North America: Intensive Agriculture Accelerates Bird Decline

For decades, North America was regarded as a paradise for birdwatchers, known for vast migration routes and spectacular flocks. A major analysis of long-term data now shows that the continent’s birdlife is under severe pressure – with increasingly intensive agriculture accelerating the decline.

Study using 35 years of data: the decline is speeding up

An international research group led by ecologist Petr Keil of the Czech University of Life Sciences Prague and biologist François Leroy from a US university analysed data from more than a thousand observation sites across the United States. Volunteers and professionals have counted birds regularly at these locations for decades, including through nationwide monitoring schemes.

The researchers examined 261 common bird species, addressing two questions: how have populations changed since the late 1980s, and is the pace of that decline itself changing?

The alarming finding: almost half of the species studied are clearly in decline, and for many of them the rate of loss continues to increase each year.

More specifically, the data show:

• Nearly 50 per cent of species are experiencing a clear long-term decline.
• The decline is accelerating in 63 species: on average, more individuals disappear each year than in the preceding year.
• Around 60 species are still increasing, but their growth is slowing – and they cannot offset the losses among other species.

This is therefore no longer simply a gradual fading of populations that might unfold over generations. Much points to a tipping point at which entire wildlife communities in farmland rapidly lose their balance.

Intensive agriculture is the main driver – ahead of climate

The analysis combines population records with land-use and climate information. This makes it possible to identify the regions where the downward trend is accelerating most sharply, and the factors that dominate there.

The pattern is clear: areas of intensive agricultural production are particularly badly affected. Vast monocultures, heavy pesticide use, and the loss of hedgerows and wetlands all directly affect birds that live in farmland or forage there.

Where agricultural landscapes have become production factories, bird populations are collapsing at a particularly rapid rate.

The researchers therefore see agriculture as a key factor amplifying other environmental pressures. Climate change also plays a part, for example through altered rainfall, heatwaves and shifts in breeding times. Yet in many regions, pressure from land use appears to be the more severe and immediate blow – one that further worsens climate impacts as peatlands dry out, soils become depleted and more fertiliser reaches rivers.

Birds of farmland and wetlands lose out, while a few thrive near towns

The accelerating decline chiefly affects species dependent on open farmland or wetlands. Typical “losers” in these systems include:

• Meadow-nesting birds such as larks and snipes, which require undisturbed grassland
• Farmland birds that breed in cereal and maize belts or hunt insects there
• Waterbirds and waders whose feeding and resting sites have been drained

Some generalist species – those able to cope with a wide range of habitats – are faring better. A number even benefit from edge habitats around towns, parks or low-density suburbs. Some woodland bird species also appear more stable, at least where larger areas of forest remain intact.

Nevertheless, the losses in agricultural landscapes are far more significant. The limited increases cannot compensate for the steep declines among characteristic farmland and wetland birds. Ecologically, this produces an impoverished bird community: fewer species, fewer specialists and more resilient “common” birds.

Why bird decline affects everyone

At first glance, this may seem like an issue only for ornithologists. In reality, it affects vital ecosystem functions – and ultimately agriculture and food security. Birds pollinate far fewer plants than insects, but they perform many other roles.

Role of birds	Example in agricultural landscapes
Pest control	Songbirds catch caterpillars and beetles that could otherwise damage crops.
Seed dispersal	Birds that eat berries spread shrubs and trees that provide shelter from wind and shade.
Indicators of environmental condition	Population declines give early warning of problems with pesticides or water quality.
Nutrient cycling	Colonies of waterbirds move nutrients between water bodies and land.

If these functions break down, this can eventually affect yields, soil quality and pest pressure. For this reason, many experts describe birds as the landscape’s “fever thermometer”: when the fever rises, it is usually not just one population that is unwell.

North America is a warning sign for Europe

Although the findings relate directly to North America, they fit disturbingly well with developments in Europe. Farmland bird populations have also been shrinking here for years. Research by the BirdLife partnership and European research institutes shows that birds in agricultural regions are suffering particularly heavy losses, while some urban species remain comparatively stable.

The North American study now adds an important detail: the decline is not linear, but is accelerating in many places. Political measures based on the assumption of a slow change spread across generations could therefore arrive too late.

Those who wait until species are close to disappearing must invest disproportionately more – and still face poorer chances of success.

What the study means for agricultural policy and practice

The data point to a simple but uncomfortable conclusion: without fundamental reform of intensive agriculture, bird decline is unlikely to be halted. Individual protected areas are insufficient when vast stretches of land between them are effectively uninhabitable for wildlife.

In practice, experts repeatedly highlight similar measures:

• More hedgerows, field margins and wildflower strips to provide food and cover for insects and birds
• Reduced pesticide use and targeted support for beneficial species
• Protecting and rewetting wetlands and ditches
• Later mowing and adapted harvesting dates in breeding areas
• More diverse crop rotations instead of large-scale monocultures

Such measures require money and land, but they may also benefit farmers through more stable yields, more pollinators, lower pest pressure and better conditions for soil organisms.

How citizens can respond

Not everyone farms hundreds of hectares. Even so, private choices also influence whether birdlife continues to diminish or begins to recover. Domestic gardens, balconies and municipal green spaces can play a surprisingly important part, especially as stepping stones between larger habitats.

Practical options include:

• Planting native shrubs and trees that provide berries and insects
• Avoiding gravel gardens and allowing diverse, flowering areas instead
• Feeding birds with clean food and cleaned feeders, especially in winter
• Putting up nest boxes and creating year-round refuges
• Supporting political pressure for more nature-friendly agricultural policy

These actions are no substitute for large-scale reforms, but they can reduce local pressure on bird populations and strengthen the resilience of those populations.

Background: what “accelerating decline” actually means

Until now, many studies have considered only whether populations are rising or falling. The latest assessment goes further by examining changes in the speed of that trend. Put simply, there is a difference between a species shrinking by two per cent every year and that loss rising from two to three, four or five per cent.

In population biology, this is described as negative acceleration: an increasing annual loss. The effect can remain unnoticed for a long time, particularly where overall population numbers are initially still high. At some point, the system tips: breeding pairs cannot find enough food, fewer young birds survive, and the species becomes extremely sensitive to further disturbance.

This is precisely the dynamic now apparently taking hold in many agricultural landscapes in North America. The continent once famed for spectacular migratory bird movements is consequently sending a clear warning signal – including to regions such as Central Europe, where agricultural structures have become similarly intensive.