todropscience:

The heartwarming moment when two waved albatross (Phoebastria irrorata) lovers recognise each other and reunite after much time apart.

This albatross is unique in being the largest bird in the Galapagos Islands, and the only albatross species found entirely within the tropics. Waved albatross mate for life; a relationship that starts with an elaborate courtship ritual. This routine is a precise sequence of moves, which includes rapidly circling and bowing their bills, clacking their beaks together and raising their bills skyward whilst letting out a “whoo-ooo” call.

Presumably monogamy evolved in situations where young have a much better chance of surviving if both parents cooperate in rearing them. Nonetheless, the amount of time and energy invested by monogamous male parents varies greatly. By the way, 90 percent of all bird species are monogamous.

• video: BBC life story