The introduction of a species that is not typical of a certain ecosystem can have catastrophic consequences. When we think of habitat alterations, we tend to immediately focus on rare exotic species that have been introduced from distant countries. But sometimes the enemy of our endemic and native species is closer than we think. The Feral domestic cats are the case in point. Its introduction into various ecosystems has caused the extinction of up to 33 species of reptiles, birds and small wild mammals in the world and has driven so many other animals to survive in a situation of extreme vulnerability.
“Many people are shocked that the cat does not belong to any ecosystem, but it is like that, because it is a domestic animal,” highlights Adrián Flores, an environmentalologist at the University of La Laguna (ULL). As it does not have an established place in the cycle of the ecosystem, its introduction causes alterations as if it were an exotic species and, if not repaired in time, it is possible that it causes irreversible damage.
It is estimated that currently its presence also threatens the survival of 8% of the species of birds, mammals and reptiles listed as critically endangered by the International Union for Conservation of Nature (IUCN) worldwide. In our country, the areas most affected by its introduction are the island areas.
Feral cats are one of the most damaging invasive species to vertebrate communities living on islands. Throughout history, according to the Higher Council for Scientific Research (CSIC), the action of these felines has contributed to the disappearance of at least 14% of vertebrates in these environments.
The work, published in Global Change Biology, It is based on a literature review of 229 cases in 120 islands around the world. Feral cats are present on most of the estimated 179,000 islands around the world.where biodiversity is very particular and any interference in its ecosystems has a much more serious impact.
At a global level, the insular regions historically most affected by the action of this feline are the Galapagos (Ecuador), Hawaii (USA), some Caribbean islands and the Canary Islands. The data shows that the biodiversity of the two Spanish archipelagos has also been affected by the action of these cats.
The case of the Canary Islands
During the investigation, the team identified some striking cases where the cat has played a fundamental role in the extinction of some vertebrates, such as the Stephens’ wren (traversia lyalli) in the Cook Strait (New Zealand) and the Socorro Dove (Zenayda graisoni) in Mexico, whose species is extinct in nature and its only existing numbers are in captivity. In addition, some subspecies of the endemic mouse (peromyscus guard) of Baja California (Mexico) have become extinct on several islands. The giant lizard of La Gomera (Gomeran Gallotia), with a small population in nature, is one of the most endangered reptiles on the planet.
Of the more than thirty species of terrestrial vertebrates introduced in the Canary Islands, feral cats are one of the greatest exponents of threat to the Canarian avifauna, as highlighted by SEO/Birdlife. Today, endemic species such as giant lizards have been reduced both in population and inhabitable surface. Scientists from Canarian universities and the Institute of Natural Products and Agrobiology (IPNA-CSIC) have found that these reptiles, which in pre-conquest times were spread throughout the archipelago, are now limited to areas inaccessible to cats , like those of cliffs.
Food: fewer rabbits, more reptiles and birds
A recent article published by ULL researchers shows that, in addition, the diet of feral cats has changed in the last 18 years, probably as a result of the spread of rabbit haemorrhagic disease throughout the islands, an animal that until now was an important part of your diet.
As a result of the lack of mammals to hunt, the cats in this part of the island have begun to exploit other resources, especially reptiles and birds. As far as reptiles are concerned, consumption has tripled since 2005. Their progressive disappearance is already generating changes in ecosystems, since they help disperse seeds and their disappearance affects the connectivity and genetic characteristics of populations of plants.
Specifically, it has caused a drastic reduction in genetic connectivity in populations of the endemic plant Orijama (Neochamaela powdery), which has also altered its genetic characteristics throughout its distribution area.
The birds, although they have not been the object of the study, also worry scientists, because “their consumption has multiplied by 16”, Flowers highlights. Among the species hunted by cats are Bulwer’s petrels, which are also in danger of extinction and whose consumption has increased fivefold. They also affect the rabiche and turquoise pigeon, the Gran Canaria blue chaffinch, the Canary stonechat and, especially, seabirds.
In the Balearic Islands, The situation of feral cats also worries biologists, because some seabirds see their nests threatened for this reason. This is the case of the Balearic shearwater (Puffinus mauretanicus) or virot, a bird of great environmental relevance that is in danger and has been the object of public recovery programs.
This doesn’t just happen on islands. A study conducted in the United States and published in Nature, reflects the devastating impact of these felines on the rest of animal life. The conclusion of the study was blunt: cats are the main threat to wildlife.
They kill billions of animals every year.
Scientists estimated that felines are responsible for the death of between 1,400 and 3,700 million birds and between 6,900 and 20,700 million mammals each year in that country alone.
The greatest threat is from strays, who are unaccounted for — between 30 million and 80 million in the United States — who kill between 23 and 46 birds and between 129 and 338 small mammals each year, according to Marra’s conclusion.
In 2020 there were 3.8 million cats in our country, both in homes and on the street. According to the Affinity study, each year 124,000 cats enter the shelters and, although they are less in number than dogs, they arrive in worse conditions than dogs. Only 4.3% are microchipped (compared to 28% of dogs) and most arrive sick or injured.
Scientists and associations insist that cats must be controlled. SEO/Birdlife insists that administrations must carry out control programs that prevent such damageas well as information and awareness campaigns among the population about the potential threat they pose to native fauna.
In the case of pets, they must remain under the control of their owners, so that they do not cause damage to biodiversity, especially when there is an express prohibition in Canarian legislation regarding the introduction of these pets into the natural environment. In the case of feral cats in important places for birds and other threatened fauna groups, the cats are not compatible with the conservation of the endangered species and contravene the legislation.
Reference study: https://www.nature.com/articles/ncomms2380