KLEEFSTRA R (2020) Going out on a moonlit night: nocturnal foraging by White-fronted Geese Anser albifrons and Barnacle Geese Branta leucopsis in relation to new and full moon. LIMOSA 93 (1): 23-27.

During the winters of 2010/11 and 2012/13 the nocturnal behavior of White-fronted Geese and Barnacle Geese was studied around a night roost at lake Terkaplester Poelen, in the central part of the Dutch province of Friesland (Fig. 1). During five dark nights with new moon and four clear nights with full moon the numbers of geese arriving at the roost in the two hours around sunset were counted and compared with the numbers of geese leaving the next morning around sunrise. In between the counts around sunset and sunrise the study site was visited during the night with night vision goggles, to see if any geese were foraging outside the night roost.
On average both goose species arrived later at the night roost during full moon than during new moon, although these percentages overlapped in both species (Fig. 2). In the case of the White-fronted Goose an average of 76.0% arrived in the two hours around sunset with new moon, of which 90.3% arrived in the hour after sunset. With full moon an average of 41.5% arrived in the two hours around sunset, all of them in the hour after sunset. Of the Barnacle Geese on average 70.3% arrived in the two hours around sunset during new moon, of which 52.7% in the hour before sunset. With full moon on average 35.2% arrived around sunset, of which 100% after sunset.
Hardly any White-fronted Geese were present in the fields around the night roosts with new moon (on average 0.3%), while with full moon 12.6% of the roosting White-fronted Geese were seen just outside the night roosts. In the case of the Barnacle Goose, this was 0% and 4.8% respectively. It was noticeable that groups of foraging geese were all found within a distance of less than 100 meters from open water. This could be the flooded grasslands of the night roosts, as well as the deeper drainage water of lake Terkaplester Poelen and adjacent canals.

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