Studies in Avian Biology No. 22:124-132, 2001.

MIGRATION OF NORTHERN PINTAIL ACROSS THE PACIFIC WITH REFERENCE TO THE HAWAIIAN ISLANDS

MIKLOS D. E UDVARDY AND ANDREW ENGILIS, JR.

Abstract. Northern Pintails ( acuta) regularly occur as winter visitorson most Pacific islands with suitablehabitat. Their breeding distributionincludes both sidesof the Pacific Rim. While large populationsbreed in Siberia and winter in , numerousNorth American breeders also winter in areas near the Sea of , Hawaiian Islands, and other Pacific island groups. Though pintail flights across the Pacific have not been well documented, scrutiny of banding returns shows that an exclusive California-Hawai‘i flyway does not exist, as was earlier proposed. Data support a more complex movement of from numerous breeding locations in the Holarctic. We summarize movements of Holarctic nesting pintails to wintering grounds in the Hawaiian Islands that include birds originating from northeastern Siberia, , and the interior prairie provinces and states of North America. We also summarize pintail movements to other Pacific archipelagoes. Finally, to close the circle around the North Pacific, we summarize movements of birds between Canadian and Alaskan breeding grounds to wintering sites in Japan. We also discuss other panmictic, Holarctic migrants and their colonization attempts in Hawai‘i.

Key Words: Anus acuta; banding return; Holarctic; migration; Northern Pintail; Oceania; panmixis.

The primary interest of a faunist is in establish- of year-round residents (the landbirds) and sea- ing the list of species that regularly occur in the sonal but regular visitors (seabirds that come to area under scrutiny. Data of a species ’ regular breed, and and Charadriiformes occurrence increase knowledge of their total dis- that winter in ).‘ Thirty-three species of tribution, which is the aim of the zoogeographer. migratory waterfowl have been recorded in the Regularly occurring species are recognized as Hawaiian Islands (Pyle 1997). Ten species are influential members of local ecosystems; thus, annual visitors with Northern Pintail (Anus acu- they play a prominent role in ecogeographical tu), Northern Shoveler (Anus clypeatu), Lesser studies. Often less attention is paid to scarce, Scaup (Aythya afinis), American (Anus ameri- rare, or irregularly occurring species, for chance canu) and Eurasian (A. Penelope) wigeons, and seems to determine their detection, and their role Green-winged Teal (Anus creccu) accounting for in community ecology appears negligible. 95% of those birds wintering in the islands (En- Regarding these “lesser” elements of local gilis 1988). fauna, interest increases when a chance visitor Our focus in this paper, the pintail, is a reg- comes from afar. Lately, the study of rarities be- ularly occurring winter visitor in Hawaii‘ and is came important on two accounts. First, it is re- a scarce or irregular visitor to other Pacific is- alized that species are to an extent dynamic; land groups. Reliable but general historical ac- the “stray” individuals caught outside of their counts claim that pintail came in large numbers regular distributional range are all potential col- to Hawaii‘ (Munro 1944). Earlier evidence is onists. The trends in their occurrence outside the suggested by the fact that the Hawaiians recog- “normal” range and throughout a longer time nized two species by name: pintail (Koloa period may reveal the nature and extent of the Mapu) and shoveler (Koloa Moha), indicating pioneering tendency of the species. Second, it is that they were an obvious component to the Ha- also realized that species composition of faunas waiian avifauna before Captain Cook discovered fluctuates; thus rare visitors may reveal trends in the islands in the 1770s. Surveys have docu- fauna1 changes. mented migratory exceeding 10,000 birds Holarctic waterfowl are among the most suc- in the mid-1950s (Medeiros 1958). We exam- cessful colonizers owing to their exceptional ined the data from biannual waterbird surveys powers of flight between breeding and non- conducted on most lowland since the breeding areas. Their ability to move long dis- 1940s (Table 1). We omit data collected from tances and tendency for dispersal have resulted 1960 through 1977 (Niihau,‘ Hawaii,‘ and Mo- in establishment of waterfowl on many remote lokai’ not regularly surveyed during those peri- land masses where food and freshwater re- ods). These data, summarized in Engilis (1988), sources are available (Weller 1980). confirm that the population size of wintering As with all remote oceanic islands, the Ha- pintails in Hawaii‘ have declined tenfold. This waiian Archipelago received its endemic avifau- decline has led to added interest by conserva- na through over-water dispersal and subsequent tionists to address habitat needs in the Hawaiian local speciation. The Hawaiian avifauna consists Islands benefiting migratory waterfowl and

