Cats are one of the top threats to US wildlife, killing billions of animals each year, a study suggests.

The authors estimate they are responsible for the deaths of between 1.4 and 3.7 billion birds and 6.9-20.7 billion mammals annually.

Writing in Nature Communications, the scientists said stray and feral cats were the worst offenders.

However, they added that pet cats also played a role and that owners should do more to reduce their impact.