The Auk 111(4):863-872, 1994

DOMINANT RED (GALLUS GALLUS) HENS IN AN UNCONFINED FLOCK REAR THE MOST YOUNG OVER THEIR LIFETIME

NICHOLAS COLLIASfiELSIE COLLIASfi AND ROBERTI. JENNRICH2 •Departmentof Biology,University of California,Los Angeles, California 90024, USA; and •Departmentof Mathematics,University of California,Los Angeles, California 90024, USA

ABSTRACT.--Theevolutionary success of individualsmust ultimately be evaluatedin terms of theirlifetime contribution of matureyoung to thebreeding population. The greater lifetime breedingsuccess of the moredominant hens in anunconfined flock of RedJunglefowl (Gallus gallus)gave crucial evidence why femaledominance hierarchies have evolved in thisspecies. The numberof chicksreared to independenceby 28 hensof one flockfrom 1982to 1988was significantlyassociated with a hen'sdominance, life-span, and yearof hatching.Of these, dominancewas by far the mostimportant factor. It, by itself, couldexplain differences in thenumber of chicksreared as shown by log-linearanalysis. This suggests that theassociations with life-spanand yearof hatchingmay result from the factthat theseare correlatedwith dominance.The top 3 hensin the peckorder added more offspring of breedingage to the populationthan did the remaining25 adult hensof the flock.Eleven of the 28 hensreared no youngsuccessfully. Received 8 March 1993, accepted 2 luly 1993.

THE DIFFERENTINDIVIDUALS in a natural pop- structure of the population, aside from greater ulation vary greatly in the numbers of young dispersionin nature, were basicallyand qual- that they manageto rear successfully,with pro- itatively similar in the two places.The Red Jun- found implicationsfor populationdynamics and glefowl is much hunted by humansand is one . The purposeof this report is to iden- of the mostwary of gamebirds (Bumpand Bohl tify and evaluatesome of the important factors 1961). We returned to the zoo population for that accountfor this differenceamong individ- information on details of behavior of individ- uals in an unconfined population of Red Jun- uals over the adult life-span. This information glefowl (Gallusgallus), taking into accountdif- would have been exceedinglydifficult to obtain ferencesin life-span,age ( of hatching), in the wild, and we feel that the observations and lifetime dominance status of adult hens. on the zoo population generally will be found Darwin (1887, vol. 1:258) concluded that the to apply in the field. We hope that the zoo stud- was the ancestorof the domes- ies will stimulate and provide some guidance tic , and much recent evidence accumulat- for future studies under the more difficult field ed since then has tended to confirm his view conditions. (Delacour 1977, Crawford 1990, Stevens 1991). The evolutionary significanceof individuals Not all breeds of domestic fowl have been thor- ultimately must be evaluated in terms of their oughly investigatedfrom this viewpoint, and lifetime reproductivesuccess in the population. it is still consideredpossible that genes from In recent there has been an increasing other speciesof junglefowl might have been emphasison the study of lifetime reproductive introduced by hybridization in some breeds successin . A recent review volume (New- (Crawford 1990, Stevens 1991). The Red Jun- ton 1989) summarized long-term studies on 23 glefowl hasthe specialadvantage that one may speciesof birds. Despite great differencesin be able to relate behavioral observations to the body size and life history, in all of thesespecies vast amount of work that has been done on the breeding life-span emerged as the major de- behavior, physiology,and geneticsof domestic mographicdeterminant of lifetime reproduc- fowl. tive successwhen measuredas fledgling pro- A field study of the behavior of Red Jungle- duction.However, where lifetime reproductive fowl in (Collias and Collias 1967) and a successwas measuredby the number of recruits parallel study of an unconfined population at to localbreeding populations rather than by the the San Diego Zoo (Collias et al. 1966) showed number of fledglings, life-span contributed that the behavior of the birds and the social much less to variance in lifetime reproductive 863 864 COLLINS,COLLIAS, AND JENNRICH [Auk, Vol. 111

MESA NORTH MESA ...... 'ß ß' Terr/foryof Male ßamph'tlh• N•THJ ,-" woodland', woodland •,,'•,,, RB,, ,jPA ",, YA.ß 4,YR oos .o,ø/....• • *w BB.:w ,,"..

