THE AUK:

A QUARTERLY JOURNAL OF

ORNITHOLOGY.

VOL. XLIrIII. OCTOBER,1931. No. 4.

THE LIFE HISTORY OF'RIEFFER'S (AMAZILIA TZACATL TZACATL) IN PANAMA AND HONDURAS. •

BY ALEXANDER F. SKUTCH.

ß (PlatesVIII-X.) UPONhis arrival almost anywherein the lowlandsof Central America,the f•rst Hummingbirdwhich the travellerwith an inter- est in ornithologyis likely to encounteris a medium-sizedspecies with brilliant, metallicgreen body and head, a bright chestnut- browntail and a long,slender, slightly curved, black bill, known to the scientificworld as Amaxiliat•acatl t•acatl (De la Llave), to Americansby the book name Rieffer'sHummingbird, and to the nativesby no nameof specificdistinction at all. It is a of wide distribution,and from below the equator in Ecuador it rangesnorthward throughtwenty-eight degrees of latitude and, crossingthe Tropic of Cancer,is found in the lower Rio Grande Valleyin Mexico? A singleindividual was once captured alive on the northernside of the river near Brownsville,Texas, but appar- ently its presencein United Statesterritory is rare or accidentals From the hot, humid lowlandsof the Caribbean coast of Central Americaand Colombiato the coolplateaus of Bogot• and Guate- mala City, this adaptablecreature fmds itself at home. It seems everywhereto prefer open country to the dark, sunlesslowland forests. At every point I have visited in the humid Caribbean lowlandsof Central America, in Panama, Honduras and Guate-

Studlea of the life histories of tropical American , No. 2. Ridgway, Birds of North and Middle America, ¾. p. 408, 1911. Bendll•, Life Hlstoriea of North American Birds, p. 22S. 1895. 481 THE AUK, VOL. XLVIII. VIII.

