Alternate Routes to Sociality in Jays—With a Theory for the Evolution of Altruism and Communal ...

18 Pages·2006·1.46 MB·English

AMER. ZOOL., 14:63-80 (1974).
Alternate Routes to Sociality in Jays—With a Theory for
the Evolution of Altruism and Communal Breeding
JERRAM L. BROWN
Biology Department, University of Rochester, Rochester, New York 14627
SYNOPSIS. The social systems of New World species of jays are compared behaviorally
and ecologically. Two lines leading to sociality are identified, one ronnectine the pair- D
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in-territory system with the colonial system and a second connecting the pair-in-territory w
n
system with the communal system. lo
Ecological factors in the evolution of communal breeding and its associated altruistic ad
behavior are considered mainly in the genus Aphelocoma, but other birds are treated ed
briefly. Three principal origins of communality and altruism in birds are identified: fro
from colonies, from a surplus of males, and by retention of young in the family, the m
latter being of greatest importance. The theory proposed for the evolution of communal h
breeding and altruism emphasizes three main processes: 1) K-selection, (2) kin selection, ttp
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and (3) kin-group selection in the same chronological order. ://a
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This paper has two goals. First, a com- evolutionary processes leading to diversity ic
parative survey of the social organization in social organization may result. A suitable .ou
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and ecology of 30 species of New World group for such an analysis might be the .c
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jays is attempted. Second, a general theory Corvidae, the family of jays, crows, magpies, m
for the evolution of communal breeding nutcrackers, and choughs, but the family /ic
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and altruistic helping at the nest in birds is too large to review here (26 genera, 102 /a
is developed. Social organization will be species) (Blake and Vaurie, 1962). I have rtic
le
viewed as resulting from natural selection limited my treatment of it to a group to be -a
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acting on individuals and kinship groups. referred to as the New World jays, all of stra
A useful way of exploring social organi- which are listed in Table 1, and mainly to c
zation is to examine the social systems in a those species with which I am familiar. t/14
group of animals that is relatively homo- With the possible exception of the pifion /1/6
geneous in terms of its morphological jay (Gymnorhinus cyanocephalus) these 3/2
adaptations yet inhabits a wide range of species seem to form a natural group (Ama- 06
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environments and exhibits a variety of don, 1944a). The group includes a wide 8
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social systems. When comparisons among variety of social organizations, environ- 6
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species within such a group are combined ments, and body sizes. y g
with detailed analyses of the population Jays, like corvids generally, tend to have ues
ecology of selected species, insights into the generalized food habits, relying mainly on t o
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large arthropods, but also taking nuts and 0
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fruits in season. Food storage is well de- A
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graTnhte MauHth o1r6's3 4r5e sefarorcmh wthaes sNuaptpioonrtaeld Ibnys tirteusteea rcohf vpelulompaegde (Tisu rccoelko rfaunl d aKndel sose, x1u9a6ll8y) . mTohneoir- ril 20
Mental Health, U.S. Public Health Service. Field morphic, the sexes being distinguishable in 19
work on Mexican jays at the Southwestern Research
the field mainly by behavior. The New
Station in Arizona was made possible by the Amer-
ican Museum of Natural History. I am indebted to World jays comprise eight genera and have
M. Slatkin, W. D. Hamilton, R. P. Bald?., J. W. their center of abundance in Central Amer-
Hardy, R. Pulliam, S. Emlen, H. Alvarez, F. A. ica, having one genus in eastern United
Pitelka, D. Ligon, C. J. Vernon, and others for crit-
States, three in western United States,
icisms and help in the preparation of this paper.
seven in southern Mexico, and two in
They are not to be blamed where I failed to follow
their advice. South America.
63
64 JERRAM L. BROWN
ALTERNATE ROUTES TO SOCIALITY
HOME RANGE OVERLAP +
AGGRESSIVE SPACING •
COLONIALITY
FOOD-SITE PREDICTABILITY.
