Birds in Europe: Their conservation status

PCB problems in the future: Foresight from current knowledge

Based on a comparative approach using PCB isomer and congener compositions in higher animals and their food organisms, the capacity and mode of PCB metabolism in small cetaceans were studied and the following conclusions were drawn: (1) Small cetaceans can metabolize some of the lower chlorinated biphenyls and this capacity seems to be the same in all species of these animals. (2) The values of MI, an index to evaluate the capacity of PCB metabolism, showed that the metabolic capacity of small cetaceans was extremely low as compared to those of birds and terrestrial mammals. (3) The structural requirements for PCB metabolism were different in animal species, in that small cetaceans have no capacity to metabolize a group of PCBs with adjacent non-chlorinated meta and para carbons in biphenyl rings. (4) No development of PB (phenobarbital)-type enzymes, and a lower activity of MC (3-methylcholanthrene)-type enzymes were suggested in small cetaceans, which implies long-term accumulation and possible reproductive toxicity of persistent organochlorines in these animals. The present approach should provide an important insight into the physiological responses of small cetaceans to persistent toxic chemicals.

Capacity and mode of PCB metabolism in small cetaceans

Concerns about anthropogenic climate change have resulted in promotion of renewable energy sources, especially wind energy. A concern raised against widespread windfarm development is that it may negatively impact bird populations as a result of bird collision with turbines, habitat loss and disturbance. Using systematic review methodology bird abundance data were synthesized from 19 globally-distributed windfarms using meta-analysis. The effects of bird taxon, turbine number, power, location, latitude, habitat type, size of area, time since operation, migratory status of the species and quality of evidence were analysed using meta-regression. Although the synthesized data suggest a significant negative impact of windfarms on bird abundance, there is considerable variation in the impact of individual windfarm sites on individual bird species, and it is unclear if the negative impact is a decline in population abundance or a decline in use owing to avoidance. Anseriformes experienced greater declines in abundance than other taxa, followed by Charadriiformes, Falconiformes and Accipitriformes, and Passeriformes. Time since windfarms commenced operation also had a significant impact on bird abundance, with longer operating times resulting in greater declines in abundance than short operating times. Other variables, including turbine number and turbine power either had very weak but statistically significant effects or did not have a significant effect on bird abundance. Windfarms may have significant biological impacts, especially over longer time scales, but the evidence-base is poor, with many studies being methodologically weak, and more long-term impact assessments are required. There is clear evidence that Anseriformes (wildfowl) and Charadriiformes (waders) experience declines in abundance, suggesting that a precautionary approach should be adopted to windfarm development near aggregations of these taxa in offshore and coastal locations. The impact of windfarm developments on bird populations must also be viewed in the context of the possible impact of climate change in the absence of windfarms.

/pdf/poor-evidence-base-for-assessment-of-windfarm-impacts-on-56yxkuo31w.pdf

Poor evidence-base for assessment of windfarm impacts on birds

Whether predators can limit their prey has been a topic of scientific debate for decades. Traditionally it was believed that predators take only wounded, sick, old or otherwise low-quality individuals, and thus have little impact on prey populations. However, there is increasing evidence that, at least under certain circumstances, vertebrate predators may indeed limit prey numbers. This potential role of predators as limiting factors of prey populations has created conflicts between predators and human hunters, because the hunters may see predators as competitors for the same resources. A particularly acute conflict has emerged over the past few decades between gamebird hunters and birds of prey in Europe. As a part of a European-wide research project, we reviewed literature on the relationships between birds of prey and gamebirds. We start by analysing available data on the diets of 52 European raptor and owl species. There are some 32 species, mostly specialist predators feeding on small mammals, small passerine birds or insects, which never or very rarely include game animals (e.g. hares, rabbits, gamebirds) in their diet. A second group (20 species) consists of medium-sized and large raptors which prey on game, but for which the proportion in the diet varies temporally and spatially. Only three raptor species can have rather large proportions of gamebirds in their diet, and another seven species may utilise gamebirds locally to a great extent. We point out that the percentage of a given prey species in the diet of an avian predator does not necessarily reflect the impact of that predator on densities of prey populations. Next, we summarise available data on the numerical responses of avian predators to changing gamebird numbers. In half of these studies, no numerical response was found, while in the remainder a response was detected such that either raptor density or breeding success increased with density of gamebirds. Data on the functional responses of raptors were scarce. Most studies of the interaction between raptors and gamebird populations give some estimate of the predation rate (per cent of prey population taken by predator), but less often do they evaluate the subsequent reduction in the pre-harvest population or the potential limiting effect on breeding numbers. The few existing studies indicate that, under certain conditions, raptor predation may limit gamebird populations and reduce gamebird harvests. However, the number and extent of such studies are too modest to draw firm conclusions. Furthermore, their geographical bias to northern Europe, where predator–prey communities are typically simpler than in the south, precludes extrapolation to more diverse southern European ecosystems. There is an urgent need to develop further studies, particularly in southern Europe, to determine the functional and numerical responses of raptors to gamebird populations in species and environments other than those already evaluated in existing studies. Furthermore, additional field experiments are needed in which raptor and possibly also mammalian predator numbers are manipulated on a sufficiently large spatial and temporal scale. Other aspects that have been little studied are the role of predation by the non-breeding part of the raptor population, or floaters, on the breeding success and survival of gamebirds, as well as the effect of intra-guild predation. Finally there is a need for further research on practical methods to reduce raptor predation on gamebirds and thus reduce conflict between raptor conservation and gamebird management.

