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Chronic Tidally-Induced Nest Failure in a Colony of White Author(s): Peter Frederick Source: The Condor, Vol. 89, No. 2 (May, 1987), pp. 413-419 Published by: University of California Press on behalf of the Cooper Ornithological Society Stable URL: http://www.jstor.org/stable/1368495 Accessed: 06/10/2009 16:04

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http://www.jstor.org The Condor89:413-419 ? The CooperOrnithological Society 1987

CHRONIC TIDALLY-INDUCED NEST FAILURE IN A COLONY OF WHITE IBISES'

PETERFREDERICK2 Departmentof Biology, Universityof ,Chapel Hill, NC 27514

Abstract.Over five seasons, I censusedan estuarinecolony of WhiteIbises ( albus)in SouthCarolina using aerial counts before and after tidal washovers. I found61% of all nestingstarts were abandoned during these tides; since not all washoverswere mon- itored,this figure is conservative.An analysisof tidegauge data indicates these destructive tideswere frequent, and predictable across seasons. This colony is growingin size,and there is circumstantialevidence of breedingsite fidelity despite the washovers. This is surprising, sinceWhite Ibises are knownfor frequentcolony shifts. Although predationat this colonywas comparativelylow, and clutchsize comparativelyhigh, breeders still suffered far moretotal nest loss thanat othercoastal colonies. I suggestWhite Ibises do not use nestingfailure, or predictabilityof failureas cuesfor abandonment,but relyon environ- mentalcues such as localfood availability and frequency of nest-sitepredation instead. Keywords: WhiteIbis, Eudocimus albus; nest failure; nest abandonment; nest .

INTRODUCTION sponse to predationmay vary with the timing in the reproductive and whether the preda- is common in cycle, Breeding-sitefidelity many avian tion was nocturnal or diurnal and the ultimateand caus- (Southern ,though proximate Southern 1979). Similarly,degree of within-sea- es of this are understood. Ulti- fidelity poorly son breedingdispersal of Blackbirds success will mold the Red-winged mately, reproductive spe- (Agelaiusphoeniceus) following nest predation cific criteriaused for nest-site choice and as cues depends on the of predator and for On a type (Monnett breeding dispersal. proximate level, Rotterman 1980). nestingsuccess itself could be a cue for breeding- Other causes of large-scalenest failure may site fidelity or abandonment.Many species are also not lead to abandonment. known to to new sites colony Though disperse followingnesting degradationof nesting substrate often leads to failure, or to remain on sites nesting following colony relocation (Weise 1978), Southern and successful attempts et al. 1977, breeding (Darley Southern(1982) found complete bulldozingand Newton 1982, Coulson and Thomas 1983, filling of a portion of a Ring-billed Gull (Larus Shields 1984, see review Rohwer How- by 1986). delawarensis)colony resulted in only a 12.2% ever, breeding dispersal following reproductive reductionof in that of the failure is variable across review in nesting part colony. species (see Similarly,Burger (1982) found nest failure of Rohwer 1986)and may oftenbe initiatedthrough entire colonies of Black Skimmers other than failure. (Rhynchops signals reproductive niger) due to nest predationwas a reliable is often in colo- pre- Breeding-sitefidelity striking dictor of colony site abandonment,whereas nest nially nesting species. Though colony abandon- failurefrom tidal inundationswas not. Since nest ment in to has been response predation frequently predatorswould returnto a in MacDonald Buck- probably colony reported(Cullen 1960, 1979, futurepredation at and some col- ensuingyears, once-predated ley Buckley 1980, Burger 1982), colonieswas predictable,but tidalwashovers were onies are known to continue chronicnest despite unpredictableat any location in Burger'sstudy predation 1949, Southernand Southern (Austin area across years. Burgersuggested that the de- In larids, abandonment in re- 1979). colony greeof predictabilityof the sourceof nestingfail- ure is an importantcriterion for colony site aban- donment. 'Received17 July 1986.Final acceptance 29 Sep- I describe chronic mass failure tember1986. Here, nesting due to tidal inundations in a of White 2 Presentaddress: Dept. of Wildlife,118 Newins- colony ZieglerHall, Universityof ,Gainesville, FL Ibises (Eudocimusalbus) that has not led to col- 32611. ony abandonment. The predictabilityof these [413] 414 PETERFREDERICK

