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. Orians (1980) ly different from territories of monogamousmales. and Wittenbergerand Tilson (1980) suggestedthat Mockingbirds are ground foragers, taking large polygynousmale passerinesusually can equally de- numbersof terrestrialarthropods; the area of lawn fend more than one nest againstpredators, and this available for foraging may be an important aspectof bigamousmale appearedto do so. territory quality (seeRoth 1979).Male 867'sterritory Male 867 consorted with each of his mates, even was among the larger territories,as Merritt (unpubl. when he neglectedto feed her young. In 56 of 71 data) found for a previous bigamousmale in this observationperiods (79%) he was seen with female population,but it was not uniquely large. 1; in 40 of 71 (56%) he was seen with female 2. In 30 The bigamousbehavior of male 867 suggeststhat of these, he was seen with both females within the individual quality apart from territory quality may same observationperiod. The male's frequenciesof be important in determining instancesof bigamy in consortingwith his two females were not different mockingbirds(cf. Borgia 1979). In the 1984 breeding 426 ShortCommunications [Auk,Vol. 103

season,for 23 monogamouspairs, 15 of 67 nestswith this casevery minor feeding of female 2's neglected eggs(22%) were preyedupon, and 26 of 52 nestswith nestlings on 10-11 June as the male switched from nestlings(50%) were preyed upon. Both egg and feeding fledglings to feeding nestlings).However, nestling periodsof mockingbirdsin southernFlorida this case differs from Logan and Rulli's (1981) in- are ca. 12 days,and thesepredation rates correspond stance in two ways. First, the latter arose through to lossrates of 0.0187nests with eggslost per day disappearanceof a male from a pair and usurpation and 0.0417nests with nestlingslost per day. Only 26 of the widowed female'sterritory by a neighboring of 67 nests(39%) produced fledglings, and only 18 of male.The widowedfemale and the malelater paired. 67 nests(27%) yielded independentyoung. In con- Second,when facedwith two broodsof young, the trast, 3 of the 6 nests (50%) of the two mates of male bigamousmale of Logan and Rulli always fed the 867 togetherproduced 6 fledglings,and all young older set of young. In contrast,male 867 stopped reachedindependence. As an additional measureof feeding female 2's young when they fledged and success,we cancompare the numberof independent switchedto feeding female l's nestlings.This behav- young producedper female. In 1984,the mean num- ior departsfrom Trivers's(1972) prediction that par- ber of independent young produced by females in ents should favor older over younger offspringin monogamouspairs was 1.2 (SD = 1.28) from a mean conflictsituations. We suggestthat male caremay be number of 3.0 nests per pair (n = 23 pairs) (Breit- more important for mockingbirdnestlings than for Tisch unpubl. data). Female 1 nested 4 times and fledglings. Such a difference should be entered into produced4 independentyoung from 2 nests.Female any equation predicting parental investment pat- 2 nestedtwice and produced2 independentyoung ternswith respectto agesof offspringcompeting for from 1 nest.Each of thesefemales produced at least parental care (Maynard Smith 1977). as many independentyoung as the averagefemale Polygynyin birds frequentlyhas been explained in the monogamouspopulation. by differencesin quality of male territories(e.g. see The male's high level of defensivebehavior may Orians 1980, Oring 1982),and without doubt this ex- have contributedto his successin producinginde- planationfits manycases. We suggest,however, that pendent young. This would argue against the hy- variability in male behavior, particularly in aspects pothesisthat female choiceof male traits strictly re- of parental care, apart from variability in quality of lated to mating successaccounts for male bigamy territorieswarrants careful investigation. (Weatherheadand Robertson1979). Presumably,a We thank Nicole McQueeny,Rose Rizzo, and Ma- newly settling female could estimate a potential rina Yong for help with the fieldwork. Natasha mate's level of defensive behavior by observing his Kline, Peter Merritt, Bud Owre, Ian Rowley, Fred overalllevel of aggression,perhaps toward both po- Schaffner,George Whitesides, and two anonymous tential predatorsand conspecificintruders, perhaps reviewers critically read and offered suggestionson toward herself. In the breeding season,mated male a previousversion of this note.We particularlythank mockingbirdshad higher attackrates against intrud- Peter Merritt for making available to us his unpub- ing conspecificsthan had unmated males (Merritt lished observations. This is contribution No. 183 from 1985). In the nonbreeding season,mated males in the Universityof Miami Departmentof BiologyPro- this populationwere moreaggressive than unmated gram in Behavior,Ecology, and TropicalBiology. males, as estimatedby frequency of involvement in conspecificchases (Breitwisch et al. 1986a). LITERATURE CITED Monogamousmale mockingbirdsin this popula- tion provide as much food to nestlingsas do females ALATALO, g. V., g. LUNDBERG,& K. $TAHLBRANDT. (Breitwisch et al. 1986b), and male 867's schedule of 1982. Why do Pied Flycatcherfemales mate with feeding young illustratesone of the potentialcosts already-matedmales? Anim. Behav.30.' 585-593. to femalesmated to a bigamousmale. He neglected BENT, A. C. 1948. Life histories of North American feeding a brood of young when he had another set nuthatches, wrens, thrashers, and their allies. U.S. of young on his territory,and two of the neglected Natl. Mus. Bull. 195. nestlingsstarved to death, while others grew at slow BORGIA,G. 1979. Sexual selection and the evolution rates. More complete staggeringof broodscould re- of mating systems.Pp. 19-80 in Sexualselection duce this potential cost(Verner 1964). Nonetheless, and reproductivecompetition in insects(M. S. our dataon nestsuccess and productionof indepen- Blum and N. A. Blum, Eds.). New York, Academ- dent young suggestthat, despitethe potential for ic Press. starvationof nestlingsnot fed daily by a bigamous BREITWISCH,R., M. DIAZ, N. GOTTLIEB,R. LEE, & J. male, bigamy may still be advantageousto females. ZAIAS. 1986a. Defenseof fall territoriesby mat- This instanceof mockingbirdbigamy is in agree- ed and unmated Northern Mockingbirds in ment with that reported by Logan and Rulli (1981) southern Florida. J. Field Ornithol. 57. and verified by Merritt (unpubl. data) in that each --, P. G. MERRITT, • G. H. WHITESIDES. 1984. bigamousmale fed only one set of young when he Why do Northern Mockingbirds feed fruit to had more than one set at the same time (but note in their nestlings?Condor 86: 281-287. April 1986] ShortCommunications 427

