July1987]
ShortCommunications
535
$ULKAVA,
$. 1969. On smallbirdsspendingthe night
in snow. Aquilo Ser. Zool. 7: 33-37.
TAYLOR,
W.K. 1971. A breeding biology of the Verdin, Auriparusfiaviceps(Sundevall) in Arizona.
an energetics.Pp. 127-204 in Granivorous birds
in ecosystems(J. Pinowski and S. C. Kendeigh,
Eds.). New York, Cambridge Univ. Press.
KNORR,O.A. 1957. Communal roosting of the Pygmy Nuthatch. Condor 59: 398.
McNICHOLL,M.K. 1979. Communalroostingof Song
WALSBERG,
G.E. 1986. Thermal consequencesof roost-
Sparrowsunder snowbank.Can.Field-Natur.93:
site selection:the relative importance of three
325-326.
modes of heat conservation.
NEWTON,I. 1969. Winter fattening in the Bullfinch.
Physiol. Zool. 42: 96-107.
PITTS,T. D. 1976. Fall and winter roosting habits of
Carolina
PORTER,W.P.
chambers.
Chickadees.
Wilson
Amer.
Midl.
85: 289-328.
Auk
103: 1-7.
ß& J. R. KING. 1978. The heat budget of incubating Mountain White-crowned Sparrows
(Zonotrichialeucophrys
oriantha)in Oregon. Physiol. Zool.
Bull. 88: 603-610.
Natur.
51: 92-103.
1969. Thermal radiation in metabolic
Science
166: 115-117.
Received11 August1986, accepted7 February1987.
ROl•IN$ON,D. E., G. S. CAM?I•ELL,& J. R. KING. 1976.
An evaluation of heat exchangein small birds. J.
Comp. Physiol. 105: 153-166.
The Center-edge Effect: The Result of a War of Attrition Between
Territorial
LuC-ALAIN
Contestants?
GIRALDEAU L3 AND RON YDENBERG 2
*Department
of Psychology,
Universityof Toronto,
Toronto, Ontario M5S 1A1, Canada, and
2Departmentof BiologicalSciences,
SimonFraserUniversity,
Burnaby,BritishColumbiaV5A 1S6,Canada
Residentbirdsoften respondmoreintenselyto simulated intrusions at the center than at the edge of
their territories[thecenter-edge(CE)effect;Falls1982].
Very few hypotheseshave been proposedto account
for the ecologicalsignificanceof the effect. Explanations of the CE effect are of two types. First, the intruders are more likely to be closerto residentsin the
center than at the edge of the territory. It follows that
if a resident'sresponseis graded as a function of the
distance to the opponent (and not position on the
territory), CE effectsmay be the result of proximity
between
contestants
rather
than of the intruder's
lo-
cation on the territory. A secondtype of explanation
arguesthat the centerof a territory hasa higher value
to a residentthan the periphery. We examinedthe
ways territory centersmight be more valuable than
the periphery and used game theory to generate predictionsfor each hypothesis.We testedthe predictions againstdata from an exhaustivereview of the
literature
on avian
territorial
defense.
The intensity of a resident's responseto intrusion
can vary continuously from mild through intense
threat displays,to outright violence.Territorial contests can be analyzed in terms of a war of attrition
(Parker 1984). In a war of attrition with no informa-
tion about opponents(Bishopet al. 1978), the evolutionarily stable strategyis to choosea persistence
time based on the ratio V/K, where V is the value of
winning and K the rate at which costscan be expendedduring the contest(Parker 1984).We assumed
that the intensity of an individual's responsedenotes
its evaluation of V/K, an assumptionsupported by
Enquist et al. (1985), Ewald and Orians (1983), and
Krebs (1982).
