Range Expansion of the Glossy Ibis in North America

Home , Glossy ibis, Ibis, Plumage, Threskiornithidae

Michael A. Patten Departmentof Biology Universityof California R•vers•de,California 92521 SanDiego Natural History Nuseum PO. Box 121390 SanDiego, California 92112 GregW. Lasley 305 LoganberryCourt Austin,Texas 78745

ABSTRACT

rangeheGlossy in bothIbisthe (PlegadisUnited States falcinellus)and Mexico has steadilysince the expanded early1800s. its In the UnitedStates, the speciesinitially colonized Florida, where breedingwas first detectedin the 1880s.This ibis remaineda local speciesin the countryuntil the 1940s,when it expandedinto the Northeast and elsewherein the Southeast,west to Louisiana.Another periodof rangestability was followed by a burstof westwardexpan- sionin the mid-1980s,coupled with a rapid expansionthroughout B the YucatfinPeninsula. The speciesreached the West Coast in Californiaand Colimashortly thereafter. It now occursannually in the western United States east of the continental divide. The vast majorityof recordsare of adultsin full breedingcondition, with mostin April andMay. We concludethe occurrence of thespecies in the Westreflects a true rangeexpansion, but this patternin con- foundedby the relativeease of detectingfull adultsin spring. INTRODUCTION Mostrange expansions are slow, with manymeasured over geologi- caltime (e.g.,McLeod and MacDonald1997). We mightexpect this slowrate of expansionif a daughterspecies from a speciationevent slowlyadapts to newenvironments and micro-habitats as it radiates awayfrom its point of origin.However, many rangeexpansions occurextremely rapidly, some possibly in associationwith speciation events(Gaston 1998), but mostthrough processes that areless clear. In a few casesrange expansions have occurred as a resultof adapta- tionsto localenvironmental change (Hilbeck and Kennedy 1998) or in responseto human modificationof habitat (Periset al. 1998). Furthermore,some expansions are cyclic, apparently in responseto oscillationsin food and climate (Patten and Erickson 2000). Unfortunately,we generallyknow little aboutmechanisms facilitat- Figure1. NorthAmerican distribution of the GlossyIbis ca. 1960 ing rapidrange expansion, whether by a native(e.g., Post et al. 1993, (A) andca. 2000 (B).Dots on mapB signifyrecent vagrant occur- Dinsmore and Dinsmore 1993, Rothstein 1994) or non-native rencesoutside the currentrange.

NORTHANERICAN BIRDS 54 241-247, 2000 species(e.g., Veit and Lewis 1996, Gipson et al. 1998, Lewis et al. 1999), althoughmost hypothesesinvoke anthropogenichabitat alteration. The rapidrange expansions underway by both of the Plegadisibis exemplify our ignorance.Over the pastthree decades there has been a vast increase in the number of recordsof the White-facedIbis (P. chihi)in easternNorth America and a concomitant increase in records of the GlossyIbis (P.falcinellus) in westernNorth America.The rangeexpansion of the latterspecies has been particularly striking.There were no validrecords in theWest in the mid-1980s(DeSante and Pyle1986), but in just 15 years it hasbecome regular on the easternedge of the conti- nentaldivide. During this sameperiod the GlossyIbis expandedits rangesouthward into Mexico (Howell and de Montes1989), was first detectedbreeding in Canada (McAlpineet al. 1988),and reachedthe PacificCoast in both westernMexico (Howell 1994) and California (see below). Herein we summarizethe westwardexpansion of the GlossyIbis and discuss several alternative hypotheses that could explain this phenomenon,ranging from an increasein observerawareness to a natural expansion into available marshland.

