Mary's journey to Bethlehem for the birth of Jesus may have involved an inspired choice of transport, according to new research.
Experts believe donkeys are better qualified than their closest relatives to cope with warmer weather and would have been ideally suited to carrying the expectant mother and her precious cargo.
Scientists at the University of Portsmouth found the animals are better adapted to hot, arid climates common in the Holy Land than other members of the horse family.
A university spokeswoman said: "We might associate donkeys with Christmas, but new research from the University of Portsmouth shows the animals are keener on hotter periods of the year.
"Donkeys, it seems, love sun and warmth.
"That's the finding of the first study to examine the conditions under which healthy non-working donkeys and mules seek shelter in hot, dry climates.
"It found that whilst mules would seek shelter from the heat and insects, donkeys enjoyed the sunshine and warmth for longer."
Equine behaviour expert Dr Leanne Proops, of the university's department of psychology, led a team who studied 130 donkeys and mules at two locations in southern Spain during a seven-week period over the summer for the research, which is published in the Journal Of Applied Animal Behaviour Science.
In both locations, researchers recorded the animals' need for shade during temperatures ranging between 14C and 37C, with vets from The Donkey Sanctuary on hand to ensure they were healthy.
Dr Proops said: "We found that donkeys are less likely to seek shelter from the heat and light than mules.
"The sensitivity of mules to higher temperatures and sunlight may be due to the geographically different evolution of horses and donkeys and their adaptations to different climates.
"Donkeys are better adapted to arid, hot climates and hence higher sunlight levels.
"In contrast, horses are more adapted to cold conditions, and our previous research has shown that donkeys seek shelter far more often than horses in cold, wet conditions.
"As a hybrid, mules often display attributes that are a mixture of both species, such as their winter hair coat growth.
"Therefore, it might be expected that mules are less adapted to conditions of high temperatures and sunlight levels than donkeys, as we found in this study."
Dr Faith Burden, director of research and operational support at The Donkey Sanctuary and co-author of the paper, said: "The majority of working equids worldwide are exposed to hot climates and, as a consequence, may suffer from issues such as dehydration and heat stress.
"By establishing the natural shelter-seeking behaviour of healthy donkeys and mules across climates, we hope to be able to inform welfare guidelines and encourage good management of these animals."