The rate at which costsare expended(K) during a
contestis set by an animal's resourceholding potential (RHP). RHP is not likely to explain the CE effect
because,although an individual's RHP can change
slowly over time, there is no reason to expect it to
changewith position on the territory. On the other
hand, there are three ways the value of winning (V)
can changewith the distancefrom the territory center
to the location of the contest. In the strategic-center
hypothesis,
losing possessionof the center of a territory more likely leads to lossof the whole territory
than does forgoing an equivalent surfaceat the periphery. The center therefore has a higher strategic
value than the periphery. Becauseall territories have
centers, the CE effect should be a characteristic of all
territorial defense. In the central-placeforaginghypothesis,
many birds feed their young with food collected on their large territories. If birds defend exclusive access to food resources located around
• Presentaddress:Department of Biology, Concordia University, 1455 ouest, Boulevard de Maisonneuve, Montreal, Quebec H3G 1M8, Canada.
a central
nest, then the value of winning exclusiveaccessdeclines with distancefrom the territory center. This is
becausethe rate of food delivery to the nest declines
536
ShortCommunications
[Auk,Vol. 104
T^BLE1. Presenceor absenceof differential responseto intrusionsat the territory center and periphery in
24 species.Information was obtained by observation(O), playback (P), or stuffed or live model (M). Territories were classifiedas central-place foraging (CPF) or central nonfood resource(CR).
Family
Species
Method
CPF
CR
Source
M
M
Yes
Yes
Nest
Nest
Spray 1978
Baeyens1981
Spizellapusilla
P
Yes
Nest
Goldman
Zonotrichia
P
Yes
Nest
Falls and Brooks 1975, Me-
O
No
Nest
Burger and Beer 1975
Haematopolidae Haematopus
ostralegus
O, M
Yes
Nest
Vines 1979
Mimidae
Dumetella
P
Yes
Nest
Harcus
Paridae
Parusmajor
P
Yes
Nest
Dhondt 1966, Falls et al. 1982
Parulidae
Dendroica discolor
O
Yes
Nest
Nolan
Setophaga
ruticilla
P
Yes
Nest
1978
Ickes and Ficken
Caseswith center-edgeeffect
Corvidae
Corvus cotone
Pica pica
Fringillidae
albicollis
1973
lemis and Falls 1982
Laridae
Larus atricilla
carolinensis
Caseswith no center-edgeeffect
Icteridae
Agelaiusicterocephalus
1973
1970
P
No
Nest
Wiley and Wiley 1980
Motacillidae
Laridae
Motacilla alba
Larus ridibundus
0
0
Scolopacidae
Tetraonidae
Numeniusarquata
Centrocercus
urophasianus
Lyrurustetrix tetrix
0
0
0
No
No
No
No
Nest
No
Davies and Houston 1981
Patterson
1965
Ens and Zwarts 1980
Trochilidae
Amazilia tzacatl
Atthis heloisa
Colibri thalassinus
0
0
0
Eugenes
fulgens
Hylocharisleucotis
Lampornisclemenciae
L. amethystinus
Selasphorus
rufus
0
0
0
0
0
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
Wiley 1973
Kruijt and Hogan 1967
Boyden 1978
Lyon 1976
Lyon 1976
Lyon 1976
Lyon 1976
Lyon 1976
Lyon 1976
Paton and Carpenter 1984
as distance
between
the food and the nest increases
(Ydenberget al. 1986).If the CE effectis the result of
central-placeforaging,then the effectshouldbe present only in territoriesthat are usedfor central-place
foraging and contain the central place. The intensity
of the resident's responseto intruders should decreasegraduallywith distancefrom the centralplace.
In the central-resource
hypothesis,
the centerof the territory may containa discreteresource(nest,young,
refuge) that makesit more valuablethan the rest of
the territory. The CE effect should occur only when
and Ficken 1970, Vines 1979), suggesting that the
number of instances of CE effects reported in the
literature may be overestimated.The prediction of
the central-place foraging hypothesis therefore is
consistent with
the distribution
of CE effects.
