Habitat destruction is the largest of the many threats to biodiversity

Mark Edwards/BirdLife Habitat destruction, over-exploitation and the effects of alien invasive species are the most prevalent threats to birds Zoom In

Humans cause the majority of threats to species, sites and habitats. These threats are often interconnected and reinforce each other. Habitat destruction and conversion for agricultural and forestry activities – and the associated degradation and fragmentation – are the biggest problems.

Most threats are caused by human activities

We cause nearly all of the many immediate threats that directly impact bird species and the sites and habitats in which they live. For example, some 95% of European Important Bird Areas (IBAs) are used for human activities, which often involve the entire site, and over 40% are subject to one or more high-impact threats. Threats are often interconnected and reinforce one another. For example, over 90% of Globally Threatened Birds (GTBs) that are currently threatened by over-exploitation are also affected by the destruction of their habitats.

Habitat destruction is the most serious threat

Habitat destruction and degradation threaten over 86% of GTBs and are currently the most serious pressures on the world’s birds. Over-exploitation and the effects of alien invasive species are also major threats and others – notably pollution and climate change – are of increasing concern. Some of these threats can be reversed, given enough resources, but others are difficult to combat and can become the final cause of extinction for species that are already reduced to tiny numbers (see box 1).

Habitat is destroyed mainly for agriculture and forestry

The expansion of agricultural activity has led to the destruction of huge areas of natural habitats, including forests, grasslands and wetlands, in nearly all regions of the world. For tropical forests, the richest habitat for biodiversity, logging is typically the first major pressure, often providing access to remote areas and leading to further clearance and degradation. The expansion and development of urban areas and infrastructure also reduces natural habitats, and new roads give access to additional areas, which results in further losses. The relative importance of these factors varies in different parts of the world (box 2), but all play a significant part in the destruction of habitats and therefore in driving ecosystem change.

Habitat degradation and fragmentation compound the problem

For many species the habitat degradation that accompanies 'selective' resource exploitation, or that occurs in habitats next to cleared areas, can have serious consequences. Many tropical forest birds, for instance, rely on pristine or near-pristine primary forest, and show low tolerance to selective logging. Even for non-threatened bird species that have adapted to rural, semi-natural habitats, the intensification of agricultural practices is causing significant population declines in temperate and tropical regions alike. The problem is made worse by the fragmentation of natural habitats across much of the world, most notably in tropical and sub-tropical forests, but also in open-country habitats (box 3). Such fragmentation results in smaller, more isolated subpopulations, with reduced possibilities for dispersal and increased risks of local and ultimately global extinction. In total, 252 bird species are considered globally threatened by a combination of small severely fragmented ranges.

Boxes: case studies and scientific analyses

Download SOWB pp.30–31 (PDF, 270 KB) containing the following:

1. Habitat destruction, over-exploitation and the effects of alien invasive species are the most prevalent threats to birds
The main threats to GTBs world-wide

2. Agriculture and forestry are key drivers of habitat destruction in IBAs in Africa and Europe
Agricultural expansion and intensification threaten 50% of African and 35% of European IBAs

3. Habitat fragmentation puts pressure on remaining natural grasslands in Argentina
About 60 grassland-dependent bird species occur in Argentina