WINTER TERRITORIALITY OF TOWNSENDS’ SOLITAIRES (MYADESTES TOWNSENDI) IN A PINON-JUNIPER- PONDEROSA PINE ECOTONE

MICHAEL G. SALOMONSON

AND RUSSELL P. BALDA

Townsends’ Solitaires (Myadestes townsendi) In this study, we wanted to determine if are poorly-known thrushes (but see Sibley Townsends’ Solitaires are territorial in winter. 1973) inhabiting western Secondly, we examined the mechanics of the from central to Alaska. Typically, solitaires ’ territorial system, i.e., how terri- they breed in mixed conifer forests but winter tories are defended, what features of the ter- in piiion-juniper woodlands or other habitats ritory are important to solitaires, and how that provide berries for food (Munro 1919, changes in those features affect the territorial Johnston 1943, Bent 1949). In Arizona, they system. Finally, we attempted to determine are summer residents of high mountains in what selective advantages individuals gain the north, bc > they winter in berry-producing by being territorial. Upper Sonoran woodlands and well-wooded Using Brown and Orians ’ ( 1970) definition Lower Sonoran canyons throughout much of of territory, it was necessary to show that the state (Phillips et al. 1964). Their migra- individuals defend relatively fixed areas which tion is apparently both altitudinal and lati- become exclusive (or nearly so; Brown 1975) tudinal. During the breeding season, they with respect to rivals, and that defensive be- forage like flycatchers, and their diet con- havior evokes escape or avoidance in rivals. sists mostly of insects. During the winter, they eat mainly fruit (Beal 1915, Bent 1949). STUDY AREA AND METHODS The solitaires ’ habit of singing and their The study was conducted in a pifion-juniper-pon- aggressiveness throughout the fall and winter derosa pine ecotone about 24 km NNE of Flagstaff, (Mailliard 1926, Skinner 1928, Lockerbie Coconino Co., Arizona in the fall and winter sea- 1939, Roest 1957) indicate that they probably sons of 1973-74 and 1974-75. The study area, about 35 ha, was located on a gently sloping plateau be- maintain winter territories. Winter territorial- tween 2,082 and 2,106 m elevation. It is bordered to ity has been reported for a number of North the east and southeast by a series of high (2,400- American including Mockingbirds (Mi- 2,700 m) volcanic cinder cones and to the southwest mus polyglottos, Hailman 1960), Plain Titmice by the San Francisco Peaks (3,801 m). These land- (Parus inomutus, Dixon 1956) and Red- forms effectively limit the mid-winter day on the study area to about 9 h. The substrate is a volcanic headed Woodpeckers ( Melanerpes erythro- soil. cephalus, Kilham 1958) and for some Palae- The understory consisted of a number of species of arctic migrants wintering in the tropics herbs and shrubs ( Laudenslayer 1973), but it was (Elgood et al. 1966, Medway 1970, Nisbet and not utilized bv the Townsends’ Solitaires. The over- story was composed of ponderosa pine (Pinus pon- Medway 1972). Pearson (1972) noted that derosa), piiion pine (Pinus edulis), Juniperus mono- warblers wintering in Uganda spent more sperma, J. deppeana, and J. scopulorum. The most time on winter territories than on breeding common juniper was J. monosperma, the one-seed territories. juniper, which produced a berry crop during the With such a large amount of time being summer of 1973. No additional berries were pro- duced by any species during the rest of the study. spent on wintering grounds, natural selection The junipers, piiions, and small ponderosas formed a should operate to produce adaptations pro- uniform stratum averaging 4 m high. Taller pon- moting survival during the winter, especially derosa pines up to 12 m high occurred occasionally, for birds (such as Townsends’ Solitaires) which and a very few widely scattered ponderosas (referred to as tall ponderosas) attained heights up to 23 m. frequently winter in cool or cold environ- Between 18 November 1973 and 20 February 1974, ments. Winter territoriality may be such an 150 cm of snow fell on the study area; between 26 adaptation, If so, then such behavior should October 1974 and 19 February 1975, 135 cm of snow fell. The mean weekly temperatures were about the impart some selective advantage to territorial same for both winters with mean lows between -12 individuals which permits them to survive and -6°C means between -4 and 1°C and mean better until the breeding season relative to highs between 2 and 9°C. The lowest temperature in 1973-74 was -16°C and that for 1974-75 was non-territorial conspecifics. -21°C. Daytime temperatures in late January and 11481 The Condor 79:148-161, 1977 WINTER TERRITORIALITY OF SOLITAIRES 149

