Map showing: a) the location of the Canary Islands (red square), b) the island of Tenerife and the Teide National Park (gray shape), and c) the location of the samples in the national park (white dots). Credit: Mammal research (2023). DOI: 10.1007/s13364-023-00728-9
Trophic ecology is the study of the food chain. In Tenerife, Canary Islands, feral cats feed mainly on rabbits, mice, rats, as well as native birds and reptiles. But new research shows that since 1986, the island’s wild cats have experienced a significant change in their dietary composition, which bodes ill for several native species.
The study, carried out by two researchers from the University of La Laguna in Tenerife, is titled “Changes in the trophic ecology of wild cats in the alpine ecosystem of an oceanic island: implications for the conservation of native biodiversity » and was published in Mammal research.
Among predators worldwide, free-ranging cats pose one of the greatest threats, and existing studies show that the predatory impact of cats is particularly heightened on islands. A 2011 study links 14% of known global extinctions of birds, mammals and island reptiles to predatory cats.
The Canary Islands, located in Macaronesia in the North Atlantic Ocean, off the coasts of Morocco and Western Sahara, are a volcanic archipelago consisting of seven main islands and numerous smaller islands. Tenerife, the largest island, includes a number of varied environments, including sandy coastal areas, cloud forests, pine forests and, at higher altitudes, alpine scrub, where climatic conditions are extreme and where very varied endemic species are found in small numbers. .
In particular, the limited populations and distribution areas of animals in alpine scrub areas expose them to a high risk of the effects of climate change and the presence of allochthonous (introduced non-native) species, including cats.
Trophic behavior of wild cats in the Canary Islands
Previous studies in the Canary Islands have shown that feral cats (Felis catus) mainly consume non-native mammals, including rabbits (Oryctolagus cuniculus), mice and rats, as well as native birds and reptiles.
A 2021 study conducted in the Montaña de Guaza area in the southern coastal region of Tenerife showed that compared to 15 years earlier, wild cats consumed native reptiles comprising more biomass in their feces (11.5 %, compared to 3.6%). and native birds comprised more biomass (39%, compared to 2.4%), but consumed rabbits containing a smaller amount of biomass (30.3%, compared to 62.4%).
In this new study, researchers sought to determine whether cats in other areas of the island had experienced a similar dietary change over a 35-year period. Focusing their 2021 fieldwork in El Teide National Park, an environment rich in alpine scrub, the researchers analyzed 301 samples of wild cat feces and compared the results to previous data.
Annual number of vertebrates absorbed by a single cat and by the feline population assuming a density of 1 cat/km2 in the Teide National Park and considering that 170 g of prey is equivalent to daily consumption. Credit: Mammal research (2023). DOI: 10.1007/s13364-023-00728-9
They found that in this region, while rabbit biomass in cat feces accounted for 73% of cats’ rabbit consumption in 1986, by 2021 this percentage had fallen to 53.9% due to a decrease of the number of rabbits available, probably due to the presence of rabbits. hemorrhagic disease virus (RHDV and its new variant, RHDV2). Expressed in terms of quantity, in 2021, cats ate about half as many rabbits as in 1986.
Comparing these results to previous data, the researchers observe: “The values obtained in this study are the lowest ever recorded for the diet of cats in the high mountain scrublands of all the Macaronesian islands studied so far and are among the lowest of all those recorded for the Canaries. He is.”
As a result, park cats have increased their consumption of native reptiles and birds. Based on the assumption of one cat per square kilometer over the total 190 km area of the park.2, researchers calculated that each wildcat consumes approximately 1,356 vertebrates each year (including 29 birds, 197 rabbits, and 875 reptiles, among others). This brings the total annual estimate of cat predation in the park to 257,737 vertebrates, including 5,587 birds, 37,384 rabbits and 166,249 reptiles, among others.
Conservation issues
Given that study data shows that wild cats in El Teide National Park prey on native species (birds and reptiles) at a rate that accounts for two-thirds of their total food consumption, the researchers highlight the importance to give priority to management and conservation actions in this area. area.
In particular, they note that two of the prey species, the Tenerife lizard (Gallotia galloti) and the ring ouzel (Turdus torquatus), serve as short- and long-distance dispersers of cedar seeds at this location, respectively.
During the coldest annual period, ring ouzel and other birds seek food and shelter in cedar areas, making them easy targets for cats. The team suggests fencing areas with cedars to keep cats away and selectively trapping them as mitigation measures.
More information:
Manuela Gómez-Alceste et al, Changes in the trophic ecology of wild cats in the alpine ecosystem of an oceanic island: implications for the conservation of native biodiversity, Mammal research (2023). DOI: 10.1007/s13364-023-00728-9
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