The Conversation * | BBC News Brazil
There are exotic species such as the American crayfish, pike, cane toad, American bullfrog and raccoon that tend to dominate statistics and reports on the impact of invasive animals on species extinction.
But few invaders have caused as much damage to biodiversity as one of the most adorable pets: the cat.
Around 4 million cats live in Spanish households alone (on average one for every 12 inhabitants). Of these, 120,000 end up abandoned on the streets every year.
In Brazil the proportion is even higher: on average there is one for every seven inhabitants, or 27.1 million, according to the Pet IPB 2022 census.
Loner and relentless hunter; Agile, fast, voracious and with a strong territorial instinct. The cat is a cruel and untamed carnivore, but also fascinating. He is an example of evolutionary perfection.
All of these characteristics make cats an extremely reluctant domesticated species with a strong tendency towards freedom and disobedience.
Largest vertebrate predator
Cats have killed more vertebrates than any other predator.
Their cosmopolitanism, their efficiency as carnivores and their enormous adaptability allowed them to colonize the entire world, from the subAntarctic islands to the hot and dry regions near the tropics.
And their high fertility makes them a demographic bomb that is very difficult to deactivate.
The fastest extinction of a species was caused by a cat.
Tibbles was the mascot of the lighthouse keeper of Stephen Island, a small rocky outcrop between New Zealand's two main islands. There lived a strange flightless night bird that resembled a lark.
The British ornithologist Lionel Walter Rothschild (18681937) described the bird in 1895 with the scientific name Xenicus lyalli the Stephen's Island Lark.
A millionaire, Rothschild bought all known dissected specimens and dedicated the bird's name to the island's lighthouse keeper, D. Lyall.
A total of 13 examples are known the same ones that the cat Tibbles laid at her owner's feet.
The lighthouse keeper, passionate about ornithology, dissected them before sending them to Rothschild. And no new specimens have been found since then.
Tibbles specializes in hunting this bird. He discovered them and singlehandedly exterminated the species in the cold winter of 1895.
As a result, the Stephen's Island lark and the dodo (Raphus cucullatus) began to share the unwanted honor of being extinct species before they were described by science.
More than 1 million birds per year
Very conservative calculations have led some authors to estimate that cats on islands like Kerguelen, in the southernmost part of the Indian Ocean, eat more than a million birds per year.
And cats are known to have caused several species of reptiles to disappear from small islands like Santa Luzia in Cape Verde in just 75 years.
This also applies to the Canary Islands, which belong to Spain.
It is estimated that the arrival of cats in the archipelago two thousand years ago is one of the causes of the disappearance of some birds, two giant rodents and the giant palmate lizard.
Despite their small stature and the countless memes about adorable kittens on social media, domestic cats (Felis catus) are killing machines, equipped with retractable claws, sharp fangs and night vision.
These powerful predators can be anything but squeamish. They are always looking for prey to hunt or carrion to scavenge. And they eat whatever there is.
Thanks to humans, cats have spread around the world over the last thousand years.
These wild cats were probably domesticated in the Middle East 10,000 years ago.
They currently live on all continents except Antarctica.
Cats have been introduced to hundreds of islands and have become one of the most widespread species on the planet.
Very varied diet
Cats' cosmopolitanism has led them to transform many of the ecosystems into which they have been introduced.
Cats transmit new diseases to many species, including humans.
Its ecological impacts exceed those caused by native cats and other mediumsized predators.
They threaten the genetic integrity of wild cats and feed on native fauna, which has led to the extinction of many species.
For all of these reasons, freeroaming cats (i.e. domestic or wild cats with access to their external environment) are among the most problematic invasive species in the world.
A metaanalysis of 530 articles, books and scientific reports published over more than a century resulted in the first complete record of the animals commonly eaten by domestic cats.
The list of victims is long: 2,084 different species.
Most of them are birds (981 species), followed by reptiles (463), mammals (431), insects (119), amphibians (57) and other taxonomic groups (33).
The most common prey items are rats, mice, sparrows and rabbits, but there are also records of cats hunting surprising prey such as Galapagos tortoises, Australian rheas and even domestic cattle.
Some of the animals on the list including humans are too large for cats to hunt.
But they reflect cats' propensity to eat carrion.
Almost 350 of these species are on several red lists of endangered species.
And many of them are already extinct.
Many are small birds, mammals and reptiles that are only found on islands where there are no natural enemies such as cats.
This means that unsuspecting prey animals do not show any defensive reactions.
Eleven of the recorded species, including the Hawaiian crow (Corvus hawaiiensis), the New Zealand quail (Coturnix novaezelandiae) and Australia's whitefooted rabbit rat (Conilurus albipes), are considered extinct.
insectivores
The data in the article is conservative. The records are a representation of the species that serve as food for cats, but cats eat far more than we can identify.
Insects, for example, make up almost 6% of the species eaten by cats.
However, this number is likely an underestimate because it is difficult to identify insect remains in cat stomachs and excrement compared to vertebrate feathers or bones.
In addition, the number of prey increases proportionally with the number of scientific publications.
And since most of the sources used for the metaanalysis come from Australia and North America, it is likely that this geographical bias obscures the totality of species consumed.
Ultimately, the animals native to these continents dominated the data set.
Future research will certainly help understand the impact of cats in other regions with exceptional biodiversity such as South America, Asia and Africa.
Then numerous creatures threatened with extinction are discovered and end up in cat litter boxes.
But the truth is that blaming cats ultimately becomes a scapegoat for a much larger problem that involves our own environmental commitments.
If we humans cannot change our behavior to protect biodiversity, why should we expect the same awareness from cats?
*Manuel Peinado Lorca is Professor Emeritus and Director of the Royal Botanical Garden of the University of Alcalá in Spain.
This article was originally published on the academic news website The Conversation and is republished under a Creative Commons license. Read the original Spanish version here.