At Birsay

We walked along the cliff at Birsay yesterday to see if there were any puffins left to photograph.  We found some but they were a long way off.  
There were a lot of nesting birds including this shag with two young .. but it looked as if they were sitting on some white sticks.  All around this area are discarded window frames, complete with broken glass and the third photo is the same group showing the broken glass shards precariously hanging virtually over their heads.
What kind of person thinks it is a good idea to dump their rubbish in a place like that, where it would be impossible to retrieve it?
Possibly people fitting new windows and getting rid of the old ones?