FORMER RANGE AND STATUS Apart from its distributionthrough various portions of the Old World,the GlossyIbis wasformerly a bird of the southeasternUnited States.Data are limited, but it would appearthat this speciesis a fairly recentcolonist of the New World (Palmer1962, Dunstan 1978), presumably arrivingin a trans-Atlanticmanner similar to the Cattle Egret(Bubulcus ibis). The first United Statesrecord was duringAudubon's lifetime, furnished by a specimenfrom Figure2. GlossyIbis in full breedingcondition at AnahuacNational Wildlife GreatEgg Harbor, New Jersey,7 May 1817(Peterson and Refuge,Texas, 14 April 1996.The rich chestnutfeathering throughout the Peterson1981). It was so rare in the New World at that head and neck is characteristicof DefinitiveAlternate plumage in both time that Audubonencountered the speciesbut once, Plegadisspecies. Photograph by Greg• Lasley. near St. Augustine,Florida, 16 January1832 (Peterson and Peterson1981). Breeding records were not obtained until the 1880s(Palmer 1962). By the turn of the twenti- eth centuryit wasonly "rare and local" along the Gulf of Mexicoand in Florida(Chapman 1912), with the largest breedingpopulation numbering only _+50pairs by the mid-1930s(Peterson and Peterson1981). However,the GlossyIbis beganto expandits range substantiallyduring the 1940s,with birdspushing north to LongIsland and westto Louisiana,becoming a breeding bird in New Yorkby the early1960s (Bull 1974)and north to Maine by the early 1970s(Oberholser 1974). This ibis first reached Honduras, Costa Rica, Panama, Columbia,and Venezueladuring this time, althoughby the mid-1970sthe specieswas "mainly a northernstrag- gler to CentralAmerica and northernSouth America" (Blake 1977). Populationsin theseareas and westward alongthe Gulf of Mexicostabilized somewhat by the late 1970s/1980s,prior to anotherburst, this time to the west and south.Thus, by the early1980s the GlossyIbis wasa bird of the southeastern United States and Atlantic Coast (Fig. 1), with local populationsin the GreaterAntilles, Figure3. AdultGlossy Ibis at Bosquedel ApacheNational Wildlife Refuge, CostaRica, and northernVenezuela and variousvagrant NewMexico, 19-24 April1999, the secondrecorded in the state.Photograph records for eastern North America east of the Great Plains byJerry R. Oldenettel. (A.O.U. 1983).

