A latest study shows that pet cats are responsible for killing up to 270 million animals every year in the UK alone.
Although domesticated, cats have retained their predatory nature and are considered to be one of the most problematic of invasive species (GISD, 2018). Introduced cats have contributed to, or been directly responsible for, 26% of modern vertebrate extinctions (Doherty, Glen, Nimmo, Ritchie, & Dickman, 2016) and are believed to be the primary threat to 8% of critically endangered mammals, birds and reptiles (Medina et al., 2011). Cats annually kill an estimated 1.3–4 billion birds and 6.3–22.3 billion mammals in the United States (Loss, Will, & Marra, 2013), and 100–350 million birds in Canada (Blancher, 2013). In Britain, estimates from a single study suggests 92 million prey over five (spring and summer) months (Woods, McDonald, & Harris, 2003).
You can read about it here: https://www.sciencedirect.com/science/article/pii/S0169204621003017
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