Nocturnal foraging behavior of breeding piping plovers (Charadrius melodus) in New Jersey

--The nocturnal foraging behavior of breeding Piping Plovers (Charadrius melodus) was studied in New Jersey using a focal-animal approach in 1989 and 1990. More than 30% of the variation in the number of plovers foraging at night was explained by stage of the breeding cycle, tidal stage, and year. The greatest numbers of adult plovers fed in the intertidal zone during the prenesting and fledgling stages of the breeding cycle. Piping Plovers were more likely to be observed feeding during late ebb and early flood tides, than other times. Time devoted to feeding per 2-rain sample was similar at each study site but differed significantly during the tidal stages. Pecking rate was higher during late ebb and early flood tides than late flood and early ebb tides. Time devoted to being alert varied depending on stage of the breeding cycle. Prenesting plovers and individuals with fledglings fed longer and were alert less per 2-rain sample than plovers engaged in incubation or brood rearing. The nocturnal peck rate of Piping Plovers was considerably lower than daytime levels. Plovers foraging at night had significantly lower peck rates when disturbed. Abundance of intertidal polychaetes varied according to tidal stage and, where present, they constituted the main food of the plovers. We suggest that nocturnal foraging is a natural behavior pattern in Piping Plovers although it may vary in intensity. Future management should include the assessment of nighttime recreational use of beaches where Piping Plovers breed. Received 31 July 1992, accepted 25 November 1992. ALTHOUGH SOME BIRDS, such as many species of owls, are nocturnal, most are diurnal and perform all their activities during the day. Recently, several researchers have examined the behavior of shorebirds both during the day and at night. Night feeding has been documented in six plover species, including Grey Plovers (Pluvialis squatarola; Dugan 1981, Pienkowski 1982), Ringed Plovers (Charadrius hiaticula; Pienkowski 1982), Piping Plovers (C. melodus; Burger 1984), Dotterels (C. morinellus; Kalas 1986), Wilson's Plovers (C. wilsonia; Robert and McNeil 1989), and Semipalmated Plovers (C. semipalmatus; Robert and McNeil 1989), as well as several other shorebird species (Burger 1984, GossCustard 1984, Robert et al. 1989). However, these data, with the exception of those in Kalas (1986), were obtained either during migration or on the wintering grounds, and there are no quantitative studies during the breeding season of nocturnal behavior of shorebirds. Furthermore, Cairns (1977) stated that, as darkness falls during the breeding season, adult Piping Plovers (C. melodus) escort chicks to cover or to their former nesting territories. Feeding occurs at night during both migration and winter because energy requirements are high due to long-distance travel and adverse weather conditions, and because it is assumed that shorebirds cannot obtain enough calories during the short days at these times (Goss-Custard 1969, 1976, Heppleston 1971, Pienkowski 1981, 1982, Myers and McCafiery 1984, Puttick 1984, Johnson and Baldassarre 1988). This suggests that the long and warm days of spring and summer afford shorebirds ample time to attend to all energy needs without feeding at night. Robert and McNeil (1989), however, showed that some shorebirds species wintering, or residing year-round in tropical environments, which are warmer and therefore less energy demanding environments, fed at night as well. They suggested that the lack of data on night foraging in shorebirds was likely due to technological difficulties associated with night observation and that night feeding may occur all year. They suggested, as did Dugan (1981), Pienkowski (1982) and Townshend et al. (1984), that increased availability of invertebrate prey at night may make it advantageous for shorebirds to forage then. Feeding activity of several shorebird species is partly a function of tidal stage (Burger 1984, Burger et al. 1977, Goss-Custard 1984). The diurnal feeding-activity rhythms of Piping Plovers during the breeding season have been linked to tidal factors and human disturbance (Burger unpubl. data). Piping Plovers breed in the interior of North