5

Social Behavior and Pairing Chronologyof Mottled Ducks during Autumn andWinter in LouisianaStuart L. Paulus

Ah.\ITUcr: Pairing chronology. agonistic and courtship behaviors, dominance rela-tions. and spatia] interactions of mottled ducks (Anas fulvigulai were studied in thecoastal marshes of southwestern Louisiana during August through February19~W-X2. Courting and agonistic activities comprised less than 1% of the timebudget of mottled ducks. and time spent in these activities was similar (P> 0.05)among paired and unpaired males and females. Courtship was initiated in latesummer: by December. 90("( of females were paired. Immature mottled ducksbegan forming pairs at five months of age. Mottled ducks and mallards (Anasplatvrhvnchos) were obserx cd courting near each other in fall. However, ol1lyO.4%of mottled ducks were observed paired with mallards or ~k du~s iAnasrubripes i. Chasing. bill threats. and inciting were common agonistic activities, andmost agonistic act ivit y was observed in fall. Pairs were dominant to unpairedbirds. a~ pairs won 94C;i- (P < 0.00 1) of contests with unpaired birds. Mottled ducksusually were observed as solitary pairs or in sma!! groups of fewer than 10 birds:35c( of all observations were of lone birds. Mottled ducks primarily associatedwith members of similar pair status. This study suggests that courtship displaysmay be more important in forming bonds between immature than adult mottledducks. Early pair formation by mottled ducks may have minimized interspecificpairing between mottled ducks and mallards .

.-\~ part of a study on mottled duck t Anasfulvigulav behavior in Louisiana,speciaJ eff ort was directed towa rd a better understanding of the social activities ofmottled ducks during autumn and winter. Investigation of these activities is

WUINI"I\/Ill II·il1ll'f. ~ 19XX Univerviry of Minnesota. Edited by Milton W. Weller and published hyt he {'n:\(:r\lty or \,linnesola Prcs s .. Minneapolis.

59

00 P;\Ul.lJS

important for several reasons. First, although courtship displays and ralrlngchronology of captive mottled ducks were studied by Weeks (1969 l.Iiule is knownof these behaviors in wild mottled ducks. Second, Paulus (19~3) suggested thatpairing chronology might be related to foraging strategies in nonbrccding Anati-naco with those species feeding on poorer quality foods (such as leafy aquaticvegetation [Sugden 1973, Paulus 1982]) forming pairs earliest. H OWCH:r. mottledducks pair early (Weeks 1969) but consume high-quality foods (such as plant seedsand invertebrates [Guidry 1977, Bellrose 1978]). suggesting that factors other thanfood choice influence pairing chronology. Third. mottled d ticks associate withmallards (Anas platyrh ynchosi during winter, yet cross-pairing is uncommon(Weeks 1969) despite similarities in courtship displays and overlap or urne of pairformation. In some areas where mallards and black ducks (Anas rubripcsi wintertogether, interspecific pairing is common (Brodsky and Weatherhead 19~4).Fourth, little is known about the influence of sex and age on time or pairing inmottled ducks. Finally, the role of agonistic activities in influencing dominancerelations and resource acquisition of mottled ducks is poorly understood.

The objectives of this study were to examine pairing chroriologv and d isplav«.agonistic behaviors. dominance relations, and spatial interactions or mottledducks. These data were used to examine the role of social behaviors and relation-ships in influencing mottled duck pair formation and distribution.

I wish to thank K. Paulus, T. Joa ncn, L. McNcase. J. Kennamer. and M. K.Causey for their help during all phases of the project. I am grateful to D. Richardfor his assistance in capturing and marking mottled ducks. I appreciate the help o(G. Baldassarre, R. Mirarchi. G. Mullen. L. Wit. and M. Joanen for assistance inmanuscript preparation and M. Weller. F McKinney. G. Hcpp. and C. Sun /cn-baker for reviewing earlier drafts of the manuscript. Financial support was pro-vided by the Louisiana Department of Wildlife and Fisheries.

