Territory Size in Megaceryle Alcyon Along a Stream Habitat

Home , Belted kingfisher, Green kingfisher, Megaceryle

TERRITORY SIZE IN MEGACERYLE ALCYON ALONG A STREAM HABITAT

WILLIAM JAMESDAVIS 1 Departmentof Biology,University of Cincinnati, Cincinnati, Ohio 45221 USA

ASSTRACT.--BeltedKingfishers (Megaceryle alcyon) defend both breedingand nonbreeding territories.The smallnonbreeding territories serve as feedingterritories, and their size is inverselycorrelated to food abundance.In the breedingseason, when nest sitesare a limitingresource, territory size doesnot significantlycorrelate with foodabundance. The averageweight of fledglings/nest,however, is significantlycorrelated with territorysize. In both seasons,kingfishers appear to use streamriffles as preferredforaging sites, although poolsare more prevalent.Riffles may representenvironmental cues by which individuals assesshabitat quality. Received19 February1981, accepted 30 September1981.

NUMEROUS studies have revealed correla- ritory defended [see Nice (1941)for classifica- tions between territory size and various envi- tion of territories]. For example, breeding ter- ronmental parameters. Most frequently, re- ritories of birds usually possess multiple source density (Pitelka et al. 1955, Stenger resources, such as nest sites and food, while 1958, Gill and Wolf 1975, Salomonson and Bal- non-breedingterritories are often only "feed- da 1977) and/or population density (Myers et ing territories" (Welty 1975); thus, in the al. 1979, 1980; Ewald et al. 1980) are cited, but, breeding season,the number and distribution as is now becoming evident, the proximate of available nest sites may influence the suit- causal mechanismsresponsible for these cor- ability of a habitat (von Haartman 1959). If relationsare not always obvious.For example, nest-site limitations restrict the total number although a negative correlationbetween terri- of breeding birds, territory sizesmay become tory size and food densitymay imply that an less dependent upon the availability of other animal has the ability to assessresource den- resources such as food. sity in relationto its needs,it may actuallyonly Belted Kingfishers(Megaceryle alcyon) are reflect the increased population pressure in overtly aggressive birds that, along small areasthat attractmany animalsbecause of high streams, defend territories with well-defined food density. Alternatively, negative correla- boundaries and maintain exclusive use of the tions might resultfrom an animal'srecognition resources on their territories. Although the of habitat factors that are directly associated strong territorial nature of this bird is well with food (Hild•n 1965, Morse 1976) rather known to naturalists,I am unaware of any pre- than its assessment of food itself. Seastedt and vious empirical studies reporting analysesof Maclean (1979) have shown that the size of the territoriality of this species.During the breeding territories of Lapland Longspurs breeding season(March-June), both the male (Calcariuslapponicus) is inversely related to the and female of a breeding pair jointly defend "expected" food density of the habitat com- the territory on which their nest is located. prised by the territory rather than to the actual Nest sites are chosen before the boundaries of food density in a given year. They conclude breedingterritories are firmly established(Da- that longspursrespond to the habitat compo- vis 1980). In the autumn, birds of both sexes, sition of an area rather than to the food den- including the young of the year, defend indi- sity. vidual territories. The present study investi- The relative importanceof different environ- gatespossible determinants of territorysize in mental parametersas determinantsof territory the BeltedKingfisher in both the breedingand size may be dependentupon the type of ter- nonbreeding seasons.

