Despite the relatively constant climate of Easter Island the amount of available breeding habitat can vary as can the general activity of P. flavescens. On Easter Island it exhibits typical territorial behaviour at water; females oviposit both in tandem and when "guarded” by a male. Males on Easter Island also defend territories away from water. These appear to be feeding territories, a possible adaptation to the scarcity of suitable prey. Body and wing measurements of 6 Easter Island specimens are compared with those of specimens collected in other parts of the world. They do not suggest significant differences between the populations.