Status of the Feral Budgerigar in Florida

J. Field Ornithol., 55(2):214-219

STATUS OF THE FERAL BUDGERIGAR IN FLORIDA

By ANNE SHAPIRO WENNER AND DAVID H. HIRTH

Although the exotic statusof the dominant urban birds in North America, the Rock Dove (Columbalivia), House Sparrow(Passer domes- ticus),and Starling (Sturnusvulgaris), is well known, we tend to be com- placentabout the establishmentof other exotic avian species.This at- titude may stemfrom the fact that these3 specieshave becomeso well established that we have ceased to view them as exotic. Recent reviews of the statusof exoticbirds in North America(Bull 1973, Hardy 1973, Owre 1973) indicatethat presentthreats of establishmentof new exotic speciesare greatestin southernareas and from membersof the parrot family. The mild, and even sub-tropicalclimates in southernCalifornia and Floridaand the highlyman-altered habitats in theseareas provide an ideal settingfor feral birds to becomeestablished as breedingpop- ulations. The most widespreadpsittacine in Florida is the Budgerigar(Melo- psittacusundulatus) which is nativeto the xeric interior of Australia.Our interest in the distributionand breeding biology of this specieswas promptedby the discoverythat feral populationsof this bird wintered as far north as Gainesvillein northern Floridaand that they nestedin naturalcavities in deadpines. Budgerigars apparently were not confined to southernFlorida; they were reproducingin the wild; and they rep- resentedat leasta potentialthreat to nativecavity-nesting species. This studydescribes the breedingrange of feral Budgerigarsin Florida,habitats they occupy,and their potential for range expansionand compe- tition with native birds.

METHODS Rangeand origin.--In November 1977, we sent questionnairesin- quiring about the local statusof Budgerigarsto 130 membersof The Wildlife Society,Florida Audubon Society,and to Florida Game and FreshWater FishCommission offices throughout the state.In addition, a requestfor information on Budgerigarsightings was printed in the FloridaOrnithological Society newsletter. Our intent wasto poll knowl- edgeableindividuals throughout the stateand not to samplea statisti- cally valid group of Floridians.Responses to thesequestionnaires and the newsletterwere used to assesscurrent range, breeding locations, and relative abundanceof Budgerigarsin Florida. Some reports were field-checkedby the authors. Habitatand population censusing.--The New Port Richey-Holidayarea on the Gulf coastjust north of Tampa was chosenfor intensivefield work on habitat use. These communitieshave large breedingpopula- tions of Budgerigarsand were convenientto reach from Gainesville. Both residentialand rural habitatswere surveyed,but it soonbecame 214 Vol.55, I•o. 2 Budgerigarsin Florida [2 15 apparent that Budgerigarsoccurred only in residentialareas and that they made heavyuse of bird feedersand nest boxes.Thereafter, we concentratedour surveyson different typesof residentialhabitat. Seven housingdevelopments were selectedfor censuswork. These representedthe following4 habitattypes: Habitat A, sparsevegetation, many bird feedersand nest boxes;Habitat B, sparsevegetation, few feedersand nestboxes; Habitat C, densevegetation, many feeders and nestboxes; and Habitat D, densevegetation, few feedersand nestboxes. In order to comparedensities of Budgerigarsseasonally and in different habitat types, transects(covered by car) were establishedin each development. Each transectwas 20 m wide (one houselot deep on each sideof the street)and includedroughly 25% of eachdevelopment. Censuseswere conducted weekly from May throughthe first weekin December 1978. Each censusbegan 15 min after sunriseand lasted approximately30 min. Starting and ending points were reversedeach week to reduce temporalbias. Densitiesof Budgerigarswithin habitats were comparedusing the non-parametricKruskal-Wallis test; pairwise comparisonsof time periodswere made usingthe Dunn method (Hol- lander and Wolfe 1973).

