Elevated Lead Levels in Urban House Sparrows: a Threat to Sharp-Shinned Hawks and Merlins?

j RaptorRes. 38 (1) :62-68 ¸ 2004 The Raptor ResearchFoundation, Inc.

ELEVATED LEAD LEVELS IN URBAN HOUSE SPARROWS: A THREAT TO SHARP-SHINNED HAWKS AND MERLINS?

RICHARDB. CHANDLER,ALLAN M. STRONG,1 AND CARLIN C. KAUFMAN Universityof Vermont,School of Natural Resources,Wildlife and FisheriesBiology Program, Burlington,Vermont 05405 U.S.A.

ABSTRAGT.--Inurban environments,lead (Pb) has been recognizedas a health threat to humans aswell aswildlife. Although this hazardhas waned since the banningof leadedgasoline and paint in the 1970s, soil and atmospheric Pb concentrationshave remained higher in disturbed habitats than in exurban habitats. Our study evaluated the threat of Pb exposure to Sharp-shinnedHawks (Accipiterstriatus) and Merlins (Falcocolumbarius) by measuringblood Pb concentrationsof the House Sparrow (Passerdomes- ticus),a favored prey speciesand a Eurasian exotic with a history of elevated Pb levels. In 2002, we found blood Pb concentrationsof urban House Sparrowsin Vermont, U.S.A., were significantly (4.5- fold) greater than in an agriculturalcontrol group. Becauseurban-dwelling Sharp-shinned Hawks and Merlins both selectivelyprey upon House Sparrows,they may be accumulatingPb. Analysisof 1970- 2002 ChristmasBird Count data confirmed an increasein wintering Sharp-shinnedHawks in Vermont and found a significantcorrelation (re = 0.456, P < 0.05) betweenthe rate of Sharp-shinnedHawk population increaseand the mean abundanceof House Sparrows.However, House Finch (Carpodacus mexicanus)abundance and rate of increase were more strongly related to the Sharp-shinnedHawk increase(r s = 0.732, P< 0.001 and re = 0.731, P< 0.001;respectively). We found no positivecorrelation betweenSharp-shinned Hawks and two common nativeNew England residents,Black-capped Chickadee (Poecileatricapilla) and Purple Finch (Carpodacuspurpureus), suggesting introduced prey speciesmay partially explain the mechanismbehind the "short-stopping"phenomenon occurring in a portion of the Sharp-shinnedHawk's range. The degree to which the exposure to lead-laden House Sparrows threatens urban raptor populations is unclear, and we recommend a more detailed examination of the contaminant levelsin urban-dwellingraptors. KEYWOADS: Sharp-shinnedHawk; Accipiter striatus;House 5parrow; Passer domesticus; Merlin; Falco columbarius; lead;migration; Pb; urban ecosystem.

NIVELES ELEVADOS DE PLOMO EN GORRIONES CASEROS URBANOS: •UNA AMENAZA PARA LOS GAVILANES Y LOS HALCONES PALOMEROS?

RESUMEN.--Enlos ambientesurbanos, el Plomo (Pb) ha sido reconocido como una amenaza para la salud humana y de la vida silvestre.Aunque este peligro ha disminuido desde la prohibici6n de la gasolinay pintufas con plomo en los 70's, las concentracionesde plomo en el sueloy la atm6sferahah permanecidomils altos en hfibitatsalterados queen hfibitatsal exterior de las urbes.Nuestro estudio evalu6 la amenazapor exposici6na plomo de los gavilanes(Accipiter striatus) y los halconespalomeros (Falcocolumbarius)a travfis de la medici6n de las concentracionesde plomo en la sangre de gorriones caseros(Passer domesticus), una presa predilecta, ademfis de set una especieex6fica Euroasifiticacon una historia de elevadosniveles de plomo. En el 2002, encontramos que las concentracionesde plomo en la sangrede gorrionesurbanos en Vermont, U.S.A., fueron significafivamente(4-5 veces)mils grandes queen un grupo controlubicado en una zonaagricola. DeNdo a que losgavilanes y halconespalomeros que habitan zonasurbanas depredan selecfivamentesobre los gorrionescaseros, pueden ellos estar acumulandoplomo. E1anfilisis de los datosde los conteosnavidefios de avesde 1970-2002confirman un incrementode losgavilanes invernantes en Vermonty encontramosuna correlaci6nsignificativa (r s = 0.456, P < 0.05) entre la tasa de incremento de la poblaci6n de gavilanesy la abundancia media de gorriones caseros.Sin embargo, la abundanciay la tasa de incremento de los pinzonescaseros (Carpo- dacusmexicanus) estuvo mas fuertementerelacionada al incremento de los gavilanes(re = 0.732, P < 0.001 y re = 0.731, P < 0.001;respectivamente). No encontramoscorrelaciones posifivas entre losazores