Study Area and Methods

. This study was conducted in coastal southwestern Louisiana. prirnaril , on Rocke-feller Wildlife Refuge and on privately owned lands within 35 krn of the rduge.Mottled ducks were observed on brackish. intermediate. and [rcsh wa tc r naturalmarshes and impoundments. The study area has been described in dcta il (l\llJilI,>

1982. 1984b).Data on social behavior and spatial relationships of llH)(tkJ d uck • were

collected concurrently with activity budget observations during :\UglI:-( throuuhFebruary. 1980-82. Observations were made wit l: a IS-40x :--potting :-CUrl:. >binoculars. and 2x nighiscopc. Activities of a focal individual ur pair \\erc rc-corded at 20-second intervals during one-hour periods ra ndornlv "L·lcctL·J duringthe day and at nonrandom periods at night. ;\11 courtxhip a nd int ru spccilic u nd

SOCIAL BEHAVIOR OF MOTTLED DUCKS Ir-.'WI;\TER hi

:::tr! 'rl·(.·ific aggressive behaviors involving focal individuals were recorded durinu,'~"('f \ .uiou periods. Most (93%) nocturnal observations occurred when the moon.••.1' hct wccn the first and last quarters. Noct-urnal observations were limited [0

!'I::d, within 30 m of the observer.W)lI:IH:\"erpossible, individually identifiable birds wearing nasal saddles labeled

.••Ith number-letter combinations (Greenwood 1977) were observed. Individuals·.~·rt"marked to provide information on age of pair formation. movements. pairt- •• od durability.and social interactions of mottled ducks, A total or716 immatureJod adult mottled ducks was marked during the study,

.'\~1:!rt.:ssiveencounters involving mottled ducks were divided into five catego-Ill": (I) Inciting , performed by females, involving a ra rid series of turns of the head"\l'r the shoulder with the beak usually pointed toward an intruder and accompa n-:(,1 h~' 'gagg' vocalizations (Johnsgard 1965): (2) Biting, one bird grabbing the,.tlln with its beak; (3) Chasing, one bird rushing another and forcing it [0 moveJ\\;I\: rapidly: (4) Bill threats, an open-bill display with the bill raised slightlyI:r\\;ml from horizontal and toward another bird: and (5) Fighting, tugging andhltlll!! or an opposing bird's breast and side feathers as well as wing-slapping and,h,l,ing, Subtle avoidance (in which one bird moved out of the path of anotherhlld:ls i[ approached) was observed but not included in the analysis because of the,lrlliL't1lty in detecting all occurrences of this behavior. Courtship displays ofmottled ducks. which have been described by Johnsgard (1965) and Weeks (1969).Inrludcd Head shake. Introductory shake. Grunt-whistle, Head-up-tail-up, Nod-." imming . Preen-behind-the-wing; Down-up. and Jump-flights. Copulatory andr,l\(l'optllatory displays included Head-pump. Bridling, Nod-swinuning . andlurn-bock-of-the-head, The species. sex, pair status. and activity of birds involved

111 -ocial interactions also were recorded,Before each observation period, the number. sex. and pair status of all mottled

duds in the area were recorded. Because of similarity of plumages. sex was.lvtcrtnincd from bill coloration (Stutzenbaker 1984) and social behaviors. Birdswere considered paired only if they mutually avoided or threatened other birds.-vnchronized their activities. and remained within 3 m of each other during most,t! (111':observation period (Paulus 1983),

During activity budget observations, thc distance between focal birds andIK'arI.:S(bird was subjectively estimated at three-minute intervals and the species.-vx. and pair status of the focal and nearest birds were recorded. From these data.Intraspecific and interspecific associations and spatial relationships were deter-mined. Frequencies of agonistic interactions and associations inv ol\'ing moulcdduds and sex ratios were evaluated via chi-square analysis of contingency tabks(SI1L'dccorand Cochran 1976,250), When chi-square analyses indicated rejection,1/ the hypothesis of independence. Goodman's (1964) simultaneous confidence-uucrval procedure was used to identify significant associations.

62 PAULUS

Results

Courting and Pair FormationCourting activities comprised less than 1% (N = 1.188 hours) of the time budget ofmottled ducks, with similar results for paired and unpaired males and females (P

> 0.05). Courtship was initiated in August, and the greatest level of courtingactivity was observed during October through December. Most courting oc-curred in early morning and late afternoon. although O.I~·(, of time was spentcourting at night.

