Interspecific and Intraspecific Aggression Among ...

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COMMUNICATIONS

J. RaptorRes.31(1):77-79 ¸ 1997 The Raptor ResearchFoundation,Inc.

INTERSPECIFIC AND INTRASPECIFIC AGGRESSION AMONG GPdFFON AND CINEREOUS VULTURES AT NESTING AND FORAGING GUILLERMO

SITES BIANCO

Departamento deBiologiaAnimal, UniversidaddeAlcalddeHenares, 28871AlcalddeHenares,Madrid, Spain

Jos• M. TRAVERSO Jardines18, 28610 Villamanta,Madrid, Spain

JAVIERMARCHAMALO TomdsBorrds12, 28045 Madrid, Spain Fi•LIX

M_ART[NEZ

PuertoCanfranc22, 28038 Madrid, Spain KEYWORDS: Aegypiusmonachus;Cinereous Vulture;, Gyps fulvus; Griffonvulture;, foraging;nesting;aggression.

two casesof intenseaggressionbetweenGriffon and Cinereous The

Food partitioning within vulture guildsreducesthe intensity of competition even when severalspeciesshare the same carcass(Ktnig 1983, Hiraldo 1977, Mundy 1982). Apparently, aggressiveencountersare minimized by the relativesizesand agesof individualsin thesefeeding groups (Alvfirezet al. 1976, Grubh 1978, Anderson and Horwitz 1979, Mundy 1982, Blanco and Martinez 1996). Interspecific and intraspecific aggressionis frequent when large numbers gather at large carcasses (Mundy 1982). Most interactionsinvolvedominancedisplays that either do not result in direct contact or, at most, result in slight disputesreduced to minor pecking and kicking. Overall, severeaggressionseemsto be avoided.

In addition to carcasses,vultures can at times also show

intra- and interspecificcompetitivebehaviorsat their nest sites.Here too, competitionmaybe passiveand regulated by the abundance,spacingand timing of breedingof the different species,or it may resultin activeaggressionand displacementamong individuals of the same species (Donfizar et al. 1989, Fernfindez and Donfizar 1991). Griffon Vultures (Gypsfulvus) and CinereousVultures (Aegypius monachus) sharefeeding and nestingsituations acrosswide areas of the Iberian peninsula, but little is known of the frequency,intensityand context of agonistic interactions that result from competition between them (Ktnig 1974, Alvfirezet al. 1976, Fernfindezand Don/tzar 1991, Hiraldo et al. 1991). In this note we report 77

Vultures. first case occurred

while

we observed

Cinereous

and Griffon Vultures feeding on a cattle carcassnear the Natural Park of Monfragfie, CftceresProvince (western Spain) in November 1992. A maximum of 94 Griffon Vultures and 48 CinereousVultures were observedgathered to feed on the carcass.Most of them were feeding on the back of the cow, but two subadult Cinereous Vultures

were feeding on the head by putting their heads inside the mouth of the cow. A first-yearGriffon Vulture approached and began to feed together with the two Cinereous

Vultures.

When

the Griffon

Vulture

had its head

inside the mouth of the cow, an adult Cinereous Vulture

approachedand attackedthe Griffon Vulture by grasping its neck with

its bill for

>30

sec. When

the Cinereous

Vulture releasedthe Griffon Vulture, it left a deep wound that bled profusely. Immediately the injured vulture abandoned the carcass,leaving a clear blood trail and disappearedinto the adjacentvegetation.The wound appeared seriousenough that it might have been lethal. The

second

case involved

of a conflict

between

two

adult (probablyfemale) Griffon Vultures at a nestingsite traditionallyused in the gorgesof the Riaza River,Segovia Province (central Spain) in November 1995. We had observedan adult pair at this nest two monthspreviously showingpair-bondingbehaviorand evencopulating.The mates were sexedwhen copulation occurred and subsequentlywere easilyrecognizedby individualplumagefeatures.The third bird wasprobablya female, basedon the size and shapeof the bill and head. The aggressive en-

78

SHORTCOMMUNICATIONS

counter began when the two presumed female Griffon Vulturesbegan to make raspingcallsand to fight at the nest site. During the fight, one of the vultureslaid on its back with its wings extended and defended itself with its legs and bill from pecking attacksby the other vulture. The two vulturescontinued to fight, alternating positions and pecking at each other's head and neck for )20 min. At the end of the fight, both femalesremained motionlesson their backs and face to face with their wings extended for about 5 min. Finally, after another 6 min of violent aggression,one of the vulturesdisplacedthe other from the nestsite.As a resultof the fight, both vultures sustainednumerousbleedingwoundson their headsand necks, especially around their eyes, mandibles, and throats.

