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.

Plastic pollution is distributed patchily around the world’s oceans. Likewise, marine organisms that are vulnerable to plastic ingestion or entanglement have uneven distributions. Understanding where wildlife encounters plastic is crucial for targeting research and mitigation. Oceanic seabirds, particularly petrels, frequently ingest plastic, are highly threatened, and cover vast distances during foraging and migration. However, the spatial overlap between petrels and plastics is poorly understood. Here we combine marine plastic density estimates with individual movement data for 7137 birds of 77 petrel species to estimate relative exposure risk. We identify high exposure risk areas in the Mediterranean and Black seas, and the northeast Pacific, northwest Pacific, South Atlantic and southwest Indian oceans. Plastic exposure risk varies greatly among species and populations, and between breeding and non-breeding seasons. Exposure risk is disproportionately high for Threatened species. Outside the Mediterranean and Black seas, exposure risk is highest in the high seas and Exclusive Economic Zones (EEZs) of the USA, Japan, and the UK. Birds generally had higher plastic exposure risk outside the EEZ of the country where they breed. We identify conservation and research priorities, and highlight that international collaboration is key to addressing the impacts of marine plastic on wide-ranging species.