20 meters J , , ] Fig. 1. Locationof nestsites of hensfrom centralflock. Left map:May 1982to April 1984.Right map: May 1984 to August 1988.Note shift of most nest sitesto southand near other roostingsite after original roost trees and many favored nesting busheswere removed. Since maps cover a seven-yearperiod, many of the nest sitesshown close together are not contemporary.

success,and the survival of young between competingfor food or not. Eachhen in the flock fledging and recruitment emerged as impor- knowsher placein relationto the others.Among tant. Furthermore, "wherever it could be stud- Red Junglefowl, as in domesticchickens, the ied socialrank emergedas a correlateof breed- alpha hen dominates all the others, while the ing successin both sexes."Social rank influenced omega hen dominatesnone and yields to all accessto prime resources,such as territory, food (Banks 1956). or mates.However, none of thesestudies report The first thing two strangehens will do on evidence for social rank (i.e. dominance status) meeting is to settle their future dominance re- over the adult lifetime of the birds in quanti- lations, either by active fighting, or by passive tative terms. submissionby one of the hens (Schjelderup- We made a study of the number of young Ebbe 1922, Collias 1943). Once decided, such raisedto independence(two monthsof age)and dominance relations often remain stable for to maturity (yearlings) over their lifetime by months or even years, based on habitual def- color-banded hens in an unconfined flock of erence by the subordinatehen reinforced by Red Junglefowlon the groundsof the San Di- occasionalpecks or threats from the dominant ego Zoo in southernCalifornia. We attemptto hen. Changes in the peck are rare and relate the number of young reared to indepen- result from active fighting and successfulrevolt dence by individual hens to life-span, year of by the subordinate . hatching or age class(cohort), and dominance The peck order in an undisturbed flock con- status.We evaluate the relative importance of fers somestability to the flock organization.A all three factors with appropriate statistical flock may be kept in a state of perpetual dis- analysis. organizationby frequently removing one hen The peck order of chickensis the classicex- and replacingher with a new strangehen and, ample of dominancehierarchies (Schjelderup- under these conditions, there is continual strife Ebbe 1922, Collias 1944, Allee et al. 1949). In in the flock with the averagehen being pecked general,cocks and hens have separatepeck or- more, getting lessfood, losing body mass,and ders. One hen has the "peck-right" over anoth- laying fewer (Guhl and Allee 1944).Guhl er hen, which consistently gives way when (1953, 1962) has summarized extensive studies pecked or threatenedby the former, whether of dominance hierarchies among . October1994] JunglefowlLifetime Breeding 865 866 COLLIAS,COLLIAS, AND JENNRICH [Auk, Vol. 111