Unfortunately, there are important problemswith
the data set that warrant caution in the interpretation
of the results. Of the 14 speciesreported to show no
CE effect,only 1 wasstudiedexperimentally.The data
for the other 13 speciescamefrom observationalstudies in which the author(s) stated that the intruders
were invariably chasedupon detection.We assumed
We collected results from 21 studies dealing with
this meant that owners used a maximum-intensity
24 speciesin 12 families (Table 1). Evidencefor a CE behavior (chase) in response to all intrusions irreeffectwasfound in 42%(10/24) of the species.Because spectiveof their location.Becausechasesare the most
the strategic-centerhypothesispredictsCE effectsfor conspicuousform of territory defense, however, the
all territories, it cannot account for the distribution
lack of CE effectsmay not be the result of observaof CE effects.The 9 specieswith CE effectsusedtheir tional bias. More quantitative evidence from experiterritories for central-place foraging, while the 14 mental studiesis required.
specieswithout CE effectsdid not. Of 15 specieswith
Although our resultsmatch the predictionsof the
a non-central-placeforaging territory, only 1 (Larus central-placeforaging hypothesis,they are also conatricilla;Burgerand Beer 1975) showeda CE effect.In sistent with the central-resourcehypothesis. All 12
L. ridibundus,
however, when proximity between con- specieson territorieswithout a centralresourcelacked
testantswas kept constantthe CE effectsdisappeared CE effects, while 10 of the 12 specieson territories
(Patterson1965).Only 2 of the 10studiesthat reported with central resources showed CE effects. Thus, alCE effectscontrolled for contestantproximity (Ickes though we can reject the strategic-centerhypothesis,
the centers of territories
contain
such a resource.
July1987]
Short
Communications
537
We thank J. Bruce Falls for numerous suggestions
we cannotdistinguishbetween the central-placeforhypothesis)and Pete
aging and the central-resourcehypothesesbecause (including the strategic-center
territories used for central-placeforaging will often McGregorfor commentingon an earlier version of
be territories with central resources.
the manuscript.L.-A. Giraldeau was supportedfrom
One could distinguish between the central-place a NSERC PostdoctoralFellowship and a NSERC opforaging and central-resourcehypothesesby inves- erating grant to Jerry Hogan. R. Ydenbergwas suptigatinghow defenseintensitychangedwith distance portedby a NSERCUniversityResearchFellowship
from the centerof the territory. Becausethe response and Operating Grant.
intensityis basedon an individual'sV/K and because
K is unlikely to changewith distance,only changes
LITERATURE CITED
in V are likely to influencethe response.The centralG. 1981. The role of the sexesin territory
placeforaginghypothesiscorrectlypredictsa decel- BAEYENS,
defensein the Magpie (Picapica).Ardea 69: 69erating decline in V with distancefrom the central
82.
place,as observedby Vines (1979)and Melemis and
Falls (1982). Unfortunately,there are no equivalent BISHOP,D. T., C. CANNINGS, •r J. MAYNARD SMITH.
1978. The war of attrition with random rewards.
modelsfor predictingthe changein defenseintensity
J. Theor. Biol. 74: 377-388.
with distance to a central resource.Arguments can
BOYDEN,
T.C. 1978. Territorial defenseagainsthumbe made for either gradual or abrupt decreasesin V
with distance. Without better predictions from the
mingbirdsand insectsby tropicalhummingbirds.
Condor 80: 216-221.
central-resourcehypothesiswe must concludethat
the observationsare consistentwith the predictions BURGER,
J., & C. G. BEER.1975. Territoriality in the
Laughing Gull (L. atricilla). Behaviour 55: 301of the central-placeforaging hypothesis.
320.
We could distinguish between the competing hypothesesby examiningthe territorial defenseof cen- DAVIES, N. B., & A. I. HOUSTON. 1981. Owners and
tral-place foragersthat do not forage on their terrisatellites:the economicsof territory defencein
the Pied Wagtail Motacillaalba.J.Anim. Ecol. 50:
tories. Only the central-placeforaging hypothesis
157-180.
predictsthe absenceof CE effectsin all cases.We have
found only three avian studiesof this type (Table 1). DHONDT, A. A. 1966. A method to establish the
boundaries of bird territories. Gerfaut 56: 404Two of the three cases,including the most detailed
408.