February 1975 averaged about 5°C higher than in and throughout the day. Observations were continued 1974. All climatic data were collected on the study for the entire winter period and were ended when area. Temperatures were recorded with a maximum- territories broke down in the spring. Data from all minimum thermometer checked at least three times observations in each winter were combined for a week. Snow depth was recorded by measuring the analysis. depth of new snow with a metric ruler soon after Preliminary observations indicated that Townsends’ every snowfall. Solitaires relied on juniper berries for food so we In the fall of 1973, seven Townsends’ Solitaires estimated the number of available berries. Two observed singing and chasing other solitaires were parallel transect lines were established about 100 m cautured and color-banded for individual recognition. apart. At 50 m intervals, the nearest juniper tree Biids were lured into a mist net by playing-a tape with berries was selected and a branch whose tip was recording of a Townsends’ Solitaires’ song recorded below 3 m high was picked at random for sampling. on the study area early in October 1973. Four of The natural foliage of the outer 0.5 m of the branch the birds disappeared within one week after banding, was measured to the nearest dm3 and the berries but an additional was banded in lanuary 1974. therein counted. The branch tip was inconspicuously Thus, a total of four birds were observed during a marked for future identification. Berries on these large Dart of 1973-74. In October 1974. three new branch tips were recounted every month to deter- birds were banded. One disappeared, but one of the mine how many had been lost. The total volume birds banded in 1973 returned to the study area, so sampled was 185 dm3 on 17 trees in 1973-74. In three birds were observed in 1974-75. 1974-75, the berries contained in 250 dm3 foliage The ages of all banded birds were determined on samples on 10 trees were counted. On the basis of the basis of interior mouth color. In juveniles and sub- these data, the quantity of berries per m3 of berry- adults this region is yellow, but at approximately one laden foliage was estimated. year of age it turns pink. We did not determine the In 1973-74, we located every berry-covered tree sex of the banded birds at the time of capture. In- in each territory. Each tree was designated as either stead, in 1973-74, once it became clear that Town- cylindrical, conical, or spherical and then the volume sends’ Solitaires were territorial, we obtained and of the outer 0.5 m shell of foliage was calculated. sexed six unbanded individuals in a similar habitat Observations showed that most of the berries were about 2 km from the study area. These birds re- contained in this outer shell. We then computed the sponded to the tape-recorded song and to other volume of berry-laden foliage in each 1973-74 ter- solitaires with the same behavior as did the banded ritory and per hectare. The quantity of berries on birds. The banded birds of 1974-75 were collected each territory was estimated by combining these and sexed at the end of the study. Also, five birds data with the number of berries per m” of berry- showing no evidence of territorial behavior in re- laden foliage obtained from the transect lines. sponse to the recorded song were collected and sexed. In the spring of 1974, we maintained a A response to the tape recording was considered on juniper berries in an outdoor cage for 8 days (Z positive (indicative of territoriality) if the subject day length about 10 h, _? temperature 2.8%) to sang and/or actively searched for the source of the determine the daily amount of berries needed to recorded song by flying to-and-fro around the maintain existence metabolism. The bird was pro- speaker. If neither singing nor searching occurred, the vided with ample water. The cage was large enough response was considered negative. to permit hopping but not flight. This experiment For both years, territorial boundaries were deter- was repeated in the fall of 1974 using one solitaire mined by plotting locations where each banded bird for 6 davs and another for 14 davs (a dav length was seen on a scaled map of the study area using a about 16 h, X temperature 2.7”d). -The‘ ’ averige method similar to that of bdum and Kuenzler ( 1955). caloric contents of a whole juniper berry (n = 100) Conflicts involving banded solitaires were observed and a juniper seed (n = 150) were determined by very carefully and their locations plotted on the map. oxygen bomb calorimetry. The stomach contents of Territory sizes were determined with the aid of a 13 Townsends’ Solitaires obtained within 2 km of compensating polar planimeter. the study area were examined. The activities of the banded birds were divided into the following categories and timed with a stop RESULTS watch: territorial activities including singing, calling, chasing other birds, and fighting; searching for and TERRITORIES AND TERRITORIAL BEHAVIOR consuming food such as juniper or mistletoe berries, insects, snow and water; quiet perching, whisper Territorial Individuals. Both immediately be- singing and grooming; and flight (not including chas- fore and after banding, all banded Town- ing).._ The duration of short neriods of flight were sends Solitaires sang, restricted their activities estimated. In 1973-74, we gathered dataon’ 283 activity bouts (27,081 bird-set) which we categor- to rather indistinct yet recognizable geograph- ized into territorial establishment (6,742 bird-set) and ic areas, searched for other singing birds in territorial maintenance (20,339 bird-set) phases on the immediate vicinity, and chased or at- the basis of behavioral changes observed in the field. tempted to chase other solitaires from their In 1974-75, we gathered data on 280 bouts (8,991 bird-set), but the two phases could not be separated. areas. These behaviors are characteristic of A bout was defined as a period of one continuous territoriality. Those banded birds that re- type of activity clearly separated from other activities mained in the study area succeeded in estab- by a distinct behavioral change. The first bout of lishing territories in every sense of Brown and any sequence of bouts was not included in the time Orians ’ (1970) definition. Five banded birds studies, nor were instances where only one bout was were unable to establish territories on the observed. The amount and type of food consumed were also noted. As nearly as possible, observation study area although they attempted to do so. sessions were divided equally among the banded birds All three banded territorial Townsends’ 150 MICHAEL C. SALOMONSON AI\D‘ RUSSELL I.’ BALDA

TABLE 1. Territory sizes and available food of Townsends’ Solitaires in different winters.

Mi%Ons Size juniper FOOd Territory (ha) berries ratio”

1973-74 t = 0.70 A 0.61 13.1 311 B 0.65 24.7 588 I C 0.74 14.0 333 i D 0.82 25.0 595 i 1974-75 .? = 3.85 E 2.48 2.4 29 F 3.74 44 G 5.34 ;:; 63

* Number of berries on trees in territory at start of winter/ minimum number of berries consumed per bird per winter.

