J. Field Ornithol., 66(•).184-191

GREAT BLUE HERON REPRODUCTIVE SUCCESS IN UPPER BAY

KATHARINE C. PARSONS AND AMANDA C. MCCOLPIN Mahomet Observatory' P.O. Box 1770 Mahomet, Massachusetts 02345 USA

Abstract.--GreatBlue Heron (Ardeaherodias) abundance, nestling production and eggshell thicknesswere estimatedat two coloniesin 1993 to provide information for public and privatewildlife managementprograms in northern Delaware.Flight directionstaken by birds departingfrom one colonywere recordedto identify primary foragingareas. Other preda- tory bird populationsin the upper DelawareBay estuaryare characterizedby relativelyhigh organochlorineresidues and low reproductivesuccess. Both heron coloniesshowed high overall reproductivesuccess. Successfifi nests produced approximately2.4 young to age 20- 40 d. Eggsfailing to hatch at one colonywere thin relativeto failed eggsfound at the second colony,and to shell thicknessdocumented in other studies.Preliminary observations suggest that herons from the two coloniesmay utilize different foragingwetlands in the region.

EXITO REPRODUCTIVO DE ARDEA HERODIAS EN LA PARTE ALTA DE LA BAH[4 DE DELAWARE Sinopsis.--Seestimaron, la abundancia,producci6n de pichonesy el grosordel cascar6nde los huevosen dos coloniasde gatzonescenizos (Ardea herodias)estudiadas, durante el 1993, en la parte alta de la Bahia de Delaware.Esto se hizo a modo de proveer informaci6n para los programasde manejo de la parte norte de Delaware. En dicha bahia se ha informado problemasde bajo 6xito reproductivoy altas concentracionesde organoclorinadosen aves depredadoras.En una de las coloniasde garzones,la direcci6n del •xtelo de las avesfue utilizadapara identificar las fireasprincipales de forrajeo. Ambascolonias de avesmostraron un •xito reproductivoalto. Los nidosexitosos produjeron aproximadamente 2.4 pichones hasta la edad de 20-40 dias. Los huevos que no eclosionaronen una colonia tenian el cascaronmuy delgado,al compararsecon los huevosque tambi6nfracasaron en la segunda colonia,y el grosorde los cascaronesinformados en otros trabajos.Las observacionespre- liminares sugieren que las dos colonias de gatzones pudieran muy bien estar utilizando diferentesanegados de la regi6n para su forrajeo. Fish-eating birds have become a focus of biomonitoring programs throughout the world becauseof their ability to yield information on the accumulation and effects of pollutants that biomagnif•v(e.g., Hoffman et al. 1990, Peakall and Fox 1987, Van den Berg et al. 1987). In addition, as tertiary consumers,their presence in aquatic ecosystemsmay imply relativelyrich faunal and floral communitiessupporting an adequateprey base. is characterizedby severaloutstanding avian communi- ties, including migrant shorebirds (Clark et al. 1993, Myers 1986) and breeding long-leggedwaders (herons, egrets,ibises; Parsons 1993, Spen- delow and Patton 1988). in upper DelawareBay supports the largest heronry on the Atlantic coast north of (Erwin and Korschgen1979, Parsons1993, Spendelowand Patton 1988). In addition, several smaller colonies of Great Blue Herons (Ardea herodias)are located within the mainland wetlandsof Delaware's coastalplain (L. Gelvin-Inn- vaer, pets. comm.).

184 Vol.66, No. 2 GreatBlue Heron Reproductive Success [ 185

The abundance of the region's avifaunanotwithstanding, productivity of some protected speciesis below normal. Bald Eagles (Haliaeetusleu- cocephalus)and Ospreys(Pandion haliaetus)in the upper bay have shown reproductiveimpairment since the mid-1970s,and eggshellthinning has been documented in both speciesby statewildlife managers(Steidl et al. 1991a,b;L. Gelvin-Innvaer,pers. comm.). Some of thesestudies have been hampered by small samples,however. As no information has been available to environmental managers on the statusof the Great Blue Heron, another abundant fish-eatingbird in the estuary,we conducteda preliminary investigationof heron reproduc- tive successand eggshellthickness.

