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Spring 1987 Bird territories: A key to understanding bird behavior Robert A. Askins Connecticut College, [email protected]

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Recommended Citation Askins, R. A. 1987. Bird territories: A key to understanding bird behavior. American Birds 41: 35-40.

This Article is brought to you for free and open access by the Biology Department at Digital Commons @ Connecticut College. It has been accepted for inclusion in Biology Faculty Publications by an authorized administrator of Digital Commons @ Connecticut College. For more information, please contact [email protected]. The views expressed in this paper are solely those of the author. BEHAVIOR

Territories:a key to understandingbird behavior

The role of amateur ornithologists in perplexingquestions arise with the ORarrivalTHE ofCAREFUL birds in FIELD spring.OBSERVER, Why do developing a major scientific theory. male Red-winged Blackbirds migrate two or three weeks before the brown, stripedfemales? Why do oriolessing in- cessantlyduring the first week of their arrival from the south? What could Robert A. Askins possibly motivate two flickers in a gar- den to flick their wings and bob their heads at each other, and then tumble together with flashing yellow wings? Scientific theories are most intriguing when they offer a single,simple expla- nation for such disparate phenomena, and the theory of territoriality has this advantage. The concept of territory providesinsights from which any ama- teur naturalist can benefit, since it ex- plainsmuch aboutthe daily behaviorof animals. Not surprisingly,the concept was originally developed by amateur naturalists, bird watchers whose pa- tience and skill for careful observation allowed them to detect a pattern in the freneticspring activity of birds. One of these bird watchers was Eliot Howard, an English businessmanwho lived in a house among pasturesand woodlands overlooking the River Sev- ern. Before leaving for work in Worces- ter. where he was director of a steel- manufacturing firm, Howard arosebe- fore daylight and spent the early morning hoursobserving the birds near his house. In 1920, after decades of watchingthe behaviorof birds,he wrote Territory in Bird LiJ& a book that greatly changedthe study of birds and other animals. Before this time, orni- thologistshad studied birds primarily by shooting them for their skins and collectingtheir eggsand nests,organiz- ing these into collectionsand naming Yellow-headedBlackbird males arrive in a breedingmarsh area befitreft,males. They evaluate the differentforms. This wasa necessary the habitat .forJood availabilio, and sql•' nest and roostsites. commit to a specificpatch an entireseason. and thereafterinvest heavily in defi,nse qf that territory.Because these decisions stagebecause it was essentialto impose havebeen made independento. f the presenceqffi, males. whenthey arrive; they are in a position some order and apply some labels to to assessthe quality or fitnessqf a male and his patch oJreal estateand to then choosea mate. the bewildering variety of thousandsof Males make habitat deciskmswhile fi•r ft,mal•:v, selecting a mate is equivalentto making a different kinds of birds. Howard, how- territory decision.Photo/S.R. Drennan.