Bradshaw (1992) critically reviewed methods somewhatarbitrary period, the young were consid- that havebeen most commonly used to calculate ered to be largely responsiblefor their own survival dominance among domestichens. Drickamer to maturity. and Vessey(1992) provided a selectedand bal- A mother hen and her small chicks form a very close family unit, and we routinely assignedchicks ancedsummary of the large and at times con- and a mother to each other simply by seeing them troversial recent literature on aggressionand interactingclose together time after time. Chick adop- dominance among vertebrate . tion and probably dumping are rare in this spe- cies.How frequently Red Junglefowllay eggsin each METHODS other'snests is not known, but this possibilityis min- imized becauseindividual hens often nest well apart The Red Junglefowl in the San Diego Zoo are de- from each other and away from the area most fre- scendedfrom 15 birds of the Indian race (G. g. murghi) quentedby the flock, and becausewe usually found and 12 birds of the Burmeserace (G. g. spadiceus). no more than one or two hens from the same flock Thesebirds were releasedon the zoo groundsin 1942, incubating at the same visit. and the current population is descendedfrom them We consistentlysought and mappednest sites(Fig. (Lint 1971). The zoo birds generally meet the criteria 1) by watching clucking hens return to their nests of Delacour (1977) for wild (versus domestic) Red after being off the nest for 0.5 to 1.0 h, generally in Junglefowl,because the great majority of individuals the morning. We could then expectto seethose hens have dark legs and the cocksmolt their neck hackles with chicks at our next visit to the zoo. Domestic hens, in the summertime. like Red Junglefowl hens, resistor refuse copulation Gray foxes(Urocyon cinereoargenteus), domestic cats when incubating and broody (clucking).At this time (Feliscattus), and Cooper'sHawks (Accipitercooperi) the ovary is regressed,the hen ceasesto lay, and the roam the zoo groundsfreely and capturejunglefowl, clutchcan be assumedto be completed(Collias 1950). especiallychicks, but we made no quantitative study The averageclutch size was 8.1 eggsfor 18 hens for of predation. which we also knew the life-span, and only about We selected one flock, the central flock, for detailed 11% of 511 eggs laid in 64 clutches became chicks study of socialbehavior and lifetime breeding suc- reared to independence. Not all nests were found, cess.Like other flocksin the zoo, this one occupied and since most small chicks are lost (Collias et al. the sameroosting trees each evening. Birdswere cap- 1966),the important criterion that we usedfor breed- tured for banding by driving them into mist nets and ing successof hens was the number of chicksthey by baiting them into nooseson the ground, which reared to independence.Of 62 chicks reared to in- were then drawn about their legs.Each bird was given dependence,46 (74%) becameyearlings (i.e. reached two colored leg bands in an individually distinctive maturity). combination(the same on each leg for rapid identi- During each visit we made opportunisticobserva- fication). tions on the peck order and continued to do so over As a rule, we visited the zoo every two months for the lifetime of the birds. To ascertain dominance re- three-day trips, observing the birds and recording lationsbetween any two birds, we tosseda bit of food, broodsfrom 1982 to 1989. Each individual, exceptthe usually a peanut, sometimesa mealworm, between three oldest hens, was followed over its lifetime. We the birds and recordedwhich one pecked or threat- also made two visits in May 1981 for preliminary ened the other away from the food. We define the assessment of the situation. The three oldest hens lifetime domination index for a hen as the proportion when the studybegan all had broodswhen they were of hens she dominatesamong all she encountersag- first observed (BB in 1981, GG and WW in 1982), so onistically. More precisely,let Na be the number of at that time they were at least of yearling age. The hens she is seen to dominate at least once during her estimateof the life-span of thesethree hens is a min- entire lifetime starting when she is classifiedas a imum estimate,but over the whole study they were yearling, and let Ns be the number of hens to which among the seven hens with the longest life-spans. she is seen to be subordinate over the same period. We judged the chicksto be able to care for them- The domination index for this hen is Na/(Na + selvesin feeding, roosting,and predator-avoidance Most hens have no dominance reversals (i.e. there are behavior when they were about two months of age, no hens that she is seen to dominate on some occa- and then we recordedthem as having been rearedto sions and to be subordinate to on later occasions).For independence.Only onehen bredin the yearin which such a hen, the domination index is simply the pro- she was hatched,and breeding by the hens generally portion of hens she is seen to dominate among all beganearly in Marchof the following year. The birds hens she is seen to encounteragonistically. were consideredto be yearlingsand adultsat the start Sincethe henson the averagelived only two years, of the calendaryear following the one in which they they interactedvery largely with their own ageclass. were hatched.Until the chicksreached independence Since the birds lived to widely different ages, the at abouttwo months,their survivalwas judgedto be domination index, which can only refer to the inter- the primary responsibilityof their mother.After this actions of a bird with living contemporaries, gives October1994] JunglefowlLifetime Breeding 867

T^I•Lœ2. Peck order among yearling and older hens in central flock (February 1986 to December 1988). Pecks or threats given subsequent to reversals of status are in boldface.