\ \
A 50 P • 50 NH
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D
(1 NESTING \ ow
0 COLONY I nlo
CLASSIC A I ad
ALTLE-PRURRITPOORSYE PIJNAOYN y / ed fro
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TUFTED JAY b/a
rtic
K-SELECTION COMMUNAL IT Y le
KIN-GROUP SELECTION MEXICAN JAY -ab
s
RETENTION OF YOUNG tra
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= PAIR H=HELPER NH = NON-HELPING NON-BREEDER HTEORMREIT ORRAYN OGRE AREA OF DOMINANCE t/14/1
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FIG. 1. Alternate routes to sociality in jays. Sociality structure. Or it may be achieved through retention /2
may be achieved by progressive overlapping of home of the young in the territory for progressively 06
ranges together with reduction of aggressive spac- longer periods, which results in a communal social 68
ing, which results ultimately in a- colonial social structure. 76
b
y
PATTERNS OF SOCIALITY: COMPARATIVE STUDY tive survey for direct links between the gu
extreme colonial and communal forms, but es
New World jays show a variety of social there is no reliable information at all for t o
n
organizations, as summarized in Figure 1 at least nine species, and the present pic- 0
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and Table 1. Sociality has evolved in two ture may well require revision as more in- A
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distinct forms, the colonial and the com- formation becomes available. The most ril 2
munal. I will attempt to show that each of common type of social organization in New 0
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these extremely social types is connected World jays is the communal system (in the 9
through various intermediate species to the broad sense). Of 24 species and isolated
classical, all-purpose territorial type. The populations for which adequate or sketchy
existence of these intermediate forms sug- information is available, 16 typically occur
gests that there have been two separate in family-sized groups during the breeding
evolutionary lines of specialization, one season, one is colonial, and 7 occur in pairs
connecting the all-purpose territorial and (Table 1). In this section I shall compare
colonial types, and the other connecting the the intermediate and extreme forms in
all-purpose territorial and communal types. each line (Fig. 1). In the following section
There is no evidence from this compara- I shall examine the ecological determinants
ALTERNATE ROUTES TO SOCIALITY IN JAYS 65
of communal systems and discuss some the young were still fed principally by die
relevant selection pressures. parents.
From the many points of difference be-
The classical all-purpose territory tween the scrub and the pifion jays, and
between regularly spaced and colonial spe-
The classical case of an all-purpose ter- cies, I would like to select one ecological
ritory from which other jays are effectively factor of primary importance, namely, the
excluded by aggressive behavior of the home range of an individual. Scrub jays
owner is represented by the California that I have studied in California and those D
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mainland populations of the scrub jay observed by Hardy (1961) in New Mexico w
n
(Aphelocoma coerulescens). Although many had home ranges of a few acres, while lo
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nests of California scrub jays have been pifion jays in Arizona had home ranges of de
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wthaet cyheeadr s,b yn on ucmaseesro uosf hoernlpitehros lo(gaiss tsd efoinveedr wa efiegwht ss qoufa rteh em itlweso, espveecni etsh oaurge h abthoeu tb otdhye from
by Skutch, 1961) have been reported. At same. The scrub jay defends all of its reg- h
the nests of several color-banded pairs that ular home range, while the pifion jay de- ttps
I watched on the Berkeley campus and at fends only its nest. Consequently, a pair of ://a
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the Hastings Natural History Reservation scrub jays shares a small foraging area with ad
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in Carmel Valley, 1957-60, no helpers were no other scrub jays, but a pair of pifion m
present. jays shares a large area with perhaps hun- ic.o
dreds of others. Scrub jay populations ex- up
An evolutionary route to coloniality pand by settling new areas, while pinon .co
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jay populations expand mainly by colony /ic
There is only one colonial New World growth. The settling of new areas by pinon b/a
jay, the pifion jay. The following account jays probably occurs during population rtic
of it is taken from the study by Balda and crashes induced by nut crop failures, but le
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Bateman (1971). Colonies of pifion jays this is poorly documented. Both species are b
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range up to a few hundred individuals. prone to have "invasion years" (Bent, 1946; tra
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The nests are clumped. Foraging is done Westcott, 1969). t/1
almost invariably in large, closely packed Just how far a species goes along the 4/1
flocks which "roll" through the open, continuum between regular spacing and /6
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grassy woodland much like a winter flock coloniality is probably determined by (i) /2
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of European starlings (Sturnus vulgaris). the spatiotemporal pattern of food abun- 66
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Spacing in the flocks through individual- dance, (ii) the probability that one small 7
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distance mechanisms is apparently often territory will supply everything needed, b
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absent. Aggressive behavior is notably rare. (iii) the intraspecific competition for re- g
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There is apparently no defense of the sources and space, (iv) the energy costs and es
colony home range against other colonies effectiveness of defense and foraging, and t o
n
(Balda, pers. comm.). Adults separate out (v) susceptibility to predation. 0
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from the flock at the inception of breeding, An intermediate position on this con- A
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court, build nests, and feed their young as tinuum is occupied by the Steller's jay ril 2
pairs. Helpers at the nest were essentially (Cyanocitta stelleri) (Brown, 1963a). Indi- 0
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absent for the first two weeks after hatch- viduals of this species extend their foraging 9
ing. At some nests in Arizona a few adult range far into home ranges of others, yet
helpers were seen during the last 4 or 5 they maintain an area of dominance
days of the nestling period. First-year birds around their nest, which is not a territory
were not observed feeding nestlings (with as strictly defined (see Brown and Orians,
one exception) (Balda, personal communi- 1970) but which results from aggressive
cation), and they were chased away by competition. The areas of dominance of
adults. Ligon (1971) saw no helpers at nests Steller's jays are relatively small compared
in New Mexico. After fledging, the con- to their home ranges, as shown in Figure 2.
tribution by helpers increased, although The Steller's jay is not in any sense of the
TABLE 1. Social systems of New World jays.
