Hormone implants bring kangaroos under control.

Contraceptive implants have made the jump from women to kangaroos. The largest real-world trial yet of hormonal implants in kangaroos has successfully brought numbers down in Victoria, removing the need to cull them through shooting. Australia currently has twice as many kangaroos as people. When numbers of wild kangaroos are locally high, the relationship between people and kangaroos can become fraught when the animals collide with cars, contaminate water supplies and damage grasslands. To control numbers, and supply the kangaroo meat industry, the Australian government approves the culling of more than 5 million wild kangaroos a year. But there is increasing opposition to this from animal welfare groups. To see if contraception could be an effective alternative, Michelle Wilson of the University of Melbourne is leading the largest real-world trial yet of hormonal implants in kangaroos. In 2013, Wilson inserted levonorgestrel (Norplant) implants – which are used by women – underneath the shoulder blades of three-quarters of the female kangaroos living in a 200 hectare area of the Western Plains of Victoria in south-eastern Australia. “There were too many kangaroos so there wasn’t enough food and they were starving and emaciated,” says Wilson. “There was also a lot of roadkill surrounding the site and a high prevalence of disease.” A follow-up study, which has not yet been published, has found that of the 75 females that were implanted, only one has become pregnant since, and the reproductive rate of that area’s population is now about a third of what is was in 2012. The strategy has been highly successful, says Phil Pegler of Parks Victoria. “It’s prevented the need for us to go back and do any more shooting.” The contraceptive method isn’t cheap. An implant plus labor, tranquilizer and anesthetic comes to around $A 250 (£130) per animal. Fertility is suppressed for about six years. Nevertheless, contraception is better long-term than shooting, says Wilson. “The problem with culling is that the population bounces back afterwards so then you have to cull again.” A real concern is the potential for side effects, because contraceptive hormonal implants, including Norplant, Implanon and Nexplanon, are known to cause mood changes, loss of sex drive, headaches, and other problems in some women. A study in female macaques found that Implanon was associated with signs of anxiety, such as higher rates of self-scratching. But Wilson says she has not observed any negative effects on health in the current trial, nor in a smaller eight-year study in kangaroos in Anglesea, Victoria. Even if contraception carries some side effects, it is still more humane than other wildlife control methods, Kangaroo contraception is starting to gain momentum elsewhere in Australia, says Wilson. A golf course in New South Wales has also begun using hormonal implants to control the local kangaroo population. Contributed by New scientist.