All is not cool in the Antarctic.
Scientists have discovered a case of not too happy feet in penguin populations feeling stressed by human activity.
Researchers tested the stress responses of King penguins in colonies disturbed by humans over 50 years.
They were compared with other King penguins living in areas not visited by humans.
However penguins have adapted, and those living in the disturbed colonies are now better able to cope with the sight of approaching humans, loud noises, and being captured.
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Natural selection must have helped them adjust, scientists believe. Over time, stress-sensitive penguins were likely to have walked away and deserted the disturbed colonies, leaving the more resilient individuals behind.
"Our findings report a case of physiological adjustment to human presence in a long-studied King penguin colony, and emphasise the importance of considering potential effects of human presence in ecological studies," said lead scientist Dr Vincent Viblanc, from the University of Strasburg in France.
"A central question for ecologists is the extent to which anthropogenic disturbances (eg tourism) might impact wildlife and affect the systems under study.
"One of the major pitfalls of such research is in forgetting that, from the perspective of the wildlife studied, tourism and scientific research are not two worlds apart."
The research is published in the online journal BMC Ecology.
Scientists carried out the study on Possession Island in the sub-Antarctic Crozet Archipelago.
They compared 15 breeding penguins from disturbed areas with 18 from undisturbed areas. All penguins selected were brooding a chick aged from two days to one month.
A human approach to 10 metres and loud noises mimicked the effects of tourists, researchers and machinery.
One "high-intensity stressor", a capture, simulated researchers taking measurements.
Penguins from disturbed areas were less stressed by noise and approaching humans than those from areas free of human activity.
After capture, their maximum heart rate increased by 42% but they recovered more quickly.
In honour of the stress-sensitive creatures, here are 20 cute pictures of penguins teaching you how to relieve tension and be positive: