SHORT COMMUNICATIONS 179

The Condor89: 179-182 0 The CooperOrnithological Society 1987

EXTRA ADULTS AT THE NEST IN BARN SWALLOWS’

MANDY M. MEDVIN, MICHAEL D. BEECHER, AND SANDY J. ANDELMAN Animal BehaviorProgram, Department of PsychologyUniversity of Washington, Seattle, WA 98195

Key words: Barn Swallow; Hirundo rustica; extra where we saw three birds together at a nest, however, adults;reproductive strategies; plumage dlflerences. one of them had the distinctive plumage of an extra adult. Moreover, in only one instance did we ever see Extra adults at the nest have been noted in a wide more than three adults at a nest. variety of bird species(for reviews, see Skutch 1961, The retention of juvenal plumage, as seen in our Lack 1968, Ricklefs 1974, Brown 1978, Emlen 1978). extra nest attendants, has not been reported in other We use the neutral term “extra adult” to refer to non- studiesof Barn Swallow extra adults(Mvers and Waller breeding adults that interact frequently and nonhos- 1977, Crook and Shields 1985, in press).Retention of tilely with the primary breedingpair at or near the nest, juvenal plumagefeatures has been found in Tree Swal- regardlessof whether they care for the young or later lows (Tachvcineta_ bicolor. Kuetzi 1941. Sheppard__ 1977) breed. In Barn Swallows, extra adults at the nest have and Mexican Jays (Aphelocomaultramarina; Brown been reported in two populations (Myers and Waller 1963, see also Brown 1978). 1977; Crook 1984; Crook and Shields, in press). The purpose of this note is to report our findings on extra FREQUENCY OF EXTRA ADULTS adults at the nest in a third population, and to point Extra adults were seen at 12 of the 13 nests (Table 1). out notabledifferences, in plumageand behavior,among Extra adults were seenat the nest as early as the initial the three populations. courtship of the primary pair. At two of the nests, the extra adult ultimately nestedwith the male (seebelow). METHODS At the remaining 10 nests, we compared the number In 1979 and 1980, we studied 13 solitary nests on the of days an extra adult was seen with the family group, grounds of the Woodland Park Zoo and in the sur- relative to the number of days the male and female rounding neighborhood, in Seattle, Washington. In were seen.On average,an extra bird was presentduring 1979, we monitored eight secondor late clutchesat the 24% of the observation periods, compared to 84% and nest, and for several weeks after fledging. In the latter 90% for the male and female respectively. We cannot context, we identified family groupsby color marking be sure that we always saw the same extra adult at a young; family groupstypically stayed together for one particularnest rather than one of severaldifferent birds. to two weeks (Medvin and Beecher 1986). In 1980, We favor the first alternative, however, for two reasons. we watched five nests during both first and second First, some of the extra adults had distinctive mark- clutches.Observation periods averaged 30 min, for a ings, and identification was unequivocal. Second, in total of approximately 175 hr. We sexedbreeding adults general, a breeding pair interacted with the light-col- by tail length (Samuel 1970), and song.Extra adults at ored extra adult in a tolerant fashion, suggestingfa- each nest were identified by plumage markers (see sec- miliarity, which contrasted sharply with their aggres- tion below); such identifications were independently sive reaction to the occasionaldark-colored intruder. confirmed by at least two observers. In addition, we The high proportion of nestswith extra adults in our marked the breeding pair at 4 of the 13 nests (Table study is similar to that seen in the New York popu- 1). lation studiesby Crook and Shields (in press), where 78% of the nestswere attended. The proportion differs RESULTS from that seenin the Ohio populationstudiedby Myers and Waller (1977) in which attendants were reported PLUMAGE DIFFERENCES at less than half of the nests. While the typical plumage of the adult Barn Swallow includes a reddish-brown breast, and deeply forked, HELPING BEHAVIOR OF EXTRA ADULTS long tail feathers, the extra adults all had either white The extra adults infrequently fed at nests. In 40 ob- or light colored breastsand/or short tail feathers, and servation hr during the nestling period, we saw only resembledjuveniles of the first clutch. The plumage of 12 feedingsby extra birds (distributed over three nests); the extra adults was so distinctive that we could easily parents typically feed that much in an hour. In the distinguish them from both primary adults and juve- postfledgingfamily groups,we observedan extra adult niles. There may have been extra adults who lacked feeding fledglingsin two groups. The feeding rate we these unique plumage markers. In virtually all cases observedis much lower than the 15% of the total feed- ing visits at nestswith extra adults observedby Myers I Received 20 January 1986. Final acceptance1 July and Wailer (1977), but it is much higher than the two 1986. feedings observed by Crook and Shields (in press) in 180 SHORT COMMUNICATIONS

TABLE 1. Extra adult sightings.

Number of days When seen?’ Nest Male Female Extras Nest CB I N PF observed seen seen seen

Aur/79 - Y Y Y 33 31 32 12 Cam/79 - - - Y 3 2 3 2 Comm/79 - Y Y 44 41 41 16 Day/79b Y - - - 15 11 9 Duck/79 Y Y Y Y 29 25 29 ii Pony/79 - - Y 12 11 12 2 Zeb N/79” - - Y Y 15 15 15 11 Zeb F/79 n n n n 6 6 6 0 Zeb/lO Y n n - 23 16 19 2 Comm/8@,e Y Y - - 16 14 14 2 DucW8@ Y Y Y - 67 52 55 10 Ele/80 Y Y - 64 52 59 11 Pony/80Q Y Y - - 21 11 13 8 aWhen an extraadult wasseen. CB = courtship/nestbuilding, I = incubation,N = nestling,PF = postfledging,y = yes,n = no, - = no observations during this phase. bObservations during secondclutch; courtship seen, but no eggslaid. cFemale marked. dMale and primary female marked. c Pony/X0was a caseof polygyny;&mm/80 a replacementfemale. The numberof times the extra femalewas seenis tabulatedonly to the point whereshe nested.

2,000 to 5,000 observation hr. Crook and Shields (in as well. At the end of the normal incubation period of press) also describe eight instances of infanticide by 15 days, however the eggshad failed to hatch. On 3 extra adults, whereasneither we nor Myers and Waller June, the third adult and the male were building a new (1977) observed any such instances. nest, approximately 10 m from the old one. The male assistedthe third bird with nest building on that day EXTRA ADULTS SOMETIMES NEST only; she completed the nest by herself. On 8 June, the At 2 of the 12 nests with extra adults, the extra adults male and primary female copulated and engaged in mated with the primary male. At one of these nests, renesting activities. The primary female completed a the primary female died, and the third adult became clutch of six eggson 16 June, and the third adult, now a replacementfemale. At the other, the male and third the secondarymate of the male, completed a clutch of adult mated shortly after the primary female’s nest five eggson 18 June.The primary female’s eggshatched failed. Subsequently,the primary female renestedwith on 1 July; the secondaryfemale ’s eggson 3 July. During the same male, thus forming a polygynous trio. We the nestlingstage, each female fed only at her own nest. describe these two casesin some detail here. The male fed once at the secondaryfemale ’s nest, but The extra adult (second female) at nest Comm/lO otherwise fed only at the primary female’s nest, and becamea replacementnester. This bird was easilyiden- spent most of his time with her. The primary female’s tified becauseof a light-colored band on her breast. young fledged on 23 July; the secondary female’s on The bird was first seen at this nest on 6 Mav 1980. 29 July. We did not see the secondarv female again. during the nest building stage.The primary fe-maleof The primary female completed a second clutch-that this nest completed a clutch of four eggson 18 May. hatched on 13 August; these birds fledged 11 Septem- We found her dead of unknown causestwo weekslater, ber. with only two eggs remaining in the nest. The next evening, the male was found sleepingby the nest with DISCUSSION the third bird; the following day the nest had fresh mud and new feathers. Within another week, the former A REPRODUCTIVE STRATEGY? third bird laid her first egg,and she completed a clutch In Tree Swallows,yearling females retain juvenile-like of four eggson 12 June. The pair stopped incubating plumage (brown versus blue-green) (Kuerzi 1941, on 19 June for unknown reasons, and subsequently Sheppard1977, De Steven 1978). Sinceour extra adults begana replacementclutch of six eggs,which was com- also retained juvenile-like plumage,perhaps they were pleted on 4 July. Four of the six eggshatched on 19 yearlings. In support of this idea, the lighter plumage July, and the young fledged by 9 August. and shorter tail feathers seen in the extra adults may The extra adult (second female) at Ponv/PO even- indicatean incompletepostjuvenile molt (Rohwer, pers. tually nested polygynously. All three birds were first comm.; Palmer 1972). In addition, Crook and Shields seen on 3 May 1980. From the start, the three birds (in press)reported that a high proportion of their extra interacted frequently (e.g., vocalized antiphonally, for- adults were yearlings. aged together). On 14 May, the primary female com- In severalearlier anecdotalreports of nest attendants pleted a clutch of five eggs,and for the next two weeks in Barn Swallows it was assumedthat the extra birds she incubated. The third adult occasionallyincubated were juveniles of the first clutch (Astley 1934, White SHORT COMMUNICATIONS 181

