Leave Fawns Alone

We are coming up to the time when deer does give birth to their fawns (Fr. faons) and I thought it was time for a bit of public education.

Young fawns are left hidden alone in the grass or undergrowth for many hours during the day, from the time they are newborn to a few weeks old.  Meanwhile their mothers go off some distance away so predators are not alerted to the presence of the fawn. The does browse on the new spring vegetation that gives them the level of nutrition they need. It is important for them to keep up the supply of milk that the fawns require to thrive. 

A Roe Deer fawn in our orchard several years ago.

Newborn fawns are very small -- not much bigger than a rabbit -- so they can remain hidden quite easily. Fawns are famous for remaining completely still no matter how close you get. If you stumble across one, please leave it alone and move away as quickly and quietly as possible.

If you are walking through lightly wooded prairie at this time of year, please keep dogs on leads. The fawns will sit tight until you are within about half a metre of them. Startling them and causing them to run uses up their valuable energy and significantly reduces their chances of survival. Under no circumstances touch them or speak to them (the human voice, no matter how soothing a tone you think you are using, is extremely frightening to them).

A Roe Deer fawn hidden in long grass in the middle of a prairie in Vienne.

Roe Deer Capreolus capreolus (Fr. chevreuil) numbers in France are increasing, but the rate of increase is slowing. Fewer fawns are being born and fewer are surviving to adulthood. Careful monitoring of the does parturition dates reveals that they haven't significantly changed from year to year, even though the date of leaf burst in the forest is now earlier by about a fortnight compared to 35 years ago when the monitoring started.

This means that the deer are no longer giving birth to coincide with peak availability of food for the mothers, which impacts on their milk supply. Roe Deer are browsers, feeding mainly on coppiced trees,  and rely on the new shoots in their forest habitat. Fawns aren't gaining weight and strength as quickly as they should and as a consequence are more vulnerable to predators, disturbance and other stresses. The likely cause of death for most fawns is lack of food, as the deer locally in the Touraine are not subjected to pressure by hunters or predators.

Scientists have concluded that Roe Deer ovulation and conception, and therefore parturition, is linked to day length, not temperature, and that they are likely to be climate change losers in the long run. This is exacerbated because does all tend to give birth around the same time (May), and those few which give birth early will not be sufficient to cause an evolutionary change. All the fawns are vulnerable at the same time, which means that extreme weather conditions, for example, could wipe out an entire generation. Other studies have indicated that Greenland caribou (reindeer) have similar issues, but that Red Deer are adapting and giving birth earlier (interestingly, by reducing gestation periods).

The average springtime (April - June) temperatures have increased year on year and are now nearly 1.5° higher than when monitoring these deer began. This rise in temperature is causing trees in particular to respond by bursting into leaf earlier. Thirty-five years ago Roe Deer gave birth exactly when the tender green shoots of many plants were available, full of nutrition before their energy goes into flowering and seed production. The mismatch between birth dates and peak vegetative flush has increased by about half a day a year. A fawn born on or before 12 May has a 50% chance of surviving to winter and adulthood. After that date, survival rates plummet, and one born at the end of May only has a 24% chance of surviving. (It should be noted that the number of days mismatch between birth date and peak vegetative flush in any given year is a better predictor of survival rate than birth date per se.) Older, heavier does tend to give birth earlier, so there is some natural selection mitigating the effects of climate change, but probably not enough in the long term, and the tendency to give birth earlier is not strongly heritable.