Social
Species Range Unit Helpers Habitat ReferencesD
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Gymnorliinus cyanocephalus, pifion j. w.U.S. C Q piiion woodland 1,15 wn
Cyanocitta crislnta, blue j. e.U.S. P N deciduous woodland 2, 9,14 lo
Cyanocitta stelleri, Steller's j. w.N. Amer. P N evergreen forest 4,5 ad
Aphelocoma coerulescens, scrub j. w.N. Amer. P N scrub, chaparral 2,3,9 ed
AApphheellooccoommaa cuolterrauinleasrciennas,, Mscerxuibca j.n j. FMlae.x., Ariz. FF IA spainned- oscarku bwoodland 231,6,7 from
Aphelocoma unicolor, unicolored j. C.Ainer. F pp cloud forest 16 h
Cyanolyca viridicyana, collared j. n.S.Amer. ?? pp cloud forest 11 ttp
CCCyyyaaannnooolllyyycccaaa pcpuuuclcmuhlilrlaoat,,a b,b ealaazcuuktrie-ft-uhhlro ojo.adteedd jj.. SCE.chLui.aaPpd..-.--PHCaonoln..d. ?FF?? pp??pp cctrllooouupddic affloo,rr eesssuttbtropical 1100,,2281,28s://aca
Cyanolyca nana, dwarf j. d
V.C.Oax. P N humid pine-oak 10,13 e
Cyanolyca mirabilis, Omilteme j. m
Cyanolyca argentigula, silver-throated j. Guer. P N? humid pine-oak 10,28 ic
CCiissssiilloopphhaa ymueclaatnaoncicyaa,n Yeau,c bautasnhy j.-crested j. NCi.Rca.-rP.-aGnu.at. pFp App chlioguhd m-foornetsatn eed gfoersest 1122.25 .oup
Cissiloplia sanblasiana, San Bias j. Yuc.-Guat. F A? deciduous forest 25 .co pi
Cissilopha beecheii, Beechey's j. Nay.-Guer. F A tropical woodland 25 m
Cyanocorax cacruleus, azure j. Son-Nay. F? pp subtropical woodland /ic
CCCCyyyyaaaannnnooooccccoooorrrraaaaxxxx vcchiyreoiaisllnaptaocrtmicenuleils,lu ,a savs,zi ,cou pulruaercrl--pencolariuepssshct jd ej.. dj. j. Bsnce.erS..aBS.zAr.iAalmzmielre.r. •?FF>•?>?? ?pPp?pPp wwtroaarprmmic ,ae hlv useamrgviraden enfnoa rfeosrtest 111111 b/article-a 7>
CCCyyyaaannnooocccooorrraaaxxx accahffyrinyasinsou,p sbs,l ,Ca pcalkuy-sechnh-necsert eje.sdt ej.d j. BnCer.R.aSz..-iAVl,m eVneeernz.e.z. p?P?p? p?N?p? lowland humid forest 11 bstrac oz
Cyanocorax cyanopogon, white-naped j. e.s.Amer. F? ?? heavy forest 11 t/1
Cyanocoiax myslacalis, white-tailed j. e.Brazil ?? pp heavy forest 11 4/1
Cyanocorax dickeyi, tufted j. Ecuad.-Peru ?? pp mesquite woodland 11 /6
CCyyaannooccoorraaxx yynnccaass, ,g grreeeenn j.j .M Ceoxl.., S. Amer. SToenx..--NHaoyn.d. PF I?? htruompiicda,l pwinoeo-dolaakn dbsarrancas 28. 26, 28 3/20
Psilorhinus moiio, brown j. S.Amer. F lor A oak forest 27 66
Calocilta formosa, magpie j. e.Mex.-Pan. F I tropical forest 17,18,2087
w.Mex. F I arid woods, savannas 18,22 6
b
P = In pairs when nesting; unaccompanied by other adults or immatures; nests regularly dispersed. y g
C i= In pairs when nesting; colonial; nests clumped. u
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F — In family-sized gioups when nesting. s
I Immature helpers common at nests, but adult helpers absent. t o
= n
A _ Adult and immature helpers common at nests. 0
N := Helpers absent or only accidental at nests. 8
A
RQe =f erFelnecdegsl:ings, and to a lesser extent nestlings, normally fed only by own parents, but commonly fed by parents not their own under some circumstances.pril 2
1—Balda and Bateman (1971). 2—Bent (1946). 3—Brown (19636). 4—Brown (1963a) .5—Brown (1964). 6—Brown (1970). 7—Brown (1972). 8—Crossin (1967)0.
