The Auk 111(3):579-587, 1994 NOCTURNAL FORAGING BEHAVIOR OF BREEDING PIPING PLOVERS (CHARADRIUS MELODUS) IN NEW JERSEY KEVIN J. STAINE AND JOANNA BURGER Departmentof BiologicalSciences, Rutgers University, Piscataway, New Jersey08855, USA ABSTRACT.--Thenocturnal foraging behavior of breeding Piping Plovers (Charadriusmel- odus)was studied in New Jerseyusing a focal-animalapproach in 1989and 1990.More than 30% of the variation in the number of plovers foraging at night was explained by stageof the breeding cycle,tidal stage,and year. The greatestnumbers of adult ploversfed in the intertidal zone during the prenestingand fledgling stagesof the breeding cycle. Piping Ploverswere more likely to be observedfeeding 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 significantlyduring the tidal stages.Pecking rate was higher during late ebb and early flood tides than late flood and early ebb tides. Time devotedto being alert varied dependingon stageof the breedingcycle. Prenesting plovers and individualswith fledglings fed longerand were alert lessper 2-rain samplethan ploversengaged in incubationor brood rearing. The nocturnal peck rate of Piping Plovers was considerablylower than daytime levels.Plovers foraging at night had significantlylower peck rateswhen disturbed.Abun- dance of intertidal polychaetesvaried accordingto tidal stage and, where present,they constitutedthe main food of the plovers. We suggestthat nocturnal foraging is a natural behavior pattern in Piping Ploversalthough it may vary in intensity. Future management should include the assessmentof nighttime recreationaluse of beacheswhere Piping Plovers breed.Received 31 July1992, accepted 25 November1992. ALTHOUGHSOME BIRDS, such as many species that shorebirdscannot obtain enough calories of owls, are nocturnal, most are diurnal and during the short daysat thesetimes (Goss-Cus- perform all their activitiesduring the day. Re- tard 1969, 1976, Heppleston 1971, Pienkowski cently, several researchershave examined the 1981, 1982,Myers and McCafiery 1984,Puttick behaviorof shorebirdsboth during the day and 1984, Johnsonand Baldassarre1988). This sug- at night. Night feeding has been documented geststhat the long and warm daysof springand in six plover species,including Grey Plovers summerafford shorebirdsample time to attend (Pluvialissquatarola; Dugan 1981, Pienkowski to all energy needs without feeding at night. 1982),Ringed Plovers(Charadrius hiaticula; Pien- Robert and McNeil (1989), however, showed kowski 1982), Piping Plovers(C. melodus;Bur- that some shorebirdsspecies wintering, or re- ger 1984), Dotterels (C. morinellus;Kalas 1986), siding year-round in tropical environments, Wilson's Plovers (C. wilsonia;Robert and McNeil which are warmer and therefore less energy 1989), and Semipalmated Plovers (C. semipal- demanding environments,fed at night as well. matus;Robert and McNeil 1989), as well as sev- They suggestedthat the lack of data on night eral other shorebirdspecies (Burger 1984, Goss- foraging in shorebirdswas likely due to tech- Custard 1984, Robert et al. 1989). However, these nological difficulties associatedwith night ob- data,with the exceptionof thosein Kalas(1986), servationand that night feeding may occurall were obtained either during migration or on year. They suggested,as did Dugan (1981), the wintering grounds,and there are no quan- Pienkowski (1982) and Townshend et al. (1984), titative studiesduring the breeding seasonof that increasedavailability of invertebrateprey nocturnal behavior of shorebirds. Furthermore, at night may make it advantageousfor shore- Cairns (1977) stated that, as darkness falls dur- birdsto foragethen. Feedingactivity of several ing the breeding season,adult Piping Plovers shorebird speciesis partly a function of tidal (C. melodus)escort chicks to cover or to their stage(Burger 1984,Burger et al. 1977,Goss-Cus- former nesting territories. tard 1984).The diurnal feeding-activityrhythms Feeding occursat night during both migra- of Piping Plovers during the breeding season tion and winter becauseenergy requirements have been linked to tidal factors and human are high due to long-distancetravel and adverse disturbance(Burger unpubl. data). weather conditions, and because it is assumed Piping Ploversbreed in the interior of North 579 580 ST^II•IœAI•D BURGER [Auk, Vol. 111 America, in the Great Lakes region, and along receivesheavy recreationaluse throughout the sum- the Atlantic Coast(AOU 1983,Haig 1985, U.S. mer. The southernmost 300 m of outer beach is used Fish and Wildlife Service 1988).Piping Plovers by off-roadvehicles during the dayand night. In 1989 typically nest on sparselyvegetated beaches or there were 13 nestingpairs of Piping Plovers.In 1990 inland