AMERICAN COOT AND BLACK-NECKED STILT ON THE ISLAND OF HAWAII PETER W.C. PATON, Redwood ScienceLab, 1700 Bayview Drive, Arcata, Califor- nia 95521 J. MICHAEL SCOTT, Condor Research Center, U.S. Fish and Wildlife Service, 2291-A PortolaRd., Ventura, California93003 (presentaddress: Idaho Cooperative Fisheriesand WildlifeUnit, Collegeof Forestry,Range, and WildlifeScience, Univ. of Idaho, Moscow, Idaho 83843) TIMOTHY A. BURR, Hawaii Dept. of Land and Natural Resources,Division of Forestry and Wildlife, Honolulu, Hawaii 96813 (present address: PACNAV- FACENGCO, Code 24-B, Pearl Harbor, Hawaii 96860) Ornithologistsstudying the wetlandavifauna of the islandof Hawaiiduring the late 1800s reportedtwo endemic species(Hawaiian Rail Porzanasand- wichensisand Hawaiian Duck Anas wyvilliana),three endemic subspecies (American[Hawaiian] Coot Fulicaamericana alai, Black-necked[Hawaiian] Stilt Himantopus mexicanusknudseni, and Common [Hawaiian] Moorhen Gallinula chloropus sandvicensis),and one indigenous species (Black- crowned Night-Heron Nycticorax nycticorax hoactli) (Wilson and Evans 1890-1899, Rothschild1893-1900, Henshaw 1902, Perkins1903). The rail is now extinct. The moorhen, althoughpresent on other islands,has been extirpated from Hawaii. The coot, moorhen and duck are classifiedas en- dangered by the State of Hawaii and the Federal government (USFWS 1983). One otherendangered endemic water bird, the stilt,was apparently absentfrom the islandfrom 1896 to as recentlyas the early 1960s (Walker 1962, Banko 1979, Patonand Scott 1985). Researchis currentlybeing con- ducted on the Hawaiian Duck by the Hawaiian Divisionof Forestryand Wildlife (HDFW), as informationon this speciesis limited(Jon Giffin pets. comm.). Surveysof the wetlandsof Hawaii conductedover the past20 years by the HDFW have providedbaseline data on the populationtrends of the coot and stilt (unpubl. data on file, Dept. of Land and Natural Resources, HDFW). The purposeof this paper is to summarizeexisting knowledge of these two endemic water birds on the island of Hawaii. STUDY AREA AND METHODS The HDFW (then the Divisionof Fish and Game) initiatedan annual cen- sus of migratory waterfowl in 1950. Native water birds were added to the count in 1958, but it was not until 1963 that all of the primarywetlands used by the coot and stilton Hawaii were included.These wetlands(Aimakapa, Opaeula, Waiakea, and Lokoaka; Figure 1) have been describedby Shallenberger(1977). Ponds on Hawaii are small, less than 11 ha (Arm- strong1973), with vegetationsurrounding the ponds generallyshort, pro- vidingfew placesfor cootsand stiltsto hide from observers.The HDFW cen- susis conductedon one day in January, surveyingall major wetlandson the island.Eight observers usually conduct the survey,with observersvarying from yearto year. A summercensus, on one day in eitherlate Julyor early Western Birds 16' 175-181. 1985 175 COOT AND STILT ON HAWAII August,was initiatedin I968 to monitorpopulation trends of nativewater- birdsduring the criticalsummer months when water is generallyscarce. From 1975 through 1979, Scott regularlysurveyed ponds in the Hilo area. Patoncensused the majorwetlands of the islandopportunistically from January 1980 throughDecember 1982. None of these surveyswere con- ducted during standardizedtidal or weather conditions;nonetheless we believethat the data give a realisticpicture of true populationfigures. Paton did the statisticalanalysis using MINITAB on the ColoradoState Universitycomputer system. A priorialpha valuesof 0.05 were considered significant. WAIPI; VALLEY LOKOAKA AIMAKAPA HILO KAILUA-KONA 0 10 20 30 KM Figure1. Map of the islandof Hawaiishowing the primarywetlands used by American Coot and Black-necked Stilt. 176 COOT AND STILT ON HAWAII RESULTS AMERICAN COOT. Informationconcerning coot population trends prior to 1958 can only be consideredspeculative. Data reportedbefore the initiation of HDFW censuseswere subjectiveand, therefore,no meaningfulinferences couldbe made to presentpopulation levels. The coot was thoughtto be a common speciesin the wetlandsat lower elevationson Hawaii in the late 1800s, though no populationestimates were reported (Henshaw 1902, Perkins1903). Schwartzand Schwartz(1952) listedthe speciesas "rare"on Hawaii, occurringin a few ponds, reservoirs,and the taro fieldsof Waipio Valley.These authors did not mentionif they visitedAimakapa or Opaeula. Quantitativedata collqcted since 1963 suggestthat the cootpopulation has risen recently. In comparingcoot winter populationfigures from 1963 to 1971 with thoseof 1972 through1981, one can seethat the numberof coots has significantlyincreased in the past decade (Mann-WhitneyTest, p=0.006; Figure 2). The median number of coots counted from 1963 to 1971 was37.5 (range20-46), whereasfrom 1972 through1981 the median countwas 62.5 (range10-110). Thisincrease occurred primarily on the west sideof the island.The coot populationat Aimakapahas increasedfrom 11 birdsin 1970 to 165 in September1984 (HDFW, Pyle 1985). The coot populationon the eastside of Hawaii hasremained relatively small(median = 7.5 birds,range 3-15 during1982). In 1968, 12 cootswere observedat Waiakea Pond, whereas none were seen at Lokoaka Pond (HDFW, summercensus data). By 1982, coot habitatuse patternson the eastside had changedand the majorityof the cootsnested and foragedat Lokoaka. From November 1980 through October 1981, no coots were observedat WaiakeaPond duringweekly surveys (PWCP pets. ohs.). 