1
9—Hardy (1961). 10— Hardy (1964). 11—Hardy (19696). 12—Hardy (1969c). 13—Hardy (1971). 14—Laskey (1958). 15—Ligon (1971). 16—Pitelka (1951). 179—
Selander (1959). 18—Skutch (1935). 19—Skutch (1953). 20—Skutch (1960). 21—Skutch (1967). 22—Wagner (1955). 23—Westcott (1970). 24—Woofenden (per-
sonal communication). 25—Hardy (personal communication). 26—Sutton et al. (1950). 27—Humberto Alvarez (personal communication). 28—Pitelka (per-
sonal communication).
ALTERNATE ROUTES TO SOCIALITY IN JAYS §7
HOME RANGE AND AREA OF DOMINANCE IN STELLER'S JAYS
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FIG. 2. Home ranges and areas of dominance of two non-overlapping, but the home ranges of different u
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male Steller's jays in the breeding season of 1959. individuals overlap extensively. For further details .c
Notice that the area of dominance is much smaller consult Brown 1963a. N = Nest. om
than the home range. The areas of dominance are /ic
b
/a
word a colonial species, since its nests ap- probably more closely related to another rticle
pear to be regularly spaced by means of species than to the other two. The phylo- -ab
the area of dominance around each. Its genetic affinities of the pinon jay are espe- stra
compromise system allows a pair to fly long cially uncertain, since in some respects it ct/1
distances to temporarily rich food supplies, resembles a nutcracker rather than a jay 4
/1
such as acorn-bearing trees so long as it (Hardy, 1969«; Balda and Bateman, 1971); /6
3
behaves subordinately while there, but it may be a link between jays and nut- /2
still to retain priority of usage in a core crackers, a jay which has acquired nut- 06
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area used for nesting and most foraging. cracker traits convergently, or a nutcracker 8
7
The system allows individuals to gain some which has acquired jay traits convergently. 6 b
of the social advantages of flocking, such I also wish to disclaim any use of the com- y g
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as in finding temporary, rich food sources parative method to establish the direction e
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and detecting predators and harassing of evolution in this discussion. Presumably t o
n
them, without the susceptibility to preda- selection could favor either direction on 0
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tion of clumped nests. In short, the social the continuum under discussion. And, of A
sayss treemsu oltfi ntgh ef rSotmel lear'dsa jpatya tmioingsh t obf e invdieiwviedd- jcaoyusr seev,o Ilv dedo fnrootm m Setaenll etro's ijmaypsl,y a nthda tS tpeilnleorn's pril 2
0
uals to an environment that is intermediate jays from scrub jays, nor the opposite. 19
between conditions which favor coloniality
and conditions which favor pairs in all-
Some evolutionary routes to communal
purpose territories.
breeding
In the above discussion I have been con-
cerned with social systems as reflections of
individual adaptations to their environ- According to Lack (1968, p. 72) in
ments. For this purpose it does not matter "true" communal or cooperative breeding,
that the pinon, scrub, and Steller's jays several adults help to feed one brood. Al-
are not a monophyletic group. Each is though it is as good a way as any to draw
68 JERRAM L. BROWN
TABLE 2. Some evolutionary routes to communal breeding.
I) Origin from colonies
A) Communal activities other than feeding young.
1) Communal building of a single large nest or "lodge" or many burrows in which com-
partments are held by males or pairs. Social weaver, Philetairus socius (Friedman,
1950); buffalo weaver, Bubalornis albirostris (Crook, 1958); palm chat, Dulus dominicus
(Wetmore and Swales, 1931); monk parrot, Myiopsitta monachus (Friedmann, 1935);
African starling, Creatophora cinerea (Lack, 1968:72); bank swallow, Riparia riparia
(Skutch, 1961).
