Polyandry in the American Jaçana (Jacana spinosa)

Abstract

LITTLE is known about the biology of any of the Jacanidae, a circum- tropical family of shorebirds that inhabit freshwater swamps and marshes. The lack of knowledge reflects the limited field research done on tropical aquatic birds in general (Birkenholz and Jenni, 1964; Lack, 1968; Orians and Paulsen, 1969). The reversal of roles of the sexes in the American Jaana (Yacana spinosa), in which males incubate eggs and rear young without help from the females has long been known (Miller, 1931). The same reversal of sex roles occurs in the Pheasant-tailed Jaana (Hydro- phasianus chirurgus) (Hoffmann, 1949, 1950.), in the Bronze-winged Ja- ana (Meto'pidius indicus) (Mathew, 1964; Collier, pers. obs.), and prob- ably in the African Greater Jagana (Actophilornis a/ricana) (Miller, 1951). Furthermore, both Hoffmann and Mathew studied small breeding popula- tions consisting of one female and two or three males. Although they inves- tigated very small, unmarked populations, and almost all of Hoffmann's excellent data were gathered in Peking at the northernmost distributional limits of the Pheasant-tailed Jaana, there is little doubt that these two species are polyandrous. Polyandry is a rare form of social organization in birds (Lack, 1968; Orians, 1969). It is known or postulated to occur in some Tinamiformes, Charadriiformes (Rostratulidae, Jacanidae), Gruiformes (Turnicidae, Pedi- onomidae, Mesitornithidae, and one Rallidae). Polyandry has been sug- gested, but not substantiated, in a number of other orders. Although the Phalaropidae have been considered polyandrous, HShn (1965, 1967) and Johns (1969) have recently shown that Wilson's Phalarope (Steganopus tricolor) is probably monogamous though it may be promiscuous. After reviewing the literature on the other two phalaropes, HShn (1967) con- cludes that no real evidence of their polyandry exists. True polyandry, defined here as one female being mated simultaneously or having simultaneous pair bonds with more than one male, is difficult to distinguish from promiscuity and successive polyandry. When polyandry is suspected, it must be verified in the field with individually marked birds. The purpose of this paper is to document polyandry and certain related phenomena in the American Jaana.. To our knowledge there are no previ- ous accounts of polyandry based on the study o.f a marked population of birds. Both authors are currently working on other aspects of the biology of the American Jagana (population dynamics and food habits, Collier; and behavior and social organization, Jenni).