Volume 41, Number I 35 is such that males leave their winter feeding grounds for a few hours each day in late winter to claim an area and protect its boundaries. Defense of the territory becomesincreasingly impera- tive as the seasonadvances, and when a female joins the male, the pair coop- erate in defending their plot against other Reed Buntings. Song is used mainly to proclaim territory-ownership to other Reed Bunting males. Often males enter a fight in full song. In Howard's view, territoriality con- sistsof two components:(1) the occu- pancyof a particularplot of groundand (2) defenseof this areaagainst intrusion by membersof the same species(other than the mate). Territories vary greatly in size, from the squaremiles patrolled by a falcon to the half acre of willow thicket claimed by a warbler. Howard even consideredthe tiny areas around the nestsof cliff-nestingseabirds to be territories, since they are defended against other individuals of the same species. A pair of Common Murres Territorialencounter between Northern (Yellow-shafted) Flickers ( Colaptes auratus). Two female ( Uria aalge) or Razorbills(Alca torda) flickers (foreground)display aggressively near a nestcavity while a male watchespassively. defendsthe few squarefeet of cliff ledge During high-intensityterritorial displays, flickers face one anotherand bob their heads.At where their nest will be built. They de- the sametime they revealthe brightyellow on the undersideof the wingsand tail by raising fend only the nest site, not a food the wingsand spreadingand twistingthe tail (Lawrence1967}. Illustration/Don Luce. source, since they forage over broad areas of ocean. Similarly, male Ruffs ever, inspired many ornithologiststo marshes.Each male selecteda promi- (Philomachuspugnax) defend tiny areas study the biology of birds in a different nent position,the top of an alder or tall on a displayarena where males congre- way, in the field watchingthe activity reed, where it sangand preened. Early gate solelyto mate with females.How- of individual birds. His conceptionof in the seasonit often left thisspot, flying ard also considered these to be territo- the territory,an areadefended by a male a long distanceto the feedinggrounds. ties,and he probablywould haveagreed during the breeding season, demon- But as spring approached, these ab- with the simple, broad definition sug- stratedhow a usefuland generaltheory sencesbecame shorter and lessfrequent, gestedby Noble (1939): "territory is any could be derived from careful bird and soon the male Reed Bunting spent defended area." watching. all of its time at its selectedspot in the Howard's book awakened many or- Howard watched the Reed Buntings marsh. nithologiststo the phenomenon of ter- (Emberiza schoeniclus)that nestedin a While female Reed Buntings were ritoriality. How could such an appar- marshy meadow near his house. The still foraging together in winter flocks, ently obviousand predominant aspect Reed Bunting,an inhabitant of marshy the males spent more and more time of bird behavior have been overlooked edgesin Europe, is a small brown finch singingtheir tinkling song from their for so long? Actually many earlier au- with black head and throat. Howard special perches. If another male ap- thors had described territorial defense noticedthat in winter thesebuntings left proachedthe perch,he wasdriven away. in birds(Lack 1944).Aristotle described the wet meadows and reed-beds,where Fighting often occurred in such situa- the defenseof largeareas by ravensand they had spent the summer, to forage tions. The male was usually not joined eagles in Historia Animalium. The in open cultivated areas, often in the by a female until late March. The pair "walks" (apparentlyterritories) of semi- company of other speciesof finches. then drove other, neighboring pairs domesticMute Swans(Cygnus olor) are They normally returned to the marsh away from the area around the singing describedin 17th century Englishgame only at night, when groupsof buntings perch. Later, nestswere built and eggs laws,and many early ornithologistsde- roostedtogether low in the rushes.Cu- laid, and the frequencyof both singing scribed territorial behavior. In 1868, a rious about how these winter habits and fightingdeclined. German biologist, Bernard Altum, changedas springapproached, Howard Howard (1920) explained these wrote Der Vogel und sein Leben (The watched the birds through the cold events in terms of the need for a plot of Bird andHis Life), a bookthat describes morningsof February.In mid-February marsh, a territory, in which a pair of territoriality in birds in much the same he noticeda change:instead of joining Reed Buntingscould find a nestsite and detail and manner as Howard's Terri- flocks of finches in the usual feeding search out enough food to raise their tory in Bird Life (Mayr 1935).Howard's areas,male buntingsscattered across the young. The competition for territories discoveryof territoriality more than 50

36 AmericanBirds, Spring 1987 yearslater was apparentlyindependent, thoughout this period. The position of since he had not read Altum's book. his territory shiftedprogressively west- More important, it was Howard who ward by a total of 50 meters between convincedothers of the generalappli- 1930 and 1934, but later returned to its cability of territory theory and the use- original location. However, femalessel- fulnessof studyingthe behavior of in- dom remained with the same male from dividual birds. one year to the next; if they survived Following Howard's lead, many or- the winter, they normally appearedon nithologistswere inspiredto study ter- anotherterritory with a new male at the ritoriality in birdsduring the 1930sand beginningof the next breedingseason. 1940s. One of the most informative Occasionallythey even switchedmates studieswas done by another amateur, during the middle of the summer, and Margaret Nice, who spent eight years raisedtheir secondbrood of youngon studyingthe SongSparrows (Melospiza another territory. Both males and fe- melodia) around her house in Colum- males defended the territory, usually bus, Ohio. Nice was a well-educated againstindividuals of the same sex. In- woman with a passion for research terestingly,many individualsbanded as (Nice 1979). She beganwatching birds nestlingsshowed up in succeedingyears at the ageof nine, and later studiedthe on territoriesin the immediate vicinity developmentof her own children (par- of their parents'territory. Nice's work had confirmed most of ticulafiy their acquisitionof language). An earlyphoto of MargaretMorse Nice taken Howard's conclusions about the nature Still later sheintensively studied garden in Chicago.circa 1920. With no formal or- birdssuch as Mourning Doves(Zenaida nithologicaltraining, she made significant of territories,but the bandingtechnique macroura), Brown-headed Cowbirds contributionsto thefield. Photocourtesy of allowed her to discover much more. She (Molothrusater), and, most important, MarJorie N. Boyer. had followed the life histories of indi- Song Sparrows. vidual birds and their offspring for so Nice's greatestcontribution was de- 1937, 1943), was basedon many hours many yearsthat shecould delineatethe veloping a method for studyingindi- of careful observationof individually boundaries of territories not only in vidual birds over a long period of time. recognizable birds. Nice found that space,but alsothrough time. The maps Howard had indicated the importance males usually returned to the same ter- of territory boundaries,and the partic- of studyingindividual birds,but he had ritory year after year, regardlessof ular males and females that occupied to dependon individual peculiarities(a whetherthey over-winteredin the local eachterritory, can be comparedthrough brokenleg, a white areaon the feathers) area or migrated.One male, the famous several succeedingyears, providing a to identify them with certainty.More 4M, lived to be at least 9 yearsold and detailedchronicle of the history of one commonlyhe wasforced to identify in- retained virtually the same territory population of Song Sparrows. dividualsby their locationon a partic- ular territory,but this meantthat many of his conclusions were based on cir- cular reasoning. How could he know that the same individual defended a territorythroughout the breedingseason if he identifiedthe individual only by its presenceon that territory?Nice was one of the first workers to overcom• this problemby usingcolor-coded leg bands. Each Song Sparrow was trapped and four plastic bands with a unique color combinationwere placedon its legs,in addition to a more permanent num- bered aluminum band. Each bird could then be identified and its behavior ob- served from one year to the next. In 1932 Nice had marked 136 SongSpar- rows, including nearly every adult on her floodplain study area. Ironically Nice came to know her birds so well that shecould identify many individual males by their songs.Each male has a unique repertoire of six to nine distinc- tive songs. male SongSparrow proclaims its territory The two-volume work, Studies in the by singingin early spring.Illustration/Julie Life Historyof the SongSparrow (Nice Zickefoose