RESULTS AND DISCUSSION Rangeand originof ferat Budgerigarsin Florida.--We received57 responsesto the questionnairesand the newsletterrequest, representing 46% of Florida's67 countiesand almostall of the countiesin peninsular Florida. The responsesindicated that Budgerigarswere breeding in coloniesof 100+ individualson the Gulf coastroughly from Hudson to Ft. Myers.Transient flockswere reported asfar north asSpring Hill, and southto SanibelIsland and Naples.On the Atlantic coast,breeding populationsoccurred near Ft. Pierce,Port St. Lucie, and Ft. Lauderdale, and transient flocks were common from Miami and West Palm Beach to north of Ft. Pierce (Fig. 1). Flocks of 30+ birds had been seen sporadicallyin Gainesville(L. Williamspers. comm.). Sightings of 1-3 birdswere reportedfor the Panhandle,areas north of Gainesville,and the Jacksonvillevicinity. Budgerigars were apparentlyabsent from the interior of the state,except for reports of smallcolonies in Winter Park (breedingstatus unknown), and they apparentlydid not occur in the Keys.Densest concentrations of breedingBudgerigars appeared to be in New Port Richey,Clearwater, St. Petersburg,Largo, Seminole,Sar- asota,Bradenton, Venice, Englewood,and Port St. Lucie. BecauseBudgerigars are easilydomesticated, possess many color vari- ations,and can be taught to talk, they have becomethe mostpopular cagedbird world-wide.Budgerigars breed prolificallyin captivity,and the pet trade in the United Stateshas been suppliedlargely by birds reared domestically.Florida is a favoredarea for commercialparakeet breedingin outdoorenclosures because of its mild climate.In addition, birdsare bred asa hobbyby manyFloridians. Intentional or accidental releasesof between I and 3000 Budgerigarsfrom these sourceswere 216] A. S. Wennerand D. H. Hirth J.Field Ornithol. Spring 1984

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FIGURE1. Breedingrange of Budgerigarsin Florida, 1978. mentionedin the responsesreceived. Another reservoirof releasedbirds has been the multitude of outdoor tourist attractions in the state, such asthe EdisonEstate in Fort Myers,where flockswere permitted to come and go at will from large aviariesabout 25 yearsago. Populationdensities and habitatselection.--Densities of Budgerigars (birds/ha) on our studyarea were calculatedat 2-month intervalsfor all 7 transectsin the 4 habitat types(Table 1). In thoseresidential areas with manybird feedersand nestboxes (Habitats A and C), numbersof Budgerigarsincreased steadily from May to Octoberprobably because of continualrecruitment of fledglingsinto the population.Greatest den- sitiesoccurred in November-December in residentialareas with sparse vegetationand many feedersand nest boxes(Habitat A). This peak coincidedwith cessationof breeding for most Budgerigarsand, thus, the additionof femalesinto the sampledpopulation (Shapiro 1979). During the breedingseason, nesting females spent 40-50 min/h inside nest boxes and were seldom counted. This peak alsooccurred at the sametime that Budgerigarsbecame muchmore gregarious, and flocksof severalthousand, often mixedwith Starlings,American Robins(Turdus migratorius), and Mourning Doves (Zenaidamacroura), began massing on utility wiresalong a major 4-lane Vol.55, No. 2 Budgerigarsin Florida [217

TABLE1. Densitiesof Budgerigars(birds/ha) at 2-month intervals(• + SD) on 7 transects in 4 habitattypes, 1978. Habitat types were as follows: A--sparse vegetation, many feeders and nestboxes; B--sparse vegetation,few feedersand nestboxes; C--dense vegetation, manyfeeders and nestboxes; D--dense vegetation,few feedersand nestboxes. Common superscriptswithin rowsindicate no significantdifference (P > .05) amongdensities.

