Acceleration and depth data on foraging behaviour of rhinoceros auklets breeding at Teuri Island

Marine top predators are expected to adjust their foraging behaviour at
multiple time scales concomitantly with changes in forage fish
availability. Rhinoceros auklets Cerorhinca monocerata rearing chicks at
Teuri Island, Japan Sea, fed on anchovy Engraulis japonicus in 2012 and
2013 (anchovy regime) but switched to sand lance Ammodytes spp in 2019 and
2020 (sand lance regime). Here, we studied their at-sea behaviour using
the GPS locations of 33 birds and the depth-acceleration records of 26
birds, and compared their foraging behaviour between these prey regimes.
At the trip scale, auklets used offshore waters (>50 m sea depth)
and coastal waters in the anchovy regime but used mainland coastal waters
(<50 m sea depth) in the sand lance regime. In the sand lance
regime, the birds also conducted more overnight 2- to 4-day trips in 2020
and spent more time flying during 1-day trips as they fed in further areas
compared to the anchovy regime. At the dive scale, auklets frequently dove
to both <5 m and 20 – 30 m depths in the anchovy regime but mainly
to <5 m depth in the sand lance regime. Within each dive, auklets
showed a greater number of fast/strong wing stroke events in the anchovy
regime than in the sand lance regime. These changes in auklet behaviour
reflected the different habitats, depth distribution, and swim speed of
the targeted prey species. Our study shows the behavioural flexibility of
a wing-propelled flying-diving seabird in response to the inter-annual
shifts in the dominant forage fish community. It also indicates the
ecological constraints on the mechanisms determining nest productivity in
this day-foraging/night-provisioning seabird.