I had borrowed an $11,000 super telephoto lens from Canon Professional Services and I only had it for a week and it was foggy the whole time I had it.  Foggier than I'd ever seen it on Block Island.  So foggy I could stand on the shore and not see the water.  But I did get this picture of a Great Egret and the one that follows. 

One thing I'll tell you if you want to take pictures of birds in flight.  They don't stand still for anything.   Your chance to get a picture goes by in a fraction of a second.  You've got to be ready.  You've got to be fast, and that will come with practice, but even so, expect a lot of less than wonderful pictures.  To put it a certain way, you have to kiss a lot of frogs to get a keeper.   But when you do get one, it's worth it.  These are beautiful birds and they deserve to be shown in their glory.