The effects of persecution on age of breeding and territory occupation in golden eagles in Scotland

Several studies have documented negative effects of persecution by humans on the population dynamics of large birds of prey. Several areas have seen a reduction in persecution in modern times, but the demography of large raptors still makes these birds vulnerable to such effects. In a GIS analysis, utilising data collected during two national censuses of the golden eagle Aquila chrysaetos in Scotland and contemporary data on the distribution of poisoning incidents (a common method of raptor persecution in Scotland), we show that persecution was associated with a reduction in the age of first breeding, territory vacancies, and the use of territories by non-breeding immatures. Persecution was therefore reducing adult survival and distribution and was probably creating ecological traps that attract mobile immatures, increasing subadult mortality in birds that may originate from persecution-free areas. Mapping a form of land management unique to moors managed for red grouse Lagopus lagopus scoticus shooting, where most poisoning occurs, we also show similar associations between golden eagle demography and grouse moor management. As such, persecution may be having a major impact on the golden eagle population of Scotland, since it occurs over a wide area and at least in some areas has continued unchecked over many decades.     

Spatial association as an indicator of the potential for future interactions between wind energy developments and golden eagles Aquila chrysaetos in Scotland

Despite their environmental benefits in generating electricity without emission of ‘greenhouse’ gases, wind farms have attracted controversy with regard to their impacts on birds, especially golden eagles Aquila chrysaetos. Evidence from USA studies suggest eagle fatalities through collision with turbines may be the main potential impact whereas for breeding eagles in Scotland, displacement from wind farm areas (indirect habitat loss) may be the primary impact. In this study, we examined the co-occurrence potential for golden eagles and wind farms in Scotland by documenting the spatial association between wind farm proposals and breeding eagle territories and areas potentially suitable for non-breeding eagles. Although there were records for over 500 wind farm proposals at various stages of development, relatively few coincided with eagle territories (ca. 4% of territories had a proposal within 3 km of territory centre). Similarly, only 2% of habitat predicted to be suitable for non-breeding eagles overlapped with proposed or installed wind farm areas. Moreover, estimates of the potential for electricity generation from all wind farm proposals, with respect to government targets for renewable energy supplies, suggested most proposals were unlikely to be constructed. We conclude that in comparison with other constraints on Scotland’s golden eagles, notably persecution, wind farms should not represent a serious concern if best practice in planning their location and minimising their impact are maintained. Potential future regional pressures on breeding eagles from wind farms are highlighted, however, and uncertainty of impact with respect to displacement or collision fatalities requires continued scrutiny.     

Modelling the effects of persecution on the population dynamics of golden eagles in Scotland

We used observations of the age structure and breeding productivity of the Scottish population of golden eagles Aquila chrysaetos together with the classic theory of population dynamics to derive current `unmanipulated' estimates of life history parameters. We then used regional differences in age structure associated with differences in persecution intensity to derive estimates of prospective `persecution-free' life history parameters. The different parameter combinations were entered into a population model to simulate their effects on the number of occupied territories over time. Most simulations suggested that with unmanipulated demographic parameters the population should decline. The disparity between these predictions and the observed apparent stability in occupied territories was ascribed to the buffering effect of a lowering in age of breeding in areas where persecution is most intense and that more favourable parameter estimates within the estimated limits may be more realistic. The results indicated, nevertheless, that currently the population is vulnerable to decline as also suggested by the apparent lack of adults to occupy vacant territories. In the absence of the estimated 3-5% annual adult mortality through persecution, modelling suggested the population would increase. Removing estimated effects of persecution on reproductive rate and preadult survival were on their own insufficient to reverse the declines predicted from unmanipulated parameters, although the effect of persecution on preadult survival may be more severe than we estimated. In the absence of persecution we conclude that the population could expand to fill currently vacant but apparently suitable habitat and have a more secure long-term status.     

