Rumour once had it that the extinction of the Stephens Island wren was the work of a single lighthouse keeper’s cat. The myth was debunked with the realisation that the extinction of the bird on the small island off New Zealand was actually the work of a feral cat colony.
Extinction is nothing new to islands. The extinction of the Mauritian dodo is an example of what can happen when islands are colonised. In addition, relative isolation from the mainland gives
rise to unusual species that adapt to a different ecological niche.
The absence of apex predators on islands allows slow creatures like giant tortoises or the flightless dodo bird to thrive, and certain species have no fear of predators.
Domestic pets, especially cats, have an impact on wildlife in ecologically sensitive areas like islands. If pet owners behave irresponsibly by abandoning unsterilised cats, or allowing them to escape, they can become feral, turning to easy targets like the indigenous fauna to meet their nutritional needs. The impact of feral animals has been felt on the Indian Ocean islands of Mauritius and Réunion.
Threatened wildlife on Indian Ocean islands
More than 20 bird species became extinct following colonisation of Réunion in the 17th century. The likely causes are hunting, habitat transformation, and rats and cats. The Réunion cuckoo-shrike, the endangered Barau’s petrel and the critically endangered Réunion black petrel are also threatened as a result.
Mauritius, and Rodrigues east of the main island, have experienced 78 extinctions. In Mauritius, the pink pigeon, Mauritius kestrel, Mauritius paradise flycatcher, echo parakeet and the smaller songbirds are threatened by the presence of feral animals.
“Wedge-tailed shearwaters and tropicbirds nest on the ground, making them susceptible to animal attacks,” says Dr Vikash Tatayah, conservation director of the Mauritian Wildlife Foundation (MWF). Of the 49 islands surrounding Mauritius, none have feral cat colonies. Feral cats have been eradicated from Flat Island and Île aux Aigrettes.
The impact of feral animals on endemic wildlife
While conducting field surveys, the MWF team encounters dog carcasses in the forests. A prime example of how dogs are dumped was seen on Île aux Aigrettes, an uninhabited island on the south-eastern side of Mauritius. MWF was conducting a reintroduction project on 400 microchipped Telfair’s skinks when someone released three dogs on the island. “Within three weeks, there were only 100 skinks left, and by the time we captured the last dog, it was starving,” Tatayah says.
MWF is working to restore Telfair’s skinks on Île aux Aigrettes through a conservation strategy known as ‘headstarting’. Young animals are raised in captivity from eggs or babies, protected in a safe environment, and released into the wild when deemed old enough to avoid their predator, the Asian musk shrew. The island must also be kept free of dogs, cats and other predators.
“Cats have the biggest impact on the biodiversity of Réunion. The population of domestic cats on the island is estimated at 160 000. The tracks of feral cats can be found everywhere on the island, including in native forests,” says Nicolas Laurent of the Ornithological Studies Society of Réunion (SEOR).
“Cats kill up to 200 adult petrels a year, a concerning figure as petrels are slow breeders. Petrels and shearwaters fall victim to light pollution too. Young birds become disorientated at night due to artificial lights,” he adds.
“As they are unable to take off, they become easy targets. Conservation operations in petrel colonies capture around 100 feral cats each year.”
In 2004, only 11 pairs of Réunion cuckoo-shrikes were recorded, Rats are to blame. “The density of rats in the bird’s native forest was estimated between 20.8 and 53.9 rats per hectare,” Laurent says.
A study of the birds found fewer females than males. This is likely the result of predation at night when the female is on the nest. Anti-rat strategies have since been implemented and the bird’s reproductive success has increased to 90%. There are now 40 pairs on the island.
Reducing cat and dog populations
“Threats and pressure on biodiversity increase every year,” says Laurent. “Réunion is governed under French laws. It is illegal to use lethal traps or poison to kill feral cats because they are classed as a domestic animal,” he clarifies. The forest cats in Réunion and Mauritius are invasive, and cannot be adopted or rehomed.
They have a significant impact on endemic wildlife. “The sale of potentially invasive species needs to be restricted on Réunion,” Laurent stresses. “People have to be aware of the impact of alien species on our biodiversity, including domestic animals like cats or dogs. Controlling feral animal populations is currently not a priority among local authorities.”
While humane euthanasia might be necessary in ecologically sensitive areas like nature reserves or breeding colonies, mass euthanasia campaigns will not solve the inherent problem. “Dramatically reducing dog numbers by culling creates new territories for new dogs to move into,” explains Carla Prayag from Humane Society International (HSI) in Mauritius.
HSI in collaboration with the Ministry of Agro Industry and Food Security has launched the No Toutou campaign to sterilise and vaccinate beach dogs. “It is also important to note that Mauritian people want dogs,” says Prayag. “Dogs are an important part of their communities.” But free-roaming dog and cat populations need to be managed and cannot occur in numbers that harm the natural environment.
The solution is to change human behaviour through education and responsible pet ownership. Keeping dogs and cats confined to yards and sterilising pets will benefit the lives of both wildlife and pets. Another option is permits and restrictions on the type of pets residents can own on Réunion.
People need to be made aware of the commitment that comes with owning a pet. Dogs, more so than cats, do not fend well without human assistance, and when they suffer the wildlife suffers too.
Written by Georgina Lockwood
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