The Introductoryshake(26%. N= 566), Grunt-whistle (22Yi). Head-up-tail-up(15%). Head shake (13%), Nod-swimming (13%). and Preen-behind-the-wing(8%) were displays observed most often in males. The Down-up display (I (';) andJump-nights (1%) were rarely' observed. Nod-swimming displays immediatelyIollowed other displays (23%). primarily the Head-up-rail-up (!-l6C;;), as well as theGrunt-whistle (6%) and Down-up (6%) displays. Male displays. especially theHead-up-tail-up. often were highly synchronized among two to four mules.

Courtship groups averaged 4.4 (range of .1-7) males and 2.2 (range of 1-7)females (N = 21). Courtship bouts involved only a few males and females at first.but they SOOI1 attracted other birds. Intensity of courting activity varied through-out the display period. Intervals of intense activity. with males courting orchasinga way nearby birds and females. Nod-swimming or Inciting. would be followed bylulls in which birds fed or spent time in other activities. Individ uals were observedleaving one courting group as courting activity waned and joining a nearby. moreactive courting group. During January and February, courting activities involvedonly two to three pairs and no unpaired birds (N = J). Courting acrivit ics lastedless than 3 minutes, and no mate-switching was observed.

Mallards were observed courting near mottled duck courtship groups in fall.Although mallard and mottled duck displavs and pairing chronology weresimilar, mallards and mottled ducks displayed to each ocher in onlv 2 of 21courtship groups.

Of 63 mottled duck copulations observed. 2 look place in September (S = 2:\ Ihours), 23 in October (N = 195 hours), II in November (N = 150 hours). 9 inDecember (N = 206 hours). IJ in January t N = 252 hours). and 5 in Fcbrua ry (S =155 hours). Precopulatory and cop ula lory displays co rn r riscd 5') .S"; of cuurtxh ipactivities of mottled ducks. Postcupularory display» h\ mules consisted oC Bri-dling followed by Nod-swimming around the female. Turn-back-of-the-head.and bathing. Females usually bathed while males performed r()stc.:()rtllat()r~displays. Pairs would copulate away [r o m the main flock: on three occa si on».copulatory activity ceased and no postcupulat orv display was gi\t:n when ..1:1intruder approached.

Females comprised 470'(1 of the population duril1g the uonbrccdiup ~ca~(ln(table 5.1). The percentage of Icrna lcx obse rvcd in t hc po p ula t io n \\'a" I()\\(.:"t in

SOCIAL IlEH,WIOR OF MOTILED DUCKS IN WINTER 63

Ta hle 5.L Mottled duck sex ratios and percentage of females paired in Louisiana fromAugust through February. 1980-82

Percentage Percentage of, lonth Ma le-, Females males females paired

Augu~l 5.1 47 53.0 21.3Scptc mbcr 203 15.1 57.0 70.6October 259 204 55.9 82.8November 176 156 53.0 84.0December 150 142 51.4 93.0January 222 210 50.7 95.8February 150 141 5t.5 100.0

September but was similar to that of males by December. The percentage offemales paired was lowest during late summer (table 5.1), but it increased rapidlyin the fall. First bonds may have been formed in late summer as males courtedand associated with females while flightless in August and September. Over 90%of females were paired hy December. and no unpaired females were observed inFebruary. On no occasion were both members of a pair marked. and markedbirds were not observed throughout the annual cycle to determine duration of thepair bond.

Only nine (0.4~C) mottled ducks paired with a member of another species: fourmales paired with female mallards. four females paired with male mallards. and amale paired with a female black duck. The latter pair also copulated. Two mottledduck-mallard hybrids. showing plumage characteristic of both mallards andmottled ducks. were observed during the study.

Siblings that wore nasal saddles remained together until about 60-70 days ofage (l ....= 120). During summer months. immature mottled ducks formed smallgroups. and 70% (P< 0.001. N= 939) of two-bird associations were with membersof the same sex. More interaction among males and females was observed in lateAugust. and first courtship activity by immature mottled ducks occurred in earlySeptember. Observations of five marked individuals showed that early bondsmay be temporary. the male and female spending only part of a day to severaldays together. Immature males acted paired but later left the female to court otherfemales, The earliest age that a nasal-saddled individual acted paired was at fivemonths: both males and females were also observed copulating at this age. Oneunpaired immature female copulated with an unpaired male and then separated.

