This appears to be...

...a deer starting to smile for the camera (on the other hand it could be a grimace!).

I managed to fit in a trip to Studley Royal Deer Park before I had to return the hired 300mm lens. The beasts were seemingly unphased by my presence, probably because there was a safe distance between us.

I have to say, I was more impressed with it than I had been photographing birds yesterday, more than likely because I was handling it better, despite deliberately using rather a slow shutter speed to test the lens performance. I could now be seriously considering buying one.