Elephants have provided further evidence of their intelligence and self-awareness in an experiment involving a stick tied to a mat.
Researchers required Asian elephants to walk on to a mat, pick up a stick and pass it to an experimenter in exchange for a food reward.
In control conditions the sticks were loose, but for the experiment the sticks were tied to the mat - meaning the elephant's body weight prevented them passing the stick to the researcher unless they walked off the mat.
The University of Cambridge study found that elephants stepped off the mat on average 42 out of 48 times during the experiment, compared with three out of 48 during the control.
Researchers said this shows elephants are able to recognise their bodies as obstacles to success in problem-solving.
The sample size was 12 elephants at the Golden Triangle Asian Elephant Foundation in Thailand, and sets of ten trials were run until the elephants passed the stick to the experimenter in five consecutive trials.
The test was devised by Dr Josh Plotnik, a visiting researcher at the University of Cambridge and founder of conservation charity Think Elephants International, and his colleague Rachel Dale.
"Elephants are well regarded as one of the most intelligent animals on the planet, but we still need more empirical, scientific evidence to support this belief," said Ms Dale. "We know, for example, that they are capable of thoughtful co-operation and empathy, and are able to recognise themselves in a mirror.
"These abilities are highly unusual in animals and very rare indeed in non-primates.
"We wanted to see if they also show 'body-awareness'."
Self-awareness in animals and young children is usually tested using the mirror self-recognition test to see if they understand that the reflection is their own.
Only a few species other than humans have shown they can do this - great apes, dolphins, magpies and elephants.
Critics have argued that the mirror test is limited in its ability to demonstrate complex thoughts and understanding, and that it may be less useful in testing animals that rely less on vision than other species.
The stick and mat test was adapted from one in which children were asked to push a shopping trolley attached to a mat on which they were standing.
"This is a deceptively simple test, but its implications are quite profound," said Dr Plotnik. "The elephants understood that their bodies were getting in the way, so they stepped aside to enable themselves to complete the task.
"In a similar test, this is something that young children are unable to understand until they are about two years old.
"This implies that elephants may be capable of recognising themselves as separate from objects or their environment.
"This means that they may have a level of self-understanding, coupled with their passing of the mirror test, which is quite rare in the animal kingdom."
The study, largely funded by a Newton International Fellowship from the Royal Society awarded to Dr Plotnik, is published in the journal Scientific Reports.