Grassland ground-nesting waders have been steadily declining across Europe. "The main factor driving wader population decline seems to be the low survival of wader nests and especially chicks," says the doctorate candidate at the Estonian University of Life Sciences Miguel Silva-Monteiro.

The extinction of insects — insect apocalypse — is a trending topic in science, and since grassland waders rely on insects, "people often correlate these two things and conclude that one causes the other; nevertheless, there has been very little research on such a link," said Silva-Monteiro.

Silva-Monteiro, along with a group of international researchers, studied the correlation between the amount of insects present in the habitat of the wader and the chick mortality rate.

Data was collected in 64 sites in five countries across mainland Europe: France, the Netherlands, Poland, Estonia and Finland. All sites had breeding waders and among them the near-threatened black-tailed godwit in the years before sampling.

In each location, the researchers also examined the number of plants and the moisture content of the soil; the results were surprising, said Silva-Monteiro.

Deceptive hypothesis

Silva-Monteiro and added that since waders are breeding in a range of habitats. "Some waders prefer more natural systems such as bogs and mires, while others favor managed habitats and inhabit coastal meadows or fields."

"We tried to find places where they are better off than elsewhere, especially in terms of food for their young," the researcher explained.

The parent birds do not feed their offspring in the foragers — the chicks must provide for themselves from the day they hatch. "Parents simply guide their young, much as chicken species do." Older birds do not forage for arthropods, but rather earthworms.

Silva-Monteiro collected insect samples from all locations, counted, measured and weighed them. "Insects were discovered to be more prevalent in grassland than in wetlands," he said, adding that people would normally assume the opposite, given that marshes are a natural ecosystem and grasslands are modified by human activity. "This relationship is, however, not as straightforward," the researcher added.

The study showed that the number of insects on farmland that are suitable food for wader chicks is greater. "In other words, the larger the potential of the environment to produce plant biomass, the greater the insect availability for young," Silva-Monteiro said. 

His research showed that although the number of waders is declining worldwide, a lack of insects is not the primary cause.

"Of course, where there is more vegetation, there are more insects. Insects eat plants. If herbivorous insects are plentiful, so are insectivorous insects such as spiders," Silva-Monteiro explained.

Because black-tailed godwit chicks are considered opportunistic feeders, foraging all available insects, Silva-Monteiro says he limited himself to counting, measuring, and weighing insects, as opposed to other studies that take insect diversity into account.

"If we had identified all of the insects," he said, "we would probably conclude that bogs have greater insect biodiversity than coastal meadows." Nonetheless, the grassland outperformed the wetlands in terms of the amount of food available to birds.

Estonia's problem is abandoned grasslands

Waders are small migratory birds that live in coastal areas and marshes. "However, in terms of the amount of food available to birds, the grassland outperformed the wetlands," Silva-Monteiro said. Estonians are likely to see waders, for instance, at the Matsalu nature reserve.

The majority of wader species are associated with conventional agriculture, the researcher explains, which is now resulting in a decline of wader populations worldwide.

"Although prior to the early 1900s only few studies were conducted, we do know that traditional agriculture helped to expand the populations of certain species," he said, adding that the same holds true for the black-tailed godwit.

The species favors semi-natural coastal meadows where little fertilizer is used, plants grow slowly, and livestock prevent their spread. "By the time the chicks hatch, the height and density of the vegetation there is optimal, helping the birds to find food and hide in the grass," the researcher explained.

As agriculture increases, grass is cut earlier using equipment instead of maintaining open swards that do not require cutting before chicks can fledge. This results in habitat loss and an increase in wader chick mortality.

"Populations of some species have declined by more than 75 percent," said Silva-Monteiro.

When adequate habitat is gone, the researcher suggests that certain species migrate from the shore to the reef, but further studies are needed to determine whether and how this occurs.

The population of waders in Europe is essentially defined by the maxim: the further east, the better. "In places where traditional agriculture has been preserved, e.g. in countries such as Ukraine and Belarus, waders are still doing well," he added.

In those areas, wader-friendly habitats are vanishing rather because grasslands become abandoned and overgrown.

A study of the five countries surveyed revealed that Finland had the most favorable conditions for waders. "We hoped Estonia would be somewhat similar to Finland but, unfortunately, we were mistaken, and Estonian populations are significantly declining," he said.

"I would say that Estonia is an excellent example of what ought to be done, at least in terms of its coastline areas," the researcher nevertheless added. Here, insecticides are prohibited on coastal meadows, grass is growing at the right time and mowing schedules facilitate bird breeding. "I would rather say that the problem for Estonia's wader population is the reed that occasionally overruns the grassland," he said.

Based on research undertaken by his colleagues, Silva-Monteiro estimated that 20 to 30 percent of Estonia's grasslands require more care than is being provided. "Protected semi-natural areas in Estonia are generally in great condition. However, soon after a part of land has been abandoned, it should be better managed," he said.

Changes in agricultural practices have been identified as the primary cause of the extinction of many species, with both agricultural intensification and farmland abandonment having a negative impact on their populations.

Farmland birds are one of Europe's most rapidly declining species groups. Ground-nesting waders are affected in particular with populations declining around 30 percent solely in the last two decades. Low survival of wader nests and especially chicks seems to be the main factor driving wader population decline.

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