STUDY AREA Pea PatchIsland (39ø35.7'N,75ø34.6'W; colony #403003 in Osbornand Custer 1978) and Cumples Woods (39ø30.0'N, 75ø37.1'W; colony #403002) are located in the upper Delaware Bay estuary approximately 16 and 27 km south of Wilmington, respectively.Pea Patch Island (125 ha) lies longitudinallyin the DelawareRiver just westof the shippinglane at Mile 60 and approximatelyequidistant from the New Jerseyand Del- awareshorelines. Cumples Woods (30 ha) is a mesophytichardwood stand on a hummock in AugustineCreek 3 km westof the DelawareBay shore- line and 10 km south of Pea Patch Island. Both colonies have been utilized by Great Blue Herons for at least 25 yr. Nesting on Pea Patch Island, a state park managed by the Delaware Department of Natural Resources,was documented first in 1964 (Cutler 1964). The site apparentlywas inactive during the 1940s(Wiese 1979). Great Blue Heronshave been a relativelyminor component(3%) of the Pea Patch colony,which is utilized by nine speciesof long-leggedwaders totaling 5000-12,000 pairs over the pasttwo decades(Parsons 1993, Wiese 1979). The monospecificCumples Woods site has been activesince 1944 (H. Brokaw,pers. comm.). Previousto settling here, Great Blue Herons ap- parently selectedtwo other nearby sitesover the period 1906-1943, but relocated due to lumbering (Lunt 1968). CumplesWoods is owned and managed by Delaware Wild Lands, Inc., the largest private land conser- vation organization in the state.

METHODS We located Great Blue Heron nestsat both sites in April-May 1993. From an observationplatform 150 m southof the Pea PatchIsland colony, we obtained behavioralobservations at 22 nestsduring 2-4 h/wk (April- June). We observed15 heron nests (June-July)from a hummock 250 m eastof the CumplesWoods colony and separatedby a creek.We recorded nestingbehaviors including adult and nestlingpresence at the nest, adult posture,nest building, copulationand nestlingposture. During 24-26 May, we conducted ground-basedsurveys of both colo- nies to determine total abundance. At this time, we collected eggshells 186] Icc. Parsonsand A. C. McColpin J.Field Ornithol Spring 1995 from beneath Great Blue Heron nests at both sites (Pea Patch Island: 17 shellsfrom 17 nests;Cumples Woods: 23 shellsfrom 16 nests).We deter- mined whether collected eggshellswere from hatched eggsor eggsthat failed to hatch based on presence or absenceof: (1) yolk/embryonic tissue adhering to shells and (2) grosslysymmetrical hatching pattern expected of successfullyhatched eggs (Olsen 1989). Eggshellsrinsed with water were allowed to air-dry for at least 1 mo. With a modified Starrett micrometer, we obtained at least three thickness measurements( _+ 0.005 mm) at the equatorof most (95%) eggshellswith inner membranes intact. In two of 40 shells,only 1-2 measurementswere obtained. Subsequently,we removed the chorio-allantoisas much as pos- sible, and obtained thickness measurements of the calcareous shell (U.S. Fish and Wildlife Service 1991). During weekly observationperiods (April-July), we recorded flight be- haviorsof herons leaving and arriving at Pea Patch Island. Flightline ob- servations were obtained at several island and mainland locations. For each heron departing the island, we recorded time and flight direction or sector (delineated by mainland landmarks). In the present analysis,we included only sectorsin which birds were clearly headed for either the (15øNNE-98øESE) or Delaware (180øS-352øNNW)mainland. We tested datasetsfor compliance with the assumptionsof parametric statistics(equality of variance,normal distribution) and performed t-tests on measuresof chick production and eggshellthickness. We performed the Fisher exact test on nest data and calculated a X2 statisticfor nominal flightline data.