Initially, the male watched the conflict from the edge of the nest site and only pecked a few times at the tips of the primaries of the fighting females.The male later flew to a nearby rock from which he observed the fight for the remainder

of its duration.

During many years of research, we have observed several hundred vulture gatherings at carcasseswhere numerous agonistic interactions have occurred. Most aggressivebehaviors have been between individuals of the same speciesand especiallybetween the more social and abundant Griffon Vulture (Hiraldo et al. 1979). These encountersnever generated woundsand usually resulted in the lossof a few neck or rarely primary feathers. The more violent encounters have involved first-year birds assaultedby older individuals indicating that immature vultures may not have yet established dominance relationships or developed appropriate social behavior. Our first observation indicates that Cinereous Vultures are capable of occasionally injuring Griffon Vultures seriously enough to result in death. Undoubtedly, their larger body size and stronger bill enables them to dominate in aggressive encounters (Ktnig 1983). Nevertheless, this behavior is exceptional and probably occurs only when large numbers of vultures, especially Cinereous Vultures, gather at a carcass. Competition for nestsitesmay be a causeof aggression between conspecificsunder conditionsof high population density (Martinez and Cobo 1993). The availability of nest

sites for

Griffon

Vultures

has

not

been

crease in the Riaza River gorge, aggressionwithin this specieswill become more violent.

RESUMEN.--Se describeun casode agresitn violentade un buitre negro (Aegypius monachus) adulto a un juvenil de buitre leonado (Gypsfulvus) en una carrofia de vaca que congreg6 un nfimero inusual de individuos de la primera especie.E1 buitre leonado pudo haber muerto como consecuenciade la gravedadde la herida producida en el cuellopor el buitre negro. Sedocumentatambitn la observacitnde una pelea muyviolentaentre dos hembras de buitre leonado en un lugar de nidificacitn ocupadopor una de ellasy supareja,lo cualseinterpreta como resultadode una fuerte competenciapor el lugar de nidificacitn en una coloniade muy altadensidadpoly lacionalen Espafia. [Traduccitn de los Autores] ACKNOWLEDGMENTS

The manuscriptwaswritten during a shortstayby the first author in the Centro de Investigaciones Bio16gicas del Noroeste (M•xico) and benefited from the comments of P. Mundy, R. Rodr/guez-Estrella, J.L. Tella and S.R. Wilbur. The staywasfinancedby a F.P.Ugrant from the SpanishMinisteriode Educaci6ny Ciencia. LITERATURE

CITED

ALvAREz, F., L. ARraS DE REYNAAND E HIRALDO. 1976.

Interactions among avian scavengersin southern Spain. OrnisScand.7:215-226. ANDERSON, J. ANDP. HORWITZ.1979. Competitiveinteractionsamong vultures and their avian competitors. Ibis 121:505-509.

ARgOgO, B., E. FERREIROAND V. G•tz•.

1990. II Censo

nacionalde Buitre Leonado (Gypsfulvus):poblaci6n, distribucitn, demografiay conservacitn.ICONA, Madrid, Spain. BLANCO, G. AND F. MARTINEZ. 1996. Sex difference in

breeding age of Griffon Vultures (Gypsfulvus). Auk 113:247-248.

DONA7a, J.A., O. CEB2tL•.OS AND C. FERNANDEZ.1989. Factorsinfluencing the distribution and abundance

docu-

mented to be a factor limiting the population size in northern Spainwhere high densitiesare reached (Arroyo

VOL. 31, NO. I

•

of seven cliff-nestingraptors: a multivariate study. Pages545-552 in B.U. Meyburg and R.D. Chancellor [Eds.], Raptorsin the modern world. WWGBP,Berlin, Germany. ANDC. FERN.4aNDEZ. 1990. Populationtrends of the Griffon Vulture Gypsfulvus in northern Spainbe-

et al. 1990, Donfizar and Fernfindez 1990). Nevertheless, tween 1969 and 1989 in relation to conservation meawe observed an increasingnumber of aggressiveintersures. Biol. Conserr. 53:83-91. actionsover the past 10 years (Martinez and Cobo 1993). FERNANDlrZ, C. ANDJ.A. DONAZAR.1991. Griffon Vultures These encounters have mainly been brief and have (Gypsfulvus) occupying eyries of other cliff-nesting amounted to nothing more than attempts to steal nest raptors. Bird Study38:42-44. material and food deliveredto nestling.Our observation GRUBH,R.B. 1978. Competitionand co-existence in Grifof actual fighting between two female Griffon Vultures fon Vultures:Gypsbengalensis, G. indicusand G.fulvus wasunusualbut it may indicate that as the densityof the in Gir forest.J. Born.Nat. Hist. Soc.75:810-814. nestingpopulation of Griffon Vultures continuesto in- HIRALDO, F. 1977. Relacionesentre morfolog/a,ecologla

