Focus

      A golden age for raptors and owls?

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      Birds of prey and owls often perch on electricity pylons. Medium-voltage poles are particularly dangerous, and can cause death by electrocution. The large number of deaths has put some Eurasian Eagle-owl populations at risk. Urgent action needs to be taken to replace these dangerous pylons throughout Switzerland. © Adrian Aebischer

      For centuries, birds of prey and owls suffered persecution. While most species were protected by law from 1926, environmental toxins severely affected the slowly recovering populations in the 1960s and 70s especially. Thanks to a range of conservation measures, there has since been an encouraging upturn, but some threats remain.

      For centuries, raptors and owls were directly persecuted by humans. The last Bearded Vulture in the Alps was shot in 1913, and the last Osprey pair bred in Switzerland in 1911. Red Kite and Eurasian Eagle-owl were on the brink of extinction. Golden Eagle numbers were also greatly diminished. Despite the ban on hunting introduced for several species in 1926, many raptor and owl populations were slow to recover. Golden Eagle, Eurasian Hobby and Peregrine Falcon were not protected until 1953, Northern Goshawk and Eurasian Sparrowhawk not until 1963.

      Fatal pesticides

      Besides illegal persecution, which still occurs in isolated cases today, the use of pesticides such as DDT, put to large-scale use from 1940, was a severe threat. It accumulates at the top of the food chain, which is why birds of prey were hit particularly hard, producing eggs with thin shells. As a result, only a single Peregrine Falcon pair bred successfully in Switzerland outside of the Alps in 1971. Following a ban on persistent chlorinated hydrocarbons (including DDT and PCB) in the 1970s in Switzerland and most western countries, the affected species started to recover. But poisoning by carbofuran, only banned in Switzerland in 2013, continued to occur regularly in farmland areas well into the 1990s, affecting the Eurasian Buzzard and Red and Black Kite. Apart from these previously unknown effects of environmental toxins, the deliberate decimation of insects also had serious consequences. The reduced food supply has affected many species, including raptors and owls, the final links in the food chain, which either hunt insects themselves or prey on small, insectivorous mammals like the shrew.

      In many European countries, birds of prey and owls were not protected until the 1970s. Until then, migrating raptors were still exposed to direct persecution. Other human influences had a positive effect on certain species: intensively managed grassland, where grass is mowed several times a year, appears to benefit less specialised species (e.g. Red and Black Kite, Eurasian Buzzard). Targeted conservation measures have helped some birds of prey and owls to recover. Habitats are being improved and additional nest sites provided for Common Kestrel, Common Barn-owl, Eurasian Scops-owl and Little Owl. In recent years, climate change has led to warmer spring and summer months, which appears to benefit Mediterranean species such as Short-toed Snake-eagle and Eurasian Scops-owl.

      Today, the populations of almost all birds of prey and owls are comparatively large – in some species, such as the Red Kite, numbers are probably higher than ever before.

      The change in the number of atlas squares (10 × 10 km) occupied by various raptor and owl species illustrates their turbulent history in Switzerland. Increased observer effort from one atlas to the next has also influenced the results.

      Knowledge gaps and current threats

      Despite a range of monitoring programmes, we still have incomplete knowledge of population trends, especially for Northern Goshawk and European Honey-buzzard, both secretive forest dwellers. Persistent pesticides are thought to have affected the reproductive rate of the Eurasian Sparrowhawk until at least the mid-1990s. Whether these effects continue to influence the breeding success of our birds of prey is unknown. Our knowledge of cavity-nesting «woodland owls» such as Boreal Owl, Eurasian Pygmy-owl and Tawny Owl comes from areas where dedicated volunteers install and monitor nest boxes. We know too little about populations and trends in woodlands where no nest boxes exist. Finally, our understanding of how man-made structures and means of transport affect mortality is limited as well.

      While most raptor and owl species in Switzerland currently show positive trends, some are declining. Critical cases include the Peregrine Falcon (due in part to illegal persecution), and in some areas the Eurasian Eagle-owl (electrocution on electricity pylons and railway power lines, collisions, traffic casualties). The Little Owl remains vulnerable, too, despite signs of recovery; in intensively farmed areas, it finds barely enough food to feed its young.

      Most raptors and some owls are long-lived, reach sexual maturity late and have a low reproductive rate. Therefore, even a small increase in mortality can affect the population trend. Current threats include habitat loss, increasing disturbance, electrocution on power pylons, collisions with overhead power lines, vehicles, trains and windows, pesticide contamination, lead poisoning from fragments of ammunition in the carcasses of game animals (which affects carrion eaters), and finally, direct illegal persecution.

      Farmland birds (e.g. Little Owl, Common Barn-owl) not only face direct habitat loss through building developments, but also struggle with food shortages as a result of intensive farming practices. Human recreation (e.g. rock climbing, paragliding, nest photography) also increasingly affects breeding success in several species. The growth of wind energy will lead to losses of breeding birds in conflict areas. Wind farms are most likely already causing declines in Red Kite and Eurasian Buzzard populations in some areas of Germany. Migrating raptors are affected as well as a result of collisions with wind turbines in their southern migration and wintering grounds.

      Number of raptor and owl species per atlas square (10 × 10 km) in 2013–2016. Diversity is highest in the Jura, on the northern slopes of the Alps and in large Alpine valleys.

      Required action

      Many threats are hard to address. In our country, these include intensive farming, heavy use of fertilisers and pesticides, extensive networks of trails etc. The problems faced by migrant species are even more complex. They reach from direct persecution to drought and rainforest deforestation. However, the replacement of dangerous power pylons in Switzerland is feasible and long overdue. We could also improve the protection of nest sites for sensitive cliff breeders. Timber should be harvested outside of the breeding season (i.e. September to February). To protect migrating birds, important migration routes such as mountain passes and ridges should remain unobstructed by infrastructure. Other desirable measures include monitoring of breeding populations and breeding success, especially for secretive woodland species.

      Text: Stefan Werner


      Recommended citation of the Atlas online:
      Knaus, P., S. Antoniazza, S. Wechsler, J. Guélat, M. Kéry, N. Strebel & T. Sattler (2018): Swiss Breeding Bird Atlas 2013–2016. Distribution and population trends of birds in Switzerland and Liechtenstein. Swiss Ornithological Institute, Sempach.

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      Subject
      Hunting
      Environmental pollution
      Conservation
      Species on the rise
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