2) Communal guarding of young in a colony or creche. Some penguins and terns (Skutch,
D
1961). o
B) Helpers feed young at a small to moderate proportion of nests. Piiion jay (Balda and w
n
Bateman, 1971); Merops bulocki and some other bee-eaters (Fry, 1972); pied kingfishers, lo
Ceryle rudis (Douthwaite in Fry, 1972); Chaetura swifts (Sick, 1959; Skutch, 1961). a
d
C) Helpers regular at most nests. Noisy miner, Myzantha melancephala (Dow, 1970); probably e
d
t(hHea rbreisllo nm, i1n9e6r,9 )M. anorina melanophrys (Swainson, 1970); some wood swallows, Artamidae fro
m
II) Origin from leks h
A) Feeding of young not involved. ttp
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1) WCoaorpbeurragt,i ve1 9c6o6)u;r ttsuhrikpe yd,i sMplealyesa gbryis mgaallelso paatv oa Ie(Wk.a Rttsu,f f,1 9P6h8i;l oWmaacthtsu s andp ugSntoakx es,( H19o7g1a)n;- ://a
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blue-backed manakin, Chiroxipha pareola (Snow, 1963). a
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B) Feeding of young involved. No cases known. e
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III) Origin connected with surplus of males due to skewed sex ratio ic
A) Feeding of young not involved. No cases known. .ou
B) Helpers feed young at a small to moderate proportion of nests. Superb blue wren, Malurus p
cyaneus (Rowley, 1965&); bushtit, Psaltriparus minimus "melanotis" (Skutch, 1961); pygmy .co
and brown-headed nuthatches, Sitta pygmaea, S. pusilla (Norris, 1958); Tasmanian native m
hen, Tribonyx morteirii (Smith and Ridpath, 1972); colonial bee-eaters, Meropidae (Fry, /ic
b
1972); colonial pied kingfishers, Ceryle rudis (Douthwaite in Fry, 1972). /a
C) Helpers regular at most nests. No cases known. rtic
IV) Origin by non-dispersal of young in species with all-purpose territories le
A) Feeding of young not involved. No clear cases. -ab
B) Htuerlepse.rs feed young at a small to moderate proportion of nests; helpers typically imma- stra
c
1) Most young of both sexes stay one year with parents before dispersal; some help feed t/1
siblings. Florida scrub jay, Aphelocoma c. coerulescens (Woolfenden, personal commu- 4
nication; Westcott, 1970); probably rufous-fronted thornbird, Placellodomus rufijrons /1
(Skutch, 1969). /63
2) Some young males stay with parents and help feed siblings; females disperse. Superb /2
0
blue wren, Malurus cyaneus (Rowley, 19656); kookaburra, Dacelo gigas (Parry in Fry, 6
6
1972). 8
C) Helpers regular at most nests; helpers typically immatures of either sex; only one pair of 76
breeding adults per territory. Tufted jay, Cyanocorax dickeyi (Crossin, 1967); brown jay, b
y
Psilorhinus morio (Skutch, 1935; Selander, 1959); probably magpie-jay, Calocitla formosa g
(Skutch, 1953). u
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D) Similar to the preceding but with both adult and immature helpers and frequently with s
two or more breeding pairs; nest building and incubation by pairs at separate nests and t o
n
without aid from helpers. Mexican jay, Aphelocoma ullramarina (Brown, 1963b, 1970, 0
1972). 8
E) Similar to preceding but frequently two or more pairs share in building, laying, and Ap
F) Sinimcuilbaar titnog parte coendei nnge sbt.u tA nnois ,e vCirdoetnocpeh aogf inpaaei ri(nDga vwisi,t h1i9n4 2t)h.e flock. White-winged chough, ril 2
0
Corcorax melanorhamphus (Rowley, 1965a). 1
9
V) Origin involves distastefulness
A) Feeding of young not involved. No cases known.
B) Helpers regular at moderate to large proportion of nests. Anis (Crotophaga, Guira).
Highly speculative.
a line between communal and non-com- have found it useful to consider a wider
munal breeding, this usage eliminates many spectrum of phenomena, including some
species with helpers at the nest from con- which do not qualify as communal breed-
sideration. In looking for possible evolu- ing by any conventional usage. I have con-
tionary origins of communal breeding I sidered as a potential precursor of "true"
ALTERNATE ROUTES TO SOCIALITY IN JAYS 69
communality any system in which some may be so primed for parental care that it
kind of cooperation in breeding activities helps to feed young not its own.
