The invention of the contraceptive pill marked the onset of the sexual revolution in the 1960s. Now, scientists are seeking to revolutionise wildlife control by adding animals to the mix. Trials are afoot in the United Kingdom and other European countries where pigeons, squirrels and wild boar are given contraceptives. Deer and invasive parakeets are also being considered.
Prompted by damage at the hands of pest species, scientists are filling bait boxes and feeders with food containing contraceptives. There is a generally held view that this is a more effective and humane way to control animal populations that have previously been poisoned, shot or trapped.
Dr Giovanna Massei of York University spoke of “creative solutions” being needed because “we are running out of options” in response to the growing economic and environmental impact of wildlife around the world. She described traditional methods, like culling, as environmentally harmful, ineffective, inhumane and increasingly opposed by the public.
The squirrel problem
Grey squirrels are a particular problem in the United Kingdom. These animals originally were not native to the country. This ended upon their introduction from the United States to England in the 1870s as a way to prettify stately homes. But they spread widely, now numbering about 3 million. They often caused the extinction of native red squirrels, of which there are now thought to be only 160,000.
Grey squirrels damage woodland by stripping bark to get at the nutritious sap found beneath. This costs an estimated £37 million a year in England and Wales, per a survey by the National Forestry Society. This makes them a greater threat to broadleaf trees than deer and disease. One broadleaf tree is the oak, which supports as many as 2,000 other species.
Trials are underway to supply grey squirrels with oral contraceptives concealed in hazelnut spread. Spreads are preferable to nuts because squirrels might bury nuts, which other species could eat. Feeders that only grey squirrels are capable of opening see use: red squirrels are lighter, so they will not open for them. Remote cameras record exactly what came to dinner. It looks like this is working: in one study, more than 90% of the grey squirrel population visited a feeder.
Then-Prince Charles played a key role in founding the UK Squirrel Accord. This comprises 39 organisations with the aim of limiting the impact of grey squirrels. It favours contraceptives for grey squirrels. Another interested party, Jason Gilchrist, an ecologist from Edinburgh Napier University, wrote that contraception “is better than the alternative: a shotgun”.
Pigeons on the pill
Then-Mayor Ken Livingstone termed pigeons “flying rats” and banned the sale of pigeon feed in Trafalgar Square, ending a decades-long tradition. When their droppings dry out and particles become airborne, they can cause a host of diseases that include salmonella and tuberculosis. At other times, these can cause accidents by making people slip. The nests they construct make a mess of buildings. Their faeces can also disfigure buildings or land on people. They are a hazard to air travel by getting sucked into jet engines or flying into cockpit windows. Their feathers clog up intakes, fans and filters, damaging machinery, like HVAC units, that requires cooling fans. Food left for them that they do not consume attracts other pests, like rats.
When it comes to contraceptive-laced corn grains, Dr Marco Pellizzari, a vet, commented: “They really love to get that”. Results have been impressive: in Ixelles in Belgium, the pigeon population was dramatically reduced by 50% between November 2022 and August 2023. Other European nations have long accomplished this: the Netherlands took up the practice in 1970, Switzerland in 1980 and Spain about 20 years back. Contraceptives are a better option than outright culling, as pigeons compensate for that by breeding more.
Wild boar and other beasts
In Europe, wild boar have been rising in number. This is thought to be on account of milder winters, reforestation and greater availability of crops. Italian farmers’ associations claimed that the population of wild boars in that country rose from 500,000 in 2010 to a million by 2020. Their numbers are expanding even in the United Kingdom. Hunting over 300 years ago made them extinct. Today, there are around 5,000 of them, thanks to accidental and deliberate releases from abattoirs, farms and parks. Wild boar face no animal predators in the United Kingdom, so the only predator they have to worry about there is humans, through hunting and car accidents. Some people regard them as pests because they attack dogs; carry diseases, like African swine fever, that affect both people and livestock; disturb cropland; eat rubbish; and cause traffic accidents. In 2022, National Farmers Union Scotland called upon the government to exterminate or at least limit the numbers of wild boar. This followed a series of lethal attacks by them on lambs or even fully grown sheep.
Contraceptives have been tested on wild boar. One way to do this is with a boar-operated system. With such a thing, only wild boars’ snouts can lift metal cones placed above food, preventing access by other animals. Dr Massei remarked: “That means we can get contraceptives into boar and only boar”.
Rodents are a major threat to agriculture. Countries often ban the use of poison on them. This is because they impact other animals, including birds of prey, that have died after eating the dead bodies of poisoned beasts. They are also considered inhumane, as animals can suffer for days after eating poison. An ecologist from Greenwich University, Professor Steve Belmain, reflected that there were few alternatives to lethal control, so “fertility control really could be a great opportunity to manage these things”.
Wild horses in the United States and elephants outside South Africa’s Kruger National Park are already given contraceptives. Britain now features more deer than at any point in the last thousand years, which causes massive damage to woodlands. Scientists are toying with the idea of giving deer contraceptives, but to date, it is not possible to administer any orally to grazing animals.
Possible problems are that contraceptives in the form of oestrogenic chemicals getting into the environment feminise male fish. Also, it is unknown what effect there might be on a predatory bird if it consumed a rodent that had eaten a contraceptive. And ethically, inability to breed might have a psychological or even physiological impact on animals. Professor Belmain warned: “We need to really understand these things as part of that regulatory process”.