--, --, & --.. 1986b. Parental invest- and K. C. Parkes, Eds.). New York, Academic ment by the Northern Mockingbird: male and Press. female roles in feeding nestlings.Auk 103: 152- ROTH,R. R. 1979. Foraging behavior of mocking- 159. birds: the effect of too much grass.Auk 96: 421- LASKEY,A.R. 1941. An instanceof mockingbirdbig- 422. amy. Migrant 12: 65-67. TRIVERS,g. L. 1972. Parental investment and sexual LOGAN,C. A., & M. RULLI. 1981. Bigamy in a male selection.Pp. 136-179 in Sexualselection and the mockingbird.Auk 98: 385-386. descentof man, 1871-1971 (B. G. Campbell, Ed.). MAYNARD SMITH, J. 1977. Parental investment--a Chicago,Aldine. prospectiveanalysis. Anim. Behav.25: 1-9. VERNER,J. 1964. Evolutionof polygamyin the Long- MERRITT,P. G. 1980. Group foraging by mocking- billed Marsh Wren. Evolution 18: 252-261. birds in a Florida stranglerfig. Auk 97: 869-872. --, & M. F. WILLSON.1969. Mating systems,sex- 1984. Observerrecognition by the North- ual dimorphism, and the role of male North ern Mockingbird. J. Field Ornithol. 55: 252-253. American passefinebirds in the nesting cycle. 1985. Song function and the evolution of Ornithol. Monogr. No. 9. song repertoiresin the Northern Mockingbird, WEATHERHEAD,P. J., & R. J. ROBERTSON.1979. Off- Mimus polyglottos.Ph.D. dissertation, Univ. springquality and the polygyny threshold:"The Miami, Coral Gables, Florida. sexyson hypothesis." Amer. Natur. 113:201-208. ORIANS,G. H. 1980. Some adaptations of marsh- WITTENBERGER,J. F., & R. L. TILSON. 1980. The evo- nesting blackbirds. Monogr. in Pop. Biol. 14. lution of monogamy:hypotheses and evidence. Princeton,New Jersey,Princeton Univ. Press. Ann. Rev. Ecol.Syst. 11: 197-232. ORING,L.W. 1982. Avian mating systems.Pp. 1-92 in Avian biology, vol. 6 (D. S. Farner, J. R. King, Received15 February1985, accepted18 October1985.