Solitaires and all six unbanded but presum- ably territorial birds that we examined were males. In 1973-74, four of the unbanded ter- ritorial birds were sub-adults (less than 1 year old), three of the four banded territorial birds were sub-adults, and two of the banded birds that disappeared were sub-adults. In 1974-75, all four banded birds were adults. None of the banded birds that successfully FIGURE 1. Territories of banded Townsends’ Soli- established a territory died during the study. taires from both winters. Darkened circles indicate In addition to territorial Townsends’ Soli- tall ponderosa pines utilized as primary song and taires, there were also nonterritorial floaters. lookout posts in both winters. Semidarkened circles These birds presumably wandered throughout are tall pines used only in 1973-74. Letters cor- respond to territories in table 1. the countryside using resources within other birds ’ territories. Their behavior can only be described as sneaky; they remained well below individual was ever clearly dominant, so own- treetop level, never making a sound. The ership of these areas fluctuated from day to floaters were always chased from a territory day. Territorial boundaries were broader and when discovered by the territory owner. Gen- less distinct than in 1973-74. erally, floaters occurred singly, but flocks of The largest territory (territory G in fig. 1, up to four birds were seen occasionally. It was table 1) was originally established during not possible to estimate the size of the floater October 1974 by a bird color-banded Orange- population, its mortality rate, nor the amount Orange. The tall ponderosa in this territory of food it consumed. The five floaters col- was the same tree used by Yellow-Blue (ter- lected in 1973-74 included an adult male, a ritory B in fig. 1, table 1) the previous year. sub-adult male, and three adult females. On 20 October 1974, Yellow-Blue returned Territories. In 1973-74, each of the four and in three days regained his former territorjr banded birds established and maintained a by forcing Orange-Orange into another unoc- small exclusive territory (fig. 1, table 1). cupied area. Yellow-Blues’ assault consisted of Each territory contained a tall ponderosa pine. considerable singing and chasing. Yellow- Once territories were firmly established, each Blue abandoned this territory about 23 No- solitaire restricted his activity to his own vember and established a new territory (ter- territory until April 1974. Boundaries of these ritory E, table 1) about 350 m from the old territories were well defined narrow lines. one. Orange-Orange then quietly reoccupied In 1974-75, the three territories averaged his former territory over a lo-day period, once 5.5 times larger than in 1973-74. Again, each again centering his activities in the same tall territory contained a tall ponderosa pine. In ponderosa. However, he did not relinquish places, the territories of the banded birds any of the interim territory, thereby ending overlapped each other and those of adjoining up with the largest territory of the study. unbanded birds. The overlapping areas were Intraspecific Territoriality. Townsends’ Sol- defended throughout the winter by each of itaires arrived on the study area in early the involved territory owners. However, no October both winters and began setting up WINTER TERRITORIALITY OF SOLITAIRES 151

territories immediately. In 1973-74, the estab- whose owner then chased both birds. This lishment phase lasted until about 1 December, disturbance frequently alerted other neigh- ending shortly after the first snowfall of the boring territory owners to the presence of the season. Territories were maintained until early floater who would then be chased from one April when banded solitaires started leaving territory to another until out of sight. Vigor- their own territories and trespassing into ous fights, consisting of grappling with feet, those of their neighbors. In some instances pecking, and flailing with wings occurred the solitaires were absent from their ter- infrequently as the culmination of confronta- ritories for many hours. At first, territories tions between territory owners. Generally were defended from trespassers but defended during fights, one or both birds repeatedly areas soon dwindled to individual distances sang a short, three-five note song which of 10 to 20 m radius. By 24 April, although sounded like a phrase from the Townsends’ the banded Townsends’ Solitaires still spent Solitaires ’ longer advertisement song. No ob- much of their time within the old territorial vious injuries occurred as a result of fighting. boundaries, they ignored other solitaires un- Boundary patrols appear to function in ter- less their individual distances were violated. ritorial advertisement and in reaffirmation of In 1974-75, the banded birds began leaving the boundary. In 1973-74, patrols were rare, their territories about 1 March 1975. Because but in 1974-75 they occurred frequently prob- ample food was still present, this probably ably because of the poor views of the terri- resulted from the unseasonably warm days in torial boundaries from the tall ponderosa January and February. We took this as an pines. During boundary patrols, the Town- indication that territorial behavior was wan- sends’ Solitaires fly from one of the taller ing so the banded birds were collected and trees to another along the boundary where sexed, and the study terminated. they perch quietly, sing, or give call notes. The Townsends’ Solitaires ’ advertisement The same trees are generally used as lookout song is melodious and variable, similar to that and song posts on all boundary patrols. Short of the Black-headed Grosbeak (Pheucticus periods of feeding often interrupt the patrols. melanocephalus) . Individual variation exists, In addition to the territorial behavior de- making it possible to recognize some of the scribed above, territorial Townsends’ Solitaires banded birds solely on the basis of song. often produced a winnowing sound which, al- Songs rarely are sung from anywhere other though probably not intended to frighten in- than the tops of trees or in the tall ponderosa truders, was sufficient to scare some birds off pines. The few exceptions occur when birds the territory. Winnowing in solitaires evi- involved in close confrontations descend into dently results from the passage of air between the trees and sing at each other. Because we the flight feathers on each downward wing observed no evidence of breeding or mate beat. It is heard just prior to touchdown when attracting activity, it appears that the only a territorial Townsends’ Solitaire approaches function of singing in winter is territorial another solitaire in or near its territory. It advertisement and defense. apparently is the result of flight characteris- Call notes are high pitched tezo notes given tics associated with a hesitant approach to- either singly or in series at a constant loud ward a presumably frightening object. Such volume. They usually are given in response approaches are much slower than typical to call notes or songs from adjacent territorial silent approaches toward familiar objects. birds although they are also elicited by the Thus, contrary to winnowing in Hylocichla sight of another Townsends’ Solitaire and spp. (Dilger 1956), winnowing in Town- occasionally are given spontaneously. Call sends’ Solitaires may be characteristic of an notes are not infrequently given from below escape drive rather than an attack drive. treetop levels, but most commonly they are However, intruders have evidently learned to given from treetops. They apparently func- associate the sound with a territorial individ- tion as low intensity advertisement signals. ual and generally flee the territory when it is Chases and fights developed when call heard. notes, songs, and winnowing (see below) Interspecific Territorialit!/. In 1973-74, only failed to frighten an intruder from the terri- two interactions of a possibly interspecific ter- tory. Although chases were sometimes in- ritorial nature were observed. In one instance, itiated without warning, fights always were a banded Townsends’ Solitaire chased a Gray- preceded by one or more of the agonistic headed Junco (lunco caniceps) out of its tall vocalizations. Chases generally ended at ter- pine, but the chase ended after about 15 m. ritory boundaries, but occasionally a floater In the other instance, a banded bird gave a was chased well into an adjoining territory horizontal stretch display toward a flock of 152 MICHAEL G. SALOMONSON AND RUSSELL P. BALDA