124 PINTAIL MIGRATION IN THE PACIFIC--U&a&y and Engilis 125

TABLE 1. CENSUS OF PINTAILS IN HAWAII‘ mainland and 16 have been retrapped on the is- lands. Additionally, a pintail banded on Maui in Year Total Pintails October 1952 was reported taken a month later 1950 1,593 from Pukapuka (Danger) Atoll in the Tuamotu 1951 1,875 Archipelago. Significantly, the Tuamotus are al- 1952 7,094 most due south from the Hawaiian chain, as are 1953 8,226 the Line Islands, where two pintails were recov- 1954 1,950 ered two to three months after same-year autum- 1955 2,653 nal banding in North America (MBMO data). 1956 3,045 Medeiros ’ analysis of these returns lead him to 1957 1,619 1958 1,126 the conclusion that the islands ’ wintering pintail 1959 1,249 population is not blown off course but are delib- 1978 897 erately flying from central California to, and re- 1979 490 turn there from, their wintering areas in Hawaii.‘ 1980 923 Of the above mentioned 107 Hawaii-banded‘ 1981 377 pintails, 45 were recovered in the San Francisco 1982 150 Estuary, California (Fig. 1). These returns also 1983 60 confirmed that pintails return to the islands one 1984 235 or several years after the initial banding there. 1985 150 1986 501 Thus, pintails repeatedly and deliberately visit 1987 203 Hawaii‘ to spend the winter, with some hying further southward after having used the islands Notrs: Data from 1950 to 1959 from Meideros (1950-1959). Countc were taken on Maui, Hawal’i, O‘ahu, and Kaua‘i Data from 1978 m in transit (Medeiros 1958). Medeiros speculated 1987 from Eneilis (1988). During 1960-1977 not all islands were sur- that the autumnal flight probably used the north- veyed and records are sketchy. The period of 197X-1987 represents the best modern data jet as all eight main lslandc including Nl’ihau were erly trade winds that originate outside central surveved. California, while for the return flight in the spring the ducks probably are helped by the westerlies. shorebirds. Understanding pintail movements to According to the MBMO banding/recovery Hawaii‘ will assist in these efforts. data, 165 pintails have been banded in Hawaii‘ Medeiros (1958) documented the movement and recovered (including 16 in Hawaii)‘ be- of pintails between the Hawaiian Islands and tween 1953 and 1960 (Fig. 1). The data reveal North America, speculating a California-Hawaii‘ that the high number of California returns in the flyway. Although this connection is correct, the total of Hawaii-banded‘ ducks matches the dis- true migration patterns are more complex. We tribution pattern, at banding, of 14 pintails band- analyzed banding data from the U.S. Migratory ed from 1951 to 1954 in North America and Bird Management Office (MBMO), Yamashina later recovered in the Pacific (Fig. 2). In addi- Institute for , Japan, and the Russia tion, the proportion of ’ share in the Center. Included in our data col- total of 165 records is 77.6% against all other lection was a summary of available literature, localities; if we compare California only with examination of specimens from the American the coastal entities of Alaska, British Columbia, Museum of Natural History (AMNH), National Washington, and Oregon, the proportions are Museum of Natural History (USNM), and Bern- 128 against 24, or 84.2%. ice P. Bishop Museum (BPBM), examination of In order to assess the relation of mainland bird observation records from the Hawaii Rare populations of pintail to the population visiting Bird Database (HRBD), and fieldwork conduct- the Hawaiian Islands, according to the banding ed by us (Udvardy 1958-1960 and Engilis and recovery results, we have compared the fig- 1984-1997). These sources enabled us to gather ures of banding effort, recoveries, and hunting considerable amounts of data indicating that pin- pressure on the Pacific coastal areas of North tails from at least half of the species circumpolar America for the years of Medeiross’ project (Ta- distribution are potential winter visitors to Ha- bles 2, 3). We excluded Alaska from these tables waii‘ and that their movements across the Pacific because there were no data available for hunting are complex. In the following discussion we try pressure or banding efforts in Alaska for the to document these assumptions. 1950s. Comparing the data in Tables 3 and 4, we NORTHERN PINTAIL MIGRATION TO THE concluded that during the 1950s California pin- HAWAIIAN ISLANDS tails were indeed providers of over 90% of the Of the 2,811 pintails banded in Hawaii,‘ 107 birds annually harvested by hunters in the tem- have been recovered on the North American perate Pacific Coast of North America and also 126 STUDIES IN AVIAN BIOLOGY NO. 22