Transects

Habi- Total tat area type No. (ha) May-June July-Aug. Sept.-Oct. Nov.-Dec. P A 3 52 0.94 + 0.48 • 1.49 + 0.21 •b 2.67 + 0.70 t• 5.51 + 2.26 c <.01 B 2 14 0.03 + 0.09 0.06 + 0.09 0.05 + 0.11 0.04 + 0.08 >.05 C 1 9 1.24 + 0.60 •b 1.21 + 0.44 •b 2.43 + 1.40 a 0.53 + 0.50 • <.01 D 1 38 0.06 + 0.14 0 0 -- >.05

highwayjust north of a Habitat A transect.Large post-breedingflocks during winter monthswere alsoreported by questionnairerespondents. These large groupsmay have been composedof local birds and/or transient birds from other areas. Whether some or all of these birds remained in New Port Richey or emigrated out of the area after De- cember is unknown. In Habitat C, fewer birds were counted on the averagein November-Decemberthan during any other time. We pre- sumethat thesebirds left this developmentand joined the flockson the wiresalong U.S. Route 19. Most parakeetswere in neighborhoodscontaining the highestden- sitiesof nestboxes and bird feeders.The absenceof residentBudger- igars in developmentsthat had few feeders and nest boxes (Habitats B and D) (Table 1) implied that nest boxes and bird feederswere prereq- uisitesfor the establishmentof breeding populationswithin suburban areas.Our datafurther suggestedthat althoughBudgerigars may prefer open habitats, they were not deterred from nesting in more densely vegetatedareas. Nestingwas frequently observed in streetlamps throughout the breeding seasonin Habitats A and C, which indicated that birds choseto remain in areaswith establishedbreeding populations,even when avail- ablenest boxes were occupied. Presumably, an amplefood supply existed to support these additional breeding pairs. In their native Australia, Budgerigarsare alsocavity nesters. They breed coloniallywhere not limited by suitablenest sites(Ward and Zahavi 1973) and as closeas possibleto one another even when cavitiesare vacant over a wide area (Immelman 1968). Roosts.--Roostingsites were locatedadjacent to a Habitat A transect and a Habitat C transect.The Habitat A roost was at the edge of the neighborhoodwithin a condominiumcomplex. Rows of condominiums werebisected by brackish-watercanals bordered by the largesttrees in the development.Other roost trees were locatedon undevelopedprop- 218] A. S. Wenher and D. H. Hirth J. Field Ornithol. Spring 1984 erties adjacentto the complex.An estimated6000-8000 Budgerigars roostedwithin approximately50 Eucalyptus,silk oak (Grevillearobusta), and live oak (Quercusvirginiana) trees along the canals,and frequented some 15 live oaks, longleaf pines (Pinuspalustris), and slashpines (P. elliottii)in the undevelopedarea. The sametrees were not usedevery night,but thisroost was used consistently from April throughDecember 1978. A visit to the roost in early fall 1980 revealedthat it was still occupied. The Budgerigarhas become well establishedas a permanentresident in many coastalFlorida communities.Its presentrange in the state is largelythe resultof multiple releasesand escapes,but a probablecon- tributing factor to its widespreaddistribution is the nomadictendency of thisspecies (Bartholomew and Cade 1963, Forshaw1969). The large post-breedingaggregations of Budgerigarsseen on our studyarea may havebeen part of this dispersalmechanism. However, the rate of range expansionin this speciesmay be retarded by a strongtendency to nest at highdensities and by abundantnest sites and food near original release sites. Responsesto our questionnaireindicated that Budgerigarscan survive the winter in northernFlorida, where they may experience 20-35 nights of frost a year. Their presencethis far north suggeststhat Budgerigars mayhave the physiologicalpotential for rangeexpansion across the Gulf coast to southern Texas and Mexico. Although we have observedBudgerigars nesting in natural tree cav- itiesand feedingon bahiagrassseeds (Paspalum spp.), these appeared to be rare events.The birdson our studyarea were heavilydependent on localresidents for food and nestboxes. The only competitionfor these resourceswas with House Sparrows.At this time, Budgerigarsdo not seem to be competingfor nest siteswith native cavity-nesters.Never- theless,in the same way that the nomadic tendenciesof this species shouldbe causefor concernabout its potential for range expansion,the presenceof an aggressivecavity-nesting exotic in such large numbers shouldbe causefor concernabout its potential as a competitorfor nest siteson native speciesin this area. The feral Budgerigar is already too well establishedas a breeding bird in coastalFlorida to make an eradicationprogram practicaleven if it wasdeemed desirable. If the Budgerigarremains a suburbanbird and heavily dependenton man, its presencewill continue to be innoc- uous.On the other hand, if its populationsoutstrip resources presently beingprovided, Budgerigars could revert to a lessman-dependent form of behavior and use natural sources of food and nest cavities. Should this happen,the Budgerigarcould become established widely across the southernedge of the United Statesand becomea seriouscompetitor with nativebirds. We stronglyrecommend that stateand federalwildlife agenciesclosely monitor the statusof this specieswith respectto breeding range and feeding habitat. Vol.55, No. 2 Budgerigarsin Florida [219

