Fat loads and flightlessness in Wilson's phalaropes

Abstract

Fat loads of about 45% of total body mass are maximal for most shorebird migrants. In preparing to fly nonstop from staging areas in North America to South America, some late-staging adult Wilson's Phalaropes (Phalaropus tricolor) amass greater loads (to 54%) and for a brief period become too heavy to fly. This condition is associated with rapid mass gain, but may involve other factors. Despite os-tensibly ideal conditions at staging areas, the phalaropes' greatest rate of fat deposition (3.4-3.6% lean body mass-day-1) is only 60-70% of the theoretical maximum. © The Cooper Ornithological Society 1997.