The number sounds disturbing: within 30 years, the number of bird breeding pairs on Lake Constance has dropped by a quarter. This is shown by a study by scientists from the Ornithological Working Group Lake Constance and the Max Planck Institute for Behavioral Biology. Accordingly, around 465,000 breeding pairs lived in Lake Constance in 1980, compared with only 345,000 in 2012.
Once frequent bird species such as house sparrow, blackbird or star had fallen particularly strong, so Hans-Günther Bauer, one of the authors of the article, published in the journal "bird world". The development on Lake Constance also confirms a pan-European trend.
According to the ornithologist, the numbers of many species also declined in other regions of Germany. However not everywhere as dramatic as on Lake Constance: "The western and southern regions are more affected than the eastern and northern." He attributes this to the more intensive agriculture in the south and west.
For the authors of the long-term study, today's agricultural landscapes are considered to be hostile to birds. "The partridge, which was once common in the agricultural landscape, has become extinct around Lake Constance, and there are no more predatory shrikes, meadow pipits and little owls today," says Bauer.
For the data collection, the scientists had counted all the birds on an area of around 1100 square kilometers around Lake Constance. Previously, the ornithologists had recorded the stocks for the first time from 1980 to 1981 and then every ten years.
One of the main reasons for the decline is the loss of food. At Lake Constance, 75 percent of the bird populations that feed on flying insects have been lost. For species that feed on non-invertebrates, it is 57 percent. "This confirms what we have been suspecting for some time: Man-made insect killing has a massive impact on our birds," explains Bauer. Among other things, the working group calls for drastic restrictions on insect and weed killers.
Europe-wide, the number of insect-living birds has dropped significantly over the past 25 years. Wagtail, Meadow Pipit or Barn Swallow - on average, the number of these birds dropped by 13 percent, according to a study published in March in the journal "Conservation Biology". And data from the pan-European bird monitoring program PECBMS show that European herds of field and meadow birds in Europe have declined 57 percent from the beginning of counts from 1980 to 2016. They include skylarks, lapwings or starlings.
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Many birds would hardly find any more habitats and breeding grounds on the intensively used areas, explains Bauer. They also disappeared from the villages and towns around Lake Constance. "Obviously, the animals in the midst of urban canyons, ornamental trees and clean vegetable gardens breed increasingly less successful." Common birds such as blackbird (minus 28 percent), chaffinch and robin (each minus 24 percent) suffered massively from the worsening living conditions.
The long-term study is a series of disturbing reports on the evolution of domestic birds. In Germany's gardens and parks, for example, fewer winter birds were seen at the beginning of the year. Tens of thousands of nature lovers counted an average of 37 animals in January, which they observed in the action "Hour of Winter Birds" of the German Nature Conservation Union (Nabu) within 60 minutes. In 2011, nearly 46 birds were reported per garden. Whether an actual decline in stocks could be the cause, should be followed closely, it was said by Nabu.
At Lake Constance species are affected very differently depending on habitat, the current study shows. While 71 per cent of the species living in grasslands and fields drastically collapsed, 48 per cent of the species living in the forest rose - only 35 per cent fell. An example is the great spotted woodpecker with an increase of 84 percent. Also around the waters on Lake Constance more species had increased than decreased - one of the winners: the mute swan.
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At first glance, the balance sheet from 1980 to 2012 appears balanced: out of the 158 birds occurring around Lake Constance, stocks of 68 species increased and 67 decreased. The total number of species even rose. In eight extinct species came 17 who have settled or resettled. Including white stork, peregrine falcon and eagle owl, which according to the ornithologists have benefited from protective measures. "Nevertheless, we are losing overall biodiversity," Bauer warns. Many species would only be found in small populations that are often no longer viable and in fewer and fewer locations around Lake Constance. "Depending on the area unit, there are fewer species on average."
Of the ten most abundant birds on Lake Constance, six stocks have decreased massively, two have remained unchanged and only two have increased. The stocks of the house sparrow, which was still the most common type in 1980, had collapsed by 50 percent. Bauer adds: "These are really staggering numbers - especially considering that the decline in birds began decades back in 1980, when we first collected data."