tidal events is examined in detail, and several ules of parentalbirds at this stage were usually explanationsfor such colony site tenacityare ex- too unpredictableto make aerial surveys accu- plored. rate.Although I took data from most destructive tides, the aerialsurveys did not encompassall of them. MATERIALSAND METHODS In order to estimate the actual extent of tidal This study was conducted on PumpkinseedIs- destruction,I examineddaily high-tidedata from land (33016'N, 79012'W), an estuarine mixed- a nearby tide gauge (NOAA #8662746 "South specieswading colony in GeorgetownCoun- Island,"5 km from Pumpkinseed,established in ty, , for five breeding seasons 1975). I defined "destructive"tides as having a (Marchthrough June, 1980, to 1984). This 8.9- heightgreater than 0.80 m above mean sea level. ha island is covered primarilyby a dense stand This was the height of the tide from which I of needlerush(Juncus roemarianus). A thin band measured the least percent nest abandonment of shrubs(Iva frutescens) along the northeastern (21.9%) using the aerial method. Because de- edge is the only elevated nesting substrate,usu- structivetides were often clumped in time, but ally occupied by nesting Great (Casme- only the first one actuallydestroyed nests, I de- rodiusalbus) and other ardeids. fined a single destructiveevent as having more On Pumpkinseed,White Ibises nest only on than five calendardays between it and the next matted-down clumps of living Juncus, and in destructive tidal event. I only considered tides many areasthese clumpsform a continuousmat. duringthe normalibis-nesting season (March20 Nesting is thereforelimited to one plane;heights throughJune 30). of 64 nests averaged0.32 m (?+0.10 m) above I then tested for a correlationbetween height the mud substrate.These Juncus nests are com- of tide and percentloss of nests duringthat tide. pletelyopen, and have no vegetationabove them. For this test, I excluded any aerial counts that In each season, I counted numbers of active could have yielded ambiguouscounts (low qual- nests on slides taken of the colony from a ity photographs,low angle of viewing, etc.). Per- fixedwing aircraftat approximately150 m above cent nest abandonmentfigures were subjectedto groundlevel. The ibis nests werecounted by pro- arcsinetransformation before the correlationtest jecting the slide onto a wall. White Ibises were to achieve homoscedasticity (Sokal and Rohlf the only white-plumagedspecies to nest in the 1969). Juncus, and counts of ibises were only made of I also documented egg predation on Pump- areas in which the rathersynchronous ibis nests kinseed.No terrestrialpredators exist on Pump- were known to be in the incubationstage. Pairs kinseed, but Crows (Corvusossifragus) and usually took less than 35 sec to exchangeincu- occasionallyLaughing Gulls (Larusatricilla) prey bation duties (pers. observ.) and the relieved on ibis . In 1984, I individually numbered member of the pair always left the island im- 468 eggs in 178 nests with indelible ink at two mediately. Thus numbers of white in the locationson the island. These eggswere recount- Juncus-coveredareas were assumedto represent ed 10 days later at one location, and nine days the number of ibis nests. This method is quite later at the other. These nests were known to accuratefor countingWhite Ibises at Pumpkin- have experiencedno tidal inundationduring this seed. In 1975, previous researcherscompared time, since the flocculent mud below nests re- similar aerial counts of markedquadrats visible tained old bird tracks.Daily egg mortalityrates from the air, with ground counts of the same were then calculatedas numberof eggs lost/days areas. The two methods resultedin greaterthan exposed (Mayfield1961, 1975). The two counts 95% agreement(P. DeCourseyand T. Murphy, were made in the firstweek of incubation,when pers. comm.). Fish Crowpredation on WhiteIbis eggsis highest I timed aerial counts to document nest aban- (Shields 1985). donments due to extremelyhigh tides. The dif- Clutchsize datawere taken both fromthe above ferencebetween counts immediatelybefore and predation study in 1984, and from 83 nests at after such tidal events was taken to be the num- which matingpatterns were observed intensively ber of nests abandonedas a result of that tide. I during 1982 and 1983 (Frederick1985, 1987). was able to quantify only one case of tidally- In all cases, clutches were counted within three induced nestlingmortality, as attendancesched- days of completion. CHRONICNESTING FAILURE IN WHITEIBIS 415