MA•CH

1997

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79

for food amongOld World vultures.Pages153-171 zn S.R. Wilbur and J.A. Jackson[Eds.], Vulture biology and management. Univ. of California Press,Berkeley --, M. DELmES ANDJ.CALDERON. 1979. E1Quebranand Los Angeles, CA USA. tahuesos Gypaetus barbatus (L). Monografias 22. M_ARTfNEZ, F. ANDJ. CoBo. 1993. Gesti6n actual de ADICONA, Madrid, Spain. ENA/WWF Espafiaen el Refugiode rapacesde Mon--, J.C. BLANCOANDJ. BUSTAMANTE. 1991. Specialtejo de la Vega (Segovia).Alytes6:507-521. ized exploitationof smallcarcasses by birds.Bird Study MUNDY,P.J. 1982. The comparativebiology of southern 38:200-207. African Vultures. Vulture StudyGroup,Johannesburg, K¸NIG, C. 1974. Zum verhaltenspanischerGeier an KaSouth Africa. davern.J. Orn. 115:289-320. 1983. Interspecificand intraspecificcompetition ReceivedI April 1996; accepted14 November 1996 y distribuci6nde los buitresdel Viejo Mundo. ActasI Reuni6n Iberoamer. Zool. Vert., La R•bida: 753-757.

j. RaptorRes.31(1):79-81 ¸ 1997 The Raptor ResearchFoundation,Inc.

HUNTING

SYNCHRONY MOLLY

IN WHITE-TAILED

KITES

F. SKONIECZNY

Departmentof Biology,HumboldtStateUniversity, Arcata, CA 95521 U.S.A.

JEFFREY R. DUNK Department of Wildlife,HumboldtStateUniversity, Arcata, CA 95521 U.S.A.

KEYWORDS: White-tailed Kite;,hunting;Elanus leucurus; California.

examinedwhether kiteshunted independent of other individualshunting. STUDY AREA AND METHODS

Hunting behavior of White-tailed Kites (Elanus leucurus) has been extensivelystudied (Barnmann 1975, Warner and Rudd 1975, Mendelsohn andJaksic 1989). Kites primarily use open to semi-open habitats for hunting (Waian 1973, Barnmann1975, Dunk and Cooper 1994). In California, kites almost exclusivelyhover while they hunt (MendelsohnandJaksic1989, Dunk 1995) and prey on smallmammals,primarilyvoles(Micromsspp.) (Hawbecker 1940, 1942, Stendell 1972).

In previousstudiesof kites,we observedthat groups of kites (2-20 individuals) appeared to hunt relatively synchronouslyand the probability of an individual kite hunting appearedto be related to whether other kites were hunting. Hunting synchronycould result from kites advertisingtheir presenceto conspecificterritory holders to potentially decreasesubsequentinteractions,or to more easilypatrol and defend a territory, or from kites respondingto variabilityin prey availabilityasa function of prey activityrhythms.Shields(1976, cited in Madison 1985) found California voles (M. californicus)exhibited ultradian rhythmsin activityvaryingfrom 2-6 hr. Daan et al. (1982) reported positivecorrelationsbetweenvole activity and timing of hunting by raptors in Europe. We

This study was conducted at the Mad River Slough Wildlife Area, Arcata,California.The area consistsof approximately 185 ha of ungrazed grasslandwith little topographicrelief. It containsvery few trees and shrubs, and fence postsand T-bars (ca. 3-m tall) provide most of the perches for raptors. The climate is maritime w•th mild

winters

and cool summers.

The studytook place from 20 November 1994-30 January 1995. We made observationsduring seven 1-2 hr periods.Randompointswithin the studyareawere established

from

which

observations

were

made.

Scan

sam-

pling (Altmann 1974) wasusedto record number of kites hunting. Using a landmark on the horizon as a starting point, we slowlyscanned(• time per scan= 90 sec,range = 45-135 sec) 360ø and recorded the number of kites

hunting (hovering). Scanswere made using binoculars. All kiteswere within approximately400 m of the observer. We waited

5 min between

scans based on Barnmann's

(1975) findingsthat mean hunting time for kiteswas5.04 min (N = 674 hunts) in this area. To determine whether kites hunted independent of other hunting kites, we compared observednumbers of kites hunting during each scanto expectednumbersunder the Poissondistribution using Chi-squareanalysis.We usedthis analysisbecausecomparisonof observedevents