Seasonal Flock Sizes of Naturalized Mitred Parakeets (Aratinga Mitrata

SEASONAL FLOCK OF NATURAt MITPF- PARA!F. F3'S (ARATINGA MITTA) LONG BCH, CHARLES T. COLLINS and LISA M. KARES, Departmentof BiologicalSciences, CaliforniaState University,Long Beach,California 90840 Flocksof naturalizedparrots and parakeetsare todaya commonsight in much of suburbansouthern California (Garrett 1986, Johnstonand Garrett 1994). Hardy(1973) reportedsix species to be commonlyencountered, and today that list includesat least 10 species(Garrett 1997, Johnstonand Garrett 1994). One of the well-establishedand common speciesis the Mitred Parakeet or Conure, Aratinga reitrata (Garrett 1997, pers. obs.). There is littledetailed information available on thisspecies, even in its native range in the subtropicalzone eastof the Andesfrom centralPeru southto northwesternArgentina (Forshaw 1989). We presenthere informationon the seasonalvariation in flocksize of MitredParakeets in Long Beachfrom 1988 to 1995; their food habits are consideredelsewhere (Garrett et al. 1997). METHODS Our studyarea was largelywithin a 4-mile radiusof CaliforniaState University,Long Beach(CSULB), in eastLong Beach,Los Angeles Co., and includedthe campusand partsof the Los Altosand BelmontShore sections of the city. Mitred Parakeetshave been presentin this area sincebefore 1980 (pers.obs.). Early accounts were of a smallgroup of perhapsonly four to eightindividuals, and the populationstayed at thislevel for severalyears, untila flockof 15 wassighted at CSULB in December1987 (pers.obs.). Our more detailedobservatons were made from 2 January 1988 until 16 December1995 with a few additionalobservations being made in Novem- ber 1996. Observationswere madelargely on an opportunisticbasis, with data recordedon flocksize, time of day, directionof flightor, if perched,the type of tree the flockwas utilizing and if the tree was alsoa foodsource. A total of 422 separateencounters were recordedon field data sheetsand transferredto MicrosoftExcel spreadsheets for analysis. RESULTS The maximumMitred Parakeetflock size per year rangedfrom a low of 25 individualsin 1988 to a highof 42 in 1994 (Figure1). Flocksof 40 to 50 individuals were observed at CSULB on two occasions in November and December 1996 (Collinspers. obs.),but the parakeetswere movingback and forth betweenseveral Eucalyptus trees, and exactflock sizes could not be determined.The largestflocks were consistentlyobserved in mid-winter, when all of the parakeetsappeared to be travelingin a singleflock. The annualmean flocksize was substantiallylower (Figure1), rangingfrom 9.6 individuals in 1993 to 20.7 in 1991. These lower values reflect the fact that 218 WesternBirds 28:218-222, 1997 FLOCK SIZES OF NATURALIZED MITRED PARAKEETS IN CALIFORNIA 45- 40 35- 30 25 - :20- 10 _ _ 1988 1989 1990 1991 1992 1993 1994 1995 Figure1. Annualmaximum flock size (dark bars) and annual mean flock size (solid line) of Mitred Parakeetsin Long Beach, California, 1988-1995. smallflocks my be encounteredat all timesof the year and that there is a pronouncedseasonal change in flock size.Flocks reached their largestsize from Novemberto February(Figure 2). By March and April smallerand smallergroups of parakeetswere observed.This trendcontinued until mid- summer,July and August,when therewere regularsightings of groupsof fewer than five individuals(Figure 2). In thesecases it seemedto be one or two pairs looselyaccompanied by singleindividuals that may have repre- sentedfledged young. By earlyfall, the parakeetsappeared to aggregateinto everlarger groups, reaching peak sizes for the year in mid-winter(Figure 2). DISCUSSION The resultsof this studyshow that there has been a dramaticincrease in the populationof MitredParakeets in the eastLong Beach area over the past 15+ years. Since these observationsare of unmarked birds it was not possibleto determineactual rates of recruitmentor dispersal.Although no nestshave been observed, it seemslogical to assumethat most,if not all, of the observedincreases are due to reproductionand recruitmentof young into the flock.Unique rasping calls heard from somemembers of the flock duringlate fall may have been from fledgedyoung, as noted in Amazona flocksby Mabb (1997a, b). Collinsobserved a copulatingpair of these parakeetsCSULB in March 1990. The near stabilityof the flock at a maximumof approximately35 birdsfor fiveyears (Figure 1) suggestedthat somedispersal was occurring.Reports by other observersof Mitred Para- 219 FLOCK SIZES OF NATURALIZED MITRED PARAKEETS IN CALIFORNIA 25 • uJ 20 o z 10 • 5 o JAN MAR MAY JUL SEPT NOV Figure2. Monthly mean flock size of Mitred Parakeetsin Long Beach, California, 1988-1995. keet groupsin areasnot far from our studyarea, e.g., LakewoodMall, but outsidethe expecteddaily foragingrange of our studygroup, tendedto support this idea. Details