The Auk 112(1):237-243, 1995

FACTORS AFFECTING REPRODUCTIVE SUCCESS OF WOOD ( AMERICANA) IN EAST-CENTRAL

MALCOLM C. COULTER• AND A. LAWRENCEBRYAN, JR. SavannahRiver Ecology Laboratory, Drawer E, Aiken,South Carolina 29802, USA

ABS?R•cr.--From1984 through 1989, we examinedthe reproductivesuccess of WoodStorks (Mycteriaamericana) at the Birdsvillecolony in east-centralGeorgia. Average fledging success rangedamong years from 0.33to 2.16fledglings per nest.For neststhat producedfledglings, prey availabilitywas an importantfactor affecting reproductive success. Yearly averageprey densitiesat foragingsites were significantlycorrelated with the averagenumber of fledglings producedfrom successfulnests. Among 243 nestsobserved, all eggsor chickswere lostfrom 104(43%) nests. Five factorswere associatedwith the lossof entire clutchesor broods.During the two driest years, 1985 and 1988, (Procyon lotor) predation eliminated almost all chicks.Many nestswere abandonedearly in 1989, following periodsof cold weather when the parentsappeared to be under stress.In 1985, the desertedthe colony before egg laying when the area experiencedfreezing weather. Following nest abandonments within the colony,paired adultsthat presumablyhad abandonedtheir nestswere involved in nest takeoversthat alsocaused the lossof eggsand chicks.Three stormsduring the studycaused the lossof a few nests.Some losses were due to unknown factors.The importanceof these mortality factorsvaried from year to year. Nest abandonmentsand subsequentaggression seemto be related to cold periodsearly in the season.Raccoon predation seems to be related to drying out of the water under the colony.This suggeststhat the storkshave a window in time when it is bestto breed--afterthe winter and earlyspring cold weather and beforethe water dries under the colony in the summer.Received 4 December1991, accepted 15 November 1992.