RIEFFER'SHUMMINGBIRD (Amaz/•/a tzaca• •) INCUBATINGIN A BOUGAINVILLEA BUSH. ALMIRANTE,P•'•.•A, M•RC• 6, 1929. 482 SKUTCH,LifeHistory ofRieffer's Hummingbird. [oct.Auk mala, I have foundit the chiefand mostabundant Hummingbird in the clearingsabout the habitationsof men, and in the banana plantations. In fact, it is the only speciesof Hummingbirdwhich in these regionsseems really a characteristicinhabitant of the lawns, gardens,orchards and ornamentalplantings about the settlements.Other kinds, which dwell in the forestsor the scrubby secondgrowth, may frequentlyventure into such clearings,at times in large numbers,as when somefavorite tree happensto be in blossom,but their visits are usually transitory,and I have not yet foundone nesting there. On the otherhand, ! have never en- counteredAmazilia within the confinesof the heavylowland forests. Accustomedas we are to birds which frequentindifferently the orchardsand gardens,as well as our lighter and more restricted woodlands,it is difficultfor onewho has not visitedthe tropicsto conceivehow strong a barrierto the wanderingsof residentbirds is formedby the edgeof the forest. There are dozensof forestdwell- ing ,especially among the smallerbirds, which one may never seea hundredfeet insidethe clearings,while the majorityof those whichprefer the latter habitat, and amongthem Amazilia,show an equal aversionto the depths of the forest. On Barro Colorado Island in Gatun Lake, Rieffer'sHummingbird has made itself at homein the narrowclearing which surrounds the laboratorybuild- ings,separated by a broadexpanse of openwater from the clearings on the oppositemainland, but apparentlyrarely penetratesthe forestwhich presses in closelyon all hands. About the habitationsof men, wherethese seem most at home, they spendtheir time probingfor insectsor nectar in the greatred blossomsof Hibiscussinensis, which is everywhere a favoriteshrub for hedges,dooryards and the town plaza, or else in the blue trumpetsof the Thunbergiawhich scrambles over fences and up the sidesof houses;or they hover beforethe coralvine, the blue flowers of Clitoria, or the blossomsof some fruit tree. At othertimes they enterthe bananagroves and poise beside the long, pendentinflorescences, where they probethe whiteblossoms cluster- ed beneaththeir heavyred bracts,swarming with the little, black, stinglessbees which gather their pollen and rich nectar. In the early morningone may seethem bathing on the dewy surfaceof the broadbanana leaves, over which they glidewith vibrant wings, Vol. 1981XLVIII] JSx•rrc•, Life History ofRieffer's Hummingbird. 488 gatheringup the heavydew drops in their plumage. They are no moresociable than other kindsof Hummingbirds,and dart fiercely at anotherof the sameor a differentspecies if he venturestoo near, but the bird attackedalmost invariably retreats at the first dashing onslaught,closely followed by the pursuer,and I have neverwit- nessedtwo birdsengaged in an encounterface to face. Their nestingperiod, as Mr. CherrieI remarks,probably covers everymonth of the year. In onepart or anotherof the Caribbean lowlandsI have foundnests with eggsin everymonth except July, Octoberand November,and my recordsinclude nestings in both the wet and dry seasons.Near A!mi•ante,in westernPanama, I 'encounteredmy first nest of this speciesjust as the bird was be- ginningto constructit on December'19, 1928, the height of the rainyseason in Bocasdel Toro province. Thence,until my depar- ture in earlyJune of the followingyear, I found17 nests,all but one in the immediatevicinity of the houseI at that time occupied. The majority of thesewere encounteredduring the drierweather, whichbegan in Januaryand continueduntil May. My friendMr. J. H. Permanreports finding a nesthere in July, 1930. On the groundsof the LancetiliaExperiment Station near Tela, Honduras, althoughthe specieswas quite abundant, I did not discoverso many nestsas at Altairante. During a sevenmonths' residence here, I found or was shownsix nests,one (whichwas nevercom- pleted)in April,one each in May andJune, two in Augustand one in September. On Barro ColoradoIsland in the Canal Zone I founda nestin whichthe first eggwas laid January11, 1931. Al- thoughthe nestingperiod, for the speciesas a whole,is unusually long,even for tropicalbirds, and is peculiarin includingboth the dry andrainy seasons,I do not knowhow many broods each female may raise,or what periodthe breedingactivities of a singleindi- vidualmay cover. We are facedwith the sameproblem in regard to other specieswhich breed at two widelyseparated periods or throughthe greaterpart of the year, the GroundDoves of the Columbigallina,for example. Several possibilitiesare thlnlrable--thesame individual may breedat intervalsthroughout the year,or shemay havetwo widelyseparated nesting periods, l G. K. Oherrle. A preliminary list of the birds of San Jose, Costa Rica. Auk, Vol. IX, pp. 822-$29. 1892. 484 SKUTCH,Life History of Rieffer's Hummingbird. [Oc•.Auk or eachindividual may have a particularseason in which it nests year after year,while another nests periodically in an entirelydiffer- ent season--butfor no singlespecies, so far as I am aware,has the problem been definitely settled. The nestsof ,4maziliaare usuallyplaced in treesor bushesin the clearingswhere the birds reside,without any distinct preference for any particulartype. Frequentlya thorny lime or orangetree is chosen,or a Bougainvilleavine, but as often a thornlesskind is selectedfor the nestingsite. Sometimeseven a low herbaceous plant is favored. I have found their elevationto vary fron 2 to 20 feet from the ground. The opencup is constructedin a variety of situations,but almostinvariably on someslender support. If some variety of citrus tree has beenchosen, it may rest in the anglebe- tweenan uprightbranch and one of its largethorns (Plate IX, rigA), attachedto both by cobweb,or in anotherkind of plant it may be placedin the axil of a slenderleaf-stalk, or in the anglebetween a thin horizontal branch and a vertical stem. Sometimes a leaf alone sufficesfor its foundation. One of the most attractively situated I everfound was attached near the droopingtip of a largefrond of the thornypeijabaye palm (Guilielmautilis), anotherwas fastened to the palmarelycompound leaf of the Brazilian rubber tree, a third straddledthe slenderrhachis of the pinnatelycompound leaf of an akce(Blighia sapida), supported on eitherside by the opposite leaflets. At timesthe bird selectsa very inadequatefoundation. I oncefound a nest attachedto a frail and decayingtwig which in its descentfrom somewherehigher in the tree had caught on a horizontalbranch and hung looselybeneath it, drapedabout with the frondsof a slender,creeping species of polypodyfern which coveredthe boughand droppedin festoonsbelow it. The one re- quircmcntof a nesting site is a horizontalsupport sufficiently slenderto be graspedby the bird'sfeet--for from sucha perchthe buildingoperations are alwaysbegun--close to somevertical or ob- liquesupport to whichthe sideof the nestmay be anchored. Fre- quentlythe nestis situatedabove or closebeside a path alongwhich peopleare constantlypassing. The nestis an opencup, formed exteriorly of weatheredstrips of grass,leaves, bits of weed,fibres and the like, and abundantlylined with soft, felted plant down,the wholebound together by cobweb VOl,19alXL'V'I•[•] J SKUTCH, .•fd•Yi•stor• ofRi•'8 Hummingbird. 485 liberallysupplied. The outer surfaceis tastefullydecorated with gray lichensand green mosses,which sometimesare allowed to hangin long,waving festoons beneath it. Rarely, as in the nestI foundon BarroColorado Island, this ornamentation is very sparing- ly applied,so that the prevailingcolor of the exterioris grayishor tawny, from the fibresand down employedin its construction. Sometimesan otherwisebeautiful nest is marredby a longpiece of a witheredgrass leaf, usedin buildingthe foundation,carelessly allowedto hang beneathit. The eggs,which are invariablytwo, are laid on alternatedays and are pure white, oblongor oblong- ovate in shape.• The mossand lichencovered nests blend so well with the green foliageamong which they are usuallyplaced that it wouldbe ex- tremelydifficult W find them, especiallywhen the white eggsare hi•den by the emeraldbird,/f the femalesat more closely. The locationsof severalnests, which otherwise I shouldprobably never havefound, were betrayed by the birds'darting off as I passedwith- in a few yardsof them. The instinctwhich leads the birdsto build a nest which blendsso well with its settinglacks fulfillment in a correspondinginst/nct to utilize this advantageby remaining motionless.Perhaps at the approachof reallyformidable enemies other than man the femaledoes remain motionless on her nest,but when most small creatures,lizards or birds even many times her sizeventure too near, shemerely darts at them and'usually puts thempromptly to flight. Individualbirds, however, differ greatly in the closenesswith whichthey covertheir eggsand yoang. One female, the closestsitter of all I found, whosenest was built in a young'lime tree in a nurserywhere men were frequentlyat work, wouldallow me.to approachwi•h;u arm's lengthbefore deserting, to returnwi•h• a fewminutes and settle down on her eggsdirectly beforeme/f I waited quietly at this distance.