Agonistic Behavior

Agonistic activities were observed infrequently, and the percentage of time spentin these activities was similar among all mottled ducks (P> 0.05), Chasing was the

64 PAULUS

predominant agonistic activity of pairs. Unpaired birds rarely chased other birds.giving mostly Bill threats (males) or Inciting (females) (table 5.2). Paired femalesIncited toward intruding males, other pairs. or their own mate. and these behaviors

Table 5.2. Relative frequency of agonistic activities of mottled ducks in Louisiana iromSeptember through February. 19BO-R2'

Initiator of displav

Unpaired Unpa irccType of Pair male femaledisplay (N= 217) (N = .14) (S = 17)

Inciting 26.3 0.0 515.XRite 6.0 17.7 II.XChase 34.6 !U~ 5.9Bill threat 28.1 67.7 23.5Fight . 5.0 5.9 0.0

'Va lues arc percentages of activities obser- vcd for a given' pairing class.

comprised 26% of agonistic activities by pairs. Fighting. which occurred infre-quently, was initiated only by pairs and unpaired males toward other pairs orunpaired males. Agonistic activities lasted less than 30 seconds. although pairedmales were observed chasing other birds over 20 rn. No differences were found intime spent in agonistic activities during day or night (P > 0.05).

Agonistic activities were observed most often in October and November. whenthreat behaviors comprised 0.5% (N = 195 hours) and 0.3S,( (,V = 150 hours) or timespent by mottled ducks, respectively. During the remaining months. mottled ducksspent less than 0.2% (N = 612 hours) of their time in agonistic activities. :\.1 os:conflicts (53.1 %, N = 273) were between birds that were feeding prior to thedispute. Agonistic behavior involving courting birds occurred 8.8% of the time.even though courting comprised only 0.2% of the time budget of nonbrecdingmottled ducks. Remaining conflicts involved birds that wen: resting (16.1 (.; ).

locomoting (13.6%), preening (6.6%). or alert (1.8%) prior to the dispute. Mostdisputes involving resting birds appeared to be over use of loafing sites on land.

Pairs and unpaired males were more: likely to threaten unpaired males thanother birds (P< 0.001) (table 5.3). Unpaired females were never observed threaten-ing paired mottled ducks. Most agonistic imcractions iuvolving other Anarinacwere with blue-winged teals (Anas cliscors), green-winged teals (A. crccca caroli-nensisi. gad wa lls (A. strepera i. or pinrails (A. acutav.

Pairs were considered dominant to unpaired birds because pairs W(Yl1 94('; 01contests with unpaired males (N = 57. P < 0.00 I) and lOW'! (.V = 14. P < o.oo I) ojcontests with unpaired females. Unpaired males and females rarely threatenedeach other and won similar numbers of contests (P > 0.(5).

SOCIAL AEHAVIOR OF MOTILED DUCKS IN WINTER 65

Table 5.3. Total number of agonistic interactions among paired and unpaired mottled ducksand other Anarinac in Louisiana from September through February. 1980-82

Winner of contest

Le-er or Unpaired Unpaired Othercontest Pair male female Mallard Anatinae"

Pair 138 4 0 3 0Unpaired male 53 20 8 0 0Unpaired female 14 J J 0 0Mallard 6 0 0Other Anatinae 2g 7 0

•Anas acuta .A. amerirana . A. rlvpeata, A. crecca carolinensis, A. discors, A. rubripes, A. strepera,Al"lhra affinis , A. americana , A. collaris, Lophodvtes cucullatus,

Associations

Mauled ducks usually were observed as solitary pairs or in small flocks offewerthan 10 birds. In 35% of observations. the nearest neighbor was more than 25 mfrom the individual or pair under observation. The largest flock observed onnatural wetlands was about 100 birds. although concentrations of several thou-sand were 'observed in rice fields. ~

Monied ducks primarily associated with members of similar pair status(table 5.4): Pairs also were more likely to be near unpaired females or alone thanwith unpaired males (P< 0.05). Unpaired males were observed more often withunpaired mottled ducks than with other species of Anatinae oralone (P< 0.05).Unpaired females associated with unpaired males in 86% of observations involv-ing mottled ducks in which the unpaired female was the focal bird. Unpairedfemales also were more likely to associate with unpaired males than to be aloneor with other Anatinae (P < 0.05).

