The Birds of Yap, Western Caroline Islands

HARVEY 1. FISHER 1

THE YAP GROUP of islands, which lies about450 miles southwest of Guam and 125 milesnortheast of the Palaus, is composed of fourmain islands: Rumung, Map, Gagil-Tomil,and Yap. There are several islets in the la­goon between Yap and Tamil islands.

The highest elevation (585 feet ) is in thenorth-central part of Yap Island (Fig. 1).Except for this hilly area, the rest of YapIsland is below 200 feet. All of Gagil-Tomilis below the 200-foot elevation, and the high­est parts of Map and Rumung are from 250to 300 feet above sea level. The greatestlength of the group is about 16 miles andthe greatest width is 6.5 miles.

Ulithi atoll is the nearest land mass, lyingabout 90 miles to the northeast. To the south­west are the Pala·us. Thus, Yap lies in a chainof islands from the Palaus in the south to

the Marianas in the north. Nove of the is­lands in the chain is widely separated fromthe others. Furthermore, to the east is thewhole group of Caroline Islands. Becausethese islands seem to form a perfect series of"stepping sto~es" for the movement of plantsand animals from the southwest Pacific tothe north Pacific through the Marianas andeastward through the Carolines to the centralPacific Ocean, it was deemed desirable tostudy birds of Yap , especially since the exten­sive work of the Whitney-South Seas Expe­ditions did not include Yap, and no moderncollections of birds from this area are known.

Preliminary investigation and collectionswere made on Yap from July 28 to August24, 1946. A total of 148 verrebrarespeci­mens were taken : 17 amphibians, 28 rep­tiles, 9 mammals, and 94 birds. No attempt

1 Department of Zoology, University of Illinois,Urbana. Manu script received April 28, 1949 .

was made to collect large series of any species; rather an attempt was made to securerepresentatives of all species present. Recordsof the reptiles and amphibians taken havebeen published ( Fisher, 1948).

The University of Hawaii sponsored thistrip. I wish 'to acknowledge the aid of theUnited States Navy in furnishing rransporra ­tion and other facilities. In particular, I wishto thank Captain O. M. Murphy, UnitedStates Navy Commander of the Yap Area,for use of various facilities at Yaptown andfor his interest in rhe project. I also want tothank Mr. EveniLevi of Tutuila, AmericanSamoa, who accompanied me from Hono­lulu; he helped greatly in many ways. Dr.Ernst Mayr has checked the identification ofall species discussed and has made criticaltaxonomic comments, many of which areincluded in the species accounts.

It is no longer possible for me to continuethese studies. Hence, it seems worth 'while toput on record the observations of this briefsurvey.

As indicated above, the islands are rela-o tively low. They are almost completely cov­ered with vegetation. Yap and Rumung showa similar zonation of vegetation . On theinner side ( toward the lagoon ) these islandshave extensive swampy areas, and mangrovesof two kinds form dense thickets at the~ater's edge. On the outer side the islandshave large areas of shallow water inside thecoral reef. For the most part, these have coraland rock substrata with little mud. At theupper ends of the tidal swamps on the lagoonside are semi-open mudflats. Above theseswamps or mudflats, or above the narrowbeach on the sea side, the dense jungle starts ,immediately ' and continues upward to an

[55 ]

56

elevation of about 200 to 250 feet on thesouthern end of Yap Island; on the northernend of Yap Island the hilly regions havedense stands of trees, but here and there areopen areas of grassland with scattered Pall- .danus trees. Most of the rolling region tothe south is this same type of savanna. Thecentral part of Rumung is much the same.

Perhaps because of their lower elevation,Map and Gagil-Tomil islands do not havethese open areas. The usual swamps andmangroves are present as a fringe about thecircumference, but tall trees cover most ofthe rest of the surface.

In the discussion of the species, the habitatswill be mentioned as mangroves, swamps,jungle, or savanna , referrin g to the varioussituations described above. An asterisk indi­cates that specimens were taken .

