Social Interactions in Flocks of Courting Wilson's Phalaropes (Phalaropus tricolor)

Abstract

A remarkable diversity of mating systems and related social behavior patterns is found in the sandpiper family Scolopacidae (including the Phalaropodinae, after Jehl, 1968). Mating systems range from territorial monogamy in the Willet (Cataptrophorus semipalmatus) (Vogt 1938), possible polygyny in the Pectoral Sandpiper (Calidris melanotos) (Pitelka 1959), polyandry in the Northern Phalarope (Phalaropus lobatus) (Raner 1972; Hilden and Vuolanto 1972) to lek promiscuity in the Ruff (Philomachus pugnax) (Hogan-Warburg 1966). In such species as the Pectoral Sandpiper (Pitelka 1959) and the Whiterumped Sandpiper (Calidris fuscicollis) (Parmelee et al. 1968), males play the active role in courtship and only females incubate, whereas the reverse is true in the phalaropes (Tinbergen 1935; H6hn 1967; Bengtson 1968). Between these extremes, other species exhibit varying degrees of role-sharing by the sexes. The strategy of pair formation in a given species probably represents a series of adaptations to a set of social and environmental conditions. Holmes and Pitelka (1966) have presented an ecological classification of social systems in calidridine sandpipers based upon the relative conservatism or opportunism in the manner of environmental exploitation. Their classification attempts to explain in particular the adaptiveness of spacing patterns of individuals during pair formation and the resulting monogamous, polygamous, or promiscuous mating system. In this paper the social phases of early pair formation in Wilson's Phalarope (Phalaropus tricolor) are examined in some detail with a view to interpreting the adaptiveness of the social behavior patterns exhibited. No attempt will be made at this stage to explain the reversal of sex roles, for which this species and its congeners are well known (Bent 1927). A later paper will deal with the interactions of the sexes during the subsequent period of avoidance of conspecifics, during which time the pair bond is completed and nesting initiated. This study follows and supplements earlier investigations into the breeding biology of W lson's Phalarope, most notably those of H6hn (1967) and Johns (1969). Names of taxa follow the classification of Jehl (1968).