analysis(Wiley and Wiley 1980),failed to find a CE
effect.The casein which an effectwas reported fails ENQUIST,M., E. PLANE,& J. ROED. 1985. Aggressive
communication in fulmars (Fulmarusglacialis)
to controlfor proximity(Burgerand Beer1975).These
competingfor food.Anita Behav.33: 1007-1020.
resultssuggestthat the central-resource
hypothesisis
incorrect. Territories
that are not used to collect food
ENS,B., & L. ZWARTS.1980. Territoriaal gedrag bij
wulpen buiten her broedgebeid.Watervogels5:
by central-placeforagersdo not showCE effects.Ad155-169.
mittedly, the nonforaging territories of the three
speciesof central-placeforagersused in this analysis EWALD, P. W., & G. H. ORIANS. 1983. Effects of resourcedepressionon use of inexpensive and esare considerablysmallerthan the territorieson which
calated aggressivebehavior: experimental tests
CE effectsusuallyare described.It is not clear,howusingAnna'sHummingbird. Behav.Ecol.Socioever, how territory size can affectthe existenceand
biol. 12: 95-101.
observationof CE effects.More experimental studies
are requiredbeforeoneor both of the hypothesescan FALLS,
J. B. 1982. Individual recognitionby sounds
in birds. Acous. Comm. Birds 2: 237-278.
be rejected.The studiesshould focuson the defense
of large territoriesthat are not usedfor central-place --,
& R. J.BROOKS.1975. Individual recognition
foraging.
by song in White-throatedSparrows.II. Effects
We conclude that the center-edge effect is not a
of location. Can. J. Zool. 53: 1412-1420.
universal property of avian territorial defense.The --,
J. R. KREBS,
& P. K. MCGREGOR.1982. Song
resultsof our analysissuggestthat the center-edge
matchingin the Great Tit (Parusmajor):the effect
effect arisesbecauseof a systematicchange in the
of similarity and familiarity. Anim. Behav. 30:
997-1009.
fitnessvalue of exclusiveuse of a territory parcel as
a function of distancefrom the central place. In the GOLDMAN,
P. 1973. Songrecognitionby Field Sparrows. Auk 90: 106-113.
caseof central-placeforaging species,we understand
how the fitnessvalue changeswith distance.A game- HARCUS,J. L. 1973. Song studies in the breeding
theoretical framework provides a consistentexplabiologyof the CatbirdDumetella
carolinensis
(Aves:
nation for the occurrence of center-edge effects. A
Mimidae). Ph.D. dissertation, Toronto, Ontario,
Univ. Toronto.
similar game-theoreticalinterpretation of neighborstranger discriminationsalso proved useful in un- ICKES,R. A., & M. S. FICKEN. 1970. An investigation
of territorial
behavior in the American
Redstart
derstandingthe underlyingecologyof aggressivebehavior (Ydenberg et al. in press).
utilizing recordedsong.Wilson Bull. 82:167-176.
538
ShortCommunications
in the Black-headed
KREBS,J. R. 1982. Territorial defence in the Great
11: 185-194.
S?i•A¾,C.J. 1978. Territorial behaviour of the Carion
Crow Corvuscorone
L. in relation to food supply:
KRUIIT,J.P., & J. A. HOGAN. 1967. Social behavior
on the lek in BlackGrouseLyrurustetrixtetrix(L.).
Ardea
an experimental study. Ph.D. dissertation, Aberdeen, Scotland, Univ. Aberdeen.
55: 203-240.
LYON, D.L. 1976. A montane hummingbird territorial systemin Oaxaca,Mexico. Wilson Bull. 88:
280-299.
MELEMIS, S. M., & J. B. FALLS. 1982. The defense
function:
a measure
of territorial
behavior.
Can.
J. Zool. 60: 495-501.
NOLAN,V., JR. 1978. The ecologyand behavior of
the Prairie
Warbler
Gull Larus ridibundus. Ibis 107:
433-459.
Tit (Parusmajor):do residentsalwayswin? Behav.
Ecol. Sociobiol.
