SOCIAL INTERACTIONS IN FLOCKS OF COURTING WILSONS’ PHALAROPES (PHALAROPUS TRICOLOR) MARSHALL A. HOWE1 Department of Zoology University of Minnesota Minneapolis, Minnesota 55455 A remarkable diversity of mating systems and earlier investigations into the breeding biology related social behavior patterns is found in of Wilsons’ Phalarope, most notably those of the sandpiper family Scolopacidae (including Hiihn (1967) and Johns (1969). Names of the Phalaropodinae, after Jehl, 1968). Mating taxa follow the classification of Jehl (1968). systems range from territorial monogamy in the Willet (Cataptrophorus semipalmatus) THE STUDY AREA AND METHODS (Vogt 1938), possible polygyny in the Pec- This study was conducted near Woodworth, Stutsman toral Sandpiper (Calidris melanotos) (Pitelka County, North Dakota, during April, May, and June 1959), polyandry in the Northern Phalarope 1969 and 1970. Woodworth is situated east of the Missouri River near the eastern border of a moraine (Phalaropus lob&us) (Raner 1972; Hilden known as the Coteau du Missouri. The vegetation of and Vuolanto 1972) to lek promiscuity in the the area consists of native and introduced grasses and Ruff (Philomachus pugnax) (Hogan-War- forbs characteristic of North American mixed-grass burg 1966). In such species as the Pectoral prairie. Pea spp, are the dominant grasses, especially Sandpiper (Pitelka 1959) and the White- in areas where grazing is frequent. Most of the region, including the main study site, is either grazed or un- rumped Sandpiper ( CaZidris fuscicollis) (Par- der cultivation. melee et al. 1968), males play the active role Potholes of various sizes are numerous but many are in courtship and only females incubate, temporary, spring snow melt being a major factor de- whereas the reverse is true in the phalaropes termining the abundance and depths of water areas in any given year. Most potholes are less than 35 ha, (Tinbergen 1935; Hijhn 1967; Bengtson but a few larger lakes up to 1000 ha or more are pres- 1968). Between these extremes, other species ent. Salinities vary greatly. Some potholes contain exhibit varying degrees of role-sharing by the fresh water with either cattails (Typha spp.) or sedges sexes. The strategy of pair formation in a given (Curer spp.) as the dominant emergent plants; others species probably represents a series of adapta- are highly alkaline with salt-encrusted shorelines and with bulrushes ( S&pus spp. ) predominating. Many tions to a set of social and environmental con- shallow notholes become comnletelv choked bv sedges ditions. Holmes and Pitelka (1966) have pre- in late i4ay and June. Stewart add Kantrud- ( 1971) sented an ecological classification of social have prepared a detailed classification of pothole systems in calidridine sandpipers based upon types in this region of North Dakota. The local area where most of my observations were the relative conservatism or opportunism in made included several shallow, freshwater potholes the manner of environmental exploitation. and one hinhlv alkaline oond about 800 m long and Their classification attempts to explain in par- 80 m wider This pond was the center of activity for ticular the adaptiveness of spacing patterns of most of the phalarope behavior described in this paper. individuals during pair formation and the re- All observations were made from an automobile or sulting monogamous, polygamous, or promis- portable blind. Rapid behavioral sequences were cuous mating system. documented verbally on tape. Durations of behav- In this paper the social phases of early pair ioral events were measured with a stopwatch. Phala- formation in Wilsons’ Phalarope (Phalaropus ropes were captured with horizontal drop-mist-nets slightly modified after the design of Johns ( 1963). tricolor) are examined in some detail with a The traps were placed over the water along shorelines view to interpreting the adaptiveness of the and operated manually from a distance of about 100 social behavior patterns exhibited. No attempt ft whenever phalaropes waded or swam beneath. Cap- will be made at this stage to explain the re- tured birds were banded with aluminum leg bands provided by the U.S. Fish and Wildlife Service and versal of sex roles, for which this species and marked for individual recognition with colored leg its congeners are well known (Bent 1927). bands and paint or dye on various parts of the plum- A later paper will deal with the interactions age. of the sexes during the subsequent period of avoidance of conspecifics, during which time RESULTS the pair bond is completed and nesting ini- COMPOSITION AND GENERAL BEHAVIOR OF tiated. This study follows and supplements SPRING FLOCKS 1 Present address: National Fish and Wildlife Laboratory, The asynchrony of the migratory periods of U.S. Fish and Wildlife Service National Museum of Natural Histay, Washington, DC. 20&O. male and female Wilsons’ Phalaropes has been 1241 The Condor 77:2433, 1975 SOCIAL INTERACTIONS IN COURTING WILSONS’ PHALAROPES 25 TABLE 1. Daily totals for each sex in spring flocks slightly downward. The back and crown (1968). feathers are often elevated, giving the bird a ruffled appearance. The form varies only Number slightly but since the duration is highly vari- Date Females Males able, it cannot be considered ritualized in its 30 April 1 9 entirety. Hiihn (1971) has called this the 2 May 0 150 Head Retraction threat position and I will 3 May 1 46 refer to it as HRT. HRT by itself is often ef- 6 May 3 37 9 May 8 16 fective in supplanting other females, particu- 15 May 13 13 larly if the defending female swims toward 17 May 13 19 another while assuming this posture. 