Thousands of starlings are due to flock above Aberystwyth in the evenings over the next three weeks.
Starlings flocking over the old college, Aberystwyth
RSPB Cymru said up to 20,000 birds are expected and it has set up a promotion event to urge people to photograph them.
They roost under the pier, making Aberystwyth one of the few towns in Wales where they flock, the RSPB said.
However, starling numbers in Wales have fallen by two thirds since 1994 and the bird is on an endangered species list.
RSPB Cymru has a stall on the seafront on some evenings to encourage people to watch and photograph the birds as they flock, before settling for the night.
Event officer Joe Hawthorne, said: "Many people find it hard to believe that they are declining so significantly.
"There are only about three places in the UK where they roost in towns and Aberystwyth is one of the few in Wales where they do it.
"It's an amazing sight when you see 20,000 birds moving around as one."
He added that although the starling was one of the commonest of garden birds, its decline elsewhere has put it on the "red list" of endangered species.
A spokesperson for RSPB Cymru said: "The event that Joe is leading at Aberystwyth pier during October is one of our Showing People Birds events, designed to encourage people to get out and about and experience wildlife first-hand.
"This particular scheme is important because it highlights the plight of starlings."