The Ancient Murrelet, Synthliboramphus antiquus, is a bird in the auk family. It breeds primarily on the Aleutian Islands and other Alaskan islands.

These birds breed in colonies, their one or two eggs being laid directly amongst tree roots or in rock crevices. These small auks are nocturnal on the breeding grounds, presumably to reduce predation, and for the same reason the young are never fed at the nest, being taken to sea a couple of days after hatching.

Ancient Murrelets move south in winter as far as California, and odd birds are found inland in the USA, carried by autumn storms. The most remarkable record of this relatively short-distance Pacific migrant was a bird found on Lundy, Devon in spring 1990. Even more remarkably, the same bird return to this British island the following spring.

This small auk species is black on the head, throat and rear neck, grey-backed, and has white underparts. The yellow bill is short and stubby. It has a small rounded black tail. The summer adults have white head streaks giving an aged look and leading to the English name. Other plumages are similar, but lack the crown streaks.

This auk's flight is strong and direct, and it flies with fast wing beats due to its short wings. These birds forage for food like other auks, by swimming underwater. They mainly eat fish, also some crustaceans and other small invertebrates.