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Nest successof White-fronted Plover Charadrius marginatus and Kittlitz's Plover Charadrius pecuarius in a South African dune field

Ingrid Tulp

Tulp,I. 1998. Nestsuccess of White-frontedPlover Charadrius marginatus and Kittlitz's Plover Charadrius pecuariusin a SouthAfrican dune field. WaderStudy Group Bull. 87: 51-54.

Nest successof White-frontedand Kittlitz's Plovers was recorded in an areaclose to the SwartkopsEstuary in SouthAfrica in September-October1997. In total,12 White-frontedPlover nests and 16 Kittlitz'sPlover nestswere found, equivalent to densitiesof 36 pairs/km2 and 56 pairs/km2 respectively. Nest success was 43% for White-frontedPlover and 42% for Kittlitz's Plover. The main causeof nestloss was floodingon the equinoxialspring tide. Althoughchicks were not tingedand the fates of individualscould not be determined,chick survival was presumably very low sinceno chicksolder than a few daysof agewere seen.

Ingrid Tulp,Tedingstraat 72, 6822 DE Arnhem,The Netherlands

INTRODUCTION were never observedroaming along the coast. They mainly The membersof the genusCharadrius that are mostnumerous roostedat the river mouthand fed in the estuaryon asbreeding birds along the coastsof southernAfrica are mudprawnsUpogebia africana. No tracksof groundpredators White-frontedPlover Charadrius marginatus (later referred to suchas mongoose, known predators of plovereggs at asWFP) and Kittlitz's Plover Charadriuspecuarius (KP). LangebaanLagoon (Summers & Hockey 1980), were found. Both specieshave a long breedingseason along the south coastof SouthAfrica lastingfrom Augustto February Visits were carded out between 0700 and 1800 hours between (Winterbottom1963, 1968). Peaksin breedingnumbers occur 3 Septemberand 20 October1997. Nestswere locatedby m December.Data on hatchingand breeding success are meansof observingadult birds leaving their nests and by scarcebut canprovide a usefultool in estimatingthe backtrackingfootprints in the sand. Eggswere measured and developmentof populationsin addititionto monitoringadult floatedto estimateincubation stage. A shortdescription of the birds. In Septemberand October 1997, nest records were kept nestsurroundings was made. If possible,the distance to the of thesetwo speciesin a SouthAfrican dune field to estimate nest at which the adult bird alarmed or left the nest was noted nest success. by countingthe number of pacesto thenest and later convertingthis to metres.Each nest was visited on average METHODS twice a week and the fate of the clutch was recorded. Nests Data were collected at a dunefield c. 6 km east of Port werevisited on the expectedhatching date to ensurethat they Ehzabeth(33 ø 52'S; 25ø 38'E) in SouthAfrica. The studyarea hadhatched. If thenest disappeared prematurely, the possible compriseda 2 km longbeach and the adjacentdune field cause of nest loss was determined. Nest survival and (Figure 1). On the landwardside, the areawas cut off from confidenceintervals were calculated using the Mayfield the Swartkopsestuary by a highway. Only the 0.25 km wide method(Mayfield 1975, Johnson 1979). A recordwas kept of areasouth of the road (dottedin Figure 1) was searchedfor thenumber of alarmingpairs with chickspresent in thearea. nestsand chicks,resulting in a total studyarea of 0.5 km2. With somepractice, a distinctioncould be madebetween The beachwas covered with stonesand partially overgrown alarm callsused during incubation and thoseused in the chick with vegetation.The vegetationon the dunesconsisted of phase. Salicorniasp., and grasses. Several sand/dirt roads traversed the dunefield.The duneswere intensivelyused by joggersat RESULTS the weekendand the beachwas frequently used by anglers In total, 12 White-fronted Plover nests and 16 Kittlitz's Plover whodrove their off-road vehiclestowards the Swankopsriver nestswere found. At thepeak of nestpresence, at least25 mouth. Two tidal inletsare used for oysterfanning. The pairs(9 WFP and14 KP) bredconcurrently in thestudy area, oysterfarm was permanently guarded by a groupof dogs. equivalentto a breedingdensity of 36 pairs/kin2and 56 pairs/ Tidalrange was 1-2 metres,but dueto a steeplydescending km2 respectively. These figures are based on nesting habitat shorethe intertidal zone was very limited. Arian predators only;the actualterritories are likely to be largerand extend werenot common.Kelp Gulls Larus dominicanuswere into the intertidal zone. The shortest distance between two presentbut not in largenumbers (several tens at the most),and nests(a WFP and a KP) was 9 m. The WFP clutchesconsisted 52

highway ...... -,;