RESULTS 100 HIGHTIDE-INDUCED NEST MORTALITY Extremelyhigh tides occurredas a resultof some combination of spring tides, strong and persis- tent northerlywinds, and high estuarydischarge. Over five nesting seasons, 61% of nesting starts PERCENT OF NESTS were abandonedduring or immediately follow- 50 ABANDONED ing extremely high tides (Table 1). Tides high to wash over nests occurredat least once enough r =.9870 each season, and -ometimes in a series, as in 1983. The minimum nesting mortality due to tides for any season was 42% (1984). I documentedthe immediateeffects of the tidal inundations and the of ibises from a 0.5 1.0 1.5 responses HEIGHTOF TIDE (meters above sea level) blind 25 m from nests. Eggsoften floated out of or were washed out wave action. In- FIGURE1. Regressionof tide heightand percent nests, by abandonmentof nestsat PumpkinseedIsland. cubating adults usually left the nest when the water was 3 to 8 cm above the bottom of the nest cup, though some attempted to incubate to 1985. The average height of the highest tide while floatingabove their eggs. In some cases, I in each event duringthis time was 0.948 m above saw eggs transportedfrom one nest to another, Mean Sea Level (?0.1137 m, n = 77 events). and laterdocumented such transport with marked This height is predictedby the above regression eggs.In severalcases, marked eggs known to have to lead to abandonmentof 50.9% of the nests. been covered with brackish to salty water for The average of the highest single tide in each more than I hr during early incubation later season was 1.143 m above MSL (?0.0936 m, hatched. n = 11 seasons), which is predicted to lead to 75.3%abandonment of nests. ACTUALFREQUENCY OF TIDAL WASHOVERS The correlationbetween height of a tide and per- EGGPREDATION cent abandonmentof nests duringthat tide was When the resultsof the two egg-predationstudy significant(r = 0.987, t = 15.05, df = 3, P < plots were combined (Table 2), 1.83 of the 468 0.001, Fig. 1). The minimum nest abandonment markedeggs disappearedper day, and over the I documentedin any singletidal episode was 22% entire 21-day incubation period (Bent 1926, (1983). Using the correspondingtide height on Rudegeair 1975, Shields 1985) 8.19% of all that date as a minimum criterionfor identifying markedeggs are estimated to have been lost to washouts, I found an average of 7.36 ( 1.804) aerialpredators. Whole clutches disappeared due destructive tidal episodes occurred per nesting to predationat a rate of 0.575 per day; 6.78%of season (March 20 throughJune 30) from 1975 the 178 marked clutches are estimated to have

TABLE1. Nestloss followingtidal inundations.

%Nest lost Year Total nest starts Tide Nests before Nests aftertide Episode Year 1980 6,669 5/8 6,310 283 95.5 90.4 1981 7,887 5/16 7,887 3,807 48.3 48.3 1982 7,814 6/18 3,416 0 100.0 43.7 1983 10,035 4/20 10,035 7,849 21.8 4/25 7,849 3,689 31.2 6/12 3,689 1,586 88.2 84.2 1984 12,973 5/16 12,973 7,467 42.5 42.5 Total 45,378 40,621 13,143 60.6* * Percentof all nestingstarts lost duringwashovers. 416 PETERFREDERICK

TABLE2. Eggloss dueto predation.

