Fat Cyclicity, Predicted Migratory Flight Ranges, and Features of Wintering Behavior in Pacific Golden-Plovers

Abstract

Annual cyclicity of body components in wintering Pacific Golden-Plovers (Pluvialisfulva), combined with ecological and behavioral features were variously studied from 1978 through 1987. The primary research site was in Hawaii at the Bellows Air Force Station (BAFS), Oahu. After fall arrival, body weights trended downward for several weeks, possibly in response to the energy required for the behaviors associated with establishing (and reestablishing) residency combined with molting. Major premigratory weight gains began in late March about I month prior to migration. Statistical correlations between body weight and fat content are described. Premigratory dehydration as an adaptation to increase flight range and/or energy stores at the migratory destination was likely. Fat-free dry weights (FFDW) at BAFS were least in the fall and greatest in the spring. For juveniles, this difference relates to overall body growth during the first wintering season. With older birds, it may reflect the environmental conditions at the respective end points of migrationpredictably favorable for southbound migrants, unpredictable for northbound birds. Plovers wintering on Enewetak Atoll and Wake Island had significantly higher FFDWs than the birds at BAFS. Possible factors in this relationship are discussed. The BAFS population contained many territorial birds, and showed high rates of survival and site fidelity over successive years. Juveniles arriving on the wintering grounds for the first time probably experience considerable mortality as they compete with established adults for space and resources. Based on wing lengths, many of the plovers involved in this study were from Alaska breeding grounds. Flyways to the tundra may involve staging areas, but specific information is lacking. Using current formulae, we describe the relationship between body weight and flight range, and provide estimates of the fat required to reach various landfalls.