THEFACTORS THAT affect reproductive success 1986, Bryan and Coulter 1991). Birds may also in birds have been a main topic in studies of abandon their nests (Frederick and Collopy avian biology(Lack 1966, 1968, Perrins and Moss 1989b). Moreover, the relative importance of 1975, DeStevens 1980, Winkler and Walters 1983, the various factorsis likely to differ between and referencescited within these papers). Re- years. productivesuccess of wading birds may vary The reproductive successof Wood Storks considerablyamong colonies and betweenyears (Mycteriaamericana) was studied at a colony in (Rodgers1987b, Frederick and Collopy 1989a). east-centralGeorgia from 1984 through 1989 The importanceof food is one factor affecting (Cou,lter 1988).We examinedthe relativeim- reproductivesuccess of wading birds(Kahl 1964, portance of different factors affecting repro- Clark 1979). In southern , a positive re- ductive successand how thesevaried from year lationshiphas been shown between the drying to year. We evaluated whether environmental rate of wetlands and both numbers of nest at- conditions influence these processes and temptsand reproductivesuccess (Frederick and whether, by influencing reproductive success, Collopy 1989a).Some wading birds had greatest these conditionscould affect aspectsof breed- reproductivesuccess or beganbreeding in large ing biology suchas phenology. numbersduring yearswith fasterdrying rates than in yearswith slowerdrying rates(Kushlan et al. 1975). Other factorsalso affect reproduc- ]•ftETHODS tive success:predation (Rodgers 1987a, Fred- We studiedthe breedingbiology of Wood Storks erick and Collopy 1989b), weather (Rodgers at the Birdsvillecolony (32ø52'N,82ø03'W) in Jenkins 1987b),and intraspecificaggression (Frederick County,east-central Georgia from 1984through 1989. The Birdsvillecolony was located in Big DukesPond in all years, except 1985 when the birds nested in •Present address: P.O. Box 48, Chocorua, New Little DukesPond about1 km from Big DukesPond. Hampshire 03817, USA. During theseyears, the colonyhas varied in sizefrom 237 238 COULTERAND ]3RYAIq [Auk, Vol. 112 a minimum of about 100 pairs in 1984 to a maximum spring followed cold weather, when the storks ap- of 193 pairs in 1987. We followed the fate of those peared to be under stress.We attributed these losses neststhat we could observewell eachyear (n = 26 to to stressinduced by the cold weather. In casesin 65) fromthe periodof egglaying (late March) through which nestswere foundempty with no apparentcause, dispersalof young(early July through early Septem- the failure was attributed to unknown causes. ber, varyingamong years). We madeobservations in It was not possibleto examinedirectly the impor- the colonyfrom 0630to 1730EST five daysper week. tanceof food availability to reproductivesuccess be- Observationsin Big Dukes Pond were made from a causeour estimatesof the numbersof fledglingspro- tower 18 m high in 1984and from a 20-m tower in duced were made visually, and we were unable to 1986-1989. In 1985, observations were made in Little assessbody condition.Therefore, we examinedthe Dukes Pond from a tree blind about 7 m high. We relationshipbetween the availabilityof potentialprey beganfollowing nestsonly after the nestscontained at foragingsites (average yearly density and biomass) eggs.The eggs and chickswere countedeach day, and averagefledglings per nest through regression and the causesof losswere determined when possi- and correlationanalyses. In theseanalyses we con- ble. sideredonly nestsfrom which at least one young We were able to count eggsin the nestsonly in fledged.Although somemortality in the successful 1987-1989. We determined the clutch size for each nestsmay have been due to predation, intraspecific nest and considered the maximum number of chicks aggression,or harshweather, any effects of foodavail- countedduring all observationsas a measureof initial ability on reproductivesuccess would be most ap- brood size. We calculatedhatching successas initial parent among these nests.We determined the avail- brood size/clutch size. We determined the number ability of potential prey by sampling their density of chicksfiedging in eachnest as the numberof chicks and biomassat foragingsites visited by storksof the alive at the time that the young couldfirst fly. Birdsvillecolony (Depkin et al. 1992,Coulter unpubl. In someyears, we believed that the reproductive data). successamong the neststhat we followed intensively Data are summarized as œ _+ I SD. In most cases, was not representativeof the entire colony due to parametric statistical tests were used. ANOVA was greaterpredation in someareas of the colonythan in usedto compareparameters among multiple years. otherareas. For all yearswe estimatedthe total num- When ANOVA results indicated significant differ- ber of nestslost to predation,and calculatedan overall ences,Scheff&'s multiple-comparison tests were used fledgingrate for the colony. to examinedifferences between specific years. When When one or two chicks in a nest were lost but not sample sizes were less than 10, nonparametrictests the entire brood,it wasusually difficult to determine were used:Wilcoxon matched-pairs signed-ranks tests, the causeof mortality.On two occasions,we observed chi-squaretest and Spearmanrank correlations.All chicks thrown from their nestsby intruding adults, statistical tests were two-tailed and were considered and on one occasionwe observeda raccoon(Procyon significantat P < 0.05.Analyses were performedwith lotor)taking a chick. In mostcases we were unable to the STATA computerstatistical package of StataCor- determine the causes of these losses. poration. More often we could determine the cause of mor- tality when an entire broodwas lost than when less than the entire brood was lost. Five sources of mor- RESULTS tality were identified.We found entire nestsmissing CLUTCH SIZE AND HATCHING SUCCESS immediatelyfollowing two heavythunderstorms, and attributed theselosses to storm damage.We observed eggsand chicksthrown from nestsby intrudingstorks The storkslaid clutchesof one to five eggs, (Bryan and Coulter 1991),and tallied theseas intra- with most clutchesconsisting of two or three specificaggressions. During dry yearswhen the swamp eggs.From 1987 through 1989, the only years under the nesttrees became dry, raccoonsentered the in whichwe couldcount eggs, the average clutch colony(usually at night) and killed nestlings.After size was 2.9 + 0.74 eggsper nest (n = 48; Table these invasions,the carcassesof dead young often 1). Significantdifferences existed between years were left in the nests. We attributed these losses to (ANOVA, F:,45= 5.99, P < 0.01). The average raccoonpredation. To corroborateour identification clutch size in 1987 was significantlydifferent of raccoonpredation and examinethe extentthat these from those in 1988 and 1989, but clutch sizes animalsintruded into the colony, F. C. Depkin spent in 1988 and 1989 were not different (Scheff&'s three nights observingthe nestswith a night scope from the tower. Somenests were occupiedone day, multiple-comparisontest). but not occupied the next. There was no indication An averageof 2.6 + 0.71 (range 0-5) chicks that the contentsof the nestshad been disturbedby hatched in 1987-1989 (Table 1). The numbers predators, intraspecific interactions, or inclement of chicksthat hatchedwere significantlydif- weather. Some of these abandonments in the early ferent between 1987 and 1988 (ANOVA, F2•5= January1995] ReproductiveSuccess of Wood Storks 239