Puffinus pacificus, Wedge-tailed Shear­water.*-Five were observed flying over thesouth entrance to Tamil Harbor.

Puffinus l'herminieri, Dusky Shearwater.-Only one was seen, at the north end ofRumung Island.

Phaethon lepturus, White-tailed TropicBird.-Twos and singles were observed sev­eral times over Map Island.

Fregata ariel, Least Man-o'-War Bird.­Observed at close range at Yaptown (onebird ) and at Balabat (three ) , August 6 and13, respectively. Nine flew over Balabat 01:

August 15. N atives reported that the speciessometimes nested on Yap Island. The bird isclosely associated with native traditions ant!customs, such as ceremonial dances, in whichits feathers are used as ornaments. Identifica­tion was made of one roughed-out skin usedas a headdress.

Sterna fuscata, Sooty Tern.-On July 30.six birds were resting on the beach at thenorth end of Rumung Island.

Sterna lunata, Gray-backed Tern. *- Onecollected from a flock of nine Tbalasseusbergii off Orila, Map Island.

. ' .~ \.

PACIFIC SCIENCE, Vol. IV, January, 1950

Thalasseus bergii, Crested Tern. *-Nineindividuals were observed on tops of pilingsof an abandoned fish trap off Orila , MapIsland.

Gygis alba candida, Fairy Tern.*-Thisspecies was abundant on all the islands inthose places where there were tall trees somedistance apart. It was not seen in the deepjungle growth or in the savanna areas andwas most frequently observed in the tallbreadfruit, banyan, and coconut trees and intall , isolated mangrove trees in the swamps.I did not find it in low shrubs such as are usedby G.a. rothschildi in the western Hawaiianislands. · .

Also in contrast to rothschildi, candida wasvery noisy at night. This constant callingwas observed on three occasions, at 9:00,10:30 P.M., and 12: 15 A.M.

The fairy tern , like th~ man-e-war bird.is frequently used as an ornament of dress.Three natives had outlines of this tern tat­tooed on their shoulders.

Anous stolidus pileatus, Common Nod­dy.*-The noddy was found only on TarangIsland in Tamil Harbor. Here, an estimated250 were seen, usually in the tops of pan­danus, breadfruit, and chestnut trees. Oldnests were found in the top whorls of pan ·danus trees, 12 to 18 feet from the ground.No nests were observed in higher or lowersites. Egg shells were found on the ground,indicating that nesting had occurred not longbefore. Some nests were apparently underconstruction, for they contained in their wallsseaweed that was still green. Furthermore.two birds carrying strands of seaweed wereobserved flying into nests.

Pluvialis dominica fulva, Pacific GoldenPlover.*-In late July an occasional singleor pair was observed. By August 15, theywere quite numerous, 15 to 25 birds in 150yards of beach, along the beaches, tidal flats,and marshes, but they did not fly or feed inflocks. They were also abundant in openareas of savanna and around the Nif airfield.

, Birds of Yap-FISHER

N

NAUT ICA MIL ES

YAP GROUPrROM JAPANESE CHART NQ;ZI07

U.S. HYDROGRAPHIC orncc

57

4- 5 II /0

FIG . 1. Th e Yap Group of islands .

Charadrius mongolus, Mongolian Dot­terel. '*'-One was collected on the mud of asmall taro patch in the jungle ~ mile westof Balab at,

Numenius phaeopus variegatus, Whim­brei. '*'-Singles, pairs, and groups of threewere commonly found on mudflats wherethere was no vegetation. Three were observedfeeding on the grass-covered airstrip at Nif.No change in numbers was observed duringour .stay.

Numenius tahitiensis, Bristle-thighed Cur­lew.'*' - Only two singles were observed, bothon rocky beaches.

Tringa glareola, W ood Sandpiper. '*'-Onewas collected on a mudflat at Moloai , YapIsland, August 10. No others were seen.