STUDY AREA AND METHODS Presentaddress: Department of Zoology,Uni- Kingfisherswere observed along a 16.8-kmstretch versityof Texasat Austin,Austin, Texas 78712 USA. of IndianCreek in ruralsouthwestern Ohio. During 353 The Auk 99: 353-362. April 1982 354 WILLIAMJAMES DAVIS [Auk, Vol. 99 the study period, Indian Creek had an averageflow 1965). Prey were classified to family, genus, or rateof 1.9 + 0.4 ma/s,although runoff produced from speciesby noting the morphologicalcharacteristics heavy rains occasionallyincreased the volume of of the respectivetaxonomic groups. Cyprinids were flow (at times by as much as 10x). Creek width and classified into one of three groups: stonerollers depth varied from 5 to 19 m and 0.05 to 1.8 m, re- (Campostomaanomalum); minnows, which included spectively,at normal flow. Turbidity was usuallylow all identifiable cyprinid speciesother than C. an- exceptafter heavy rains. Substratevaried; looserock omalum,or unidentified cyprinids, which included was predominant in riffles, while gravel and sand all specimensthat could not be identified to genus. were the usual substrateof deeper pools. Nesting The second method (1 June-23 June) involved plac- banks suitableto M. alcyonoccur regularly along In- ing velcro collarsaround the necksof nestling king- dian Creek where the water erodes soil from bor- fishers for a period of 2 h from 0700 to 0900. This dering banks. Secondary forest growth dominates procedureprevented the young birds from swallow- much of the creekline. Dominant tree species are ing food brought to them by the adults, and, as a Americansycamore (Plantanus occidentalis), sand bar result, fish accumulated at the entrance of the nest willow ($alix interior), several maple species (Acer chamber. Weight, length, and speciesof these fish spp.), and a variety of oaks (Quercusspp.). were recorded.Additional data on prey size and type The bulk of the datawas collectedbetween Ianuary were collectedas kingfisherswere observedfishing 1978 and October 1979. Kingfishers were banded or when items were dropped into the mist net during with U.S. Fish and Wildlife bands and marked with banding of adults. lead-free paint along the edge of the rectrices,using Estimates of food abundance were obtained for six a combination of four colors. Individual birds could nonbreeding territories (SeptembersOctober1978) easily be identified in the field within a 50-m range and for six breeding territories (June 1979) by sam- using binoculars. pling the entire length of each territory by electro- The territory size of marked individuals was mea- shocking. A shortage of manpower prevented fish sured as length (m) instead of as area, becauseter- sampling on any of the 21 nonbreedingterritories ritories followed the course of the stream. Territory measured in 1979, but in October 1979, 1,200 m of sizes were assessedby recording the movement of Indian Creek were electroshocked,with pools and marked individuals that were "herded" along their riffles sampledseparately, in order to documentthe territories (Wiens 1969). By walking along the relative locationof the different fish species.Electro- stream,I forcedthe residentkingfisher(s) to fly ahead shockingwas accomplishedby suspendingtwo elec- until the end of the territory was reached. At this trodes, positioned at opposite ends of 1.3-m pole, in point the kingfisher(s)would reversedirection to fly the water while moving upstream at a constant back into its territory. The locationsof the up- and speed. Current was supplied to the electrodesby a downstream boundaries were determined a mini- 110-volt AC (1,500 watt) generator. Shocked fish mum of five times by this method. The site of ag- were collectedin nets by two personsfollowing a gressive confrontation between adjacent territory third person carrying the electrodes.Fish collected holders was used to confirm boundaries between ter- were counted and classified accordingto size and ritories. Lateral boundaries of territories were de- speciesbefore they were retumed to the stream. Fish marcared by the treeline along the edge of the mortalitywas reducedto lessthan 1% by supplying stream. The following information was later trans- oxygen to the collectingbuckets via air-stone and ferred to detailed maps: length and width of stream, portable air pump. depth measurementsof stream, lengths of pools and Electroshockingwas the method of choicefor sev- riffles, lengths of exposed banks, location of nests, eral reasons:(1) it was more practical for sampling and number of perchesalong the stream'sborders. long stretchesof streams(seining was the altemative Riffles were defined as turbulent flow (5-15 cm in method); (2) sampling of only surfacefish was de- depth) connectingpools. Six nonbreedingterritories sired; and (3) although small fish are generally less were measuredin the fall of 1978, 11 breeding ter- sensitive to sampling by this method than larger ritories in the spring of 1979, and 21 nonbreeding fish, the size of fish vulnerableto predationby king- territories in the late summer and fall of 1979. fishers(4-14 cm) appearseasily sampledby electro- Two methods were used to determine the size and shocking (McCormack 1962; results of preliminary speciesof prey selectedby Megacerglealcyon. In the samplingby the author).Fish were assignedinto five first (24 May-23 Iune), I assessedthe speciesand size size classes: 4-5.9 cm, 6-7.9 cm, 8-9.9 cm, 10-11.9 of prey brought to the nest by observingadult feed- cm, and 12-14 cm. Fish smallerthan 4 cm and larger ing activity with the aid of blinds and a 20x tele- than 14 cm were excluded from the samples, as these scope.Because kingfishers carry prey in their beaks, extreme sizeswere never seen taken by kingfishers. I could estimatefish size by comparingthe length of For each fish species, 15 specimensin each size the fish with the bird's bill (culmenlength of indi- classwere weighed to obtain an averageweight for vidual birds was recorded during banding; Drent that size class.These averagedweights were multi- April 1982] KingfisherTerritory Size 355