H I couldscarcely have desireda nest locatedmore conveniently for studythan the first of this speciesI everfound. I wasat the • Dimensions of a typical nest: External diameter 1 • inches, external height 1 ]g inches; internal diameter 1 k/inches, internal depth • inch. Eggs (a clutches measured): average 0.55 X0.•4 inches, largest 0.56 X0.34 and 0.55 X0.36, m33ailest 0.•3 X O.•Yi. 486 SKUTCH,LifeHistory ofRieffer' sHummingbird. [oct.Auk time engagedchiefly in work with the microscopein a little frame buildingwhich servedas officeand laboratoryat the now aban- donedexperimental station of the UnitedFruit Companybeside the great ChanguinolaLagoon, twenty milesfrom Almirante,Panama. On the afternoonof December19, I raisedmy headfrom my work and noticeda Hummingbird,of a kind still unknownto me,perched on the petioleof a ramie plant (Boehmerianivea) just outsidethe window,scarcely three yards from whereI sat,and separatedfrom me only by a screen. An oddnessin her mannerof perchingat- traeted my attention, and looking more intently, I perceived somethinglight colored almost hidden beneath her. When she flew off, I went out to examineher perch and found there a little tuft of plant down,fastened in the anglebetween the hairy petiole and the stem with cobweb,a pieceof white thread, and several hairs from the cattle which grazed all about the small enclosure. During the succeedingdays, as I sat at my work-tableporing over bits of bananatissue, Amaxilia labored steadily at her growingnest. The rite of adding a new bit of material followedan invariable routine. Returning with a tuft of down in her slenderbill, she wouldalight softly on the incipientnest, push in the stuffwhere it was needed,and then proceedwith the shapingof the structure. Shebent down her head, and moving around and around, with her longbill shapedthe substanceto the contourof her body. As she pressedthe yielding down more closelyto her breast,she erected the bronze-greenfeathers of her crown,and her foldedwings vi- bratedas thoughshe thrilled in anticipationof the completednest andthe nestlingsit wasintended to cradle. Thenshe sat facing in a setdirection, and from the wayher body bounced up anddown, I concludedshe must be kneadingthe material togetherwith her toes,although, being hidden beneath her, i wasunable to seethem in action. Sometimesshe would dart away and then, as though the kneadingand shapinghad not beendone to her satisfaction, returnwith empty bill to continuethe moulding operation s. So, asthe nestgrew, it becamejust largeenough to fit snuglyabout the centralportion of her body,leaving neck and head,rump and tail, protruding beyond its rim. Hummingbirdsof this speciesdo not seemto haveany prescribed order for the addition of the various elements of which the nest is 1Fol.1931 XI•lrIII1 j SK•rrcH,Life History ofRieffer's Hummingbird. 487

composed.This particularbird beganwith a wad of down,then boundaround it stripsof fibrousvegetable material, such as grass bladessoftened by partialdecay, and fastened them there with cob- web. Othersbegin with stripsof grassand bananaleaf epidermis, addingthe downlater whenthey canget it. It seemsto bemerely a matter of convenience,or'luck in findingthe propermaterials. I oncefound a nestbuilt entirelyof fine grassand piecesof weeds, but so devoidof lining that the eggstouched the branchon which it rested. This wasdoubtless because down for the liningwas not available,and under favorable conditions the downylining is added simultaneouslywith the fibrousmaterials which impart rigidity to the structure. Although the lichensand mossesappear to be merelyan ornamentof the nest,and do not constitutean essential part of the structure,they are often addedbefore the foundation portionsof the walls are completed. Aswith otherspecies of Hummingbirds,the femalecarried on all of her household duties without assistance from her mate. The two sexesare not distinguishablewith certaintyon the wing,but I neversaw a singleinstance where two birdstook an interestin the nestor its contents--unlessindeed one was trying to rob it, as we shalldescribe later. By the twenty-second,the bird had made a goodstart, but duringthe ensuing four days the rain fell in torrents, soakingthe unfinishedstructure, and duringthis periodthe builder made few visits to her work, and accomplishedlittle. On the twenty-sixth,drier daysreturning, she resumed her work with re- newedardor until, twelve days after its commencement,the nest had beencompleted, and the first white eggwas entrustedto it. Sheincubated the singleegg sporadically during the followingday but the next was not depositeduntil the secondday after. The solitarymother brooded faithfully (Plate IX, fig. 2), and after.six- teendays (the usualperiod) both eggshatched. The newly emergednestlings were like ugly grubs,blind, black- shinned,and nakedexcept for two linesof short,tawny down ex- tendingthe lengthof the back,one on eitherside of the middleline. The slenderbill of the adult was representedby a mere bump, hardlylonger than that of a newlyhatched Pauraque (Nyctidromus albicollis). At intervalsone of the gracelesscreatures reared up spasmodically,opening wide its yellow-linedmouth in a voiceless 488 SKUTCH,Life History of Rieffer's Hummingbird. [oc1•.Auk call for nourishment,to sink again exhausted,with droopinghead, into the nest. The mother's time for the first week was divided betweenbrooding and feedingher offspring,which she did in the customarymanner of the family, by regurgitation. Sitting upright on the rim of the nest,she thrust the rapier-likebill into the nearest gapingmouth, pushing it downuntil it seemedthat it must pierce the entrailsof the nestling. Then with a convulsivejerking of the bodyshe regurgitated a portionof the contentsof her cropinto that of herinfant. Bothnestlings were as a rulefed at eachreturn to the nest, and often eachwas given food twice, alternately. When the nestlingsare older, sometimeseach is fed four times at a single visit of their mother. After feeding,she usually returned to brood- ing, repeatedlythrusting out her long, white tongueas she sat on the nest. Thoughduring the day sheflew off, twitteringher com- plaint at my too near approach,at night shewould permit me to advanceand touchher on the nest,in the beamof a flashlight. With theseconstantministrations theyoungstem grew amazingly, and at the ageof six days,when the beadyblack eyes first began to peep out of the still-nakedhead, and the bill had lengthened considerably,they quitefilled the bottomof their downycup. The next day the eyeswere fully open,and the tawny tips of the feathers beganto protrudefrom their sheaths. When the nestlingsreach this stageof their development,the motherceases to coverthem at night, but withdrawsto perch at a distance. Before retiring on that seventhnight of their lives,I wentout to lookat the nestlings, and to my disgustfound their dead bodiesswarming with small brown ants, the fierce, stingingkind called "Fire Ants" by the natives, which filed up and down the stem of the ramie plant, swarmed over the nest and fed on their flesh. I have little doubt that the ants attackedthe nestlingswhile they still lived, for I had seenthem receivefood early that afternoon,and on anotheroc- casionwitnessed still smallerants attack living nestlingsof Passer- ird's Tanager (Ramphocoeluspasserinii). The swarmsof ants continuedto flow over the nestlingsuntil their flesh was entirely consumed,and noughtbut a little heap of tiny bonesremained in the nest. Five daysafter this massacreof innocents,I wasbent overmy microscopewhen I hcard.awhirr of wingsclose by, andlooking up,