Volume 41, Number I 37 often requiresa large territory. Conse- quently, althoughclosely related species of birds tend to have similar territorial behavior,they may have very different sortsof territoriesif they live in dissim- ilar habitatsand protect differenttypes of resources. The relationshipbetween habitat and territory is well illustrated by Crook's (1964) comprehensivestudy of the be- havior of 70 speciesof weavers.These attractive birds are a conspicuous fea- ture of the landscapein Africa and parts of Asia. The malesof most specieshave brilliant yellow-and-blackor red-and- black color patterns, and they weave elaborate, spherical nestswith small en- trance holes. Crook studied many spe- cies of weavers. garnering additional information from the writingsof British colonial administrators who had been amateur bird watchers. Nearly every human settlement in Africa has a tree filled with woven nestsand chattering, flutteringweavers, so theseconspicuous and intricate weaver societies were ir- resistiblesubjects for many naturalists. Nice with two of her daughters,Constance and Janet,in the late 1940s.Nice servedas a Some speciesof weavers have large mentorand role modelfor many. The MargaretNice OrnithologicalClub in 22•rontowas territories. while others defend a tiny namedin herhonor Theclub began after women were denied membership to thethen all male spacearound their nests.Crook found birdingclubs. Photo/Smithsonian Institution. that this differencedepended upon the Many studiesof the territorial sys- out, cliffs favorable for nesting (with habitat. The weavers of the tall, lush tems of particular speciesof birds fol- wide enough ledgesand proper protec- rain forests of West Africa are insect- lowed the field work of Howard and tion from the surf) are in short supply, eaters, and both the male and female Nice. The new evidencewas presented so many seabirdsdefend small territo- gatherfood for the young.Insects are a within the framework of a continuous ries in the immediate vicinity of their relatively abundant and dependable debate about the definition and func- nests.In this case,territoriality evolved sourceof food. so a pair of weaverscan tion of territories(Lack and Lack 1933, becausethere was competition for a re- defend a plot of forest large enough to Nice 1941, Hinde 1956). Later Brown source(nest sites),and the resource(a provide food for themselvesand their (1964) publishedan essaythat presented compact area) could be defendedby a young. Hence, the forest weaversare the concept of territoriality in a new pair of birds. generally territorial, with individual way. He emphasizedthat aggressivede- Brown's theory allows for greater pairs spaced regularly throughout the fenseof space(territoriality) will evolve flexibility in discussingterritories, since forest.Also, becausethe bestprotection only if two conditionsare met. First, any resource--food,a nestsite, a place againstpredators in the thick rain forest there must be competition for some to roost, a mating site, or a spacecon- is to be quiet and unobtrusive, these scarceresource and enoughcompetition taining all of these-•can be both in weaversare very secretive,hiding their to make the time, energy,and risk re- shortsupply and defendable.His theory nestsin densevegetation. quired for aggressivedefense worth- also indicates what must be measured-- In contrast the weavers of the African while. Second, the resource in short the level of competition for resources savannah are gregarious, foraging in supply must be defendable.If the re- and the concentration and permanence largeflocks in open country and nesting source is mobile, transient, or widely of resources--to explain the presence in large colonies,with dozens or even scattered,it may be impossible(or pro- or absenceof territorialityin a particular hundredsof nestsin a singletree. The hibitively expensivein terms of time species. seedsthese savannah weavers feed upon and energy)to defend.As Brownpoints One implication of Brown'stheory is are concentrated in local areas. Because out, this may be the case with many that habitat determinesthe type of ter- these concentrations are sporadic and seabirds, which forage over broad ritory a bird will defend.Individuals will temporary. they cannot be protected stretches of the ocean that cannot be defend a resourcethat is in short supply and monopolizedby a territorial pair. defendedagainst other individuals.De- and that can be protected,and different The weaver flocks must move across fending a small patch of ocean would resources will meet these conditions in largeexpanses of the savannahto find not be useful, since the prey are tran- differenthabitats. If nestor displaysites theseconcentrations of seeds,much as sient and require constant searching. are defended, the territories will be seabirds must move to find schools of However, as Howard (1920) pointed small, but defenseof the food supply fish on the ocean surface.Foraging in