FIGURE 1. Northern Pintails banded in Hawai‘i and recovered anywhere. of pintails annually banded there. The recoveries Coast (Fig. 1). One bird was recovered in the in California are predominately from the fall Anadyr Region of eastern Russia (lat. 62” 5 ’ N, when hunting pressure is at its highest. Also, long. 179” 1 ’ E). The later bird was a hatching- pintails arrive in California earlier than most year male banded on Maui, Hawaii,‘ 22 Febru- species of migratory waterfowl, boosting the ary 1954. It was shot on the breeding grounds California figures (Miller 1985). These facts, 29 May 1960. These multiple recoveries strad- overlooked by Medeiros, contributed to the pre- dling the Bering Sea provide another migration dominance of California in the Hawaiian band- link from the Holarctic to the Hawaiian Islands. ing and recovery data. However, California re- We speculate that Arctic nesting pintail probably mains a critical area for pintail, supporting over make the transoceanic flight direct from south- 50% of those wintering in the United States ern Alaska/Siberia to the Hawaiian Islands, in- (Heitmeyer et. al. 1989); thus it probably serves tercepting the leeward islands (e.g., Midway and as a principle staging area for Hawaiian-bound Laysan), resting, and then moving to the main pintails. This still needs to be confirmed through islands. Just as plausible, however, is a move- modern marking and tracking studies. We note ment of Alaskan birds south along the Pacific that banding recoveries support the notion that Coast of North America, into California, and pintails could equally originate from other Pa- then across the Pacific. This movement may be cific Coast localities such as Mexico, Oregon, or Washington (Figs. 1, 2). indirectly supported by banding evidence of A second pattern of movement can be seen Alaskan birds as nearly 80% of those recovered from birds banded in Hawaii‘ and recovered in have been taken in California (Austin and Miller the Arctic. Five birds banded in Hawaii‘ in the 1995). The early arrival of pintails to Califor- 1950s were recovered in the Arctic: one in the nia-males arrive in numbers by late August Aleutian Islands; another in the Yukon-Kuskok- (Miller 1985)dould allow time for birds to re- win Delta, an important breeding ground in fuel and make the flight to the Hawaiian Islands. western Alaska; and two on Alaskas’ South Again, this high return rate of Alaskan-banded PINTAIL MIGRATION IN THE PACIFIC--Udvardy and Engilis 127

. “h .

. . : _ -- .

FIGURE 2. Northern Pintails banded anywhere and recovered in the Pacific (triangles = recovery location, dots = banding location). pintails can be biased by the high number of America, where males tend to outnumber fe- birds shot in California. males in most studies on the wintering and breeding grounds (Bellrose et al. 1961, Miller POPULATION DEMOGRAPHY OF PINTAIL 1985, Rienecker 1987, Austin and Miller 1995, WINTERING IN THE HAWAIIAN ISLANDS Migoya and Baldassarre 1995). The higher num- From Medeiross’ banding data we note that her-of males recorded in waterfowl populations Hawaii‘ had a sex ratio skewed towards females has been speculated to be the result of a high (Table 4). This is atypical for what has been re- mortality rate (increased predation due to habitat ported for pintails (and other ducks) of North fragmentation) of adult females during the

TABLE 2. HUNTING PRESSURES ON PINTAIL 1950-1956 AT PACIFIC COASTAL AREAS

Yew British Columbia Washington Oregon California

1950 69,600 109,500 (est.) 1,945,300 1951 94,830 114,900 2,966,OOO 1952 72,620 111,250 4,659,OOO 1953 94,940 97,800 4,599,500 1954 93,940 112,600 3,46 1,600 1955 70,490 128,200 3,312,700 1956 71,940 117,700 3,526,OOO Totals 568,360 79 1,950 913,620 (est.) 24,470,lOO Yearly Mean 81,194 113,136 130,517 3,495,729

aFigures represent reponed birds taken by hunters during the legal hunting season of each year. Source: state and provincial huntmg records obtained m wnting by M.D.E Udvardy 128 STUDIES IN AVIAN BIOLOGY NO. 22