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62 MARCH 2004 LE^I) LF•VELS IN HOUSE S?APmOWS 63

y dos avesnativas, residentes comunes de New England, los paros de gorra negra (Poecileaoicapilla) y los pinzonespurpfireos (Carpodacuspurpureus), sugiriendo que las especiespresa introducidaspueden explicar parcialmente el mecanismoque se encuentra detrfis del fentmeno de "parada corta" que ocurre en una porci6n del rango del gavilan. E1 grado en el cual la exposici6na gorriones caseros cargadoscon plomo amenazaalas poblacionesde rapacesurbanas, no es claro y recomendamosun examen mils detaliado de los nivelesde contaminantesen las rapacesque habitan en las urbes. [Traducci6n de C•sar Mfirquez]

Urban ecosystemsare highly-modified land- Dunn and Tessaglia1994) and we have witnessed scapescharacterized by severe disturbancesand severalMerlin and Sharp-shinnedHawk attackson high proportionsof introducedspecies (Beisinger House Sparrowswithin our study area. Addition- and Osborne 1982, Gilbert 1989, Blair 1996). ally, documentation of elevated Pb levels among These ecosystemsare circulationand accumulation urban songbirds(Getz et at. 1977), a PeregrineFal- sites for a suite of environmental contaminants in- con that contracted a Pseudomonas infection as a cluding lead (Pb), a toxic trace metal remaining result of preying on Rock Doves (Columbalivia) in street dust and soilsfrom the leaded gasera and with elevated Pb levels (DeMent et at. 1986), and from the use of leaded paints (de Eduardo et at. the documentation of at least seven species of 1997). Typically,urban ecosystemsdo not provide North American raptors that have died from Pb high-qualityhabitat for most wildlife speciesas ev- poisoning (Locke and Friend 1992) warrant fur- idenced by low speciesrichness (Beisinger and Os- ther investigationof the role of House Sparrowsin borne 1982, Blair 1996); however, as cities, towns, Pb accumulationin raptors. and agriculturalexpansion have impacted the nat- We paid special attention to Sharp-shinned ural landscape,new or modified niches have aris- Hawksbecause of the recentlydocumented "short- en. Within the United States,many native wildlife stopping" phenomenon, in which a portion of speciesfrom a variety of taxa are adaptingto hu- their easternpopulation has reduced its migration man-modified ecosystemsand, in certain cases, distanceand remained in New England through- have become successfulat exploiting these new out the winter (Duncan 1996). This short-stopping niches.Raptors such as Merlins (Falcocolumbarius), appearsto explain partiallythe substantialdecreas- Peregrine Falcons (Falcoperegrinus), Red-tailed es in numbersof Sharp-shinnedHawks at fall hawk Hawks (Buteojamaicensis), Cooper's Hawks (Accipi- watch sitesalong the EastCoast during the pasttwo tercooperii), Mississippi Kites ( Ictinia mississippiensis),decades (Duncan 1996, Viverette et al. 1996) and and Eastern Screech-Owls (Otus asio) have altered may be tied to increasedprey availabilityin urban their habitat use patternsto take advantageof ur- ecosystems.Although the ecological mechanism ban resources (DeMent et al. 1986, Sodhi and Oti- behind the short-stoppingphenomenon hasyet to phant 1993,Viverette et at. 1996, Boatand Mannan be investigated,if selectedurban prey speciesex- 1999, Kaplan 2000, Berger 2001). hibit higher Pb loads than do exurban prey, Sharp- Although these casessuggest successful adapta- shinned Hawk populationscould face a toxicolog- tion to urban environments, the coststo raptors in ical risk. urban ecosystemshave not been fully evaluated. Previousornithological studies (e.g., DeMent et Boat and Mannan (1999) illuminated a few of the al. 1986, Sodhi and Otiphant 1993) in urban en- environmental threats facing urban Cooper's vironments and our observationsof raptors in ur- Hawks,but they focusedprimarily on human activ- ban regions of Vermont led us to the prediction ity around nests,automobile collisions, and diseas- that House Sparrows may pose a toxicological es. Other sublethal effects may also counteract threat to urban Sharp-shinnedHawks and Merlins. short-termpopulation increases.In this study,we Consequently,we examined the following hypoth- examined the potential toxicologicalthreat posed eses:(1) a portion of the Sharp-shinnedHawk pop- by elevatedPb levelsin a common, synanthropic utation has shifted its migratory behavior in re- prey species,the House Sparrow (Passerdomesticus). sponseto the increasedfood availabilityassociated House Sparrowswere chosenas a focal speciesbe- with human-modified environments, and (2) in ur- causethey are a preferred prey item for Merlins ban areas, Pb continues to be a threatening trace and Sharp-shinnedHawks (Accipiterstriatus) in de- element to wildlife, persistingin some avian food veloped landscapes (Sodhi and Oliphant 1993, chains. Our goal was to determine whether Pb is 64 CHANDLER ET AL. VOL. 38, NO. 1 persistentin the prey baseof these two raptors, and blood samples from birds in three locations. Our exper- if so, are wintering populations consumingHouse imental siteswere located in two urban areas in Burling- ton, Vermont; one in a high-density residential district Sparrows affected by potential toxicological and the other in the businessdistrict. Busy roads and threats? sidewalks were features common to both locations, and within these areas House Sparrowsseemed to aggregate METHODS around low, dense vegetation. The residential district was a primarily residential neighborhood interspersed with We analyzed ChristmasBird Count (CBC) data from 1970-2002 in 11 of 18 Vermont count circles (National some small businesses.The netting site within the businessdistrict wasclose to a central park, large parking lots, Audubon Society 2002). These 11 circles represent all thosewith data from at least 1975, the first year of Dun- and buildings taller than 10 m. Small conveniencestores, banks, and restaurants were more common here than can's (1996) analysisof the Sharp-shinned Hawk short- within the residential district. Our reference site was a stopping phenomenon. Vermont was selected as a rep- conventional dairy farm in a rural region of Vermont, resentative study region in New England because its approximately 55 km southeastof Burlington. We used wintering Sharp-shinnedHawk population has increased mist nets to capture House Sparrowsprior to collecting significantly (Duncan 1996). In Vermont, Merlin popu- < 1 dl of blood from the alar vein of each bird in hepar- lations are not large enough in winter to analyze using CBC data. The mean annual rate of Sharp-shinnedHawk anized capillary tubesfrom a smallpuncture made using a 22-gauge needle. The samples were frozen (below population increase was determined for each CBC circle -20øC) until analyzed. by regressingthe number of birds/party hr on count All sampleswere diluted five-fold and analyzedfor Pb year. Rates of Sharp-shinned Hawk increase were re- on a Perkin-Elmer SIMAA 6000 graphite furnace atomic gressedon mean abundancesand mean annual rates of absorption instrument equipped with a transversely-heat- change of House Sparrowsand three reference species: ed furnace, Zeeman background correction, autosam- House Finches (Carpodacusmexicanus), Purple Finches pier, and electrodelessdischarge lamp. A matrix modifier (Carpodacuspurpureus) and Black-capped Chickadees consisting of ammonium phosphate, Triton X-100, and (Poedieatricapilla), with each CBC circle assumedto be nitric acid was mixed with all samples.Quality-control an independent data point. Mean abundance for each CBC circle was calculated as the mean number of indi- samples included a method blank, laboratory control vidualsencountered (1970-2002)/party hr. This measure samples,and a standard reference (NIST 955bl, Lead in Bovine Blood). Blood masswas low, preventinganalysis allows for relative rather than absolute comparisonsof of matrix spike or duplicate samples.However, two cap- species abundances among CBC circles. Mean annual illary tubes from the same individual were used as field rates of change were calculatedfollowing the samemeth- duplicates, which showed identical blood Pb concentra- odologyas defined abovefor Sharp-shinnedHawks. tions. Laboratory Quality Assurancedata were acceptable We selectedHouse Sparrowsas a focal speciesbased and showed low blank levelsand good accuracy.Concen- upon our observationsof urban predator-prey interac- tration units are reported in parts per million (mg/1) tions, their high abundance in urban areas of New Eng- with a detection limit of 0.005 ppm. land, and their history of Pb accumulation (Getz et al. 1977). House Sparrowslikely accumulatePb when in- Because of the paucity of information available con- cerning raptors in urban environments,we haveincluded gesting grit for digestivepurposes (Gionfriddo and Best observations from the field that indicated either modi- 1995). This speciesis alsoregularly taken by both Merlins fied foraging behaviors or potential threats to these spe- and Sharp-shinned Hawks in human modified habitats cies. All observationswere collected opportunisticallyby and falls within the preferred size classof prey taken by both raptors (Lowther and Cink 1992, Sodhi and Oli- the authors on raptors inside Burlington'scity limits. phant 1993, Dunn and Tessaglia1994). RESUI,TS Our reference species were all winter residents and recognized prey speciesof Sharp-shinned Hawks (Bild- Sharp-shinnedHawks showed significant increas- stein and Meyer 2000). We chose these speciesbecause es in 9 of 11 Vermont count circles between 1970 their habitat associations differ from those of House and 2002. These rates of change were positively Sparrows,making them appropriate speciesfor evaluat- ing the hypothesisthat Sharp-shinnedHawks are short- correlated with mean winter House Sparrow abun- stopping in responseto the abundance of urban exotics. dances (F = 8.2, df = 1, 9, P < 0.05, re = 0.476; Black-cappedChickadees are a common winter resident Fig. 1), though not with House Sparrowmean an- in New England associatedwith natural and human-mod- nual rate of change (F = 0.171, df = 1, 9, P > 0.6, ified habitats. Purple Finches are generally considered forest dwelling species,although they are alsoa common re = 0.019). They were inverselycorrelated with visitor to birdfeeders. House Finches are the most syn- mean abundanceof Purple Finches(F = 6.7, df = anthropic of the references species,found in urban and 1, 9, P < 0.05, re = 0.4255); and highly positively residential areas but are more readily found in suburban related with both mean abundance (F = 24.5, df areas than House Sparrows (Blair 1996). = 1, 9, P < 0.001, re = 0.732; Fig. 2) and mean Pb concentrations in venous blood are good indicators of acute or chronic environmental exposure as well as of annual rate of change (F = 24.4, df = 1, 9, P < body Pb burden (Reiser and Temple 1981, Hunter 1986). 0.001, re = 0.731; Fig. 2) of House Finches.The To examine Pb levels in House Sparrows,we collected Sharp-shinnedHawk population increasewas not MARCH 2004 LEAD LEVELS iN HOUSE S?•amows 65