Vol. 1931XI•llIII1 j 8KUTCH,Lgf½ History of Rieffer's Hummingbird. 489 noticeda Rieffer'sHummingbird pulling fibresfrom a soft hemp cordwhich I had left hangingfrom .one of the slatsof the shutter of my workwindow. Poisedon vibrantwing, she pulled backward and away from the house,while her brilliantgreen throat gleamed in theafternoon sunlight, and her tail sent forth intermittent flashes of chestnutas shespread and closedit in controllingher flight. Then shedarted away with the fibresin her bill, but soonreturned and,poising before the desertednest in the ramie,pulled out a bill- ful of down. I followedher flight aroundto the smallcashew tree whichstands close beside the porchon the otherside of the building. In a crotchnear the top of this tree a new nest had beenbegun. The bird workedrapidly, tearing away large billfulls of downfrom the old nest and incorporatingit into the new. Shealso hovered beneaththe raftersof the porchroof, seekingstrands of cobwebas bindingfor her nest,and paid repeatedvisits to the cordfor fibres. The nestwas completed and the first egglaid after a week'swork. The secondegg followedtwo daYs later, but for someunknown reasonthe bird failedto incubate,and for a weekthe eggslay cold in the nest. Then it was attackedby a differentRieffer's Hum- mingbird,which pulled it to pieces,for the sakeof the downit con- rained, to usein the constructionof her own nest nearby. I feel confident that the bird which built this nest in the cashew was not the individualwhose nestlings had beendevoured by the ants,for shewas occupiedwith a secondnest in the sametree at the time the other wasincubating her secondclutch of eggsin the ramie. Six weekspassed after the death of the nestlings,and all that remainedof the nest in the ramle was its basalportion, a shallow cup of grassand fibreswith hardly any lining, darkenedand dis- coloredby the weather. Then on March 4 I found a singleegg restingon the hard, impactedbase, but freshbits of grasshad been added to the walls aroundit, increasingtheir height, and new lichensdecorated the exterior. Even after the secondegg had been laid, on the followingday, the bird continuedto build up and line the old nest, until it appearedas solid and comfortableas when new. I suspect,from Hummingbirds'known attachment to their nestingsites, that it was the originalbuilder returned to attempt once more to raise a brood in her old nest. For the first few daysafter the eggshatched, everything about [Auk 490 SKUTCH,Life History of Rieffer'sHummingbird. [oct. the nest proceedednormally, but even beforethe nestlingsopened their eyesto the light of day, the first of a longseries of tribulations visited them. The leaf on which the nest rested had in time died and becomedetached, but the nest,bound to the leaningstem with fibresand cobweb,merely pivotedaround to the lower side,where it hung at an angleprecarious to its tenderoccupants. I straight- enedit out and fastenedit in placewith pins. Other leavesabove the nestfell a few dayslater, and the nakednestlings were exposed to the full glareof the afternoonsun. They sat with necksstretch- ed upward,mouths widely gaping,and glassy,staring eyes. Once I saw the motherperch on the rim of the nest with wingspartly spread,attempting to shieldthem fromthe sun'srays, but her posi- tion was not well calculatedand her shadowunfortunately fell to one sideof them, and they continuedpanting. Later she covered them on the nest, but one nestling,pushing its head out between her wing and body, continuedto gasp. Fearing they might suc- cumb, I attempted to arrangea shade,but I had not yet learned the toughnessof youngHummingbirds. When the first-bornnestling was a weekold, its body beganto bristlewith the pin-feathersand the eyesopened. By the follow- ing day the tipsof the feathersbegan to protrudefrom their sheaths, and that night for the first time the motherpassed the night apart from her offspring. The young birds had now becomea trifle crowdedin the nest, and the next day I noticed that the structure had begunto split downwardfrom the rim. A few hours later I lookedup frommy workjust in time to witnessa mostlively scene. The wholeside of the nesthad givenaway, dropping one of the nest- lingsto the ground,while the secondwas slipping down, but strug- gling desperatelyto crawl back onto what remainedof its ruined home. Clingingby its feet, it attemptedto supportand raiseitself by hookingits shortbill overthe remnantof the structure. The excitedmother hovered above it, a pieceof down held in her bill, as thoughattempting to saveat leasta trifle from the generaldebacle. I watcheduntil the squirmingnestling hung by a singlefoot, then hastenedout to securethe danglingbird and pick the other unin- juredfrom the ground,while the motherretired to the electricwire overheadand continuedher distressedtwittering. From a circular pieceof brownpaper I fashioneda shallow cone, which I tiedto the Vol. 1931XLVIII] j Sxnwc'•,Life History ofRieffer's Hummingbird. 491 stemof the ramieas near the positionof the fallen nest as practicable, and lined it with raw cotton. Then I placedthe squirmingnest- lingsin their artificial cradlewhich, after a little hesitation,was acceptedby their mother,who soon returned to feedthem. I soonreceived a strikingdemonstration of the accuracyand persistencyof a bird's senseof location. Returning to feed her youngsters,from force of habitthe mother poised first in the position of the oldnest, now completely fallen, then after a momentdropped to the artificial structure a few inches lower down. Even after visitingthe nestlingsseveral times in theirnew abode, she continued to hoverfirst before the oldposition, neglecting for themoment the actual nest in plain sight. I marvelledat the vitality of the youngHummingbirds. Expo- sureto the sun,a four-footfall, repeatedhandling by fingersmany times larger than themselves,had not killed them. Now a •till moresevere ordeal awaited them--twenty-four hours of rain with hardlya let up, and somebeating tropical downpours in the inter- val. The mother had definitely ceasedto cover them, and the scantfoliage of the ramiewhich remained above the nestafforded slightprotection. After a nightof this severepunishment, I watch- ed themthrough much of the drearyday. Whenthe heavydown- pourscame, and the big dropsbeat ceaselessly upon them, the two- week-oldbirds sat in the improvisednest with eyesclosed and bills pointingstraight to heaven,shaking their heads fr(•m side to side whenstruck by a particularlylarge drop. Their buddingplumage gave little comfort,and the cool rain soakedthem to the skin. Amaziliaattended them faithfully the wholeday. At intervalsbe- tweenthe heavy showersshe came, her black bill dustedwith the white pollenof the bananaflowers in whichshe had beenprobing, perchedon the rim of the papercup, and fed her wet offspring. Often one or the other or sometimesboth of the nestlingsrefused to acceptnourishment, when she gently touched its bill onceor twicewith hersas thoughto coaxit to take food,but oftenit was too wet and miserableto be tempted. At eachvisit sheran over the plumageof the nestlings,or a part of the nest,with her tongue, an act I never witnessedin dry weather,and from the way her throat worked,I concludedshe was sucking up someof the excess water. And with theseunfailing maternal ministrations, the un- 492 SKu'rcu,Life History of Rieffer's Hummingbird. [oct.Auk fledgedbirds pulled throughthe ordeal. Then I beganto under- stand somethingof the secret of the wide distribution and great abundanceof the species. Their nestinghabits appear very im- perfect,for the nest seemsto sacrificeutility to beauty, and in a region where a large proportionof the birds build some sort of coverednest to protectits occupantsfrom burningsun and beating rain, theirsis opento the sky, and moreoveris too small to aeeom- modate the two nestlingsuntil they are ready to leave it. Their successas a speciesresides rather in the inherenttoughness of fibre of the nestlings,coupled with the indefatigableattentions of the devoted mother. Before leaving the nest, the fledglingsacquired the plumageof the adults, althoughthe colorswere not so bright, and tufts of brown down still adheredto the tips of the greenfeathers, giving them a rather roughappearance. Two daysbefore their departure from the nest, when I attemptedto touch them they would ruffle up their feathersand attack a fingerwith their bills, which were still considerablyshorter than the adult's. The first bird flew off as I was examining the nest, at an age of 21 days. The folded wingsspread and beganto whiff, in a momentit roseinto the air and, uttering a low twitter as it went, flew away until it was lost from sight amongthe bananas. The maidenflight showedpower and control. The secondbird left two days later, aged 22 days. The mother continuedto feed them by regurgitationfor a number of days after their departure,but I am unable to state just how long. The nestlingperiod of thesebirds was perhapsa few dayslonger than normal becauseof the untoward circumstancesattending it. In the easeof anothernest I watchedin Panama,the nestlingstook flight at the agesof 19 and 20 days, respectively. From a nest near Tela, Honduras,the nestlingsdeparted at agesof 18 and 19 days, respectively,while from a secondnest both departedat the age of 19 days.