120' m 60- . 1963'1 I I I I I I 70I I I I I I' I ! I I 810I Figure 2. American Coot winter HDFW censusresults from 1963 to 1981. 177 COOT AND STILT ON HAWAII The breedingbiology of the coot was recentlysummarized, but included virtuallyno data for Hawaii Islandbecause most work was done with this specieson Oahu (Byrd et al. 1985). Cootsnest at Aimakapaand Opaeula with young observedduring all monthsof the year. However, peak nesting activitiesappear to occur in July with l0 incubatingpairs observedat Aimakapa and 5 incubatingpairs at Opaeula (PWCP). Coleman (1978) reported two nesting peaks on Oahu: November-Februaryand June- October. Coot nestshave been recorded at Lokoaka, but nestinghas not been observedat Waiakea since 1978 (JMS pers. ohs.). Four pairs of coots establishednests at LokoakaPond in 1982, with a minimumof 8 youngpro- duced (PWCP pers. ohs.). BLACK-NECKED STILT. The statusof thisspecies on Hawaii Islandremains uncertain. There are no fossilsknown of this speciesfrom Hawaii Island (Olson and James 1982). S.B. Wilson collected 1 adult female stilt in June 1896 labelled "Hawaii, H.I." (Carnegie Museum 55460), which is most likelyfrom HawaiiIsland (Banko 1979). We couldfind no otherrecords of stiltbetween 1896 and 1961 on the island. No other ornithologistdoing work in the late 1800s recorded stiltson Hawaii (Rothschild 1893-1900, Henshaw 1902, Perkins1903). It isnot knownif any of thesemen visited Opaeula, but Perkins (1893) definitelyvisited Aimakapa to collectbirds. Munro (1944) specificallystated that "thereseems to be no recordof it [stilt]from Hawaii." 30 z 10' '9613I I I I I P 171011 I I i I I I I 80I I Figure3. Black-neckedStilt winterHDFW censusresults from 1963 to 1981. 178 COOT AND STILT ON HAWAII The first documented record we could find of stilts on Hawaii was of two birds seen at Aimakapa in August 1961 (Walker 1962). Since1963, the stiltpopulation has remained relatively stable (Figure 3). A comparisonof the island'sstilt population from 1963 to 1971 versus1972 to 1981 yielded no significantdifference between the two periods (Mann- Whitney Test, p=0.103). The median count for 1963 to 1971 was 27.5 (range11-36), whereasfrom 1972 to 1981 the mediancount was 20 (range 11-26; HDFW). The higheststilt count on Hawaii was in January1968, when 36 birdswere recorded,but 35 stiltswere countedas recentlyas 17 October 1982 (PWCP pets. obs.). Stilts nested at Aimakapa and Opaeula during the 1960s and 1970s (EugeneKridler and Robert Shallenbergerpers. comm.). Five stilt chicks were observedat Aimakapa in May 1982 and one chick at Opaeula on 25 September 1982 (PWCP pers. obs.). On Oahu, the stilt breedingseason usuallyextends from March throughAugust but is concentratedin May and June (Coleman 1981). We did find a differencebetween summer and winter HDFW stiltcensuses (Mann-Whitney Test, p = 0.04), althoughthe biological implicationsof this observationare unclear.Surprisingly, the winter counts (median= 24, range= 16-36) were greaterthan the summercounts (me- dian-- 19, range= 15-27). Becausestilts are thoughtto breedprimarily prior to the summercensus, we wouldhave expectedto seehigher counts in July- August. The higher winter counts may be the result of post-breeding movementsbetween islands; however, theseresults warrant further study. There is only one reportedrecord of a stilton the eastside of Hawaii. One bird was observedflying over Lokoaka on 11 April 1981. A sightinglater the same week in the Mountain View area was probablythe same bird. Our data suggestintra-island movements of stilts, primarily between Opaeula and Aimakapa. Censuseson 19 July, 26 July and 16 August1981 showedthe samenumber of birds,but in differentproportions, at Aimakapa and Opaeula (16:14, 18:12 and 22:8, respectively).Inter-island movements of stilts have been documented between Kauai and Oahu, and Maui and Oahu (E. Kridler and R. Coleman pers. comm.). Intra-islandmovements of banded birdshave alsobeen documented(E. Kridler and R. Coleman pers. commo). DISCUSSION Increasesin the cootpopulation on Hawaiiare probably due to changesin humanuse