0.0025

r 2 -- 0.4758 P < 0.05 0.0020

o.oo15

0.0010

0.0005

0 5 10 15 20 Mean Number of House Sparrows/Party Hour Figure l. Rate of Sharp-shinnedHawk populationchange was significantly correlated with abundanceof House Sparrowsin VermontChristmas Bird Counts,1975-2002.

0.0025 - correlated with either abundance or mean annual rate of change in Black-cappedChickadees (F = 0.1, df = 1, 9, P > 0.7, fi = 0.012; F = 0.5, df = 1, 9, P > 0.45, fi = 0.052; respectively)or with mean annual rate of change of Purple Finches (F = 4.9, df = 1, 9, P > 0.05, re = 0.354). o.oolo Blood Pb concentration differed among House Sparrowsin the three studygroups (F = 10.16, df 0.0005 = 2, 24, P < 0.001; Table 1). We found no differ- ence in Pb concentrations between the two urban groups(t = 0.873, df = 11.7, P = 0.40); therefore, 0 1 2 3 we combinedresidential district (N = 8) and busi- Number of Hou• Vinch•/Pa•y Hour ness district (N = 8) into a single urban category. Blood Pb concentrations were more than 450% 0.0025? 0.0020I F=0.7•05 Table 1. Blood lead concentrations in House Sparrows P < 0.00• in Vermont, 2002 varied significantlyamong three habitats. •"o.oolo.oolo 5 ß • MEAN BLOOD PB .c0.0005 • CONCENTRATION LOCATION N - SD (ppm) a