Heteroscelus incanus brevipes, W ander­ing Tatler.'*' - As would be expected, severalindividuals were seen on rocky stretches ofbeach, but they were just as numerous Oil

small mudflats and around small patches of

58

~_; FIG. 2. Dense jung le grow th, 150 feet eleva­..' tion, Dugar, Yap Island. Habitat of Rhipidura,

M onarcha, and Myzomela.

taro in the dense jungle. One was observedin an open area of the savanna region.

Arenaria interpres, Tu rn sron e .v-c-Oneflock of five and one flock of two were ob­served on Yap Island, August 6 and 16,respectively.

Crocethia alba, Sanderling.'*'-Occasionalindividuals were found along the beaches.

Demigretta sacra, Reef Heron.-of 14individuals observed on beaches and mudflatsfrom July 28 to August 16, 11 were darkgray, one was light gray, and two were whitein color.

Nycticorax caledonicus, Rufous Nigh tHeron.-Two were in the edge of jungleadjoining the"Nif airfield.

Ixobryc hus sinensis, Chinese Least Bit­tern. '*' ----,-These bitterns were most numerousaround the water-filled bomb craters in theNif airfield; on one occasion, 49 were seenin 4 hours. However, individuals were pres­ent around permanent and temporary rain­filled depressions in all parts of the islands.Each taro patch, no matter how small , hadat least one bittern . They were abundant inthe mangroves, in places a bird every 100yards. Mayr (1945: 285) stated that thisspecies was mostly nocturnal. I found itusually active in the daytime-feeding, call­ing, and flying about from one pond to an­other . Its call was not heard at nigh t.

PACIFIC SCIENC E, Vol. IV, January, 1950

Anas (superciliosa ?).-The "dark, femalemallard with white line above its eye," ob­served by Levi and me probably was superciliosa. It was on the saltwater lagoon justoff Yaptown. Captain O. M. Murphy saidthat the birds were 'frequently seen aroundthe craters in the Nif airfield and that theywere present throughout the year, but I didnot find them there.

Gallus gallus, Domestic Chicken.-A fewsemi-domestic fowl were found in the jung lenear the native villages. I was told that be­fore the war such feral chickens nested in

. many different places. Dur ing th e na va J

blockade in the latter part of the war theJapanese military forces hunted down mostof them for use as food.

Po li ol im n a s cinereus collingwoodi,White-browed Rail.'*' - Mathews in 193q

described the subspecies, micro~esiaeJ a;cistated that Micronesian specimens were inter­mediate between collinguroodi from the Phil­ippines and specimens from Vulcan Island.Examination of 32 specimens of "micronesiae" and a series of collinguioodi failed tosubstantiate his remarks. Mayr (in litt. )stated, "To this subspecies (collingiooodi) belong also the specimens from Talaut Islarids,Palau, Guam, and Ruk. There are somecharacters peculiar to each locality but the dif­ferences betwe<:n populations of these islands

FIG. 3. Grassy swamp, 20 feet elevation, Rumu,Yap Island . Habitat of Poliolimnas cinereus,

.i

Birds of Yap- FIsHER

are not sufficiently constant and conspicuousto permit separation from collin gwoodi."

These rails were present in all suitable taropatches or marshy areas that were investi ­gated. Th ey were not found in saltwatermarshes but were present in marshes of brack­ish water less than 200 yards from the seaand only 2 to 5 feet above sea level. Allareas found to be occupied by this species hadthree things in commo n: mudflats, shallowwater (2 to 4 inches) , and clumps of heavymarsh grasses.

,Apparently the size of a taro patch haslittle to do with the number of rails present.I never found more than one pair in anyisolated marsh or taro patch , and I investi­gated 13 such places, ranging in size fromcircular areas 50 feet in diameter to swampscontaining 3 to 5 acres. A pair was collected

.from each of two smaller taro patches; duringthe following 3 weeks no rails were seenthere, although the areas were visited everyother day during that time. On two occasionsindividuals were flushed from dense grasssome 50 yards from swampy areas. On bothoccasions the birds flew strongly and swiftlyto cover in the swamp. I never saw thisspecies more than 5 feet from heavy, grassycover.

