CALIFORNIA

BIRDS

Volume 3, Number 1, 1972

DO FLOCK IN HAWAII, A LAND WITHOUT PREDATORS?

Edwin O. Willis

Birdsof a feathersometimes flock together,as anyoneknows who has ever seen blackbirdsor sandpipersin fall. More surprisingly,in many parts of the world birdsof different feathersflock together.H. W. Bates (1863), in his classic"Naturalist on the River Amazons," reportshow the empty forest seemedto come alivewith dozensof kinds of birds whenever one of the diverse Amazonian "mixed flocks" passedby. Lessspectacular but similarmixed flocksof Plain Titmice, Hutton's Vireos, and other birds can be seenin California oak woodland. Those who watch for mixed flocks will be surprised how common they are, from migrant warblers among Common Bushtitsin chaparralto CactusWrens among Black-throated Sparrows on the desert. Some mixed flocks gather for obviousreasons, such as the gulls one seesat garbagedumps or the flocksof birds that follow army ants for flushed insectsin tropical America. The birds in most complex flocks,however, seem to congregateand follow each other without obvious reasons.Probably no biologist can say what a warbler gainsby followingBushtits about, althoughmany biologists nowadaysare studying mixed flocks. Reasonssuggested for mixed flocks mostly fall in two categories.Perhaps the birds lead eachother to food, or avoid competingfor food, by watchingeach other. Perhapsthe birdsavoid predation by associatingwith eachother. One I studied in , the small Spotted ( naevioides),definitely spent lesstime callingor fleeing nervouslywhen it associatedwith birds of other species(Willis, in press).This gaveit the opportunityto stareat the groundto forage. Calif. Birds 3:1-8, 1972 1 FLOCKING OF BIRDS IN HAWAII