:

..-'-•;,:..:½•:.•½•;•:•,.•,½•;•½•;:.:!:i•.... '•':'?•":'•;:;•½:':i,'1111•!i i;•;•'i•:•"-• -

"i,'•- ' :'" ;-' Swartkops ...... ½_ •-,--.,,•. • '•'•_• • ½ '•'".,•' • . '..--0:0•0½ .. •'e•, River

. ::..':..,'-•: ...::-- ..--.- .::., .,..•-., , ,, •½...... •.... ._ beach dune 500m I [•] water

Figure 1. Studysite at theSwartkops river mouthwith nestlocations. Nests of White-frontedPlovers are indicated with an opendot, nest of Kittlitz'sPlovers with a closeddot. Only the area south of theroad (dotted line) was intensively searched for nest/chicks.The edge of thebeach represents the mean high water.

of one (1 nest),two (7) or threeeggs (4, meanclutch size: Excludingthe egg laying period, the incubationperiod for this 2.25); all KP nestscontained two eggs. The incubationof the nest lasted26 days. first nestsfound probably started on August21 (WFP) and August27 (KP), while the last observednests were startedon Total daily survivalof the nestswas 97% and 99% for WFP 5 and6 Octoberrespectively (Figure 2). The f•rsteggs andKP respectively(Table 1). Sincea nestcan be lostin the hatchedon 16 (WFP) and 22 September(KP); the last had still egg-layingstage, this period needs to be includedin not hatchedby the end of the study. calculationsof nestsurvival. Using 26 daysas the length of theincubation period, 2-4 daysfor theegg-laying interval The majority of the WFP nestswere found on the beachon (Summers& Hockey1980) andmean clutch size of two eggs, sandysubstrate with someshingle (Figure 1). Nestswere the completenesting period including egg-laying for WFP lined with shellsor vegetablematter. Apart from two nests addsup to 28-30 days. For KP the incubationperiod could not that were in a clumpof grass,all nestswere exposedon all be derivedfrom the databut 23-26 daysand a laying interval sides. KP nestswere mainly foundin the more vegetatedparts of 1-2 daysare given in Cramp& Simmons(1983), resulting of the dunesand along the sandytracks. Threeof thesenests in a nestingperiod of c. 24-28 daysfor a two eggclutch. The were built on top of a small (1 m high) dune. The nestswere probabilityof survivinga completenesting period was 43% lined with small leaves. and42% for WFP andKP respectively.

On mostnest visits, KP coveredup their eggswith sandand The main causeof nestloss was flooding by high tides. On 18 plant materialbefore leaving the nest. Only when they were September,when the springtide reachedan evenhigher level takenby surpriseand the nestwas left in a hurry,was egg- thannormal because of theequinox, a largeproportion of the coveringskipped. In WFP, egg coveringwas never observed studyarea was inundatedand nine nestswere flooded (3 WFP, (contraryto Liversidge1965 andSummers & Hockey 1981). 6 KP). Apartfrom these losses, one WFP nestwas predated, The mean distance between observer and nest at which the onedeserted and one was driven over by anoff-road vehicle. incubatingparent left the nestwas larger in KP (27m, range=12-75m, n=31) thanin WFP (22m, range=10-50m, Unfortunatelythe chickscould not be ringed,so no detailson n-39). On severaloccasions KP werenot evenseen leaving chickgrowth and survival were collected. However, during an the nest,suggesting that the meandistance that causesthe bird attemptto catchadult and young plovers with torchlightsand to leavethe nestis even larger. handnetson the nightof 20 October,a groupof four people coveredthe completestudy area and a total of only four chicks Sincenest checks were not carriedout daily, the exact wasfound. Threewere KP chicks,of whichtwo were only a incubationperiod (the time betweenlaying andhatching of the few daysold. The otherchick was approximately a weekold last laid egg) couldonly be establishedfor one WFP nest. andthe WFP chickabout four days. During visitsin daytime, 53

