Intensive Farming and Climate Change: Why Bird Populations Are Declining

Anyone who remembers seeing dense flocks of birds over fields during childhood will often notice only silence today. A new assessment of long-term data from North America clearly reveals where declines are progressing especially rapidly – and what is driving them: large-scale intensive farming with heavy use of pesticides and fertiliser.

Study finds that almost one in two species has declined substantially

The research team examined populations of 261 bird species in North America from 1987 to 2021. The figures came from systematic counting schemes in which volunteers and specialists record birds each year according to fixed protocols.

• Period covered by the study: 34 years
• Species assessed: 261 bird species
• Average population decline: around 15 per cent
• Species with clearly declining populations: 47 per cent
• Species with accelerating declines: 24 per cent

The researchers considered more than the overall loss; they also assessed whether declines were accelerating over time. This is precisely what is happening in almost a quarter of the species studied: their populations are not merely falling, but collapsing ever faster.

Hotspots of accelerating bird losses are concentrated primarily in areas with extensive arable land and high use of pesticides and fertilisers.

These patterns are not coincidental. The analysis identifies a clear link between farming intensity and the rate at which bird populations are shrinking. The more chemicals are used and the more uniform the land becomes, the sharper the decline.

How intensive farming harms birds

Intensive farming accelerates biodiversity loss through several mechanisms at once. It often begins with the complete conversion of natural habitats into cropland or land for animal feed.

Habitat loss caused by landscape conversion

Areas that once contained hedgerows, wet meadows, woodland or species-rich grassland are now frequently replaced by large, uniform fields. This conversion removes several vital resources at the same time:

• Nesting sites in hedgerows, trees and field margins
• Places to shelter from predators
• Varied food sources, including seeds, berries and insects
• Features that moderate the microclimate, such as shade and windbreaks

The fragmentation of the landscape by tracks, roads and irrigation systems adds to the pressure. Many species are sensitive to these breaks because they interrupt movement routes and isolate small remaining habitat patches.

Pesticides primarily disrupt the food chain

The study makes clear that the use of insecticides, herbicides and fertilisers is a central part of the problem. These chemicals do not mainly kill birds directly; instead, they undermine the basis on which the birds survive.

Insects are one particularly affected part of the ecosystem. Many songbirds, including familiar farmland species such as larks and swallows, depend heavily on insects during the breeding season. They feed them to their chicks because protein-rich food supports rapid growth.

Where insects disappear because of pesticides, birds simply lose their food – especially during the sensitive breeding period.

Insecticides often kill insects directly, while herbicides remove the plants on which they depend, and heavily fertilised, uniform crops provide scarcely any habitat. Fertilisers can also indirectly alter the composition of plant and insect species, for example through nutrient enrichment of soils and water bodies.

For birds, this means:

• Fewer insects and seeds in fields
• Less structural diversity across the landscape
• More toxins in food chains when residues are consumed

Global warming increases the pressure on bird species

The study also links bird data with temperature trends. It shows that rising temperatures are associated with general population declines, whereas intensive farming is particularly correlated with the acceleration of those declines.

The impact is greatest in regions where farming is becoming more intensive while temperatures are also rising markedly. Bird numbers there not only fall more quickly, but populations also recover less effectively from extremes such as heatwaves or droughts.

Intensive farming and climate change act like two mutually reinforcing stress factors – particularly for populations that are already weakened.

Researchers suspect a twofold effect. Farming changes the microclimate, for instance through a lack of shade, dry soils and the removal of trees that would otherwise bind carbon dioxide. At the same time, global warming shifts the timing of flowering, insect emergence and migration. Birds may then arrive too late, after the peak food supply has already passed.

Global scale: farming as a leading driver of biodiversity decline

The North American study fits into a worldwide pattern. An assessment by the International Union for Conservation of Nature, IUCN, concludes that populations of 61 per cent of all bird species are declining globally. Agricultural expansion and intensification are among the most important causes.

The new study stresses that many of these processes occur at the same time. Birds are therefore placed under a form of constant stress, reflected in lower breeding success, poorer health and higher mortality.

Are there alternatives? Opportunities through different forms of farming

Researchers do see ways to break this cycle. Regenerative and less intensive farming methods are considered promising approaches for better reconciling agriculture with biodiversity conservation.

How farmland can become more bird-friendly

Several measures have shown positive effects on bird populations in studies and practical projects:

• Reduced use of pesticides and mineral fertilisers
• Retaining and creating hedgerows, field copses and flower strips
• Avoiding vast monocultures in favour of smaller fields and crop rotations
• Mowing grassland later, so young birds can fledge
• Leaving fallow land and field margins uncultivated

These steps benefit more than birds alone. They generally also support pollinators such as bees, improve soil fertility and make ecosystems more resilient to extreme weather.

Why the issue matters to people as well

Birds are more than merely “beautiful companions in the sky”. They eat pest insects, disperse plant seeds and serve as early-warning systems for environmental problems. When their populations collapse, this points to fundamental disruption within ecosystems that will ultimately affect farming itself.

Where birds disappear, entire ecosystems often tip out of balance – with consequences for harvests, water systems and the climate.

Many familiar European farmland birds, including the lapwing, grey partridge and skylark, show trends very similar to those of their relatives in North America. This makes clear that the study's findings cannot simply be dismissed as a distant problem: they also indicate risks for agricultural landscapes in German-speaking regions.

What terms such as intensive farming and regenerative agriculture mean

Intensive farming generally refers to systems designed to achieve high yields per unit of land. Typical features include large fields, extensive machinery, targeted breeding and high inputs of fertiliser and plant protection products. This approach can deliver large production volumes in the short term, but it often comes at the expense of soil quality, biodiversity and landscape structure.

Regenerative agriculture pursues a different aim: soils should become more fertile over the long term, store carbon and provide habitat. Farmers may use diverse crop rotations, cover crops, minimal soil cultivation, measures that build humus, and the integration of hedgerows or tree strips. Such systems can reduce chemical use, improve water absorption and create habitats for birds and insects.

The new study underlines how urgently land use needs to be reconsidered. Birds respond sensitively to changes in landscapes and climate. Their populations indicate whether an agricultural system is functioning in balance or is already reaching its ecological limits.