|A “binge and fast” approach to life – storing up body fat at some times, then living off reserves during migration, courtship and breeding – means that birds are particularly susceptible to pollution.|
In the 1960s, it became apparent that DDE, a breakdown product of the pesticide DDT, caused eggshell thinning. Because DDE is persistent and accumulates in fat, birds at the top of the food chain, including birds of prey and seabirds, were particularly affected, several being brought close to extinction. Effects linked to DDT include skewed sex ratios and female-female pairing in gull populations. Fish eating birds are particularly exposed to chemical contaminants. However, with the banning of DDT, populations have virtually returned to normal in some species such as the Baltic guillemot. But where DDE contamination remains significant eggshell thinning continues to be a problem, other populations are still at risk – for example, the peregrine falcon in Canada and Russia, and the coastal peregrine falcon in Britain.
Other, current-use chemicals, like flame retardants also lead to contamination of birds eggs.
In birds, pollutant related effects include: abnormal production of the egg yolk protein in male birds which is normally produced in females; deformities of the reproductive tract; embryonic mortality; reduced reproductive success including egg-shell thinning; and poor parenting behaviour.
CHEM Trust report Effects of Pollutants on the Reproductive Health of Male Vertebrate Wildlife - Males Under Threat, by Gwynne Lyons, shows that male fish, amphibians, reptiles, birds and mammals have been harmed by chemicals in the environment. Widespread feminisation of male vertebrate wildlife is highlighted. These findings add to mounting worries about the role of hormone-disrupting or so-called ‘gender-bending' chemicals in the environment, and the implications for human health.
The Vulture Crisis – nature’s recyclers at risk
Pharmaceuticals in the environment can also harm wildlife. For example, vulture numbers have collapsed in India, Pakistan and Nepal due to them being poisoned by a veterinary drug called diclofenac. The decline started in the 1990s and some vulture species are at risk of becoming extinct. This is a serious problem, particularly as vultures play an important role in ecosystems, clearing up dead carcases and preventing the spread of disease. Since some vulture populations have decreased by 95%, wild dog populations have increased to fill the ecological niche, with the attendant increased risk of rabies, attacks on people and other diseases.
Diclofenac (a non-steroidal, anti-inflammatory, pain-killing drug) is to blame for the vulture declines. Exposure of vultures to diclofenac comes from its use to treat domestic livestock. Vultures are highly susceptible to kidney failure caused by diclofenac and are killed by feeding on the carcass of a cow soon after it has been treated with a normal dose. Studies show that only a small proportion of livestock carcasses need to contain diclofenac to result in the observed decline in vultures. To India's millions of Hindus, cows are holy animals that cannot be harmed, so they may be treated with pain killers until the time of death, but even in countries where there are less qualms about killing cows, there is still a serious problem.
In 2004, Birdlife, along with the UK Royal Society for the Protection of Birds (RSPB) and local bird charities, called upon governments in Asia, Africa, Europe and the Middle East, where the vulture is under threat, and manufacturers of diclofenac, to ban the use of this drug for veterinary medicine, throughout the range or former range of these vultures. They noted that such action was especially urgent in Bangladesh, Bhutan, Cambodia, India, Myanmar, Nepal and Pakistan because they represent the main range states of the three currently threatened species.
In 2006, the Indian Government thankfully banned the production and sale of diclofenac for veterinary use. There is a suitable alternative which is available and this needs to replace urgently the use of diclofenac. It is certainly hoped that the African vulture will not suffer the same fate as those in Asia, particularly as cattle farming in Africa is on the increase.
Diclofenac is still used as a human drug and can be bought over the counter at pharmacies in the UK for the treatment of headaches, period pain and symptoms of cold and flu. Unfortunately, it seems that the human injectable form of diclofenac is now being used on cattle and vultures are still at risk.
Current ‘asks’ of environmental groups trying to save the vultures in Asia are:
- A ban on the marketing of the large sizes of the injectable form of diclofenac for humans.
- Prevention of the use of non-steroidal, anti-inflammatory drugs from areas designated as ‘vulture havens’, which are being developed in conjunction with breeding programmes.
- Help to maintain vulture breeding programmes.