Table: 5.~. Total number of associaiions among paired and unpaired mottled ducksand otherAnatinae in Louisiana from September through February. 1980-82

Nearest neighbor

Individual Unpaired Unpaired Blue- or green- Otherobserved Pair male female Mallard winged teal Anatinac' None"

Pair 1.591 25R 213 668 620 938 2.525Unpaired ma le 94 IllS is 32 137 54 172Unpaired female: 15 209 20 5 27 39 78

•Anas acut a. A. americana, A. clvpea ta, A. rubripes . A. strepera, Avthya affinis . A. americana .A. collaris. Lophodytes cucullatus .

·:-';0 bird within 25 m of focal bird.

00 PAULUS

Discussion

Courting and Pair FormationCourtship, which allows ducks to assess the status and suitability of potentialmates, is important in pair bond formation and reinforcement (Heinroth 1910.McKinney 1975, Cheng et al. 1978). However. mottled ducks. like mallards(Weidmann 1956) and gad walls (Paulus 1984a). formed many pairs prior [0 peakcourting activity. Courtship activities comprised only 0.1% of the urne-activitybudget of mottled ducks in September, yet 71% of females observed were paired.Presumably, early pairs arose through associations among individuals with fewhighly visible social displays or through re-Iorrna tion of the previous year's bonds,

Adult male and female mottled ducks may remain paired until July or earlyAugust (Paulus 1984b). Males that had completed the wing molt were observedcourting flightless females in August. Two males seemingly paired to Flightlessfemales left the, hens each night to fly to other areas of the marsh.

Immature mottled ducks began forming pairs at about five months of age.Ducklings were first observed in late March and April. thus these birds may havebegun forming pairs in September. These data suggest that adults formed earlypairs and that the pairs formed after mid-September were comprised mostly ofimmature mottled ducks.

Higher levels of courtship activities involving mottled ducks began in October.five months after the peak of hatching. Lebret (1961) believed that the primaryfunction of courting displays was to red uce hostile tendencies among individ uals.Thus, an important function of courting displays may have been to red uce hostiletendencies among immature mottled ducks. allowing for subsequent Iormat ionof first-time bonds. Late-season courting displays involved only paired birds,These displays may have been important in reaffirming or testing bonds. or theymay have reflected the male's interest in obtaining a new mate (see Mc Kinney andStolen 1982).

Mottled duck displays were similar to those of mallards (Johnsgard 1960.1965). Head-up-tail-up and Down-up displays were performed by several malt:mottled ducks simultaneously. and often after females performed Nod-swim.Unlike mallards and black ducks (Joh nsgard 1960). mottled ducks rarely per-formed Down-up displays. Down-up displays comprised 25-46~;(. of displavs(excluding Introductory shakes and Preening-behind-the-wing) by mallards andblack ducks but only 1% of mottled dud displays. A/I Down-up displa~'" hymottled ducks took place during [he period of peak courting activiiv ill 1~IIC

September and October. Johnsgard (1900) also noted that Down-up disrla:~were most common during the period or peak courting activity in mallard, a nublack ducks.

Down-up display frequency was correlated with the number of rna lcx in

SOCIAL BEHAVIOR OF MOTTI.ED DUCKS IN WINTER 67

courting groups in mallards and black ducks (Johnsgard 1960). The low frequen-cy of Down-up displays among mottled ducks may have resulted from the smallsize of couning groups and the few males. In penned mottled ducks. Weeks (1969)found that Down-up displays comprised 18% of courtship displays. presumablycecause close proximity induced sufficient stimuli to elicit that display.

