Nocturnal and diurnal feeding behaviour of migratory shorebirds at a Northumberland Strait stopover site

Abstract

Nocturnal feeding is known to occur in several species of shorebirds, particularly in tidal environments. This behaviour is thought to be done either out of necessity – because energy from food cannot be sufficiently gained at other times of day – or out of preference – because it is advantageous to feed at night compared to other times of day. In Atlantic Canada, Semipalmated Sandpipers (Calidris pusilla) feed nocturnally in the Bay of Fundy, a stopover site used during their summer migration. These nocturnally feeding birds are known to make use of a tactile feeding behaviour known as skimming, common amongst sandpiper species. While the Bay of Fundy is known to host hundreds of thousands of Semipalmated Sandpipers each year, other stopover sites in Atlantic Canada host more diverse shorebird populations. Several species of shorebird are known to feed during stopover in the Northumberland Strait, however, there is a lack of research how these birds feed at night. We examined feeding behaviour, including foraging (pecking and probing) and skimming, of Semipalmated Sandpipers, White-Rumped Sandpipers (Calidris fusciocollis), and Semipalmated Plovers (Charadrius semipalmatus) during the day, evening, and night at Petit-Cap Beach, New Brunswick. We compared foraging rates and skim times across species and time periods, and determined the predictors behind these behaviours, to understand what drives nocturnal feeding. At night, we found that Semipalmated Sandpipers skimmed more than White-Rumped Sandpipers, and seemed to switch from foraging to skimming more quickly. Both species foraged more and skimmed less when moon illumination was high, though White-Rumped Sandpiper foraging and skimming were more influenced by polychaete abundance. Semipalmated Plovers did not feed at night, and had the lowest foraging rates during the day and evening. We found that birds that are capable of skimming will feed at night and make use of this behaviour, meaning that skimming ability of individual species likely plays some role in driving nocturnal feeding. As these skimming birds were also longer-distance migrants, we cannot rule out the energetic demand of migration as a driving force behind nocturnal feeding as well. These findings suggest birds may feed nocturnally for both necessary and preferential reasons, broadening our understanding of the drivers behind nocturnal feeding in the Northumberland Strait