occurs between individuals other than a The helpers in the pinon jay and terns
mated pair. In Table 2 the entire gamut is (Skutch, 1961) probably fall into the cate-
arranged according to hypothetical modes gory of rather frequent accidents, but in
of origin. Within each type of origin I have the red-throated bee-eater (Merops bulocki)
arranged the cases B through F in order helpers are regular (Fry, 1972). The ratio
of their grade or level of evolutionary spe- of 1.5 males per female favors the occur-
cialization for communal breeding. If it is rence of extra males at some of the nests D
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assumed that a complex level must have in a colony. These helpers are usually one w
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evolved ultimately from a simpler level, year old and are thought in most cases to lo
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each grade can be interpreted as having be progeny of the same pair from the pre- de
d
evolved from the preceding one and as be- ceding year. Other colonial species of bee- fro
ing a preadaptation for the following one, eaters have similarly skewed sex ratios, and m
if one exists. This is not to say that a lower in some, helpers are known or suspected, h
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grade cannot be derived from a higher one. but most have not been studied. Solitary s
The numbered categories within a grade species of bee-eaters have an even sex ratio ://a
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are not intended to be ranked or ordered and lack helpers. Thus, the communal bee- ad
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(e.g., I A 1, 2). Three types of origin, the eaters combine elements of the three types m
colonial, the lek, and the male-surplus of origins. They should cause us to have ic.o
types apparently lead rather quickly to some reservations about the earlier conclu- up
evolutionary dead ends so far as communal sion that communal breeding did not .co
m
breeding is concerned. The fourth, or non- evolve from colonial breeding. However, /ic
dispersal type, has led to the most ex- in the vast majority of colonial species se- b/a
tremely specialized modes of communal lection seems to have favored selective rtic
breeding known in birds. New World jays feeding of one's own young by making pos- le
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are well represented in the non-dispersal sible exquisite abilities for individual rec- b
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type but have only one species in the co- ognition (Beer, 1971). tra
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lonial type and none in the male-surplus A variety of communal phenomena other t/1
or lek types. All the types will be at least than feeding the young has evolved in co- 4/1
briefly considered because they help place lonial species (A 1, 2), but in all these the /6
3
the jays in better perspective, but emphasis contribution of each individual clearly aids /2
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will be on the non-dispersal type. its own offspring directly and involves no 66
8
Although it has been generally felt that significant individual sacrifice. Participa- 7
6
communal social organizations have not tion in the communal phases of nest build- b
y
arisen from colonial ones, since the pair is ing in the social weaver (Philetairus socins) g
u
typically the basic social unit in colonial and monk parakeet (Myiopsitta monachus) es
species and even in the lodge-builders is probably necessary to acquire ownership t o
n
(e.g., Crook, 1965), helpers feeding young of a nesting compartment. The role of kin 0
8
at the nest have recently been discovered selection in such cases, if any, has not been A
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in a few colonial species, including the explored, but since the colonies in these ril 2
pinon jay. Such cases are rare, however. A species are often quite large, the average 0
1
colonial system provides many opportuni- coefficient of genetic relationship among 9
ties for an individual to feed young not its colony members must be quite small, as
own. Often nests are located in the midst can be appreciated from Figure 3.
of hundreds or thousands of others of the Cooperative courtship, such as that in
same species, or young herd together into the ruff (Philomachus pugnax) and blue-
a dense creche containing hundreds of mo- backed manakin (Chiroxiphia pareola), is
bile young. Under such conditions adults not communal breeding as generally con-
may occasionally make a mistake and feed ceived, but it involves an unusual kind of
the wrong young, but it is amazingly rare. cooperation in the breeding cycle. Here
An adult which has lost its own young again, the role of kinship, if any, remains
70 JERRAM L. BROWN
10-i F = COEFFICIENT OF INBREEDING
it
F:2N -(2N -l)(l-m)2
e e
m= IMMIGRATION RATE
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SOCIO-DEMES, ca
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N = EFFECTIVE POPULATION SIZE .c
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FIG. 3. Relationship between average coefficient of value of r that was estimated using uncorrected data b
gsieznee, tNic , raetl avtairoinosuhsi pe,q uril,i barinad b eetfwfeecetniv et hep ooputublraetieodn- ifmrommi gfriaetlido no braseterv aatsi o0n.s0;3 ,N aen dw ra sa se s0t.i9m. aWteidth aas c2o.r6-, /artic
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ing effects of immigration, m, and the inbreeding rection for overlapping generations Ne would be -a
effects of small population size. The range of socio- about 3.9 and r would be 0.8. The immigration rate bs
deme sizes found in Mexican jays is shaded. (A per generation could be higher or lower than the tra
sstorcaiion-tdse; maen i se cao d-deemmee thisa t biosu bnoduendd ebdy beyc osloocgiaicl aclo no-r yaes aarnly e simtimmaitger aotifo tnh er aptee,r gwehniecrha tihoans rbaeteen. used here ct/14
geographical constraints.) The triangle marks the /1
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3
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to be explored, although it is known that (1958, p. 177) and to increased survival 0
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in one case of group display the groups are rates deriving from the protection acquired 6
8
7
composed of sibling males (wild turkey, by the occasional sacrifice of one member 6