Over Sarff of mottled duck copulations during the study occurred in Novemberand December. Copulatory activities may have been used by females to assess themale's suitability as a breeding partner (McKinney 1975). or may have served tostrengthen pair bonds. Copulatory activity probably did not result in the insemi-nation of females until late in the season. since mottled duck males are notreproductively fertile until late December _or January (Allen 1980).

The lime of pair formation in Anatinae has been related to resource use andfood choice (Paulus 1983). energy costs and benefits of maintaining pair bonds(Daly 1978. Afton and Sayler 1982). time of nesting (Weller 1965). and time ofacquisition of the alternate plumage (Sibley 1957. Weller 1965, Wishart 1983.Paulus 1984a). Birds consuming lower quality diets and spending much of theirtime feeding to meet nutrient needs may enhance their ability to acquire anddefend preferred foods by forming pairs (Paulus 1983). However, food choice andcompetition appeared less significant as factors explaining early pairing inmottled ducks as compared with other Anas because mottled ducks (1) selectedplant seeds and animal matter (St utze nba ker 1984). foods of high nutrientcontent (Sugden 1973. Paulus 1982): (2) spent less than half their time feeding(Paulus 1984b); and (3) were widely scattered over available areas, rarely inter-

. acting aggressively with other individuals. The limited time spent in defense ofpair bonds or food resources (Paulus 1984b) and the moderate temperaturesduring winter also suggest that energy costs of defending mates were minimalwhen compared with the potential benefits derived from early pairing (also seeAfton and Sayler 1982).

Pairing chronology probably was influenced by time of nesting and plumagecharacteristics. Mottled ducks formed pairs but also began nesting in Louisianaabout one to three months before mallards and pinta ils nested on northernbreeding grounds. Except for bill coloration. mottled duck hens and drakes arenearly indistinguishable. Because courtship displays seem to playa limited role informing bonds. early pair formation and long-term bonding may be favored toreduce chances for species recognition errors. Nearly equal sex ratios. earlypairing. and limited aggressive interactions among mottled ducks add evidencesupporting Brown's (1982) hypothesis that nearly equal sex ratios are favored inspecies that maintain the longest pair bonds and have reduced sexual dimor-phism and int rarnale comperirion.

0/1 PAULUS

Early pair formation also appeared important In preventing cross-pamngbetween mottled ducks and mallards. Although mallards outnumbered mottledducks by about a 10: I ratio in late winter. the mallards do not arrive in largenumbers until November or December (H. A. Bateman. unpub!. reps .. La. Dcp.Wildl. and Fish .. 1980-82). By the time mallards were undergoing the period ofrapid pair formation, most mottled ducks had already formed pairs. Pairsassociated with mallards in numbers similar to that predicted by chi-squareanalysis, but it was uncommon for unpaired mottled ducks to be observed nearmallards. Mottled ducks and mallards courted near each other. yet they rarelyparticipated in courting groups of the other species. Because of similarity ofdisplay types among the two species. future studies should examine factorslimiting interspecific courting activities among mallards arriving before ~o-vember and mottled ducks in Louisiana.

Agonistic Behavior and Associations

Mottled ducks. like other Anatinac (Alexander and Hair 1979. Jorde 19~L Hcpp1982, Paulus 1984a), spent little time in agonistic activities. Agonistic behavior wascommon during mottled duck courtship activities. Males and females occurred innearly equal numbers, and individuals of both sexes competed for mates. '\1anybirds were already paired before the peak courting activities. probably intensifyingcompetition among individuals for remaining potential mates.

Most wintering waterfowl form large congregations. However. White andJames (1978) found that mottled ducks were the least social of waterfowl speciesobserved in Texas; in this study. mottled ducks were observed alone in over one-third of observations. Several factors may ha ve fa vorcd red uced social it y amongmottled ducks. Their nonmigratory status rnayhave allowed greater familiaritywith local habitats (Southwick 1953) and lessened their need to rely on flocking asa means of gaining information about resource conditions (Ward and Zahavi1973) or of detecting predators (Page and Whitacre 1975. Pulliam and Millikan1982). Also, mottled duck displays associated with territorial defense were firstobserved in January. Lack of associations among pairs in winter may have rc-fleered dispersal of pairs over the marsh in anticipation of breeding activities.

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