19 May 27 30 If HRT does not succeed in repelling a sub- ordinate female, the defender may lunge to- ward her without taking flight. Hiihn (1967) well documented (Bent 1927; Oring and Davis has termed this posture with the neck ex- 1966; Hijhn 1967; Johns 1969). The female tended horizontally the Head-Forward pose. abundance peak precedes that of males during It may occur on land or on water and is ac- both northward and southward migrations. companied by running or swimming move- The records I obtained for spring birds in cen- ments. Since it is clearly a threatening action, tral North Dakota conform to the usual pattern I prefer to call it Head-Forward Threat (HFT). (Table 1). During spring migration the birds In terms of the amount of energy expended, are highly gregarious, often with the birds 1 HFT must be considered a higher intensity m or less apart, and both sexes mix freely. So- threat than HRT, which precedes it in a11 cial facilitation is strong during such activities cases. Typically, HFT is given only when the as feeding, bathing, and preening. Although subordinate female, after failing to respond to most feeding occurs while the birds are swim- HRT, approaches within about 1 and 1.5 m of ming in open water, exceptionally cold wea- the defender. Both HRT and HFT are illus- ther may necessitate shoreline feeding, in trated by Hiihn ( 1967:225). which case small, stationary territories are de- Failure of a subordinate female to retreat fended against conspecifics of either sex. Ex- from HFT usually causes the defender to fly cept in these shore-feeding situations, aggres- directly toward her. Although Hiihn (1967) sive interactions related to feeding occur only did not assign a name to this behavior, it com- rarely. prises part of a ritualized sequence involving AGONISTIC BEHAVIOR both birds and should be considered a high- intensity threat display. I will refer to it as Courtship behavior is common in spring flocks Flying Threat ( FT) . As soon as the defending and two lines of evidence indicate that mi- female initiates FT, the threatened bird takes grants as well as local residents are involved: flight directly away from her. The pursuer (1) courting Wilsons’ Phalaropes are seen in flies after the other several feet, banks areas where they are not known to breed; and abruptly, and alights on the water; the pur- (2) courting groups larger than the local breed- sued bird immediately banks in the same di- ing population are seen in some breeding Io- rection and also alights. Several nearly identi- calities. The most conspicuous feature of these cal sequences of this sort may occur in rapid groups is aggression among females in the succession, Often FTs’ follow directly from presence of a male. In the context of pair for- HRTs’ and some females may perform FT mation, therefore, hostile interactions among from a distance of up to 7 m. females are a regular occurrence. Occasionally, an intruding female will not Instances of female aggressive behavior in react to FT and an overt attack results, in spring groups of Wilsons’ PhaIaropes have which the defending female lands on the been described in part by HGhn ( 1967), Johns others’ back and pecks at the back of the head (1969), and others. One female selects a male as described by Johns (1969). The attacked and defends his mobile position against other bird often responds with a similar attack and femaIes which swim to within about 3 m or the two may alternate positions for as long as otherwise indicate attraction to the male. The several minutes before one finally supplants defending female usually orients herself away the other. More often, however, the bird be- from or oblique to the male at a distance of neath tolerates the attack for a short period of about 1 m or less and, at the approach of an- time, with the neck extended vertically, and other female, adopts a threat posture, with the then flies away. neck retracted and bill directed forward or Most aggression observed in courting flocks 26 MARSHALL A. HOWE tively difficult to observe. Arbitrary “intensity values” (after Recher and Recher 1969) re- flecting relative amounts of time and energy expended were assigned to each parameter (HFT=l, FT=2, overt attack = 3).