Hatched Age not Hatched 1983 Hatched 1985 Hatched 1986 1987 known a

RW YS RB YA• BW WP PR GP PA GY2 YR2 AA GR3 GR2 RA2

RW -- 8 4 3 1 1 1 3 YS -- 17 18 4 2 8 5 8 1 2 8 RB 4 1 -- 15 1 7 4 2 7 2 5 1 7 YA2 3 -- 2 6 9 2 3 1 5 BW -- 3 2

WP -- 6 1 1 PR 1 -- 6 10 1 2 12 GP -- 2 PA 2 --

GY2 1 YR2 AA 3 GR3 GR2 1 I 2 RA 2

Adult when first observed. the best estimate of the dominance status of a bird to independence during a seven-year period, over its lifetime. The peck orders for all observed while the rest of the hens failed to raise any encountersare given in Tables1 and 2, for early (1982- young to independence.The broodsfailed (eggs 1986)and late (1986-1988) periods,respectively. The or chicks lost) for seven hens (25%), and four greatmajority of possiblepaired interactionsbetween all the birds were observed. hens(14%) apparently never had eggsor chicks. Nicholas and Elsie Collias made the behavioral and Of the 28 hens of the central flock whose ap- population observationsat the zoo. Robert Jennrich proximate life-spans were known, 17 hens that evaluated the relative importance and interrelations rearedchicks to independencehad averagelife- of the major factors in reproductive successof the spansof about three years (35 months),and the hens using a log-linear model analysis.The analysis II hens that failed to rear any young to inde- used the statisticalprogram SAS PROC NLIN (SAS pendence had average life-spansof about two Institute 1985).Nonparametric statistical tests are from years (23 months; t = 2.1126, P < 0.025, one- Siegel and Castellan (1988). tailed test). The average lifetime domination index of successful hens was 0.51 and that of unsuccessfulhens was 0.30 (t = 1.8359,P < 0.05, RESULTS one-tailed test). The four most successfulhens (BB, GG, WW, Tables I and 2 show the peck order in the YS) in their lifetimes raised more chicks (30) to flock from November 1982 to December 1988. independencesuccessfully than did the 24 re- Females BB, GG, and WW were the most dom- maining hens combined (29 chicks),and these inant birds in the central flock and kept the four hens also averagedabout twice the life- sameposition in the peck order over their adult span and over twice the dominance status of lifetime while in this flock. The peck order the remaining 24 hens (Table 3). shown here is generally linear, but Table I il- We also consideredthe life-span and average lustratesa triangle involving GW who pecked dominance status of the different age classes WB who pecked GB who in turn pecked GW. (cohorts) of adult hens in the central flock that The peck order amonghens showsconsiderable hatched from 1981 to 1987 in relation to their stability over time, but there were occasional breeding success(Table 3). The age classrefers reversalsof dominanceand thesepersisted (Ta- to the year in which each class of hens was bles I and 2). hatched. The most dominant and successful hens Only about 60% of the 28 hens in the flock belongedto the oldestage class (Table 4). Hens with known life-spansmanaged to rear young in each age classusually dominated the birds 868 COLLIAS,COLLIAS, AND JENNRICH [Auk, Vol. 111

TABLE3. Lifetime breeding successin relation to age class(year hatched), life-span, and dominancestatus of 28 hens in the central flock of Red Junglefowl,1982-1989.

No. chicks reared to Life-span Domination Hen Year hatched (months) index Independence Maturity BB Before 1982 57 1.000 7 7 GG Before 1982 47 0.950 10 9 WW Before 1982 41 0.900 11 10

GW 1982 37 0.684 3 3 WA 1982 36 0.529 3 3 WB 1982 30 0.684 0 0 GB 1982 24 0.632 0 0 YR 1982 18 0.667 5 2 GR 1982 17 0.454 2 0 GY 1982 17 0.222 1 0 YW 1982 17 0.110 1 0 YA 1982 13 0.000 0 0

YS 1983 71 0.522 5 4 RB 1983 57 0.520 0 0 YA2 1983 47 0.500 3 1 RW 1983 41 0.364 2 2 BW 1983 33 0.176 2 1 BA 1983 21 0.143 0 0 RA 1983 20 0.461 1 0 YB2 1983 12 0.454 0 0 GP 1985 34 0.125 1 1 WP 1985 26 0.429 1 1 PA 1985 25 0.125 0 0 PR 1985 18 0.461 0 0

