A REVIEW OF SOME ASPECTS OF AVIAN FIELD ETHOLOGY 1 ROBERT W. FICKEN AND MILLICENT S. FICKEN T•E last 30 yearshave seen the developmentof a new approachto the study of behavior, which has increasinglyinterested ornithologists as they have attemptedto understandavian biologyfully. This new ap- proachis now known as ethology. Both amateur and professionalorni- thologistshave contributedto its progressfrom the beginning. A basictenet of ethologyis that all behaviorof animalscan eventually be understood.The ethologistattempts to explainbehavior functionally (what doesit do for the animal?), causally(what are the internal and externalfactors responsible for each given behavior?),and evolutionarily (what is the probablephylogeny of the behavior,how doesit contribute to th'esurvival of the species,and what are the selectivepressures acting uponit?) (seeTinbergen, 1951, 1959; Hinde, 1959b). Somebasic proceduresare essentialin an ethologicalstudy (Hinde, 1959b: 564). The first step is to describeand classifyall the behavior of an animal, at the same time, if possible,dividing the behavior into logicalunits which can be dealt with furtherin other disciplines--particu- larly physiologyand ecology(see Russellet al., 1954). Althoughstudies often beginqualitatively, they eventuallyshould be quantified. Generali- zations,which are to be valid for many species,must be basedon work using closelyrelated speciesfirst, and more distantly related ones later. The animal is studied as an integrated whole. Some workers, notably Konrad Lorenz, keep and breed animalsin captivity under closescrutiny. Most of this paper dealswith communicationof birds. We have stressed particularly the analysisof displays,their evolution,and their relation to taxonomy--topicsof great interest to systematicornithologists as well as to ethologists.In addition, we discusscertain maintenanceactivities. LITERATURE OF ET•OLOC¾ Much of the early ethologicalliterature appearedin Europeanpublications, but it is now also appearingin this country frequently. The principal journalsare: Animal Behavioar (formerly British Journal of Animal Behaviour), Symposiumof the ZoologicalSociety of London,Journal of Comparativeand PhysiologicalPsychology, Zeitschrlftfiir Tierpsychologie,and Behaviour(with monographsappearing as supple- ments in the last two). Papers on avian ethology also appear frequently in the major ornithologicaljournals. Standardreference books on ethologyare The study of instinct (Tinbergen,1951), Learning and instinct in animals (Thorpe, 1963), and Social behaviorand organizationamong vertebrates(Etkin, 1964). Recent monographson individual speciesinclude those by Marler (1956a) on the Chaffinch (Fringilla coelebs);Hinde (1952), Great Tit (Parus major); Tinbergen • Written at the request of the A.O.U. Committee on Research. 637 The Auk, 83: 637-661. October, 1966 638 FI(2KENAND FICKEN, Avian Field EthoIogy [ Vol.Auk 83 (1953), Herring Gull (Larus argentatus); Moynihan (1955b), Black-headed Gull (L. ridibundus); Curio (1959a), Pied Flycatcher (Muscicapa hypoleuca); Simmons (1955), Great Crested Grebe (Podiceps cristatus); and Immelmann (1959), Zebra Finch ( Taeniopygia castanotis). Some outstanding examples of comparative ethological studies are those by Lorenz (1952) on dabbling ducks, Meyerriecks (1960) on herons, Tinbergen (1959) and Moynihan (1955b, 1956, 1958a, b, 1959, 1962) on gulls, Andrew (1957a, b) on em- berizine finches and (1961a) other passerines,Itinde (1955-1956) on carduelines, Dilger (1960) on parrots (Agapornis), McKinney (1961) on eiders (Somateria), Curio (1959b) on flycatchers (Muscicapa), and L•ihrl (1960-1961) on nuthatches ( Sitta) . ETHOLOGICAL CONCEPTS Sincethere are severalrecent reviews of ethology (Emlen, 1955; Thorpe, 1963; Hinde, 1959b, 1961; Eibl-Eibesfeldtand Kramer, 1958), we shall discussonly a few critical conceptsand terms of particular interest to field students.Many of the theoreticalconcepts are still controversialand will undoubtedlybe modified substantiallyin the future. The glosseries of Verplanck (1957) and ThOrpe (1951) contain many definitionsof ethologicalterms. Someactions of animalsare variable, othersmore stereotyped,and the two kinds often occur togetherin a behavioralsequence. "The variable introductoryphase of an instinctivebehaviour pattern or sequence"is calledappetitive behavior and the act terminatinga behaviorpattern or sequenceis the consummatoryact (Thorpe, 1951). Tinbergen (1951: 106) givesan exampleof a sequencein which a PeregrineFalcon (Falco peregrinus)searching for food beginsby randomlyroaming over its hunt- ing territory. This appetitive behaviorcontinues until a stimulussituation is encountered(e.g., a flock of teal executing fligh't maneuvers). Such situations may cause the falcon to abandon its