Migration by radio-tagged Pacific golden-plovers from Hawaii to Alaska, and their subsequent survival

Auk, The, Jul 1997 by W, Oscar, Anne, Mary, J, Alan, Et al

OSCAR W. JOHNSON,1 NILS WARNOCK,2,3,8 MARY ANNE BISHOP,4,5 ALAN J. BENNETT,6 PATRICIA M. JOHNSON,1 AND RONALD J. KIENHOLZ7

1Department of Biology, Montana State University, Bozeman, Montana 59717, USA; 2Environmental and Resource Sciences, University of Nevada, Reno, Nevada 89512, USA; 3Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada;

4Pacific Northwest Research Station, LL S. Forest Service, P O. Box 1460, Cordova, Alaska 99574, USA; 5Department of Fisheries, University of Washington, Seattle, Washington 98195, USA; 6Lake Clark National Park and Preserve, P O. Box 2643, Kenai, Alaska 99611, USA; and (7)210 7th Street NE, Dilworth, Minnesota 56529, USA

Many Pacific Golden-Plovers (Pluvialis fulva) and other shorebirds winter in the Hawaiian Islands. This is the first landfall for mid-Pacific migrants after overwater flights of 4,000 km or more from Alaska (Johnson et al. 1989, Johnson and Connors 1996). Previous findings (sightings of marked birds and winglength measurements) showed Alaska affinities for golden-plovers wintering in Hawaii (Johnson and Connors 1996), but there had been no attempt to demonstrate movements between the two regions using radiotelemetry. We made such an effort in spring 1996 by radio-tagging plovers on wintering grounds in Hawaii just before their migration. Some of these birds were later found at three sites in Alaska, including a breeding ground.

Methods.-Plovers were trapped (by the Johnsons and Kienholz) from 18 to 23 April 1996 in Honolulu, Oahu, Hawaii. Capture was in the predawn using mist nets placed on winter territories. We determined sex from the dimorphic breeding plumage and identified first-year (i.e. yearling) birds from their retained juvenal primaries (Johnson and Johnson 1983, Johnson and Connors 1996). Each bird was weighed ( 1 g) and marked with a U.S. Fish and Wildlife Service band plus a unique combination of colored plastic bands, all placed on the tibiotarsi Twenty plovers had 1.65-g, 60-day radio transmitters (Holohil Systems Limited, Carp, Ontario, Canada) glued to clipped feathers on their lower backs (Warnock and Warnock 1993). Based on chronology of body molt (Johnson and Connors 1996), transmitters probably were retained until at least late June or early July. Although body masses at departure were unknown, the transmitters must have averaged less than 1% of total mass (the last 10 birds captured, from 20 to 23 April and nearing departure, weighed 162 to 200 g, X = 183 g). We captured 16 birds on lawns at the National Memorial Cemetery of the Pacific (NMCP), and four on lawns at the Honolulu Zoo. The NMCP provides excellent wintering habitat that supports about 100 plovers; a much smaller group winters at the zoo. The radio-tagged birds were conspicuous residents on winter territories (all plovers at the NMCP and the zoo are territorial) and were easily monitored by direct observation or with a hand-held antenna. Abandonment of territories is a clear indicator of migration (either actual departure or premigratory aggregation elsewhere), and we checked territories several times a day for presence or absence of radio-tagged birds. Pacific GoldenPlovers on Oahu are very faithful to specific winter territories from season to season (Johnson and Connors 1996). Thus, it was relatively simple to determine survival after return migration in the fall.

In Alaska, plover radio frequencies were monitored almost entirely by air (Iverson et al. 1996) at major shorebird stopovers along the coast and at two inland breeding locations (Fig. 1). Search dates varied from site to site, the overall range was 23 April to 28 June 1996. Bishop and Warnock coordinated and integrated the search for radio-tagged plovers with concurrent studies of radio-tagged Western Sandpipers (Calidris mauri).

Results.-Three of the 20 radio-tagged plovers were detected in Alaska (Table 1, Fig. 1). Bird No. 9 was recorded during the first monitoring flight at the Copper River Delta on 27 April. Signals were heard at the east end of the delta (Controller Bay) on the mornings of 27 and 28 April; by the morning of 29 April the bird had moved about 100 km to the western part of the delta (vicinity of the Egg Islands), where it remained until last detected on the morning of 5 May. No. 9 was found again on 29 and 31 May during two aerial surveys by Bennett across breeding grounds in the Mulchatna and Nushagak River regions northwest of Lake Iliamna. Signals from plover No. 10 were recorded by Bennett on the same breeding grounds on the same dates. The two individuals were located about 16 km apart at 59o37'N, 156o47'W (No. 9) and 59(deg)42'N, 156(deg)33'W (No. 10). Bird No. 20 was detected on 1 May near the town of King Salmon. Nineteen of the 20 birds (95%) returned to Oahu in fall 1996 and reoccupied their previous winter territories. The missing individual was No. 20.

Discussion.-Pacific Golden-Plovers were discovered nesting northwest of Lake Iliamna in 1994 (Bennett 1996), which may indicate breeding over a relatively large area in southwestern Alaska. Although the status of Nos. 9 and 10 was not confirmed on the ground, finding both individuals at specific locations on Bennett's study site during two flights in late May leaves little doubt that they were nesting. Notably, Nos. 9 and 10 occupied neighboring winter territories in the NMCP. We conclude that some fraction of plovers wintering on Oahu, and probably elsewhere in Hawaii, breeds in southwestern Alaska. Bird No. 20 was recorded about 130 km southwest of the coordinates given above and may have been en route to the same general region in which Nos. 9 and 10 were found.