Mobbing Behavior of a Pair of Elegant Trogons
Author(s): Jack F. Cully, Jr.
Source: The Condor, Vol. 88, No. 1 (Feb., 1986), pp. 103-104
Published by: University of California Press on behalf of the Cooper Ornithological Society
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103
SHORT COMMUNICATIONS
The Condor 88:103-104
? The Cooper Ornithological Society 1986
MOBBING BEHAVIOROF A PAIR OF ELEGANTTROGONS1
JACK F. CULLY, JR.
New Mexico 87131 USA
Departmentof Biology, Universityof New Mexico, Albuquerque,
Key words: Elegant Trogon;GreatHornedOwl;mobbing;move-onhypothesis;predatordeterrence.
Mobbingbehavior among birds is considereda mechanism of predatordeterrence;however,the benefitsof mobbing to small or passively mobbing species is not clear
(Cully and Ligon 1976, Curio 1978). Most species mob
by giving loud calls combined with wing and tail flitting
that, together,appearto attractadditionalbirds of many
species. I report here my observationson the mobbing
behaviorof a pairof ElegantTrogons(Trogonelegans)to
a GreatHornedOwl (Bubovirginianus).Althoughthe trogons maintained a substantialdistance between themselvesandthe owl,theircallsquicklyattractedotherspecies,
some of which mobbed very aggressively.By attracting
more aggressivespeciesto mob, small birds may be able
to have predatorsdriven away from their territoriesand
derive the same benefits as the more aggressivespecies
(the "move on" hypothesisof Curio [1978]).
On 4 July 1970 at the South Fork Campgroundin the
ChiricahuaMountains, ChiricahuaCounty, Arizona, I
tethereda live GreatHornedOwl 60 cm above the ground
at the base of a small tree. It was immediatelymobbedby
a pair of ElegantTrogons.(I laterdiscoveredthat the tree
containedtheir nest.) I observedthese birds for approximately 30 min beforeI terminatedthe sessionby moving
the owl away from the area. After the owl was removed
the trogonsfreely enteredtheir nest. I watchedthe birds
from behind some shrubsat a distance of about 10 m.
Calls were recordedon a Uher 4000 Report-Ltape recorderat 3.5 IPS using a Uher M514 microphone.The
calls were analyzed on a Kay Electric Company Sonagraph6061B. I did not attemptto count calls or flits, and
I did not attemptto measurethe durationof the response.
Within 1 min after I exposed the tetheredowl, a male
trogonbeganto mob from a distanceof about 15 m. He
was perchedon a branchapproximately5 m high in full
view of the owl andme. Within2 min afterthe maletrogon
beganmobbinghe wasjoined by his mate. Althoughtheir
calls wereloud and attractedvariousotherbirds,no other
trogonsjoined the mob.
The male trogon flew to a branch in view of the owl
about 15 m away. He called and occasionallyflitted his
wings and tail. There was very little jumping or flying
betweenperches.Whenthe femalearrivedshetook a perch
with more cover about 6 m from the owl, and also began
to call.Bothtrogonschangedtheirperchesduringthe mobbing session, but they never approachedthe owl closer
than 6 m.
ElegantTrogonsuseda wing-tailflitwhilemobbing.The
trogonsfirstrapidlyflickedthe wings (durationabout 0.1
sec), and then slowlyraisedand loweredthe tail (duration
approximately1.0 sec). Therewas no bowingof the body
associatedwith the flit.
Trogonmobbingcalls consistedof a rapidseriesof loud
staccatochucksgiven in phrasesof 4 to 10 notes (Fig. 1).
The male'scalls soundedhigherpitchedthanthe female's,
but otherwisethey weresimilar.Harmonicsrangedin frequencyfrom 1.0 to 2.5 kHz in the male and from 0.5 to
6.0 kHz in the female. The dominant harmonic of the
male was centeredat 1.5 kHz, that of the female at 0.8
kHz. Since high-frequencyharmonicsattenuatefasterin
woodlandsthanlow frequencies(Martinand Marler1977),
the shorterfrequencyrange recordedfor the male may
have resulted from my recordinghis calls at a greater
distance.Mobbingcallphrasesrangedfromapproximately
0.5 to 1.2 sec in duration.The individualnotes were regularlyspacedat 0.1 to 0.12 sec intervals.Eachnote of the
phrasewas of similar duration(0.08 sec) and frequency
range.The energyof the calls was given in a rapidburst.