TABLE1. Clutch size and hatching success(œ + SD) brood sizes between other years were not sig- of Wood Storks at the Birdsville colony in east- nificant (Scheff•'s multiple-comparisontest, P central Georgia, 1987-1989. > 0.05).

Hatch- The storksproduced an averageof 1.37+ 1.32 No. chicks ing fledglingsper nest.Fledging success varied sig- No. hatched success nificantlyamong years (ANOVA, Fs,•s•= 27.76, Year nests Clutch size' per nest (%) P < 0.001).Average fledging successesin 1984, 1987 19 3.26 + 0.65 2.95 + 0.71 91 1986,and 1987 were greaterthan the averages 1988 14 2.23 + 0.65 2.29 + 0.47 93 in 1985, 1988,and 1989 (Scheff•'s multiple-com- 1989 15 2.67 + 0.72 2.47 + 0.74 93 parison test, P < 0.001). Total 48 2.85 + 0.74 2.60 + 0.71 92 We felt that mortality may not have been ßEggs per nest. evenly distributed in the colony, and that the breeding successfor the nestswe followed may havebeen higher than the overallbreeding suc- 4.54, P < 0.05; Schefffi'smultiple-comparison cessfor the entire colony.Particularly in 1985, test, P < 0.05), but other differences between 1988,and 1989,there seemedto be much higher years were not significant. Overall hatching mortality in areasof the colony where we did success was 92%. not follow individual nests. Therefore, we cal- In addition to the nests in which we counted culateda reproductivesuccess for the entire col- the eggs,there were other nestsfor which we ony based on overall observations. Our esti- could not count the eggsand in which all eggs matesfor reproductivesuccess of the entire col- were lost before hatching. These were not in- ony tended to be lower than fledging success cluded in the above analysesbecause we were for the followed nests, but the differences were unable to count the eggs.These were lost either not statisticallysignificant (Wilcoxon matched- throughaggression when intruding birdsthrew pairs signed-rankstest, n = 6, P > 0.05). The the eggsfrom the nestsor abandonment,and correlationbetween fledging rate in followed are discussedbelow as mortality factors. nests and the entire colony was significant (Spearmanrank correlation = 0.94, n = 6, P < FLEEK ING SUCCESS 0.01).

The averageinitial brood size for 1984-1989 CAUSES OF MORTALITY was 2.7 + 0.74 (n = 190; Table 2). Brood sizes variedsignificantly among years (ANOVA, Fs,•84 It was difficult to identify the causesof mor- = 11.34, P < 0.001). Initial brood sizes in 1986 tality of eggsand chicksexcept when the entire were significantlylarger than brood sizes in clutch or brood was lost. For 104 (43%) of the 1985, 1988, and 1989, and initial brood sizes in nests that we followed, the entire contents of 1984and 1987were significantlylarger than the the nestswere lost and no chicksfledged. The sizesrecorded in 1989 (Scheff•'smultiple-com- numbersof nestsfrom which no young fledged parison test, P < 0.05). Differencesin initial variedsignificantly among years (X 2 = 60.75,df

TABLE2. Initial broodsize and fledging successof Wood Storksat Birdsvillecolony in east-centralGeorgia.

