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whom shoulda Mockingbirdbe aggressive?
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ReproductiveSynchronyand PredatorSatiation:an AnalogyBetween
the Darling Effectin Birdsand Mast Fruitingin Plants
MICHAEL
GOCHFECD
Departmentof Environmental
andCommunity
Medicine,Collegeof MedicineandDentistryof New Jersey,
RutgersMedicalSchool,Piscataway,New Jersey08854USA
Breeding synchrony characterizes many taxa.
Somefactorsimpose or selectfor synchrony,while
others entrain it on a more immediate, proximate
basis. Observed synchronyin a population representsa compromisebetweensynchronizingand desynchronizingfactors.Avian ecologiststracediscussion of synchronyto F. FraserDarling (1938), who
proposedthat, in gulls, synchronywas adaptive in
minimizing predation on young. He assumedthat
a predator has a finite appetite and that there is no
recruitment of predators (Gochfeld 1980: 256). As
long as the numberor biomassof youngwasbelow
this predation threshold(a term he did not use), all
might be consumed.Synchronoushatchingwould
yield a superabundanceof young for a brief period,
allowing some to surviveas predatorsbecamesatiated. Darling's model is attractivein linking evolution and ecology(selectionvia reducedpredation)
with behavior and physiology(socialfacilitation in
large groupsenhancingneuroendocrinestimulation
leadingto increasedsynchrony).Despitethis attractiveness, few studies have found support for the
model.A relationbetweensynchronyand groupsize
or improved productivity is demonstrablein some
studies (Hall 1970, Collias et al. 1971, Burger 1979,
Gochfeld 1979), while Nisbet (1975) found evidence
for timing and predatorsatiation.Somestudieshave
found no evidence for the model (Orians 1961,
MacRoberts & MacRoberts 1972).
The complexitiesof studying these interrelated
JULY1982]
ShortCommunications
factorsin wild birds have led to frustration. Logistic
problemsarise in documentingreproductivesuccess
over a range of colonysizes, densities,and degrees
of synchrony.Also, predation is seldom witnessed
and must be measuredindirectly. In particular cases,
desynchronizingfactorsmay operatemore strongly,
leadingto low synchrony,or alternativesynchronizing factors (e.g. weather, seasonalfood variation)
may operate (seeGochfeld 1980).
It is hearteningto find analogiesamongothertaxa,
587
ator satiation is unimportant. The analogyof mast
fruiting shouldencourageornithologiststo searchfor
avian systemssuitablefor studying the Darling Effect in general and predator satiation in particular.
LITERATURE CITED
ARNOLr>,S. J., & R. J. WASSERSUG.
1978. Differential
predation on metamorphic anurans by garter
snakes (Thamnophis):social behavior as a pos-
sible defense.Ecology59: 1014-1022.
for examplethe apparentroleof synchronous
calving
BURGER,
J. 1979. Colony size: a test for breeding
of ungulates(Estes1966) or the metamorphosisof
synchronyin Herring Gull (Larusargentatus)
col-
anurans(Arnold and Wassersug1978)vis-a-vis predator satiation. An important analogyseeminglyoverlookedby ornithologistsis the mastfruiting of plants
discussed in detail by Janzen (1969, 1971, 1976).
Many plant seeds are subject to intense predation,
and many chemical and dispersive strategieshave
evolved to minimize predation. Janzen (1969) hypothesized that synchronous or mast fruiting
achievedpredator satiation. Among the critical assumptionsare (1) seedsare available to the predator
for a shorttime in superabundance,
and (2) predators
cannotmaintain high populationsin the absenceof
the food source. These assumptionsunderlie the
Darling Effect as well. If predatorpopulationsbuild
up as food increases,satiationwill not occur;in fact,
increased predation pressure might render synchrony maladaptive in somecases.
Janzen's (1971) scenario on the evolution of mast
fruiting involves plants storing energy for one or
more years and then producing a massive crop.
Plants fruiting out of synchronywould be quickly
selected against, and predators might find years
when the food sourceis not available. By analogy,
chicks hatching outside the peak would be vulnerable to predation (Nisbet 1975), and chick-predators
would not linger at a colony when chicks were unavailable(unhatchedor too large to eat). The analogy
betweenmast fruiting and the Darling Effectseems
a good one, though the time scalemay be years in
the former and weeks in the latter.
onies.
Auk
96: 694-703.
COLLIAS, N. E., J. K. VICTORIA, • R. J. SHALLINBERGER. 1971. Social facilitation
in weaverbirds:
importanceof colony size. Ecology52: 823-828.
DARLING, F. F. 1938. Bird flocks and the breeding
cycle. Cambridge, Cambridge Univ. Press.
ESTES,
R. D. 1966. Behaviourand life history of the
wildebeest. (Connochaetestaurinus Burcheil).
Nature
212: 999-1000.
GOCHFELD,
M. 1979. Breeding synchrony in Black
Skimmers: colonyus. subcolonies.Proc. Colonial Waterbird Group 2: 171-177.
--.
1980. Mechanismsand adaptivevalue of reproductive synchronyin colonial seabirds. Pp.
207-270 in Behavior of marine animals, vol. 4.
Marine birds (J. Burger, B. Olla, and H. Winn,
Eds.). New York, Plenum Press.
HALL,J. R. 1970. Synchronyand socialstimulation
in colonies
of the Black-headed
Weaver
Ploceus
cucullatusand Vieillot's Black Weaver Melanopteryx nigerrimus.Ibis 112: 93-104.
JANZEN,D. H. 1969. Seed-eaters versus seed size,
number, toxicity and dispersal.Evolution 23: 127.
--.
--.
1971. Seedpredation by animals. Ann. Rev.
Ecol. Syst. 2: 465-492.
1976. Why bambooswait so long to flower.
Ann. Rev. Ecol. Syst. 7: 347-391.
MACROBERTS,M. H., & B. R. MACROBERTS. 1972.
Social stimulation of reproduction in Herring
Judgingfrom the numerouspapers that open by
and LesserBlack-backedgulls. Ibis 114:495-506.
citingDarling (1938),onemustassumethat his modNISBET,I. C. T. 1975. Selectiveeffectsof predation
el has had heuristic value in challenging ornitholoin a tern colony. Condor 77: 221-226.
gists to investigatea complexinteractionof factors. ORIANS,G. H. 1961. Social stimulation within blackFailure to find supportingevidencein some cases,
bird colonies. Condor 63: 330-337.
or the operationof alternativesynchronizingfactors
in other cases,cannotbe taken as evidence that pred- Received22 October1981, accepted7 January1982.