Table 1. Nest successof White-fronted and Kittlitz's Plover The survival •'• startincubation•--• hatch probabilityis givenon a dailybasis and for thecomplete incubation period of 30 (White-fronted)and 28 days(Kittlitz

White-fronted Plover Kittlitz's Plover no. nest-days 210 192 no. nests hatched 6 10 no. nests flooded 3 6 no. nestspredated 1 0 no. nestsdestroyed 1 0 no. nests deserted 1 0 daily survival Kittlitz's Plover probability 0.972 (0.949-0.995) 0.970 (0.945-0.995) survivalprobability for layingand incubationperiod 0.430 (0.210-0.866) 0.423 (0.203-0.864)

Table 2. Timing of the equinoxalspring tide in the years1979-1999. The date of the equinoxalspring tide shiftsforward between years by 2-5 daysfor 2-3 yearsin arow andthen jumps back 10-11 daysin the next year.

I Sept I oct year date(September) year date (September) 1979 22 1989 16 week 1980 25 1990 20 Figure2. Thetiming of startof incubationand timing of hatching,as 1981 29 1991 25 observedor as derivedfrom incubationstage. 1982 18 1992 27 no chicksolder than a few dayswere seen. By October20, 12 1983 23 1993 17 nestshad hatched and approximately 24 chicksranging in age 1984 26 1994 21 from 2 to 34 daysshould have been present in the studyarea. 1985 30 1995 26 WFP chicksfledge at 35-38 days;KP at 26-32 days(Urban et 1986 19 1996 28 al. 1986), whichmeans that if any hatchedchicks had still 1987 24 1997 18 beenalive at thisstage, the oldestones would have just 1988 26 1998 21 reachedfledging age. Giventhe observationsnoted above, I assumethat a verylarge proportion of thechicks did not reach asa selectivepressure on layingdate. Ploversmight adaptso fledgingage. Apartfrom predation, food shortage or that eithertheir eggshave alreadyhatched before the disturbancemight have caused the deathof chicks. equinoxalspring tide, or they startnesting only after this event. The predictedequinoxal spring tide overthe past20 yearsfell DISCUSSION anytimebetween 16 and30 September(a 14 dayperiod is self- Data on hatchingsuccess of thesetwo ploverspecies are very evident,since spring tides occur at new andfull moon;Table scarce.For White-frontedPlover only one study(Summers & 2). The differencein timingwas as much as 11 daysbetween Hockey1980) mentions a daily survivalprobability of 0.9545 consecutiveyears. Therefore, the variation in the date on resultingin a probabilityof survivinga 32 dayincubation whichan arealike thiswill flood may be too largeto selectfor periodof 24.7%. At LangebaanLagoon, where this study was birdsthat time their nestingactivities relatively early or late. undertaken,predation by mongoosescaused most of thenest The neststhat were on smalldune tops and at moreinland sites losses.Breeding success was 0.08 and0.14 youngper pair per mightreflect an alternativeform of adaptationto the dynamic seasonin two successiveyears. Recordsof Kittlitz'sPlovers' environment.Furthermore the plovers'breeding season is very hatchingsuccess range from 19 to 77% (del Hoyo et al. 1996). long (June-January,Summers & Hockey 1980) andall soxxsof Breedingsuccess ranges between 0.5 andless than two young factorsother than flooding of thenests may affectbreeding perpair. Nestfailures are reported to be mainlycaused by Success. flooding,vehicles and predators. The nestsuccess recorded in thisstudy falls well withinthe reportedrange. The maincause Althoughno thoroughstudy of the chicks'fate was carriedout, of nestloss in this studywas floodingof nestson a single very few chicksmore than a coupleof daysold wereobserved. occasion:the equinoxial spring tide on 18 September.The Also,the number of territorialpairs decreased in theperiod nestswere checkeda few hoursbefore high tide on this day. aftermost clutches had hatched. If parentsstill havechicks On no otherspring tide did the waterlevel gethigh enough their alarmis unmistakable.Unless the parents(with chicks) thatthe study area flooded. If the equinoxalspring tide is a movedinland away from the studyarea andremained veryregular event, with little variationin timing,it mightact 54

