Bird Bath

I don't know how this has happened, but my bird bath has sprung a leak.  I guess that's what you get for buying a cheap one (or should that be cheep one - ha ha!).  I only noticed the other day that the water level had dropped significantly, and the damp patch below the bath on the patio was not drying away despite how hot it is outside.  I thought it might just be that one of the birds had just had a vigorous bath - which wouldn't be the first time I've seen that - especially as the water was an alarming shade of brown.  But closer inspection reveals a split in the polyresin.  And I have absolutely no idea what could have caused it.  It doesn't look like something a bird or an animal could have done, and it certainly wasn't me.  A mystery.