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It doesn't matter whether it is a human child crying, or the call of a lost fawn: Mammals know a young creature in need when they hear it.

A study has found that the sound of a crying child is recognised and acted upon by wild deer. 

During tests, wild mule and white-tailed deers ran to the rescue of distress calls made by various mammals including humans, cats and even infant silver-haired bats. 

During tests, wild mule (stock image pictured) and white-tailed deers responded equally to the cries of their own fawns as those of humans, cats and even infant silver-haired bats. Researchers wanted to test the theory that mammal mothers can recognise the distress call of any infant, regardless of species

The researchers wanted to test the theory that a mammal mother's instinct can recognise calls of any infant, regardless of species. 

Previous studies have found that humans react to the distress calls of their own children, but also infant pets such as dog and cats.

The same has been found for domestic dogs, who have been known to react to the cries of newborn humans.  

However, in both instances, it was assumed this was as a result of the domestication of these animals.

To see if this theory rang true among wild animals, Susan Lingle of the University of Winnipeg in Canada and Tobias Riede from Midwestern University in Glendale, Arizona record the cries of various infant mammals.

This included humans, fur seals, cats, dogs, young yellow-bellied marmots, sea lions, domestic cats, silver-haired bats, and several other deer species.

They also recorded more generic animal sounds such as birdsong and coyotes barking.

Each of these recordings were played using hidden speakers to wild female mule and white-tailed deers in Canada, while researchers monitored the deer's behaviour from afar.

The calls were played as they would normally be heard, as well as at various altered pitch levels.

A positive response was recorded if the deer approached the speaker, which is similar to how they would react if their own fawn was crying.

When the frequency of the individual calls was similar to that of a young mule deer, the female would approach the speaker - regardless of which mammal the cry belonged to.

The female deer came within 32 ft (10 metres) of the speaker, indicating a stronger response, when the calls of seals, marmots, and other deer species were played.

She came within 82ft (25 metres) during the calls of sea lions, bats and humans.

However, she didn't approach when the pitch fell outside the range of her fawn's call.

Recordings were played to the deers using hidden speakers, while researchers monitored the deer's behaviour. A positive response was recorded if the deer approached the speaker. The deers came within 32ft (10 metres) of the speaker during the calls of fur seals (left) , marmots (right) and other deer species

The deers came within 82ft (25 metres) during the calls of sea lions, cats bats and humans. However, they didn't approach when the pitch fell outside the range of her fawn's call

To test whether she was simply responding to pitch, rather than the type of call, the researchers then played the generic noises.

In every instance, the female deer did not react to these control sounds, even when they were played at the same pitch as the fawn's call, suggesting the mothers could distinguish between the two types of noises.

'Acoustic structure, behavioural context, and caregiver responses to infant distress cries are similar across mammals, including humans,' said the researchers.

'Our results suggest that acoustic traits of infant distress vocalisations that are essential for a response by caregivers, and a caregiver's sensitivity to these acoustic traits, may be shared across diverse mammals.

They also state that the results could explain why the frequency of distress calls differs among mammals, to make it easier for species to identify each other.

The findings are published in the journal The American Naturalist.

To test whether the deers were responding to pitch, rather than the type of call, the researchers played control noises, such as birdsong (stock image). The female deers did not react to these sounds, even when they were played at the same pitch as the fawn's call, suggesting they could distinguish between the two types of noises