The Auk 122(1):187–204, 2005 © The American Ornithologists’ Union, 2005. Printed in USA.

FORAGING AND TERRITORY ECONOMICS OF SEXUALLY DIMORPHIC PURPLE-THROATED CARIBS (EULAMPIS JUGULARIS) ON THREE HELICONIA MORPHS Ems J. Tjrjqj,1 Rtns S. Gtqirs, si Aqj}jn U. Kziq Department of Biology, Amherst College, Amherst, Massachuse s 01002, USA

A.—We observed territorial Purple-throated Caribs (Eulampis jugularis) on three Heliconia morphs (H. caribaea and the red-green and green morphs of H. bihai) on the island of St. Lucia, West Indies, to examine how calculated costs and benefi ts compared with observed pa erns of Heliconia use. Across the three years of our study, H. caribaea territories defended by Purple-throated Carib males were sig- nifi cantly smaller in area and had higher densities of fl owers than red-green H. bihai territories, and both kinds of Heliconia territories defended by males were smaller and had higher densities of fl owers than the green H. bihai territory maintained by a female. In the period (0630 to 1400 hours) during which birds maintained territories, total maintenance costs were more than met by energy obtained from territories, but only 2 of 13 territories provided suffi cient nectar to meet birds’ energy requirements for 24 h. Birds supplemented their energy intake from Heliconia territories by forag- ing at fl owers in the rainforest canopy, and the percentage of time a territorial bird spent foraging in the canopy was inversely correlated with energy production on its Heliconia territory. The smaller territory areas and higher fl ower densities of H. caribaea territories lowered males’ foraging time and energy costs per fl ower on H. caribaea as compared with red-green H. bihai territories, theoretically allowing them to meet their energy demands in less time and at lower cost. Males’ estimated forag- ing time and energy costs were greatest at the green morph of H. bihai; compared with females, they would save a higher proportion of time and energy by foraging at H. caribaea and the red-green morph of H. bihai. That asymmetry between males and females in relative gains from foraging at each of the three Heliconia morphs may further reinforce resource partitioning between them, in addition to diff erences in size and fi ghting abilities. Received 6 September 2003, accepted 31 August 2004.

Key words: Eulampis jugularis, foraging behavior, Heliconia, hummingbird, Purple- throated Carib, territoriality.

Economía de Forrajeo y Territorialidad en la Especie Sexualmente Dimórfi ca Eulampis jugularis en Tres Formas de Heliconia

Rjzrjs.—Observamos individuos territoriales de Eulampis jugularis en relación con tres formas de Heliconia (H. caribaea y las formas roja-verde y verde de H. bihai) en la Isla de Santa Lucía, Indias Occidentales, para examinar cómo los costos y benefi cios calculados se comparan con patrones observados de uso de Heliconia. A lo largo de los tres años de nuestro estudio, los territorios de H. caribaea defendidos por machos de E. jugularis fueron signifi cativamente menores en tamaño y presentaron mayores densidades de fl ores que los territorios de la forma roja-verde de H. bihai, y ambos tipos de territorios de Heliconia defendidas por machos fueron menores y presentaron mayores densidades de fl ores que los territorios de la forma verde de

1E-mail: [email protected]

187 188 Tjrjqj, Gtqirs, si Kziq [Auk, Vol. 122

H. bihai mantenidos por una hembra. En el período (0630 a 1400 horas) durante el cual las aves mantuvieron sus territorios, los costos totales de mantenimiento fueron alcanzados y superados por la energía provista por los territorios, pero sólo 2 de los 13 territorios brindaron sufi ciente néctar como para alcanzar los requerimientos energéticos por 24 h. Las aves suplementaron la energía provista por sus territorios de Heliconia forrajeando en fl ores en el dosel de la selva, y el porcentaje de tiempo que un ave territorial pasó forrajeando en el dosel se correlacionó inversamente con la producción de energía en sus territorios de Heliconia. Los territorios más pequeños y las mayores densidades de fl ores de los territorios de H. caribaea disminuyeron el tiempo de forrajeo de los machos y los costos energéticos por fl or en H. caribaea comparada con los territorios de la forma roja-verde de H. bihai, teóricamente permitiéndoles a los machos alcanzar sus demandas energéticas en menos tiempo y a un costo menor. Las estimaciones del tiempo de forrajeo y de los costos energéticos de los machos fueron mayores para la forma verde de H. bihai. Comparados con las hembras, los machos ahorrarían una mayor proporción de tiempo y energía forrajeando en H. caribaea y en la forma roja-verde de H. bihai. Esta asimetría entre machos y hembras en las ganancias relativas obtenidas por forrajear en cada una de las tres formas de Heliconia podría reforzar la repartición de recursos entre ellos, además de las diferencias en el tamaño y en las habilidades para la lucha.