Studygroup SS S. Central Total Eggsmarked 213 255 468 Clutchesmarked 80 98 178 Daysexposed 10 9 Eggloss/day 0.70 1.13 1.83 Clutchloss/day 0.20 0.38 0.56 Eggloss/incubation* 6.90% 9.27% 8.19% Clutchloss/incubation 5.25% 8.04% 6.78% * 21 days (Rudegeair1975, Kushlan1977, Shields 1985). been lost to predatorsover the entire incubation the southeastern U.S. (Table 3) suggests that period. Though predationwas only measuredin Pumpkinseed breeders have relatively large one season, numbersof Fish Crows and Laugh- clutches. ing Gulls on the island did not change dramat- Table 4 comparesegg and nest mortalitiesdur- ically over the four seasons duringwhich I was ing incubation of Pumpkinseed breeders with studying nesting ibises from a blind (Frederick similarmeasures in othermajor coastal colonies. 1985). By comparison,ibises breedingon Pumpkinseed sufferedfar less egg predation. BREEDINGSITE FIDELITY? DISCUSSION White Ibises are known to have nested contin- uously on PumpkinseedIsland since 1967, and On the Pumpkinseed colony, nest destruction probablyearlier. In the 10 years for which ac- from tidal washoversis frequent,and by far the curate estimates are available, the nesting pop- most importantcause of nestingfailure. My mea- ulation has grown steadily (Table 1). Pumpkin- sures of tidally-inducednest loss are probably seed thereforeseems to be a particularlystable quite conservative. First, the aerial counts did White Ibis colony, especiallysince this species is not measurepartial loss due to washover, noted for frequentcolony shifts (Rudegeair1975, which frequently occurred in the higher nests Kushlan 1977, Ogden 1978). However, it is un- without resultingin abandonment.Second, the known whetherthe colony stability is primarily aerial method did not attempt to quantify due to site fidelityof individuals.Sporadic sight- drowningof nestlings due to washovers, which ings of banded and wing-flaggedbirds indicates was known to occur on several occasions. Fi- some adults returnin successiveyears, but these nally,the aerialsurveys were not madeafter every observationswere incidental, and cannotbe con- washover, and the data from the tide gauge in- sideredquantitative. More importantly,it is un- dicate this may have led to considerableunder- known whether these individuals experienced estimation. The actual extent of tidally-induced tidally-inducednest failurebefore returning. nest mortality is difficultto estimate since it is unknown how many nests were vulnerable on COMPARATIVENESTING PARAMETERS each of the washoverdates. It is clear, however, A comparisonof clutchsizes at the Pumpkinseed that destructive tides were quite likely in any colony with similar data from other colonies in nesting season.

TABLE3. Comparisonof primaryclutch size of WhiteIbises at differentcoastal colonies.*

Location Numberof clutches Meanclutch size Source SouthFlorida 290 2.20 Kushlan1977 WestCentral Florida 208 2.07 Rudegeair1975 CoastalLouisiana 100 1.97 Hammatt1981 WilmingtonNorth Carolina 312 2.23 Allen-Grimes1982 755 2.53 Shields 1985 PumpkinseedIsland 380 2.55 Thisstudy * Inlandcolonies not includedbecause they usuallyhave significantlylarger clutch sizes (Rudegeair1975, Kushlan1977). CHRONICNESTING FAILURE IN WHITEIBIS 417

