Breeding biology and nesting ecology of the white-faced storm petrel (Pelagodroma marina eadesorum) colony in Laje Branca, Maio Island, Cabo Verde: Insights from experimental studies and medium-term field observations

Abstract

Seabirds are considered key indicator species for the global health of the marine environment. However, some populations are still poorly known. Here we combine experimental studies with field observation over three years (2019-2021) to determine the breeding biology and nesting orientation preference of the white-faced storm petrel (Pelagodroma marina eadesorum) colony in Laje Branca, Maio Island, Cabo Verde. We estimated the size of this colony at 2,440 breeding individuals. White-faced storm petrels showed an even distribution throughout the sandy plateau on Laje Branca, with similar occupied burrow densities in habitats close to the sea compared to the interior of the islet. Experimental results indicate that there is no influence of burrow orientation on burrow’s selection. The breeding season started in mid-November and ended in mid-June, with most burrow occupancy occurring between early February and April. There was an average occupancy rate of 59% in artificial burrows. The mean incubation period was 47 days (±7.08 SD) and breeding success was 64%, being respectively the lower and upper limits recorded for P. marina. We estimate a total of 1,220 occupied burrows (0.36 occupied burrows/m2) out of 3,162 burrows for the islet (0.93 burrows/m2). Considering the general decline of seabird populations worldwide and in Cabo Verde in recent centuries, the fact that Laje Branca has no permanent human presence and has a relatively high breeding success means that it is considered a site of national importance for the reproduction of this species and for the global conservation of the species.