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). Using these values, average scores per aggressive act were calculated for each category of birds. Observations were continued throughout the period of social courtship. The results are presented in table 2 and figure 1. Since observations were made only on actively courting birds, the totals do not reflect accurately the amount of aggression per unit time. However, the relative totals, expressed as a percentage of the total for all birds, provide a measure of the distribution of FIGURE 1. Relative frequencies of Head-Forward aggressive activity among the participants. Threats, Flying Threats, and Overt Attacks in court- The high value for defending females (78.1%) ing Wilsons’ Phalaropes. indicates that these females do not act only in response to aggression by subordinate females. is among females but males occasionally ex- They evidently must direct frequent threats hibit aggression toward females (Hiihn 1967). toward any nearby female in order to estab- The threat and attack postures used by males lish and maintain a dominant position. If any are identical to those described for females. stimuli other than proximity alone (except Aggression by an unpaired male may be possibly orientation toward the male) are elicited by any female that approaches within necessary to elicit threat from a defending fe- 2 or 3 ft, especially if she faces him. A female male, it is not apparent. Perhaps vocalizations involved in hostile encounters with other fe- or subtle posture changes play a role. The males is particularly prone to male attack. A need for relatively high aggressive levels in female epigamic display, Chugging, frequently defending females is probably related in part elicits aggression from unpaired males (in 17 to the mobile and social nature of the courting of 45 cases observed) but is not a necessary process, which inevitably leads to encounters stimulus. Among paired birds, agonistic re- with strange females. sponse to Chugging is less common and the The very low percentage of total aggression display is often incorporated into a precopula- attributable to subordinate females (4.4%) tory sequence. Chugging is described in de- does not necessarily imply a correspondingly tail below. low aggressive tendency. More likely it re- In order to better describe interactions and flects the inhibiting effect of threats by the to clarify roles of males and females, aggres- female in the dominant position. Although sive behavior during active periods of court- they were not quantified, even HRTs’ by the ship was quantified. Whenever groups of defending female often cause a nearby subor- birds were found courting, they were ob- dinate to withdraw. Only rarely will a subor- served as long as possible and the total num- dinate female spontaneously threaten a domi- ber of HFTs,’ FTs,’ and overt attacks by each nant one. Most threats by the former are participating bird (one male, one defending retaliatory. female, and several subordinate females col- Males are intermediately aggressive be- lectively considered as one) recorded. HRTs’ tween defending and subordinate females, ac- were not quantified because they were rela- counting for 17.5% of the total aggression

TABLE 2. Aggressive behavior during social courtship (observation time = 429 min).

Total no. of 70 IIf total Total intensity Mean intensity per aggressive acts for all birds score” aggressive act

Defending Female 304 78.1 511 1.68 Subordinate Females 17 4.4 2.24 Males 68 17.5 z 1.28

Totals 389 100.0 636 1.63

a Scores were assigned to behavior patterns as follows: Head-Forward Threat = 1, Flying Threat = 2, Overt Attack = 3. (See text for explanation and fig. 1 for breakdown of aggressive acts. ) SOCIAL INTERACTIONS IN COURTING WILSONS’ PHALAROPES 27 quantified from courting groups. This rela- tively low figure, when compared with the 78.1% for defending females, may be attribut- able in part to the lower levels of testosterone in males than in females (Hiihn and Cheng a. 1967). The relationship between testosterone levels and aggressiveness has long been real- ized (Co&as 1950). But, since males of this species are the objects of competition among females instead of being the competitors them- selves, one should naturally expect relatively fewer agonistic encounters involving males during the period of courtship. The role of a bird in a courting party deter- mines not only the frequency with which ag- gression is expressed but also the types of threat utilized. This is illustrated by figure 1 and the “average intensity” scores in table 2. FIGURE 2. Displays of courting female Wilsons’ The occurrence of overt attacks is relatively Phalaropes. a. Wu vocalization, standing. b. Wa low for all birds. The greatest differences be- vocalization in flight. c. Chug (broken line indicates normal neck position). d. Loon Flight. tween defending females, subordinate females, and males are found in the frequencies of HFTs.’ No HFTs’ were recorded for subordi- The most frequently heard call is a short, nate females, whereas they occurred with a nasal Emt, the basic call from which most frequency of 38% in defending females and other phalarope calls appear to be derived. 75% in males. It is largely this disparity that Ernts are used by both sexes and often seem accounts for the differences in average inten- to function as contact signals in a wide variety sity scores. of contexts. During social courtship, however, Differential usage of HFTs’ by different they are given primarily by females and the birds probably represents differences in threat rate of delivery increases in direct proportion effectiveness rather than in aggressive motiva- to the intensity of aggressive behavior. Cer- tion. Each bird seems to maximize threatening tain vocalizations and motor patterns of males efficiency by using the simplest threat which can also stimulate females to produce a burst can supplant the target bird. A defending fe- of Ernt calls (see below). Because several fe- male can frequently supplant another with a males are usually involved in these situations, simple HFT. This has the further advantage I have not been able to determine whether de- allowing her to remain close to the male. Sub- fending females or subordinate females give ordinate females, however, are probably un- most of the calls. It is also not clear whether able to supplant with HFTs.’ For these fe- they are given in a definable pattern by indi- males higher-intensity threats or attacks, viduals. Until a more specific function can though used sparingly, have a greater likeli- be attributed to this call in a courtship situ- hood of supplanting the defender and also ation, I prefer to apply the general term, Con- bring them closer to the male. Males rarely tact Emt, to it in all situations. need to resort to FTs’ or overt attacks since Less frequently heard is the Wa call of fe- they are dominant in such situations and easily males (after Hiihn 1967). This is a relatively supplant any females with HFTs.’ loud, hollow-sounding call given singly or sev- eral times in succession. It is normally used to THE ROLE OF VOCAL COMMUNICATION communicate over distances longer than 15 ft. Vocal behavior is not as conspicuous in this Often a female uses it in flight before landing species as in more territorial shorebirds which in a group of courting birds. Its occasional use perform aerial displays. The tendency for prior to copulation in paired birds suggests Wilsons’ Phalaropes to be gregarious during that its function may be epigamic, but I have early pair formation minimizes the need for not observed any overt male response to it loud, complex vocal signals, but vocalizations The postures geared toward short-range communication during early pair formation. play an important role. In this paper I will adopted as the Wa call is given are distinctive only attempt to describe briefly some of the and are illustrated in figure 2 a and b. calls associated with this stage of the breeding A third important vocalization, used fre- cycle and suggest possible functions. quently by defending females, is the Purr, a 28 MARSHALL A. HOWE low-frequency, guttural call audible only at monly. These flights are usually associated very close range. The Purr is probably identi- temporally with aquatic social courtship and cal to the pittera pittera call described by involve many of the same vocalizations and Johns (1969). It is given in the HRT posture, displays. Although I was unable to mark many often immediately following a FT to another birds participating in aerial chases, marked female. The fact that the Purr is also used be- birds known to be paired were almost never tween members of a pair after a bond is observed to take part. This evidence suggests formed suggests that it may function as a that most participants in aerial chases are un- means of inhibiting male aggression, either paired and the