Pollution remains a serious concern

Ian Denholm Pesticides continue to poison birds on a large scale Zoom In

Pollution of the environment has direct and indirect impacts on birds – an indication of the wider problems it creates for man and biodiversity alike.

Pollution of the wider environment has direct and indirect impacts

Bird populations are directly impacted by environmental pollution, through mortality and sublethal effects such as reduced fertility. Pollution can also have strong indirect effects, by degrading habitats or reducing food supplies, and overall it threatens 187 Globally Threatened Birds (GTBs). The types of pollution that affect bird populations are very diverse. Water-borne nutrient pollution from point sources (e.g. fish-farms, sewage outfalls) and from more dispersed sources (e.g. agricultural run-off) can devastate otherwise productive wetland and coastal habitats, through inducing algal blooms, poisonous 'red tides', fish-kills and the formation of permanently oxygen-less .dead zones., as in parts of the Black Sea and Gulf of Mexico. Other waterborne pollutants that can affect birds and their habitats include pesticide residues, run-off from land-fill, suspended sediment from excessive soil erosion, heavy metals, salts and trace elements that are poisonous in excess (e.g. selenium).

Little is known of the long-term effects of many pollutants

Huge areas of farmland, rangeland, forest and wetland are treated with poisonous synthetic chemicals each year to control competitor species of plants, animals, micro-organisms and diseases. To enhance crop yields across the developing world, agriculture is becoming increasingly reliant on such biocides, many of which have been banned or restricted in other nations. Unfortunately, the side-effects and longer-term impacts of such pesticides and herbicides are often ignored or simply not known by those who use them (see box 1).

Birds can indicate the effects of pollutants

Bird populations are often good indicators of the impacts of pollutants, for instance in the well-documented case of the negative impact of DDT on populations of Peregrine Falcon and other raptors, and also for other less well known .persistent organic pollutants. (box 2). For example, the calcium-rich food needed for adequate eggshell development in nesting birds is less available in areas with increasingly acid rain, and this is manifested in eggshell thinning and population declines (box 3). Birds are often the most visible sign of the environmental problems caused by oil slicks or spillages of toxic chemicals in wetlands. These episodes can often be disastrous for biodiversity and for local economies (box 4).

Boxes: case studies and scientific analyses

Download SOWB pp.40–41 (PDF, 309 KB) containing the following:

1. Pesticides continue to poison birds on a large scale

2. Persistent organic pollutants continue to accumulate in the environment

3. Acid rain continues to exceed critical loads in industrialised regions

4. Oil spills significantly reduce populations of seabirds and are costly to clean up