A nine-year study of successful breeding in a Bonelli’s eagle population in southeast Spain: a basis for conservation

We analyse the factors influencing breeding success in a healthy population of Bonelli’s eagle (Hieraaetus fasciatus) from south-east Spain, a raptor that has suffered a serious decline in Europe. Between 18 and 33 pairs were annually monitored during the period 1994-2002. Several factors that may affect four breeding parameters were studied, namely human presence, vegetation, relief, climatic factors, intra- and inter-specific relationships, diet, prey abundance, nest building, adult mortality and age of reproduction. A consistently high breeding success was registered during the study period (productivity=1.43, SD=0.11), which was probably the result of high adult survival, adequate prey availability and mild weather conditions. However, a certain vulnerability to the presence of golden eagles (Aquila chrysaetos) and to human disturbance was observed. One interesting result was the reduced survival of young chicks on north-facing cliffs owing to colder conditions, which may partially explain the decline of the Bonelli’s eagle populations along its European distribution limits. We discuss the role of this healthy subpopulation in an Iberian metapopulation context, and propose that the potential interference of golden eagles should be taken into account when designing management strategies for Bonelli’s eagles. Finally, we pinpoint some conservation priorities and the importance of reducing the main causes of adult mortality (i.e. shooting and electrocution) to assure successful reproduction and survival of this species.     

Variations in the age of mates as an early warning signal of changes in population trends? The case of Bonelli's eagle in Andalusia

Methods to evaluate population trends have recently received particular attention because of the decreasing patterns shown by several species since the nineteenth century. We have studied demographic traits of the Bonelli's eagle (Hieraaetus fasciatus) population of Andalusia (southern Spain) for 20 years (1980-2000). This species is endangered and is suffering a rapid decline in most of its distribution range. Although our study population has remained stable for the last 10 years, both age at first breeding and productivity have decreased during the last 5 years. We propose that age at first breeding could be used as a potential early warning signal to detect possible future changes in population trends of long-lived species with deferred maturation age. In particular, in this species spatial variation in demographic traits could help to detect whether unnatural events such as shooting are decreasing age at first breeding and productivity. If occupation of territories by non-adults is caused by human persecution, conservation efforts in the particular case of Bonelli's eagle have to be directed to protect those breeding territories where an increase in the percentage of pairs containing at least one non-adult individual would be detected.     

Regional conservation priorities for a large predator: golden eagles (Aquila chrysaetos) in the Alpine range

We compared the density of golden eagles (Aquila chrysaetos) and their nest dispersion, productivity and diet in Alpine and pre-Alpine areas. The comparison was made at two spatial scales: (1) at the territory level within two contiguous populations, and (2) at the population level, using published data for 22 populations scattered across four countries (France, Switzerland, Germany and Italy). Availability of golden eagle's main prey species was higher in Alpine than in pre-Alpine regions. The potential foraging ranges of pairs of eagles in the pre-Alps had larger amounts of woodland and lower amounts of suitable foraging habitat than those of Alpine pairs. At both spatial scales, density and productivity were lower in the pre-Alps. Also, pre-Alpine populations were characterised by a lower percentage of main prey species in the diet, which was significantly correlated with productivity, and by a higher breadth of diet, which was negatively correlated with density. Overall, higher prey availability and habitat suitability in the Alps resulted in higher density and breeding success, in a manner compatible with theoretical metapopulation models. We suggest that priority be given to conservation of eagle populations in high quality Alpine habitat, and that conservation action be carried out by a mixture of site-protection measures and conservation of the wider environment.     

Rabbits as a keystone species in southern Europe

A keystone species is one that is crucial in maintaining the organization and diversity of their ecological communities. We tested the idea that rabbits act as a keystone species in southern Europe by exploring relationships between rabbit abundance and the abundance and diversity of raptor species. At 20 sites in southern Spain we assessed rabbit abundance through counts of animals along transects and assessed the number of raptor individuals and species through watches from vantage points. In a further 120 locations we also derived an index of rabbit abundance, from pellets and compared this to the presence or absence of the critically endangered Spanish imperial eagle. Rabbit abundance was positively associated with the number of observations of raptors, the number of raptor species and the number of species of conservation concern. Sites with the most rabbits had higher conservation value. Moreover, the presence of Spanish imperial eagle was strongly associated with sites where rabbits were at high density. We conclude that rabbits do act as a keystone species and we suggest that conservation efforts should focus on improving the status of this small-game species in southern Europe.     