>-

1973-74, 12.9% I- 1974-75, 12.8%

m establishment, 16.M

0 maintenance, 11.8%

;-

, -

I-

I

B_

I-

)- 0 I song callnote cnase t1gtlt song call note cnase fight

Territorial Activities Territorial Activities

FIGURE 2. Percentages of Townsends’ Solitaires ’ winter time devoted to various types of territorial behavior. Left graph compares establishment and maintenance phases in 1973-74. Right graph compares total times for the two winter periods. Percentages for each period are summed in the legends.

Western ( Sialia mexicana). The ing berries but could have been viewed as head and neck were extended horizontally, competitors by solitaires once both species feathers were sleeked, the bill was gaped, a were foraging on the ground. The Pygmy zuaaa call resembling the scold of a Stellers’ Nuthatch was chased when both a solitaire Jay (Cyunocittu stelleri) was given, and the and the nuthatch were hawking insects from wings and tail were partially extended and the formers’ tall ponderosa. quivered. The flock was not chased. No Despite the fact that interspecific terri- Townsends’ Solitaire was seen in the flock toriality was more pronounced in 1974-75, although a similar flock containing a solitaire juniper berry consumers were apparently less was seen two days later. plentiful than in 1973-74. In 1973-74, flocks In 1974-75, however, definite interspecific of Evening Grosbeaks (Hesperiphonu VCS- territoriality occurred. In 62.5% of the ob- pertina) numbering 100 or more individuals, served chases, Townsends’ Solitaires chased and flocks of American Robins (Turdus mi- Gray-headed Juncos, Western Bluebirds, and gratorius) containing about 200 individuah in one instance, a Pygmy Nuthatch (Sitta were common, as were Sage Thrashers (Oreo- pygmaeu) . One banded Townsends’ Solitaire scoptes montanus) seen singly or in pairs. In often chased small flocks of Gray-headed 1974-75, no Sage Thrashers were seen, Even- Juncos and Western Bluebirds for as long as ing Grosbeaks were not seen after mid- 2 min. During these chases, he forced the November, and American Robins were ob- flocks into the air and then prevented them served infrequently singly or in small flocks from relanding within the territory. The of not more than 12 birds. The numbers of waaa call often accompanied these chases. Gray-headed Juncos and Western Bluebirds In 1973-74, only about 0.14% of territorial were about the same each winter. activity time was devoted to interspecific en- Territorial Time Budgeting. During es- counters, whereas, in 1974-75, 43.5% of this tablishment in 1973-74, proportionately more time was so spent. time was spent in territorial activities than Interspecific territoriality was apparently during territorial maintenance. The difference directed toward juniper berry consumers. resulted from less time spent chasing, calling, Western Bluebirds ate many juniper berries; and fighting during maintenance (fig. 2). Gray-headed Juncos were never observed eat- Also, less time was devoted to perching activi- WINTER TERRITORIALITY OF SOLITAIRES 153

TABLE 2. Metabolic coefficients, daily existence energy requirements, and daily energy consumption of captive Townsends’ Solitaires.

Consumption/day EAiZFbW Metab. kc& (kcal)‘e Coeff.

Bird 1 32.1 221.5 69.8 24.6 35.3% Bird 2 30.1 192.8 60.8 23.8 39.2% Bird 3 31.0 199.1 62.8 24.2 38.5% R 31.1 204.5 64.5 24.2 37.6%

:’ Averaged over 8, 6, and 10 days. b Based on an average of 315.31 calories/berry flesh. c Computed using Pimm’s (1976) equation, 10 h photo- period, and 2.8oC mean ambient temperature.

Large quantities of berries had fallen to the ground under some of the trees. FIGURE 3. Mean monthly quantities of one-seed The captive solitaires consumed an average juniper berries per mzJof berry-laden foliage. Smaller of 204 berries per day (table 2). The caloric graph is an enIargement of the data for the Iast six content of an average juniper berrys’ flesh months of the study. (seeds are passed through solitaires intact) was calculated to be 315.31 calories. There- ties (which may have a territorial function) fore, the birds ’ average gross energy intake during maintenance. It appears that once ter- was 64.5 kcal/day while maintaining existence ritories were firmly established, the birds metabolism under a 10-h photoperiod at 2.8”C. changed from territorial to foraging activities Using Pimms’ (1976) equation, we estimated (see figs. 4, 5). that the caged solitaires needed 24.2 kcaliday The total amount of time spent in territorial for existence metabolism; hence, their meta- activities for both winter periods was about bolic coefficient (energy for existence metab- the same although apportioned differently. In olism/gross energy intake) was about 37.6%. 1974-75, less time was devoted to intraspecific Existence energy measures the energy re- defensive singing and calling whereas more quirements of birds whose activities are re- time was spent chasing (all species) and stricted by a cage. Thus, the energy needs of fighting (solitaires) than in 1973-74 (fig. 2). free-living birds should be higher because they are more active. The magnitude of the FOOD AVAILABILITY AND increase depends upon the types and dura- FORAGING BEHAVIOR tions of the activities. Nevertheless, existence In the summer of 1973, a huge crop of berries energy can be used to estimate the energy re- was produced on about one-third of the Junip- quirements of free-living birds (Kendeigh erus monosperma trees. Although called 1970). Because wintering Townsends’ Soli- “berries,” these fruits are actually modified taires spend so much time perching (see conifer cones with fleshy, fused cone scales Perching and Aerial Activities), we believe usuaIly containing one seed. No additional that the existence energy estimate for the berries were produced the following summer; captive birds closely approximates the mini- thus, the 1973 crop provided most of the mum energy needs of free-living solitaires Townsends’ Solitaires ’ food for both winters where the mean winter photoperiod was 9 of the study. In October 1973, each m3 of h. mean temperatures were between 4”and berry-laden foliage contained about 20,000 l”C, and the mean body weight was 31.7 g berries. The number of berries declined stead- (n=12;R=2936g). iIy throughout the study (fig. 3). The amount of food available to each ter- Throughout the 1973-74 winter period, the ritory owner, with respect to his minimum bluish berries, averaging 7 mm in diameter, energy needs, was estimated. Based on the were clustered in huge masses on the branch average dailv berry consumption of the caged tips. They were plump, juicy, and soft. Al- birds ( 204 berries), each territorial solitaire though some fell to the ground each month, had to eat at least 42,000 berries in 1973-74 to they were never as concentrated there as on maintain existence energy. We calculated the trees. In 1974-75, the remaining tree- that berry consumption rates doubled the next borne berries were shriveled, leathery, dry, winter SO 1974-75 solitaires should have con- and widely scattered throughout the foliage. sumed about 84,000 berries. Actual consump- 154 MICHAEL G. SALOMONSON AAW RUSSELL I.’ BALDA

