424 ShortCommunications [Auk,Vol. 103 Parental Behavior of a BigamousMale Northern Mockingbird RANDALLBREITWISCH, RONALD C. RITTER,AND JULIAZAIAS Departmentof Biology,University of Miami, CoralGables, Florida 33124 USA The Northern Mockingbird (Mimuspolyglottos) is a 1) paired, raising at least one fledgling to indepen- typically monogamouspasserine (Bent 1948, Verner dence. Female 105, of unknown age, was banded in and Willson 1969) in which male bigamy has been November 1982. Female 246 (female 2) was at least 1 documented occasionally(Laskey 1941, Logan and yr old when banded in early May 1984. We suspect Rulli 1981,Merritt unpubl. data). Hypothesesfor the she was the same unbanded bird we observed in late infrequencyof polygyny in mockingbirdsand other March 1984 on male 867's territory but on the side monogamouspassetines center on a relativelysmall oppositemost of female l's activity. By 29 March, it variance in (1) quality of territories establishedby was clear that male 867 had acceptedfemale 2's set- males,(2) quality of male parental care or other as- tlement on his territory; they were seen repeatedly pects of male behavior important in raising young, within 1 m of one another without apparent aggres- or (3) male traits strictly related to mating success. sion. We here provide information pertinent to the latter Between 29 March and 19 June, we observed male two hypotheses. 867'sinteractions with his matesduring 71 sampling Verner and Willson (1969) considered North periods on 60 different days (œ= 59 min, total = 69.8 American passetinesto be polygynousonly if >5% h). We quantified male feeding of young during an of males in a population have two or more mates additional 30 sampling periods on 24 days between simultaneously.However, even single instancesof 30 April and 19 June (œ= 57 min, total = 28.7 h). Ob- polygynyin typically monogamousspecies are inter- servationof nestling feeding was facilitatedby fre- esting becausethey may clarify the reasonsfor the quent placement of the open cup nests in sparse relative infrequency of polygyny in these species. vegetation. Sampling was distributed throughout We assumethat bigamy is not the result of an error daylight hours. Using binoculars, RCR and JZ ob- in mate choiceby a female mating with an already- served from exposedlocations. RB, having handled matedmale and that sucha female knows she is pair- nestlings of this male, observed from a blind (see ing with a mated male and is choosingthe best mat- Merritt 1984). In each period, the observer main- ing option available to her at that time (cf. Alatalo et tained visual contact with male 867. al. 1982).In the casereported here, for instance,the Twice in the breeding season,male 867 had two secondfemale to arrive paired with a mated male setsof young simultaneouslyrequiring feeding. A that shared a territorial boundary with an unmated third time, he had three setsof young on his terri- male. It is reasonable to assume she made a choice tory, all begging for food (Fig. 1). In each case,he between at least these two males. fed only one set of young. In the first overlap (6-11 We observed the behavior of a single bigamous June),the male fed female l's fledglingsand ignored male mockingbird for 98.5 h in the 1984 breeding the food needs of female 2's nestlings. In 659 min of seasonand quantifiedthis male'sbehavior with re- observationbetween 29 May and 11 June (when fe- gard to feeding nestlingsand fledglings, defending male l's fledglingswere 3-16 days out of the nest), eggsand nestlings,and consortingwith mates.We the male fed the fledglings 119 times vs. 1 feeding also compared his behavior with that of monoga- by female 1 (and 8 feedingsby an unidentified par- mous males in the same population. The overall ent). Female 1 had a new clutch of eggs for most of framework for comparative analysesof these data is this time (Fig. 1). The male fed the first brood of an inquiry into the consequencesof bigamyfor both female 2 (13 feedingsvs. 17 feedingsby female 2, in femalesmated to a bigamousmale mockingbird. 180 min on 30 April and 1 May). He also fed female This population of individually color-banded l's nestlings(40 feedingsvs. 