Adaptive range selection by golden eagles in a changing landscape: A multiple modelling approach

Land abandonment is causing considerable woodland expansion in many mountainous areas of Europe, with potential repercussions on conservation-sensitive species typical of open habitats. We examined the potential impact of such changes on an alpine golden eagle population, by estimating the ranges potentially used by the eagles for foraging through different techniques (concentric circles of different radii and a tessellation-method based on telemetry data). Compared to randomly located territories, eagles selected ranges farther away from conspecifics, characterised by a rugged topography and rich in main prey species and in open habitats favoured by their main prey species, such as grassland, shrubs, xerophytic vegetation and rocky outcrops. Similarly, nest spacing and breeding success were related to the availability of optimal foraging habitats, also favoured by the main prey species of the eagles. Even though woodland-variables did not enter any of the stepwise models, eagles were dependent on grassland habitats, currently lost to woodland at a rate of about 0.5-1% per year, and on shrub vegetation rapidly evolving into woodland, which accounted on average for almost 10% of the eagle ranges. Long-term loss of such habitat may imply up to a 66% woodland increase for some eagle ranges. Given the complexity of the uncovered relationships and difficulty to make firm predictions, subsidies to halt the abandonment of traditional agro-pastoral practices seem urgently needed.     

The effects of land use and climate on red kite distribution in the Iberian peninsula

The main breeding populations of the red kite (Milvus milvus L.), have been declining in the Iberian peninsula during the last decade. However, there is a lack of regional assessments of habitat suitability that identifies limiting ecological factors for the species and areas with conservation problems. In this work we present a regional model for the distribution and abundance of breeding red kites in the Iberian peninsula. The occurrence and estimated abundance in 100 km² UTM squares resulting from road censuses were modelled with broad-scale explanatory variables obtained from satellite imagery, thematic digital cartography, climatic data and spatial coordinates. The occurrence model incorporated mainly climatic variables and had a good discrimination ability, while the abundance model incorporated mainly land-use variables and had a lower explanatory power (r²=0.14). The predictions somewhat overestimated the results of the censuses, and this agrees with the decline of population size and range observed for this species in the Iberian peninsula. These models are relevant in the conservation of the species: first, they suggest the limiting factors for red kite in the Iberian peninsula, and, second, they generate predictive maps pointing out both areas in which conservation problems may be acute (suitable locations that are unoccupied), and areas where no data is available but the red kite is likely to be present (thus guiding further survey and research).     

Prey density, prey detectability and food habits: the case of Bonelli’s eagle and the conservation measures

In the diet of raptors the presence of prey-species is influenced by their abundance and the ground-level vegetation in territories, this situation being analysed for the Bonelli’s eagle (Hieraaetus fasciatus) in south-eastern Spain. First, the minimum number of prey-items for the reliability of results was tested, obtaining between 15 and 30 prey-items depending of pair. Second, differences in prey frequency and productivity among pairs was analysed, finding an interpair shift in both variables, but there was no relationship between the frequency of prey-species in the diet and productivity. Third, it was found that the percentage of European wild rabbit in the diet was less correlated with its abundance in territories than with the surface of open land in the same. This suggests that accessibility to rabbits would be more important for the Bonelli’s eagle that the absolute abundance of this prey type. Thus, open land is the single variable selected by a multiple multiple-regression analysis explaining the frequency of rabbits in this raptor’s diet. Birds as prey complemented the diet when open-land scarcity in the territories implies low rabbit detectability and consumption. Conservation measures proposed concerning the increase of prey availability in this declining population should consider both the absolute prey density and prey detectability, avoiding extensive reforestation in territories and favouring vegetation structure suitable for prey detection by eagles.     