RESULTS

We counted 389 Great Blue Heron nests in 182 trees at the Pea Patch Island colony;69 nestsin 17 treeswere countedat CumplesWoods. Most herons on Pea Patch nested in tupelo (Nyssasylvatica), red maple (Acer rubrum), and sweet gum (Liquidambar styraciflua).Herons at Cumples Woodsused American beech (Fagusgrandifolia) and white ash (Fraxinus americana).Two dead ashesat CumplesWoods held 15 nests(22%). All trees used by Great Blue Herons on Pea Patch Island were alive. We estimated that nestlings were 2-3 wk old when first observed, on the basisof chronologiesdetermined from nests that produced young where we observed copulation, and from similar studies (Butler 1992). Most (85-95%) heron pairs observedat both siteswere successfulin rais- ing at leastone chick to 20 d after hatch (Table 1). The averagemaximum number of young observed per nest was similar in both colonies (Table 1). The average number of young observed (per nest) at the age when they are capable of sustainedflight (50-60 d) was somewhatlow relative to published accounts(Table 1; review of 16 studiesin Butler 1992), but becauseit was difficult to determine preciselythe nestling agesfrom be- havioral observations,we interpret this result with caution. Eggshellthickness (with membranes) at Pea Patch Island ranged from 0.320 to 0.404 mm; at CumplesWoods thicknessranged from 0.277 to Vol.66, No. • GreatBlue Heron Reproductive Success [ 187

TABLE1. Productivit7y• of Great Blue Herons at CumplesWoods and Pea Patch Island col- onies, New CastleCounty, Delaware 1993. Successfulnests were those in which at least one chick was observed.

CumplesWoods Pea PatchIsland

# successful nests 14 19 # unsuccessful nests b 1 3 Maximum young observed' 2.4 _+ 0.6 (14) 2.3 _+ 0.9 (19) # young 40 d -- 2.4 ___0.9 (14) # young50 d -- 1.6 _+ 0.8 (12)

dAveragechick productionto 40-50 d (i _+ SD [n]). •' Fisher exact test; m• = 4; m,_,= 15; NS. • t = 0.1487; df = 31; NS.

0.428 mm. Eggshellsfrom hatched eggswere similar in thicknessat both colonies (Table 2); however, shells from eggs that failed to hatch were thinner at Cumples Woods. We recorded a total of 68 herons departing Pea Patch Island to main- land destinationsduring 2029 min of observations(New Jersey mainland: 980 min; Delaware: 1039 min). Eight-four percent were headed toward NewJersey (x 2 = 31.1, df = 1, P< 0.001). During behavioralobservations of the Cumples Woods colony,we recorded only a few herons leaving the site. All of these either landed in Augustine Creek or flew farther east along the creek.

DISCUSSION

Estimates of Great Blue Heron abundance at both colonies over the past 20 yr have been obtained by a variety of methods, making interpre- tation difficult. In 1993, heron abundance at Pea Patch Island (389 nests) waswithin reported ranges(2-727 nests;Wiese 1979, L. Gelvin-Innvaer, pets. comm.), but the Cumples Woods colony (69 nests) was apparently

TABLE2. Eggshellthickness (mm) of Great Blue Heron eggsfound at the CumplesWoods and Pea Patch Island colonies,New Castle , Delaware 1993. Eggshellsof eggs consideredto have hatched or found dead on the ground were measured with and without inner membranes. Given are i + SD (n = number of nests, except in cases where eggshellsfrom more than one egg per nestwere collected,and where eggsfrom the same nest did not all hatch).

