They are 'nostrils' to let the pressure that builds up behind the screen escape.
Explanation. When something this size punches its way through the air , the air gets pushed out to the sides and it flows much faster. The slipstream - that flows past closest to the edge of the screen - tries to get back to where it was and it swirls back behind the screen creating an eddy - but also pressure on the inside of the screen. You can see this happening if you look at a rock sticking out from the river bed. The water behind the rock is either stationary or it is flowing upstream. (Canoeists use these for a bit of a rest when tackling the water in fast flowing rapids).
You might also notice as you are driving along that the fly or the bee that just manages to escape being hit by the winscreen, often overtakes your right arm and knocks itself out on the inside of the screen.
This also happens on the ST1300 - but the screen isn't fixed at the bottom like it is on the 1100. So the pressure behind the screen can escape at the bottom to be swept up the screen and into your face - unless you fit one with flip-up lip which directs the airflow over your helmet,
The same thing happens behind your back - often giving the sensation of being pushed forward. It tends to happen on both sides of you - wind swirling in from the right hand side to push forward behind you, then from the left. Alternating from one side to the other. This is of little consequence if you ride solo, but if you put a top box on the back riding solo, it can make the back end feel very unstable. The ST1300 has a mount which allows the top box to slide left and right - to provide a little movement to reduce the effect that it has on the bike. Fitting a pillion between you and the top box helps smooth out the air flow, so the eddy happens long after you have got out of the way. But you will feel it if you ride behind a van or lorry / truck.