Birds of prey as limiting factors of gamebird populations in Europe: a review

Organochlorine compounds and shell-thinning in british merlins falco columbarius

Capsule The main factors are past and present human activities, especially the introduction of rats to islands. Aims To assess factors that influence breeding distribution and abundance of Storm-pe...

Factors affecting breeding distribution of Storm-petrels Hydrobates pelagicus in Orkney and Shetland

Among other things, this study confirms that Merlins nesting near afforested areas continue to rely on open country for their hunting.

https://www.tandfonline.com/doi/pdf/10.1080/00063658409476815

Breeding season foods of Merlins Falco columbarius in Northumbria

Summary 1. Livestock grazing is an important form of land use across the globe and changes in grazing pressure can have profound effects on vertebrate populations. 2. In Scotland, over the last decade sheep numbers in many areas have declined from historically high levels, providing an opportunity to explore the implications of these declines for biodiversity. 3. The hen harrier Circus cyaneus is a bird of high conservation importance in the UK, and a species that may be heavily influenced by the indirect effects of sheep on habitat and prey. The hen harrier population on the Orkney Islands in Scotland has been monitored since 1975 and represents an ideal case study for considering the impact of sheep de-stocking on a key predator. 4. Declines in the harrier population were associated with a doubling in sheep numbers between the early 1980s and the late 1990s. Subsequently, as sheep numbers have fallen the harrier population has recovered. These changes indicate an association but no clear mechanism, so we tested whether reductions in sheep numbers have led to increases in harrier prey or preferred foraging habitat. We then tested whether breeding output over the last 33 years correlates with sheep stocking levels or variation in weather conditions (rainfall and temperature). 5. Orkney sheep numbers declined by about 20% between 1998 and 2008. Surveys in 1999 ⁄ 2000 and repeated in 2008 showed increases in rough grassland, the preferred harrier foraging habitat, and increases in a key prey species, the Orkney vole Microtus arvalis orcadensis. 6. Overall, hen harrier breeding output over the last 33 years was significantly negatively correlated to both sheep abundance and spring rainfall. 7. Synthesis and application. This study provides strong evidence for the consequences of changes in sheep numbers on a top predator. Our results indicate that reductions in sheep numbers are likely to prove beneficial for some upland species, particularly small mammals and their predators.

http://www.globalraptors.org/grin/researchers/uploads/449/sheep_densities_2011.pdf

Long-term impact of changes in sheep Ovis aries densities on the breeding output of the hen harrier Circus cyaneus

In order to ascertain the effects of aero-generators on breeding birds, two moorland plots in Orkney's West Mainland were censused each year between 1981 and 1989 One plot was immediately adjacent to the aero genera for site while the other acted as a control Although the bird populations in the plots were not large enough to state categorically that the aero-generators caused no declines, their effects appear to have been minimal The only species to have been adversely affected by the development of the site was Red-throated Diver Gavia stellata and its decline was probably the result of factors other than the operation of the aerogenerators

Eric Meek

Papers

Organochlorine compounds and shell-thinning in british merlins falco columbarius

Factors affecting breeding distribution of Storm-petrels Hydrobates pelagicus in Orkney and Shetland

Breeding season foods of Merlins Falco columbarius in Northumbria

Long-term impact of changes in sheep Ovis aries densities on the breeding output of the hen harrier Circus cyaneus

The effects of aero-generators on moorland bird populations in the Orkney Islands, Scotland