Correlates of abundance and breeding success in the globally threatened Hinde's babbler (Turdoides hindei) and its congener, northern pied babbler (T. hypoleucus)

We investigated the relationship between habitat quality, abundance, group size and breeding success in the threatened Kenyan endemic Hinde's babbler (Turdoides hindei; Family Timaliidae), a co-operative breeder mainly associated with riverine thickets in cultivated areas. At two intensively cultivated sites, significantly more Hinde's babbler groups occurred in areas retaining at least 3% thicket cover, while breeding outcome improved where cover exceeded 9%. Despite previous concerns over low breeding success, the percentage of young birds present (17%, n=424 birds aged) was similar to that of a sympatric congener, the northern pied babbler (T. hypoleucus) (12%, n=162), and comparable with that of two other African congeners. Although breeding outcome was positively correlated with adult group size, there was no evidence that larger groups monopolised more favourable habitat or defended larger territories. Group density showed a positive, non-linear relationship with adjacent cover, levelling out where this exceeded 15-20%. Our findings suggest that even a modest increase in thicket cover may significantly raise the density and productivity of Hinde's babblers at these sites.     

Human attitudes towards wolves, a matter of distance

The objective of this study was to test the hypothesis that distance is an important factor affecting attitudes towards wolves, i.e. people living far from wolf territories have more positive attitudes towards wolf conservation than those living within or close to wolf territories. We used multiple regression (an ordered probit model) with both socio-economic variables and information about the respondents’ distance to the nearest wolf territory. We found that favourable attitudes towards wolf conservation were positively associated with distance to the nearest wolf territory. The variable distance to the nearest wolf territory affected attitudes just as much as the variables of membership of nature conservation organisations, being a hunter, owning livestock, or owning a hunting dog. This was true even on the micro-level, i.e. people living in wolf territories had a more negative attitude towards conservation of wolves than people living just outside. Furthermore, we suggest that attitudes towards wolves are more likely a result of indirect experience than direct experience of wolf presence. Our findings are important when interpreting studies of human attitudes towards conservation of controversial species in general and large carnivores in particular, and should be used when designing future surveys of human attitudes towards conservation and management initiatives.     

The evaluation of key sites for breeding waders in lowland Scotland

This study considers the selection of sites based on the densities of breeding waders that would be considered to be distributed widely across common habitats in Scotland: so-called ‘wider countryside’ species. Five methods to provide a hierarchical classification of sites are assessed. Fifty percent of the populations of redshank (Tringa totanus) and snipe (Gallinago gallinago) occur on just 2 and 4.5% of Scottish lowlands, respectively, yet neither are suitably protected by conservation measures and both would benefit from a carefully targeted approach to their conservation. Three species, lapwing (Vanellus vanellus), curlew (Numenius arquata) and oystercatcher (Haematopus ostralegus) are more appropriately considered to be dispersed species. We propose that, if the density of a breeding wader on a site exceeds the threshold level predicted for the top 1% of Scottish lowland for that species, and if the area of the site exceeds 1 km² then that site be considered to be a key site for farmland waders. The minimum density (in pairs km⁻²) must exceed 16.8 for lapwing, 10.1 for oystercatcher, 6.1 for snipe, 7.5 for curlew or 3.6 for redshank.     

