Mate, Site, and Territory Fidelity in Piping Plovers

MATE, SITE, AND TERRITORY FIDELITY IN PIPING PLOVERS

SUSAN M. HAIG • AND LEWIS W. ORING Departmentof Biology,The Universityof North Dakota,Grand Forks, North Dakota58202 USA, and Delta Waterfowland WetlandsResearch Station, Portage la Prairie,Manitoba RIN 3A1, Canada

ABsTRaCT.--Breeding-sitefidelity, territory retention, and mate fidelity were examined in a color-bandedpopulation of monogamousPiping Plovers(Charadrius melodus) breeding at five focalsites in southernManitoba from 1981to 1986.Frequent nest destruction by predators and stormsprovided numerousopportunities for birds to changemates and territoriesduring and amongbreeding seasons. Between years approximately 70% of survivingadults were site faithful. Males did not return significantlymore often than females,and both sexesreturned regardlessof previousreproductive success. Although former mateswere presentin subsequent years,30 of 37 birds changedmates. Birds that changedmates from the previousyear and whose mateswere presentin subsequentyears had experiencedpoorer hatching success the previousseason than thosethat retainedmates. Birds that retainedmates did not improve their reproductive successover the previous year. After nest destructionduring the breeding season,most adults kept mates (34/52 pairs) but changed territories. Birds changed territories significantly more often, and moved significantly farther, following nest destructionby storm than following predation.Birds that retained mates during the breeding seasonfledged more chicks than those that changed. Received5 June1987, accepted 19 November1987.

IDENTIFICATIONof individual behavioral phe- shorebirdsthat often breed repeatedly in the notypesand subpopulationdemographic char- same area (Wilcox 1959, Cairns 1982, Wiens 1986, acteristicsexposes a vast amount of variation in Haig 1987a).Throughout their breeding range organismswith even the most rigid socialsys- Piping Ploversnest in highly ephemeralbeach tems (Bekoff1977, Oring et al. 1983,Mock 1985, habitat that is regularly washed out or other- Beissingerand Snyder 1987).In birds more than wise altered (Haig et al. 1988). Previous studies 90% of the speciesexhibit a primarily monog- of monogamousshorebirds indicate that mate amousmating system(Lack 1968,Oring 1982). retention and site fidelity may producegreater Until recently, monogamy generated little in- relative reproductivesuccess (e.g. Soikkeli 1970, terest, largely becauseof a belief that excep- Hale and Ashcroft 1982, Lessells 1984, Gratto et tional mating systemshad more potential for al. 1985).Therefore, one might predictthat Pip- contributing to an understandingof the evo- ing Ploversexhibit similar patterns.The dy- lution of avian social systems.Even in monog- namicenvironment they inhabit, however,pro- amousspecies mate choiceand re-pairing occur vides occasions for birds to reassess mates, throughout an individual's lifetime, and pre- territories, and breeding sites within and be- sent many optionsfor variation in this social tween years. system(Ford 1983,Rowley 1983,Wickler and Seibt 1983, Anderson 1985, Mock and Gowaty STUDY AREA AND METHODS 1985,Oring and Saylet in press).In this paper The study was conductedfrom 1982to 1985in Man- we reportenvironmental and socialfactors that itoba(Fig. 1). One hundredto 120Piping Ploversbred can lead to variability in mate retention, site annually in Manitoba on 10 sitesin the southernpor- fidelity, territory retention, and reproductive tion of the province (Haig 1985, 1987b).We selected successin the monogamousPiping Plover(Cha- study areasfrom among these sites. radrius melodus). Stony Beach(50ø14'N, 98•7'W) is a 2-km stretch of Piping Plovers are biparental, territorial narrow (œbeach width = 11.5 m), sandy, pebbled beach located 13 km east of Delta Waterfowl and Wet- lands ResearchStation on a beach ridge separating •Present address:Department of Zoological Re- the Delta Marsh from Lake Manitoba. Three to 5 pairs search,National ZoologicalPark, SmithsonianInsti- bred there in 1982-1985. tution, Washington, D.C. 20008 USA. ClandeboyeBay (50ø15'N, 98ø6'W) is located2.2 km