1941, Williamson 1941). Myers and Waller ( 1977) ver- tional Science Foundation predoctoral fellowship to ified that juveniles of the first clutch may sometimes Andelman, and University of Washington Graduate feed nestlingsof the secondclutch. Our study suggests, School Research Fund and National Science Foun- however, that some of the extra nest attendants seen dation grants to Beecher. in these earlier studiesmay have been yearling adults, who owing to the retention of juvenile-like plumage were mistaken for iuveniles. LITERATURE CITED If our extra adults were indeed yearlings, we can ASTLEY, A. 1934. Young swallows assistin building consider the hypothesis that they were following an a secondnest. Br. Birds 28:204. age-related conditional reproductive strategy (Brown BARRENTINE,C. D. 1978. The biology of bridge nest- 1983, Ligon 1983). Yearlings are at a competitive dis- ing Barn and Cliff swallowsin central Washington. advantage to older birds on the breeding ground in M.Sc.thesis, Central Washington Univ., Ellens- three respects.First, they have no reproductive expe- burg. rience. Second,they are unfamiliar with the area; Barn BROWN,J. L. 1963. Social organization of the Mex- Swallowyearlings disperse from their natal area,whereas ican Jay. Condor 65:126-153. adultstypically return to the areawhere they previously BROWN,J. L. 1978. Avian communal breeding sys- bred (Mason 1953, Samuel 1971, Barrentine 1978, tems. Ann. Rev. Ecol. Svst. 9: 123-155. Shields 1984). Third, yearlingsgenerally appear in the BROW, J. L. 1983. Cooperation-A biologist’s di- breeding area after experienced adults have already lemma. Adv. Study Behav. 13:1-37. returned (Barrentine 1978; Shields,pers. comm.; Med- CROOK,J. R. 1984. Barn swallow (Hirundo rusticu) vin and Beecher,unpubl. data). Yearlings arriving on social behavior: nest attendance, aggression,and the breeding grounds therefore might respond to re- sexually selected infanticide. Ph.D.diss., State productively unfavorable circumstances(e.g., habitat Univ. of New York, Syracuse. saturation, a biased sex ratio) by associatingwith a CROOK,J. R., AND W. M. SHIELDS. 1985. Sexually breeding pair and using the experiencethey gain (e.g., selectedinfanticide by adult male barn swallows knowledgeof those individuals and of the area) to im- (Hirundo rustica).Anim. Behav. 33~754-761. prove their breedingsuccess the following year. In ad- CROAK, J. R., AND W. M. SHIELDS. In press. Barn dition, if conditions were to become favorable, they Swallow nest attendants:Helping or harrassment. might breed later that same breeding season. In line Anim. Behav. with this hypothesis,we note that along with our ob- DE STEVEN,D. 1978. The influence of age on the servationsof two attendant females subsequentlymat- breeding biology of the Tree Swallow Iridoprocne ing with the primary male, Crook and Shields(in press) bicolor.Ibis 120:516-523. observedsix attendant males mating with the primary