This photo has caused a bit of confusion. I had first labeled it as Red Deer but a friend said it was a Sika Deer. SNH contacts are split on whether it is a Fallow Deer or a Sika Deer with a possibility of hybrid Red x Sika Deer.
I have personally seen Red, Roe and Fallow Deer on the Loch Lomond National Nature Reserve but I am unsure on the id characteristics of Sika Deer. Maybe the photo is not good enough for a positive identification. At least we can say that it is not a Roe Deer.