These nets are supposed to deter birds, mainly pigeons and gulls. 

Rather than deterring them, they often end up getting trapped and unable to free themselves. 

Recently, there was a pigeon trapped in one of these nets on a ledge around 14 feet high on the shop next to where I work. 
After being reported several times to the RSPCA and fire brigade by different people, the pigeon was still there. 24 hours later. 

Finally I managed to get one of the shops further down to force open a window and reach the pigeon. By this time it was dead.

It had struggled the whole time to free itself only to become more entangled. This can only be described as a torturous death and shouldn’t be something that happens.
A lot of these nets are out of sight, so often these birds torture go unseen.  

Not only are these nets a danger to wildlife, they are a danger to the people who then try to help the poor birds trapped in them.