Breeding success of Eleonora's falcon (Falco eleonorae) in Cyprus revisited using survey techniques for cliff-nesting species

The global breeding population of Eleonoras falcon is distributed from the Canary Islands in the west, across the Mediterranean Sea, to Cyprus in the east. The remoteness of nesting colonies, which are predominantly located on sea cliffs and islets, renders breeding success estimation a challenging task, requiring a composite approach to assess each of the breeding stages. Early estimates of the breeding success of Eleonoras falcon suggested that Akrotiri colony in Cyprus had the lowest breeding success among all the colonies throughout the species breeding range, at a level seemingly unsustainable, suggesting the colony might have been in danger of gradual extinction. Here we use a diversity of survey methods using boat, ground and aerial surveys, with the incorporation of photography and photogrammetry, to reassess the breeding success and the effect of nest characteristics on the Eleonoras falcon breeding population in Cyprus. During a six-year study, we found that Cyprus hosts ~138 {+/-} 8 breeding pairs and that breeding success equals 1.54 {+/-} 0.85 fledglings per breeding pair, thus considerably higher than previous estimates. In addition, by analyzing temporal variation in breeding and nest characteristics, we found that early breeding and reuse of nests positively influence breeding success, but physical nest characteristics have a limited effect on colony productivity. The range of survey methods employed, as well as the array of photography techniques utilized, highly enhanced the efficiency and accuracy of this study, allowing us to overcome the challenge of inaccessibility of nesting cliffs.