268 The Auk 105: 268-277. April 1988 April 1988] PipingPlover Mate and Site Fidelity 269

Fig. 1. Piping Plover study areasin southernManitoba, 1981-1985. eastof StonyBeach and is composedof two sandspits vulnerable to extensive flooding when northerly bordering the channel that unites the Delta Marsh winds were greater than 25 km/h (velocity verified with Lake Manitoba. The western sandspitis 95 m at Delta Waterfowl and Wetlands Research Station long (œbeach width = 20.7 m) and is bordered by a weather station).Given almostconstant heavy winds densestand of saplingwillows (Salixspp.). The east- in Manitoba, the threat of inundation at all sites was ern sandspitis 975 m long (œbeach width = 46.7 m) common.Heavy wind, rain, and snowstorms in April- and is bordered by dune grasses(Poa spp.) and scat- Juneaccentuated the phenomenon.Each summer in- tered cottonwoods(Populus spp.). Five to 8 pairs used undation up to the vegetation line occurredat all sites the area from 1982to 1984,and 2 pairs bred there in at least twice (and up to four times at certain sites). 1985. Severeweather not only affectednest successbut re- Twin Lakes Beach(50ø20'N, 97ø53'W),located 13 km shapedbreeding sites. northeastof ClandeboyeBay, is a 4-km-longsandspit Breedingbirds (50 males,47 females)at all study developedfor recreationaluse by cottageowners. The siteswere capturedin mist nets and given individual southern1 km, usedby Piping Plovers,is similar in combinations of color bands. In 1984 and 1985 inter- width and dune structureto ClandeboyeBay (œ beach nationalflags (Myers et al. 1983)were usedas part of width = 20.1 m). Migrating birds used Twin Lakes the color-band combination. Chicks (n = 122) were Beachas a stagingarea, and 1-2 pairs bred there an- caughtby hand shortly after hatch and color-banded. nually. We obtainedlife-history patterns for 81 pairsof marked West Shoal Lake (50ø20'N, 97ø36'W) is a shallow, adults and their offspring. alkali lake located32 km eastof ClandeboyeBay and Approximately2,900 h were spentobserving focal 70 km west of Grand Marais. Approximately75% of birds at Stony Beach(1981-1984), Clandeboye Bay Piping Plovers in the province used the southern (1981-1984), and West Shoal Lake (1984-1985). Marked shoreduring the breedingseason and during spring birdswere observeddaily from arrival in mid-April and fall migration. The 5 km of southern shoreline until departure in mid-August. Each day, each ob- comprisesa series of long (1-3 km),sparsely vegetated server (n = 3 or 4) watched birds 3 times for 2-3-h peninsulasthat undergo extreme daily and seasonal periods so that all focal pairs were observedat least variation in the amount of exposedalkali beach. once.Observation periods were usedto identify num- The Grand Marais (50ø30'N, 96ø40'W)sites include ber and distribution of Piping Plovers present;in- a 0.75-km-longx 35-m-widesandspit separating Lake dividual,nest, and chicklocations; pair combinations; Winnipeg from Grand Marais Marsh, and the south- individualbreeding chronologies; nest stage and suc- ern 0.5 km of a 1-km-long,narrow (beachwidth: 10- cess;chick stageand success;and various socialin- 22 m) island, located approximately 1 km offshore teractions. from the sandspit.Two to 3 pairs nestedon the spit, Observationswere made from 10 3-m-high en- and 5-6 pairs nestedon the island. closedtowers, 2 3-m-high scaffoldingplatforms, and Eachstudy area,by virtue of narrow beachwidths, 3 modified muskrat houses (Nuechterlein 1980). flat terrain, and adjacentlarge bodiesof water, was Flaggedreinforcing bar rods were stakedat 25-m in- 270 HAIGAND ORING [Auk,Vol. 105 tervals along the beach at Clandeboye Bay, Stony turned to the specificlocation (_+25 m) on a breeding Beach,and West ShoalLake to verify site fidelity and site where it bred the previous year. territory size. Numbered black stakes15 cm high were A nest is consideredsuccessful if it produced one used to mark all Piping Plover nestsencountered. To chick.Similarly, an individual is successfulif it hatched reduce disturbance to nesting areas, observerswere at leastone chick per year. Fledging (i.e. observation present on beachesonly during banding and to in- of sustainedflight by the individual chick) at least spect nests that had been destroyed. Eggs in nests one chick from a nest was used as a more stringent were observedfrom blinds or vegetatedareas adjacent criterion for nest or individual success in some in- to beaches. Nest loss was attributed to storms if the stances. site was washedout and a storm had just taken place. Values are reported as means _+SD. Disappearanceof clutchesin the absenceof a storm was attributed to predation. Unless a specific cause RESULTS was obvious (e.g. predator tracks to nest during a storm), indeterminant cases were eliminated from In eachstudy area Piping Ploversused only analyses. certainlocations year after year for nestingter- Surveysof potential Piping Plover habitat and cen- ritories.Pairs initiated pebble-lined nest scrapes susesof known Piping Plover breeding sites were 25-100 m apart on multipurposeterritories. Fe- carriedout in southernManitoba. During weekly cen- maleslaid 4 eggsper clutch that took 4-8 days susesat Stony Beach,Clandeboye Bay, Twin Lakes (œ= 6.2 + 1.0, n = 10) to complete.Incubation Beach, and West Shoal Lake, the total number of adults, nests, and chicks was recorded, as well as identifi- of clutchesby both malesand femalesbegan cation of marked birds and their mates.Weather per- after the first egg was laid and continued for mitting, weekly censusesof all four siteswere carried 22-31 days (œ= 25.7 + 2.5, n = 9) past clutch out simultaneously or within a 24-h period to mini- completion. Overall (n = 73 nests), 1.1 + 1.6 mize distortion of overall population estimates.Sim- chickshatched per nest. Once chicks hatched, ilar data were collected in censusesconducted every parental care varied: some broods were cared 3 weeksat Grand Marais and annually (1982-1987)at for by both parents,while in othersthe females other Piping Plover breeding sites in the province. desertedthe broodwithin 10days, leaving males Piping Plovers are highly monomorphic, but most to carefor chicks.Fledging rates averaged 0.9 _+ breeding adults can be sexedthrough observationof 0.9 (n = 80) chicksper nest.Adults renestedup copulation position and various courtship displays to two times if nest destruction occurred but (describedby Cairns 1982).During copulationmales were observed on females' backs in all but two in- never raised more than one brood per season. stances. In these two cases known females mounted Hence,all adults(n = 163bird years)except one malesfollowing attempted copulation by their mates. female were monogamous.Parents of first-nest Plumagebrightness also distinguished breeding males broodsspent significantly more days with chicks from breeding femalesin mostcases. Typically, males than parentsof chicksthat hatchedfrom renests have brighter and more extensiveblack breast and (Mann-Whitney U = 1.5, N• = 10, N: = 6, P < foreheadbands, and brighter orangebills. Many males 0.01).Hatching and fledging ratesdid not differ had a black mustache in the malar region. Mustaches significantly between first nestsand renests. appeared on some females but were much lighter Frequent nest destruction by storms and than those of males. All banded birds were photo- predatorsduring the breeding seasoncreated a graphed to evaluateand verify sexing from year to situationwhere focal breeding adults had mul- year. Only birds that were consistentlycategorized to the same sex were used in data analyses.We could tiple nestsand mates (Table 1); even so, many not sex chicks. birds in the population did not attain a mate or We define "monogamy" as occurring when an in- initiate a nest. Among all adults a significant dividual formed one pair bond at a time during the numberdid not reproducesuccessfully in any breedingseason. "Perennial monogamy" refers to an given year (X2 = 10.9, 1 df, P < 0.005). The Lake individual that maintained a pair bond with the same Manitoba and West Shoal Lake sites differed in matefor two or moreconsecutive years. A "pair bond" population size and reproductive success(Table is a union between two birds that resulted in the 2), but the overall pattern was similar: lessthan laying of at leastone egg. "Mate retention" occurred half of the breedingpairs were successfuleach when the reuniting of a former pair resulted in the laying of at least one egg. An individual exhibited year. "site fidelity" (or "retention") when it bred in the Of 72 nestsmonitored from laying of the first samearea (e.g. Stony Beach,West Shoal Lake, etc.) as eggthrough destruction or fledging,63.8% were the previousyear. "Territory fidelity" (or "retention") subsequentlydestroyed. Low nest success(in is more specificand refers to an individual that re- all casesof nest loss,the completeclutch was April 1988] PipingPlover Mate andSite Fidelity 271