These catastrophictides have not causedcom- TABLE4. Comparisonof reproductivefailure during plete abandonmentof the colony. However, it is incubationin WhiteIbis colonies. difficultto attributethe colony stabilityto breed- ing-site fidelity of individuals that experienced Eggpredation tidally-inducednest failure. Though a few indi- Egg Nest Total nest loss loss loss Source viduals are known to have nested on the colony (%) one year and returnedthe next, this is not nec- 8.2 6.8 >61.0* Thisstudy essarily indicative of the majority of the birds, 40.7 42.4 43.0 Shields1985 or of individuals that lost their nests 27.4 - 41.0 Allen-Grimes 1982 specifically - - 79.3** Hammatt 1981 to tides. The strongest circumstantialevidence * Nest loss on Pumpkinseedprobably an underestimate(see Discus- comes from 1980 (Table 1). In that year, over sion). ** Majorsource of nest loss in Hammatt'sstudy was "mostlydue to 90% of all nesting starts failed due to high-tide hightides." washover. The following year showed no reduc- tion of nesting and in fact an increase in the breedingpopulation. So unless there was a 90% ditions. However, the benefits of such low egg turnoverof the island'spopulation (12,054 birds) predationwould seem to be offset by the tidally- between 1980 and 1981, many of the same birds inducedmortality. In fact, the Pumpkinseedcol- that were washed out returnedto breed the next ony experiences a greater loss of nests during year. Though this level of turnover is not im- incubationthan any of the othercolonies studied possible, it would be surprisingfor such a stable to date. colony. It seems more prudentto propose that a Another hypothesis is that Pumpkinseedhas substantial proportion of the ibises were site only recentlybegun to experiencethese extreme faithful despite nest failure due to tides. tides as a result of sea-level rise, and that ibises Why White Ibises may not abandon this col- continue to nest in what was once a much safer ony in favor of a site not affected by tides is colony. In coastal South Carolina,sea-level rise unclear.There are several possible explanations since 1922 (0.25 cm/year)is considerablyhigher for such tenacity. First, the ibises may persist than the global average,due in part to a sinking because local feeding conditions are especially coastal landmass(Hicks et al. 1983, Kana et al. favorablefor the productionof eggs and young. 1984). This ratecould have accountedfor nearly The relativelylarge clutch sizes at Pumpkinseed 5 cm of increasein averageheight of high tides may reflect abundant local food sources, high on Pumpkinseedsince White Ibis began nesting preyavailability, or shortdistances to food (Rud- there sometime in the 1960s. However, even if egeair 1975, Kushlan 1977). White Ibises breed- high tides were 5 cm lower then, mean highest ing at Pumpkinseedare known to feed on a salt tides of the season are predictedto have caused marsh 3 km from the colony, and in the rich at least 69%abandonment of nests present,and bottomlandswamps of two largefreshwater rivers mean highest tides in any tidal event are pre- 15 to 20 km away (Bildstein 1983). However, dicted to have led to a 44.6%loss of nests. Tidal Pumpkinseed is not the only nesting site that inundation, then, has probablyalways been an would allow the ibises to take advantageof those importantcause of nesting failureon Pumpkin- conditions. There are six other isolated islands seed. within 3 km of Pumpkinseed in Winyah Bay, Burger(1982) found that tidally-inducednest that are not washed over by tides, and that have failure in Black Skimmers was not associated vegetation quite similar to that of other coastal with colony desertion and suggested skimmers White Ibis colonies (Allen-Grimes1982, Shields did not abandonin responsebecause tidal wash- and Parnell1986). A move to these islandswould overs were unpredictableacross years. The same place the colony even closer to feeding areas. reasoningis difficultto applyto the Pumpkinseed Second, the Pumpkinseedcolony may be at- case. Althoughthe exacttiming ofwashovers was tractive because there is so little egg predation. difficult to predict within any one season at Indeed, the infrequentpredation is probably a Pumpkinseed,several washoversoccurred there directresult of the low intertidalvegetation, which in each season. In fact, over 86% of nests are offers predators (Fish Crows) no surveillance predictedto have been abandonedfrom the high- perches,or nestingsubstrate. Pumpkinseed is one est single tide alone. While reproductivesuccess of only two islands in the bay offeringsuch con- ultimatelydetermines the of abandon- 418 PETERFREDERICK ment cues, the cues themselves may not be re- North Carolina.M.S.thesis, Univ. of North Car- liable in every situation. Though White Ibis will olina, Wilmington. O. L. 1949. Site a behaviortrait of on occasion nest on grass clumps