[Auk,Vol. 104
VINES,G. 1979. Spatialdistribution of territorial aggressivenessin Oystercatchers,Haematopusostralegus.Anim. Behav. 27: 300-308.
WILEY,R. H. 1973. Territoriality and non-random
mating in SageGrouse,Centrocercus
urophasianus.
Anim. Behav. Monogr. 6: 87-169.
--,
& M. S. WILEY. 1980. Territorial behaviour
of a blackbird: mechanismsof site-dependent
Dendroica discolor. Ornithol.
dominance.
Behaviour
73: 130-154.
Monogr. No. 26.
YDENBERG,g. C., L.-A. GIRALDE•U, & J. B. FALLS. In
PARKER,
G.g. 1984. Evolutionarily stablestrategies.
press. Neighbours,strangers,and the asymmetPp. 30-61 in Behaviouralecology:an evolutionary
ric war of attrition. Anim. Behav.
approach (J. R. Krebs and N. B. Davies, Eds.).
Sunderland,
--,
Massachusetts, Sinauer Assoc.
PATON,D.C., & F. L. CARPENTER.1984. Peripheral
foraging by territorial Rufous Hummingbirds:
defenseby exploitation.Ecology65: 1808-1819.
PATTERSON,
I.J. 1965. Timing and spacingof broods
& D. L. KRAMER. 1986. Interference
competition,foragingasymmetries
and the social
relationshipsof central place foragers.Theoret.
Pop. Biol. 30: 26-44.
Received
28 August1986,accepted
7 February1987.
On the Extent and Sourceof Instability in Avian Nomenclature, as Exemplified by
North
American
STo•s
Birds
L. OLSON
Departmentof VertebrateZoology,NationalMuseumof Natural History,
Smithsonian
Institution,Washington,
D.C. 20560 USA
(1908:x): "the whole courseof scientificnomenclature
has shown that the law of priority--lex prioritatis--is
the one great underlying principle." Dissenting
viewpoints had been expressedpreviously,and attempts were made to set some sort of a statuteof
nithology.The need for this originatedin part from limitation in modificationof the law of priority, or
to adopt the nomenclaturethat had been usedby the
the debatable viewpoint that birds are "very well
known globally, and mostproblemsin their nomen- most previous authors, the so-calledauctorumpluriclature have been solved with a resulting high level morumprinciple. Theseeffortsto abrogatethe law of
of stability" as opposedto "imperfectly known" in- priority were rejectedunequivocallyby the A.O.U.
vertebrategroupswhose "nomenclatureis still in a Code (1908: xlvii): "The 'statute of limitation' prinstate of flux ..." (W. J. Bock, SCON chairman, memciple is akin to the auctorum
plurimorum
rule; both are
Utopian, and both radically set at defiance the lex
orandum of 8 May 1986).
Although SCON stoppedshort of departingfrom prioritatis."
Later, however, a reactionagain aroseto the strict
the restof zoologyanddecidedit shouldwork within
the framework of the International Code of Zoolog- application of the law of priority, and further atical Nomenclature, the committee agreed at the outset temptswere madeto modify it (reviewedby Mayr et
to embrace a "Principle of Established Usage," be- al. 1953:215-220). This eventuallyled to the notorious
causethe fundamentalprinciple of the International Article 23b (the "fifty year rule") of the International
Code, the Law of Priority, was perceived as a threat Codeof ZoologicalNomenclature(ICZN 1964),a rule
socontentiousand unsatisfactorythat it was changed
to the stabilityof avian nomenclature.
In the first half of this century, most systematic in the next edition of the Code,althoughit washardly
ornithologists, at least in North America, were con- improved. At present, all casesinvolving "unused"
tent to follow the law of priority,in conformance
with seniorsynonymsare supposedto be referred to the
the Code of Nomenclatureas set forth by the A.O.U. ICZN while "existing usage" is maintained. "Estab-
Among the proposalsconsideredat meetingsof the
Standing Committeeon Ornithological Nomenclature
(SCON) held during the XIX International Ornithological Congressin Ottawa, June 1986, was one to
createa separateset of rules of nomenclaturefor or-