I was at the Dawlish Warren Nature Reserve on Sunday and there are Dartmoor Ponies there grazing over winter. I noticed a Magpie sitting on the back of one of the ponies, but then a bit later noticed that it was sitting on its head and bending down to the eye of the pony, presumably to pick off flies or parasites? There was no aggressive behaviour from the Magpie and the pony appeared to be completely unmoved by its actions - it all seemed very civilised and symbiotic! I can't find any other reference to this specific interaction, so I would be interested to know what others think may be happening.
Richard
Dartmoor ponies, being warm blooded mammals, will be home to fleas, ticks and many other parasites. You will have seen flies regularly hanging around cattle, horses and other livestock, so do fleas, ticks and other insects. These parasites will be food for the magpies, and other birds, as well.
If you watch carefully in fields, open ground and anywhere where livestock feed, you will regularly see magpies perched on livestock, appearing to hitch a ride, when really, they're insect hunting.
Mike
Flickr: Peak Rambler
(Pardon the Scottish Accent)