0 0.1 0.2 0.3 Urban, business district 8 0.083 _+ O.068 Mean Annual Rate of House Finch Increase Urban, high-density residential district 8 0.108 + O.O42 Figure 2. Rate of Sharp-shinned Hawk population Urban combined 16 0.095 --+ 0.053 changewas significantlycorrelated with abundance (a) Reference 11 0.021 -+ 0.012 and rate of change (b) of House Finches in Vermont Christmas Bird Counts, 1975-200% •Ez•4 = 10.16, P< 0.001. 66 CHANr)L}m •T AL. VOL. 38, No. 1 greater in urban (N = 16) than agricultural (N = modified environmentsmay have respondedto in- 11) House Sparrows (t = 5.183, df = 16.9, P < creasingHouse Finch populations,which alsolike- 0.001). Despite significantlyhigher blood Pb con- ly enabled them to exploit abundant,stable House centrations, the combined urban mean of 0.0953 Sparrowpopulations. Thus, it is plausiblethat both ppm is probablynot high enough to affect survival speciesof raptors are curtailing their southward or reproductiverates negatively (Getz et al. 1977, migrations to take advantage of the increased in- Redig 1984). However, we found substantialindi- troduced prey base. vidual variation, with one individual exhibiting a Theoretical arguments regarding the costsand blood Pb concentration of 0.209 ppm. benefitsof migration support our hypothesis.Rap- Sharp-shinnedHawks, Cooper's Hawks, Merlins, tors, like other migratory birds, are believedto de- Peregrine Falcons,Red-tailed Hawks, and Bald Ea- part their breeding grounds in responseto the de- gles (Haliaeetus leucocephalus)were all observed teriorating conditions brought about by winter within Burlington's urban zone during the winter climates (Rappole 1995). BecauseNeotropical mi- 2001-02. On five occasions,Sharp-shinned Hawks gratory songbirdstypically comprise the vast ma- or Merlins were observedeither hunting or feed- jority of Sharp-shinnedHawk's diet (Bildsteinand ing upon House Sparrows. We did not observe Meyer 2000), it is probable that fall migration of thesetwo speciespursuing prey speciesother than theseprey speciesis the most important reasonfor House Sparrows. this raptor's migration. Assuming migration is a trade-offbetween breeding seasonproductivity and DISCUSSION mortality during migration and the nonbreeding Our results provide support for the hypothesis season,it is possiblethat increased food resources that population increases in wintering Sharp- at higher latitudes (e.g., House Sparrows and shinnedHawk populationsin Vermont are strongly House Finches) might alter the cost-benefitratio correlatedwith prey availabilityin human-modified of migration such that winter mortality at higher environments. Our anecdotal observations of these latitudes is lessthan or equal to migration mortal- raptors hunting in urban environments,combined ity + winter mortality at lower latitudes. Thus, with previous studiesshowing House Sparrowsto Sharp-shinned Hawks could be expected to in- be the codominant prey speciestaken by Sharp- crease in areas with high populations of resident shinned Hawks at birdfeeders (Dunn and Tessaglia prey species.The Black-cappedChickadee and the 1994) suggestthat large House Sparrow popula- Purple Finch, two common winter residentsin New tions provide a plausible causalmechanism for the England, do not appear to be associatedwith win- increaseof winter raptor populations.Though we ter population increasesof Sharp-shinnedHawks. did demonstrate that Sharp-shinned Hawks in- Rather, our data suggestedthat House Sparrow creased proportionally with mean densities of and House Finch populations provided the prey House Sparrows,we found that House Finch abun- base that has led to increasedwinter populations dancesand rates of changewere more stronglyre- of Sharp-shinnedHawks in Vermont, as a result of lated to changesin raptor numbers.That we found short-stoppingmigratory patterns. Becauseof the no significant relationship with mean annual rate differencesbetween these prey species'habitat as- of House Sparrowincrease supports the hypothesis sociations, we conclude that the increase in hawks that House Fincheswere primarily responsiblefor appearsto be most rapid in urban and residential attracting these hawksinto urban and suburbanar- areas. The inverse relationship between Purple eas. However, we also suggestthat House Sparrows Finches and Sharp-shinnedHawks may also indi- are an important food source for raptors within cate that the short-stopphenomenon is not occur- these modified habitats. Merlins in particular are ring in natural habitats. known to feed almost exclusivelyon House Spar- Our results also showed that blood Pb concen- rows,which can comprisemore than 70% of prey trations were measurable in House Sparrow pop- items taken in urban environments (Sodhi and Oli- ulations, and compared to rural populations,were phant 1993). In fact, in Vermont, there was a ca. 4.5x higher in urban areas (Table 1). Thus, strong correlation between the rate of House despite the fact that Pb has been banned in gaso- Finch increase and mean abundance of House line and paint for over 20 yr, environmentalsourc- Sparrows(F = 31.8, df = 1, 9, P < 0.01, •2 = 0.76). es are still sufficientlyabundant to showmovement Consequently,raptors that have adapted to these into higher tropic levels.However, this