TABLE 3. BANDING OF PINTAIL 1950-1956 AT PA- TABLE 4. SEX RATIOS OFBIRDS BANDED INTHE HA- CIFIC COASTAL AREAS WAIIAN ISLANDS (MEDEIROS 1950-1959)

Bntl\h Sex ratio YCLV Calumhin Washmgton Oregon California YS1‘ i-4 (Males to Females) 1950 28 110 234 9,334 1951 417 0.63 1951 26 774 544 19,360 1952 856 0.84 1952 31 656 102 17,570 1953 644 0.65 I953 0 433 574 16,737 1954 446 0.94 I954 5 143 1,000 16,514 1955 478 0.50 1955 5 625 2,93 I 2 1,475 1956 0 988 1,651 15,759 Total 95 3,729 7,036 116,749 Source:U.S. Migratory Bnd Managementoffice records. patterns changed in Hawaii.‘ A more abbrevi- ated migration occurs with the main bulk of pin- tail arriving in the islands, marked by hatching- breeding season (Johnson and Sargeant 1977). year birds (based on the timing of their body The disproportionate numbers of females seen in molt; A. Engilis, unpubl. data) by late October, Hawaii‘ may therefore be the result of female peaking in November, and stabilizing at a few pintails’ tendency to exhibit philopatry to their hundred birds through the winter. We speculate winter quarters (Rienecker 1987, Anderson et al. that the early arrival of male pintails to Hawaii‘ 1992), coupled with the effort required to reach was lost during the years of continental decline the Hawaiian Islands. In addition, pintails un- (mortality?) from 1975 to 1985 leading to the dergo a sex-segregated migration as males move observed, abbreviated migration and decline in to molting grounds earlier than females, in some Hawaii.‘ In the late 199Os, a few early flocks cases arriving months earlier (Fuller 1953, Oring have again been observed in late September; 1964, Salomonsen 1968, Bellrose 1976). Both most are comprised of male birds (A. Engilis sexes appear prone to wander, particularly young and A. J. McCafferty, pers. obs.). During the birds, as is revealed in the specimen record. Of same period, pintail numbers have increased on the 42 pintail specimens examined from Pacific the continent (USFWS 199613). islands, 25 were hatching-year birds and 17 were adults. Medeiross’ trapping and banding data MOVEMENT OF NORTHERN PINTAIL also revealed a decline in pintail age ratio ACROSS THE PACIFIC throughout his study (Table 5). This decline was To complete the assessment of pintails mi- also reflected in the Pacific flyway pintail pop- grating across the Pacific, we assembled data for ulation and was the result of a severe drought in pintail banded in North American and recovered the prairie provinces of depressing con- in Eurasia. One movement of birds between the tinental waterfowl populations (Ducks Unlimit- continents has been documented, with part of the ed 1990). population breeding in eastern Siberia and win- The timing of pintail migration to Hawaii‘ has tering in the western United States (Dementev’ apparently changed in the past five decades. The and Gladkov 1952, Henny 1973). Again the decline of pintails in North America has been banding recoveries (N = 423) yield a more com- well documented, and we have seen a similar plex pattern of movement across the North Pa- decline in Hawaii‘ (Engilis 1988, Ducks Unlim- cific than first thought. To make sense of these ited 1990, Austin and Miller 1995). Not only has data, we combined the patterns of movement there been a decline in numbers, but the period into three groups. of arrival has decreased as well. In the 1950s Medeiros documented birds arriving, in num- bers, as early as mid-September. His banding re- cords revealed that the early arrival was marked TABLE 5. RATIOS OF WINTERING NORTHERN PINTAIL by small flocks of males, followed by females ADULTS TO JUVENILES IN THE PACIFIC FLYWAY AND THE and hatching-year birds that arrived in October. HAWAIIAN ISLANDSBASEDONBANDINCRECORDS(MED- Pintail numbers peaked in November. This sex- EIROS 1950-1959) segregated migration pattern has been docu- mented for other waterfowl in North America, YtXU Hawai‘l PacilicFlywaya particularly in California where male pintail 1951 1.19 3.50 comprised over 90% of the total birds arriving 1952 2.07 3.70 in August but only 53% of the total wintering 1953 0.51 0.50 population once females arrived (Miller 1985). 1954 0.72 0.50 By the mid-1980s to present, pintail arrival il Extrapolatedfrom Bellrose et al. 1961. PINTAIL MIGRATION IN THE PACIFIC--Udvardy and E&is 129

,o es-9 *. - V

FIGURE 3. Northern Pintail banding recoveries in Asia below 50” N; birds banded in North America (triangles = recovery location, dots = banding location).