1973- 74

m establishment, 8.3 Y, m 1973-74, 14.11:

a- 0 maintenance, 16 X, 0 1974-75, 14.36

insects juniper mistletoe snow water insects juniper mistletoe snow water berries berries berries berries Sustenance Sources Sustenance Sources

FIGURE 4. Percentages of Townsends’ Solitaires ’ winter time devoted to locating and consuming various foods. Left and.right graphs compare the same periods as the corresponding graphs in figure 2.

tion was undoubtedly higher in both winters. than during maintenance. They accomplished Each territory had enough tree-borne berries this through shorter feeding bouts and faster at the start of the winter periods to supply feeding rates (table 3). Although Kendeigh these needs although the ratios of available et al. (1969) reported that birds feed most food to needed food were smaller in 1974-75 actively in the early morning, the solitaires ’ than in 1973-74 (table 1). The territory with feeding activity increased toward midday as the smallest ratio (table 1: E ) was occupied territorial activity declined. by the bird that was most active in interspe- Water consumption was higher in 1974-75 cific territoriality. In 1974-75, many addi- than in 1973-74, apparently to compensate for tional berries were available on the ground the dryness of the juniper berries (fig. 4). beneath some of the trees, but these were ig- Consumption of moist mistletoe berries was nored by the solitaires until after territories 7.9 times greater in 1974-75, possibly as a were established. supplementary water source. Desert-dwelling None of the 13 stomachs examined con- House Finches (Carpoducus mexicanus) are tained anything other than juniper berries. thought to receive much of their water from Nevertheless, Townsends’ Solitaires ate mis- mistletoe berries ( Walsberg 1975). tletoe berries (Phoradendron sp. ) in the field. Throughout 1973-74 and early in 1974-75, In 1973-74 these berries made up less than 90% of the time solitaires spent foraging for 3% of the diet, and in 197475 they equaled 7.2% of the diet based upon field estimates of TABLE 3. Juniper berry feeding factors of free- the number of each type of berry consumed living Townsends’ Solitaires in different winter pe- and the average dry weight of each type of riods. berry collected from where the solitaires were feeding. Insect-eating was noted only twice FkX- Estab. Maint. Total Total Signif. tar” 1973-74 1973-74 1973-74 1974-75 of diff. during the study. The solitaires spent less time foraging for A 13.2 28.9 P < 0.002 juniper berries during territorial establishment A 24.7 8.5 P < 0.002 P < 0.01 and throughout 1974-75 than they did during B 51.1 94.9 B 83.3 24.5 P < 0.002 maintenance or 1973-74 (fig. 4). Neverthe- C 4.2” 3.6b NS less, when daily berry consumption rates were C 3.6 2.7 P < 0.05 compared, we found that the birds ate 2 times a A: j, no. of foraging set/berry consumed; B: P no. set/ more berries in 1974-75 than in 1973-74 and feeding bout; C: f no. berries consumed/bout. h Adjusted means from analysis of covariance. Unadjusted 1.2 times more berries during establishment means: Establishment = 3.5, Maintenance = 3.6. WINTER TERRITORIALITY OF SOLITAIRES 155

60

50 -

7523 - 1973-74. 721%

40 - E F

m z + 30- z F x ; a zo-

10 -

01 whisper quiet grooming whisper quiet B-grooming singing perching singing perching Perching Activities Perching Activities