Percent Fledglingsper nest Year Initial broodsize a Fledglingsper nest• successb for entire colony• 1984 2.87 + 0.80 (24) 2.23 + 0.99 (26) 78 2.04 1985 2.26 + 0.81 (23) 0.52 + 1.05 (27) 23 0.33 1986 3.15 + 0.59 (39) 2.65 + 1.00 (40) 84 2.16 1987 2.82 + 0.63 (49) 1.98 + 1.13 (50) 70 1.96 1988 2.31 + 0.48 (16) 0.09 + 0.28 (35) 4 0.35 1989 2.23 + 0.63 (39) 0.83 + 1.01 (65) 37 0.63 Total 2.66 + 0.74 (190) 1.37 + 1.32 (243) 52 1.25

ßChicks per nest. œ+ SD (n). b 100(fledglings per nest/initial broodsize). cEstimated for entire colony (seeMethods). 240 COULTERAND BRYAN [Auk,Vol. 112

TABLE3. LOSSOf entire nestcontents due to differentmortality factors for WoodStorks of Birdsvillecolony in east-centralGeorgia, 1984-1989.

Nests lost (% nests lost) 1984 1985 1986 1987 1988 1989 Total Mortality factor (26a) (27) (40) (50) (35) (65) (243) Raccoonpredation 0(0) 18(90) 0(0) 2(29) 13(36) 0(0) 33(32) Intraspecificaggression 0(0) 0(0) 0(0) 2(29) 9(25) 5(14) 16(15) Abandonment 0(0) 0(0) 0(0) 0(0) 0(0) 7(19) 7(7) Inclement weather 0(0) 2(10) 0(0) 1(14) 0(0) 2(6) 5(5) Unknown 3(100) 0(0) 2(100) 2(29) 14(39) 22(61) 43(41) Total nests lost 3 20 2 7 36 36 104

No. nests observed.