Two trips were made at night to areas inwhich rails fed in the daytime. In 4yz hoursof observation no birds were seen and nocalls were heard.

At Balabat, at 10:30 A. M ., on August 11,I saw an adult run across a small opening inthe middle of an abandoned taro patch over­grown with water grass. A few seconds lateranother adult followed; it wa s collected.When I retrieved the bird I found I had alsocollected a chick. At 2:30 P. M. on August 12in a similar area, I watched two adults and

, a bro()d of four chicks feeding in water 1 inchdeep. During the entire 40 minutes thisgroup was watched, both adults kept their

' tails up in the air and jerked them verticallyat 5-second intervals. They kept in a close

59

FIG. 4. Elevated trail in sea level swamp, Bala­bat, Yap Island. Habitat of lx obrycbus and Polio­limnas.

group, except for occasional straying by achick; when a chick strayed the parent called,k-uk , k-uk, k-uk, in contrast to the usual,hard , ku k, kuk , ku k. So near to each otherdid these birds stay that I was able to collectall six with a single shot from a 4 1O-gaugeshotgun at a distance of about 25 yards.

The adults were a male and a female. Thechicks were covered with black down. Theirlegs were dull blue. The distal third of boththe upper and lower mandibles was dirty­ivory in color; the middle third, extendingproximally to the middle of the externa lnares, was black. The basal third was washed­yellow. The call of these chicks, whose bodylength was 2 inches, was much like that ofday-old domestic chickens, but finer, shrille r,and weaker.

Ducula oceanica monacha, MicronesianPigeon.*-These were not numerous on theislands, but one could be certain of seeingfive or six in a half-day. It was seldom seenin the savanna area, except at ' dusk whenthere was considerable movement betweenwooded regions. As a rule, the birds werefirst observed high in the barer branches oftrees 30 to 60 feet in height, but one wascollected while it rested on a nest some 20feet from the ground in a breadfruit tree; thenest was old and empty. The call is a singleaugh or ungh.

()O

FIG. 5. Typical taro patch swamp, Omin , MapIsland. A pair of rails nested here.

Gallicolumba xanthonura, Ground Dove."-Comparison of specimens from Yap and theMarianas revealed little significant difference.The only female from Yap was somewhatdarker above and particularly darker belowin the throat and breast; specimens from theMarianas are more rufous cinnamon in theseparts of the body. Size seemed to be identicalin the two series.

This species is uncommon on the island;I saw only 14 (singles, except for a maleand a female collected together ) in 4 weeks.It appeared to be limited to mangrove th ick­ets in or near water and was not seen any­where in the interior of Yap Island.

Rhipidura rufifrons versicolor, Rufous­fronted Fantail.*'-Mayr (in litt. ) wrote asfollows:

The Yap race which I had not previouslyseen is more distinct from the races of theMarianas Islands than I had expected. Theextensive, buffy, ochraceous wash of belly andflanks is missing. The well-defined, clear,white upper throat is another striking differ­ence as are the gray-brown flanks. The upper­parts are darker and more rufous with thecontrast between rump and back much lesspronounced. Actually, the Yap bird is, inthe coloration of its underparts, much moresimilar to the Solomon Islands races and inparticular to brunnea from Malaira Island. It

PACIFIC SCIENCE, Vol. IV, January, 1950

differs from that race by the more extensivewhite tips on the tail feathers and broaderwhite edges on the feathers of the breast andmiddle of the abdomen. The rufous zone onthe lower back is more reduced. There is amore distinct grayish wash in the black por­tions of the tail feathers. The similarity isso striking that I wouldn 't be surprised if Yaphad actuall y been colonized from Malaita.