elevatedPb M_•RCH 2004 LEAD LEWLS IN HOUSE SP•omows 67 level was not lethally threatening to House Spar- toxins are present in urban prey speciesand a sig- rows, which have been shown to sustain higher nificant proportion of a raptor population alters its concentrations(Getz et al. 1977). It is plausible migratory behavior to exploit these prey. The risks that sublethal effects might make individualswith of such a scenario is impossibleto assesswithout elevated blood Pb concentrationsmore susceptible measuring the actual Pb levels in a population of to predation (Peterle 1991:108). urban raptors (Newton 1998), and unfortunately Although our results showed an increase in no such data have been collected. We also note Sharp-shinned Hawk populations in areas with that Pb levels have not been measured in House high House Sparrow populations and elevated Finches. These uncertainties, as well as the lack of blood Pb concentrationsin this prey species,the knowledgeof biologicallyincorporated Pb intake threat to urban raptors was equivocal. Several tox- rates in birds of prey indicate the need for stronger icity studiesof raptors have indicated that in con- avian bioaccumulation models and more research trolled conditions,Pb can biomagnifyto threaten- into urban ecosystems.Data on sublethal physio- ing or lethal levelswhen lead-ladenprey species logical, behavioral, and reproductive effects (e.g., were consumed.The infection leading to the death Burger 1995) are also needed. We suggestthat a of an urban Peregrine Falcon was contracted as a study be performed similar to that of Wood et al. result of its susceptibilityto infection from contin- (1996), in which thorough toxicological testsare ual depredation of Rock Doveswith blood Pb levels conducted on New England's wintering urban avi- approximately nine times higher (œ= 0.901 ppm) an communities, especially birds of prey. This than those found in our study of House Sparrows would allow for a detailed comparisonof contam- (DeMent et al. 1986). A controlled toxicological inant levels in urban and exurban environments. experiment in which a Pb acetate trihydrate solu- Although Wood et al. (1996) concluded that de- tion was administered to nine raptors of three spe- creased numbers of migratory Sharp-shinned cies found that blood Pb levels between 5 and 8 Hawks could not be explained by toxicologicalfac- ppm led to clinical signs in five individuals and tors, nonmigratory individualswere not sampled in death in four (Reiser and Temple 1981). that study; however, this may be the population Conflicting information on accumulation rates segmentmost at risk to increasedPb levels. and effects of lead are common. These discrepan- ACKNOWLEDGMENTS cies are typicallyexplained by differencesin study design and interspecific variation in susceptibility The University of Vermont's Honors College and Of- to Pb (Peterle 1991). Franson et al. (1983), for in- fice of SponsoredPrograms provided financial support for this project and dcservesrecognition for its efforts to stance, reported no major physiologicaleffects on provide support to undergraduatesinterested in scientif- American Kestrels(Falco sparverius) with blood Pb ic research.Thanks to the National Audubon Societyand levelsas high as 33 ppm. Wild predatory birds may the Cornell Laboratory of Ornithology for use of CBC be affected differently by contaminationthan cap- data and the many ChristmasBird Count volunteers for tive birds because of differences in metabolic rates their continued effort. Robert Taylor at TexasA&M conducted the Pb analyseswith patience and humor. We and behaviors.For example, predators may not be thank Monument Farms and the residents of Burlington, able to forage as effectivelywith high contaminant Vermont for their resources, suggestions,and enthusi- loads (Peterle 1991). The relativelyshort duration asm. For technical assistance and comments we thank of laboratory experiments also may not reveal sub- Terri Donovan and Peter Jones. The manuscript was greatly improved with the suggestionsof our referees:M lethal risks posed by long-term Pb exposure.The Martell, R.W. Mannan, and TJ. McBride. Finally, Mary Peregrine Falcon death also suggestedthat risk of Willson and the Project Chucao crew were instrumental infectious disease may have increased with in- in editing the manuscript.Mist netting and blood sam- creased Pb load, a threat possiblyexacerbated in pling was done in accordancewith the guidelinesof the the wild. These factors make it difficult to deter- University of Vermont's Institutional Aafimal Care and Use Committee (IACUC No. 02-092). mine the threat to raptors feeding on House Spar- rowswith the blood Pb concentrationsreported in LITERATURE CITED this paper. Therefore, we suggestthat the proba- B}•IS•NG}m, S.R. ,•,:D D.R. OSBORN}•. 1982. Effects of ur- bility of biomagnificationof lead is worthy of fur- banization on avian community organization. Condor ther investigation. 84:75-83. Urban raptors may face a significanttoxicologi- BERGEa,C. 2001. Urban raptors.Natl. Wildl.39:30-37. cal threat if, as our data indicate, high levels of BILDSTEIN,K.L. Mr) K. MEy•}•.2000. Sharp-shinnedHawk 68 CHANDLER •T )d•. Von. 38, NO. 1

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