TABLE1. Annual individual reproductive effort of TABLE3. Breeding-sitefidelity of Piping Plovers in Piping Plovers breeding in southern Manitoba, southernManitoba by previousyear's reproductive 1982-1985. success.Sample sizes(in parentheses)are the number of individuals monitored. n Mean Range SD No. of mates 71 1.3 0-2 0.5 Previous Percentagereturn No. of nests 80 1.6 0-3 0.6 success Males Females Overall Eggs laid/female 78 6.2 0-12 2.3 Chicks hatched 92 1.7 0-4 1.7 Chicks hatched 73.3 (15) 54.5 (11) 65.4 (26) Chicks fledged 94 0.9 0-4 1.4 Nests failed 76.5 (17) 57.1 (14) 67.7 (31)

destroyed)was attributed to storms(23.8%), pre- hatchedchicks the secondyear), and 50% (22/ dation (40%)by skunks(Mephitis mephitis) and 44) were unsuccessfulagain or did worse red fox (Vulpesvulpes), or human interference. (hatchedchicks the first year, failed the follow- First nests were destroyed 72% of the time, ing year). whereasonly 43.3%of renestswere destroyed. Piping Plovers that returned to a site varied Sixty-eightpercent (44 / 65) of breedingadults in mate or territory fidelity, or both (Table 4). returned to their previous breeding sites the Males stayedon territories more often than did next year. Eighteen birds that did not return to females, but more than 70% of both males and previousbreeding sites the next year were seen females paired with new mates. Where success at different breeding sites in Manitoba or re- was known among birds that changed mates, turned to their old breeding sites two or more only 40% (10/25) of birds had been successful years later (dispersal patterns were discussed in hatching chicksthe previous year. On the further by Haig 1987a).Therefore, 71% (44/62) other hand, 4 of 7 perennially monogamous of birds known to survive returned to their for- pairswere successfulthe previousyear. Among mer breeding sites. perennially monogamous pairs, 1 pair im- There was no significantdifference in return proved its successthe following year, 4 pairs patterns among males and females, nor was the hatched chicksagain, and 2 pairs failed. likelihoodof return influencedby previousre- Closer examination of pair-bond dissolution productive success(Table 3). Birdsthat returned indicatedthat 30 of 37 of the returning birds' did not significantly improve their reproduc- mates were present on the study area the fol- tive success.Where subsequent reproductive lowing spring, and reuniting was theoretically successwas monitored, 50% (22/44) were as suc- possible.When both membersof the pair were cessful(had chicks hatch again) or improved presentthe following spring, however, 20 of 30 their success(did not hatchchicks the first year, pairsdid not reunite.Birds that subsequently changedmates, but whosemates were present, had poorerhatching success (hatch vs. no hatch) TABLE2. Population reproductive successof Piping Plovers at Lake Manitoba and West Shoal Lake, Manitoba, 1982-1985. TABLE4. Interyearmate fidelity and territoryreten- tion of Piping Ploversbreeding in southernMan- West Shoal Lake itoba, 1982-1985.Sample sizes (in parentheses)are Lake Manitoba Total the number of individuals monitored. Asterisks in-

Years 1984-1985 1982-1985 1982-1985 dicate significant differencesbetween males and Birds 61 37 98 females (X2, P < 0.01). Pairs 33 20 53 Nests 45 27 72 Males Females Overall Pattern (%) (%) (%) Chicks fledged per: Changed mate 73.1 (26) 78.6 (14) 75.0 (40) Breeding pair 1.5 0.3 1.0 Changedterritory 41.0 (39)* 85.7 (14) 52.8 (53) Pair with Changed mate brood 3.1 1.3 2.7 Changedterritory 26.3 (19)* 100.0(11) 53.3 (30) Kept territory 73.7 0.0 46.7 Percentage Kept mate pairs fledg- Changedterritory 42.9 (7) 33.3 (3) 40.0 (10) ing chicks 48.5 20.0 37.7 Kept territory 57.1 66.7 60.0 272 HAIG AND ORING [Auk, Vol. 105

