Phenological divergence, population connectivity and ecological differentiation in two allochronic seabird populations

Abstract

Phenological divergence between conspecific populations breeding sympatrically is increasingly recognized as an important evolutionary process that may lead to allochronic speciation. However, the extent to which adaptation to differences in the timing of breeding may contribute to this process remains unclear. In this study, we assessed breeding phenology, population connectivity, and niche differentiation of two allochronic populations we of the Cape Verde Storm-petrel (Hydrobates jabejabe). We monitored nesting activity, marked individuals, tracked individuals during both the breeding and nonbreeding periods, and determined the trophic niche during both the breeding and nonbreeding periods. Timing of breeding for the two allochronic populations segregated into a hot (March-August) and cool (September-February) season (hereafter, hot and cool populations). These periods matched the two annual pulses of oceanic productivity around Cabo Verde, suggesting allochrony was primarily driven by a biannual cyclicity in food availability. Despite their allochronic breeding, there was, however, low differentiation between the hot and cool populations in spatial use, daily activity patterns, and trophic niche during both the breeding and nonbreeding periods. Further, the exchange of breeders between seasons, as documented through the recapture of marked individuals, may hinder seasonal adaptation by each population and ultimately, allochronic speciation. Consequently, allochrony alone may not be sufficient to drive speciation unless reproductive isolation between populations is complete or populations become strongly adapted to the environmental conditions associated with their timing of breeding.

Migratory Movements and Activity Patterns of White-Faced Storm-Petrels Pelagodroma marina Breeding in Cabo Verde

“…This pattern is well-documented for seabirds, such as gadfly petrels (Pastor-Prieto et al ., 2019) and little shearwaters (Ramos et al ., 2020). However, previous studies on Storm-petrels of the family Hydrobatidae have shown a weak relationship between activity and moon brightness (e.g., Militão et al ., 2022; Medrano et al ., 2022). Further research is needed to understand if the foraging behaviour of the Hydrobatidae and Oceanitidae storm-petrels families usually differ, which may reflect trophic differences.…”

“…We analysed changes in the daily proportion of time spent on the water, based on wet-dry data collected in the geolocators, under the assumption that it is an indicator of resting sessions (e.g., Militão et al ., 2022; Medrano et al ., 2022) during the non-breeding period. Two of the six tracks from the geolocators had incomplete wet-dry data (due to memory issues) and were excluded from the activity patterns analysis.…”

“…geolocators were attached to a metallic ring on the tibia using stainless steel wire (Supplementary Electronic Material, Figure 2). These devices have been used to study individuals of similar-weight species in the north Atlantic and Pacific, such as leach's Storm-petrel Hydrobates leucorhous (Pollet et al, 2014(Pollet et al, , 2019 and the Cape Verde Stormpetrel H. jabejabe (Medrano et al, 2022) without causing detrimental effects.…”

Between‐year and spatial variation in body condition across the breeding cycle in a pelagic seabird, the Red‐billed Tropicbird

“…Cabo Verde, consists of 10 volcanic islands that lie between 600 and 850 km west of Senegal, Africa (Figure 1a,c), located at the eastern boundary of the North Atlantic subtropical gyre at the southern limit of the Canary Current (Fernandes et al., 2005). The waters around St Helena are characterised by a generally low chlorophyll a concentration with substantial variation in spatial distribution between years (maximum range 0.3–0.5 mg/m 3 ) (Thorpe et al., 2020), whereas Cabo Verde is considered a more productive oceanic region with more enriched waters (chlorophyll a concentration range 0.06–4.1 mg/m 3 (Medrano et al., 2022; Silva, 2022; Vieira, 2019)).…”