FIGURE 5. Percentages of Townsends’ Solitaires ’ winter time devoted to different types of perching be- havior. Left and right graphs compare the same periods as the corresponding graphs in figure 2. juniper berries was spent in trees. After 15 De- PERCHING AND AERIAL ACTIVITIES cember 1974, the Townsends’ Solitaires began In both winter periods, more time was spent feeding more intensely on the ground, and by in perching activities than in all other activi- 26 January 1975, they spent more than 95% of ties combined (fig. 5). Perching activities the time they devoted to foraging for juniper are characterized by their lack of extensive berries on the ground. After the shift, forag- motion. Quiet perching includes slight body ing in the trees took place within 0.5 m of the and head movements related to maintaining ground whereas, prior to the shift all foraging watchfulness over the surrounding country in the trees took pIace above 1 m. We com- and quite probably the territory in particular. pared the mean number of foraging seconds/ Birds engaged in grooming or whisper sing- berry consumed, the mean number of seconds/ ing appear to be less attentive to their sur- berry feeding bout, and the mean number of roundings than birds that perch quietly. berries consumed/bout, but we found no In the 1973-74 maintenance phase, banded significant differences between foraging in Townsends’ Solitaires spent less time quietly the trees and on the ground. perching than during the establishment phase Some of the berries the Townsends’ Soli- and more time grooming and whisper singing. taires picked from the ground and trees were Perching activities also occupied less time dropped. Although in most cases this ap- during the maintenance phase; the extra time peared to occur accidentally while the birds apparently was used in foraging. In 1974-75, attempted to swallow the relatively large (in the distribution of time among the perching relation to bill size) berries, some may have activities closely resembled that in the estab- been rejected because they were too hard or lishment phase of 1973-74, with most time dry. If solitaires rejected berries on a large devoted to quiet perching (fig. 5). This scale, rejection most likely occurred visually may indicate a high state of territorial prior to picking. Berries that had been dam- vigilance in the establishment phase and aged by insects differed in external appear- throughout 1974-75. On a 24 h basis, perching ance from undamaged ones and were more accounted for about 27% of the day (table 4). woody than fleshy. If these activities occur at or near existence 156 MICHAEL G. SALOMONSON AND RUSSELL P. BALDA

TABLE 4. Daily time budget of territorial Town- sends’ Solitaires in winter. I 1973-74

u 1974-75 Percent of 24 h day

Establish- Mainte- 1973-74 Activity ment nance Total 1g::;:5

Territorial” 5.7 4.1 4.6 2.4 Aerialh 0.8 0.4 Foraging 3.3 z.: 5.3 z.4” Perching 29.8 25:2 27.0 2617 Night

Roosting 60.4 64.6 62.5 62.5 Juniper Ponders Aerial Other - 0.1 0.1 - l?dixau h.JLocations of Activities Total 100.00 100.0 99.9 100.0 FIGURE 6. P ercentages of Townsends’ Solitaires ’ :*Excluding chases and aerial fights. b Including chases and aerial fights. winter time spent in different trees or other locations within territories. Tall Pine refers to the tall ponder- osas shown in figure 1. metabolic levels (as seems likely), then they are an energetically economical means of maintaining vigilance. During the establish- views of the territories, and only 26.6% of the total time was spent in them. However, more ment phase of 1973-74, 63.4% of the perching occurred in the tops of trees or in the tall time was spent boundary patrolling than in 1973-74. All time spent in the tall pines (82% ponderosa pines, but during the maintenance phase, this was reduced to 57.7%. In 1974-75, of which was spent in perching activities) may 71.2% of the perching took place in the tree- involve territorial vigilance regardless of other tops or tall pines compared to a winter aver- activities in which the birds engaged. age of 59.2% during 1973-74. In an unusual situation in 1973-74, one of Flight, aerial chases, and aerial fighting the banded birds and an unbanded Town- probably were the most energy-demanding sends Solitaire shared the same tall ponderosa activities. Teal (1969) estimated the cost of pine for the entire wintering period. The flight in small birds at 10 times the resting territory boundary apparently bisected the metabolic rate. More time was devoted to tree, and each bird was always observed to be these activities in 1974-75 than in 1973-74 on his own side. The birds tended to ignore (fig. 6). The establishment phase had more each other when both were in the tree al- aerial activity than the maintenance phase. though they never were observed singing Thus, these activities were most prevalent simultaneously from the tree. At other loca- during periods of intense territoriality and tions along their common boundary, they de- when territories were large. Because many of fended their territories from each other in a the differences between the 24 h time budgets typical fashion. Welch (1975) mentioned a resulted from increases in aerial activity somewhat similar situation for Savannah Spar- rows ( Passerculus sandwichensis) . (table 4)) it appears that territorial establish- ment is energetically more costly than main- The amounts of time spent by territorial tenance, and large territories are more costly Townsends’ Solitaires in other locations dif- than small ones. The energetic costs of activi- fered from one winter period to the next. ties such as foraging and singing have never While on boundary patrols in 1974-75, soli- been measured, but various authors (Orians taires frequently used medium-sized ponder- 1961, Schartz and Zimmerman 1971) have osas, taller pifions, and dead snags that pro- estimated that these costs are near those of truded above the average treetop level as song existence or resting metabolism. and lookout