near the AUSTIN, tenacity, ground the CommonTern (Sterna hirundo). Bird-Banding (Kushlan 1973, Hammatt 1981), they rarely nest 20:1-39. in tidally-affected areas. It is therefore not sur- BENT,A. C. 1926. Life histories of North American prising that they do not show adaptations to nest marshbirds. U.S. Nat. Mus. Bull. 135. failure from tides. In the time frame of natural BILDSTEIN, K. L. 1983. Age-relateddifferences in the flockingand foragingbehavior of White Ibises in selection, most physical events such as storms a South Carolinasalt marsh.Colonial Waterbirds and tides may be unpredictable, and Burger has 6:45-53. probably correctly suggested predictability to be BUCKLEY,F. G., AND A. BUCKLEY.1980. a key feature of abandonment cues. At a more selection and marinebirds, p. 69-112. In J. Bur- B. L. Olla, and H. E. Winn Behavior proximate level, the Pumpkinseed ger, [eds.], example sug- of marine . Vol. 4. Plenum Press, New gests that abandonment is not cued through a York. recognition of such predictability by individual BURGER, J. 1982. The role of reproductivesuccess in birds. colony site selection and abandonmentin Black Skimmers Auk 99:109-115. The fact that White Ibises on Pumpkinseed (Rhynchopsniger). J. AND C. S. THOMAS.1983. Matechoice did not abandon the in the COULSON,C., apparently colony in the KittiwakeGull, p. 361-376. In P. Bateson face of such continued nest failure is particularly [ed.], Mate choice. CambridgeUniv. Press, Lon- interesting because this species is otherwise so don. prone to colony relocation. It seems clear that CULLEN, J. M. 1960. Some adaptationsin the nesting of terns. Proc.XII Ornith.Congr. (1958): 153-157. White Ibis do not rely on past nesting failure per DARLEY, J. A., D. M. SCOTT, AND N. K. TAYLOR. 1977. se as a proximate cue for colony abandonment. Effectsof age, sex, and breeding success on site Instead, they may rely on specific environmental fidelity of Gray Catbirds.Bird-Banding 48:145- cues such as local food abundance or predator 151. when where and when to nest FREDERICK, P. C. 1985. Mating strategiesof White activity deciding Univ. North Because Ibis (Eudocimusalbus). Ph.D.diss., (Kushlan 1976, Ogden 1978). breeding Carolina,Chapel Hill. dispersal following nest failure is so variable FREDERICK,P. C. 1987. Extrapaircopulations in the among species (Rohwer 1986) and conditions mating system of White Ibis (Eudocimusalbus). (McNicholl 1975, Southern and Southern 1979, Behaviour 100:170-201. R. B. 1981. in a Monnett and Rotterman I that HAMMATT, Reproductivebiology 1980), suggest heronry. M.S.thesis, Louisiana State many species of birds do not use breeding failure Univ., Baton Rouge. as a cue for breeding dispersal, but rather rely on HICKS,S. D., H. A. DEBAUGH,AND L. E. HICKMAN. specific stimuli that may often be related to 1983. Sea level variationsfor the United States, such as food abundance or 1855-1980. NOAA report, U.S. Dept. of Com- breeding failure, pred- MD. ator densities. Nest failure not merce, Rockville, accompanied by KANA, T. W.,J. MICHEL,AND J. R. JENSEN. 1984. The those stimuli may result in site fidelity. physical impact of sea level rise in the area of Charleston,S.C. In M. C. Barth and J. G. Titus ACKNOWLEDGMENTS [eds.],The greenhouseeffect and sea level rise.Van I thankKeith Reed Joanna NostrandReinhold, New York. Bildstein, Bowman, Burger, in the Flor- and David Westneatfor reviewingearlier drafts of this KUSHLAN, J. A. 1973. White Ibis nesting was from ida .Wilson Bull. 85:230-231. paper. This study funded by grants Sigma J. A. 1976. Site selection for col- Xi, The ExplorersClub, The FrankM. ChapmanMe- KUSHLAN, nesting morial and onies by the AmericanWhite Ibis Eudocimusal- Fund, Tokyo BroadcastingCorporation. bus in Florida.Ibis 118:590-593. Logisticalsupport was generouslyprovided by the staff of the Belle W. BaruchInstitute of MarineScience and KUSHLAN, J. A. 1977. Populationenergetics of the AmericanWhite Ibis. Auk 94:114-122. Coastal Research. I especially thank Roberta Mc- MACDONALD, S. 1979. Firstbreeding record of Ross's Cutchen,Betsy Haskin, Keith Bildstein, Rhett Tahl- Gull in Canada.Colonial Waterbirds1:16. bert, and Paul Kinney for their invaluableassistance in the field. The tide data was MAYFIELD, H. F. 1961. Nesting success calculated height generouslypro- from Wilson Bull. 73:255-261. vided by the National Ocean Survey section of the exposure. National and OceanicAdministration. MAYFIELD, H. F. 1975. Suggestionsfor calculating Atmospheric nest success. Wilson Bull. 876:456-466. LITERATURE CITED McNICHOLL, M. K. 1975. Larid site tenacity and group adherencein relationto habitat.Auk 92:98-100. ALLEN-GRIMES,A. 1982. Breeding biology of the MONNETT,E. W., ANDL. M. ROTTERMAN.1980. The White Ibis (Eudocimusalbus) at Battery Island, influence of cause of nest failure on subsequent CHRONICNESTING FAILUREIN WHITEIBIS 419