Z4Z NORTH AMERICAN BIRDS glossyibis

Rosa9 May (Williams1999). In 2000 one wasphotographed at Bosquedel Apache 21-22 April andwhat may well have been the samebird wasseen there 12-13 May (S. O. Williams in littO. Despitean unconvindngreport of a flock of 60 near La Paz,Baja California Sur,25 May 1996(Carmona et al. 1997), thisspedes has reached the Pacificstates only in Colima in western Mexico (Howell 1994) and in California.The first record for the latter was of an adult in DefinitiveBasic plumage at Twentynine Palms 29-31 August 1999 (McCaskie 2000). Three more birds were pho- tographedin spring/summer2000 near the south end of the Salton Sea in the vicinity of Calipatriain the Imperial Valley:an adult in DefinitiveAlternate Plumage27 May-8 August(M. A. Patten et al.), another 1-15 July (Fig. 4; P. A. Ginsburget al.), and a bird in Definitive Figure4. Breedingadult Glossy Ibis in a floodedfield near the southend of the SaltonSea, Basicor FirstAlternate plumage 1-8 July _+12km w. of Calipatria,Imperial County, California, I July 2000. This bird represented the (M. A. Pattenet al.). third record for California.All four recordsfor that state are since late August 1999. Thus,the pasttwo decadeshave wit- Photographby KennethZ Kurland. nesseda significantincrease of recordsof the GlossyIbis in westernNorth America RECENT RANGE EXPANSION (rs = 0.80,P < 0.01), witha particularly sharp increase since the mid- Beginningin themid- to late 1980s,the Glossy Ibis began to push 1990s(Fig. 5). All birdswest of theGreat Plains have been detected westward into Texas and southward into the Yucatfin Peninsula of fromlate March to lateAugust, with a distinctpeak from mid-April Mexico(Fig. 1); its expansioninto the latterarea was well-docu- to mid-May(Fig. 6). Thetemporal pattern of recordsin theWest is mentedby Howelland de Montes (1989). In Texas,the firstrecord probablya combinationof thereal pattern and an artifactof identi- was of a bird at Ft. Worth 3-6 November1983 and returning20 ficationease. Because the GlossyIbis retractsfrom morenortherly October-15December 1984 (Pulich 1988,Lasley 1989). Within a climesduring winter and returns to thoseareas during summer, it is fewyears it wasevident that the species was regular on theUpper reasonableto concludethat many records at thisseason are of spring TexasCoast (Fig. 2), with_+25 records west to theDallas/Fort Worth "overshoots:'Yet at the same time adult Plegadisin alternate area and to Austin and San Antonio on the Edwards Plateau (see plumageand full breedingcondition are by far the easiestage dass below).It haseven been recorded south to the lowerRio Grande to identify,so we expectthat records will be skewedtoward spring. Valley(Haynie 1993) and thrice far westin the Trans-Pecosregion: However,this speciesregularly undergoes post-breeding dispersal at El Paso29 April-4 May 1992and twiceat BalmorheaLake, 29 northwardalong the AtlanticSeaboard and elsewherein the East. April1997 (Peterson and Zimmer 1998) and 2 May2000 (Lasley et Thus,fall records of vagrantsshould also be expected, and a number al.2000). By 1995 so many records had accumulated that the species of recordsfor Texasare from September-November, including birds wasdropped from the TexasBird Records Committee review list westto FortWorth (Lasley1989). (Haynie1996). Both Colorado and New Mexico have experiencedsimilar individualsat SweitzerLake 27 March 1986,in Weld County 25-28 Mayincreases.1988, Innearthe Erieformer, 7-9 thereMay were1989, butandfour atOrlando valid records Reservoir by 1990,4July of 14 ofthe decade thespecies wasannual ineastern Colorado, particu- larlyin spring,with nearly 30 reportsaccumulating (W. P.Lisowsky in1990litt.). (AndrewsFor example, andRighter1992, +10were reported B. K.Percival(but not in necessarilylitt.). By thedocu-end mented)onein western26April-13Colorado, July near1999 Edwards,and 8April-23 Eagle MayCounty, 2000,24-28 including April 2000(Truan andPercival 1999,2000). Spring1999 also saw Wyoming's first record, of a birdat Jackson 4 May 1999(Truan and Percival 1999). Just a fewyears earlier, the specieswas added to thestate list for New Mexico, when an adult in breedingcondition was videotaped at BosqueRedondo, DeBaca 1996 1998 2000 County,14-15 April 1995 (New Mexico Ornithology Society Bulletin Year 24:61,S. O. Williamsin litt.). Sincethat time four-fiveadditional recordshave accumulated, all of them in 1999 and 2000. Three were Figure5. Recordsof the GlossyIbis, 1984-2000, west of the Great photographedduring spring 1999, at Bosquedel ApacheNational Plains(westTexas, Wyoming, Colorado, New Mexico, California, and WildlifeRefuge 18-24 April (Fig.3), BitterLake 24 April, and Santa Colima).

