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Nest-Site Selection of American Oystercatchers (Haematopus Palliatus) in Salt Marshes

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Nest-Site Selection of American Oystercatchers (Haematopus Palliatus) in Salt Marshes NEST-SITE SELECTION OF AMERICAN OYSTERCATCHERS (HAEMATOPUS PALLIATUS) IN SALT MARSHES BROOK LAURO AND JOANNA BURGER Departmentof BiologicalSciences, Rutgers University, Piscataway, New Jersey08854 USA ABSTR•CT.--Wedocumented flexibility of American Oystercatcher(Haematopus palliatus) nest-siteselection at marshhabitats in New York, New Jersey,and North Carolina.In New York we examinedthe relationshipof nest-siteselection to tidal flooding and found that birds chosenest sitesnonrandomly with respectto marshyareas. Three typesof habitat patch siteson marshislands chosen were sand,wrack (tidally washed-updead organicmaterial), and Spartinapatens grass. Nests on sandy siteswere lesssusceptible to tidal flooding than nestson wrack or grassbecause they were higher in elevation.There wasa positivecorrelation betweenthe numberof nestsand the length of sandbeach. Hatching successwas higher for eggsplaced on sand than for eggson grassor wrack. The locationof sandynest sitesused by birdschanged little betweenyears resulting in low turnoverrate. Wrack and grass locations changedbetween years resulting in a high turnover rate. Birdsused different habitatsin different geographicareas. In North Carolina,all nestswere on sand;none were on wrack or grass.In New York and New Jerseynests were placedon sand,wrack, and grass.Comparisons of nest characteristicsshowed that sandsites in North Carolinawere larger and drier than sand sitesin New York and New Jersey.Comparisons between years in New York and New Jerseywere different becauseof the availability of wrack. Received22 October1987, accepted16 September1988. BIRDSselect breeding habitatsbased on biotic parative examination of habitat selection.The and abiotic factors of the environment. This traditional nesting habitat is describedas sand producesa nonrandom spatial distribution of dune on barrier island, although recently oys- nests.Breeding-habitat selection can be divided tercatchers have nested in marsh habitat (Froh- into three categories(Burger 1985):(1) General ling 1965,Zaradusky 1985). Habitat studieshave habitat use involves choice of a broad habitat been conductedon other marsh-nestingspecies type suchas an oak forest,salt marsh,or prairie; (Beer 1966;Bongiorno 1970; Burger 1974, 1977, (2) territory acquisition involves selection of an 1980;Burger and Lesser1978; Montevecchi 1978; area vigorouslydefended by one or both mem- Howe 1982), but we know of no comparisons bers of a pair; and (3) nest-site selection in- of a salt-marshnesting speciesin different geo- volves the choice of the actual nest location graphical regions. including the substrateon which the nest is Oystercatchersgenerally nest in open habi- placed, cover around the nest, and food avail- tats that are sparselyvegetated (Webster 1941, ability. Legg 1954, Harris 1967, Heppleston 1972, Hart- Flexibility in nestinghabitat is critical to re- wick 1974, Martinez et al. 1983, Summers and productive successin birds becauseindividuals Cooper 1977). Most speciesnest near the shore- within populationsmust adapt to differencesin line, but EuropeanOystercatchers (Haematopus habitat physiognomy.This is particularly true ostralegus)and Mageltanic Oystercatchers(Hae- for the American Oystercatcher(Haematopus matopusleucopodus) also nest in inland habitats palliatus)because habitat physiognomychanges (Baker1973, Buxton 1961, Fatla et al. 1966,Hep- over the breeding range (Not 1984), which ex- pleston1972, Miller and Baker 1980).Thus, some tends from Massachusettsto SouthernArgen- speciesare flexible in choiceof nesting habitat. tina (Hayman et at. 1986). Available descrip- Another indicationof flexibility in nesting-hab- tions of nesting habitat of the American itat selectionis the recent range expansionof Oystercatcher(Baird et al. 1884,Bent 1929,Stone American Oystercatchers(Post 1960, Post and 1967) provide no detailed quantitative or corn- Rayner 1964, Zaradusky 1985), American Black 185 The Auk 106: 185-192.April 1989 186 L^UROAND BURGER [Auk,Vol. 106 Oystercatchers(Haematopus bachmani; Eley 1976), long but not very wide. We censusedonly the bay and European Oystercatchers (Buxton 1961, side of the barrier island. Dobbs 1970). We calculated turnover rate (after Erwin et al. 1981) to examinethe stability of nestsites from year to year. Nest sites from 1983 were surveyed in 1984 to note STUDY AREA AND METHODS if siteshad changed.We noted new sitesin 1984.The turnover rate is We observed 31 nests (1983) and 59 nests (1984) in New York at Great South Bay and South Oyster Bay (40ø37'N,73ø24'W) between the Wantagh StatePark- T=•[• + •22' way and Oak Beach.Ninety-one marsh islands lay betweenthe JonesBeach