AA 1986 33 0.600 4 2 GY2 1986 17 0.250 0 0 YR2 1986 15 0.000 0 0 GR2 1987 23 0.000 0 0 of the next younger age class(Tables ! and 2). known life-spans (Table 3). These three hens More of the chicksthat reachedmaturity (i.e. were alsoat the top of the peck order (Tables! becameyearlings [26]), were offspring of the and 4). three hens of the oldest year classthan were A plot of the number of young reared to in- produced(20) by the remaining 25 hens with dependence(number of young) against domi- nanceof the hens(Fig. 2A) showsa relationship between these two variables.Similar plots of TABLE4. Lifetime breeding successand dominance the number of young againstlife-span (Fig. 2B) of different age classesof hens in an unconfined flock of Red Junglefowl. and against age class (Fig. 2C) show weaker relations. Mean no. chicks Log-linear-modelsignificance and goodness- Meanlife- domin-Mean reared per hen to of-fit tests were carried out for each plot. For Year hatched span at-ion Indepen- Ma- the plot of number of young y on dominance (n hens) (months) index dence turity d, it was assumedthe countsy have indepen- Before 1982a (3) 48 0.950 9.3 8.7 dent Poissondistributions with expectations: 1982 (9) 23 0.442 1.7 0.9 1983 (8) 38 0.392 1.6 1.0 f = e•+•d. (1) 1984 Breedinglargely failed 1985 (4) 26 0.285 0.5 0.5 This definesa log-linear Poissonmodel (e.g. see 1986 (3) 22 0.283 1.3 0.7 Haberman 1974).The curve displayedin Figure 1987 (1) 23 0 0 0 2A is the maximum-likelihood fit under this

• Year of hatchingunknown for three startingadult hensin 1981and model to the data displayed. As can be seen 1982. from Table 5, dominance is a very significant October1994] JunglefowlLifetime Breeding 869

12 TABLE5. Pearsonchi-square statistics for six log-lin- A o ear Poissonmodels. The X• is goodness-of-fitsta- tistic for indicated model and X•2 is difference chi- squarestatistic for significanceof indicatedvariable in indicated model. f=eC•+•Bd Vari- øø Model(log f) X• ablea X• df P-value 109.61 27 0.0000 fid 31.85 26 0.1981 o o o d 77.76 1 0.0000

oo o tim 74.23 26 0.0000 m 35.38 1 0.0000 o o o % 38.79 22 0.0149 c 70.82 5 0.0000

O.I•D co o coo o o fi,d + fi2m 28.86 25 0.2698 d 45.37 1 0.0000 o'.o o!2 o'.4 o'.6 o'.8 1'.o m 2.99 1 0.0838 dominance status fid + % 27.92 21 0.1424 d 10.87 1 0.0010 c 3.93 5 0.5595

12' dominance, m = months of life-span, c = age class. B o

o predictor of number of young (X•2 = 77.76, P = f=e•+•Bm 0.0000). The chi-squarestatistic for the signifi- cance of a particular term is obtained by sub- o tracting the goodness-of-fitchi-square for the model from the goodness-of-fitchi-square sta- tistic for the model with the term omitted. Here o o the two models are a + /•d and a and the sub- co o traction gives X 2 = 109.61 - 31.85 = 77.76. Moreover, the Pearsonchi-square goodness-of- o •o •o•o fit test for model 1 is not rejected(Xg 2 = 31.85,

cooco oa•o o o P = 0.1981). This says that dominance alone lb 2b 4'o 7b 8b provides a reasonablyadequate fit. A similar lifespan in months analysis using life-span shows that it also is a highly significant predictor (P = 0.0000), but that it alone does not provide an adequate fit (P = 0.0000). Becauseage classis not expected 12 ÷ c to be ordinally related to the number of young, an exponentialrelation similar to that in model 1 is not expected. One can, however, use an exponential relation that treats age classas a categoricalvariable; when this is done, ageclass is a highly significant predictor of number of young (P = 0.0000), but it alone is not an ade- quate predictor (P = 0.0149). These results say that dominance,life-span, and ageclass are each highly significant predictorsof the number of young, but that only dominance is, by itself,