random searching,but what follows is still appetitive behavior of a more specializedkind--the flock of teal may releasesham attacks by the falcon, resulting in the isola- tion of a member of the flock. The final stoop, capture, kill, plucking, and eating form a relatively simpleand stereotyped"chain of consumma- tory acts." Stereotypedmovements, many of which serve as consummatoryacts, have been termedfixed patternsor fixed action patterns (Thorpe, 1956). Investigationof such patterns led to the modern conceptsof instinctual behavior. Instinct as exemplifiedby these actions is a stereotypedpat- tern of behaviorwhich is inherited and specific (Hinde, 1959b). In addition, instinctualbehavior may be characterizedby the accumu- lation of reaction specificenergy (now often referred to as specificaction potential or S.A.P.) which is defined by Thorpe (1951) as "the state of the animal responsiblefor its readinessto perform the behaviourpatterns 190•t•] F•½•:E•^•) F•½•:•,Arian Field JEthology 639 of oneinstinct in preferenceto all otherbehaviour patterns." He points out that this specificreadiness "diminishes or disappearswhen the con- summatoryact of the chargedinstinct h'as been performed."However, if the actionis not released,the S.A.P. accumulates.The thresholdfor releaseof the particular act is then loweredand the action may occur without any externalstimulus. Such action is often called a vacuum activity,overflow activity, or "Leerlaufreaktion"(Lorenz, 1950; Thorpe, 1956). Lorenzobserved this in a captiveStarling (Sturnus vulgaris) whichrepeatedly performed all the behaviorpatterns of insecthunting, catching,killing, and swallowing,without any discerniblestimulus (Tin- bergen,1951: 61). Lorenzpostulated a mechanismwhich would prevent the occurrenceof an act before the animal encounteredthe specific en- vironmental stimuli. This "block" has been termed the innate releasing mechanism(I.R.M. or, more recently,R.M.) (Lorenz, 1950; Thorpe, 1956). The I.R.M. is "selectivelyresponsive to a specialstimulus situa- tion"(Tinbergen and Perdeck, 1951: 2). Thisconcept was introduced to accountfor the factsthat animalsoften respondto a particularstimulus situationwith specificresponses even though they have never encountered the situationbefore, and that, in suchcases, the animaloften responds to only a very limited part of the total stimulussituation. Releasers are structures or actions that emanate sign stimuli which are perceivedby an animal. Releasersoften reach a high degreeof specialization,and their evolutionmay parallel that of the associated specificresponse (Lorenz, 1935). Tinbergen (1953: 197), using models, showedthat in Herring Gulls the red spot on the parent's bill is the primary releaser of the pecking responseof the chick. Neither the back- groundcolor of the bill or head color are releasers;in fact, the presence of the head is not even necessary. Although most of the examples of releasersand their sign stimuli are derived from experimentalstudies of visual stimuli, the conceptsare also applicableto olfactory, auditory, and tactile ones (see Lorenz, 1950). Supernormalsti•nuli are those that are even more effective than the natural stimuli; for example, Tinbergen (1951: 43) foundthat oystercatchersprefer a clutchof five eggsto a natural clutch of three and an abnormally large egg to one of their own. Drive has been defined by Thorpe (1951) as "the complexof internal and external statesand stimuli leading to a given behaviour." Thus, this term may includethe stimuli, specificaction potential, and innate releas- ing mechanismsinvolved in a given behavioralact. Becauseof the dif- ficulties of determining internal states without experimentation, the term tendencyhas been used recently to indicate"the readinessto showa par- ticular type of behaviouras observedunder natural conditions"(Hinde, 1955-1956,as givenby Marler, 1956a: 5). Causalfactors include both 640 F•½izE3r^•DFmizE3r, Arian Field Ethology [ Vol.Auk 83 externaland internal stimuli leadingto a givenbehavior (Tinbergen, 1959: 29) and thus causationis approximatelysynonymous with the term drive or motivation. Displacementactivity has been used in two ways. It sometimesmeans behaviorwhich is thought to have been activated by one or more drives which are not the drives normally associatedwith it. In other use it refers to the performanceof a behaviorpattern out of the contextof behavior with which it is normally related (Thorpe, 1951). The first definitionis highly controversial(see lersel and Bol, 1958; Rowell, 1961; Sevenster,1961); the secondis more useful for the field observer.One exampleof displacementactivity is that of fighting Great Tits which "may suddenlystart to peck at a bud or pick up leavesand then throw them over their shoulders--activitiesnormally