CRAY FISH 133%

NON- 60 M INNOWS 10,2% •u• 50 36"/. M INNOWS 12.7% LL. •.0 29 LL C) STONEROLLERS • 3ø• % 20

UN IDENTIFIED 10, CYPRINIDS •X\\\\\\\\\\\\\\\I 2•1%

1•3 ' 3'0 ß 5"0 ' /*-6 6-8 8-1010-12 12-14 NUMBER OF PREY SIZE CLASS (CM) Fig. 1. Foodcapture data. Shown are the speciescomposition (graph A) and size (graphB, hatchedbars) of prey items taken by kingfishers.Data are from observationsmade on 22 dates and from velcro collar method (seetext for details). Open bars in graph B representthe expectednumber of fish in each size class that should be taken by kingfishers, calculatedfrom the percentageof each size classpresent in electroshockingdata (breeding season1979, total number of fish sampled = 3,678).

plied by the number of individuals sampled within deserted, but in each case new, successful nests were each size class; then, all size classes were added to- made within the original territory. gether to obtain the total gramsof fish per species. The number of grams of each specieswere added RESULTS together and divided by the length of stream sampled to obtain the total gramsper meter of stream. Prey andforaging behavior.--Cyprinid species Relative food abundanceper territory was calculated comprisethe majority of the kingfisher'sdiet from thesedata (grams.meter-•'territory •). (Fig. 1A); stonerollers(C. anomalum)were ob- Preferredforaging sites of individual birds were servedmost frequently. If, as suspected,a sub- identified. Each time a bird was observedforaging, stantial proportion of the unidentified cypri- selectedstream parameters of the immediatehabitat nids in Fig. 1A are C. anomalum,this species were recorded,e.g. whether the individual was seen would be under-representedin the figure. In fishing in a shallowpool (depth < 30 cm), a riffle addition, the percentageof crayfish(Cambarus (as previously defined), or deep pool (depth > 30 cm). Both sexes were included, and data were col- spp.) may not reflect the importanceof this lectedon 15 separatedates during the fall of 1979. species;19 of the 21 observationsof kingfishers BetweenApril and June 1979, data were collected bringing crayfishto the nest occurredduring from 14 nests on Indian Creek. Recorded were: (1) periodsof high water and high turbidity when number of eggs laid, (2) number of eggs hatched, fish were difficult to catch. (3) weight of nestlings (g), (4) incubation period The size range of fish taken by kingfishers (days), and (5) number of young fledged.To sample is shown in Fig. lB. Also shown is the "ex- eachnest, I dug an entrancefrom the top of the bank pected" distribution of prey, calculatedfrom down to the backsideof the next chamber. A pre-cut the proportion of each size classrepresented plywood door assemblywas used to resealthe nest chamber between visits. Nests were checked an av- in the electroshockingdata from Indian Creek erage of once a week; near fledging, nests were (data are pooled from all territories). A Chi- checkedevery other day. Data collectionis more like- squaretest showedno differencebetween the ly to causenest desertionearly in the nesting cycle observedand expectedsizes taken (X• = 5.08; (i.e. before incubation) than after the eggs have 0.3 > P > 0.2; df = 4), indicating that king- hatched. In very early spring (1979), two nests were fishers take prey of different sizes in propor- 356 W•LL•AMJAMES DAVIS [Auk, Vol. 99