3 5 6 inance statusd of hens; (B) life-span m in months; age class and (C) age classc of the hens. On abcissa,1 refers Fig. 2. Number of young rearedto independence to youngestage class(1987) and 7 to oldestage class by 28 hens in their lifetime plotted against:(A) dom- (hatched before 1982). •70 COLLIAS,COLLIAS, AND JENNRICH [Auk, Vol. 111

•BB tus of the adult hen was by far the most im- portant factor. •YR •BY •BW •'GW •'YR •AP <•GP Yearling hens often fail to raise chicksto in- , I I I dependence in their first year after the one in •YB• •'YS •AG •'WBr which they hatched,but may breedsuccessfully in later years.When successin the first year and

•GG the averagesuccess in later yearsfor each hen was compared, a Wilcoxon matched-pairs, •YA •GW •YW •'GY •RW <•RW •'RA •'WP •'PY signed-rankstest (Siegeland Castellan1988) for eight hens for which we had more than one •GY• •GP •PR •'YBr •YR• •'AY• year'sbreeding record gave a P-value of 0.005 (one-tailed test). I , We comparedthe dominancestatus of 20 Red •'RA• •'AR• Junglefowl hens in the central flock with the dominance status of their mothers. There was no significant correlation (r = 0.09). However, •ww the different generationswere intermingled as they occurrednaturally. Most henswere daugh- •WB •GB •GY •GR •GR •AR •RA •RB •BB ters or granddaughtersof the three top hens in the flock. The more seniorhens of the older age Fig. 3. Matrilines, showing descendants that classestended to dominate hens of younger reachedat leastyearling age, of three top hens (BB, generationsregardless of relationship.Figure 3 GG, WW) in peck order of central flock. showsthe yearling descendantsof the three top hens. These three hens and someof their year- ling offspring comprisedtwo-thirds (6 males sufficientto explain the variation in the number and 6 females) of the 18 emigrantsfrom the of young, at leastto the degreeexpected under central flock roost to other flock roosts from our log-linear model. Life-span alone and age 1982 to 1988. classalone fail by significantmargins to explain this variation. DISCUSSION Since life-span is correlatedwith dominance (r = 0.523), it is possible that the relation be- The resultsof our study are consistentwith tween number of young and life-span may re- the principle that relatively few individuals of- suit only from this correlation. To investigate ten produce most of the young added to the this we considereda log-linear model of the breeding population in the next generation form (Newton 1989).Statistical analysis showed that an important reasonfor this result was the high f = ea+i•ld+i•2m' dominancestatus of the more productive hens. using both dominanced and life-span m. The This result was based on the lifetime dominance chi-squaresignificance tests given in Table 5 statusand breeding successof 28 hens in one indicate that dominance is very significant in large flock over a seven-yearperiod. It would this model (P = 0.0000), but life-span is not (P of coursebe desirable to study other flocks in = 0.0838). This says that after accountingfor this fashion. However, such data are difficult to dominance,life-span does not havea significant obtain and, as yet, there seem to be no com- effect.A similar analysisusing dominanceand parable data in the literature. That the results age classwith the latter treatedas a categorical have general significanceis strongly implied variable indicatesagain that dominanceis quite by the many studiesthat have been done on significant (P = 0.0010), but age classis not (P peck orders of domestichens using aggressive = 0.5595). precedenceto food as the primary criterion for In conclusion,among the adult hens of this dominance. Dominant mother hens, therefore, flock, all three of the factors--dominance, life- shouldgenerally be able to nourishtheir chicks span,and age class--are strongly related to the more adequatelythan do subordinatehens. number of young reared to independence. While the degree of egg dumping is appar- However, in our study, lifetime dominancesta- ently still unknown for Red Junglefowl, such October1994] JunglefowlLifetime Breeding 871 conspecificegg parasitismis likely to be infre- in part on what we chooseto measure.There quent. Any egg dumping that occurredwould may be other correlationsbetween reproduc- not seriouslyaffect the validity of the conclu- tive successof the hens and factors as yet un- sion that by far mostof the apparentreproduc- measured. Thus, the dominance status of mother tion was by the more dominant hens. If a sub- hens has not been separatedfrom differences ordinate hen laid an egg in the nest of a in certain other correlates of motherhood, in- dominant hen, the latter might be creditedwith cluding such things as effectivenessin protect- an extra young one. Conversely,if a dominant ing the young from predators,skill in guiding hen laid in the nest of a subordinate hen, this chicksto food or shelter, or diligence in brood- would reduce the number of chicks credited to ing the chicks. the dominant bird. Nevertheless,despite such In conclusion,we have managedstatistically hypotheticalqualifications, or any genetic ad- to evaluatethe relative importanceof life-span, vantagefrom effectiveegg dumping, the facts age class,and dominancefor number of chicks are that the more dominant hens still succeeded reared successfullyby the hens in one uncon- in rearing by far the greatestnumber of young fined flock of Red Junglefowl o,•er a seven-year to independence.In nature, the lower popula- period, but even these factors are highly cor- tion densitiesthat generallyprevail (Colliasand related and often work together. Dominance Collias 1967) would make egg dumping even statusof the hen givespriority to food and other less likely. resources,and was the most important factor in The dominancefactor can be analyzed fur- our study. Many of the factors accounting for ther into terms of genetics.Siegel and Dun- variation in numbers of chicks reared are un- nington (1990) recently have reviewed the be- known. However, the large contribution to the havioral geneticsof . For example,Guhl next generation coming from the most domi- et al. (1960) effectively selected for high and nant hens, and most probably also from the low levels of aggressivenessin two different mostdominant cock,suggests that somegenetic strainsof White Leghornscarried to the F4gen- basisfor aggressivenesswill be maintained in eration. Beginning with the F2 generation, the the population. two lines showedsignificant differences in the percentageof initial paired encounterswon or ACKNOWLEDGMENTS lost, as well as in high or low ranks in the peck We thank the ZoologicalSociety of San Diego for orderswhen hens from the two lines were put permissionto do the researchat the San Diego Zoo, in the same flock. However, there was no sig- and the zoo personnelfor their help, especiallyA. C. nificant correlation in our study between the Risser,K. C. Lint, D. Rimlinger, and L. Ordonez. We dominance statusof hens and of their daugh- appreciatehelp in netting someof the birdsfor band- ters, indicating considerable importance of ing by Karen Collias, Elizabeth Flint, Mr. and Mrs. nongeneticand environmental factorshelping K. Morgan, and Mr. and Mrs. E. Taylor. We thank Lee to decide dominance status. Drickamer, Ron Mumme, Gary Schnell, and Randy Senescence in domestic hens was reviewed Thornhill for helpful commentson the manuscript. The researchwas funded by a grant from the Uni- by Hutt (1949:333-339).Production of eggstends versity of California, Los Angeles. to decline in successiveyears after the first year