Massive immigration balances high anthropogenic mortality in a stable eagle owl population: Lessons for conservation

The modern anthropized landscape is a major source of hazards for large animals such as raptors. Collisions with cables, vehicles and trains, as well as electrocution cause casualties, which may negatively impact populations. Yet, demographic studies of that impact remain scarce, which is an impediment to evidence-based conservation action. We studied the dynamics of an eagle owl (Bubo bubo) population in the northwestern Alps (Switzerland). We estimated, firstly, its demographic parameters using a Bayesian integrated population model; secondly, the frequency of different types of casualty through radio-tracking. Thirdly, we investigated the effects of reductions of human-related mortality on population trends. The breeding population was small but remained fairly stable during 20 years, suggesting that it was apparently in a good shape. However, survival probabilities of all age classes were very low (?0.61), productivity fairly good (0.93), and immigration very high (1.6 females per pair and year), indicating that the population operated as a sink. Half of the mortality was caused by infrastructure, with electrocution accounting for 24% of all fatalities. The elimination of electrocution would result in a strong population increase (17% annually). Under that scenario, immigration rate could decline by 60% and the population would still remain stable. Given that the supply of recruits from elsewhere is likely to continue, we can expect a rapid local population recovery if dangerous electric pylons are mitigated systematically. Our study demonstrates that detailed demographic analyses are necessary to diagnose problems occurring in populations and to identify efficient conservation actions.     

Alarming houbara bustard population trends in Asia

Relative abundance and density estimates of Asian houbara were assessed during the breeding season in two breeding grounds of migrant populations (China and south Kazakhstan) and in one breeding ground of a resident population (Oman), between 1998 and 2002. For the study period, the relative abundance was from 0.004 to 0.06 individual per km driven and density estimates varied from 0.01 to 0.2 houbara per km². Relative abundance and density of houbara declined by 63% and 69%, respectively in China, by 60% and 49%, respectively in Kazakhstan and by 50% and 75%, respectively in Oman. Overall, an average of 27-30% annual decline in both relative abundance and density was observed for the three regions. Despite being legally a strictly protected species in China, Kazakhstan and Oman, houbara are heavily hunted and poached on all their migration routes and wintering grounds. The current levels of hunting and poaching are not sustainable and without the immediate agreement and implementation of international conservation measures, the Asian houbara may face extinction in the wild in the foreseeable future.     

The effect of Mediterranean dehesa management on lizard distribution and conservation

Management of dehesas (i.e. oak woodland pastures) creates a patchwork of sectors that differ in their structure and composition of understorey vegetation. We analysed whether different management techniques affect the populations of several species of lizards (Podarcis hispanica, Psammodromus algirus, Psammodromus hispanicus, Acanthodactylus erythrurus, and Lacerta lepida). Multivariate analyses showed that lizards preferentially used forested areas with scrub while they avoided open herbaceous areas. The abundance of lizards increased when the understorey bushy vegetation increased. In contrast, grasslands or cereal fields were scarcely occupied even if holm oak trees (Quercus ilex) were present, apparently because low shrubs were scarce here. Therefore, some of the traditional management practices of dehesas may negatively affect lizard populations. These conclusions could have wider implications for the design of wildlife reserves within dehesas, which has been previously based on the umbrella species concept (e.g. some dehesas are managed for imperial eagle Aquila adalberti conservation), without considering habitat requirements of other representative animal groups.     

Large mammal population declines in Africa’s protected areas

Protected areas (PAs) are the cornerstone of global conservation efforts but their performance in maintaining populations of their key species remains poorly documented. Here, we address this gap using a new database of 583 population abundance time series for 69 species of large mammals in 78 African PAs. Population abundance time series were aggregated to form a multi-species index of overall change in population abundance. The index reveals on average a 59% decline in population abundance between 1970 and 2005. Indices for different parts of Africa demonstrate large regional differences, with southern African PAs typically maintaining their populations and western African PAs suffering the most severe declines. These results indicate that African PAs have generally failed to mitigate human-induced threats to African large mammal populations, but they also show some successes. Further development of our index could help to measure future progress towards post-2010 targets for reducing biodiversity loss.     