Although found on all the islands, they aremost abundant on Tamil. Th e edges of lowundergrowth in lowland jungles and theedges of mangrove swamps seemed to be fav­orite habitats, but a few were seen far backin the jungle. Without exception, the birdswere found in twos or in family groups; threebroods of nearly fledged young ( three in eachbrood ) were following pairs on Augustll.

They are constantly on the move and arewary, but they, at this season at least, camein toward squeaking noises. They respondedbest to the sound of two pieces of seasonedwood being knocked together, as when ashesfrom a pipe were knocked out by hitting itagainst a gunstock. As one ' moved along atrail these birds frequently flew out ahead,displaying .vigorously. They became mostactive just after sundown and before totaldarkness.

Monarcha godeffroyi, Monarch Fly­catcher.*' - Specimens collected showedmuchindividual variation in extent of the black ,brown, and white coloration. Two birds inbrown coloration , similar to M. takatsukaefrom Tinian, were taken. Both were adultfemales, on the basis of degree of ossificationof the skull and development of the ovaries;one was feeding nearly grown young. Imma­tures collected were dirty-black or brownish­black with dirty-white markings. Males werewhite-backed with white ventra, and the fe­males had a white ring of varying extentabout the neck. .

On all islands of Yap , the species wasabundant along the trails in heavy jungle.In this habitat the species was usually found20 or more feet up in the vegetation; not 10

Birds of Yap:-PIsHER

FIG. 6. Sea level swamp, Balabat, Yap Island .Habita t of Poliolimnas and Ix obrychus; in sur­rounding mangroves Gallicolumba xantbonura wascollected.

the ' low understory as was Rbipidura. How­ever, this flycatcher was also observed perchedon bare pandanus limbs ( 10 to 20 feet high)in the savann a region; here, it flew out afterinsects in' typical flycatcher fashion. Mayr( 1945: 92 ) noted that this seldom occurred

.in Monarcha; he also stated that the taildrooped vertically as the bird perched motion­less. The tail was never drooped in themonarchs of Yap.

Aplonis opacus kurodai, Micronesian Star­ling.*-Three specimens from Yap agreefairly well with orii Takatsukasa and Yama­shina from the Palaus, but the gloss on thebirds from Yap seems to be more blue green,less bottle green; this may be due to slightlygreater wear on the specimens from thePalaus. The bill seems slightly longer on rhebirds from Yap (Mayr, in lirr.).

The species was abundant on all the islandsin all types ofcover except the savanna. Birdswere most numerous, however , in the tops ofhigh trees and were seldom, if ever, encount­ered in low, dense brush. The tops of coconuttrees were much used as singing perches, .andhau trees (Hibiscus tiliaceus) were frequentedfor their fruits. No nesting birds were found,but one juvenile was observed ( August 7 )begging and receiving food, and an adult wasobserved carrying food on August 16. As in

61

other places, this species is in frequent con­flict with other species; on Yap, Myzomelacardinalis and Monarcha were the chief vic­timsof this conflict.

Myzomela cardinalis kurodai, CardinalHoney-eater.*'- It is unfortunate that theseries of skins from Yap contained only oneof a female, for the races are more clearlypronounced in the females. The one femaleagrees closely with an adult female k obayashifrom Palau; both have distinct olive edgesto the tail feathers, and the red is restrictedtothe top of the crown and does not extendto the nape ; the comparative blackness ofthe scapulars in the Yap bird is perhaps dueto its fresh plumage. The only differencebetween these two females is that the red ofthe crown and throat of the specimen fromYap is more cherry red, 'less scarlet, and thereis a more pronounced 'zone without red be­tween the upper throat and breast and be­tween the crown and back. The wing andtail of the Yap race appear to be somewhatlonger. The bill of the Yap birds appears to

be longer than that of the Palau birds, butmeasurements do not confirm this visual im~

pression. The edge of the newly molted pri­maries seems more olivaceous in Palauanthan in Yap males. The under-tail covertsof birds from Y ap seem blacker than in birdsfrom Palau. On the basis of .the specimensbefore me I would not be inclined rorecog­nize k urodai, but it must be considered thatthe Yap series is in full molt. (Mayr, in litt.)

