Wanderer of the deepest seas: migratory behaviour and distribution of the highly pelagic Bulwer’s petrel

Abstract

Small-sized nocturnal Procellariiformes are abundant predators in oceanic areas worldwide and are thought to play an important role in many marine food webs as consumers of superabundant mesopelagic prey. However, the spatial ecology and foraging behaviour of the great majority of these species remain largely unknown. We studied the non-breeding distribution and at-sea activity of a migratory small-sized Procellariiform, the Bulwer's petrels Bulweria bulwerii, from the Selvagem Island colony (subtropical Northeast Atlantic). We found that soon after breeding Bulwer's petrels migrate towards deep (mean depth of 4416 m), open oceanic waters of the tropical Atlantic, spending the winter far from shelf and shelf-break areas, on regions avoided by most other avian migrants in the Atlantic. When at sea, Bulwer's petrels spent more time flying during the night ([90 %, all year round) than any other seabird studied so far. This nighttime activity was not influenced by the lunar cycle, suggesting that this highly specialised nocturnal seabird is probably very well adapted to locating and capturing prey even in very dark conditions. The results from the present study may have important implications for the identification of important bird areas in the marine realm, whose boundaries have been delineated so far mostly on the basis of the distribution and behaviour of better studied medium-to large-sized seabirds.Keywords At-sea activity Á Bulwer's petrels Á Migration Á Procellariiformes Á Seabirds Zusammenfassung Wanderer ü ber der Tiefsee: Zugverhalten und Verbreitung des hochgradig pelagischen Bulwersturmvogels

The diet of a nocturnal pelagic predator, the Bulwer’s petrel, across the lunar cycle

“…The mesopelagic prey consumed by Bulwer’s petrels are very likely captured during their vertical migrations at night, since these petrels are known to significantly increase their flight activity during darkness, with a peak after sunset when most organisms of the deep scattering layers start ascending closer to the surface 34, 35 . Moreover, the analysis of stomach contents of seabirds shot at different times of the day revealed, based on the degree of prey digestion, that Bulwer’s petrels and other avian predators of mesopelagic fish ingest their prey mostly at night 37 .…”

“…While the occurrence of mesopelagic species in the diet of seabirds and other surface predators has been generally related to nocturnal foraging, it is still not fully understood whether the presence of mesopelagic prey results from active predation or from scavenging of floating remains at the surface 44 . The mesopelagic prey consumed by Bulwer’s petrels are very likely captured during their vertical migrations at night, since these petrels are known to significantly increase their flight activity during darkness, with a peak after sunset when most organisms of the deep scattering layers start ascending closer to the surface 34 , 35 . Moreover, the analysis of stomach contents of seabirds shot at different times of the day revealed, based on the degree of prey digestion, that Bulwer’s petrels and other avian predators of mesopelagic fish ingest their prey mostly at night 37 .…”

“…Bulwer’s petrels are shallow divers, reaching at most around 5 m depth 33 . Previous studies of Bulwer’s petrels showed predominantly nocturnal flight activity at sea 34 , 35 and a high reliance on mesopelagic prey 36 – 38 , although some studies also report consumption of surface prey 39 . Given that mesopelagic prey are generally found in deeper oceanic layers, usually at depths below 200 meters, such prey are hypothesized to become available to Bulwer’s petrels only at night, when species of the deep scattering layers ascend towards the water surface to feed.…”

An overview of migratory birds in Brazil

“…Records in Brazil are quite rare, with only one photographic record for Campos dos Goitacazes/RJ in December (Klein, 2011). However, recent geolocation studies determined that parts of the Brazilian territorial sea are regular wintering areas between August and May (Dias et al, 2015).…”

Monitoring of mercury in the mesopelagic domain of the Pacific and Atlantic oceans using body feathers of Bulwer's petrel as a bioindicator

“…Some seabirds, such as the Bulwer's petrel (Bulweria bulwerii), are specialised predators of mesopelagic prey (Neves et al, 2011;Harrison et al, 1983;Spear et al, 2007;Waap et al, 2017). Their low variability in diet (Spear et al, 2007;Waap et al, 2017) and wide spatial distribution (Dias et al, 2015;Brooke, 2004) makes them ideal candidates to monitor oceanic mercury contamination over multiple ocean basins. The Bulwer's petrel is a small (ca.…”