Breeding success of Eleonora’s falcon in Cyprus revisited using survey techniques for cliff-nesting species

The global breeding population of Eleonora’s Falcon (Falco eleonorae) 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
Eleonora’s Falcon suggested that the 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 including 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 Eleonora’s Falcon
breeding population in Cyprus. During a 6-yr study, we found that Cyprus
hosts ~138 ± 8 breeding pairs and that breeding success equals 1.54 ± 0.85
fledglings per breeding pair, and thus is 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, enhanced the efficiency and accuracy of this study, allowing us
to overcome the challenge of inaccessibility of nesting cliffs.