StomachPumping: Is Killing SeabirdsNecessary?

PETERG. RYAN AND SUSAN JACKSON FitzPatrickInstitute, University of CapeTown, Rondebosch 7700, South Africa

Many seabird speciesregurgitate when handled, pumped and killed after varying intervals. The allowing diet assessmentwithout killing birds (e.g. amount (mass and number of prey items) of food see Ashmole and Ashmole 1967, Harrison et al. 1983). recoveredby stomachpumping was expressedas a Other seabirds,notably penguins (Wilson 1984) and proportion of the total stomachcontents (determined petrelsaway from their breedinggrounds (Harrison by dissectingout the oesophagusand proventricu- et al. 1983,pets. obs.), are lesswilling to regurgitate. lus) and compared with the total stomach contents. A quantitative,but nonlethal,sampling technique is In addition, single CapePetrels (Daption capense), Sal- neededfor diet studieson theseseabirds, particularly vin's Prions (Pachyptilavittata salvini),and Wilson's in view of the growingopposition toward the killing Storm-Petrels (Oceanitesoceanicus) were collected at of animals for biological research. sea off southern Africa, then similarly tested. Emeticsand stomachpumps have been usedto ob- Mean pump efficiency(the proportion of food re- tain stomach contents from seabirds, but results have coveredby a single pumping) was 89.2%(SD = 13.3) beenunsatisfactory (Wilson 1984,Duffy and Jackson by massand 99.1%(SD = 2.0)by numberof prey items MS). Wilson (1984)described a simple techniquefor (n = 10). The proportionof food (by mass)recovered samplingstomach contents in seabirds,but it hasbeen by a singlepumping was negativelycorrelated with suggestedthat it doesnot always recoverthe entire total stomach content mass in the 7 White-chinned stomachcontents (Lishman 1985;but see Horne 1985) Petrels examined (Fig. 1; r = -0.85, P < 0.01 on arc- and is less effective on birds that have full stomachs sine transformeddata). The proportion of prey items with tightly packed contents (Lishman 1985). We recoveredwas also negatively correlated with the to- tested the efficiency of Wilson's stomachpump on tal number of items present(r = -0.67, P < 0.05, n = four speciesof petrel and review its usein other birds. 10). Approximatelyequal massesand numbersof the Seven White-chinnedPetrels (Procellariaaequinoc- three prey types were recovered, irrespective of tialis)(mean mass 1,250 g) from Marion Island (46ø52'S, stomach fullness. When stomachs were less than 20% 37ø51'E)each were fed a large meal (125 g) of squid full, the entire contentswere removed by a single (Loligosp.), lightfish (Maurolicusmuelleri), and antarc- pumping. The three other petrel speciestested all tic krill (Euphausiasuperba) in equalproportions, then yielded 100%of their stomachcontents.