VOLUME54 (2000), NUMBER1 243 IDENTIFICATION AND AGEING Asa resultof theextreme difficulty or impossibilityof separatinga The identificationof Plegadisibis requires dose views, in goodlight, BasicI froma DefinitiveBasic bird, the timing of post-juvenalmolt is of bare-partpattern and colorationand featheringaround these of criticalimportance. Glossy Ibis generally do not undergothis molt areas;various other plumage features are identical, as is voice.This untilSeptember/October (Cramp and Simmons 1977). Based on field topichas been covered well by Pratt(1976), Howell and de Montes experience,not on a definitive,quantitative study, it appearsthat post- (1989), Kaufman(1990), the NationalGeographic Society (1998), juvenalmolt takes place on thewintering grounds, as Plegadis that are andSibley (2000). However, there are important identification points still obviousfall migrantsare in full Juvenalplumage even in late thatbear repeating. Furthermore, as it iswith manyspecies, proper- November.Conversely, around the Salton Sea in southeastern ly judgingage and conditionis an importantfirst step in identifica- California,where thousandsof White-facedIbis regularlywinter tion, which is difficult when the bird is not in alternate (Shufordet al. 1994),birds transifioning into BasicI canbe seenby plumage/breedingcondition. Indeed, to our knowledgepositive mid-August,but eventhere most retainfull Juvenalplumage until species-levelidentification of juvenilesis impossible,even with a laterin thefall (Pattenpers. obs.). specimen,excepting relying on sizeextremes. The GlossyIbis aver- Adultsin DefinitiveAlternate plumage are easily identified by the ageslarger than the White-facedIbis, sex for sex (Table 1; contra rich chestnuthead and neck,glossy purple mantle and underparts, Sibley2000); indeed, a Glossyamidst a largeflock of White-facedis andglossy green wing coverts and tertials. The White-faced Ibis tends often the largestbird (Lasleyper. obs.).Thus, the largestPlegadis to showa bit lessolive in the head at this season,but this featurevaries shotfidbe male Glossy, whereas the smallestshould be female White- substantially,such that mostbreeding adult Plegadis ibis look basical- faced.However, there is overlapin size(Table 1), makingidentifica- ly the samein generalplumage color. The prindpalplumage differ- tion on measurementsalone sometimes problematic. ence,obviously, is the oftenbroad but sometimesnarrow border of whitefeathering surrounding the bareskin on theface of a Table1. Mensuraldata for the Glossyand White-faced Ibis, White-facedIbis, the featurethat gives the spedes its name. presentedas mean[range], in millimeters(data from Blake 1977). Birdsin this plumagegenerally also exhibit breeding Notethat, withinsex, the Glossyaverages larger, but there is conditionbare-part coloration, with the White-faced show- overlapin measurements(especially the bill). ingbright-red to moderate-pinkfacial skin and the Glossy flat wing exposedculmen tarsus showingdark-blue to grayishfacial skin. The latter species haswell-defined blue, bluish-white, or palegray borders to males the facialskin, both from the eyeto the culmen(the 1oral Glossy(n= 11) 288.3 [275-294] 131.0 [127-137] 103.1 [99.2-112] stripe)and the eye to thegape (Pratt 1976, Kaufman 1990). White-faced(8) 269.6 [261-280] 133.9 [118-143] 94.6 [91-98] Thesestripes are on theskin itsel• the featbering surround- [emales ing the faceis whollydark. The loralstripe bulges toward the middle,whereas the lower stripe is evenin width,such Glossy(n = 8) 262.2 [252-275] 104.2 [95-1141 81.8 [78-88] that the loral stripeis bolderand easierto see(Jonsson White-faced(10) 243.5 [238-249] 103.6 [100-111] 70.0 [63-73] 1992;cf. Fig. 4). Also,the loral stripe crosses over the base of the culmen,but the lower one stopsat the gape(white It is straightforwardto distinguishbetween a Plegadisin Juvenal featheringsurrounding the facialskin of a White-facedIbis crosses plumageand one in basicplumage. A uniformmuddy-brown head underthe chin).Note that someWhite-faced Ibis showa paleloral andneck lacking white streaking and the dull brownunderparts char- stripeon the facialskin, but thisstripe is narrow,ill-defined, and pre- acterizeJuvenal plumage (Kaufman 1990). Juveniles exhibit a variable sentonly on adults,which have pink/red facial skin and thus do not amountof whitesplotching on the throat,which ranges from exten- posean identificationproblem anyway (Howell and de Montes1989, sive(Fig. 7) to absent.At this ageindividuals tend to havea much NationalGeographic Society 1998). shorterbill than do adults(Table 2), with full adultbill lengthbeing Legand bill coloris morevariable, with thedifferences oversimpli- acquiredwithin three-sixmonths of hatching.Basic plumage, both fiedin mostfield guides (e.g., National Geographic Society 1998). The Definiteand BasicI, is characterizedby a darkbrown or brownish- White-facedIbis doestend to haveuniform red legswhen in high gray head and neck coveredwith fine white streaking.Apparently breedingcondition, but we notemany Glossy Ibis in the samecondi- BasicI and DefinitiveBasic are not distinguishable(Cramp and tioncan show all redlegs. Similarly, although the Glossy tends to have Simmons1977), although there may be sometendency for adultsto graylegs with red intertarsaljoints ("knees"), we notethis same pat- retainsome purple iridescence in the wing coverts,whereas juve- tem on manyWhite-faced lbis. Bill color is evenmore variable, with niles/first-winterbirds are uniform greenabove (Howell and de perhapsthat of the White-facedaveraging slightly pinker, although Montes1989). Based on an examinationof specimensat theAmerican not enoughso to be an aidto identification.Lastly, adult White-faced Museumof NaturalHistory, apparent adults in basicretain glossy Ibishave bright red irides; adult Glossy Ibis and all immaturePlegadis purpleundertail coverts, whereas immatures have dull green undertail havebrown irides (Howell and de Montes 1989,Kaufman 1990). coverts.Obviously, the colorof thesefeathers would be difficultto Diagnosticadult bare-partcoloration is generallynot acquired assessin the field. until Decemberor Januaryof the firstyear of life.Many Plegadis in BasicI plumagecannot be identifiedeither, although some hatch-year Table2. Rangeof bill length(mm) of juvenile P. chihiacquire red eyesby September(Patten pers. obs.) and some GlossyIbises during the firstsix months of life hatch-yearP. falcinellus acquire pale facial stripes by August (Howell (datafrom Cramp and Simmons 1977). andde Montes1989, S. E. Finneganpers. comm.) or exceptionallyin Aug/Sep Oct/Nov Dec/Mar July(J. L. Dunn pers.comm.). However, many immatures will lack male 98-113 108-132 120-134 diagnosticbare-part coloration until theirfirst spring (i.e., when they are 9-10 months old), and thus will not be identifiable. female 86-102 95-103 101-111 Plegadisibis take two yearsto acquirefull adult plumage,but