38 American Birds, Spring 1987 flocksmay help thesebirds detect pred- ators,since there are more eyesto watch for activity in the surroundinggrass- lands. Although they cannot defend their food supply, these savannah weavers can defend their small nest sites from other weavers,and it is important that they do so, since nest sitesare in shortsupply. Savannah weavers prefer to nestin specialand relatively unusual placesthat offerprotection from snakes and other predators.They concentrate their nestsin treessurrounded by water or a human village,or next to a hive of bees or the nest of a hawk. Each male weaver builds a domed grassnest and hangsupside down from it, displaying with fluttering wings and singinguntil he attracts a female. The female then takesover the nest,lays eggs, and raises the youngalone. Seeds are an abundant and concentrated source of food, so the female can feed the young without the Theprimary preoccupation oJ male Red-wtngedBlackbirds during spring is the defenseof a male'shelp. Meanwhile the malebuilds breedingterritory. This speciesis a colonialbreeder and is regularlypolygvnous. Vigorous a new nest and attempts to attract an- aggressivedisplays are costlyparental investment& but whensuccessful competitive behavior other female. The males constantlyde- allowsaccess to multiple.females.instead o•f just one,the potentialreproductive payo# is fend the tiny territories around their obvtous.Photo/S.R. Drennan nests from other males. Like the forest weavers,they defend an area, but it consists of a few branches around a group of nestsin a tree rather than a largetract of forest.In both cases,how- ever, the territory protectsan essential resource(food supply or nest site) that is in shortsupply and defendableagainst other weavers. Generally birds defend territories only againstother individuals of the same species. There are exceptional cases,however, in which the territory is defendedagainst other species.This is often the case with those colonial birds, like weaversand many oceanicbirds, in which two or more kinds of birds live in the samecolony. In thesecases, nest site territories are protected from any intruder, regardlessof species.Also, in- dividuals of some specieswith larger territories defend them against other speciesthat have similar food and nest site requirements. This is the case for the Yellow-headed Blackbirds (Xan- thocephalusxanthocephalus) and Red- winged Blackbirds (Agelaius phoeni- ceus),two closelyrelated birds that oc- cupy the samemarshes in north-central and western North America. Orians and Willson (1964) studied the interactions CaspianTerns are highlygregarious, assembling to breed,.feed and boldly mob predators. between these two blackbirds at Turn- Theyare unusually vo•l withharsh, clipped cries serving aggression. advertisement o•fterritoo½, andmaintenance o•fcontact between parent and young. Nest sites are small and dosely spaced. bull National Wildlife Refuge in Wash- Whenadults in densecolonies actively defend these sites. pairs with small territoriesmay ington.Nearly all of the marsheson the sul7krminimal predation because closely packed adults together.form an extremelyeffective wildliferefuge support both species,and meanso•f de•fense. Photo/S.R. Drennan.

Volume41, NumberI 39 torial map. The dramaticchanges in the habits of birds during spring--the break-up of winter flocks, the sudden morning chorus of bird song,the elab- orate and aggressivedisplays between neighboringmales and pairs--are all signs of territorial defense. These in- sightsinto bird behavior are the result of the skill, patience and curiosity of amateur naturalists such as Eliot How- ard and Margaret Nice. Their contri- butions formed the basisof the theory of territoriality and changedthe meth- odologyof field ornithology.