TABLE5. Comparison of previous hatching success TABLE6. Intrayearmate and territory fidelity of Pip- among Piping Plovers that retained territories in ing Ploversbreeding in southernManitoba, 1982- southern Manitoba with those that changed terri- 1985.• Sample sizes(in parentheses)are number of tories.Sample sizes (in parentheses)are the number individuals monitored. of individuals monitored. Males Females Overall Percentagethat hatchedchicks Pattern (%) (%) (%) in previous yeara Changedterritory 63.6 (22) 70.8 (24) 64.7 (46) Pattern Males Females Combined Changedmate 40.7 (27) 28.0 (25) 34.6 (52) Changed mate Kept territory 28.6 (14) 100.0(2) 37.5 (16) Changedterritory 62.5(8) 100 (19) 88.9(27) Changed territory 44.4 (9) 33.3 (12) 38.1 (21) Kept territory 37.5 0.0 11.1 • Differenceswithin sexeswere not significant(P -< 0.05). Kept mate Changedterritory 62.5 (16) 62.5 (16) 62.5 (32) Kept territory 37.5 37.5 37.5 the previous seasonthan those that retained Data representbirds that renestedfollowing nestfailure. mates,although the difference was not significant (X2 = 3.23, 1 df, P < 0.075). Three pairs that remained together failed in their first nest- son, and 7 of 96 remained in the area but did ing attemptsthe following year.All threepairs not renest. Following nest destruction more terminated their pair bonds before renesting. adults changed territories than remained on Therefore, previoussuccess did not affect site previous territories (X2 = 5.6, 1 df, P < 0.05), fidelity, but birds that were not successfultend- but most did not switch mates (X2 = 4.8, 1 df, ed not to retain mates. P < 0.05) (Tables 6 and 7). If the second nest When changing mates, 8 of 13 males paired was destroyed,most birds desertedtheir terri- with females that were present on the study tories (X2 = 14.4, 1 df, P < 0.005), and most did site the year before.The other 5 malespaired not renest (X2 = 6.8, 1 df, P < 0.01). Birds re- with unbanded females that may have been nestingfor a secondtime did not changemates presentin the area the previousyear but were (X2 = 19, 1 df, P < 0.005). not present on any of the focal sites.Seventy- Territory retention and mate switching were one percentof females(5/7) pairedwith males uncommonamong renesting birds but warrant presentthe year before. more thorough examination. First, there was no Territory retention,and distancesmoved by relationship between birds changing matesand birds that changed territories, varied with suc- the numberof daysof laying or incubatingthey cess.Males that changed territories had better had invested in first clutches(Mann-Whitney reproductive successthe previous year than U, not significant). Furthermore, the source of those that retained territories (Table 5). The two nestdestruction did not significantlyaffect mate- femalesthat returned to the sameterritory had switching tendencies.After nest destructionby been successfulthe previousbreeding season a storm, 8 of 26 changed mates;5 of 14 birds and also kept the same mate. Previously suc- whose nests had been depredated changed mates. Seven of 9 Lake Manitoba birds renested cessfulmales and females that changed territories moved 1-2 territories away. Birds that with individuals not presenton the study area changedterritories following nestfailure trav- eled significantly farther than those that TABLE7. Intrayear pair-bond retention following changedterritories following a successfulyear destruction of Piping Plover nests in southern (Mann-Whitney U = 36, N• = 17, N2 = 9, P < Manitoba, 1982-1985. a

0.05). Seventy-eightpercent (7/9) of malesand Pair bond 50% (4/8) of females that changed territories followingprevious nest failure actually changed Dissolved Persisted Year (%) (%) n breeding sites. Territory- and mate-retention options avail- 1982 58.3 41.7 12 1983 33.3 66.7 6 able to returning birds were available to re- 1984 42.9 57.1 14 nesting birds within years as well. Following 1985 15.0 85.0 20 nest destruction 50 of 96 adults renested on one 1982-1985 34.6 65.4 52