A tsju jsq to studies of territo- in defense varies in relation to fl uctuations rial behavior is that the benefi ts derived from in availability of a single fl oral resource or exclusive access to a resource must outweigh in relation to manipulations of the quality of the additional costs expended in defense of artifi cial resources (e.g. Gill and Wolf 1975, that resource (Brown 1964). For many animals, Carpenter and MacMillen 1976, Ewald and the defended resource is food, and a number Carpenter 1978, Powers and McKee 1994; but of studies have a empted to quantify the costs see Wolf and Hainsworth 1971, who exam- and benefi ts of feeding territories for both ver- ined hummingbird territorial defense of both tebrates (e.g. Smith 1968, Gill and Wolf 1975, native and introduced plants). Yet studies of Carpenter and MacMillen 1976, Davies 1976, the community ecology of nectar-feeding birds CliV on 1990) and invertebrates (Hart 1985). indicate that most nectar-feeding avian species Nectarivorous birds have played a promi- visit the fl owers of several diff erent species of nent role in studies of territoriality, because plants (Snow and Snow 1972, Feinsinger 1976, their food resources can be easily quantifi ed Wolf et al. 1976, Kodric-Brown et al. 1984). and manipulated, which facilitates examina- Understanding how the costs and benefi ts of tion of how their aggressive behaviors vary territorial defense change with the species of in relation to food availability. Nectar-feeding plant defended and the kind of defender is sunbirds, honeycreepers, and hummingbirds thus a critical step for understanding how fl o- defend territories for short intervals, such as ral resources are partitioned between species a day or a week, and abandon them as soon as or sexes of territorial individuals, and also for nectar levels fall below some lower threshold of understanding how coevolutionary relation- availability (Gill and Wolf 1975, Carpenter and ships between nectar-feeding birds and their MacMillen 1976, Trombulak 1990). At the other food plants may have developed. extreme, nectar-feeding birds cease territorial Here, we examine the costs and benefi ts behavior during times of nectar superabun- of territorial defense by the Purple-throated dance, because no additional benefi ts in terms Carib (Eulampis jugularis) at their Heliconia food of access to nectar result from the extra expense plants on the island of St. Lucia, West Indies. of defense (Gill and Wolf 1975, Carpenter and Although the sexes are alike in plumage, they MacMillen 1976, Carpenter 1987, Armstrong exhibit extreme sexual dimorphisms in body 1991). mass and bill morphology. Males are 25% Most studies of territorial defense by nectar- heavier than females, yet bills of females are feeding birds have focused on how investment 30% longer and 100% more curved than bills January 2005] Hummingbird Territoriality 189 of males (Wolf 1975b, Temeles et al. 2000, E. J. Szi~ Aj si Mjmti Temeles unpubl. data). Previous work on St. Lucia demonstrated that the Purple-throated We performed the study on the island of St. Carib is the sole pollinator of two species of Lucia, West Indies, from approximately 20 May Heliconia plants (Temeles et al. 2000, Temeles to 1 July 2000, 2001, and 2002 at three rainforest and Kress 2003). Males normally defend dense reserves: Quilesse (13°51’04”N, 60°58’34”W), patches of a red-bracted morph of H. caribaea, Des Cartiers (13°50’12”N, 60°58’34”W), and whose short, straight fl owers and greater num- Barre de L’Isle (13°54’58”N, 60°57’33”W). At ber of fl owers per infl orescence correspond to both Quilesse and Barre de L’Isle, the primary their shorter, straighter bills and larger bodies food plants of the Purple-throated Carib during and energy needs. Females normally trapline- that part of the year are the red-bracted morph forage at undefended patches of H. caribaea and of H. caribaea and the green-bracted morph of a green-bracted morph of H. bihai, whose lon- H. bihai; whereas at Des Cartiers, the primary ger, more curved fl owers and fewer fl owers per food plants are the red-green-bracted and infl orescence correspond to their longer, more green-bracted morphs of H. bihai (Temeles et al. curved bills and smaller bodies and energy 2000). Because of sexual diff erences in the use of needs. Females also commonly intrude onto these Heliconia species, however, male Purple- male territories to steal nectar, and less oV en throated Caribs were associated with H. caribaea defend territories of H. caribaea or H. bihai. At or the red-green morph of H. bihai; thus, in each rainforest reserves where H. caribaea is rare year, we selected two male territories that pri- or absent, a red-green-bracted morph of H. marily or exclusively comprised H. caribaea and bihai takes its place. That morph has shorter, two male territories that primarily comprised straighter fl owers and a higher fl oral reward the red-green morph of H. bihai. In 2001, we per infl orescence as compared with the green- observed a single female defending a territory bracted morph, but not as compared with at Des Cartiers reserve, consisting primarily of H. caribaea. Males at those reserves associate the green-bracted morph of H. bihai; it was the primarily with the red-green morph, whereas only female territory we found during May and females associate primarily with the green June in 2000, 2001, and 2002. morph (Temeles et al. 2000). The plants.—Heliconia caribaea and the two Temeles et al. (2000) and Temeles and Kress morphs of H. bihai contain an average of 12 (2003) hypothesized that sexual diff erences fl owers per bract, except for the terminal bract, in Heliconia use by Purple-throated Caribs which may contain 10 fl owers (E. J. Temeles on St. Lucia resulted from social dominance, and W. J. Kress pers. obs.). Within bracts, each whereby larger, dominant males excluded fl ower opens sequentially and lasts for a single smaller, subordinate females from the more- day (Temeles and Kress 2003). Average number rewarding H. caribaea and red-green morph of of bracts per infl orescence diff ers among the H. bihai. Females, by default, associated with three Heliconia morphs, with H. caribaea bear- the less-rewarding green-bracted morph of H. ing approximately twice as many bracts per bihai. Studies by Wolf (1975b) on the island of infl orescence (9) as the red-green morph (5) or Dominica, ~120 km to the north of St. Lucia, green morph (4) of H. bihai. Those diff erences provide some support for that hypothesis: in bract numbers among the Heliconia morphs males dominated females, and banana (Musa result in corresponding diff erences in energy sapientum) territories defended by females rewards per infl orescence (Temeles and Kress had lower densities of fl owers than banana 2003). At peak fl owering, all the bracts of an territories defended by males. Here, we pres- infl orescence may bear fl owers on the same ent time and energy budgets of male Purple- day, but during the present study, percentages throated Caribs and examine their costs and of fl ower-bearing bracts per infl orescence aver- benefi ts of foraging on and defense of the three aged 33% in 2000, 12.5% in 2001, and 21.5% in Heliconia morphs. We also examine whether the 2002 (n = 471 infl orescences). Hence, following smaller size and lower energy requirements Stiles’s (1978) terminology, none of the Heliconia of female Purple-throated Caribs give them a morphs was in “good bloom” (i.e. with >50% of foraging advantage over males at the green- infl orescences bearing fl owers). The year 2001 bracted morph of H. bihai. was one of the worst drought years on record 190 Tjrjqj, Gtqirs, si Kziq [Auk, Vol. 122