The honey-eaters were present in all suit­able habitat on all islands. They were moszabundant in low brush, no matter whetherthis brush was in the jungle, in ' otherwiseopen country, or in a mangrove swamp. Iiitheir brush habitat the birds appeared to beweak flyers, their fluttery flights seldomlonger than 15 feet, but on August 21 onewas observed over the center of Tomil Har­bor, more than Y2 nautical mile from land.

As a rule, they were observed in pairs, buton August 7 a brood of three was following

62

a pair. On August 10, a female (collected)was starting a nest in the outer tips of ?

branch some 10 feet from the ground .Another female (collected, but unfit for aspecimen) was observed carrying food onAugust 10.

Zosterops conspicillata hypolais, BridledWhite-eye.*-The Yap subspecies, hypolais,is strikingly different from all the other racesof the species. It is by far the most grayishrace of the species. The eye-ring is inconspic­uous and the dark area under the eye is gray­ish rather than blackish. The white loralregion is much reduced. The upperparts aregray', with a greenish tinge, most conspicuouson rump and crown. The underparts aresomewhat like those of rotensis but slightlymore yellowish, less buffy, particularly on theflanks. The size seems the same as in mostother races of this species in which the wingvaries between 55 and 58 millimeters inlength in adult males. (Mayr, in litt.)

This species was usually confined to theundergrowth at the edge of the jungle. Onecould find it in numbers from 2 to 15 inalmost every such area 100 yards long.

. Rukia [Kubaryum] oleaginea, Large YapWhite-eye.*-This species differs from therelated Zosterops conspicillata by beinglarger, darker, and more brownish olive. "Ingeneral coloration it is remarkably similar tosanfordi from Ponape. It is somewhat darker,particularly on the crown, forehead, andlares. There is an extensive blackish zone mthe malar region and under the eyes, whichis barely indicated in sanfordi. The under­parts also are darker and more grayish, whilein sanfordi they are more brightly greenishbuff. Rump and tail, as well as the edges ofthe primaries and secondaries,are duller. Thelegs are duller, more grayish horn color ratherthan yellow as in sanfordi. The two principal

PACIFIC SCIENCE, Vol. IV, January, 1950

differences between the two species are, how­ever, in the shape of the bill, which is nearlytwice as long as in sanfordi, and in the eye­ring which is obsolete in sanfordi. The ex­posed culmen measures about 14 millimetersin oleaginea and over 20 in sanfordi." (Mayr,in litt.)

In the month spent on Yap, only two indi­viduals were observed; one on August 6, 1mile northwest of Yaptown, Yap Island, andone on August 7, less than Y.4 mile from thesame area. One was in a bush overhanginga swamp in dense jungle, and the other wasin low, thick underbrush 200 yards from aswamp.

Lonchura punctulata, Weaver-Finch.*­The .three skins agree best with a series ofthe race cabanisi from the Philippines. Theyare also rather similar to the race topela fromthe Asiatic mainland but are distinguishedfrom this subspecies by the fine barring ontheir flanks and by a less extensive brownarea on the throat. (Mayr, in litt.)

This weaver-finch was found in all openand grassland areas on the islands. Flocks of40 were observed in the shorter, dry grassof the savanna regions, and they were espe­cially numerous in flocks of 5 to 20 birdsalong grassy roads and wide trails where theywere feeding on seeds. Some immatures werebegging for and receiving food on August 16.

This species probably was introduced onYap.

REFERENCES

FISHER, HARVEY 1. 1948. Locality recordsof Pacific Island reptiles and amphibians .Copeia 1948 (1) : 69.

MAYR, ERNST. 1945. Birds of the SouthwestPacific. xix + 316 pp. Macmillan Co..New York.