posts. In 1973-74 when boundary patrolling was minimal, these trees were largely ignored (fig. 6). The percent of time UTILIZATION OF TREES spent in juniper trees in 1974-75 was less than In 1973-74,43% of the total time was spent in in 1973-74, but the percent of time spent on the tall ponderosa pines located in each terri- the ground was greater as a result of the tory (fig. 6). These trees, presumably be- changes in foraging locations. cause of the excellent views that they af- During the establishment phase of 1973-74, forded, served as lookout posts and primary about 22% of the Townsends’ Solitaires ’ time song posts in the small territories, thereby was spent on the tops of trees, not including eliminating the need for boundary patrols. In the tall ponderosa pines. Once territories were 1974-75, the tall pines did not provide clear established, however, only 7% of the time was WINTER TERRITORIALITY OF SOLITAIRES 157 spent on the treetops, and for the entire ritory owners’ needs (Wilson 1975). This winter period, time spent on the treetops probably results from natural selection favor- averaged 10.8%. By contrast, in 197475, ing the solitaires with large territories con- 36.6% of the time was spent on treetops. Soli- taining excessive food supplies (providing taires rarely perched on top of the tall pon- much more food than they require to meet derosas, but instead, perched 1 or 2 m below energetic needs). These can serve as insurance the top in a place which gave good views of against overexploitation of the food by other the territory. species and nonterritorial solitaires, and as insurance against natural “disasters” DISCUSSION such as heavy snows which may de- stroy or make inaccessible part of the food It has often been postulated that one impor- supply. (Both winters of this study were tant function of territoriality is to secure a food relatively mild compared to other recent win- supply for the territory owner, although, with ters around Flagstaff.) Wintering solitaires few exceptions (Stenger 1958, Holmes 1970, could easily assessthe total food supply avail- Zahavi 1971), substantiating data have been able to them at the very beginning of the difficult to gather (Hinde 1956). The data winter periods thus facilitating territorial es- presented here show clearly that protection of tablishment on the basis of food availability. the food source is the function of winter ter- The birds could not assess the magnitude of ritoriality in Townsends’ Solitaires. Their ter- food use or of disasters in advance of winter. ritories are strictly feeding territories, used If winter territories are to provide only the neither for mate attraction nor for any other amount of food needed during an “average” breeding activities. They are abandoned in winter, then periodic and unpredictable catas- the spring when the birds migrate to breeding trophes (deep snow, ice storms, etc.) could grounds in quite different habitats. effectively destroy the birds or cause them to In 1973-74, when food was abundant and of leave their territories. Under these harsh high quality, many male Townsends’ Soli- conditions, a territorial system based on an taires including both adults and sub-adults, “average” winter is not a viable selective were able to establish small exclusive terri- option. In contrast, selection for an appar- tories, but in 1974-75, when food was less ently (but not really) extravagant territorial abundant and poorer in quality, fewer birds system would insure better survival under the established territories and the territories of rare circumstances of extreme environmental successful individuals were larger than in the conditions. previous winter. Based upon scant evidence, Townsends’ Solitaires whose territories con- it appears that sub-adult males were excluded tain excessive food should survive the winter from establishing territories by competition in better condition than nonterritorial floaters from more experienced and/or aggresive adult or birds whose territories contain insufficient birds in 1974-75. In both winters, some food supplies and, therefore, should be in banded birds, apparently less aggressive or better condition for migration and breeding. less experienced, were unable to establish ter- Smith (1968) showed that tree squirrels ritories on the study area. These individuals whose territories contained excess food sur- may have succeeded in establishing territories vived winter better than individuals whose in less suitable habitats or among less aggres- territories contained just enough food to pro- sive neighbors elsewhere, or they may have vide for their needs. Jenkins et al. (1963) existed as floaters near the study area. Fe- found that nonterritorial Red Grouse (Lago- males apparently do not establish territories pus Zagopus)suffered higher winter mortality in the piiion-juniper-ponderosa pine ecotone than territorial birds as a result of greater but persist as nonterritorial floaters along predation, starvation, and disease. with some males. Verner (in litt.) suggests that maximization It is noteworthy that each territory, regard- of territory size functions to reduce the num- less of its size, contained much more food than ber of breeding members of a species, thereby its owner required. None of the territories increasing the relative fitness of more aggres- was devoid of food when abandoned at the sive individuals. He suggests further that end of the winter periods. Clearly, wintering defense of space, per se, has become the pri- Townsends’ Solitaires are maximizing terri- mary selective agent maintaining territoriality. tory size with regard to their food supply However, large territories probably result in- rather than optimizing it, i.e., defending an directly from selection for the defense of ex- area just large enough to yield a minimally cesses of some other requisite such as food. sufficient amount of energy to meet the ter- In wintering Townsends’ Solitaires, it appears 158 MICHAEL G. SALOMONSON AND RUSSELL P. BALDA

