Cats in search of food can alter their purr to a higher pitch to get their owner's attention, new research suggests. (CBC)

House cats aren't usually known for being shy about asking for food, but new research suggests some are cagier than usual: embedding a meow-like cry in an otherwise contented purr to get their owner's attention.

Writing in the Tuesday issue of the journal Current Biology, a group of researchers led by Karen McComb of the University of Sussex in England said the purrs of hungrier cats include a high-pitched sound, one that human respondents find difficult to ignore.

The researchers played recordings of these purrs to 50 human volunteers, and found that even people who don't own cats were affected by the sound, finding the purr to be more urgent and less pleasant than the normal deep rumble of a contented cat.

"The embedding of a cry within a call that we normally associate with contentment is quite a subtle means of eliciting a response," Karen McComb of the University of Sussex said in a statement.

"Solicitation purring is probably more acceptable to humans than overt meowing, which is likely to get cats ejected from the bedroom," she said.

Not all cats use this form of purring, she said. The behaviour most often develops in cats that have one-on-one relationships with their owners, while cats in larger households where they must vie for attention tend to rely on meowing to get their voices heard.