lake shores (Wilcox 1959, Cairns 1982, there were 12 pairs. North Corson'sis a state park located at the south- Haig and Oring 1985).Piping Ploversare listed ern tip of Ocean City. The nesting area (the south- asthreatened and endangeredboth in the Unit- ernmost 2 km of outer beach and 750 m of inlet beach) ed Statesand Canada (Sidle 1985, Haig 1985). receivesonly minimal artificial light becauseit is lo- Major reasonsfor the decline of the Atlantic cated more than 1.5 km from the nearest residential CoastPiping Plover populationsinclude lossof lighting and over 5.5 km away from concentrated habitat, increased predation, and human dis- light sources.The width of the beach between the turbance (U.S. Fish and Wildlife Service 1988). dunes and waterline varies between 20 and 200 m Of these factors, the effect of human distur- depending on tidal stage. The area receivessimilar bancehas received the greatestattention (Flem- levels of recreational use as Brigantine Beach, but ming et al. 1988, Burger and Gochfeld 1991, much lessvehicular use (only park rangersand staff Burger unpubl. data, Goldin pers. comm.,Grif- during the day). In 1989 there were seven nesting pairs and in 1990 there were six. fin and Melvin pers. comm.). However, all of Whale Beachis approximately1.6 km southof North these studieswere conductedduring the day Corson's.The nesting area is locatedentirely on the and focusedprimarily on adult and chick for- outer beach as there is no inlet. The width of the aging behavior. Since no one has previously beach, depending on tidal stage, varies between 30 studied Piping Plovers at night, the lack of and 100 m. It receivesmuch lesslight from artificial nighttime human disturbancedata on the birds sourcesthan either Brigantineor North Corson'sand is not surprising. Recreationistsdo not congre- recreational use is also lower. There is no vehicular gate en masseon beachesat night, but they are use. In 1989 there were 12 nesting pairs and in 1990 there were 9. nonethelesspresent. Their activitiesrange from The three beaches mentioned above have similar fishing and camping,to walking, jogging, and sloping intertidal zones and similar vegetation. Fur- driving off-road vehicles (Strauss1990). ther descriptionscan be found in Burger (1991). We report on nighttime observationsof Pip- Mantoloking is a beachon New Jersey'snorthern- ing Ploversin New Jerseyduring the 1989and mostbarrier island. The nesting area is comprisedof 1990breeding seasons. Our main objectiveswere 2.4 km of outer beach. It receives minimal artificial to determine:(1) foraging behavior of Piping light and recreationaluse. There are no vehiclesper- Plovers;(2) effectof tide, study site, and breed- mitted except those of the beach patrol. The width of ing stage on foraging behavior; (3) effect of the beach, 10 to 50 m depending on tidal stage, is nighttime human disturbanceon foraging be- much lessthan any other study site. The slope of the havior; and (4) day and night prey availability. intertidal zone is greater than 20ø which is markedly different from the other three study sites.There were seven nesting pairs in 1990. METHODS Each study site was divided into five oceanfront transects(250 m x 50 m). These transectswere estab- We studied Piping Plovers from 1 April to 15 Au- lishedprior to the nestingseason. Piping Ploverswere gust in 1989and 1990at three New Jerseylocations: observed between 2000 and 0500 EST, three to four Brigantine Beach (39ø22'30"N, 72ø24'30'W), North nights a week using a Lenzar light-image intensifier. Corson's (39ø12'30"N,74ø38'30"W), and Whale Beach The night scopeallowed us to observeindividual (39ø10'30"N,74ø40'W). A fourth study site, Mantolo- Piping Plovers from 100 to 120 m away depending king (40ø03'N,72ø40'W), was examined in 1990 only. on the amount of artificial and natural light (moon- All sites were located on barrier beach islands. light) present. All behaviors normally observed in Brigantine Beach is 1.0 km north of the center of full daylight (e.g. feeding, preening, brooding, dis- Atlantic City. The amount of artificial light emitted tractiondisplays) could be detectedand distinguished from Atlantic City and the surroundingresidences from eachother. The night scopealso made it possible createsan almost perpetual full-moon effect on the to distinguish individual Piping Plovers from other beach.The major nestingarea is on the southernmost shorebirds of similar shape and size (e.g. Semipal- 2 km of outer beach(i.e. beachfacing ocean),and 1 mated Plovers C. semipalmatus;Sanderlings, Calidris km of inlet beach (i.e. perpendicular to oceanfront alba) from over 100 m. and facing inlet waters). The width of the beachbe- During each night of observationwe gatheredtwo tween