Characteristics of occupied habitats and identification of sites for restoration and translocation of New England cottontail populations

Since 1960 the range occupied by New England cottontails (NEC, Sylvilagus transitionalis) in the northeastern United States has declined dramatically. Populations in some regions are known to be vulnerable to extirpation, but little was known about the status of populations in most areas. A recently conducted (2000-2004) range-wide survey identified five disjunct populations within approximately 14% of the historic range of NEC. We incorporated the results of this survey into a geographic information system to examine habitat features associated with remnant populations of NEC at two spatial scales. The regional scale characterized habitats within our survey sample units, 7.5 min topographic quadrangles (quads, ∼40 × 10 km) that were occupied by NEC or vacant. The landscape scale described habitats within a 1-km radius of occupied patches and an equivalent sample of vacant patches. At the regional scale, northeastern and southeastern populations were associated with human-dominated habitats with a greater abundance of developed and disturbed lands, less forest coverage, more edge habitats, and less snow fall than unoccupied quads. Landscapes occupied by NEC in these regions were characterized by a greater abundance of potential dispersal corridors than unoccupied landscapes. In contrast, quads occupied by NEC in the southwestern portion of the historic range were in rural areas that were dominated by forests and agricultural fields. At the landscape scale, southwestern populations were affiliated patches of habitat surrounded by more agricultural lands than patches that were not occupied by NEC. Logistic regression models were then developed to identify habitats suitable for restoration or translocation within each region. We suggest that initial restoration efforts be directed toward expanding existing populations of NEC. Next, habitat connections should be developed among these populations. Finally, new populations should then be established via translocation in portions of the historic range that are vacant. In addition to promoting New England cottontails, management of early-successional and shrub-dominated habitats in the northeastern United States will benefit other taxa of conservation concern that are dependent on these habitats.     

Reduced breeding success in white-tailed eagles at Smøla windfarm,western Norway,is caused by mortality and displacement

Climate change scenarios and efforts to reduce CO₂ emissions have increased the focus on wind power and other renewable energy sources. Despite producing “clean” electricity, windfarms do have impacts on the environment. We studied the impact from a coastal windfarm on the breeding success of white-tailed eagles (Haliaeetus albicilla) at Smøla, western Norway by means of a BACI (before–after–control–impact) approach. The objective was to compare pre- and post-construction breeding success. A 10 year dataset from 47 eagle territories were analyzed using a generalized linear mixed model. Successful breeding was used as a response variable, while distance to turbines, distance to roads and before/after turbine construction were used as predictors. There was a significant effect of the interaction between time period and distance to turbines, showing that territories within 500 m from the turbines in the post-construction period experienced significantly lower breeding success than the same territories before construction. We found that this effect was most likely due to territories being vacated. The results emphasize the importance of using a BACI approach when assessing possible effects from wind-power production on breeding birds, especially for species breeding at low densities. It also emphasizes the importance of conducting thorough pre-construction studies on vulnerable bird species.     

Scale-dependent homogenization: Changes in breeding bird diversity in the Netherlands over a 25-year period

Changes in breeding bird diversity in the Netherlands between 1973-1977 and 1998-2000 were evaluated by testing three hypotheses related to the loss of biodiversity: (1) species diversity is declining, (2) biotic homogenization is increasing and (3) rare species are declining more severely than abundant species. Using data collected for two successive national breeding bird atlases, changes in diversity were assessed at different spatial scales (local, regional and national) and among species characteristic for different landscapes (farmland, woodland, heathland, wetland, coastal habitats and urban habitats). National species richness, diversity and equitability had increased between the two atlas periods, with more species increasing than decreasing in range and abundance. Most species in the large groups of woodland and wetland birds showed positive trends, whereas most in the smaller groups of heathland, reed-breeding and meadow birds showed negative trends. However, findings varied between regions and localities. Increases in species richness occurred mainly in regions in the low-lying, western part of the country which were previously relatively poor in species. By contrast, species richness decreased in some previously species-rich regions in the eastern part of the country. This has resulted in a homogenization of breeding bird communities between regions. We advocate the conservation and restoration of regional identity as a priority for landscape planning in the Netherlands. We did not find a clear relation between species abundance and trends, although both rare and very abundant species tended to decrease on average.