French long-term data: Imidacloprid ban and the cautious return of insect-eating birds

New long-term data from France suggest that, since the ban on certain insecticides, populations of insect-eating birds such as swallows and warblers are beginning to recover cautiously. The figures are still a long way from a happy ending, but they offer a rare glimmer of hope in an otherwise bleak picture of biodiversity loss - and they are once again fuelling Europe’s debate about agricultural chemicals and species diversity.

How an insecticide thins out whole bird populations

At the heart of the new analysis is imidacloprid, which for decades was among Europe’s most widely used neonicotinoids. These active substances target the nervous system of insects and were meant to hit crop pests above all. In reality, they ended up in soils, streams, earthworms - and ultimately in birds’ food chains.

Thomas Perrot and his team analysed data from almost 2,000 monitoring sites across France, collected between 2013 and 2022. The datasets reveal a consistent pattern: wherever imidacloprid could be detected, numbers of insect-eating birds fell markedly.

In regions with higher imidacloprid contamination, insect-eater populations shrank on average by more than a tenth.

Before the substance was banned, the declines were around 12.7%. Even after the ban, the negative effect persisted at about 9%. This points not only to the chemical’s harmfulness, but also to its persistence in soils and waters.

Granivorous species - seed-eaters such as finches - and more adaptable “omnivorous” bird species reacted far less strongly, or showed no measurable response at all. Because they depend less on insects, this helps explain the findings: neonicotinoids affect birds primarily via their food supply - insects - rather than only through direct poisoning.

Direct exposure and an empty table

For insect-eaters, imidacloprid is damaging in two ways:

• Less prey: insect populations crash, and chicks struggle to find enough food.
• Direct effects: residues from treated seed or contaminated water can harm birds’ nervous systems directly.

According to the study, imidacloprid was detected not only in arable soils, but also in surface waters, earthworms, and even in the tissues of small mammals and birds. In other words, the active substance moves through the entire agricultural ecosystem.

Ban since 2018 - and the first signs of recovery

Since 2018, neonicotinoids have no longer been permitted for use on fields in the EU. The aim at the time was primarily to protect bees and other pollinators. The fact that some monitoring sites now show insect-eating birds increasing again is seen as an important indication that such bans can be effective.

The French researchers describe their results as a “cautious but measurable” recovery: the gap in population density between heavily contaminated and less contaminated sites is narrowing. Put simply, more insect-eaters are reappearing on fields that were previously more strongly poisoned.

The trend is not reversing overnight, but it is reversing - a warning signal is becoming a cautious signal of hope.

This recovery is far from uninterrupted. Imidacloprid is long-lived: according to recent studies, residues can continue to act in soil for years after the last application. There have also been exceptions in practice. In France, sugar beet growers received emergency authorisations in 2021 and 2022 to use neonicotinoid-treated seed. As a result, environmental contamination remained higher for longer in some regions than the ban on paper would suggest.

Many pressures at once

Pesticides are only one of the factors pushing birdlife in farmed landscapes into decline. The study therefore places its figures in a broader context:

• Habitat loss: hedgerows disappear, grassland is ploughed up, field margins are sealed over.
• Climate impacts: shifting seasons alter food availability during breeding periods.
• Intensive farming: fewer fallow areas, more monocultures, more frequent use of fertiliser.

All of these pressures act together, making it difficult to attribute improvements to any single policy change. Even so, the clear contrast between insect-eaters and seed-eaters underlines how strong the insecticide’s specific influence is.

Why not all bird species respond in the same way

In their analysis, the researchers examined 57 bird species across 1,983 sites. A key finding was that insect-eaters responded in an almost linear way: the more imidacloprid in the surrounding environment, the lower the population counts.

For seed-eaters, the pattern was less clear. In some cases, their numbers even reached a short-lived peak at medium contamination levels before dropping again. This could reflect indirect effects, such as shifts in competition or changes in plant availability.

There were also strong geographical differences. Insect-eaters remain comparatively common in many areas of central, north-western and eastern France. In more southern parts of the country, seed-eaters tend to dominate. These patterns relate to climate, soil types and cropping systems - and to farmers’ respective pesticide strategies.

Landscape structure also matters

Another decisive factor is the landscape itself. The study broadly distinguishes between heavily intensified regions and areas with more semi-natural elements.

Where hedgerows, wildflower strips and remnants of meadows are missing, even after a ban there is often little left but an ecological emergency.

In regions with extensive or organic agriculture, the researchers found much more stable bird populations. Structural features such as field copses or wide margins provide refuges and nesting sites where insects can persist. Even where some land had previously been treated with neonicotinoids, nature has a better chance to recover in these settings.

A new tool: how toxic is a field overall?

One particularly relevant element for future agricultural policy is the study’s concept of Total Applied Toxicity (TAT). This indicator aims to quantify how toxic the combined mix of all applied pesticides is for different groups of organisms.

That brings a persistent problem into focus, one that often falls through the cracks in approval processes: farmers rarely apply just one active substance. Many fields are treated with cocktails of fungicides, herbicides and insecticides. TAT tries to represent this overall burden, rather than assessing individual substances in isolation.

For bird populations, that means: even if neonicotinoids disappear, other products may continue to put pressure on insects - and therefore on insect-eating birds. This helps explain why the recovery is demonstrable but relatively modest.

What this means for farming and policy

The findings from France convey several clear messages:

• Banning individual active substances can lead to measurable improvements.
• The effects emerge slowly and can be blunted by other toxins.
• Without better habitats in farmland, any upward trend remains fragile.

Through its Farm to Fork strategy, the EU has set itself the goal of cutting pesticide use substantially. Implementation has proven difficult in many member states, not least because of resistance from chemical companies and parts of the agricultural sector. The French data now add weight to the argument that stricter rules are not merely symbolic - they can have measurable effects on biodiversity.

What neonicotinoids are - and why they remain so controversial

Neonicotinoids are a class of active substances that act on insects’ nervous systems. They are often used as seed treatments: the seed is treated before sowing, and the substance later distributes through the plant. The intention is that pests die as soon as they start feeding.

This becomes problematic for several reasons:

• Pollinators such as bees and bumblebees ingest residues via nectar and pollen.
• Soil organisms such as earthworms are exposed continuously.
• Some of the chemicals enter streams and rivers through drainage and run-off.

For birds, the consequences are fewer insects, more toxins in the food chain, and disrupted breeding timing. The French study therefore joins a growing body of international research linking neonicotinoids systematically to declines in bird populations.

What would need to change next

Perrot’s team argue that attention should extend beyond simple chemical bans. In their view, several steps are needed in parallel:

• Expansion of agroecological farming with fewer pesticides and more diverse crop rotations.
• More mandatory ecological infrastructure such as hedgerows, wildflower strips and small ponds within arable landscapes.
• Stronger financial support for farmers switching to systems with reduced reliance on chemicals.
• Independent long-term research into the combined effects of pesticide mixtures, using indicators such as TAT.

For consumers in German-speaking regions, these findings are more than a glimpse across the border. They also indicate how decisions closer to home can matter: whether buying more organic produce, supporting local hedgerow-planting schemes, or backing political choices - much of what affects birdlife in France also plays a role between the North Sea and the Alps.

The good news is that where policy, science and farming pull together, swallows, warblers and other insect hunters are becoming more common again. The less good news is that the pace is still nowhere near fast enough to close the gaps left by past decades. Even so, these quiet gains show that the switch can be flipped - provided the rules are not only passed, but enforced consistently.

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