data from riffles and pools were combined. 59 NO. OF Although it was evident in the field that sig- FISH nificantlymore fish were taken from riffles, the initial data couldnot be analyzedto determine the differencein the number of fish occurring between these areas. Such data were available, • n 3119 however, for the 1,200 m of Indian Creek elec- troshockedin October 1979. Using these data, the distribution of prey species (fish) was found to be significantlygreater in riffles than in pools (n,oo•= 12, •, = 48.65 g/m; nr•fae.•= 12, ir = 195.46 g/m; t = -3.11, P < 0.01, df = 22; see example in Fig. 2). Stonerollerswere most commonly found in the riffles (X2= < 400m234, P • 0.001, df = 1), while other cyprinids, Fig. 2. Distribution of fish in pools and riffles of taken as a group, showedno preferencefor rif- a typical nonbreeding territory. Hatched bars rep- fles or pools (X2 = 1.29, P > 0.2, df= 1). resent numbers of fish caught in riffle sections;open Campostomaanomalum is known to be a riffle bars representnumbers of fish caught in pools. species(McClane 1978). In the nonbreeding season,kingfishers use streamhabitats differentially: during 80 obser- tion to the relative abundance of each size. vations, kingfishers were found fishing long Appropriate data are not available to test ad- riffles 71.3% of the time, along shallowpools equately whether or not kingfishersselect in- 20% of the time, and at deep pools8.7% of the creasinglylarger prey acrossthe nestingseason time, despite the fact that riffles comprised to feed their progressivelylarger young. The only 36% of the stream's length (X•= 35, size distribution of the fish electroshocked in P < 0.001, df = 2). Unfortunately, foraging the nonbreeding season suggeststhat small data were not collectedfor the breeding sea- fish are more abundant than would be pre- son, but my observationsindicate that king- dictedfrom the springdata (X2 = 79, P >>0.01). fishers behave similarly in the spring. More- It is unknown whether or not kingfisherstake over, the predominant use of C. anomalumas on-the-averagesmaller prey in the non-breed- food in the breeding seasonsuggests that they ing season,but field observationconfirms that fish primarily along riffles. they continue to feed mainly on fish (Davis Territories.--Territories defended in the 1979 1980). breeding seasonwere more than twice as large In both seasons, stonerollers are the most as those defended in the 1979 nonbreeding abundant prey species,comprising 70% of the season (breeding, n = 6, i = 1,030 + 219 m; total fish sampled by electroshockingin the nonbreeding,n = 21, i = 389.29 + 92.63; t = nonbreeding season (data pooled from 1978 3.55, P • 0.005, df = 31). The data are incon- and 1979) and 72% in the breeding season; clusive as to whether or not food is a causal cyprinidsother than stonerollerscomprise 20% factor affecting territory size. For example, the and 21%, respectively.There is no statistical size of nonbreedingterritories is significantly difference in the proportion of stonerollersto inversely related to food density (g/m; r •= "minnows" between seasons (X2= 0.109, -0.98, n = 6, P < 0.01), while the size of P > 0.7, df = 1; total fish sampledin the nonbreeding territories is not significantlycorre- breeding season= 3,578, in the breeding sea- lated (r = -0.71, n = 6, P > 0.05). Care must son = 3,678), although noncyprinid species be exercisedwhen interpreting causalrelation- are more abundantin the non-breedingseason ships from simple correlations: in both sea- (X2 = 32.68, P < 0.001, df = 1). This relatively sons, the negative correlationsmay result from large proportion of stonerollersexplains the the indirect effect of intruder pressure, i.e. large proportion of this speciesin the king- more birds are attracted to higher food densi- ilsher's diet (Fig. 1A). Eipper (1956) also re- ties (Myers et al. 1980). ports that stonerollersare a favorite prey of As mentionedpreviously, riffles containsig- kingfishers. nificantly more fish than do pools, and king- During the initial electroshockingruns, the fishersforage more often at riffles. If riffles are April 1982] KingfisherTerritory Size 357

Fig. 3. Riffle length versus size of nonbreeding territories on Indian Creek, 1978. Riffle length and territory size are measuredin meters. Data points fit an exponentialequation (representedby the dashed line) with r s = 0.75, n = 19 and P ( 0.01. an important cue, one would expect territory Starting in March, confrontations between size to be inverselyrelated to total riffle length, males along sections of streams containing as is the case(shown in Fig. 3) for nonbreeding nesting banks were a commonsight, suggest- territories (n = 19, r 2= 0.75, P < 0.01). Al- ing the presenceof more males than nesting thoughriffle length and breedingterritory size banks. In addition, females seemedin surplus are not significantly correlated (n = 8, r = as well, because, on two occasions when the -0.45, P > 0.10), breeding territories that female of a pair disappeared, a new female have a greater concentrationof riffles around took her place with the resident male. White the nestare significantlysmaller than otherter- (1953)and Hamas (1974)also reported nest-site ritories, as is shown in Fig. 4 (.• = 827.5, n = limitations for the Belted Kingfisher. An esti- 4; ß = 1,213.75, n = 4; t = -3.76, P •0.01, mate of the number of kingfisherscompeting df = 6). These resultsmight be explainedby for nests is not available due to the fact that postulating different functions for breeding birds were not banded until after territories and nonbreedingterritories: nonbreeding ter- were established. ritories appear to be essentiallyfeeding terri- Relationships of territory size and food tories, while breeding territories contain two abundance with reproductive successare sum- important resources, food and a suitable nest marized in Table 1. Significantcorrelations oc- site. cur between the following setsof parameters: Nest-sitelimitation and reproductivesuccess.- (1) territory size vs. averageweight of fledg- Suitable nesting banks appear to be in short lings (r = 0.93), and (2) food density (g/m) vs. supply.Of 24 banksalong a 10.6-kmsection of number of birds fledged/nest(r = 0.96). The Indian Creek, 13 banks were occupiedby nest- fact that food density (g/m) is significantlycor- ing pairs, 6 banks were unsuitable for oc- related with number of fledged/nestwhile ter- cupation due to substrate characteristics(com- ritory size is not (r = -0.45) suggeststhat the posedof a high percentageof clayand/or stone) size of the territory is less important than food or location near areas receiving much use by density for production of offspring. humans (e.g. dredging operations), and 5 banks remained unoccupied due to competi- DISCUSSION tive exclusionby territorial individuals. Belted Kingfishers are not colonial nesters and will Nest sites,food, and territorysize.--Both the defend unoccupied nesting banks from con- scarcityand location of nest sites in relation to specificsif they are within their territories. riffles appear to influence territory establish- 358 W•LL•AMJAMES DAWS [Auk,Vol. 99