III Amazilla sitslightly on her nest,and a greaterportion of her body protrudesabove it than is the easewith mostother birds (see Plate VIII and Plate IX, Fig. 2). This is the outcomeof the closeness ¾ol. 1931XL¾III] j SKwrcH,Life History of Risffer's Hummingbird. 493 with whichshe moulds it to the centralportion of her body,and then oftencontinues to add downto the interiorafter the eggshave beenlaid, furtherdecreasing the sizeof the cavity. The nestling, at the timeof its departure,is almost•s largeas the adult,and naturallythe two are very muchcrowded in the smallnest (Plate X, Fig. 2). Beforethey depart,the wall is alwaysmore or lessflared outwardby the pressureof their bodies,while oneor the other is forcedto an uncomfortableposition on the rim. Especiallywhen the nestis softenedby waterduring rainy periods,it is sometimes literallyburst asunder by the pressureof the growingbodies it con- tains. In onecase which came under my observation,the nestsplit downthe side,then turnedalmost inside out and droppedits two helplessoccupants on the ground. I found them next morning, after a showerynight, in the grassbeneath the ruinedstructure, amongwandering fire ants whichprobably would eventually have devouredthem had I not replacedthem on the remainsof their nest, where they sat a week more beforethey were able to fly away (PlateX, l•ig. 1). Two or threeof the attemptsto build a nestwhich I witnessed seemedto be the work of youngor inexperiencedbirds, and were soonabandoned by the builders. On the riverwoodtree growing besidethe old lagoonbehind our houseI founda nest whichhad been started on a slender,unbranehed horizontal twig. Since therewas at that pointno leaf or otherlateral projection to prevent its slippingsideways, it grewinto a lopsidedaffair and the position wasabandoned as untenable. At anothertime I sawa bird try to attachmaterial in the angleformed where the endof a leafhappened to toucha neighboringbranch. The leaf slippeddown and split the little wad, andthe bird madea newattempt to build,equally futile, not far off. Doubtless these were the first ill-considered attempts of youngbirds to build. A surprisingaspect of the Hummingbirds'behavior, as I watched them near Altairanteduring th.e early part of the year 1929,was the persistencywith whichthey pilferedmaterial from eachother's nests. Amongbirds which nest in colonies,from primitive species like cormorantsand heronsto highlyspecialized orop•ndolas, the removalof materialfrom neighbors'nests, either by stealthor by force,is a commonand well knownmisdeed, but amongspedes 494 SKUTCH,Life History of Rieffer's Hummingbird. [Oct.Auk whosenests are solitary,and there is probablyno bird lesssocial than the Hummingbird,the pilferingof nestmaterial, sofax as my readingand personalobservation go, rarely occurs,and is never sufficientlyprevalent to interfereseriously with the successof re- production. Around our houseat the researchstation, however, larceny of this kind was shockinglyprevalent, and I believethat about half of the failures to rear a brood are to be attributed to this aberration of instinct. The conditionwas probably local and possiblyeven seasonal. It wasinduced to a largeextent, I think, by the inadequatesupply of downfor lining the nests,added to the closeproximity in which the nestswere placed,sometimes 100 feet or lessfrom eachother, which made robbery easier than a long expeditionafield to gatherdown. To this may be addedthe bird's passionfor bringingmore down to a nest which containsits full complementof eggs,and is alreadyquite adequatelylined. The balsatrees growing along the banksof the lagoonwhich ran in front of thehouse might have furnished excellent material, but the near- est of thesewas several hundred yards distant, and the long,pris- matic podsdid not beginto ripen and shedtheir massesof silky, resilientdown, in which the seedsare embedded,until the peak of the nestingseason had passed. Becauseof the shortageof down, eggswere sometimes laid in nestsconstructed entirely of piecesof grassand weed, ornamentedwith a few bits of mossand lichen, but devoidof any lining, which was added later as opportunity arose. The presenceof eggsin a nest did not renderit sacredto other Hummingbirds. I have alreadymentioned the destructionof a nestwhich contained two eggs,but theseeggs had beenabandoned a weekbefore another bird beganto pull out the downfor her own nest. A little more than a month later a secondnest was begunon a lowerbranch of the samesmall cashew tree. Becauseof repeated depredationsby anotherHummingbird, this nest progressedvery slowly;by the time the first eggwas lald, there was only a very precariousbed to receiveit, and it restedin contactwith the limb. The ownercontinued to build up the nest aroundthe egg,but the vandalismof the other bird (or possiblythere were several)con- tinued,until the egg,deprived of all support,fell to the groundand broke. Vol. 1931][LVIII] j S•rcH,Life History ofRieffer's Hummingbird. 495