= 5, P < 0.001) and reflected the same rank We put up metal flashing(about ! m high) at order among years as the fledging successfor the base of this and all other nest trees to dis- the colony.Five factorsin order of importance couragethe .However, on 1 July, a that were responsiblefor lossesof entire nest raccoon was again seen in the same tree. It contents were raccoon predation, unknown climbedover the flashingand exploredthe tree, causes,intraspecific aggression, cold weather, but killed no chicks. and storm damage.The relative importance of During this period, the remainsof chickswere these factors among followed nests varied observedin nestsor nearby branches.The col- among years (Table 3). ony of 108nests produced only about36 chicks Raccoonpredation.--Predation typically oc- in 1985. Because most of the chicks were lost curred late in the breeding season, and in- during this period and becausewe found re- volved the loss of chicks. In almost all instances mains of chicksin many of the nests,we felt (87%), the entire brood was lost. Predation was that much of the losswas due to predation. very heavy in 1985 and 1988,accounting for 90 The flashingseemed to havelittle effect.Many (43%)instances of mortality. Predationwas not nests were lost before we could erect the flash- recorded in 1984 or 1986, and was recorded at ing. Once the flashingwas put up, we suspect low levels in 1987 and 1989. Both 1985 and 1988 that the raccoonsmay have climbed over the were very dry years(Coulter unpubl. data), and flashing with or without the help of the but- the predationoccurred in Juneand July.In 1985, tonbushthat was commonthroughout the col- the storks bred in Little Dukes Pond, where ony. they nested in trees bordering the shoreline. In 1986, when the birds again nestedin Big While it never becamedry under the trees,but- Dukes Pond, we recorded raccoons in the col- tonbush (Cephalanthusoccidentalis) growing ony when it becamedry in mid-June.We put among the trees allowed the raccoonsto reach up flashing on all nest trees, including trees the nest trees from the shore with little risk of with neststhat we were not following. We re- predationby alligators(Alligator mississippiensis). corded two dead chicks,with evidencethat they At 1800 on 27 June 1985,predation of a chick had been killed by a raccoon,in a nest we were by a raccoonwas observed.A raccoonwas seen following with three chicks.The surviving chick climbing one of the trees that we monitored subsequentlyfledged. We did not recordother about 5 m from our observation post. The rac- instancesof predation among the nestswe were coon examined a dead chick in a nest that had following, but noted evidence of predation been abandoned. When the raccoon was about elsewherein the colony. 1 m below an active nest, the chicks became In 1987,we observedraccoons in the colony excited. The raccoon climbed to the nest and late in the season,but recordedlittle predation. grabbeda chick,killing it with a bite at the base The water under the colonydried by late July of the neck. The parent and two remaining and we saw raccoonsshortly thereafter.By this chicksstayed near the far side of the nest(<0.5 time many of the chickshad fledged and only m away) and snappedtheir bills a few timesat chicksin the very late nestssuffered predation. the raccoon. The raccoon climbed down the tree In 1988, a very dry year, we observedrac- with its prey. coonsin the colony after the swamp had dried January1995] ReproductiveSuccess of WoodStorks 241 underneath the nest trees in mid-June. F. C. alreadyoccupied nests in 1987, 1988,and 1989. Depkin spenta night in the blind and observed In thecase of nesttakeovers, the new pair threw raccoonsavoiding flashing by climbing trees the eggsor chicksfrom the nestand occupied withoutflashing and moving among trees above the nests. This accounted for 30% of nest losses the flashing. We observedcarcasses of in 1988 and 14% in 1989. In 1989, we recorded chicksin the nestsfollowing the event. From nestabandonment prior to thesenest takeovers. the 101 nestsin the colony (maximum count) Previouslypaired birds from abandonednests with about233 chicks,we estimatedthat only mayhave been involved in the aggression(Bry- 35 chicks survived (0.35 fledglings per nest). an and Coulter 1991). Nest abandonment also The raccoonpredation in each year was con- may have precededthe aggressionobserved in centratedover a period of about a week. 1988,although the situationwas lessclear. We Cold weather.--In mid-April (the incubation did not record nest takeovers in 1984, 1985, or period) 1989, the area experienced a cold, wet 1986. period that appeared to alter the storks' nest- Aggressionwas primarily directed at adults attendancebehavior. The birds stayedon their on nestswith eggs,although on two occasions nestsfor longerperiods of time and,when they (28 May 1987 and 2 June 1987) we observed left to forage,they were gonefor longerperiods chicks(13 and 38 daysold) being thrown from of time than we recordedfor incubatingbirds neststhat we were following. The chickswere at other timesof year and in otheryears. During thrown from their nestsby malesfrom adjacent this cold spell, six nestswith eggs among 19 nestswhile the.parents were absent. neststhat we followed were abandoned(Bryan Stormdamage.--We recorded five instancesof and Coulter 1991). nestslost during thunderstormsin 1985, 1987, Therewere other casesof what might be con- and 1989. Following a severe thunderstorm sideredabandonment that occurredduring the during the afternoonand evening of 11 June courtship and nest-building periods that oc- 1985,one egg and six chickswere found in the curred beforeegg laying. In 1985,we first re- water under the nest trees the next day. The cordedstorks at the colony on 4 March, earlier storm causedmortality in two of the neststhat than in other years.The numbersof storksin- we were following, but probablycaused mor- creasedto over 100 by 18 March. A cold front tality in other nestsas well. Again, following a with freezing temperaturespassed through the severethunderstorm on the afternoon of 22 June Birdsville area on 19 March. We counted 50 1987,both chicks were missingfrom oneof the storksat the colonyon that day. The numbers followednests. Other chicks in the colonymay decreasedand no storkswere seenin the colony alsohave been lost during this storm. Following after 24 March. The storks had abandoned the heavy rains on 8 and 9 June 1989, two of the colonyduring courtshipand nestbuilding, be- neststhat we werefollowing were missing, pre- fore any eggshad beenlaid and movedto Little sumablyto destructionduring the storms. DukesPond, about i km away,where they bred Unknownfactors.--Many losses occurred for that year. which we could not determine the causes(Table In 1988,the storksreturned to the colonyin 3). Most of the losses due to unknown causes mid-March. In late March, we noticed birds were recorded in 1988 and 1989. Some of these courting and beginning to build nestsin an area may have resultedfrom someof the factorsdis- of the colonywhere we did not follow individ- cussed above. ual nests.After a few days,the area was aban- doned, and at the same time we noticed an in- IMPORTANCE OF FOOD AVAILABILITY creasein courting birds in another area. This happenedtwice more in late March and early The ability of the parentsto provideadequate April. These instancesin 1985 and 1988 oc- food to their chicksmay have affectedrepro- curredbefore any eggshad been laid. They are ductive success. None of the causes of entire- not casesof abandonmentaccording to the def- nestlosses were obviouslyrelated to foodavail- inition above, but could be considered analo- ability,although there may havebeen indirect gous processesduring the pre-egg stage. relationships.To determinethe importanceof Intraspecificaggression.--We recorded large food availability,we examinedthe relationship groupsof storks"mobbing" nest trees resulting betweenaverage yearly prey densityat forag- in lossof nestsand pairs of birds taking over ing sites and the average number of young 242 covr• •D BR¾• [Auk,Vol. 112

