Elephants that paint, birds that make music: Do animals have an aesthetic sense?

Some forty years ago, the first gallery exhibition of paintings not of but by chimpanzees shocked the art world and precipitated much debate. The animals had produced abstract paintings pleasing to the human eye. Did this mean they had an aesthetic sense, an appreciation of beauty? Elephants, too, can paint - sales of their canvases are now being used to raise money for zoos and conservation - and so can seals and several other species. Is this really art, or are the paintings more or less accidentally pleasing to us but not to the animal itself? How can we decide whether these strokes of paint are art or mere daubing, made without awareness or any degree of artistic motivation or aesthetic sense? A similar question can be asked about other forms of art, especially music. Birdsong, for example, may be music to our ears, but do the birds appreciate it as an art form?