Meleagris gallopavo) (Watts, 1968; Watts of a group, as in butterflies (Turner, 1971). by
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and Stokes, 1971). As will be argued below, these factors in u
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An origin of communal breeding through birds are conducive to the evolution of st o
an excess of males is indicated by the many communal breeding. It is worth noting n
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cases of helpers at the nest summarized by that anis are said to possess a "disagreeable 8
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Skutch (1961) in which the helpers are odor" (Davis, 1940). Whether they actually p
nearly always adult males. It was recently are avoided by predators is a point which ril 2
pointed out by Smith and Ridpath (1972) merits testing in the field and laboratory. 01
9
that this situation through kin selection The most likely mode of origin of the
should favor brothers helping each other, advanced forms of communal breeding is
and this is usually the case in the Tas- by retention of young from earlier broods
manian native hen, in which the young are for longer and longer periods. The com-
driven away by their parents before they parative series in the New World jays
can help with the next year's brood. illustrates and supports this theory (Table
A fifth factor in Table 2, distastefulness, 1, Fig. 1). The group contains species at
is highly speculative. It could lead to re- various grades of specialization, the widest
duced dispersal of the members of a family extremes being found within one small
in the manner described by Fisher in 1929 genus (Aphelocoma).
ALTERNATE ROUTES TO SOCIALITY IN JAYS 71
The lowest grades are found in the scrub carried to an extreme.
jay. California mainland populations do The highest grades of communal breed-
not have helpers; territories are defended ing have not been found in jays. These
by pairs and young disperse from their differ from the system of the Mexican jay
parents in their first fall, often forming by the participation of adult helpers in the
large flocks. Some at least breed in their nest building and incubation phases so
first spring (personal observation). In con- that two or more pairs may build and lay
trast, in the isolated Florida populations in the same nest. Only once have I ob-
studied by Woolfcnden (personal communi- served two females laying and incubating D
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cation) and Westcott (1970) young nor- in one nest in the Mexican jay (unpub- w
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mally remained within their parental terri- lished), but in the anis (Davis, 1942) and lo
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tory until their second year. Although they the white-winged chough (Rowley, 1965a) d
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nenotrsm ailnly trheem atienrerdit orayw, ayt hferyo mo ctchaesiiro npaallry- dthoixs icaclolyn,d ittihoen oicsc ufrarierlnyc e coomf maonnis. (PMaarar-- d from
acted as helpers. Thus, the first indications chant, 1960) in pairs also seems to be more h
of communal breeding are accompanied common than in the Mexican jay. ttps
by delayed reproduction and reduced dis- In brief, comparative study suggests that ://a
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persal. It is perhaps noteworthy that the communal breeding may have originated a
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total population in Florida is rather small in more than one way, and that the prin- m
and is dissected into demes by its occur- cipal way probably involves retention of ic.o
rence in small areas of thickets isolated the young in the family in a unified, so- up
from each other. cially integrated flock. The plausibility of .co
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The next higher grades are characterized this evolutionary pathway to sociality in /ic
by the regular retention and non-dispersal jays is strengthened by the existence of a b
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of young which then regularly help feed series of species with intermediate degrees rtic
the next generation raised by their parents. of specialization. Since communal behavior le
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Each flock contains only one breeding pair, is so common among New World jays, the b
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and the young presumably usually leave possibility must be taken seriously that in tra
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the flock as they mature. This condition some cases breeding in isolated pairs may t/1
has been studied in the tufted (Cyanocorax have evolved from breeding communally, 4/1
dickeyi) (Crossin, 1967) and brown jays rather than vice versa. /6
3
(Psilorhinus morio) (Skutch, 1935, 1960; /2
Selander, 1959) and probably occurs also ECOLOGY AND NATURAL SELECTION IN 066
COMMUNAL BREEDING 8
in the magpie jay (Calocitta formosa) 7
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(Skutch, 1953). Comparative studies of behavior and so- b
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The highest grade of communal breed- cial organization are useful for recognizing g
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ing presently known in jays is represented different grades of specialization and pos- es
by the Mexican jay (Brown, 1970, 1972). sible connecting links between them, but t o
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The genus Cissilopha also shows some of they do not reveal why evolution might 0
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the same features, but few details of social have proceded in one direction or another. A
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organization for it are available (Hardy, To gain insight into the selective forces ril 2
1969c; personal communication). In the involved, it is necessary to compare the 0
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Mexican jay the young continue to remain ecology of related communal and non-com- 9
with their parents; when mature they munal species. In this section I shall use
breed in pairs in their home flock at sep- ecological information from my continuing
arate nests and most individuals probably study of the Mexican jay to develop hy-
live their entire lives within their home- potheses concerning the selection pressures
flock territory. Young do not attempt to promoting communal breeding in jays.
