Surreptitious albatross
The surreptitious albatross is a large bird that only touches the ground during mating season, utilising thermals to hover high up in the sky the rest of the time where they are difficult to discern from the ground. Another fact about this bird is that it is actually an eagle that masquerades as a type of albatross, giving rise to the nickname "shark o' the sky," given to it by Wee Mad Arthur. The surreptitious albatross has no enemies that it can’t easily digest. Other unsuspecting birds will join it as it circles in a city's thermal bloom providing a ready meal for the albatross.
Wee Mad Arthur states that there are only two people that know about it, himself and the Professor of Ornithology at Unseen University, and he is the one that told the professor about it. He hitches a ride on one to travel to Howondaland from Ankh-Morpork using the new method of travel he learned from the Nac mac Feegle(sic): the craw step. The albatross appears only and briefly in Snuff.