EMLEN, S. T. 1978. The evolution of cooperative femalewithin the samebreeding season, and three males breeding in birds, p. 245-285. In J. R. Krebs and doing so during the following breeding season.More- N. B. Davies [eds.], Behavioral ecology: an evo- over, 90% of the returning extra adults nested in areas lutionary approach. Sinauer Associates, Sunder- where they had attended the previous season.Crook land, MA. and Shields (1985) however, focus on a different hy- HARRISON.C. J. 1969. Helpers at the nest in Austra- pothesisconcerning the reproductive behavior of their lian passerinebirds. Emu 69:30-40. extra adults.Arguing from the occurrenceof infanticide KUERZI.R. G. 194 1. Life historv studiesof the Tree in their population, they suggestthat the extra males Swallow. Proc. Linn. Sot. New York 53:1-52. were actively interfering with the breeding efforts of LACK, D. 1968. Ecological adaptations for breeding the primary pair to increase the probability of mate in birds. Western Printina Services,Bristol. acquisition. LIGON, J. D. 1983. Cooperation and reciprocity in In conclusion, our study and those of Crook and avian social systems.Am. Nat. 121:366-384. Shields (1985; in press)and Myers and Waller (1977) MASON,E. A. 1953. Barn Swallow life history data suggestthat conditional reproductive strategiesmay be based on banding records. Bird-Banding 24:91- more characteristicof Barn Swallowsthan thoughtpre- 100. viously. At present,we cannot accountfor the notable MEDVIN, M. B., AND M. D. BEECHER.1986. Parent- differences among these three studies concerning the offspringrecognition in the barn swallow (Hirundo characteristicsand behavior of the extra Barn Swal- rustica).Anim. Behav. 34:1627-1639. lows, except to suggestthat they may be genuine pop- MYERS,G. R., AND D. W. WALLER. 1977. Helpers at ulation differences;e.g., perhaps the sex ratio in our the nest in Barn Swallows. Auk 94~596. population was female-biasedwhile that of Crook and PALMER,R. S. 1972. Patterns of molting, p. 65-102. Shields was male-biased. We hope that future studies In D. S. Famer and J. R. King feds.], Avian bi- will enable us to identify the ecologicaland life history ology. Vol. 2. Academic Press,New York. factors that give rise to these differences. RICKLEF~.R. E. 1974. The evolution of co-ouerative We thank Woodland Park Zoo for permitting us to breeding in birds. Ibis 117:531-534. _ observe nests on zoo grounds, P. Berg, S. Crinean, S. SAMUEL,D. E. 1970. Field methods for determining Edmonds, and K. McDonald for their assistancein the sex of barn swallows (Hirundo rustica). Ohio data collection,and M. Fitch, R. Foster, M. Lombardo, J. Sci. 71:125-128. G. Shugart, and W. Shields for commenting on the SAMUEL,D. E. 1971. The breeding biology of Barn manuscript. Funds for this study were provided by a and Cliff Swallows in West Virginia. Wilson Bull. Frank M. Chapman Memorial grant to Medvin, a Na- 83:284-301. 182 SHORT COMMUNICATIONS