pair and breed until the age of three years
Old theories: climate and geography
or more. At this grade, the delayed repro-
duction and reduced dispersal which was Various authors have remarked on the
first noticed in the Florida scrub jay are correlations between communal breeding
72 JERRAM L. BROWN
and climate or geography. Rowley (19656) jay (Hickey, 1952; Laskey, 1958) are known
regarded the social system of Malurus to breed in their first year as is the Cali-
cyaneus in southeastern Australia as an fornia scrub jay (Pitelka in Amadon,
adaptation to "a widely varying climate." 19446; Brown, personal observation), but
In a review of communal breeding Row- the Florida scrub jay probably breeds first
ley (1968) suggested that dispersal of the at two years of age (Amadon, 19446; West-
annual crop of young is not so urgent cott, 1970). Clutch size in the Arizona pop-
where the winter (or non-breeding season) ulation of the Mexican jay is usually four
is not so rigorous as that in the Northern or five, as it is in the Arizona subspecies D
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Hemisphere. Harrison (1969) considered of the scrub jay (Bent, 1946). Survival rates w
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that the likeliest common factor under- of Mexican jays one year old or older on lo
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lying the high frequency of communal my study area have been quite variable; de
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btor ebeed incgli mamatoe,n gm sepnetcioiensi nogf Aaruisdtirtayl iaann db iurdns- t.4h2ey i nw e1r9e7 0a-7t 1l e(ans t= . 9654 )i,n an1d96 9.8-700 i n( n1 =97 12-07)2, from
predictability of rainfall. Fry (1972) pointed (n = 39), for an average of .72. Correspond- h
out the prevalence of communal breeding ing data are not available for the scrub ttps
in "hot climates," as compared with the jay (but see Linsdale, 1949); however, ://a
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cool Temperate Zones of the world. None Hickey's study of band returns for adult ad
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of these correlations is without numerous blue jays indicates survival rates of .55-.63. m
exceptions. I submit that there is one more In a small sample (n = 22) of paired adult ic.o
basic, principal underlying cause of these Steller's jays a survival rate of at least .91 up
correlations, namely, that communal breed- was recorded in one year (Brown 19636), .co
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ers are nearly all non-migrant, permanent but this must have been exceptional. In /ic
residents. It is well known that rather long British jays (Garrulus glandarius) Holyoak b
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migrations are characteristic of most species (1971) used ring recoveries to calculate sur- rtic
of birds north of the tropics, but are com- vival rates in the first, second, and subse- le
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paratively rare in the tropics. Since it is quent years as .60 (n = 89), .45 (n = 53), b
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better in terms of fitness for a helper to and .59 (n = 44) respectively. Although tra
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aid his parents than to aid strangers (Ham- few comparative data for jays are available, t/1
ilton, 1963, 1964), we may expect the mix- the Mexican jay seems to have a relatively 4/1
ing of individuals on migration to select high rate of survival, with the exception /6
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against helpers and communal breeding. of the catastrophic winter of 1970-71. /2
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Probably another deterrent to communal Demographic data for other communal 6
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breeding in temperate and arctic-alpine breeders are vague or unavailable, but 7
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areas is the greater frequency of r-selection Corcorax delays reproduction until the age b
y
in those areas than in the tropics (discussed of four years (Rowley, 1965a), and Malurus g
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further below). cyaneus helpers delay reproduction for one es
year (Rowley, 19656). In other communal t o
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jays reproduction is delayed at least a year 0
Demographic portrait of a communal 8
and yearlings possess distinctive coloration A
breeder: evidence for K-selection p
(e.g., Cyanocorax dickeyi, Psilorhinus, Calo- ril 2
Judging from its demography, the Mexi- citta, Cissilopha). 01
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can jay is relatively K-selected in the sense
of MacArthur and Wilson (1967). This is
Reduced dispersal in communal breeders
made most apparent by comparing the
Mexican jay to the closely related scrub The question of dispersal is an im-
jay and other north Temperate Zone jays portant one since according to the theory
(which are relatively r-selected). of Hamilton (1963, 1964) we should expect
A delay in the age of first breeding until helpers (altruists) to be closely related to
about three years is the principal curtail- the parents and young that they help. The
ment of reproduction in the Mexican jay. commonest origin of helpers seems to be
The Steller's jay (Brown, 1964) and blue for the young to remain with their parents