activity is related to pair for- when the female is actively threatening other mation. birds or when she is in violation of the individ- Hijhn (1967) noted that aerial chases in ual distance requirement of a male. Wilsons’ Phalarope are nearly always initiated The Chug is used by females and directed by males taking flight. My observations sup- toward males at close range. It is visually and port this. Only 5 of over 300 chases that I ob- vocally distinct and there appears to be no served were initiated by females and each of male homologue. When performing this dis- these was the second, third, or fourth in a se- play, the female swims within several feet of ries of short chases, the first of which was ini- the male, expands the neck feathers, and ex- tiated by the male. The active role of the male tends the neck vertically with the bill directed extends beyond the initiation of a chase, how- forward (fig. 2~). A low-amplitude, frog-like ever. After a flight has begun, males often vocalization, quite unlike any other call of the swoop down over swimming females, causing repertoire, is repeated several times. She may them to fly up and join the chase. Although face the male or swim parallel to or ahead of no quantitative data were collected on this him. The form of the display suggests homol- behavior, its frequency was great enough to ogy with the imposing posture of Red Phal- indicate that swoops are directed at females aropes (Phalaropus fulicarius) and Northern rather than occurring near females by chance Phalaropes (Hiihn 1971). Chugs are often alone. The result is a larger group of courting performed in the absence of other females but females and presumably a corresponding in- may also be given by individuals in groups. crease in competition among them. The aggressive reaction of males to Chugs dur- A further indication that the males’ role in ing social courtship has already been men- aerial chases is that of a leader rather than the tioned. Since this display may also occur in object of a pursuit is the tendency to hover precopulatory situations, it seems to be related occasionally in one spot, with wing-beats directly to the formation of the pair bond. above the horizontal and legs dangling. Hov- The only prominent male vocalization dur- ering usually takes place less than 20 ft above ing this stage of pair formation is a rapid se- the ground or water and normally lasts less ries of Ernt calls given in the HRT posture. than 5 sec. Females hover around a hovering The male swims away from the defending fe- male and often one swoops at another from male as the call is given and sometimes takes above, sometimes making bill contact on the flight, initiating an aerial chase (see below). nape region of the bird beneath. These ag- This call, termed the Courtship Ernt because gressive interactions might result at times in of the context in which it occurs, seems to in- the defending female being supplanted, al- duce females to give Contact Ernts and also though I have been unable to document any provokes inter-female aggression. During ac- such case. Hovering males almost always give tive agonistic sequences, the tempo of the in- Courtship Ernts, the same call which provokes dividual notes of the Courtship Ernt increases inter-female aggression on the water. noticeably and the total duration of the call One other behavior pattern of males in aerial may be prolonged. The Courtship Ernt and chases is a fluttering of wings below the hori- behavior patterns accompanying it are the only zontal through a very narrow arc. This mainly suggestions of an incitive male role in aquatic occurs shortly before landing. Fluttering was social courtship. first described by Hahn (1967), who sug- gested a homology with Rattling (Tinbergen AERIAL CHASES 1935) in Northern Phalaropes, a precopulatory Aerial activities also play an important pair- display in which rapid fluttering of the wings formation role. As soon as males arrive in the produces easily audible noise. In Rattling, spring, short flights consisting of a male being however, the wing-beats are above the hori- pursued by several females take place. Later zontal. The function of fluttering is not clear. in the season, longer flights of several minutes Two displays are given by females during reaching altitudes of 500 ft or more occur com- aerial chases. One is the Wa call given with SOCIAL INTERACTIONS IN COURTING WILSON’S PHALAROPES 29

TABLE 3. Duration of aerial chases.