1986 and Coulter 1991).'Cold weather early in the seasonmay stressthe storks and lead to nest ß 1984 desertions.Although pairsdo not staytogether 1•7 ß from year to year and pair bondsare established

1985 each year (Kahl 1972), pairs that have aban- donedtheir nestsmay maintain their pair bonds ß 1989 within a season,and these birds subsequently ß may take over nestsoccupied by other birds. Drying of the swampunder the nestingtrees

1988 may be important in allowing raccoonpreda- tion. Although we put flashingaround the base ß of the trees,raccoons got around the flashing, and it is unclearwhether flashinghad any effect on predationlevels. Alligators in the water un- der the colony are probably a more effective deterrent to raccoonscoming near the nestsof WoodStorks. As long asthere waswater under the colony,alligators were present.They seem 0 5 10 15 to be attracted to the colony, where they eat Averageprey density (items per squaremeter) stork chicks and regurgitated food that occa- sionally fall from nests.Raccoons appear to be Fig. 1. Averagenumber of WoodStork fledging deterredfrom entering the colonyby the pres- amongfor successful nests at Birdsville colony by year ence of alligators, since we only recorded rac- in relationto averagedensity of potentialprey at foraging sites. coon predation when the water under the nest trees was dry and alligatorswere absent.The swampbecame dry under the nest treesin four fledgedfrom successfulnests (Fig. 1). The re- of the six years of this study (Coulter unpubl. lationshipwas significant(Spearman rank cor- obs.).During theseyears, it becamedry in June relation = 0.83, n = 6, P < 0.05). or July when chicks were still in the nests. Cold temperaturesand cold fronts passing DISCUSSION through the areain February,March, and April may stressstorks, leading to abandonmentand/ Averageannual reproductive success of Wood or nest takeovers.The winter and early spring Storksat the Birdsvillecolony varied from 0.33 coldmay limit storksfrom breedingearlier than to 2.16 fledglingsper nest from 1984 through they do. However drying of the swampunder 1989.Among neststhat we followed, 4 to 84% the colony appearsto establishconditions en- of the chicksthat hatchedfledged each year. abling raccoon predation. Chicks from early Prey availability was an important factor influ- nestsare likely to avoid the raccoonpredation encing fledging success,at least among those by fledging before the water dries under the nestsfrom which young fledged.No young colony. fledged from 104 (43%) of the nests that we The potential impact of mortality from rac- followed. Large numbersof nestswere lost in coon predation late in the seasonand cold tem- 1985, 1988, and 1989, and the storksproduced peraturesearly in the seasonsuggests that these an averageof lessthan one fledgling per nest. two phenomenaform limits for the timing of Few nests were lost in 1984, 1986, and 1987; the breeding of storksin east-centralGeorgia. We storksproduced about two fledglingsper nest suggestthat the window for initiation of breed- in these years. ing is determinedby the onsetof drought and Factors that accounted for the loss of the en- colony drying in June and July. tire nest contentsincluded raccoonpredation, stressinduced by coldweather, intraspecific ag- gression,storm damage, and unknown factors. ACICl•OWLEDGMEN'rs We have suggestedthat someof the abandon- We are gratefulto the SavannahRiver EcologyLab- ment and subsequentintraspecific aggression oratory for their support throughoutthis work. We may be related to spring cold periods (Bryan are fortunate to have worked with a dedicated, en- January1995] ReproductiveSuccess of Wood Storks 243 thusiastic,and hard-working crew: S. L. Coe (1986- 1992. Food of nestling Wood Storksin east-cen- 1988), F. C. Depkin (1986-1988),T. L. Gentry (1988- tral Georgia.Colon. Waterbirds15:219-225. 