Symbiosis

From the U.S. Fish and Wildlife Service, Mountain-Prairie Region:

Symbiosis: interaction between two different organisms living in close physical association, typically to the advantage of both.

That just about sums up what's going on between this magpie and these moose calves on Seedskadee National #WildlifeRefuge. The bird gets a free meal, while the moose are rid of ticks and other parasites that can lead to a number of serious health issues, some of which can be fatal. 

Photo: Tom Koerner / #USFWS