Meall duration Time period k,“,’ (=c) SD. A. 29 Apr.-8 May 23 14.4” 16.5 B. 9 May-18 May 19 38.7 34.0 C. 19 May-28 May 50 28.4 25.9 D. 29 May-7 June 17 26.7 19.3 Totals 10gb 27.0 24.3 * Significantly shorter than means from periods B, C, OI D (PSanderling (Calidris &a) aerial chases. In mechanism for spacing pairs must also be con- this paper I have shown that in Wilsons’ Phal- sidered. This potential function of aerial arope, a species in which females chase males, chases has been most intensively studied in chases are initiated by the male, who plays an the Anatidae. Smith (1968) drew a functional active role in determining their course, dura- distinction between the courtship chases of tion, and the number of females participating. Pintails (see above) and chases initiated by Crook (1962) felt that aerial chases in Plo- paired males during the pre-egg-laying and ceid weavers promote maturation of the neuro- egg-laying stages. The latter type of chase ap- endocrine mechanism controlling sexual ten- pears to be an attempt on the part of a paired dencies, particularly in females. Others male to drive away strange pairs flying over- studying aerial chases have come to similar head, the net result being a dispersion of pairs. conclusions (Tinbergen 1939; Summers-Smith This interpretation has been made for a wide 1963). Phillips and van Tienhoven (1962) variety of waterfowl (Hochbaum 1944; Sowls showed that Pintail females collected from 1955; Dzubin 1955; McKinney 1965). aerial chases arising from spring flocks had The evidence for a spacing function in Wil- only partially developed ovaries; therefore sons’ Phalarope, however, is weak. Chases in- they concluded that these flights are probably volving paired phalaropes rarely occur. Four associated with pair formation. No data were marked, paired females were observed care- available to show that ovary size increased fully prior to and during the egg-laying period through the period of aerial chasing, although and none was ever seen to join chases, even SOCIAL INTERACTIONS IN COURTING WILSON’S PHALAROPES 31 when chases passed directly overhead. Several (Tryngites subruficollis) exhibits a form of times, however, paired males initiated chases lek behavior in which the territories are larger with strange females. But in each case the than those of the above species and the loca- chase was very short and circular and did not tion of the lek itself may vary (Parmelee et al. result in females being led away from the nest 1967). This species is apparently promiscuous area. If aerial chases by Wilsons’ Phalarope (R. T. Holmes, pers. comm.). Another cali- function in part as a spacing mechanism, it is dridine, the Pectoral Sandpiper, may not es- most likely a passive process in that the male tablish pair bonds and the male territories are flies until only he and one female remain and apparently relatively static and probably too then both land in an area where no conspe- large to be considered part of a lek system cifics are present. There is some evidence for (Pitelka 1959). The Ruddy Turnstone (Are- male territorial defense unrelated to aerial nariu interpres) under certain circumstances chases, but this occurs later during the period may perform apparent courtship behavior in of nest-building (Howe 1972). nonterritorial, social aggregations with males displaying before females (Parmelee and Mac- ADAPTIVENESS OF SOCIAL PAIRING Donald 1960). Except for the reversal of sex The early stages of pair formation in Wilsons’ roles, this feature superficially resembles the Phalarope involve intense social competition social and mobile pattern of Wilsons’ Phal- in mixed-sex flocks on the water and in aerial arope more than the pairing behavior of any sexual chases. Competition for potential mates of the scolopacids. Of the species mentioned takes place among females, which are larger, above, the Pectoral Sandpiper (Pitelka 1959) more colorful, and much more aggressive than and the Ruddy Turnstone (Bergman 1946) males. Males, however, play an active role perform aerial chases (males pursuing a fe- by initiating and determining the course and male) at some point during the breeding cycle. duration of aerial chases. Males also make