SUMMARY Respondentsto a 1977 questionnaireand newsletterrequest reported a Floridabreeding range for feral Budgerigarsfrom Hudsonto Ft. Myers and near Ft. Pierce, Port St. Lucie, and Ft. Lauderdale. Intentional and accidentalreleases from tourist attractionsand by amateur and com- mercial breedersaccount for the presenceof feral Budgerigarsin the state. Habitat and populationcensusing studies revealed that mostparakeets occurredwhere nest box and bird feeder densitieswere highestand that, although they may prefer open habitats,Budgerigars did nest in more denselyvegetated neighborhoods. GreatestBudgeriar densities were noted in the November-December censusinginterval, probably because post-breeding females and newly- fledgedyoung had joined the censusablepopulation.

ACKNOWLEDGMENTS We acknowledgethe financial support of the Florida Agricultural ExperimentStation in this project, and we thank Drs. J. W. Hardy, L. D. Harris, R. F. Labisky,and W. R. Marion for their helpfulcomments andsuggestions. This is Contribdtion 5354 of theJournal Series, Florida Agricultural Experiment Station, Gainesville.

LITERATURE CITED

BARTHOLOMEW,G. A., ANDT.J. CADE. 1963. The water economyof land birds. Auk 80: 504-539. BULL,J. 1973. Exoticbirds in the New York City area. WilsonBull. 85:501-505. FORSHAW,J. N. 1969. Parrotsof the world. Doubledayand Co., Inc., New York. HARDY,J. W. 1973. Feral exotic birds in southernCalifornia. Wilson Bull. 85:506-512. HOLLANDER,M., ANDD. A. WOLFE.1973. Nonparametricstatistical methods. J. Wiley & Sons, New York. IMMELMAN,K. 1968. Australianparakeets. 2nd. ed., rev. A. Ziemsen,Wittenberg. OWRE, O. T. 1973. Exotic avifauna of southeast Florida. Wilson Bull. 85:491-500. SHAPmO,A. E. 1979. Status,habitat utilization, and breedingbiology of the feral budgerigar(Melopsittacus undulatus) in Florida. M.S. thesis,Univ. of Florida, Gainesville. WARD,P., ANDA. ZAHAVI. 1973. The importanceof certain assemblagesof birds as "information-centres"for food-finding.Ibis 115:517-534. Schoolof Forest Resources and Conservation,University of Florida, Gainesville, Florida 32611. (Present addresses:(ASW)--Florida Game& FreshWater Fish Commission,4005 S. Main St., Gainesville,Florida 32601; (DHH).-- Schoolof Natural Resources,University of Vermont,Burlington, Vermont 05405). Received8 Feb. 1983; accepted30 Jan. 1984.