slippery landing place

bird lovers are funny old people. some are even funny young people. they’ve even put up signs to warn them that their landing places might be a bit slippery
https://www.funkypancake.com/blog/stuff3/2006/01/IMG_6018-thumb.jpg
if they are slippery then they’ve only got themselves to blame.
https://www.funkypancake.com/blog/stuff3/2006/01/IMG_6020-thumb.jpg
and what is a landing stag anyway ?