Cliff ledges and crevices are important for a range of species. The cliff ledges in the Snowdonia mountains host a number of locally and nationally rare species, including the Snowdon lily (Gagea serotina). Similarly, the ledges on the limestone in South Gower host the locally abundant, but nationally rare, yellow whitlow-grass (Draba aizoides) along with many other species. Cliff ledges are also critically important for the important seabird colonies scattered around the Welsh coastline, especially for the guillemot (Uria aalge), razorbill (Alca torda) and Kittiwake (Rissa tridactyla) populations. Rock crevices also host a number of breeding bird species including the internationally rare red-billed chough (Pyrrhocorax pyrrhocorax). These crevices can also host some of the less common fern species.