nest site selection by female Red-wingedBlack- SHIELDS, M. A., AND J. F. PARNELL. 1986. birds. Am. Zool. 20:788. predationon eggs of the White Ibis at BatteryIs- NEWTON, I. 1982. Fidelityto breedingarea and mate land, North Carolina.Auk 103:531-539. in SparrowHawks (Accipiter nisus). J. Anim. Ecol. SHIELDS, W. M. 1984. Factorsaffecting nest and site- 51:327-341. fidelity in Adirondack Barn Swallows (Hirundo OGDEN, J. C. 1978. Recent populationtrends of co- rustica).Auk 101:780-789. lonial wadingbirds on the Atlanticand Gulf coast- SOKAL, R. R., AND F. J. ROHLF. 1969. Biometry.W. al plains, p. 137-154. Nat. Aud. Soc. Res. Report H. Freeman,San Francisco. #7, Wadingbirds. National Audubon Society, New SOUTHERN, L. K., AND W. E. SOUTHERN. 1979. Ab- York. sence of nocturnalpredator defense mechanisms ROHWER, S. 1986. Selectionfor adoptionversus in- in breedinggulls. Proc.Colonial Waterbird Group fanticideby replacement"mates" in birds,p. 353- 2:91-101. 395. In R. F. Johnson [ed.], Currentornithology. SOUTHERN, L. K., AND W. E. SOUTHERN. 1982. Effect Vol. 3. Plenum Press, New York. of habitatdecimation on Ring-billedGull colony RUDEGEAIR, T. J. 1975. The reproductivebehavior and nest-site tenacity.Auk 99:328-331. and ecology of the White Ibis (Eudocimusalbus) WEISE, J. H. 1978. Heron nest-site selection and its Ph.D.diss., Univ. of Florida,Gainesville. ecological effects, p. 27-34. Nat. Aud. Soc. Res. SHIELDS,M. A. 1985. An analysis of Fish Crow pre- Report #7, Wadingbirds. National Audubon So- dation on eggs of the White Ibis at BatteryIsland, ciety, New York. North Carolina.M.S.thesis, Univ. of North Car- olina, Wilmington.

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