c•500t ,• 40•,(1037) oo-I 363(765) 362(757) z

• 300-

w• • • • ,' ' .... ,.;"•d223 ...... (,0• 2 273(1282)

• 100' z• ,' •..

100 300 500 700 900 1100 1300 DISTANCE FRON NEST Fig. 4. Cumulativeriffle length versus distance &om nest. On the ordinateis the cumulativelength of shallowwater (depth • 15cm) as the distance from the nest increases symmetric•ly by 25m onthe abscissa. Datawere obtained from detailed maps made of eachterrito•, whichincluded location and length of riffles andpools along the stream. Adjacent numbers represent total length of sh•lowwater (primarily riffles), and numbersin parenthesesrepresent lengths of territories. mentby Megacerylealcyon. Theoretically, nest- mineswhether or not a particularpair of king- sitelimitations can suppress the breedingpop- fisherswill defenda large or smallterritory. ulation density and thus lead to a lower level Evidence is not in favor of a random selection of competitionfor food than would occurif all of nest sites, however. First, males arrive at potentialbreeders were ableto nest.A scarcity least a month before the females to find a suit- of nest sites is often observed for birds (see able nesting bank (somemales in mild winters Temple 1977), and field observations indicate remain the year around). Second,within most competition for available nesting sites for breeding territories along Indian Creek, more kingfishers(Davis 1980). Accordingly, territo- than one suitablenesting bank was available riality in the breedingseason may primarily from which to choose. serve to secure a nest site, while the need to In the event that food is concentrated near defend a food resourceis secondary.This a nestsite, defense of a smallterritory may save study presentsdata that supportthis hypothe- a pair time and energy both in defenseof the sis becauseterritory size and food abundance territory and in the transportof fish backto the (g/m) are not significantlycorrelated. nest. To feed a nest full of youngkingfishers Other data, however,suggest that food dis- may require considerable time and energy. tributiondoes influence the size of breeding Using data from Vessel (1978), I calculatethat territories, in that territory size appearsto be at maximumgrowth rate eachnestling can con- establishedin a consistentrelation to the prox- sume approximately11.2 fish/day.Given 15 h imity of productivefood patchesnear the nest of daylight, eachadult of a pair would need to (Fig. 4), i.e. the smallestterritories enclosethe catch2.6 fish/h in order to feed sevenyoung, richestfood sources.Hole-nesters typically se- not including fish for themselves.During un- lect a nest site beforeestablishing their terri- favorableweather, this may be a difficulttask, tories (von Haartman 1957)•a generalization one that is aggravatedif food is locatedfar from that accuratelydescribes the BeltedKingfisher the nests. As a result, access to an uncontested (Bent 1940, Davis 1980). Unless kingfishers and rich foodsource may be criticalfor raising evaluatefood abundanceduring nest-sitese- a full clutch of young kingfishers.As Seastedt lection, my data imply that an element of and Maclean(1979) have pointed out for Lap- chance enters into the equation that deter- land Longspurs,habitat quality may be better April 1982] KingfisherTerritory Size 359

TABLE1. A summary of correlations(r) and significancelevels between reproductive parameters,territory size, and food abundance. Sample size (n) varies due to the facts that not all territories were sampled for food or nest data were incompletefor some territories.

