Do cliff geomorphological dynamics shape seabird nest site selection? A case study of guillemots (Uria sp.) and black-legged kittiwakes (Rissa tridactyla) in Iceland

Cliffs are significant breeding habitats for numerous species of seabirds. Yet, few studies have investigated the relationship between seabirds and cliffs, particularly regarding spatial and temporal variation in cliff characteristics and seabird nesting patterns. This study aims to address this gap by focusing on the nesting site selection of kittiwakes and guillemots in relation to geomorphological dynamics. The study followed a three-step approach, starting with identifying factors controlling geomorphological dynamics in Icelandic cliffs, leading to a typology of geomorphological functioning, and finally assessing whether there is a correlation between geomorphological instability and seabird nest site selection. To do so, a diachronic series of photographs from Skoruvíkurbjarg cliff (Northeast Iceland) and Krýsuvíkurberg cliff (Southwest Iceland) was analyzed using photographic comparison, which was then confirmed by on-site observations. The factors identified as having the greatest influence on the stability of cliffs, specifically the site (sheltered or seafront) and its profile (rectilinear or rugged), give rise to three main types of geomorphological functioning of cliffs. Geomorphological dynamics appear to have limited influence on seabird nest site selection, as the most stable type was progressively abandoned by seabirds, and no evidence of pre- or post-adaptation in response to geomorphological instability was observed. Nevertheless, this interdisciplinary study, combining ecology and geomorphology, highlights the value of long-term visual records in documenting both physical and population changes over time, offering insight into conservation priorities.