GROUP 1 GROUP 2 Three birds were recovered in Europe and one Below the 50” N parallel, 21 North American- in western Siberia. The first bird, a drake, was banded pintails have been recovered in Japan, 1 banded in northern California and shot eight in Korea, and 2 in Sakhalin Island, Russia. Of years later in western Siberia. Another drake, these 24 birds, all were winter visitors: 5 were also from California, and was recovered two banded on the Aleutian Islands; a scattering years later from the Arctic coast of Russias’ came from the tundra or northern parklands of Kara Sea. A third, an immature drake from the Canada; 11 were in a cluster from the southern Canadian maritime province of Nova Scotia, Canadian and northern U.S. prairies; and another was found in Chechia two and a half years later. scattering originates in California and other These records provide an example of the mech- western states (Fig. 3). These data corroborate anism whereby these circumpolar, spe- Hennys’ data (1973) and, in addition, show that cies mix their genotype so that no specialization there is an unknown, but sizable number of could occur, supporting the notion that the Hol- North American pintails that regularly winter in arctic pintail population remains panmictic and the region of the Sea of Japan, the area which opportunistic, thus adapted to varying climate is also a wintering ground for some portion of conditions (Udvardy 1969: 180-l 8 1). The last of the East Asian breeding population (Dementev’ these cases defies all speculations; an adult fe- and Gladkov 1952, Ornithological Society Japan male from northern California that was found 1974, Meyer de Schauensee 1984). Further, four six years later in the Ukraine (Rienecker 1987, female pintails, all banded within 5 days of one 1988). another on the Aleutian Islands, were recovered The remaining 420 pintails mentioned above in Japan: three of them 40, 52, and 64 days after were divide into two groups: those recovered in their banding date, respectively. The fourth was Asia below 50” N (group 2) and those above it recovered, also in Japan, a year later. These four (group 3). females, banded in “immature” , ex- 130 STUDIES IN AVIAN BIOLOGY NO. 22

12d 16d 160” 166 140* 12d

FIGURE 4. Localities where Northern Pintails have been recorded in the Pacific Ocean (banding, sight and specimen records). Sources: Reichenow (1899, 1901), Schnee (1901), Baker (1946), Gallagher (1958-1959), Yocum (1964), Fosberg (1966), Amerson (1969), Ely and Clapp (1973), Palmer (1976), Pratt et al. (1987), Engilis (1988), Stinson et al. (1997), specimens from American Museum of Natural History, National Museum of Natural History, Bernice P Bishop Museum, and sight observation records Hawaii Rare Bird Database).

emplify the regularity of visiting and returning in a great circle route or follow a coastal route to winter grounds (cf. philopatry of Rohwer and along the Pacific Rim. Anderson 1988), reminding us of similar data To close the circle around the pintails of the from Medeiross’ banding returns in the Hawai- Hawaiian Islands, we looked at the rest of Oce- ian Islands. It is tempting to suggest a Canada- ania (Fig. 4). Our scrutiny of the pertinent lit- Japan flyway on a great circle route from the erature, banding records, and museum speci- North American prairies through the Aleutian mens shows that every island group of central Chain, Kamchatka, and the Kuril Islands. Oceania has received pintail visitors, often in numbers. We mention here two special cases as GROUP 3 extremes. During the period when the Marshall The remaining 396 banded birds recovered in Islands were German colonies, Anton Reichen- Asia were there predominantly as spring-sum- ow reported in 1899 about an autumnal mer arrivals because 338 of them were found migration viewed at Jaluit Atoll by reliable pub- from April to July, 55 in the fall months, and lic officers and documented by specimens sent only 3 in the winter. Beside Henny (1973), a to the Berlin Museum as pintails, Green-winged number of publications deal with drought dis- Teals, and (Aythya valisineria). placement of pintails to Alaska and beyond “Zn ununterbrochener Folge ungeheure keilfor- (Derksen and Eldridge 1980; Hestbeck 1995, mige Schwiinne” (large numbers in uninterrupt- 1996). Thus, there is a sizable movement be- ed sequence of enormous v-shaped flocks) tween breeding grounds in eastern Siberia and moved over the atolls of Bikar, Utirik, Ailuk, wintering areas in North America. It is not Jemo, Likiep, and Wotje from north to south in known whether these birds fly over the ocean or the fall, and back again in May (Reichenow PINTAIL MIGRATION IN THE PACIFIC--U&&y and Engilis 131