of laying. Maternalmotivation may alsodecline LITERATURE CITED with age. In the JapaneseNagoya breed of do- mestic fowl, Saeki (1957) found a steady de- ALLEE,W. C., A. E. EMERSON,O. PARK, T. PARK,AND crease after the first laying year in the per- K. P. SCHMIDT. 1949. Principles of ecol- centageof hens that becamebroody and in the ogy. W. B. Saunders,Philadelphia. averagenumber of broody periodsper hen each BANKs,E.M. 1956. Socialorganization in RedJungle year. However, we do not believe senescence Fowl hens (Gallusgallus subsp.). 37:240- 248. wasan important factorinfluencing the number BRADSHAW,R. H. 1992. Describingsocial order in of chicks reared in the central flock of Red Jun- laying hens (Gallusdomesticus). J. World glefowl, since the three oldest hens were also Assoc. Vols. 15 and 16:81-92. the hens which raised most young in their life- BUMP,G., AND W. H. BOHL. 1961. Red Junglefowl time (Table 5). and Kalij .U.S. Fish and Wildlife Ser- The identification of significantcauses of dif- vice, Washington,D.C., Spec.Sci. Rep., Wildlife ferencesin lifetime breeding successdepends no. 62. 872 COLLIAS,COLLIAS, AND JENNRICH [Auk, Vol. 111

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