Alonissos animal welfare:

Mother and kittens on the donkey track near Patitiri

One of the many features of Greek islands which visitors encounter is the number of stray and feral cats. It's not unusual for holiday makers to adopt a cat (or cats) during their stay and provide some food for them -despite some tour operators attempts to discourage this. The long gone specialist holiday company Laskerina even went as far as warning against putting out milk for cats on the grounds that it would attract snakes "snakes love milk". I like a challenge and felt obliged to trawl the internet for some evidence of that but failed to find anything to back up that assertion at all. It's not even good for them. That said, milk is often not good for cats either (or hedgehogs for that matter) so if you are going to feed strays give them what they need -meat (and water, of course). Cat food is readily available in Greek mini markets just like anywhere else.
But what about the ones you can't help and the winter months when there are few visitors? That is where organisations such as ASAP (Alonnisos Society for Protection of Animals) comes in. Providing year round care and help for all animals (not just cats) this local charity carries out a range of activities including feeding programmes, re-homing for cats and dogs, and importantly bringing in vets to the island to provide medical care and spaying and neutering.
Of course, many islands have similar organisations so if you have a favourite Greek island and want to help the animals there try doing an internet search under "animal welfare" (or similar) to find the
Regards, David.
Edit on 25/1/2018: I have removed the previous links to ASAP as they are no longer valid. It seems that due to changes in Greek law ASAP no longer operates in an "official" capacity. I have been assured, however, that supporters on the island continue to work to help the animals there -look out for them if you are visiting the island.