CumplesWoods Pea Patch Island P With membranes 0.347 _+ 0.044 (15) 0.372 _+ 0.029 (17) 0.0682 Hatched 0.365 _+ 0.038 (8) 0.374 _+ 0.029 (11) NS Dead on ground 0.329 - 0.039 (9) 0.378 _ 0.026 (5) 0.0315 Shell only 0.302 _+ 0.041 (13) 0.321 _ 0.024 (8) NS Hatched 0.314 _+ 0.031 (7) 0.321 _+ 0.024 (8) NS Dead on ground 0.279 _+ 0.005 (7) -- -- 188] K. C.Parsons and A. C. McColpin j. FieldOrnithol. Spring 1995 at a record low (71-400 nests;Erwin and Korschgen1979, H. Brokaw, pers. comm.). We detecteda significantproportion of the CumplesWoods population in dead trees, probably resulting from a recent gypsymoth (Porthetria dispar)infestation (H. Harvey, pers. comm.). The number of nestsper tree at Cumples Woodswas approximately twice that at Pea Patch Island. Two new coloniesof 13-14 nestseach (Appoquinimink River, 8 km swof CumplesWoods; Taylor's Gut, 15 km se) were detectedduring December 1993 by stateofficials (L. Gelvin-Innvaer,pers. comm.). Birdsfrom Cum- ples Woods were probably moving to these sites.Burkholder and Smith (1991) correlated the gradual decline of a Great Blue Heron colony in Ohio with loss of nest trees in a reservoir. Production of nestlingsat both Pea Patch Island and CumplesWoods waswithin levelsexpected to maintain the population, and comparedwell with other studies(see reviewin Butler 1992). Approximatelyone-third of collectedeggshells from both sitescame from eggsthat failed to hatch. Crow predation of other long-leggedwader eggson Pea Patch Island was an important factor of mortality (Parsons1993), and one Great Blue Her- on shell (of five shellsfrom eggsthat failed to hatch [Table 2]) collected there had obvioussigns of avian predation. Eggshellthickness of CumplesWoods' herons suggests that thesebirds may be exposed to shell-thinningcontaminants, possibly DDE (Cooke 1973,Hickey and Anderson1968). Shellsfrom eggsthat failed to hatch at Cumples Woods were much thinner than shellsfrom Pea Patch Island (Table 2). Shell thicknessat Cumples Woods was among the thinnest recorded for Great Blue Herons in North America (Faber and Hickey 1973,Fitzner et al. 1988,King et al. 1978,Laporte 1982, Ohlendorf et al. 1977, Speichet al. 1992). Mean thicknesswith membraneswas 7% and 13.5% thinner than pre-DDT era shell thickness(pre-1947 Great Blue Heron shellsfrom southeasternU.S.; Ohlendorf et al. 1977) at Pea Patch Island and CumplesWoods, respectively. Total DDT in Peregrine Falcon (Falcoperegrinus) eggs from 58 km north and 67 km southof the studysite in the estuarywas 18.2 and 11.1 ppm (wet mass), respectively(Jarman et al. 1993). In studies of Great Blue Herons, 13 ppm total DDT led to 20% reduction in shell thickness (Laporte 1982), and shell breakage (Faber et al. 1972). Although both coloniesare located in the samewatershed, and herons from different coloniesmay overlapforaging ranges (Butler 1992), pre- liminary flightline observationsindicate that Great Blues from Pea Patch Island may be feeding mainly in New Jersey,whereas Cumples Woods' herons are probably feeding in Delaware (this study,Wiese 1976). For- aging Great Blue Herons are territorial (Butler 1992) and are thus likely to reflect wetland quality at a relativelyfine-grained spatial scale. We ob- served heron pairs at nest siteson Pea Patch Island 3-4 wk before mean laying datesin 1993, suggestingthat contaminant loads,if present, could result at least in part from foraging in local wetlands. Many of northern Delaware'slow-lying wetlands were impounded dur- Vol.66, No. 2 GreatBlue Heron Reproductive Success [ 189 ing the 1950-1960s to create waterfowl habitat (Carter 1992, Sullivan et al. 1991). To a lesser extent, New Jersey'sextensive wetlands in Salem County were similarly altered (Sullivan et al. 1991). These closed, sedi- ment-ladened freshwatersystems are likely to trap non-point source con- taminants. Waterbirds utilizing freshwater sitesgenerally show higher res- idue levelsthan birdsfeeding in marine systems(King et al. 1978,Speich et al. 1992). In addition, a recent study of organochlorine residues in Great Blue Herons found DDT/DDE levelswere explained by proximity to agricultural lands (Speich et al. 1992). Examining eggshell thicknessto assesspotential exposure to DDE has been suggestedby severalauthors (Cooke et al. 1976, Fox 1979). Oppor- tunisticcollection of shellsfound under nests(Cooke et al. 1976, Speich et al. 1992, Steidl et al. 1991a) further improves the cost-effectivenessof this approach and eliminateslethal samplingof eggs.It is especiallyuseful to water resourcesmonitoring to examine this in a speciessuch as the Great Blue Heron that is known to be sensitiveto the thinning effectsof DDE (Faberand Hickey1973, Fitzner et al. 1988,King et al. 1978,Laporte 1982, Speich et al. 1992). Most studies, including ours, however, have failed to document reproductiveimpairment in herons as a result of shell thinning (Butler 1992, Fitzner et al. 1988, Speich et al. 1992). In general, Great Blue Heron populations have been stable or increas- ing over the past 30 yr (Butler 1992, Robbins et al. 1986). Great Blue Herons, a speciesthat is physiologicallysensitive to shell-thinningcontam- inants, but whosepopulations may be relativelyinsensitive, are appropri- ate long-term indicators for the area.