1899, 1901 j. Another observed migration to- umented on Molokai,‘ Maui, and Kauai‘ during ward north and north-east in the vicinity of the late 1980s. After the decline of wetlands and Kwajalein Atoll was documented in May 1900 aquaculture on Oahu‘ s’ North Shore in 1992, the (Schnee 1901). population of Fulvous Whistling Ducks crashed The pintail is also an uncommon, but regular dramatically, so that by 1998 only one bird re- winter visitor to the Mariana Islands, occurring mained on the James Campbell National Wild- regularly on the main islands of Guam (numer- life Refuge (A. Engilis, Jr., pers. ohs.). It is of ous sites), Saipan (Lake Susupe), and Tinian interest to note that the whistling duck has high (Hagoi Marsh; Stinson et al. 1997). Kuroda populations on the Pacific Coast of North Amer- ( 1961) linked the pintail that reach Micronesia ica only in western Mexico. Thus it is conceiv- to the “Nearctic Hawaiian Flyway” (cf. Baker able that these birds originated from there, as 1953), referring to the now unrecognized North could migratory pintail as stated earlier. A Mex- American race (A. acuta tzitzihoaj. However, ice-Hawaii‘ tie is also suggested by other va- with the prevailing storms across Japan moving grants that have occurred in Hawaii:‘ e.g., Little east and southeast, it is conceivable that the Blue Heron (Egrettu cueruleu), Laughing North American connection to the Marianas are (Lams utricillaj, and Great-tailed Grackle actually birds originating from the “Canada-Ja- (Quisculus mexicanus; Pyle 1997). pan” corridor. PIED-BILLED GREBE SUMMARY OF COLONIZATION EVENTS The Pied-billed Grebe (Podilymbus podiceps) BY HOLARCTIC MIGRANTS IN HAWAII‘ has bred in Hawaii‘ since the mid-1980s. A sin- The winter range of Northern Pintail is per- gle bird arrived to overwinter in 1984 on Ai-‘ haps the most widespread distribution area of all makapa Pond, located on the Kona Coast of Ha- species of waterfowl (Palmer 1976, Austin and waii.‘ It left in the spring of 1985. Two birds Miller 1995). Pintail are prone to disperse and returned the following fall, remained, and gave wander as is evident by the banding, observa- rise to a population on the pond that remained tion, and specimen information synthesized stable at a dozen birds throughout the late 1990s here. The species has been recorded on all con- (R. David, unpubl. data). These two birds re- tinents except Antarctica and shares ancestry mained and have given rise to a population on with the endemic island form in the Southern the pond that remains stable at about a dozen Hemisphere, Eatons’ Pintail (Anus eutoni). Hol- birds. Dispersal records on Kauai,‘ Maui, and on arctic species prone to wandering have given other wetlands of the island of Hawaii‘ are be- rise to the majority of known endemic water- coming more frequent in recent years, probably birds and most landbirds of North Pacific islands representing young birds that may have origi- (Fleischer and McIntosh this volume). The ma- nated from Aimakapa‘ Pond (HRBD, unpubl. jority of the species that have colonized are data). those whose resources naturally fluctuate, both on a regional and seasonal pattern. Many of GREAT BLUE HERON AND WHITE-FACED IRIS these are representative of highly volatile spe- Although they have not yet been recorded cies such as fringillid finches, frugivorous breeding, two Holarctic ciconids are now regular thrushes, waterbirds (rallids, shorebirds, and residents in small numbers, the Great Blue Her- ducks), and raptors, the latter whose populations on (Ardeu herodius) and White-faced Ibis (Ple- erupt relative to fluctuating small mammal num- gudis chihi). Great Blue Herons continue to bers. Colonization events have been rarely doc- wander through the chain and at times form umented on island groups, and although pintail small groups, often roosting among nesting col- have yet to be recorded nesting in Hawaii,‘ other onies of Cattle Egrets (Bubulcus ibis) and Black- Holarctic migrants have. We summarize three crowned Night Herons (Nycticorax nycticorax). cases where colonization has led to, or is sus- What drives these birds to disperse to the Pa- pected to