New Delhi, May 16 -- When a British citizen turns 100, they get a message from the monarch. It's a tradition dating back to 1917 when King George V started sending telegrams to congratulate citizens on landmark birthdays.

But Sir David Attenborough is no ordinary citizen. And he didn't get just a letter or a telegram.

In a video produced by the BBC's Natural History Unit, a relay race of animal couriers helped deliver the 100th birthday message from King Charles in Balmoral Castle in Scotland to Attenborough at Royal Albert Hall in London.

A border collie handed the letter to an eagle who dropped it on a hedgehog who carried it wedged between its spines till a red squirrel picked it up. A flock of geese, an otter, a swan, a duck, a fox...