The formation of pairs through group inter- use of vocal signals which stimulate agonistic action in Wilsons’ Phalarope probably results interactions among females. The display rep- from certain selective advantages conferred ertoire of the species is small and the vocal- upon individuals which form flocks. All spe- izations are geared toward short-range com- cies of phalaropes are highly social during mi- munication. Territorial behavior at this stage gration and winter, and to a lesser extent of pairing is restricted to defense by a female during the nesting season. Moynihan (1962) of a small area surrounding a mobile male; the postulated that one function of feeding in elaborate aerial displays characteristic of most flocks is that flock members benefit from shorebird species which maintain pairing ter- food organisms flushed by other members. ritories are absent. All of these factors in com- Observations of Wilsons’ Phalarope by Sieg- bination constitute a strategy of pair forma- fried and Batt (1972) suggest that larger flocks tion which makes Wilsons’ Phalarope, and may facilitate food procurement, presumably possibly the Northern and Red Phalaropes, because larger quantities of prey items are unique among the Scolopacidae. Even dis- stirred up to within reach of the birds. Fur- counting the reversal of sex roles, which is ther observations by Siegfried and Batt (1972) more highly developed in the phalaropes than and also Williams (1953) suggest that similar in any other scolopacid, the pattern of estab- enhancement of feeding may be derived from lishing a pair bond through aggressive inter- commensal association with other aquatic spe- action and sexual display in tight social aggre- cies, specifically the Northern Shoveler (Anus gations is a significant departure from the clypeutu) and American Avocet (Recuruiros- usual pattern of advertisement within terri- tru americana), respectively. If this advantage tories established and defended by one sex. of flock-feeding persists into the first part of The few other scolopacids which have social May when much of early pair formation takes pairing systems exhibit certain basic differ- place, it could constitute a strong selective ences from the phalaropes. The true lek spe- pressure for a group-oriented pairing system. cies such as the Ruff (Hogan-Warburg 1966) It is also possible that Wilsons’ Phalaropes and the Great Snipe ( GaZZinugo media) (Fer- favor larger bodies of alkaline water, which dinand 1966) differ in that the display grounds support a more abundant invertebrate fauna and individual territories within them are than small bodies of fresh water. Censuses static and no prolonged pair bond develops of breeding birds in North Dakota by Robert as a result of interactions of the sexes. Wil- E. Stewart (pers. comm.) indicate a positive sons’ Phalaropes form a bond which continues correlation between the distribution of phal- through the egg-laying period (Hahn 1967; aropes and the distribution of alkaline sloughs. Howe 1972). The Buff-breasted Sandpiper My own local observations suggest a similar 32 MARSHALL A. HOWE relationship : areas near alkaline sloughs har- fied for males, defending females, and subor- bor larger breeding populations of phalaropes dinate females. The differences among them and the slough serves as the primary feeding in total aggression and relative use of differ- place. While this relationship may effect a ent aggressive displays are interpreted in terms clumped distribution of phalaropes, however, of motivation levels and dominance relation- it does not by itself account for a need for ships. A female display given to males at close maintaining tight groupings. range, Chugging, is described. Chugging is By exploiting an exposed feeding niche with the only display given exclusively by females. little potential for concealment, Wilsons’ Phal- Aerial chase behavior is described in detail. aropes risk direct exposure to avian predation. Behavioral data from marked birds and from Particularly in spring, when alternate plumage a frequency distribution of aerial chases is worn, birds on the open water can be highly through the period of courtship indicate that conspicuous. Lone birds