Swallows, titmice and many other insectivorous bird species have declined sharply in recent years in the United States and Canada due to pesticides and fertilizers destroying their food supply. This is the conclusion reached by ecologists who published an article in the journal Condor: Ornithological Applications.
“Grasslands are becoming the most vulnerable ecosystems on Earth, as their rich soil is ideal for expanding agricultural land. Pesticides and fertilizers are being used more and more, which greatly affects the life of animals. Already, we can say that birds living in natural meadows feel much better than their counterparts from the fields,”says Dave Shutler from Acadia University (USA).
Scientists have identified the five largest mass extinctions of species in the history of life on Earth. The most significant is considered the "great" Permian extinction, when more than 95% of all living things inhabiting the planet disappeared, including bizarre beast-lizards, close relatives of mammalian ancestors, and a number of marine animals.
Two years ago, ecologists announced that now a new, sixth mass extinction of animals is taking place on Earth. According to their calculations, in the epochs preceding the Anthropocene - the human century, about two species of mammals disappeared every hundred years for every ten thousand species of animals that existed at that time. In the last century and the current century, their number has increased 114 times.
The first victims of this extinction, as ecologists from the University of Saskatchewan (Canada) have found, may be common swallows and other common insectivorous birds that live in the vicinity of agricultural fields and wild meadows in North America.
Scientists came to this conclusion by studying the diet and observing the growth of chicks of several hundred tree swallows (Tachycineta bicolor) living in the south of Alberta and elsewhere in Canada. They were interested in whether the diet of birds living near farmers' fields and in remote corners of nature, untouched by man, is different.
As explained by Christy Morrissey, one of the observers, scientists initially expected that the diet of "field" and "forest" swallows would be very different. In nature, these birds prefer to feed on aquatic insects living in swamps and flooded meadows, while plowed fields should be dominated by "land" pests.
Morrissey and her colleagues tested whether this is actually the case by catching dozens of birds and measuring the proportion of oxygen, nitrogen and carbon isotopes in their blood. Their ratio, as the scientists explain, directly depends on the environment in which the swallows' food "grew", which makes it possible to accurately reveal their diet.
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Much to the surprise of scientists, both groups of birds ate about the same set of insects, which was dominated by aquatic arthropod species. The reason for this, as subsequent observations showed, was that birds rarely hunted in the territory of cultivated fields, even if they lived next to them, preferring to get food from the banks of rivers, lakes and other bodies of water.
This negatively affected the condition of the swallows - they had to make more efforts to search for food, as a result of which their own weight and the mass of their chicks were noticeably below normal.
Such changes in their lives, associated, according to ecologists, with pesticides and the destruction of meadow ecosystems, may be one of the reasons for the sharp decline in the number of American insectivorous birds in recent years.