They are strategically place to stop the waterfall tray from tipping over into the pond.
Plus they add a bit of humour to the whole affair.
I think we are all sometimes far to serious in life, and to me things like this can break up that feeling and make us laugh.
Of course the waterfall has its purpose too, in this picture you will see the swan sat on a bag of ceramic rings, these are in their to catch and bits and bugs in the water as it flows back into the pond, its just one stage of many in the filtration of the pond.
Speaking of that I am working at the moment on designing a Bio filter that will use fast spiral flow of water and roots of plants to catch the rubbish in the water, but until I make it this is my present solution. of course i could go out and buy a filter pump with sponges in side etc but where is the fun in that, plus the bio will use only natural stuff to do the filtration.
Keep and eye out for the post - Bio Filtration system to keep pond clear and bug free.
Some other garden tips....