Food abundance

Territory size Grams/meter Total grams

r n P r n P r n P

Number fledged/nest -0.45 8 NSa 0.96 5 0.02 -0.27 5 NS Averageweight of fledglingsper nest 0.93 7 <0.01 -0.50 5 NS 0.62 7 NS Total weight of fledglingsper nest -0.22 7 NS 0.76 5 NS -0.39 5 NS

• NS = P > 0.05.

represented by food density than by total the question of why kingfishersdefend the quantity. sizes of territory that they do is still not an- When food is not concentrated near the nest, swered. it might be advantageousto defend as large a There are two prevailing hypothesesthat ad- territory as possible, first, becauselarger ter- dress the causal relationship between food ritories may contain greateramounts of food abundance and territory size (Myers et al. (total biomass/territory)and, second,because 1980).The first is the "sufficientresource" hy- larger territories may contain a more reliable pothesis(see Verner 1977), which is derived food supply, i.e. a larger supplyof alternative from the classicalconcept that the basic func- food resources.During fluctuations in water tion of territoriality is to secureadequate re- levelsfollowing heavy or prolongedrains, fish- sources.This hypothesisstates that individu- ing becomesdifficult, and kingfishersare ob- als shoulddefend only thoseresources that are ligated to switch to crayfishas prey, a food required. The secondhypothesis predicts that item not found in riffles. Perhaps as a conse- competition is most severein areasof high re- quenceof both thesefactors, parents with larg- sourcedensity, leading to increasedcosts of er territories that fledge the same number of defense;as a result, territory size is limited by offspringas thosewith smallerterritories may competition for resources(Seastedt and Mac- produceheavier young. Theseincreased fat re- lean 1979; Myers et al. 1979, 1980). Relevant serves could increase the chances of survival data on the BeltedKingfisher are not yet avail- of fledglings(Lack 1966), becausethe first few able to enable a choicebetween thesehypoth- weeks after leaving the nest is a most critical eses; circumstantial evidence, however, favors period for young kingfishers.Early attemptsat the latter. Expansion of breeding territories fishing are most often failures for the young was observed twice, once in 1978 (Davis 1980) birds, becausethey are weak flyersand appar- and oncein 1979, after an adjacentpair of king- ently must learn how to fish (Bent1940, White fishers deserted their territory due to human 1953, Davis 1980);the fact that parentscontin- interference at their nests. These observations ue to feed fledglings suggeststhat young have supportthe hypothesisthat breedingterritory difficultyin obtainingtheir own food. Because size is limited by competition. In a reverse Megacerylealcyon typically raises only one sense, severe nest-site limitations may pro- clutchper year, the survivalof fledglingsmay mote large breeding territories by reducing markedlyaffect the relativefitness of breeding competition. pairs. It appearsthat assessingthe relative val- In the nonbreedingseason, territories of in- ue of large versus small territories in terms of dividuals were remarkably constant in size. reproductivesuccess may depend upon envi- During prolongedrains, nonbreedingterrito- ronmental circumstances. As argued above, ries were often deserted but were reestablished the weight at fledgingmay be important when by the original owners with the original the environment fluctuates,but fledging more boundaries when the water levels returned to but lighter young may increasefitness in a normal. In December, some territories gradu- more constant, productive environment. Both ally increasedin size as kingfishersbegan to strategiesmay be utilized by kingfishers,but disappear,presumably due to their migration 360 WILLIAMJAMES DAVIS [Auk,Vol. 99 south. When and how many birds migrated nest site, breeding birds are able to use habitat appeared to be related to the severity of the cues as important parameters in establishing weather. During cold periods, accumulationof territory size. Only one pair defended a terri- ice along the stream blocked accessto fishing tory larger than expected,when size was pre- areas;the few birds remainingduring the win- dictedby the criterionof the cumulativelength ter months (December-February) seemed to