The bird whichI finallycaught in the act of helpingherself to the ingredientsof this nest had herself a remarkablehistory, and was the worst suffererfrom the practiceof pilferingwith which I becameacquainted. Her ownnest, or rather the beginningof it, was situatedin a crotchnear the top of a gnarledand spreading cashewtree which stoodin a cornerof the lawn, about 50 yards distant from the last. The behaviorof the bird, which I watched closely,seemed to indicatethat shewas young or inexperiencedin the art of nestbuilding. I first noticeda smalltuft of fluffymate- rlal in the cashewtree onthe morningof February26, and later in the day witnessedthe bird addingto it. The followingmorning all but a few shreds of the accumulation had vanished. On the next morning,again, I sawthe bird carryingmaterial to the same crotch,but by noonthere was little to showfor her efforts. I re- solvedto spendthe afternoonin an attemptto clearup the mystery. Early duringmy vigil, the bird sat for half an hour on her mere rudimentof a nest,and a little later a freshlybroken egg lay on the groundbeneath the tree. Its fall escapedmy notice. The bird had beenso impededin her buildingthat when the momentfor the de- positionof the eggarrived she had no adequatenest to receiveit, and it fell to wasteon the ground. Thereafter,throughout the afternoon,she made frequent .t•ps to andfrom the nest,each time bringingfresh materials which were addedaccording to the usual routine. Having shapedthe nestwith bill and feet, shewould fly to a twignot far off,pause there a fewmoments and then,apparent- ly not satisfiedwith her work, return and repeat the wholeproce- dare. Onceshe went through this performancefour times in quick succession,without the additionof any new material. Frequently, too, shewould hover beside the nest,remove some loose particle in her bill, then, alightingon the nest, return it oncemore to the structure. Oncea bit of downfell away and as it wafted down- ward shedarted from the nest,quick as thought,caught it deftly in her bill, and returnedit to a placein the pile. At intervalsshe hovered before the blossoms of the hibiscus bush which stands nearby,or probedthe little cashewflowers with the tip of her long bill, then restedfor a while on oneof its limbs. On the whole,she workedfaithfully, but by four o'clockthe resultof her toilswas a looseand untidy aggregationof fibres,bits of deadgrassand down, [Auk 496 S•:UTCH,Life Historyof Rieffer'sHummingbird. •Oct. not yet worthy of the name of nest. Whatever had been taking advantageof her effortsfailed to appearthis particularafternoon, and asthe sunwas sinking low I wentoff, disappointed. I returned at sunsetonly to find that the marauderI had so desiredto sur- prisehad beenbusy in my absence. The crotchwas almost bare and the bird, her maternal instincts again frustrated, perched stoically on a nearby twig. For the next two weeks she continued her fruitless efforts to build. Doubtless she would have acted more wisely to have shifted the site of her endeavorsto some distant tree or bush, but she showedthe strongattachment to a locality characteristicof her kind. During the interval shemoved the site of the intended nest to a crotchfarther from the centerof the sametree, then back to the old location,then onceagain to the new, but all to no ad- vantage,and she seemedforedoomed to failure. Later shebegan her nestamong the branchesof an avocadotree which grew closebeside the cashew,but the changeof location broughtwith it no changeof fortune,and oncemore she moved back to her originalsite in the cashew. Here, onecloudy morning toward the end of March, I witnessedthe most cunningact of thieveryI have ever seena bird perform. Time and time againI have watchedMontezuma Orop•ndolas (Gymnostinops montezuma) snatchlong bananafibres from eachothers' nests, and even bills, but there was a straightforwardnessin their mannerwhich be- tokenedan absenceof guile. The presentinstance was different. The Hummingbirdhad just addeda billful of material to her in- eipientnest--it never advancedbeyond this stage--and darted off to pluck a lichenfrom the bark of a neighboringavocado tree. A strangeRieffer's Hummingbird flew up at this junctureand evident- ly observingthe builderof the nest, which was in plainsight, perched on a twiglow in the cashewtree. Here shesat soquietly that when the other returned she failed to notice the intrusion,--else she would without doubt have assertedher lordshipover her domain-- but calmly attachedthe lichen to the nest. No soonerhad the unsuspectingbird flownoff whenthe thief eoolyadvanced from her retreat and, hoveringbefore the massof down,pulled out a sizable billful and darted out of sight. When the ownerof the nest re- turned, she continuedher futile building as though nothing had gone amiss. 'THE AUK, VoL. XLVIII. I:'LXTEX.