must be especially predominantly unpaired birds participate. The vulnerable. Selection should favor the evolu- chases probably serve to ensure synchroniza- tion of a social tendency as a defense against tion of the sexual cycles of potential pair mem- the potential hazard of predation under these bers and do not have a significant effect on the conditions. Although I have not witnessed en- spacing of pairs. Vocalizations used in all so- counters between Wilsons’ Phalaropes and cial courtship activities are described briefly. avian predators, I have seen a flock of North- Possible selective pressures leading to the evo- ern Phalaropes respond to a flying Marsh lution of a social pairing system are discussed. Hawk (Circus cyuneus) by circling it rapidly and erratically as a highly compact unit in a ACKNOWLEDGMENTS single plane. From a distance this flock at This paper is based on part of a dissertation submitted times banked in such a way as to reflect sud- in partial fulfillment of the requirements for the de- den flashes of sunlight, giving it the appear- gree of Doctor of Philosophy from the University of ance of a miniature flying saucer. Such a Minnesota. I am esoeciallv grateful to D. Frank Mc- Kinney for advice and guidance throughout the course highly coordinated response suggests that of the study. H. Nelson and L. Kirsch kindly pro- there has been strong selective pressure for a vided housing, laboratory facilities, and logistical social reaction to avian predators. While this support at the Woodworth Station of the Northern mobbing reaction may be only a consequence Prairie Wildlife Research Center, U.S. Fish and Wild- life Service. I am indebted to J. Burger and R. T. of a flocking tendency, its effectiveness over Holmes for criticallv reading an earlier draft of this individual anti-predator responses may have manuscript and providing numerous valuable sug- been a significant force in the evolution of gestions. J. Cutler prepared the figures and illustra- phalarope sociality. tions. Financial support was received through an NDEA predoctoral fellowship, grants from the So- Thus flocking, both as an adaptation for in- ciety of the Sigma Xi and the Frank M. Chapman creasing feeding efficiency and as a predation- Memorial Fund of the American Museum of Natural inhibiting mechanism, provides a social sub- History, and NIH Training Grant 5 TO1 GM01779 strate from which social pair formation can from the National Institute of General Medical Sci- evolve. Though proof for these adaptations ences. is wanting, both seem plausible for a species LITERATURE CITED feeding on surface and subsurface inverte- brates in an exposed, aquatic environment. ARMSTRONG, E. A. 1955. The wren. Collins, Lon- Other functions of flocking, such as facilita- don. 312 p. BENCTSON, S. 1968. Breeding behaviour of the tion of mate attraction (Collias and Collias Grey Phalarope in west Spitsbergen. Var FBgel- 1969), are also possible for Wilsons’ Phala- varld 27: 1-13. rope but supporting evidence is not available. BENT, A. C. 1927. Life histories of North American shorebirds. Vol. 1. U.S. Natl. Mus. Bull. 142:1- 420. ’ SUMMARY BERGMAN, G. 1946. Der Steinwalzer, Armaria i. in- The social behavior patterns of early pair for- terpres ( L. ), in seiner Beziehung zur Umwelt. mation in Wilsons’ Phalarope are examined. Acta Zool. Fennica 47:1-151. COLLIAS, N. E. 1950. Hormones and behavior with Courtship is initiated within groups of birds special reference to birds and the mechanisms of swimming in open-water situations during hormone action, p. 277-329. In E. S. Gordon spring migration, Three main features dis- [ed.], A symposium on steroid hormones. Univ. of Wisconsin Press, Madison. tinguish courting groups from feeding groups: COLLIAS, N. E., AND E. C. COLLIAS. 1969. Size of aggression among females in the presence of a breeding colony related to attraction of mates in male; female sexual display to a male; and a tropical passerine bird. Ecology 50:481488. CROOK, J. H. 1962. The adaptive significance of aerial chases in which females pursue a male. pair- formation types in weaver birds. Symp. Aggressive disnlavs are described and quanti- Zool. Sot. Lund. 8:57-70. SOCIAL INTERACTIONS IN COURTING WILSONS’ PHALAROPES 33