REFERENCES BROWN, J. L. 1964. The evolution of di- versityin avian territorialsystems. Wilson Bull. 76:160-169. CROOK, J. H. 1964. The evolution of social organization and visual communication in the weaver birds (Ploceinael. Behav- iour Suppl. 10:1-178. HINDE, R. A. 1956. The biologicalsignifi- Black-leggedKittiwakes nest in coloniessometimes so large as to defycredibility. This species cance of the territories of birds. Ibis 98: is verysite tenaciouswith territorial behaviorprobably limited to the nestsite. Displaysare 340-369. still impe.rfectlyunderstood, but defense of thenest stte and the small area surrounding it often HOWARD, E. 1920. Territory in bird life. becomesextremely aggressive. Photo/S.R. Drennan. J. Murray, London, UK. in everycase they have mutually exclu- emergesfrom suchstudies is a seriesof LACK, D. 1944. Early referencesto territory sive territories. Red-wingeds establish non-overlappingterritories for mem- in bird life. Condor 46:108-111. their territories in March, before the and L. LACK. 1933. Territory re- bers of the same species,and broadly viewed. Brit. Birds 27:179-199. Ye!!ow-headeds have returned from the overlappingterritories for membersof LAWRENCE, L. De K. 1967. A compara- south, and Red-winged territories ini- different species.For example, the ter- tive life-historystudy of four speciesof tially cover the entire marsh. In April ritories of Black-capped Chickadees woodpeckers.Ornith. Monogr 5:1-156. the larger Yellow-headeds arrive and (Parus atricapillus) can be superim- MAYR, E. 1935. Bernard Altum and the drive the Red-wingedsfrom the parts posed on those of the White-breasted territory theory. Proc. Linn. Soc. New York 45:24-38. of the marsh with deep water and sparse Nuthatch (Silla carolinensis)which, in NICE, M. 1937. Studies in the life history vegetation (usually the center). The turn, overlaythose of the Wood Thrush of the Song Sparrow. !. A population Red-wingedstypically retain territories (tlylocichla mustelina). Although all studyof the SongSparrow. Trans. Linn. only on the periphery of the marsh. In three speciesfeed on insects,they forage Soc. New York 4:1-247. Washington State, Ye!!ow-headedsare in differentplaces (foliage, bark, and leaf --. 194I. The roleof territoryin bird life. dependenton emergingdamselflies to litter, respectively). Am. Midland Naturalist 26:441-487. feed their young, and these are most The territories of woodland birds can __. 1943. Studiesin the life historyof the Song Sparrow. II. The behavior of the be envisioned as three-dimensional abundant in the more open areasof the Song Sparrow and other passefines. marsh (Orians 1980). Red-wingeds, volumes, rather than two-dimensional Trans. Linn. Soc. New York 6:1-328. however, can feed their young a great areas. For instance, Williamson ( 1971) __. 1979. Researchis a passionwith me. variety of insects, and they nest suc- described the territories of Red-eyed The Margaret Nice Ornithological Club cessfullyon the edge of the marsh or Vireos (Vireo olivaceus) in a mature and ConsolidatedAmethyst Communi- even in upland areas. The two species Maryland forest as 85 foot high cylin- cations, Inc. Toronto. Canada. NOBLE, G. K. 1939. The role of dominance use the same threat displays and songs ders,one to two acresacross, extending in the social life of birds. Auk 56:263- againstone another that they would to from near the forest floor to the top of 273. defendtheir territoriesagainst members the canopy. Yellow-throated Vireos ORIANS. G. H. 1980. Someadaptations of of their own species. (Vireofiav•frons)nest in the sameforest, marsh-nesting blackbirds. Princeton Despite other examplesof this sort, but they largely limit their activity to University Press,Princeton, New Jersey, birds do not generally exclude other the highest stratum. Their pancake- USA. __. and M. F. WILLSON. 1964. Inter- speciesfrom their territories.Walk into shapedterritories cover about ten acres specificterritories of birds. Ecology 45: a woods in eastern North America and in the upper canopy of the forest.Thus, 736-745. you may see a tanagerand an oriole one Yellow-throated Vireo territory WILLIAMSON, P. 1971. Feeding ecology singing from the same tree. If you might cap the top often Red-eyedVireo of the Red-eyed Vireo (Vireo olivaceus) caughtthese resident birds and marked cylinders. and associated foliage-gleaning birds. each one with a combination of leg It is only after long and careful ob- Ecol. Monogr. 41:129-152. bands,you could follow them and map servation that the piecesof the puzzle --Dept. of Zoology,Connecticut their territories, much as Nice did with of bird behaviorbegin to fit togetherlike College,New London.Connecticut Song Sparrows. The pattern that the interlocking boundarieson a terri- 06320

40 American Birds,Spring 1987