UPPER. RIEFFER'I• HUMMINGBIRDS,13 DAYI•OIA), RESTINGON THEIR HS? (SHOW II•l PLITE I) •,•"rEa rrs coi•LtP•. MAaCH 25, 1929. LOWER. RI•.•ER'8 HU•M•'•GBIRDS, 16 DaYSOr,O, m THEIRNEST IN 14.F•"l13 •'elig'iosa. TE•.x, HoI•oUaAs, SE•'rE•BER 8, 1930. ¾ol. 1981XL¾IIIl j SKUTCH,LdfeHistory ofRieffer's Hummingbird. 497

On anotheroccasion a Tody Flycatcher(Todirostrum cinereum finitimum),the samewhose nesting I describedin an earlierpaper, ! madean inroadon•hls Hummlngbird'saccumulation of down. The Flycatcherhappened upon it duringthe courseof an exploration of the bark of the cashewtree for any cobwebwhich may have lurked in its crevices,to use in constructinghis own nest not far distant, and when he cameacross this rich mine of suitablematerial did not hesitateto make the best of his find, returningtwice to carry away more material. Thus a tuft of white milkweedsilk, which I had seenthe Hummingbirdcarry off from the nest of another,eventually found its way into the Tody Flycatcher'spend- ent nest..Since the material of the Flycatcher'sfirst nest was employedin the constructionof a secondafter the nestlingsin the formermet with disaster,and the second,found unsatisfactory, was torn apart to furnishsubstance for a third, it is interestingto speculateof how many differentnests this tuft of milkweedsilk may have formed a part. Forat least31 .days, according to my notebook, this long-suff.er- ing Hummingbirdcontinued her attempts to establisha nest. I first madeher acquaintanceon February26, her last attemptwas observedon March 29. I have recordsof twelvefresh beginnings of her nest,each of whichwas more or lesscompletely obliterated, andI havelittle doubtthat shesuffered many more reverses which I failed to observe,since her efforts to build were more or lesscon- tinuous,and I madeno attempt to chronicleall of her varied for- tunes. She sltemated betweenfour differentbuilding sites, two in the cashewtree and two in the avocadowhich grew beside it, 'andmade at leasteight changes of locationbetween these four positions,probably at leastseveral more whichI failed to record. As time went on, her behaviordisclosed increasing bewilderment anddistress. Oftenwith emptybill shewould return to the barren crotchwhere she had been building,and with feet and bill go throughall the motionsof shapinginvisible materials to her body. Sheseemed to suffera stronghallucination of the presenceof the stuffshe had previouslyadded. Sometimes,after addingmaterial in theusual manner, she began to fly off,but immediatelyreturned to sit on it, then flew off and returned, for half a dozen times in

