The Effect of Moonlight on Scopoli's Shearwater Calonectris diomedea Colony Attendance Patterns and Nocturnal Foraging: A Test of the Foraging Efficiency Hypothesis

Abstract

Moonlight is known to affect the nocturnal behaviour and activity rhythms of many organisms. For instance, predators active at night may take advantage from increased visibility afforded by the moon, while prey might regulate their activity patterns to become less detectable. Many species of pelagic seabirds attend their colony only at night, in complete darkness, avoiding approaching their nest sites under moonlight. This behaviour has been most often interpreted as an antipredator adaptation ('predation avoidance' hypothesis). However, it may also reflect a lower foraging efficiency during moonlit nights ('foraging efficiency' hypothesis). Indeed, moonlight may reduce prey availability because preferred seabird prey is known to occur at higher depths in moonlit nights. Using high-accuracy behavioural information from data loggers, we investigated the effect of moonlight on colony attendance and at-sea nocturnal foraging in breeding Scopoli's shearwaters Calonectris diomedea. We found that birds departing for self-feeding trips around the full moon performed longer trips than those departing around the new moon. On nights when the moon was present only partly, nest burrow entrances took place largely in the moonless portion of the night. Moreover, contrary to predictions from the 'foraging efficiency' hypothesis, nocturnal foraging activity increased according to moonlight intensity, suggesting that birds increased their foraging activity when prey became more detectable. This study strengthens the idea that colony attendance behaviour is strictly controlled by moonlight in shearwaters, which is possibly related to the perception of a predation risk.

A new algorithm for the identification of dives reveals the foraging ecology of a shallow-diving seabird using accelerometer data

“…Given that birds performed only short trips during early chick-rearing, the number of dives during the afternoon was higher during short trips than during long trips. The dive rates per hour recorded in this study differed from observations of Rubolini et al (2015) who noticed a peak of dive activity at 21:00 (local time) when we observed the minimum dive rates. This difference might be methodological, based on the estimation of dive occurrences using compass loggers.…”

“…Dive data from previous studies on Scopoli's shearwater are in line with our results: Grémillet et al (2014Grémillet et al ( ) recorded 9 ± 8 (2012 and 49 ± 47 (2013) dives per trip using TDRs during chick-rearing, while our algorithm recorded 84.7 ± 156.4 dives per trip in the same period. Rubolini et al (2015) recorded an average of 0.35 ± 0.02 dives per hour using compass loggers during chick-rearing. Compass loggers identified dives using temperature variations recording every 5 s. In the same reproductive phase, our algorithm identified 1.7 ± 1.6 dives per hour.…”

“…Given that compass loggers use only temperature variation to record a dive, is it possible that some of their recordings might be preening events instead of real dives. Indeed, at 21:00, birds usually aggregate in front of the colony (raft) waiting for good conditions to visit the nest (Rubolini et al 2015).…”

“…Indeed, diurnal foraging might be more profitable than nocturnal for visual predators (McNeil et al 1993). However, Scopoli's shearwater also forages at night (Rubolini et al 2015). At this time, shearwaters can take advantage on the migration to the surface of some prey species at night, such as crustaceans and squids (Spear et al 2007).…”

Brood-guarding behaviour in Bulwer's Petrel (Bulweria bulwerii)at two East Atlantic colonies

“…The lunar cycle is known to impact colony attendance in small nocturnal Procellariiformes (Mougeot & Bretagnolle 2000). In general, birds attend the colony more often on dark, new-moon nights, which is usually explained as an anti-predator behaviour (Rubolini et al 2014). The lunar cycle may also affect the foraging success of Bulwer's Petrels by influencing the sub-surface availability of mesopelagic fishes and squids (Hernandez-Leon et al 2002), which represent the bulk of their diet (Neves et al 2011).…”