1989), L. C. Huff (1984-1986), S. D. Jewell (1984-1985), DE STEVENS,D. 1980. Clutch size, breeding success, W. B. Lee (1984),L. S. McAllister (1984),D. E. Manry and parental survival in the Tree Swallow (Iri- (1989), K. L. Montgomery (1988-1989),L. A. Moreno doprocnebicolor). Evolution 34:278-291. (1988), M. A. Rubega(1986), D. J. Stangohr(1987), W. FREDERICK,P. C. 1986. Conspecificnest takeovers J. Sydeman(1985), N. K. Tsipoura(1987), J. M. Walsh and egg destructionby White .Wilson Bull. (1985-1987),B. E. Young (1986)and D. P. Young (1989). 98:156-157. J. Meyers, who directedthe stork projectfrom June FREDERICK,P. C., ANDM. W. COLLOPY.1989a. Nesting 1983 through April 1984, laid the groundwork for successof five ciconiiformspecies in relation to samplingmethods at foraging sites.L. Garrettof the water conditionsin the Florida .Auk PatuxentEnvironmental Science Center provided in- 106:625-634. valuable assistancein locating references.P. Freder- FREDEmCK,P. C., AND M. W. COLLOPV. 1989b. The ick, H. W. Kale, and an anonymousreviewer made role of predation in determining reproductive helpful commentson an earlier draft of this paper. successof coloniallynesting wading birds in the We also thank M. H. Smith, J. W. Gibbons, and W. D. Florida Everglades.Condor 91:860-867. McCort for their indispensablesupport throughout IG•-IL, M.P. 1964. Food ecologyof the Wood Stork this project.This researchwas supported by the Unit- (Mycteriaamericana) in Florida. EcoLMonogr. 34: ed StatesDepartment of Energy,Savannah River Op- 97-117. erations contract DE-AC0976SROO-819 with the Uni- IG•-IL,M.P. 1972. Comparativeethology of the Ci- versity of Georgia,Institute of EcologySavannah Riv- coniidae.The Wood Storks(genera Mycteria and er EcologyLaboratory. ). Ibis 114:15-29. KUSHLAN,J. A., J. C. OGDEN,AND A. L. HIGER. 1975. Relation of water level and fish availability to Wood Stork reproductionin the southernEver- LITm•TURE CITED glades,Florida. U.S. Geol. Survey, Open File Re- port 75-434. Tallahassee,Florida. BRYAN,A. L., JR., AND M. C. COULTER. 1991. Con- LACK,D. 1966. Population studiesof birds. Clar- specificaggression in a Wood Stork colony in endon Press, Oxford. Georgia.Wilson Bull. 103:693-697. L^c•c,D. 1968. Ecologicaladaptations for breeding CLARK,E. S. 1979. Factorsaffecting the initiation and in birds. Methuen, London. successof nestingin an east-centralFlorida Wood Pmmu•qs,C. M., AND D. MOSS. 1975. Reproductive Storkcolony. Proc. Colon. Waterbird Group 2:178- rates in the Great Tit. J. Anim. Ecol. 44:695-706. 188. RODGERS,J. A. 1987a. On the antipredatoradvan- COULTœR,M. C. 1988. Foragingand breeding ecol- tagesof coloniality:A word of caution.Wilson ogyof WoodStorks in east-centralGeorgia. Pages Bull. 99:269-271. 21-27 in Proceedingsof the Third Southeastern RODGERS,J. A., IR. 1987b. Populationdynamics of Nongameand EndangeredWildlife Symposium. Wood Storks in north and central Florida, U.S.A. (R. R. Odom, K. A. Riddlebergerand J. C. Ozier, Colon. Waterbirds 10:151-156. Eds.). Georgia Dep. Nat. Resources,Game and Wi•qxI2a, D. W., AND J. R. WALTERS.1983. The de- Fish Division, Atlanta. terminationof clutchsize in precocialbirds. Curt. DEPKIN, F. C., M. C. COULTER,AND A. L. BRYAN, JR. Ornithol. 1:33-68.