The frequencyrange and amplitudecharacteristicsof
the calls of many speciesof mobbingbirdsarewell suited
to facilitatelocatingthe callingbirds,which makesit easy
for more birds to join the mob (Marler1955, Marlerand
Hamilton 1967, Martin and Marler 1977). The calls of
ElegantTrogons are similar. High frequenciesattenuate
quickly,makinga wide frequencyrangeuseful for determiningthe distanceto the source(MartinandMarler1977).
The calls were repetitiveand beganand ended abruptlycharactersthat enhanceddirectionfinding.
Trogonmobbingwas passivecomparedto that of many
otherspecies.Gray-breastedJays(Aphelocomaultramarina), which joined the mob within 1 min after the male
trogon began calling,jumped and flew constantly,often
diving within 5 cm of the owl's head. Passerinemobbing
is characterizedby loud calls, numerousjumps and flights
from perch to perch,and frequenttail flits (Hinde 1954;
Cully and Ligon 1976, in press).In passerines,the tail flit
Male
4
0
4'
A
I
i..
N
I
6
A
"
Female
4-
0
I
I
I
'
I
..
0
Time In Seconds
' Received 18 March 1985. Final acceptance7 September 1985.
.
' .. .I
. .............
i
' ..I.
1
FIGURE 1. Sonogramsof male and femaleElegantTrogon mobbingcalls.
104
SHORTCOMMUNICATIONS
usedin mobbingprobablyaroseas a flightintentionmovement (Daanje 1950, Hinde 1954). A component of the
evidence for its origin as a flight intention movement is
the changein posturethat accompaniesthe wing and tail
movements;the movementis similarto theposturalchange
that often precedesflight.This componentof the flit (the
change in posture)is missing from trogon mobbing tail
flits. This suggeststhat in mobbingthe importantfactor
is movement,whichenhancesvisibilityto otherbirdsand
perhapsconfusionof the predator(but see Curio 1978).
Trogon mobbing may illustratethe value of mobbing
among small birds or other passively mobbing species.
Althoughthese species are not likely to drive largepredators from their territories,their calls often attractother,
more aggressivebirds such as jays. Oftenwhen I placeda
captive owl on a perch to observethe responsesof other
birds, the first species to mob were smallerspecies such
as PlainTitmice(Parusinornatus)or Black-throatedSparrows (Amphispizabilineata). When jays arrived they
mobbed aggressively;on several occasions they startled
the tethered owl sufficientlyto cause her to fall off her
perch.This suggeststhat mobbingmay benefitthe smaller
speciesby atttractinglargerbirdswho can forceowls, particularysmall species, to flee.
I thank J. D. Ligon, J. Wiens and B. Woodwardfor
reviewingdraftsof this paper.
LITERATURECITED
CULLY, J. F., JR., AND J. D. LIGON. 1976. Comparative
mobbingbehaviorof Scruband Mexicanjays. Auk
93:116-125.
CULLY, J. F., JR., AND J. D. LIGON. In press. Seasonal
factors in mobbing intensity of the Pinyon Jay. Z.
Tierpsychol.
of avianmobCURIO, E. 1978. The adaptivesignificance
bing. I. Teleonomic hypothesesand predictions.Z.
Tierpsychol.48:175-183.
DAANJE, A. 1950. On locomotorymovements in birds
andthe intentionmovementsderivedfromthem.Behaviour3:48-98.
HINDE,R. A. 1954. Factors governingthe changesin
strengthof a partiallyinbornresponse,as shown by
the mobbing behaviour of the Chaffinch(Fringilla
coelebs).I. The nature of the response and an examinationof its course.Proc.R. Soc. Lond.Biol. Sci.