Z44 NORTH AMERICAN BIRDS glossyibis

AlternateI and BasicII areextremely similar to correspondingadult plumages.Therefore, adults in DefinitiveBasic plumage and all birds 14 by theirfirst spring should have species-specific bare-part coloration, at leastin termsof eyecolor and facial skin color/pattem. As a result, adultsin wintercan be identifiedwith goodviews in goodlight, as the •o •0 facialskin will be darkgray with well-definedwhitish or palegrayish borderson a GlossyIbis (Fig. 8) butwill be dull pink on a White-faced Ibis(Fig. 9), with thelatter also having red eyes. However, we notethat eyecolor can be surprisinglydifficult to determinewithout good light and good optics (and with the bird fairly close).Even so, on California'sfirst GlossyIbis, a bird in DefinitiveBasic or Basic II/AlternateI at TwentyninePalms 29-31 August1999,"The bare facial skinwas fairly dark gray, lacking either red or bluetones. The upper edgeof the facialskin was bordered by a distinctpale gray stripe that Jan Feb Mar .•or May Jun Jul Aug Sep Oct Nov Dec ran from the upperedge of the eyeto the baseof the culmen,and Month bulgingoutward in the center.The loweredge of the facialskin was alsobordered by a distinctgray stripe, this one a bit thinnerand less Figure6. Seasonalpattern of GlossyIbis records west of the Great Plains. visibleat a modestdistance and running from the lower edge of theeye to thegape. It curveddownward slightly at thegape, but did not cross underthe chin" (Patten pers. obs.). It wasthus identifiable as a Glossy thecentral coast of Texas(Lasley et al. 1997),but hybridization has not Ibis,despite not being in alternateplumage or breedingcondition. yetbeen detected. However, these species "freely interbred" in captiv- As a œmalcautionary note, we note that the White-facedIbis is ity (Palmer1962:517), so we anticipatethat hybridswill occurin undergoingan eastwardexpansion that mirrorsthat of the Glossy, nature(see Patten 2000). Potential hybridization obviously adds a withvagrant records now annual on theAtlantic Coast. Co-expansion complicatedand tricky wrinkle to fieldidentification, but the possi- of thesesister species has brought them into sympatryin southern bility shouldbe bornein mind if an ibisis encounteredthat exhibits Louisiana(A.O.U. 1998, J. V. Remsenpers. comm.) and recently along mixed or intermediate characters.