Presumably,if there were no predatorsthere would be no reasonfor such birds as Spotted to join other species;they could forageas they pleasedwithout keepingnear other alert birds.Mixed flocks bound togetherby warinesswould be absent;flocks would be associatedwith feedingopportunities only. Birds in an area without predatorscould form a natural ex- periment.If flocks like thoseof the Vireo and the Titmouseexisted in such an area, it would be likely that thesemixed flocks do form for food reasonsalone. Birds and other organismsin placeswithout predatorslose their defensivemechanisms rapidly. Island birds are notablyfearless, and plantson Hawaiiseldom have spines or poisons (Carlquist,1970). Warner(1968) found Hawaiianhoneycreepers do not sleep with their heads in their back feathers,and are therefore easy prey for introducedmosquitoes. The problemis, it is rare to find a placewithout predators.It is especiallydifficult to find sucha placewith many speciesof birds,so that one can get mixed flocks.The naturalexperiment, however, has been performedon certainoceanic archipelagos that have few or no predators.As Darwin found during the voyageof the Beagle,the isolatedarchipelago of the Galaparoshas many speciesof finchesbut hardly any native predators.However, there are many somewhat predatorylizards on the Galaparos. Evolutionon the HawaiianIslands has produceda groupof land birds as diverse as the Darwin's Finches, in a land almost without predators.There are open-countryHawaiian Hawks (Buteo solitarius} on the island of Hawaii and Short-earedOwls (Asio ]lammeus} on all islands, but no predatory native mammalsor reptiles. Unless the hawk and owl fed on insectsand nestlings,they may have come to Hawaii as new immigrantsafter the Polynesiansintroduced rats; they seldom eat adult birds. If there were mixed flocks of the diverse nativeHawaiian birds, they surelycould not be causedby predation except perhapson the islandof Hawaii itself. The Drepanididae,or Hawaiianhoneycreepers, are a fascinatingly diversegroup of birds. Havingevolved from one or two originalkinds of birds, so far back that nobody now knows whether they were tropical honeycreepersor Northern finches, the many types of drepanididsnow possessthe widest variety of types of bills in any bird family. There are smallwarblerlike ones with straightbills (the Anianiau, Loxops parva} or slightlyalecurved ones (the Amakihi, Loxops virens}, others with vireolike bills (the Creeper,Loxops maculata, of the forest undergrowth,and the Akepa, Loxops 2 FLOCKING OF BIRDS IN HAWAII coccinea,of the leafy tree crowns)and f'mallystrange rare creatures with downcurvedbills over 2 inches in length (the Akaialoa, Hemignathusprocerus]. One, the Akiapolaau[Hemignathus wilsoni], has a short, straightlower mandiblethat it usesto flake bark off trunks with woodpeckerlikehammering, while its long downcurved upper mandibleprobes for insectsin crevices.The related Nukupuu [Hemignathuslucidus] differs mainly in having the short lower mandibledowncurved. Related birds, mostly the size of large spar- rows, had thick finchlikebills or even parrofiike onesto crackseeds or tear opentwigs. Regrettably, most f'mchlike birds except the Palila [Psittirostrabailleui] are now rare or extinct. Another line, mostly extinct now with the exception of the common red Apapane[Himatione sanguinea]with its short, slightly decured bill and the fairly common red and black Iiwi [Festiaria coccihealwith its long downcurvedbill, adds to the diversityof the native Hawaiian avifauna. In addition, there are a little native flycatcher, the Elepaio {Chasiempsissandwichensis}, two native thrushes(including the Omao, Phaeornisobscura}, and numerous introducedbirds. The avifaunais certainlydiverse enough that mixed flockscould form, althoughthe nativebirds have suffered greatly and many are now rare or extinct. Introducedmosquitoes brought them introduced diseases(Warner, 1968), introducedants killed insects they fed on (Zimmerman,1970), and the original forestswere reducedto a quartertheir originalextent (Carlquist,1970). G. C. Munro, one of the collectorsat the rum of the century,saw the native Hawaiian birds duringtheir horrible decline.In 1944, he recorded his memoriesand field notes of half a century on the islands.On Kauai, he reports,the Creeperformed small flockswith Akepas.The constantchipping of the Creeperattracted other birds. To find certain rare species,such as the Nukupuu,he followedthe chippingof the Creeper. Since there were no native predatorson Kauai other than Short-earedOwls, Munro's report interestedme greatly. Richardsonand Bowles(1964:29) reportedAnianiau often foragetogether with Amakihi. It seemedthat there might indeedbe mixed flockson Hawaii in the absenceof predators. However,one must be cautiousof reportsof mixed flocks.Even birds that ignore each other occasionallycome in contact, and an observerwho comes up at that moment will think the birds are associating.Sometimes birds mobbingan observerwill attract other species.One needsto watch critically to see if birds actually follow each other. 3 FLOCKING OF BIRDS IN HAWAII