of the studyareas, 39 of 96 were not seenagain • Data representpairs in which at least one memberof pair renested on any studyarea for the remainderof the sea- on a study site in Manitoba. April 1988] PipingPlover Mate and Site Fidelity 273 before nest destruction. All West Shoal Lake itoba, Piping Plover site fidelity may be inten- birds paired with birds that were presentbefore sified because of a lack of suitable, stable habitat. nest failure. Censusesand distribution information (Haig The number of days investedin the previous 1985,1987b; Haig and Oring 1985)indicate there clutch did not affect the likelihood of territory is a vast amount of undisturbed beach habitat retention. Rather, the likelihood of changing in the region,yet over 90%of the Piping Plovers territories was related to the source of nest de- in Manitobawere foundon our studysites (Haig struction. Piping Plovers changed territories 1987b). The nearest population, in northern significantlymore often following nestdestruc- Minnesota,is sufferingfrom a declinein habitat tion by a storm than following nest predation quality, and the number of breeding sitesthere (X2 = 6.67, 1 df, P < 0.05). Birds whose nests is decreasing(Wiens 1986, Haig and Oring 1987). had been destroyedby a storm changed terri- Many nonbreeding birds were present at West toriessignificantly more often than not (22/27 ShoalLake, further suggestingthere was a lack changed;X 2 = 10.7, 1 dr, P < 0.005),while only of suitable nest sites at other locations. 11 of 32 pairs whose nestshad been depredated Many birdsare lesslikely to return to an area changedterritories. Furthermore, birds that re- after poor breeding successthe previous year nested following storms moved significantly (e.g. Martin 1974, Darley et al. 1977, Brooke farther from their first nest sites than did birds 1978,Harvey et al. 1979,Oring and Lank 1982, whosenests had been depredated(z = 3.74,P < Oring et al. 1983,Blockstein 1986, Weatherhead 0.01). There was no difference in reproductive and Boak 1986). Piping Plovers returned re- successamong birds that changed territories gardlessof their previous successat sites in comparedwith birds that stayed on territories Manitoba and Minnesota (Wiens 1986). This in- following predation (5/9 pairs that stayed dicates a lack of suitable alternatives, or reflects hatched chicks vs. 4/6 pairs that changed ter- the species'preference for breeding in ephem- ritories) or storm destruction (10/21 pairs that eral sites where annual nest destruction is com- stayedhatched chicks vs. 3/6 pairsthat changed mon. Becauseexperience in an areacan improve territories) of first nests. an individual's lifetime reproductivesuccess, it Five pairs that switched mates took approx- is not surprisingthat returning birds in Man- imately 13 __+6.4 daysto initiate a new clutch; itoba had higher reproductivesuccess than the 11 pairs that remainedtogether took 8.3 + 1.5 overall populationfor any given year. The in- days. Hatching successin secondnests where creasingage of adults also leadsto greater re- birds retained mates(n = 26) was 42.3%,slightly productive success,but we could not make de- higher than successfor birdsthat changedmates tailed comparisonsamong age classes. (35.7%nests produced hatchlings, n = 16). Birds Social factorsmay contribute to the site fi- that retainedmates were significantlymore suc- delity of Piping Ploversin southern Manitoba. cessfulin fledging chicksthan birds that chose In someinstances Piping Ploversnest as single new mates (X2 = 11.6, 1 df, P < 0.005). pairs (e.g. Twin LakesBeach), but in many in- stances(e.g. Chain of Lakes,North Dakota;Big DISCUSSION Quill Lake, Saskatchewan)they nest in large concentrations (Harris et al. 1984, Prindiville Piping Plovers, like other charadriids (re- 1986).A tendencyto nestin looseaggregations viewed by Oring and Lank 1982, Haig 1987a), eliminatesthe useof smaller,seemingly viable tend to return to breeding sitesin subsequent sites simply becauseof a lack of appropriate years. Familiarity with an area may facilitate social stimuli. acquisition of food, territories, and mates and While most adult Piping Plovers exhibit may enhance territory defense and predator breeding-sitefidelity, the ephemeralnature of avoidance (Shields 1982, 1984; Moore and Ali their nestinghabitat preventssome individuals 1984; Dobson and Jones 1986). Although there from returning to previous territories or nest are potentialbenefits to sitefidelity, lack of oth- sites. Changes in the microhabitat and social er breeding-siteoptions may alsoinfluence re- structureat breedingsites also lead to changing turn patterns.When local population densities territoriesif suitableareas of higher quality are are high, a bird may be more successfulif it availableelsewhere. Song Sparrows (Melospiza returns to a familiar area than if it moves else- melodia;Weatherhead and Boak 1986), Eurasian where (Weatherhead and Boak 1986). In Man- Sparrowhawks (Accipiter nisus; Newton and 274 HAIGAND ORING [Auk, Vol. 105

Marquiss 1982), and Black-billed Magpies (Pica for success.Therefore, either mate retention does pica;Baeyens 1981) changed and, consequently, not matter, or the factors involved are so diverse upgraded territory quality when conditionsin and variable that differences are not measur- their present territories deteriorated. able.Males can benefit by returningto the same Greenwood(1980, 1983)predicted sex-biased territory, but if environmental or social con- sitefidelity amongmonogamous territorial birds ditions change,they may be more successfulif when resourcesare defended by one sex to at- they change territories. Females also respond tract members of the opposite sex. Selection is to variableconditions but are not restrictedby hypothesizedto favor site fidelity in the former acquiring territories. Eachyear they must reas- and dispersalin the latter. Data for Piping Plo- sesstheir choiceof territory and mate. vers generally support this hypothesis, al- Nest destructionand renestingare common though the differencebetween the sexesis not events during the breeding seasonfor Piping statistically significant. Generally, monoga- Ploversin Manitoba.For somebirds remaining moussandpipers (Oring and Lank 1982,Gratto on the sameterritory with the samemate allows et al. 1985) and plovers (Haig 1987a)lack any rapid renesting. Subsequentreproductive suc- statisticaldifference in return patternsbetween cessis improvedbecause they are familiar with the sexes,although males usually return more their surroundingsand matesand need not in- often than females.Female Piping Plovers are vesttime in acquiringnew matesand territories not constrainedby territory acquisition,and the (Soikkeli 1970,Harvey et al. 1979,Parker 1981). benefit of pairing with a familiar individual Many species,including Piping Plovers,are less providesone explanation for return ratesclose likely to reuse a nest site or territory after a to males.Longer-term studies of Piping Plovers poor breeding experience early in the season may reveal sexbiases in survivorshipthat will (Greig-Smith 1982). Changing territories may better explain these patterns. Wilcox (1959) facilitate finding a better mate, decreasethe found that only 13% of female Piping Plovers chance of repeated predation, avoid resource lived past 5 yearsof age, comparedwith 28% of depletion on the first site, or improve territory males.It is problematic,however, asto whether quality. Piping Plovers frequently change ter- the females he monitored had dispersedto oth- ritoriesafter their nestshave beendestroyed by er sites or died. a storm. Indeed, the territory and surrounding Birds can enhancetheir lifetime reproductive area may be so altered that it is no longer suit- successby finding and retaining a mate in a able for nesting. Furthermore, there is the stable environment (e.g. Brown 1966, Nelson chance of repeated washout. 1966,Conroy 1972,Mills 1973,Brooke 1978, O1- Following nest depredation Piping Plovers lason and Dunnet 1978, Newton and Marquiss usuallyremain on their territoriesand placethe 1982, Coulson and Thomas 1983, Rowley 1983, next nestswithin 30 m of the previous nests.If Cuthbert 1985). For migratory birds, finding a nestpredators are patchily distributed,dispers- previousmate is encumberedby fluctuationsin al before renestingcan decreasethe chanceof arrival times, variation in site fidelity and site future nest depredation. If predators are uni- stability, and differential mortality rates be- versally distributed, it doesnot pay to disperse tween the sexes (Soikkeli 1967, Holmes 1971, (Rohwer 1983). BecausePiping Plover territo- Coulson and Thomas 1983, Rowley 1983, Ella- ries in Manitoba tend to be clumped, moving son 1986). Most shorebird speciesare limited to a new territory on the current site should by thesefactors, but many reunite with former not decreasethe chancesof future predation. mates if both are present (Soikkeli 1967, Hale Furthermore, the time involved in dispersalfol- and Ashcroft1982, Oring and Lank 1982,Gratto lowing predation may not be compensatedfor et al. 1985, Warriner et al. 1986). by any benefit from a reduction in the proba- Many long-term studies have outlined the bility of predation on the new nest (Wunderle potential benefits of mate retention, but few 1984).Reproductive success for Piping Plovers have examinedthe effectof previous reproduc- was not improved for birds that changed ter- tive successon perennial mate retention (Roh- ritories following predation, and the benefit in wer 1983,Rowley 1983). In southernManitoba, moving seemssmall. where a few pairs contribute most of the new Generally,if new territoriesare unavailable, individuals to the population and nest destruc- dispersal may not result in improved repro- tion is common,there is no predictablepattern ductive success(Weatherhead and Boak 1986). April1988] PipingPlover Mate and Site Fidelity 275