Figure7. Typical Plegadis in Juvenalplumage, in thiscase a White-facedIbis at FurnaceCreek Ranch in DeathValley, California, 16 August 1991.The extent of splotchywhite feathers on the chinand throat is variable,ranging from extensiveto essentiallyabsent. Regardless, thissplotching is characteristicof Juvenalplumage only. Note the lackof whitestreaking on the headand neck, with eachinstead being uniformmuddy brown. Identification to speciesis generallyimpossible at thisage (exceptby range).Photograph by MichaelA. Patten.

VOLUHE54 (2000), HUHBER3 245 CONCLUSIONS The GlossyIbis is rapidlyexpanding its range westward,with records now annual on the east- ernslope of thecontinental divide and westward to western Colorado, inland California, and coastalColima, Mexico. This expansion appears to bea realphenomenon, perhaps related to the creationof wetlandhabitats (e.g., sewage ponds, golfcourses) in the previouslyarid portions of the southern Great Plains and the desert Southwest.The vastmajority of recordsof the GlossyIbis in the Westare of adultsin high breedingcondition in Apriland May, suggesting a strongelement of observerbias is involved. Still, both Plegadisare migratory,retracting fromnortherly dimes in winter,so the possibil- itythat spring records are the result of a prepon- deranceof springovershoots cannot be elimi- nated,as it isclearly confounded with detectabil- ity.Nevertheless, we suspectthat careful scrutiny of adultsin winterwill yieldfurther records in the West.Additional field data,with an accurate Figure8. Typicaladult Glossy Ibis in basicplumage at the KennedySpace Center, Florida, picture of seasonaloccurrence, will be needed to 6 March1997. The white streakingthroughout the headand neckis characteristicof determinethe extentand rateof rangeexpan- basicplumage and is notfound on birdsin juvenalplumage. Pale facial stripes remain sionand thence to explorecausal factors behind throughwinter, but vary in conspicuousnessfrom distinctiveto ratherfaint but visible the expansion. with a carefulstudy. Photograph by GregW. Lasley.

Fiõure9. TypicalWhite-faced Ibis (riõht) in basic/first-alternateplumaõe, with a like-plumaõedGlossy Ibis (left), at MitchellLake near SanAntonio, Texas, 12 May1991. The red iris and dull pink facial skin remain throuõh the winter, but sometimes require close views to be seenwell. Photograph by 6re9 • •sle•

Z46 NORTHAMERICAN BIRDS ibis

ACKNOWLEDGMENTS Lasley, G. W., C. Sexton, W. Sekula, M. Lockwood, and C. Wethank Jon L. Dunn,Shawneen E.Firmegan, Steve N. G.Howell, William Shackelford.1997. Texas Region. Field Notes 51:1020-1023. P Llsowsky,Brandon K. Percival,Peter Pyle, J. V. RemsenJr., and Sartor O. Lewis,J. C., K. L. Sallee,and R. T. Golightly.1999. Introduction and WilliamsIII forkindly supplying information about distribution, identifi- rangeexpansion of nonnativeRed Foxes (VulDes vulDes) in canon,and ageing.George E Barrowcloughand ChristineBlake kindly California.American Midland Naturalist142:•72-381. allowedPatten to examinespecimens at theAmerican Museum of Natural McAlpine,D. E, J.Finne, S. Makepeace, S. Gilliland, and M. Phinney. I-hstory,funded in part from a grantfrom that institution 1988. First nestingof the GlossyIbis, Plegadisfalcinellus, in LITERATURE CITED Canada. Canadian Field-Naturalist 102:536-537. AmericanOrnithologists' Union (A.O.U.).1983. Check-list of North McCaskie, G. 2000. 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