Social Behavior and Pairing Chronology of Mottled Ducks ... ... 5 Social Behavior and Pairing...

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Transcript of Social Behavior and Pairing Chronology of Mottled Ducks ... ... 5 Social Behavior and Pairing...

  • 5

    Social Behavior and Pairing Chronology of Mottled Ducks during Autumn and Winter in Louisiana Stuart L. Paulus

    Ah.\ITUcr: Pairing chronology. agonistic and courtship behaviors, dominance rela- tions. and spatia] interactions of mottled ducks (Anas fulvigulai were studied in the coastal marshes of southwestern Louisiana during August through February 19~W-X2. Courting and agonistic activities comprised less than 1% of the time budget 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 late summer: by December. 90("( of females were paired. Immature mottled ducks began forming pairs at five months of age. Mottled ducks and mallards (Anas platvrhvnchos) were obserx cd courting near each other in fall. However, ol1lyO.4% of mottled ducks were observed paired with mallards or ~k du~s iAnas rubripes i. Chasing. bill threats. and inciting were common agonistic activities, and most agonistic act ivit y was observed in fall. Pairs were dominant to unpaired birds. a~ pairs won 94C;i- (P < 0.00 1) of contests with unpaired birds. Mottled ducks usually 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 associated with members of similar pair status. This study suggests that courtship displays may be more important in forming bonds between immature than adult mottled ducks. Early pair formation by mottled ducks may have minimized interspecific pairing 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 of mottled 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 hy t he {'n:\(:r\lty or \,linnesola Prcs s .. Minneapolis.

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  • 00 P;\Ul.lJS

    important for several reasons. First, although courtship displays and ralrlng chronology of captive mottled ducks were studied by Weeks (1969 l.Iiule is known of these behaviors in wild mottled ducks. Second, Paulus (19~3) suggested that pairing chronology might be related to foraging strategies in nonbrccding Anati- naco with those species feeding on poorer quality foods (such as leafy aquatic vegetation [Sugden 1973, Paulus 1982]) forming pairs earliest. H OWCH:r. mottled ducks pair early (Weeks 1969) but consume high-quality foods (such as plant seeds and invertebrates [Guidry 1977, Bellrose 1978]). suggesting that factors other than food choice influence pairing chronology. Third. mottled d ticks associate with mallards (Anas platyrh ynchosi during winter, yet cross-pairing is uncommon (Weeks 1969) despite similarities in courtship displays and overlap or urne of pair formation. In some areas where mallards and black ducks (Anas rubripcsi winter together, interspecific pairing is common (Brodsky and Weatherhead 19~4). Fourth, little is known about the influence of sex and age on time or pairing in mottled ducks. Finally, the role of agonistic activities in influencing dominance relations 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 mottled ducks. 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. Richard for 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 in manuscript 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 natural marshes 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:-( throuuh February. 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 during the 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. pair t- •• od durability.and social interactions of mottled ducks, A total or716 immature Jod 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 move J\\;I\: rapidly: (4) Bill threats, an open-bill display with the bill raised slightly I:r\\;ml from horizontal and toward another bird: and (5) Fighting, tugging and hltlll!! 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 another hlld: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 of mottled 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 and r,l\(l'optllatory displays included Head-pump. Bridling, Nod-swinuning . and lurn-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. Birds were 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 and IK'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 moulcd duds 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 Formation Courting activities comprised less than 1% (N = 1.188 hours) of the time budget of mottled ducks, with similar results for paired and unpaired males and females (P > 0.05). Courtship was initiated in August, and the greatest level of courting activity was observed during October through December. Most courting oc- curred in early morning and late afternoon. although O.I~·(, of time was spent courting 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 (';) and Jump-nights (1%) were rarely' observed. Nod-swimming displays immediately Iollowed other displays (23%). primarily the Head-up-rail-up (!-l6C;;), as well as the Grunt-whistle (6%) and Down-up (6%) displays. Male displays. especially the Head-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 orchasing a way nearby birds and females. Nod-swimming or Inciting. would be followed by lulls in which birds fed or spent time in other activities. Individ uals were observed leaving one