Non‐breeding distribution and at‐sea activity patterns of the smallest European seabird, the European Storm Petrel (Hydrobates pelagicus)

Abstract

Determining the non-breeding distribution and activity patterns of migratory animals is essential to understand the trade-offs across breeding, moulting and migratory periods and to evaluate the differential levels of exposure of these animals to threats throughout the year. By taking advantage of the current miniaturization of geolocators, during the breeding season of 2019, we deployed geolocators on 10 European Storm Petrels Hydrobates pelagicus breeding on Benidorm Island, Western Mediterranean, to determine the distribution and activity patterns of this small seabird species. Of the eight individuals that were recaptured with usable geolocation data, all individuals migrated to the North Atlantic Ocean, ranging between the Canary Islands and south of Iceland. They possibly take advantage of the more productive waters in the North Atlantic areas explored during the non-breeding period compared with the Western Mediterranean areas explored during the breeding period. This migratory pattern contrasted with the partial migration described for individuals breeding in the Central Mediterranean. Tracked individuals were more synchronous in their prenuptial than in their postnuptial migratory phenology, probably due to a higher probability of breeding success related to earlier arrival to the breeding area. At-sea activity data indicated that individuals spent more time on the water at night (and especially on those nights around the new moon) during the first half of the non-breeding period (matching the dates of the moulting period of the species). Although birds may begin to moult their feathers while breeding, some seemed to overlap the moulting period with the postnuptial migration. Our results show that multicolony studies are needed to understand the drivers of distinct migratory patterns at intra-and inter-population levels and how small migratory species trade-off the overlap of moult with other energetically demanding activities such as breeding or migrating.

Using long‐term data series to design adequate protected areas that ensure the conservation of inconspicuous small petrel species

“…In our study, the presence of individuals from different breeding populations at different distances and at different times of the annual cycle could explain the occurrence of the species in two distinct periods with very different temperatures, which could be related with two waves of species presence in our study area in different seasons. Indeed, the key marine areas identified in this study congregate birds that breed in the north of the Peninsula and those breeding in the North Atlantic in their migration movements towards the African coasts (Sanz‐Aguilar & Lago, 2021), but also birds of the Mediterranean subspecies, which winter in the Iberian Atlantic coasts (Lago et al., 2019; Militão et al., 2022). Unfortunately, the lack of regular campaigns throughout all seasons, as well as the relatively low conspicuousness of the species, made it challenging to conduct models which take into account potential intra‐annual variability.…”

“…A second important core area for the ESP was located in the Gulf of Cádiz, in the southern part of our study region. This zone has recently been identified as one of the most important wintering areas for Mediterranean ESP (Militão et al., 2022). Additionally, the Gulf of Cádiz has been revealed as a key area for a significant number of seabird species that feed in this area outside the breeding season, including the critically endangered Balearic shearwater Puffinus mauretanicus (Arroyo et al., 2020).…”

“…Moreover, the use of complementary methodology such as GPS devices, would improve the knowledge on the distribution of these species (Bolton, 2021). Currently, the small size of seabirds like the ESP still greatly limits the use of most GPS devices, but technological progress in its miniaturisation is offering recent and novel results (Lago et al., 2019; Militão et al., 2022).…”

“…To be effective, a SPA must cover the entire annual cycle of a species, and because breeding, wintering and migratory ESPs use the Atlantic Iberian arc across the year (Militão et al., 2022; Sanz‐Aguilar & Lago, 2021), we analysed ESP occurrences during the overall period 2005–2019, without season differentiation. In addition, to consider the annual variability between the most suitable zones, we evaluated the consistency of the ESP distribution across the years by analysing the annual distribution separately.…”

“…However, the Mediterranean subspecies faces greater conservation concerns as it comprises less than 10% of the total population and is restricted to a few predator‐free islands in the Mediterranean basin (Lago et al., 2019; Sanz‐Aguilar & Lago, 2021). Both subspecies can be found in the Atlantic Iberian arc during specific periods of the year (Carboneras et al., 2021; Militão et al., 2022) and at least 15 SPAs have been declared in the area with the aim of protecting the ESP among other seabird species (Arcos et al., 2009; BOE, 2014; Pereira et al., 2018; Ramírez et al., 2008).…”