Synchronized Life Cycles in the Orange‐Crowned Warbler and Its Mallophagan Parasites

Abstract

The purpose of this study was to determine the relationship in timing of important stages of the life cycles of mallophagen lice and the cycles of the subspecies of the Orange—crowned Warbler (Vermivora celata) which they parasitize. The timing of breeding in the mallophagans Ricinus picturatus and Menacanthus sp. coincides with the timing of breeding in the subspecies of host warbler, resulting in sufficient numbers of lice for transfer to the newly available juvenal warbler hosts. No eggs are laid during the periods of avain molt; any eggs present would be lost with the feathers as they are dropped. Breeding is very limited in the winter when reproductive effort would be wasteful; opportunities for dispersal are rare at this time, and birds are extremely efficient at keeping their numbers of lice at a minimum. Several lines of evidence suggest that the timing of breeding in R. picturatus and Menacanthus sp. is controlled by the reproductive hormones of V. celata. Hormones are available to these lice with feed on the blood of their host. Peak breeding in the louse populations coincides with peak production of reproductive hormones in avian populations and lasts only as long as the breeding season of the subspecies parasitized. Juvenal birds which are not producing great quantities or reproductive hormones never carry louse eggs. During the fall molt periods, the gonads are in a refractory state and produce a minimum amount of reproductive hormones. During the late fall and in mild winters, birds frequently exhibit some reproductive behavior which accounts for the limited egg laying by lice at this time. Though hormone production may be moderately high during the winter, release to the blood is usually restricted. Members of the mallophagan genus Philopterus normally do not feed on blood, and in this group the life cycle is not so closely coordinated with that of the Orange—crown.