In Manitoba, territories or mates, or both, be- an monogamy(P. A. Gowaty and D. W. Mock, come available when nestsare simultaneously Eds.).Ornithol. Monogr. 37. destroyedor through habitat alteration. Early- BAEYENS,G. 1981. Functional aspectsof serial mo- summerstorms usually destroymany nestssyn- nogamy:the Magpie pair-bond in relation to its territorial system.Ardea 69: 145-166. chronously,providing opportunitiesto obtain BEISSINGER,S. R., •r N. F. R. SNYDERß 1987. Mate de- new mates or territories. New nesting territo- sertion in the Snail Kite. Anim. Behav. 35: 477- ries also are createdthroughout the seasonby 487. evaporation of Manitoba lakes. BEKOFF,M. 1977. Mammalian dispersaland the on- Resource depletion on territories has been togenyof individualbehavioral phenotypes. Am. proposedas a factor influencing intrayear dis- Nat. 111: 715-732. persal patterns(Nice 1937, Greig-Smith 1982). BLOCKSTEIN,D.E. 1986. Reproductive behavior and We did not measure food abundance, but ter- parentalinvestment of Mourning Doves(Zenaida ritories that were deserted (and not completely macroura).Ph.D. dissertation,Minneapolis, Univ. Minnesota. washed out) following first-nest destruction were inhabited immediately by a new pair that BROOKE,M. DE L. 1978. Some factorsaffecting the laying date, incubation and breeding successof usually stayedfor the remainder of the breed- the Manx Shearwater,Puffinus puffinus. J. Anim. ing season.Resource depletion therefore was Ecol. 47: 477-495. not critical.Because Piping Ploversforage both BROWN,D. A. 1966. Breeding biology of the Snow on and off their territories, the importance of Petrel Pagodramanivea (Foster). A.N.A.R.E. Sci. food abundanceand quality on the territory is Rep., Set. B (1) 89: 1-63. lessened. CAIRNS,W.E. 1982. Biologyand behaviourof breed- Finally, intrayear mate switching was not ing Piping Plovers.Wilson Bull. 94: 531-545. commonin Piping Plovers,but we observedit CONROY,J. W. H. 1972. Ecologicalaspects of the more frequently than hasbeen reportedfor oth- biology of the Giant Petrel, Macronectesgiganteus (Gmelin), in the maritime Antarctic. Brit. Antarct. er single-brooded monogamousspecies (re- Surv. Sci. Rep. 75: 1-74. viewed by Rohwer 1983). Even among non- COUI•SON,J. C., & C. S. THOM^S. 1983. Mate choice monogamousavian species,the phenomenonis in the Kittiwake Gull. Pp. 361-376 in Mate choice rarely reportedand is usuallythe result of nest (P. Bateson,Ed.). London, Cambridge Univ. Press. failure (Rohwer1983). A relativelyhigh occur- CUTHBERT,F.J. 1985. Mate retention in CaspianTerns. rence among Piping Plovers in Manitoba may Condor 87: 74-78. stem from easy accessto new mates after fre- DARLEY,J. A., D. M. Scott, & N. K. TAYLOR. 1977. quent nest destruction.Intrayear mate switch- Effectsof age, sex, and breeding successon site ing may be reportedmore frequently when mo- fidelity of Gray Catbirds.Bird-Banding 48: 145- nogamy is examined on a finer scale. 151. DOBSON,F. S., & W. T. JONES.1986. Multiple causes ACKNOWLEDGMENTS of dispersal.Am. Nat. 126: 855-858. ELtASON,B.C. 1986. Femalesite fidelity and polyg- We gratefully acknowledgethe field assistanceof yny in the BlackpollWarbler (Dendroicastriata). P. Blair, A. Blumton, M. Bousfield,L. Brodsky,T. Auk 103: 782-790. Brokke, M. Burke, B. Destocher, J. Dixon, G. Dobush, FORD,N.L. 1983. Variationsin mate fidelity in mo- L. Drahuschak,M. Fournier, C. Fraser,A. Haig, D. nogamousbirds. Pp. 329-356 in Current orni- Haig, R. Lanctot,J. Laystrom,S. Oring, R. Robinson, thology,vol. 1 (R. F. Johnston,Ed.). New York, M. Schrank, S. Sobkowiak, C. Thomas, M. Walker, and Plenum Publ. T. Wolf. Supportwas providedby Delta Waterfowl GRATTO,C. L., R. I. G. MORRISON, & F. COOKE. 1985. and Wetlands Research Station, World Wildlife Fund Philopatry, site tenacity,and mate fidelity in the (Canada),University of North Dakota, National Zoo- SemipalmatedSandpiper. Auk 102: 16-24. logicalPark, Committee on the Statusof Endangered GREENWOOD,P.J. 1980. Mating systems,philopatty Wildlife in Canada (COSEWIC), and National Science and dispersal in birds and mammals. Anim. Be- Foundationgrant DCB 8608162to L. Oring and A. hav. 28: 1140-1162. Fivizzani. We thank A. H. Brush, R. Crawford, F. ß 1983. Mating systemsand the evolutionary Cuthbert, B. Eliason, D. Lieberman, and J. Waiters for consequencesof dispersal. Pp. 116-131 in The reviewing the manuscript. ecologyof animal movement (I. R. Swingland LITERATURE CITED and P. J. Greenwood, Eds.). Oxford, Clarendon Press. ANDERSON,M. G. 1985. Variationsin monogamyin GREIG-SMITFI,P. W. 1982. Dispersalbetween nest- Canvasbacks(Aythya valisineria). Pp. 57-66 in Avi- sitesby StonechatsSaxicola torquata in relation to 276 HA•cAND ORING [Auk, Vol. 105