are lacking, however, and dispersalfrom natal areas and the formation of new flocksremains a topic for future study. Mitred Parakeet flockshave also been reported from such nearby (> 10 milesaway) areas as Norwalk,Garden Grove,. Cerritos and San Pedro (Garrett 1997, pers. comm.). A seasonalchange in daytimeflock size, like that documentedhere, has alsobeen notedfor Arnazona parrotsin the San GabrielValley (Froke 1981, Mabb 1997a). These changeshave been attributedto reproduction(Froke 1981, Mabb 1997b); largenocturnal roosts are maintainedthroughout the year (MabbI997a). In nativeenvironments parrots often form multispecies flocks(Forshaw 1989, Chapmanet al. 1989). Largecommunal roosts may serve as information centers (Ward and Zahavi 1973). The information- centerhypothesis suggests that birdscongregate in largergroups to facilitate the exchangeof informationbetween group members,particularly when food resourcesare low or clumpedand when suchinformation would be most valuable.In Costa Rica, parrot flocks,away from large communal roosts, were smaller than expected during the time of food limitation (Chapman et al. I989). These authorsthought that rapid depletion of smallerclumped resources tended to counterthe advantagesof largerflocks and resultedin the smallerflocks they observed(Chapman et al. 1989). Someof the foodseaten by MitredConures in the Long Beacharea, suchas Eucalyptus,although patchily distributed, are quiteabundant and not easily depleted.This wouldtend to promotethe largerflock sizes we observed.It 220 FLOCK SIZES OF NATURALIZED MITRED PARAKEETS IN CALIFORNIA wouldbe worthwhile,however, to determineif the largerflocks are maintainedthroughout the day,particularly when they feed on lessabundant and potentiallydepletable food sources. A majorityof the observationsreported in this studywere made on the CSULB campuswhere the parakeetsmade extensiveuse of the several speciesof Eucalyptustrees plantedas ornamentals.They made particular useof E. sideroxylonvar. rosea, which provided a flowerand nectar source during the winter months. Observationswere also made at a favorite roostingplace in a groupof approximately20 palms(Trithrinax sp.) near the junctionof OceanBlvd. and LivingstonBlvd. in the BelmontShore area. Karesobserved the parakeetsleaving this roost between 06:00 and 06:30 shortlyafter sunrise;they were frequentlyobserved feeding on Eucalyptus flowers and nectar at CSULB within about an hour of this time. Beyondthis, the dailymovements of theseparakeets were not followed and clearlywould be worth furtherstudy. The impressionwe got from our observationswas that theydid not stayat any one foraginglocation for long, usuallyless than 30 minutes,before moving on to other spotsup to a mile or more away. Their movementswere highlyvariable from year to year, presumablyrelating to localizedfood abundances.For example,the parakeetswere frequenfiyobserved on the upper campusof CSULB duringthe wintersof 1989-90 and 1990-91 when ornamentalfig trees(Ficus nitida retusa)were fruiting.The parakeetshave rarely utilizedthese same trees sincethen, probablybecause of low fruitproduction resulting from extensive pruning.Similarly, large flocksof these parakeetswere observedin the CSULB Eucalyptustrees in the latefall of 1996 butrarely during the restof the winterof 1996-1997. Again, thiswas presumablydue to a shiftin the availabilityof localizedfood sourcesand changesin the parakeets'daily foragingpatterns to utilizethem. Nearlyall of the foodsources of theseMitred Parakeets were exotictrees plantedin the area, mostlyas ornamentals(Garrett et al. 1997). Accord- ingly, not much foragingcompetition between these parakeetsand native birdspecies would be expected.Froke (1981) similarlyfelt that interspecific competitionwas not a significantfactor in his nearbystudy area. The few interspecificinteractions we observedwere mostlybetween the parakeets and American Crows, Corvus brachyrhynchos,another speciesrapidly increasingin the southernCalifornia urban environment (pers. obs.). In each casethe crowwas the aggressor,often chasing parakeets from tree to tree. The spreadof naturalizedparrots and parakeetsin southernCalifornia is viewedwith some apprehension,as some specieshave the potentialto be seriousagricultural pests. Studies of thesefree-ranging birds are stillin their infancyand muchmore remains to be learnedabout the dynamicsof these increasingpopulations. Note addedin proof: A flock of ca. 40 Mitred Parakeetswas seenin the studyarea on 28 September1997. LITERATURE CITED Chapman,C. A., Chapman,L. J., and Lefebvre,L. I989. Variabilityin parrot flock size: Possible functions of communal roosts. Condor 9I:842-847. 221 FLOCK SIZES OF NATURALIZED MITRED PARAKEETS IN CALIFORNIA Forshaw,J. M. 1989. Parrotsof the World, 3rd

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