Researcher Short Articles


It’s all in the poo: life, death and hormones in a wild population of deer

By Alyson Pavitt - University of Edinburgh


Look around a field of animals. It may not be immediately apparent but all of them are different from one another. They’ll have different combinations of past experiences, different behavioural traits, and even subtle biochemical differences. In fact they may differ from one another as much as we do, albeit less obviously. My NERC funded PhD focuses in on one small part of this individual variation; how do hormone concentrations differ between animals? And what does this fundamentally mean for individuals and for the future of their populations?

The Isle of Rum off the west coast of Scotland is home to what is arguably our most famous population of red deer. We know many of the deer by name and have spent the past forty years watching their individual dramas play out in the Rum foothills. The past few years have also seen field assistants (and more recently me) sitting amongst the herds, clutching plastic bags and waiting fervently for the characteristic tail twitch that signifies a sample is on its way. It may not be glamorous, but measuring faecal hormones is the only real way of understanding how stressful different animals are finding their situation, and whether this is actually affecting things as fundamental as their reproduction and survival.

Our deer offer the almost unique opportunity to look at hormonal variation within and between years amongst animals in their natural habitat, not just for a couple of years, but in some cases I can look back across two decades of births and deaths to track individual and population changes through their hormones. Most of these deer I’ve never met, many died long before my PhD was even imagined, but using observations, measurements, and invaluable samples collected across the years, I can reconstruct their lives and explore the roles that hormones like testosterone have played in shaping them.

This research already appears to be bearing fruit. Testosterone levels in newborn calves, for example, may actually be influencing who lives and who dies within their first (and most difficult) year of life. And it is the calves that live – those who survive their first tough winter – that have the potential to go on to shape the future generations on the island.

Two calves in the evening sun. At this age distinct characteristics are already arising.
The little female on the right (with the expandable ID collar) was particularly playful and inquisitive, she was even interested in investigating me until she realised my shoelaces weren’t edible!