previous breeding success.Ornis Scandinavica NELSON,J.B. 1966. The breedingbiology of the Gan- 13: 232-238. net Sula bassanaon the Bass Rockß Scotland. Ibis HAIGß$. M. 1985. Statusof the Piping Plover in 108: 584-626. Canada. Ottawaß Natl. Mus. Canada. NEWTONßI., & M. MARQUISS.1982. Fidelity to breed- 1987a. The population biology and life his- ing area and mate in SparrowhawksAccipiter ni- tory patternsof the Piping Plover. Ph.D. disser- sus.J. Anita. Ecol. 51: 327-341. tation, Grand ForksßUniv. North Dakota. NICE,M.M. 1937. Studiesin the life history of the 1987b. Piping Ploversin Manitoba--a status Song Sparrow 1. A population study of the Song report on the speciesand initial recoveryplan Sparrow. Trans. Linnean $oc.New York 4: 1-247. for the province.Occas. Pap. Provincial Mus. Al- NUECHTERLEIN,G.L. 1980. Courtship behavior of the berta 9: 243-247. WesternGrebe. Ph.D. dissertation.Minneapolisß ß W. HARRISON,R. LOCKßL. PFANNMULLER,E. Univ. Minnesota. PIKEßM. RYAN,& J. SIDLE. 1988. Recoveryplan OLLASON,J. C., & G. M. DUNNET.1978. Age, expe- for the Piping Plover (Charadriusmelodus) of the rience, and other factorsaffecting the breeding Great Lakes and northern Great Plains. Wash- successof the Fulmar, Fulmarisglacialis, in Ork- ington, D.C.ßU.S. Fish Wildl. Serv. ney. J. Anim. Ecol. 47: 961-976. ß& L. W. ORING. 1985. Distribution and status ORING,L.W. 1982. Avian mating systems.Pp. 1-92 of the Piping Ploverthroughout the annualcycle. in Avian biologyßvol. 6 (D. S. Farner and J. R. J. Field Ornithol. 56: 334-345. KingßEds.). New YorkßAcademic Press. --, &---. 1987. Populationstudies of Piping ß& D. B. LANKß 1982. Sexual selectionß arrival Plovers at Lake of the Woods, Minnesota, 1982- timesßphiloparry and site fidelity in the polyan- 1987. Loon 59: 113-117. drousSpotted Sandpiper. Behav. Ecol. Sociobiol. HALEßW. G., & R. P. ASHCROFT. 1982. Pair formation 10: 185-191. and pair maintenancein the RedshankTringa to- ß --, & $. J. MAXSON. 1983. Population tanus. Ibis 124: 471-490. studies of the polyandrousSpotted Sandpiper. HARRIS, W. C., G. WAPPLE,R. WAPPLE,K. DESMET, & Auk 100: 272-285. $. LAMONT. 1984. SaskatchewanPiping Plovers ß & R. $AYLER.In press. Waterfowl mating 1984. Saskatoon, Saskatchewan Nat. Hist. Soc. systems.Anniversary text for the Delta Water- HARVEYßP. H., P. J. GREENWOODßC. M. PERRINS,& A. fowl and Wetlands Research Station. MARTIN. 1979. Breedingsuccess of Great Tits in PARKERßH. 1981. Renestingbiology of Norwegian relation to age of male and female parent. Ibis 121: 186-200. Willow Ptarmigan.J. Wildl. Manage.45: 858-864. PRINDIvILLE,E. M. 1986. Habitat selectionand pro- HOLMESßR.T. 1971. Densityßhabitatß and the mating ductivity of Piping Ploversin central North Da- systemof the WesternSandpiper (Calidris mauri). kota. M.S. thesisßColumbiaß Univ. Missouri. Oecologia7: 191-208. LACKßD. 1968. Ecologicaladaptations for breeding ROHWER,$. 1983. Selectionfor adoption versusin- in birds. London, Methuen. fanticide by replacement"mates" in birds. Pp. LESSELLSßC. M. 1984. The mating systemof Kentish 353-395 in Current ornithology,vol. 3 (R. F. John- Plovers Charadrius alexandrinus. Ibis 126: 474-483. stonßEd.). New Yorkß Plenum Press. MARTINß$. G. 1974. Adaptations for polygynous ROWLEY,I. 1983. Re-matingin birds. Pp. 331-360 in breeding in the Bobolink,Dolichonyx oryzivorus. Mate choice (P. BatesonßEd.). Londonß Cam- Am. ZooL 14: 109-119. bridge Univ. Press. MILLSßJ. A. 1973. The influence of age and pair- SHIELDS,W. M. 1982. Philoparry, inbreeding, and bond on the breedingbiology of the Red-Billed the evolution of sex. AlbanyßState Univ. New Gull Larusnovaehollandiae scopulinus. J. Anita. Ecol. York Press. 42: 147-162. ß 1984. Factorsaffecting nest and site fidelity MOCKßD.W. 1985. An introductionto the neglected in Adirondack Barn Swallows (Hirundo rustica). mating system.Pp. 1-10 in Avian monogamy(D. Auk 101: 780-789. W. Mock and P. A. Gowaty, Eds.). Ornithol. SOIKKELI,M. 1967. Breedingcycle and population Monogr. 37. dynamicsof the Dunlin (Calidrisalpina). Ann. Zool. ß & P. A. GOWATY.1985. Avian monogamy. Fennica 47: 158-198. Ornithol. Monogr. 37. 1970. Dispersal of Dunlin Calidrisalpina in MOOREßJ., & R. ALI. 1984. Are dispersaland inbreed- relationto sitesof birth and breeding.Ornis Fen- ing avoidancerelated? Anita. Behav.32: 94-112. nica 47: 1-9. MYERS,J.P., J. L. MARON,E. ORTIZ,V. GASTO,M. HOWEß WARRINER,J. $., J. C. WARRINER,G. W. PAGEß& L. E. R. I. G. MORRISONß & B. HARRINGTON. 1983. $TENZEL.1986. Mating systemand reproductive Rationaleand suggestionsfor a hemisphericcol- successof a small population of polygamous or-markingscheme for shorebirds:a way to avoid Snowy Plovers.Wilson Bull. 98: 15-37. chaos.Wader Study Group Bull. 38: 30-32. WEATHERHEADßP. J., & K. g. BOAK. 1986. Site infl- April1988] PipingPlover Mate and Site Fidelity 277

