You should reposition those guests looking like snakes or
lizards away from the glass doors. Give them the newspapers to read
Seriously, lots of bird species commit suicide this way.
With many it's because the glass is so clean they just don't see it - with
others it could be their reflection causing aggressive behaviour chasing away
I always keep my windows nice and grubby which saves
lots of work and allows birds to see the obstruction before hitting it. It also
still allows me to see out (just), and prevents hopeful perverts from seeing
Not an easy problem to solve without putting in some sort
of visual barrier which may not be acceptable.