142:306-331.
of some animalcalls.
MARLER,
P. 1955. Characteristics
Nature 176:6-8.
III. 1967. MechaMARLER,
P., ANDW. D. HAMILTON
nisms of animalbehavior.Wiley, New York.
1977. Soundtransmission
MARTIN,
K., ANDP. MARLER.
and its significancefor animal vocalization.Behav.
Ecol. Sociobiol. 2:271-290.
TheCondor88:104-105
? The CooperOrnithologicalSociety 1986
SPITEFULNESS,ALTRUISM, AND THE COST OF AGGRESSION:
EVIDENCE AGAINST SUPERTERRITORIALITY IN TREE SWALLOWS'
RALEIGH J. ROBERTSON,
H.
LISLE
GIBBS2
AND
BRIDGET
J. STUTCHBURY
Departmentof Biology, Queen'sUniversity,Kingston,OntarioK7L 3N6, Canada
For such spitefulnessto evolve, the benefitsto the suKey words: Superterritory;aggression; hole-nesting;
TreeSwallow.
individualmust exceedthe costs. The excluperterritorial
sion of a potential breederby an inhibitoryindividual
resultsin an equalincreasein relativefitnessamongstall
is a spiteful behavior in which an in- breeders,whetheror not they inhibit others.In contrast,
Superterritoriality
dividual'srelativefitnessis improvedby reducingthe fit- the costs of the extra aggressionrequiredto defend adnessofothersthroughinhibitingthemfrombreeding,rath- ditional resourcesmay be relativelygreatand are borne
er than throughan absolute increase in fitness (Verner only by the inhibitingindividual(s).It is thereforeunlikely
to the individualwill
1977).Tree Swallows(Tachycinetabicolor)are obligatory thatthe benefitsofsuperterritoriality
hole-nesters,and a singlepair can defend additionalsites exceed the costs. Colgan (1979:605) succinctlysummanot essential for successful reproduction(Harris 1979, rizedthis argumentwith his commentthat "Colloquially,
Muldal et al., 1985), thereby preventing conspecifics spitefulnesshas become altruism." Since the potential
from using those nest sites. Harris(1979) suggestedthat benefitsofsuperterritoriality
to the individualarelow, the
the main function of surplus nest site defense in Tree evolution of inhibitorybehaviorin Tree Swallowswould
Swallowsis to depressthe reproductivesuccessofpotential requirea verylow cost to the aggressionrequiredto defend
breeders.However, Robertsonand Gibbs (1982) found extra nest sites. We provide evidence againsta low cost
that Tree Swallowsdo not orienttheiraggressivenest de- of aggression.This evidence includes injuriescaused by
fense in relationto the location of surplusnest sites and aggressiveencounters,anda seasonaldeclinein aggressive
concluded that Tree Swallows defend a circularradius defenseby residents,which suggestsa trade-offbetween
around their nest site, which may encompassadditional time and energyexpended on intraspecificnest defense
nest sites. A commentaryby Harris(1985) indicatesthat and otheractivitiessuch as parentalcare.
the issue of superterritorialityin Tree Swallows is still
Ourstudyis basedon two populationsof TreeSwallows
unresolved.Here,we arguethatthe conditionsunderwhich at the Queen's University Biological Station, Chaffey's
superterritorialbehavior would evolve do not occur in Lock, 50 km north of Kingston, Ontario, Canada.The
Tree Swallows.
New Land(NL)populationconsistsof about60 pairsthat
breed in nest boxes which are distributedover several
hayfields.The NortheastSanctuary(NES)populationhas
1 Received 1
April 1985.Finalacceptance17 September about 35 breedingpairs,with both artificialand natural
1985.
nest sites over shallowwater.During 1985 in the NL, we
2 Presentaddress:Division of BiologicalSciences,Unicaught9 birdswithinjuriesthatgenerallyconsistedof large
versity of Michigan,Ann Arbor,Michigan48109 USA.
bare areason the back of the head and neck, and some-