, but this may be explained in terms of the lower energetic value of Zostera at Strangford Lough compared with other sites. 5 When reparameterized with energetic values from previous studies, the model predictions for Zostera consumption were comparable with estimates derived by standard techniques. 6 Synthesis and applications. This approach offers a novel, efficient and widely applicable method to investigate the relationship between consumers and their food sources. It may have application in deriving site carrying capacities and in quantifying agricultural damage by consumers.