ACKNOWLEDGMENTS

We thank the DelawareDepartment of Natural Resourcesand DelawareWild Lands,Inc. for accessto field sitesand unpublisheddata. In particular,we are grateful to David Roth- stein, SusanLaporte, Ron Vickers, Lisa Gelvin-Innvaer,Dave Carter and Rusty Harvey for guidanceand interest. Bill Seyfert and George McConnell of the State Park provided essentiallogistical support. The EnvironmentalAir Force and Dave Twichell pro- vided aerial photographsof Pea Patch Island. We thank field workersCris Winters, Pam Kalamanis,Pain Furtsch and Kevin Eddings.Nick Brokaw,Mike Erwin and an anonymous reviewermade thoughtful commentson an earlier draft of the manuscript.Financial support for the project came from the Delaware Department of Natural Resourcesand Manomet Observatory.

LITERATURE CITED

BURKHOLDER,G., ANDD. G. SMITH. 1991. Nest treesand productivityof Great Blue Herons (Ardea herodias)at Knox Lake, north-central Ohio. Col. Waterbirds 14:61-62. BUTDIn, R. W. 1992. Great Blue Heron. In A. Poole, P. Stettenheim, and F. Gill, eds. The birds of North America, No. 25. The Academyof Natural Sciences,, Penn- sylvaniaand American Ornithologists'Union, Washington,D.C. C•TER, D. B. 1992. The Thousand Acre Marsh. Tech. Rep., Delaware Dept. Natural Re- sources,Dover, Delaware. 119 pp. CLARK,K. E., L. J. NILES, ANDJ. BURGER.1993. Abundance and distribution of migrant shorebirdsin DelawareBay. Condor 95:694-705. Cooing,A. S. 1973. Shell thinning in avianeggs by environmentalpollutants. Environ. Pollut. 4:85-152. 190] K. C. Parsonsand A. C. McColpin j. FieldOrnithol. Spring 1995