delity in Song Sparrows.Anita. Behav.34: 1299- Wincox, L. 1959. A twenty year banding study of 1310. the Piping Plover. Auk 76: 129-152. W1CKLER,W., & U. $E1BT.1983. Monogamy: an am- WUNDI•RLE,J. M., JR. 1984. Mate switching and a biguousconcept. Pp. 33-50 in Mate choice (P. seasonalincrease in polygyny in the Bananaquit. Bateson,Ed.). London, Cambridge Univ. Press. Behaviour 88: 123-144. W1ENS,T. P. 1986. Nest-site tenacity and mate retention in the Piping Plover (Charadriusrnelodus). M.S. thesis, Duluth, Univ. Minnesota.

From "Notes and News" (1888, Auk 5: 223):

"The subjectof the voluntary interlocking of the space,and that consequentlyoverlapping at the tip, primariesin soaringbirds (seeJan. Auk, pp. 126, 127) or 'interlocking,'is simply impossible.It was shown cameup again for discussionat the meeting of the that the wing must be partly closedbefore the tips New York Academyof Sciences,held Jan.9 last, and of the primariescan be broughtnear enoughto over- formed the specialtopic of the evening. The discus- lap, and that if they shouldoverlap--which they can sionwas opened by a paperby Mr. J.A. Alien, entitled do only in the partly closedstate of the wing--they 'On the Flight of Birds, with specialreference to re- would fail entirely to aid in relieving muscularstrain cent alleged discoveriesin the Mechanism of the in keepingthe wing distended.In short,it wasshown Wing,' in which he answeredcertain criticisms made that the 'interlocking' claimed was not only an im- at the previousmeeting of the Academy,reflecting possibility,but waswholly unnecessaryas a provision on the motivesand animusof the ornithologists,and for relieving musculartension in flight. Yet the ad- then tookup the structureof birdsin relationto flight, vocateof the new discoveryrefused to be convinced, describingat somelength the bonesand musclesin- and statedthat if any oneexpected him to 'backdown' volved, and the arrangementand structureof the they would find themselves'mistaken in their man,' feathers.The alleged'new muscles'were shownto or wordsemphatically to this effect.Those interested have been well known for over a century, and by in the original paper and in the discussionwhich means of a freshly-killed Buteoborealis it was dem- followed it will find the subjectquite fully reported onstratedthat the tips of the primaries, when the in the Academy's'Transactions' (Vol. VII, giving re- wing is fully extended,as in soaring,do not even portsof the meetingsfor Novemberand December, toucheach other, but are separatedby a considerable 1887, and January, 1888)."