Data from: Pre-laying movements of male and female Scopoli's Shearwaters Calonectris diomedea in the Central Mediterranean

In Procellariiformes the pre-laying period is a prime determinant of a population's reproductive output, particularly given their reliance on a single annual clutch of only one egg. Despite its importance, it remains one of the least studied life-phases of procellariiform seabirds. Here we present the pre-laying movements within the central Mediterranean of Scopoli's Shearwaters Calonectris diomedea breeding in Malta. We tracked 16 birds (six pairs and four additional females) with GPS devices in spring 2016. We found that males exhibit an extended absence from the colony during the females' pre-laying exodus, resulting in both sexes embarking on distant and prolonged foraging trips. These trips differed in terms of duration and distance from the foraging trips preceding them, in both males and females. Body mass changes over the pre-laying period suggest that during this time females invest nutrient acquisition into the developing egg, while males build up body reserves in order to take on the first incubation shift. This highlights the existence of different energetic requirements between the sexes during the pre-laying period. The implications for pair synchrony, food availability and bycatch risk during the pre-laying period are discussed, emphasising the transnational responsibility to safeguard the future of this declining seabird.