Thus, when my wife Yoshika and I went to Hawaii, I looked for mixed flocks. I quickly found that someof the other thingsI looked for, such as rare or reportedlyextinct birds, were very hard to find. As Berger(1970) reports,bird studyon Hawaiiis very difficult for a variety of reasons.Many of the nativebirds are so rare or restricted to undisturbedforests that a major expeditionis neededto hunt them down. I tried hiking in to somesuch places, such as a 10-mile mountainclimb to the upperKipahulu Valley on the eastside of the extinct volcano Haleakala on the island of Maui; but I found that I had only three or four hoursof birdingbefore I had to starthiking back. Naturally, I missedthe rare species. However,if one gets to relativelyundisturbed forests above 1000 meters elevation,he finds that the remainingnative birds of Hawaii are often remarkably common and far outnumber the introduced birds in someareas. On our first day on Hawaii,in the forestsof ohia trees and tree-fernsalong KilaueaCrater, it seemedthat every other treetop had its Apapaneor two, every fifth tree a tail-flickinglittle Amakihi. These are the two commonestsurviving honeycreepers, common on all the larger Hawaiian islandsfrom the last scrubby ohiasin the crater of Haleakaladown to the slopesabove Honolulu. 'From Kilauea, we went to cabinsat PohakuloaState Recreation Area in the dry saddlebetween the massivevolcanoes of MaunaKea and Mauna Loa. In the dry scrub and eucalyptus,House Finches, House Sparrowsand CaliforniaQuail outnumberednative birds. The pretty little Red-billedLeiothrix (Leiothrix lutea] were in flocksof up to 10 birds, and I watchedsmall groups of introducedWhite-eyes (Zosteropspalpebrosus] and a few Amakihi follow one suchflock. There were many White-eyesand Amakihis away from this mixed flock, however. From Pohakuloa,I drove up on the slopesof MaunaKea to what provedthe best birdingarea on the "Big Island"of Hawaii.This was the scrubby, low grassywoodland of mamane and naio trees at Andrew Berger'sstudy area above Puu Ulaau cabin. Here, Elepaio flitted from bushto bush,Amakihi were more commonthan Elepaio, crimsonApapane and Iiwi paradedfrom treetop to floweringtreetop, and Palila whistledfrom a few of the mamanetrees. The scoldingof a few Leiothrix, almost the only introduced birds besides the commonWhite-eyes and grass-dwellingSkylarks, brought in the most excitingbird--a bright yellow Akiapolaauwith its absurdlyshaped bill, to tap on branchesinside a mamanenear me and then to perch near me as I squeakedand drew in curious Amakihi from all 4 FLOCKING OF BIRDS IN HAWAII directions.One feds sad that this forest is graduallydying, mainly from overgrazingby fetal sheepand goatsthat are protectedfor Hawaiianhunters. There are still many nativebirds, but 'I still had not seen a mixed flock. The Iiwi and Apapaneconcentrated in floweringtrees, but that wasall. Akipuka,an islandof tall ohiaand other trees amid the lavaflows at Mile 22 from Hilo, wasanother exciting area near Pohakuloa. On a foggyaftemoon, it wasbursting with the strangesongs of Omaoand Iiwi. The weird chirpsof Apapanecame from the treetops,and Amakihi and Elepaioflitted lower.The birdsstill crisscrossedwithout formingmixed flocks,however. Even thoughthere is a hawk on the Big Island, we left with the impressionthat only introduced birds--ones whose ancestorsrecently fled hawks and other pre- dators--formed mixed flocks. On Maul, I hiked up over the tim of HaleakalaCrater from the few ohia trees at Paliku Cabin, then down throughgrassland on the north sideof the volcanobefore dropping down into the cloudforest of the ruggedupper KipahuluValley. Here I finally found Creepers, or rather familiesof them found and chippedbusily at me. There wereAmakihi, Apapane,and Iiwi all over the place, but no mixed flocks,in the clutteredtree-ferns and lichensand gnarledohia trees. On the way back down Kaupo Gap, I saw a few birdsbut no flocks in the dry scruband streamsidekoa forests. We birded little on Oahu, exceptfor introducedbirds in the lower Makiki Valley at Honolulu.We savedthree daysfor the highlandsof Kauai, a forestedplateau which everybodyagreed is the best place for native birds on the islands. At our cabins at Kokee State Park there were many introduced trees among the native koas, but native birds still outnumberedintroduced White-eyes, Hwa-Meis [Garrulax canorus), and Cardinals [Richmondena cardinalis). To the usual Elepaio,Amakihi, Apapaneand Iiwi the little yellowAnianiau added variety. There were plenty of birds, but no definite flocks. Yoshika saw one group in which Apapaneand Amakihi seemedto associate with Elepaio,however. To see other native birds we went up past the Kaumahina Lookouts,where the rain-drenchedforests of the Alakai Swampspill over into the huge'canyons and wrinkledcliffs of the westernwall of Kauai. On the rainy first day we found Akepa as well as the four commonerdrepanidids along the divide,and wereinterested that the Akepa seemedto be in family groups.The next day the weather clearedbeautifully, for one of the few dayseach year in which rainy FLOCKING OF BIRDS IN HAWAII