that the amount of food on the territory is The solitaires ’ territorial system is centered biologically more important than the size of around the tall ponderosa pines located in the territory itself. It seems logical that each territory. The use of these trees as pri- regardless of the nature of the defended re- mary lookout and song posts reduces the need source, maximization of the territory for that for energetically costly boundary patrolling by resource should result in the spatially large enabling territory owners to detect intruders territories and also in behaviorally induced easily and quickly. Because solitaires perch interference competition for the resource, within the foliage of the tall pines rather than thereby forcing some individuals to accept in exposed locations on the tops (as they do resource-poor territories or to become floaters. on other trees when patrolling), their use of Townsends’ Solitaires relegated to such situa- tall pines may also reduce exposure to pred- tions presumably survive the winter less well ators and to the elements while enabling them than those on territories providing excessive to maintain watch over their territories. The quantities of food. The reproductive potential presence of tall pines may make the ecotone of those that do survive may, indeed, be lower an optimum habitat for territorial individuals. than that of resource-rich territory owners. Pifion-juniper woodlands lacking tall pines This, however, is an incidental effect of a ter- were searched for solitaires during the fall of ritorial system the main function of which 1973 and, although they contained vast num- is to enhance survival through the winter by bers of jumper berries, they were not occu- providing ample food for the territory owner, pied by solitaires as rapidly as the ecotone. In not a direct effect of a concerted effort to re- the absence of tall pines, solitaires may prefer duce the fitness of other potential breeders steep-sided canyons where territories can be within the population. Winter territory also observed from high prominences. The pres- may provide experience useful in establishing ence of Townsends’ Solitaires in such canyons breeding territories, especially for immature during the winter has been noted frequently birds. (Bent 1949). The importance of the tall pon- Territory sizes of wintering Townsends’ derosa to the territorial system apparently Solitaires are probably reached through a decreases as territories become larger and complex interaction of time and energy con- more difficult to monitor from one location, siderations (economic defendability of Brown The abundance of food in 1973-74 made 1964), aggressive tendencies of neighbors, and interspecific territorial defense unnecessary an individually variable settling response even though the densities of all juniper berry stimulated by some quality of the habitat. consumers were noticeably higher than in Hilden (1965) d escribed habitat selection in 1974-75. Indeed, the abundance of juniper terms of proximate and ultimate factors. Juni- berries may have attracted many more birds per berries are undoubtedly an ultimate fac- to the area than would have wintered there tor in the Townsends’ Solitaires ’ territorial sys- otherwise. Interspecific territorial defense tem but may also act as a proximate factor that against virtually hundreds of birds would have releases the settling response. The masses of been impossible. In 1974-75, although food tree-borne berries may serve qualitatively as a was not scarce, it was apparently inconspic- means of assessing the richness of the food uous enough to cause many birds of all berry- supply. When berries are scarce, few birds consuming species to pass over the area and are stimulated to settle, and those that do, to stimulate interspecific territoriality in perceive the “need” for large territories to Townsends’ Solitaires. provide ample food. Maximum territory size Perching occupies much of the territorial is limited by competitive interactions with solitaires ’ time budget and, because it requires neighboring birds and/or by the size at which little energy expenditure above that needed for it is no longer energetically economical to existence metabolism, it is probably a means defend a territory. Plentiful berries stimulate of conserving energy. Because so much perch- many more birds to settle; less space is per- ing occurs in tall ponderosas and on tree- ceived as necessary to provide ample food tops, it is also an energetically economical and, indeed, increased competition for terri- way to maintain watch over the territories. tories may make large territories indefensible. As a result of perching, territorial solitaires In either situation, territories are probably the are able to spend about 21 of every 24 h at maximum size possible given the existing set or near existence metabolism levels during the of environmental conditions. When food is winter. Although quantitative data are un- abundant, territory size may approach the available, field observations indicate that minimum acceptable by Townsends’ Soli- floaters, by comparison, spend less time perch- taires. ing and more time flying as a result of being WINTER TERRITORIALITY OF SOLITAIRES 159 chased from territory to territory. Because foraging in the two locations, three factors flight requires so much energy, floaters would must be considered in evaluating the ad- be expected to need much more energy than vantages of one site over another: (1) the territorial birds. amount of time spent foraging per unit of During the establishment phase of 1973-74 food eaten, (2) the amount of energy ex- and throughout 1974-75, foraging bouts were pended per unit of food eaten, and (3) the shorter than during corresponding winter distribution and abundance of the food. Other periods. Presumably, this occurred during es- factors such as predation also influence choice tablishment because migrants, floaters, and of feeding-site but probably were not as im- territorial neighbors increased the frequency portant here because we saw no indications of trespass, thus requiring more vigilance than of greater predation pressure at the time of during maintenance. Larger territories, harder the foraging shift. In those trees that had to defend than small ones, also required more berries in 197475, the berries were sparsely vigilance. Long periods of time spent forag- but evenly distributed throughout the outer ing, because of the location of the food within foliage whereas on the ground under those the foliage or on the ground, would increase trees, berries were evenly, but more densely the chances of another solitaire entering the distributed. To maintain the same feeding territory undetected. By shortening the dura- rate in both places (as solitaires did), a bird tion of feeding bouts and increasing the num- would have to cover the distance between ber of berries consumed per bout, the soli- berries on the tree in a shorter time than on taires were able to check their territories more the ground thereby expending more energy often, yet were able to eat more food than in for each berry that was consumed. Given the corresponding periods. same feeding rate, the amount of energy ex- Feeding bouts were shortened by reducing pended to gather each unit of food should in- the amount of time spent inspecting juniper crease as the distance between the units berries prior to picking and eating them. If increases. Thus, it became energetically more inspections were important for discerning and economical to feed on the ground once the rejecting bad berries (those that had suffered berries were more concentrated there than in insect predation and consequently developed the trees. Solitaires foraging in the trees in woody flesh), then a frenetic feeding rate 197475 could not, with few exceptions, ob- may have been less efficient than a more tain more than two berries without moving at leisurely one as a result of increasing the least 25 cm, but birds foraging on the ground amount of poor quality, indigestible food that could easily eat 4 or 5 berries without chang- was eaten. The metabolic coefficient of soli- ing locations. taires feeding on juniper berries is about 37.6%, much less than the 76-80% coefficients SUMMARY of granivorous birds (Kendeigh 1969), the 68.5% coefficient of insectivorous male Dick- Winter territoriality of male Townsends’ Soli- cissels ( Spiza americana, Schartz and Zimmer- taires was studied in a piiion-juniper-ponder- man 1971) and the 49% coefficient of Phain- osa pine ecotone near Flagstaff, Arizona. opeplas (PhuinopepZa nitens) feeding on Winter territories were not related to any re- mistletoe berries ( Walsberg 1975). With such productive activities, but to food availability; a low metabolic coefficient, a reduction in high they served to secure a food supply. Up to quality food intake could lead to a detrimental 97% of the Townsends’ Solitaires ’ winter diet energy balance. This may account for the consisted of berries from the one-seed juniper fact that more food was eaten during periods (Juniperus monosperma). In the winter of with frenetic feeding rates even though time 1973-74 when berries were plentiful, terri- budgets and, hence, energy budgets for all tories were small and delimited by well-de- periods were similar. fined narrow boundaries. Territories were The shift from foraging in the trees to for- larger and overlapped in the winter of 1974- aging on the ground that occurred in 197475 75 when berries were more scarce; boundaries presumably took place because the juniper were less distinct. In each winter, every ter- berries were more accessible on the ground ritory had ample food for its owner. throughout 197475. Its timing was not cor- In 1973-74, territorial establishment and related with any other noticeable behavioral maintenance phases were clearly distinguish- change; thus the solitaires simply may not able because of behavioral changes. The es- have realized previously that food was more tablishment phase was characterized by in- abundant on the ground. Although no sig- tense territorial activity and lasted from early nificant differences existed in any aspects of October until about 1 December. Territories