unnoticed,chick survival was very low. birdsof Europe,North Africa and theMiddle East; the birdsof the WesternPalearctic. Vol. 3. OxfordUniversity Press, Possible reasons for the assumed low chick survival at Oxford. Swartkopsare predation,starvation, disturbance or a combinationof thesefactors. Although it cannotbe excluded, Harrison, J.A., D.G. Allan, L.G. Underhill, M.Herremans, A.J. no directclues pointing to high levelsof predationof the Tree,V. Parker,C.J. Brown (eds). 1997. The atlas of southern chickswere found. Apart from Kelp Gulls, no otheravian African birds.Vol. 1: Non-passerines.Birdlife SouthAfrica, predatorswere common. During all visitsonly onebird of Johannesburg. prey, a Marsh Owl Asio capensis,was observed;these are known to feed mainly on rodents(Harrison et al. 1997). Hockey,P.A.R. 1997.African Black Oystercatchersbetween Familieswith youngchicks were mostlyfound in the transition the tides.African Birds& Birding2: 28-34. zonebetween the beachand the dunes(WFP) and amongstthe dunevegetation (KP), wheredisturbance by peopleregularly Johnson,D.H. 1979.Estimating nest success: the Mayfield occurred.Disturbance may reducefeeding time and can method and an alternative. Auk 96: 651-661. hamperaccess to favourablefeeding areas. Liversidge,R. 1965.Egg-covering in Charadriusmarginatus. Mean annual survival rate for adult White-fronted Plovers is Ostrich 36(2): 59-61. 87.6% (Summers& Hockey 1980). Data on survivalrates of youngbirds (until the secondyear) are not available,but if we Mayfield,H. 1975.Suggestions for calculatingnest success. assumethis to be in the rangeof the survivalrates of the Wilson Bulletin 87: 456-466. northernhemisphere plovers that closely resemble White- fronted Plovers, Kentish Plover Charadrius alexandrinus Page,G. W., L.E. Stenzel,D.W. Winlder & C.W. Swarth. (64%, Pageet al., 1983),each pair hasto raise0.4 youngper 1983.Spacing out at Mono Lake:breeding success, nest yearto maintaina stablepopulation. density,and predation in the SnowyPlover. Auk 100: 13-24.

Informationon the statusof both speciesin SouthAfrica is Summers,R.W. & P.A.R.Hockey 1980. Breeding biology of limited but for White-frontedPlovers there is thoughtto have theWhite-fronted Plover (Charadrius marginatus) in the beenan overall declinein populationand breeding success due south-westernCape, SouthAfrica. J. Nat. Hist. 14(3): 433- to increasinguse of beachesby off-roadvehicles and holiday 445. makers(Harrison et al. 1997). For anotherbeach-breeding wader,the African Black OystercatcherHaematopus moquini, Summers,R.W. & P.A.R.Hockey 1981. Egg-covering it hasbeen suggested that, in mainlandsituations, breeding behaviourof theWhite-fronted Plover Charadrius marginatus successhas declined due to increasingrecreational use of Ornis Scand. 12 (3): 240-243. beaches,while it hasremained constant on islands(Hockey 1997). del Hoyo,J., A. Elliott & J. Sargatal(eds.) 1996. Handbook of theBirds of theWorld. Vol. 3. Hoatzinto Auks. Lynx Edicions, In addition to data on status, information on the different Barcelona. factorsaffecting reproductive success is essentialto estimate theirimpact on populationdynamics. This is especiallytrue of Urban,E.K., C.H. Fry & S. Keith(eds) 1986. The Birds of specieswhich might be affectedby humanuse of their Africa Vol. II. Academic Press,London. breedingareas, in orderto be ableto identifyproblems in time. Winterbottom,J.M. 1963.Comments on the ecology and ACKNOWLEDGEMENTS breedingof sandploversCharadrius in southernAfrica. Rev. I wishto thankJane Turpie and Phil Hockeyfor providingthe Zool. Bot. Afr. 67: 11-16. opportunityto carryout this study. Paul Martin helpedwith trackingthe chicksat night andprovided additional W•mterbottom 1968. A check list of the land and fresh water informationon theplovers in thisarea. JaneTurpie collected birdsof thewestem Cape Province. Annals of theSouth data on datesof equinoxaltides. Hans Schekkermanand Ron African Museum 53:1-276. Summerscommented on an earlierversion of thispaper. REFERENCES CrampS. & K.E.L. Simmons.(eds.). 1983. Handbook of the