of riffles. This pair initially defendeda smaller usecrayfish more extensively, as gauged by the territory (approximately 830 m) but increased accumulation of their exoskeletons in the win- its size after the adjacentdownstream territory ter roosting nests examined. How dependent was deserted due to human interference at the kingfishersare on crayfishin the winter is still nest. In addition, the relationship between the unknown. Accumulationof exoskeletonsmay size of nonbreedingterritories and riffle length only indicate that these parts are not digestible (Fig. 3) suggeststhat kingfishersmay assess while most parts of fish are digestible (White habitat quality (amount of food available) by 1953). In terms of the proportionof digestible observing the length of fifties present. biomass/preyitem, fish are probably a higher A "new" functionof territoriality.--The view quality food item. adopted in this study and held by most biol- Proximate cues to assess resource abundance.- ogistsis that territoriality evolvedbecause de- Although fish availability may fluctuateduring fense of essentialresources directly enhances the season (Davis 1980), particular habitat pa- the reproductive successof the defender (Nice rametersassociated with food may remain rel- 1941, Lack 1943, Hinde 1956, Brown 1964). But atively constant,e.g. the amountof riffles pres- recently, it has been proposed that territorial ent along a section of stream. Thus, if direct behavior could also be adaptive by decreasing assessmentof food by kingfishers is difficult, the successof one's reproductivecompetitors Megacerylealcyon may instead respondto hab- (Verner 1977). For example, if the cost of de- itat parameters such as riffles. Morse (1976) fense of a resource is minimal, the benefit in believes that warbler speciesrespond to cues terms of relative reproductivesuccess may be that are easily monitored and are correlatedto substantial if an individual can prevent con- important factors. Similarly, data on Sparrow- specificsfrom obtaining a nest or food. A cru- hawks (Accipiternisus) (Newton et al. 1977)and cial assumptionof the hypothesisof "super- Lapland Longspurs (Seastedt and Maclean territories" is that the cost of defense is not 1979) indicate that these speciesrespond to al- prohibitive. Along this line, Rothstein (1979) ternative habitat parameters rather than as- arguesfor the evolution of "inhibitory traits," sessingfood density directly. Other speciesare like aggression,in animals that use specialized known to search for specific prey types by nest sites or utilize highly concentratedfood searchingfor specific sites or patches,rather resources. In the present study, 28% of the than the prey item itself (Royama1970, Parus available nest sites appearedto remain unoc- major; Alcock 1973, Agelaiusphoeniceus; Tin- cupieddue to exclusionof potentialnesters by bergen1976, Sturnus vulgaris). The Little Green extant territory owners. Such aggressivebe- Kingfisher(Chloroceryle americana) also prefers havior, characteristicof territorialityin Mega- to fish along riffles within a stream habitat. cerylealcyon, could be an "inhibitory trait" as Out of 62 observationsmade by the author in describedby Rothstein. If so, territoriality in Costa Rica during the summer of 1981, the this speciesmay be adaptive not only because Green Kingfisherwas found foragingalong rif- it secures resources essential to survival, but fles 84% of the time. Kingfishersmay not in- also becauseit excludescompetitors from re- nately recognize riffles but instead learn to sourcesthat are not utilized by a defender. associatethem with food by positive rein- Several investigators (Getty 1979, Pleasants forcementsubsequent to fishing successalong and Pleasants1979) have voiced strong criti- riffles. Future experiments that manipulate cismof this hypothesis.More empiricalstudies food abundance are needed to determine the are needed to determine whether or not ani- role of habitat parameters(riffles) in the assess- mals do defend territories larger than are ment of habitat quality. neededto fulfill their own requirements.More The general pattern displayed in Fig. 4 sug- extensivedata on reproductivesuccess and ter- gests that in addition to choosinga suitable ritory size are required, and animals that have April 1982] KingfisherTerritory Size 361

