Wintering ground fidelity and other features of Pacific Golden-Plovers Pluvialis fulva on Saipan, Mariana Islands, with comparative observations from Oahu, Hawaiian Island

We radio-tagged and uniquely color-banded Pacific Golden-Plovers Pluvialis fulva wintering on Saipan, Mariana Is. (n= 36, of which 24 were radio-tagged), and Oahu, Hawaiian Is. (n= 10, all radio-tagged) in spring 2005. The birds departed in late April from both locations, and their transmitter frequencies were then monitored from small aircraft in several regions of Alaska. The only signals detected were those of four Oahu plovers. During southbound passage in August, one of the Saipan birds was sighted in Japan. Fall returns to the study sites were 72% (26/36) on Saipan and 90% (9/10) on Oahu. Each of the Oahu birds reoccupied its previous wintering territory. Because most Saipan plovers were non-territorial and often difficult to locate, we probably did not find all returnees during fall surveys. Thus, the actual fidelity at Saipan was likely similar to that on Oahu where returns in the first fall after banding averaged 86% over 21 seasons. Although connectivity between Saipan and Alaska remains a possibility, finding no radio-tagged Saipan birds in Alaska suggests linkage with nesting grounds in Siberia. The most likely route for northward passage from Saipan is via Japan. There are also possible connections with major fulva stopovers in Mongolia and adjacent Russia. Compared to ploverson Oahu, the Saipan birds were relatively lean and had much less alternate* feathering. These features of Saipan plovers presumably reflect a spring migration strategy in which substantial fattening and prealternate molting occurs at stopovers while en route to breeding grounds. To what extent unusually dry conditions on Saipan in spring 2005 might have influenced pre-departure fattening and molting is uncertain.