Auk, VOL XLVII, pp. 313-322. 1930. 498 SK•C•,Life History ofRieffer's Hummingbird. [Oct.Auk succession,seemingly afraid to leave her nest unguarded. One morningshe seemed undecided as to which of two sitesin the avo- cadotree to entrusther efforts,for shewent throughall the motions of buildingin one,then flew to the otherside of the treeand repeated the procedurein the other empty site, then back oncemore to the former. After severalsuch alternations she at length settledon one, and continuedto build there for the remainderof the day. Her effortsat a nest becameincreasingly lax, and her successive attempts were mere formlessmasses of the usual constituents. Likewiseher instinct to defendher territory becamebenumbed, and she permitted Anis and other birds to rest on her premises. Finally, toward the end of March, her feverishefforts to perform her biologicalduty ceased,and no nest ever gracedthe gnarled limbs of the cashew tree. The attachmentof the Hummingbirdto a particularnesting site is not usuallyquite so strong as that of the poorbird whosefortunes we have just followed. Usually, so far as my observationgoes, the bird selectsas its own a rather restricted area, and if the first nest is destroyed,builds again not in the identicalsite, but in a similar site a short distanceoff. The new nest may be begunless than a week after the destruction of the old. About half of the failuresto rear offspringwhich cameunder my noticeat Almirante were, I believe,to be attributed to the thievish propensitiesof the birdsthemselves. At the heightof the nesting seasonin Februaryand March, birdswould begin to build,perhaps getas far aslaying one or botheggs, and then the nest mysteriously disappear. Althoughin mostof thesecases I did not happento be presentwhen the nestwas brokenup, it is hardly likely that an egg-eatinganimal would have carried off or devouredthe nest,and in severalinstances, one of whichI havealready mentioned, the eggs were found beneath the ruined nest in a condition which indicated that no attempt had beenmade to consumethem. A summaryof the fate of the 17 distinctnests (not countingof coursethe many attemptsof thebird which tried so long to buildin thecashew tree) which I observedat the researchstation near Almirante,gives an idea of the tremendous difficulties under which the birds labored here. The much smallernumber of nestingswhich came to my noticeat Lancetilia,Honduras, were attendedby much greater success. Vol. XL¾IIII 499

A•mirante Lancetilia Total numberof nestsbegun ...... 17 5 Number of nests in which one or both eggs were laid ...... 13 Total numberof eggslaid ...... 24 Number of nestsin whichboth e•s hatched.. Number of nestsin whichone egg hatched .... 1 Total numberof nestlingsborn ...... 11 Number of nestsin whichyoung were raised... 3 Numberof nestlingsraised ...... 6 Surprisinglysmallas it is,the'number ofnestlings wMch lived to leave the nest at Almi•ante would have been smaller still had it not beenfor my timely intervention,to which four of the six nest- lingswhich survived owe their lives,--the two for wMchI madeth• artificial nest, and the pair wMch were pickedup from the ground after their nest's collapse. Had I been the detachedobserver merely,the Hummingbirdpopulation at the researchhouse would havebeen augmented by but two fromall the seventeennests wMch I found. Sincetwo eggsare invariablylaid in eachnest if every- thinggoes well, the total possiblenumber of fledglingswas 34. In reality, evenif everybird had beensuccessful in raisingtwo birds in each nest, the actual increasein populationwould have been smallerthan this,for many nestswere made only because previous oneshad beendestroyed, and had successattended every nesting, there would have been a smaller number of nests. Mr. Woods • in Ms study of Costa'sHummingbird (Calypte costae) in California, foundthat only 19 youngwere fledged out of 29 nestscontaining eggs,or a possible58 birds. TMs is a much better recordthan that of the Altairantebirds, but not nearly so goodas that of the muchsmaller number at the LancetiliaExperiment Station. Like myself,Mr. Woodssaved an unstatednumber of nestlingsby fast- eningup their nests,and here alsosuccess of reproductionwould have been still smaller without human intervention. But I doubt whetherit is possible,in studiesof ,M• kind,to forma justestimate of the actualsuccess of reproductionof the speciesin any region. Thosenests which are the firstto be foundby the studentare prob- ably just the onesmost likely to be encounteredby the birds'

• Robert S. Woods. The H•mmtngbirds of California. Alik, VoL XLIV, 297-818. 1927. 500 SKUTCH,Life Hi•tory of Rieffer's Hummingbird. [Oct.Attk enemies,and hencegive an exaggeratedidea of the dangerswhich beset the nest. Those nests so well concealedthat they escape observationwould probably, had we any way of knowing their outcome,make a better showing. A comparisonof the results of Mr. Wood's study of Costa's Hummingbirdwith mine of Rieffer'sHummingbird indicates that the lengthsof the important periodsin the history of the nest are essentiallythe same in the tropical and temperatezone species. The normal incubationperiod for both is 16 days. The young Costa's Hummingbird remains in the nest from 20 to 23 days, Rieffer'sHummingbird from 18 to 23 days. Costa's Humming- bird, too, has the habit of laying its eggsbefore the nest has been completed,and someof the nestsbecome broken down at the sides and flattenedout beforethe youngare ready to leavethem. 3509 Clark's Lane, Baltimore,Maryland.