specializednest-site or food requirementsthat LACK, D. 1943. The life of the Robin. London, H. F. are easily defended should be critically evalu- & G. Witherby. ated. 1966. Population studies of birds. Oxford, Clarendon Press. MCCLANE,A. J. 1978. McClane'sfield guide to fresh- ACKNOWLEDGMENTS water fishes of North America. New York, Holt, I would like to thank T. C. Kane, my major advi- Rinehart and Winston. sor, and Fred Wasserman, D. R. Osborne, and Linda McCORMACK,J. C. 1962. The food of young trout Mealey for contributing helpful suggestionsduring (Salmo trutta) in two different backs. J. Anim. the first drafts of this paper. I also appreciate the Ecol. 31: 305-316. valuable commentsof J. P. Myers and two anony- MORSE,D. H. 1976. Variables affectingthe density mous reviewers. Mike Bishop, Lisa Aren, and Mas- and territory size of breeding spruce-woods tin Mount made the study possibleby volunteering warblers.Ecology 57: 290-301. their time to collect field data. Financial support MYERS,J.P., P. G. CONNORS,& F. A. PITELKA. 1979. came from Sigma Xi, University of Cincinnati Re- Territory size in wintering Sanderlings:the ef- searchCouncil Summer Fellowships, and University fect of prey abundance and intruder density. of Cincinnati Graduate Student Research Funds. Auk 96: 551-562. This study fulfilled in part the requirementsfor an --, --, & --.. 1980. Optimal territory M.S. degree. size and the Sanderling:compromises in a vari- able environment. Pp. 135-158 in Foraging behavior: ecological,ethological, and psychologi- LITERATURE CITED cal approaches(A. C. Kamil and T. D. Sargent, ALCOCK,J. 1973.Cues used in searchingfor foodby Eds.). New York, Garland STPM Press. red-wingedblackbirds (Agelaius phoeniceus). Be- NEWTON, I., M. MARQUISS, D. N. WEIR, • D. MOSS. haviour 46: 174-188. 1977. Spacing of Sparrowhawk nesting territo- BENT, A. C. 1940. Life histories of North American ries. J. Anim. Ecol. 46: 425-441. cuckoos,goat-suckers, hummingbirds and their NICE, M. M. 1941. The role of territory in bird life. allies. U.S. Natl. Mus. Bull. 176. Amer. Midl. Natur. 26: 441-487. BROWN,J. L. 1964.The evolutionof diversityin PLEASANTS,J. M., & B. Y. PLEASANTS.1979. The avian territorial systems. Wilson Bull. 76: super-territoryhypothesis: a critique, or why 160-169. there are so few bullies. Amer. Natur. 113: DAVIS,W. J. 1980.The BeltedKingfisher (Megaceryle 609614. alcyon).'its ecologyand territoriality.Unpub- PITELI(A, •F. A., P. W. TOMICH, & G. W. TREICHEL. lished Master's thesis. Cincinnati, Ohio, Univ. 1955. Ecologicalrelations of jaegarsand owls as Cincinnati. lemming predators near Barrow, Alaska. Ecol. DRENT,R. H. 1965.Breeding biology of the Pigeon Monogr. 25: 85-117. Guillemot, Cepphuscolumba. Ardea 53: 99-160. ROYAMA,t. 1970. Factors governing the hunting EIPPER,A. W. 1956. Differencesin vulnerabilityof behaviour and selectionof food by the Great Tit the prey of nestingkingfishers. J. Wildl. Mgmt. (Parusmajor L.). J. Anim. Ecol. 39: 619-668. 20: 177-183. ROTHSTEIN,S. I. 1979. Gene frequenciesand selec- EWALD, P. W., G. L. HUNT, & M. WARNER. 1980. tion for inhibitory traits, with specialemphasis Territory size in western gulls: importanceof on the adaptivenessof territoriality.Amer. Nat- intrusion pressure, defense investments, and ur. 113: 317-331. vegetationstructure. Ecology 61: 80-88. SALOMONSON,g. G., & R. P. BALDA. 1977. Winter GETTY,T. 1979. On the benefitsof aggression:the territorialityof Townsend'sSolitaires (Myadestes adaptivenessof inhibition and superterritories. townsendi)in a pition-juniper-ponderosa pine Amer. Natur. 113: 60•609. ecosystem.Condor 79: 148-161. GILL, F. B., & L. L. WOLF. 1975. Economics of feed- SEASTEDT,t. R. & S. F. MACLEAN.1979. Territory ing territorialityin the Golden-wingedSunbird. size and composition in relation to resource Ecology 56: 333-345. abundance in Lapland Longspurs breeding in HAARTMAN,L. VON. 1959. Adaptationin hole-nest- Arctic Alaska. Auk 96: 131-142. ing birds. Evolution 11: 339-347. STENGER,J. 1958. Food habits and available food of HAMAS,M. J. 1974. Human incursionand nesting Ovenbirdsin relationto territorysize. Auk 75: sitesof the BeltedKingfisher. Auk 91: 835-836. 335-346. HILDf•N, O. 1965. Habitat selection in birds. A re- TEMPLE,S. T. 1977. Endangered birds. Madison, view. Ann. Zool. Fennica 2: 53-74. Wisconsin, Univ. Wisconsin Press. HINDE, R. A. 1956. The biologicalsignificance of TINBERGEN,J. M. 1976. How Starlings(Sturnus vul- territories of birds. Ibis 98: 340-369. garis L.) apportiontheir foragingtime in a vir- 362 WtLLmMJAMœs DAws [Auk,Vol. 99

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