SHEPPARD,C. D. 1977. Breedingin the Tree Swallow, SNAPP,B. 1976. The occurrenceof colonial breeding Iridoprocnebicolor: its importance for the evolu- in the Barn Swallow (Hirundo rusticu) and its tion of coloniality. Ph.D.diss., Cornell Univ., Ith- adaptive significance.Ph.D.diss., Cornell Univ., aca, NY. Ithaca, NY. SHIELDS,W. M. 1984. Factors affecting nest and site WHITE, W. W. 1941. Bird of first brood of swallow fidelity in Adirondack Barn Swallows (Hirundo assistingto feed second brood. Br. Birds 34: 179. rustica).Auk 101:780-789. WILLIAMSON,K. 1941. First brood of swallows as- SKUTCH,A. F. 1961. Helpers among birds. Condor sisting to feed second brood. Br. Birds 34:221- 63: 198-226. 222.

The Condor 89:182-185 0 The CooperOrnithological Society 1987

DELAYED BREEDING IN YEARLING MALE GROUSE: AN EVALUATION OF TWO HYPOTHESES’

RICHARDA. LEWISAND IAN G. JAMIESON~ Department of Zoology, Universityof Alberta, Edmonton, Alberta T6G 2E9, Canada

Key words: Blue Grouse; Dendragapus obscurus; speciesthe cost of breeding for young males should be delayed breeding; territory quality; female choice; similar to that of older males. He therefore concluded polygyny;survival. that a difference in cost of breeding for young and old males was unimportant as a factor favoring delayed In most monogamous speciesof birds males and fe- breeding. The two hypothesesproposed by Wiley and males commence breeding at approximately the same Wittenberger are not mutually exclusive in that both ages,whereas in specieswith polygynousmating pat- consider female choice to be a factor in the evolution terns males often initiate breeding at older ages than of delayed breeding. However, they differ in that Wit- females (Selander 1965, Orians 1969, Wiley 1974). Al- tenbergerconsidered female choice by itself sufficient though yearling males in these latter speciesmay be to explain delayed breeding by males, whereas Wiley physiologicallyable to breed (e.g., Orians 1961, Eng believed a cost factor also was important in the evo- 1963, Hannon et al. 1979) they usually are presumed lution of this behavior pattern. to be nonbreedersif they do not defend breeding ter- We studied the demography and behavior of Blue ritories. In contrast,yearling females of the samespecies Grouse (Dendrugapusobscurus) in two areasof coastal often lay eggsand are capable of raising young. British Columbia from 1977 to 1983. This specieshas In papers on the evolution of mating patterns in a mating system in which there are no pair bonds be- grouse, Wiley (1974) and Wittenberger (1978) pro- tween males and females, and thus males breed pro- posed explanationsfor a postponementof breeding by miscuously.Our objective is to use information from males relative to females in polygynousspecies. Both this intensive study of a single speciesto evaluate Wi- authorsbelieved that females may breed preferentially ley’s and Wittenberger’s hypothesesfor the evolution with older males,and hencethat female choiceof mates of delayed breeding in male grouse. In doing so we couldbe a factorselecting for delayedbreeding by males. recognizethat it is problematic to test hypotheseson Further, Wiley suggestedthat the cost of breeding for the origin of a behavior pattern. Nevertheless, we can youngmales of polygynousspecies may be greaterthan examine how delayed breeding might currently be that for older males,this possiblyowing to their relative maintained by selectionpressure. We ask the question: inexperiencein defending territories, advertising to fe- is female choice by itself an adequateexplanation for males, and performing courtshipdisplays, which could the postponement of breeding by yearling male Blue increase their susceptibility to mortality. This would Grouse? be particularly true-if young males were relegated to taking low aualitv territories (Wiley 1981). According RESULTS to Wyley then, both female choice-and a’greater cost GENERAL BEHAVIOR OF MALE BLUE GROUSE of breeding for younger males relative to older males likely contributed to the evolution of delayed breeding. Adult male Blue Grouse occupy territories that serve Wittenberger (1978) however, argued that within primarily as areas for advertising and displaying to females (Bendell and Elliott 1967, McNicholl 1978). Territories generally range between 1 and 4 ha in size I Received 27 January 1986. Final acceptance 31 and usually include elevated portions of land such as July 1986. hills, knolls, or ridges (Bendell and Elliott 1967, 2Present address:Department of Zoology, Univer- McNicholl 1978, Lewis 1985). Males generally hoot sity of Auckland, Auckland, New Zealand. (sing) from these elevated regions, which probably fa-