have lead to, a Hawaiian breeding pop- cific islands remains unclear, as do the mecha- ulation of a Holarctic migrant. nisms of how they navigate to the islands year after year (wintering shorebirds and waterfowl). Fur.vous WHISTLING-DUCK Mayr (1953) discussed the migration of birds The Fulvous Whistling Duck (Dendrocygnu across the Pacific speculating that historically bicolorj apparently reached Hawaii‘ under its the islands of the Pacific were more massive, own power in 1982 when a flock of six birds thus providing better opportunity for coloniza- suddenly appeared on Oahu‘ (Leishman 1986). tion. He also suggested two patterns affecting They began nesting on Oahu‘ s’ North Shore, ex- Holarctic birds, that of route abbreviation and panding to nearly 30 birds in under five years. route prolongation. The Northern Pintail might Dispersal records of individual birds were doc- more readily fall into the latter group of mi- 132 STUDIES IN AVIAN BIOLOGY NO. 22 grants, a species whose migration patterns have these movements. The evidence bears out a been elongated as a result of global climate complex setting for migratory waterfowl in the changes and expanding breeding range north- Pacific, fortunately observers of the past had the ward, away from traditional wintering grounds. foresight to band pintails to help us elucidate Baker (1953) further alluded to the fact that oce- these movements herein. What has become clear anic islands provide excellent wintering grounds is that pintail remain a regularly occurring com- due to the absence of mammal and reptilian ponent of the Pacific island avifauna, represent- predators. Both authors discussed their findings ing a link to the mechanics of island coloniza- with an emphasis on northern nesting shore- tion from the Holarctic fauna1 region. birds, including those species where the majority ACKNOWLEDGMENTS of the known population winters in the Pacific: In assembling the data for this paper we received Bristle-thighed Curlew (Numenius tahitiensis), enthusiastic help and data from many fellow wildlife Pacific Golden Plover (Pluvialis fulva), Wander- researchers such as C. Kessler, B. H. Powell, .I. M. ing (Heteroscelus incanus) and Gray-tailed (H. Sheppard, K. Smith, and G. J. Wiles, all of the U.S. hrevipes) Tattlers, and Bar-tailed Godwit (Li- Geological Survey. The following provided banding data for our studies: B. Trost of the U.S. Fish and mosa lapponica; Baker 195 1, Mayr 1953). Wildlife Service for information on pintail banded in Finally, migration out over the Pacific Ocean North America; M. Yoshii of the Yamashina Institute has rarely been observed, owing to paucity of for Ornithology for information on pintail in Japan; in observers and opportunities. A great “corridor” the 1960s A. Vinckurov of the Russia Ringing Center, of migrating Alaska pintails was observed in the Moscow, for data on pintails in Russia. The original fall in southern British Columbia, and another hunter and banding data from the 1950s has been cour- one moving from Alaska southwest across the teously provided by the departments of wildlife of Ha- wai‘i, Alaska, British Columbia, California, Oregon, Pacific has been postulated (Bellrose 1976, Washington, and the U.S. Fish and Wildlife Service. Campbell 1990) and backed by observations B. O’Hara and A. Morton of Ducks Unlimited created (Martin and Myres 1969). We uncovered one all figures and M. Doyle helped with many of the tech- specimen of American Wigeon (AMNH nical details while working on the data. We would also 131716) collected by C. H. Townsend in 1891 like to thank M. LeCroy (AMNH), I? Angle (USNM), from the USS Albatross, “500 miles NW of and C. Kishinami and R. L. Pyle (BPBM) for access to specimens and assistance while working with col- Oahu”,‘ documenting yet another species ’ lections. K. Evans and .I. M. Scott provided helpful movement across the Pacific. Perhaps new tech- comments on the manuscript. The junior author thanks nologies for tracking large birds (satellite telem- M. Udvardy and family for their support of the manu- etry and Doppler radar) may help shed light on script after M. D. E’s untimely passing.