barrier island and Long Is- where S• is the number of sitesoccupied only on the land. The islandsranged in size from < 1 ha to 844 first census,N• is the total number of sites occupied ha; the median was 40.58 ha. We defined a marsh on the first census,S2 is the number of sitesoccupied island as an area surrounded by 30-cm-deepwater at only on the secondcensus, and N2 is the total number low tide and not connectedto either Long Island or of sitesoccupied on the secondcensus. the barrier island. We chose 30 cm becauseyoung We collectedthe following data for nest sitesand chicks were unable to walk to nearby islands at this randomly chosensites on islands:the percentageof depth.The dominantspecies of vegetationin the study vegetation,sand, and wrackwithin 1-m and 5-m radii area were Spartinaalternafiora and S. patens. around the nest, width and length of nest sites In 1984,we examined19 nestsin BarnegatBay, New and distanceto water (creek or bay). A random point Jersey(39ø45'N, 78ø08'W). Barnegat Bay contains259 for each nest was chosenfrom a grid systemof each salt-marsh islands between the barrier island and the nesting island. Measuresof these nest-sitecharacters mainland.The predominatespecies of vegetationwere yielded informationon the degreeof protectionpro- S. alternafioraand S. patensin the wetter areaswith vided from tidal flooding. We also comparedyears Iva frutescensand Baccharishalimifolia in drier areas usingthe samenest characters. All comparisonswere (Burger and Lesser1978). madeusing Kruskal-Wallis Chi-square tests rather than In 1984, we examined 18 nests at Battery Island, analysisof variancebecause the data were not dis- North Carolina (33ø54'N, 78ø01'W), a natural island tributed normally. with depositsof dredgedmaterial. It was dominated We measured nest-site elevation on the sandy by a densegrass community of primarily S.patens and dredge-spoilarea of North Line Island (40ø38'N, a maritime shrub thicket dominated by Xanthoxylum 73ø29'W)because we assumedcompetition for sitesto americanurn,Ilex vomitoria,Quercus virginiana, Juniperus be great due to the high concentrationof breeding virgiana,Myrica cerifera,B. halimifoliaand I. frutescens pairs (9 in 1983;14 in 1984).We useda Nixon level (Parnell and Soots 1979). accurate to 0.03 m to measure elevation (above sea In New York we collected data for each nest site to level) with respectto survey markers. examine habitat-use flexibility and adaptations to We collecteddata on hatchingsuccess in New York marsh habitats. We defined a nest site as the nest in 1983 and 1984. A nest was considered successful scrapeand the surrounding habitat patch. A habitat if at least one chick hatched. We did not determine patch is classifiedby its substrateof sand, wrack, or fledgling successbecause the parentsled the chicks S. patensgrass (see Fig. 1). Sand patchesare created away from the nest after hatching. when dredgedspoil is depositedon the marsh.Wrack We examinedgeographic variation in nest-sitese- patchesconsist of dead organic material that washes lection between New York, New Jersey,and North up on the marshduring tidal flooding. Grasspatches Carolina by comparingthe percentageof vegetation, are on naturally high regions covered by S. patens, sand, and wrack within 1-m and 5-m radii around easily distinguishedfrom S. alternafioraareas. Sandy the nest, length and width of the nest site, and dis- patchesare higher in elevationand lesssusceptible tance to water. to flooding than wrack and grasspatches. Low sites were thosein which nestswere placedon grassand wracksubstrate; high siteswere thosein which nests RESULTS were placed on sand substrate. In New York we useda measuringwheel to survey Adaptationsto marshnesting in New York.--The the dimensionsof all high sites.The area of all sites was calculated from these measurements to determine number of nestson high siteson marshislands if there was a differencein frequencyof nest siteson was significantlygreater with respectto avail- the barrier island comparedto marshislands, and if able sand than the number of nests on high there was a correlationbetween the length of sand sites on barrier islands in 1983 and 1984 (1983: beach and number of nests.We used length for the X2 = 21.6, df = 1, P < 0.005; 1984: X2 = 56.4, df correlation calculationbecause most sandy siteswere = 1, P < 0.005). There was no relationship be- April 1989] OystercatcherNest-site Selection 187 Sand Deposit AverageSolIdaHigh o$• Tide Line S;artlna alte•nafl•r= Fig. I. Profileof marshisland habitat, illustrating the differencesin elevationof the threebasic types of nest-sitelocations: sand, grass, and wrack. tween number of nests and island size but there nest characterswere significantly different for was a positive correlation for number of nests low sites,but only 17%of characterswere dif- and length of sandy areas(1983: r = 0.69, P < ferent for high
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