DZUBIN, A. 1955. Some evidences of home range PAR~~ELEE, D. F., ANI) S. D. MACDONALD. 1960. in waterfowl. Trans. 20th N. Amer. Wildl. Conf., The birds of west-central Ellesmere Island and p. 278-298. adjacent areas. Natl. Mus. Canada Bull. 169:1- FERDINAND, L. 19686. Display of the Great Snipe 103. ( Gallinago me&a Latham). Dansk Omithol. PARILIELEE. D. F.. H. A. STEPHENS, AND R. H. Foren. Tids. 60: 14-34. SCK&DT. 1967. The birds of southeastern HILDEN, 0. AND S. VUOLANTO. 1972. Breeding biol- Victoria Island and adiacent small islands. Natl. ogy of the Red-necked Phalarope PhaZaro& Zo- Mus. Canada Bull. 22231-229. batus in Finland. Ornis Fenn. 49:57-85. PAR~~ELEE, D. F., D. W. CREIRTER,AND W. D. GRAUL. HOCHBAU~\I, H. A. 1944. The Canvasback on a 1968. Summer schedule and breeding biology prairie marsh. Amer. Wildl. Inst., Washington, of the White-rumped Sandpiper in the Central D.C. 207 p. Canadian Arctic. Wilson Bull. 80:5-29. HOGAN-WARBU~G, A. J. 1966. Social behavior of PITEL~A, F. A. 1959. Numbers, breeding schedule the Ruff, Philomachus pugnar (L.). Ardea 54: and territoriality in Pectoral Sandpipers of north- 109-229. ern Alaska. Condor 61:233-264. Hijrrx, E. 0. 1967. Observations on the breeding PHILLIPS, R. E., AND A. VAN TIENHOVEN. 1962. biology of Wilsons’ Phalarope (Steganopus tri- Some physiological correlates of Pintail repro- color) in central Alberta. Auk 84:220-244. ductive behavior. Condor 64:291-299. N~HN, E. 0. 1971. Observations on the breeding RANER, L. 1972. Forekommer polyandri hos smal- behaviour of Grey and Red-necked Phalaropes. nabbad simsnappa (Phalaropus lob&us) och Ibis 113:335348. svartsnappa ( Tringa err&opus)? Fauna och HSHN, E. O., AND S. C. CHENG. 1967. Gonadal Flora. no. 3: 135-138. hormones in Wilsons’ Phalarope ( Stegunopus tri- color) and certain other birds in relation to plum- RECHER, H. F., A;\TUJ. A. RECHER. 1969. Some as- age and sex behaviour. Gen. Comp. Endo- pects of the ecology of migrant shorebirds. II. crinol. 8: 1-11. Aggression. Wilson Bull. 81: 140-154. HOL;\IES, R. T., AND F. A. PITELKA. 1966. Ecology SIEGFRIED, W. R., AND B. D. J. BATT. 1972. Wil- and evolution of sandpiper (Calidritinae) social sons’ Phalaropes forming feeding association with systems. Proc. Int. Ornithol. Congr. XIV (ab- Shovelers. Auk 89:667-668. stract), p. 70. S~IITH, R. I. 1968. The social aspects of reproduc- HOWE, M. A. 1972. Pair bond formation and main- tive behavior in the Pintail. Auk 85:381-396. tenance in Wilsons’ Phalarope, Phalaropus tri- SOWLS, L. K. 1955. Prairie ducks. Wildl. Manage- color. Unnubl. Ph.D. thesis. 169 D. ment Inst., Washington, D.C. 193 p. JEHL, J. R., Jk. 1968. Relationships-in the Cha- STEWART, R. E., AND H. A. KANTRUD. 1971. Classi- radrii ( shorebirds ) : a taxonomic study based on fication of natural ponds and lakes in the glaci- color patterns of the downy young. San Diego ated prairie region. U.S. Bur. Spt. Fish & Wildl. Sot. Nat. Hist. Memoir 3:154. Res. Publ. 92, p. l-57. JOHNS, J. E. 1963. A new method of capture uti- SU~Z~IERS-SMITH, D. 1963. The House Sparrow. lizing the mist net. Bird-Banding 34:209-213. Collins, London. 269 p. JOHNS, J. E. 1969. Field studies of Wilsons’ Phal- TINHERGEN, N. 1935. Field observations of east arope. Auk 86:66&670. Greenland birds. I. The behaviour of the Red- MCKINNEY, F. 1965. Spacing and chasing in breed- necked Phalaroue (Phalarovus Zobatus L.) in ing ducks. Wildfowl Trust 16th Ann. Rept., p. spring. Ardea 24:1>2. ’ 92-106. TINBERGEN, N. 1939. The behavior of the Snow MOYNIHAN, M. 1962. The organization and prob- Bunting in spring. Trans. Linnaean Sot. New able evolution of some mixed species flocks of York 5: l-94. neotropical birds. Smithsonian Misc. Coll. VOoT, W. 1938. Preliminary notes on the behavior 143(7):1-140. and ecology of the eastern Willet. Proc. Lin- ORING. L. W.. AND W. M. DAVIS. 1966. Shorebird naean Sot. New York 49:8-42. migration at Norman, Oklahoma: 1961-1963. Wilson Bull. 78: 166174. WILLIA%f S , G. C. 1953. Wilsons’ Phalaropes as PARMELEE, D. F. 1970. Breeding behavior of the commensals. Condor 55: 158. Sanderling in the Canadian high Arctic. Living Bird 9:97-146. Accepted for publication 14 September 1973.