Mt. Waialeale,off acrossthe ohia woodlandsof the Alakai Swamp, could be seen all day. I hiked through the boggy meadowsand patchy woodlandsof the Swamp,adding Creepers to the five other honeycreepers.The Creepersdid chip a little, as Munro reported,but only at me. I beganto wonder if the other birds Munro had seen with themhad just cometo the chippingat him. The first two CreepersI sawwere in a bird flock with an Anianiau and two Amakihi plusan Elepaio,but the flock seemedto dissipate like clouds over Kaumahinaas I watched.The rest of the Creepers were paired,but were wanderingapart from other species.At no time did the fairly numerousAkepa of the canopyjoin them, and I wonderedhow they coulddo so when the Creepersseemed to stay so low and Akepa so high. Alas, I saw none of the rare Nukupuuand Akaialoathat Munrothought joined such flocks. At placeslike Volcano House,Puu Ulaau, Kipahulu,Kokee, and the Alakai we saw hundredsof Hawaiianhoneycreepers of eight species.The generalimpression we had is that they are abundant comparedto tropicalbirds in Panama,that they scatterall over the place, and that they wander singly, in pairs, or in small groups. Practically none were in definite mixed flocks, except in a few floweringtrees. The few mixed flocks we saw could almostbe explained by random movement or by temporary attraction to outsidethings like my squeaking.The honeycreepersmostly seemed to lack alarm calls,although the chippingof Creeperswas a deCmite antipredatornoise connected mainly with dangerto youngbirds. So, our preliminarystudy suggeststhat lack of predatorsleads to lack of alarm calls and to few or no mixed flocks on Hawaii; do mixed flockselsewhere form to watch out for predators?Before we can concludethis we need to look for other possibilities.My wife and I were only able to spendten days (14-23 September1971) lookingfor mixed flockson Hawaii. Perhapsthere are bird flocksat some other season,even though we went in a nonbreedingmonth, when mixed flocks are usually best in other parts of the world. Perhapswe did not get far enoughinto the foreststo see mixed flocksin which rare Nukupuuand Akaialoamight play a part. Even if mixed flocks are rare on Hawaii, it mightbe that they are rare for some reasonother than lack of predators.Island birds are typically few in numbersof speciesbut high in numbersof in- dividualscompared to mainland areas,and Hawaii is no exception. Island trees and insectsare similarlylow in numbersof speciesand high in numbersof individualscompared to mainlandtrees and 6 FLOCKiNG OF BIRDS IN HAWAII FLOCKING OF BIRDS IN HAWAII insects.The lack of similarly foragingbird specieson islandscould lead to lack of flocking.The high numbersof individualbirds and of food sourcesof a few typescould removeany necessityfor a bird to join others to searchfor rare food. Perhapswe shouldlook at other islands,ones with predators,to seeif there are mixed flocks on those islands. Moreover,the Hawaiianhoneycreepers are peculiarbirds, not very diversedespite their diversity.Many of them, both birdswith straight and long curved beaks, feed on nectar from the common ohia flowers.Most of them are treetopbirds, exceptthe Creepersand a few rare species.It might be that they come from nonflocking ancestors,or that their nectar and fruit-eatinghabits force them not to be sociable. This is not true of other fruit-eatingbirds, for Moynihan (1962) found fruit-eatinghoneycreepers do form mixed flocks in Panama;and I have repeatedlyseen such flocks in the Amazon. However, more study is needed, both on Hawaii and in other areas,to see if absenceof predation causesa lack of mixed flocks.

SUMMARY

Mixed flocksseemed rare amongnative land birds on Hawaii. The absence of native predators may have allowed birds to wander separately.

LITERATURE CITED

Bates, H. W. 1863. The naturalist on the fiver Amazons. Murray, London. Berger, A. J. 1970. The present status of the birds of Hawaii. Pacific Science 24: 29-42. Carlquist, S. 1970. Hawaii: A natural history. Natural History Press,Garden City, N.Y. Moynihan, M. 1962. The organization and probable evolution of some mixed species flocks of neotropical birds. Smithsonian Misc. Coilns., 143 (7): 1-140. Munro, G, C. 1944. Birds of Hawaii. Tongg PublishingCo., Honolulu. Richardson, F. and I. Bowles. 1964. A survey of the birds of Kauai, Hawaii. Bull. Bernice P. Bishop Museum 227. Warner, R. E. 1968. The role of introduced diseasesin the extinction of the endemic Hawaiian avifauna. Condor 70: 101-120. Willis, E. O. in press.The behaviorof Spotted Antbirds. A.O.U. Monographs. Zimmerman, E. C. 1970. Adaptive radiation in Hawaii with specialreference to insects.Biotropica 2: 32-38. Department of Biology, Pn'nceton University, Pn'nceton, N.J. 08540. 8