97 feedingsby female mockingbirdsinhabits the main campusof the Uni- 1, in 489 min between 16 and 25 May). Between 6 versityof Miami in CoralGables, Dade County, Flor- and 11 June, with only female 2 feeding her nest- ida (Merritt 1985) and has been under continuous lings, they grew very slowly (Breitwisch unpubl. study since 1979. The birds are largely habituatedto data). The nest was not kept clean, and the young humans and allow observersto approach as close as were plastered with dried feces. One of the three 5-10 m (Breitwischet al. 1984). Male 867, the subject emaciatednestlings died, almostcertainly from star- of this study, was banded in March 1980, at an age vation. From 6 to 11 June, the male fed female 2's of at least 1 yr. Prior to 1984, he was monogamous. nestlings1 or 2 times vs. 33 feedingsby female 2 (in In 1980 he produced two fledglings but only one 300 min); the feedings by the male were on 10 and survived to independence(= ca. 2 weeks after fledg- 11 June when he was still feeding female l's fledg- ing). There was one fledgling in 1981 that died be- lings. On 10-12 June,when the two remainingnest- fore reachingindependence. Male 867 apparentlywas lings were 4-6 daysold and female l's fledglingshad unmated in 1982. In 1983, he and female 105 (female been out of the nestfor 15-17 days,the male abruptly April1986] ShortCommunications 425 ceasedfeeding the fledglings and began rapid deliv- 3 ery of food to the nestlings.Between 12 and 17 June, the male fed the nestlings 64 times vs. 47 feedings E's N's F's by female 2 (in 404 min). The growth rate of the LU• 2 young increaseddramatically, and they attainedtyp- 3 321 I ical fledgingweights of healthyyoung. In the second Z 3 brood overlap (14-18 June), the male continued to feed female 2's nestlingsand completelyneglected feeding female l's nestlings.The growth rate of fe- male l's nestlingswas very slow (Breitwischunpubl. 3 3 data), and apparently one of her nestlingsstarved. 3 3 2 2 However, in contrast to his behavior in the first over- z u. 2 lap when female 1 had fledglings and female 2 had nestlings,the male stoppedfeeding female 2's young when they fledged,and he beganfeeding female l's nestlings(16 feedingsvs. 12 feedingsby female 1, in APRIL MAY JUNE JULY 120 rain on 18 and 19 June). From 18 to 26 June, he Fig. 1. Nesting scheduleof two female mocking- continued to feed female l's nestlings and was not birds mated to a bigamousmale. Numbers of eggs observedto feed female 2's fledglings. This neglect (cross-hatchedbars), nestlings (open bars),and fledg- of fledglingsis in markedcontrast to typical monog- lings(hatched bars) at eachstage of nestingare shown amous male mockingbird behavior; males provide aboveeach nest. Brood reduction is indicatedby mul- more food to fledglings than do females (Zaias and tiple entry aboveand a dashedline within the nest- BreitwischMS). It alsocontrasts with this male'spre- ling stagefor a nest.A predationevent is symbolized vious rate of feeding female l's fledglings between by an "X." The "?" for nest 1 of female 1 indicates 29 May and 11 June. that the clutch was completeupon discovery. The male defendedhis eggsand nestlingsvigor- ously.In the 1983breeding season, he was known as a notably aggressivemockingbird in the campus (X• = 2.67, df = 1, P > 0.05). Furthermore, he used the population,attacking human intruders when he had two parts of his territory equally. He was observed young on his territory. In the 1984 breeding season, on female l's half (although not necessarilywith the one of us (RB) quantified male and female behaviors female) in 68 of 71 periods(96%) and on female 2's in defending eggsand nestlingsagainst assistants ex- half in 54 of 71 periods(76%); these frequencies were amining eggs and removing nestlings for growth not different (X• = 1.61, df = 1, P > 0.05). However, measurements(Breitwisch MS). Male 867 significant- he sangwith different frequencyin the two halves ly differed from the monogamousmales in the pop- of his territory. He sangon female l's half in 43 of ulation. He approachedmore closely (Mann-Whit- 71 periods (61%) and on female 2's half in 23 of 71 ney U-tests for egg defense, z = 4.53, P < 0.05, and periods(32%) (X 2 = 6.06, df = 1, P < 0.05). If songin nestling defense, z = 8.51, P < 0.05), hovered over mockingbirdsfunctions primarily in male-femalein- assistantsmore closely when defending nestlings teractions(see Merritt 1985),this differencemay in- (Mann-Whitney U-test, z = 3.34, P < 0.05), and made dicatesignaling by this male to his first mate in pref- closerpasses when attackingassistants (Mann-Whit- erence to his second mate. ney U-tests for egg defense, z = 1.91, P = 0.05, and Mockingbird breeding territories are all-purpose nestling defense, z = 5.98, P < 0.05). He also more territories,although birds in this populationwill leave frequentlyfollowed assistants off territory(G = 102.6, territoriesto foragefrom nearby fruiting trees(Mer- df = 1, P < 0.05). He occasionallyattacked assistants ritt 1980, Breitwisch et al. 1984). We did not assess working at a nest in an adjacentterritory and was the quality of territoriesheld by mockingbirdsin this the only mockingbird(of 24 malesand 25 females) population,but the male'sterritory was not obvious- to extend defenseto a neighbor'snest.