, A. A. BELL,AND I. PRESTT.1976. Egg shell characteristicsand incidence of shell breakagefor grey heronsArdea cinereaexposed to environmentalpollutants. Environ. Pollut. 11:59-84. CUTLER,D. A. 1964. Middle Atlantic coastalregion. Audubon Field Notes 18:500-502. ERWIN,R. M., ANDC. E. KORSCHGEN.1979. Coastalwaterbird colonies:Maine to Virginia, 1977. U.S. Fish Wildl. Serv., Biol. Serv. Prog., FWS/OBS-79/08. FAt•ER,R. A., ANDJ.J. HI(:rd•V.1973. Eggshellthinning, chlorinated hydrocarbons,and mer- cury in inland aquaticbird eggs,1969 and 1970. PesticidesMonit. J. 7:27-36. --, R. W. RISEBROUGH,AND H. M. PRATr. 1972. Organochlorinesand mercury in com- mon egretsand great blue herons. Em4ron. Pollnt. 3:111-122. FITZNER,R. E., L.J. BLUS,C.J. HENNY,AND D. W. CARLILE.1988. Organochlorine residues in Great Blue Herons from the northwestern . Gol. Waterbirds 11:293-300. Fox, G. A. 1979. A simple method of predicting DDE contaminationand reproductive successof populationsof DDE-sensitivespecies. J. Appl. Ecol. 16:737-741. HICKS5;J. j., AND D. W. ANDERSON.1968. Chlorinated hydrocarbonsand eggshellchanges in raptorial and fish-eatingbirds. Science 162:271-273. HOFFMAN,D.J., B. A. RATTNF_R,.AND R.J. HALL. 1990. Wildlife Toxicology,Part 3. Environ. Sci. Technol. 24:276-283. JARMAN,W. M., R.J. NORSTROM,M. SIMON,S. A. BURNS,C. A. BACON,AND B. R. T. SIMONEIT. 1993. Organochlorines,including chlordane compounds and their metabolites,in per- egrine-falcon,prairie-falcon, and clapper-raileggs from the USA. Em4ron. Pollut. 81: 127-136. KING, K. A., E. L. FLINKINGER,AND H. H. HILDEBRAND.1978. Shell thinning and pesticide residuesin Texas aquaticbird eggs,1970. PesticidesMonit. J. 12:16-21. L•PORTE,P. 1982. Organochlorineresidues and eggshellmeasurements of Great Blue Heron eggsfrom Quebec. Col. Waterbirds5:95-103. LUNT, D.C. 1968. Taylors Gut in the Delaware State. Middle Atlantic Press,Wilmington, Delaware. M•RS, J.P. 1986. Sex and gluttony on Delaware Bay.Nat. Hist. 95:68-77. OHLF•NDORF,H. M., E. E. I•a. As, A•D T E. I•lSER. 1977. Organochlorine residuesand eggshellthinning in Anhingasand waders.Proc. Colonial Waterbird Group 1977:185- 195. OLSEN,G. H. 1989. Problems associatedwith incubation and hatching. Proc. Assoc.A•San Vet. 1989:262-267. OSBORN,R. G., AND T. W. CUSTER. 1978. Herons and their allies: atlas of Atlantic coast colonies,1975 and 1976. U.S. Fish Wildl. Serv., Biol. Serv. Prog., FWS/OBS-77/08. PARSONS,K. C. 1993. The Pea Patch Island Wader Colony: a proactive plan for natural resourceprotection and management.Tech. Rep., Delaware Dept. Natural Resources, Dover, Delaware.37 pp. PEAICALL,D. B., ANDG. A. Fox. 1987. Toxicologicalinvestigations of pollutant-relatedeffects in Great Lakesgulls. Environ. Health Perspect.71:187-193. ROBBINS,C. S., D. BYSTRAR,.AND P. H. GEISSLER.1986. The breeding bird survey:its first fifteen years, 1965-1979. U.S. Fish Wildl. Serv., Res. Publ. 157. SPEICH,S. M., J. CALAMBOKIDAS,D. ¾V. SHEA, J. PILARD,M. WITTER,.AND D. M. FRY. 1992. Eggshellthinning and organochlorinecontaminants in westernWashington waterbirds. Col. Waterbirds 15:103-112. SPENDELOW,J. A., AND S. R. PATTON. 1988. National atlas of coastalwaterbird colonies in the contiguousUnited States:1976-1982. U.S. Fish Wildl. Serv. Biol. Rep. 88(5). STEIDL,R.J., c. R. GRIFFIN,AND L.J. NILES. 1991a. Gontaminantlevels of ospreyeggs and prey reflect regional differencesin reproductivesuccess. J. Wildl. Manage. 55:601-608. --, .AND•-. 1991b. Differential reproductive successof ospreysin New Jersey.j. Wildl. Manage. 55:266-272. SULLIVAN,J. K., T. HOLDERMAN,AND M. SOUTHERLAND.1991. Habitat statusand trends in the DelawareEstuary. Tech. Rep., DelawareEstuary Program. 170 pp. U.S. FISHAND WILDLIFE SERVICE. 1991. Eggshellthickness measurement and interpretation: technicaloperating procedure. Patuxent Wildl. Res.Gntr. VAN DEN BERG, M., F. BL?d'qK,C. HEEREMANS,H. WAGENAAR,AND K. OLIE. 1987. Presence Vol.66, No. 2 GreatBlue Heron Reproductive Success [ 191

of polychlorinateddibenzo-p-dioxins and polychlorinateddibenzofurans in fish-eating birds and fish from the Netherlands. Arch. En;qron. Contam. Toxicol. 16:149-158. WIESE,J. H. 1976. A studyof the reproductivebiology of herons,egrets, and ibis nesting on Pea Patch Island, Delaware.Manomet Bird ObservatoryRes. Rep. 143 pp. ß 1979. A studyof the reproductivebiology of herons,egrets, and ibisnesting on Pea PatchIsland, Delaware. Final InterpretiveRep. 255 pp. Received 8 Feb. 1994; accepted 28 Jun. 1994.

SCIENTIFIC COLLECTING AND PERMITTING

Representativesof the Ornithological Council and the Association of SystematicsCollections recently met with leaders in the U.S. Fish and Wildlife Service about scientific collecting and permitting. FWS has agreed to streamline its policies and regulations,ensure biological foun- dations for its regulatory actions, provide for standardization among regions, and allow flexibility in case of unusual circumstances.For more information, contact Richard Banks, National Biological Service, or Dan Petit, Fish and Wildlife Service, Office of Migratory Bird Management.