(D. Anthony pers. comm.), and many Heliconia the area of territories and numbers of clumps, bracts contained aborted fl owers. stalks, infl orescences, bracts, and fl owers of We measured nectar production over 24 h by each Heliconia species within each territory. each of the three Heliconia morphs by covering In previous studies (Temeles et al. 2000, infl orescences with mesh bags to exclude animal Temeles and Kress 2003), we determined that visitors and then extracting nectar from picked territory owners, especially those defending fl owers using 25- and 50-µL capillary pipets. We patches of H. bihai, abandoned Heliconia terri- performed a similar analysis to assess rates of tories and moved into the rainforest canopy at nectar production per hour. Although cover- ~1400 hours AST. Accordingly, we watched each ing infl orescences with mesh bags excludes territorial bird for a period of fi ve hours during large visitors (birds and ants), it is ineff ective in the morning and early aV ernoon (approximately excluding nectar mites, which consume fl ower 0700–1300 hours AST). For each territory, two to nectar (R. Colwell pers. comm.). We recorded four observers watched the territory owner to mites on the fl owers of all Heliconia species and maximize observations of the bird’s activities. morphs, however, and we assume that mites With the exceptions noted below, our time bud- aff ect nectar production by all Heliconia spe- get analyses followed the protocols of Wolf and cies and morphs equally. Moreover, because Hainsworth (1971) and Gill and Wolf (1975). hummingbirds cannot physically exclude mites We recorded the following daytime activities, from fl owers, our measurements refl ect the measured to the nearest second: “si ing,” actual amount of nectar per fl ower available to during which time the bird was perched in its the birds. territory (preening and looking around were Gill and Wolf (1975) noted that one benefi t included in this category); “foraging,” during of territorial defense for sunbirds was greater which time the bird was actively searching for standing crops of nectar on defended than nectar or feeding at fl owers (time spent fl ying on undefended areas. Although that benefi t between fl owers was included in this category); presumably resulted from exclusion of intruders “fl ycatching,” which denotes the time birds from defended patches of fl owers, an alternative were observed foraging for insects around their explanation is that defended fl owers were some- perches; “chasing,” in which territory owners how “be er” and produced more nectar than actively fl ew at an intruder and evicted the undefended fl owers (Gill and Wolf 1975). To intruder from the territory; “perch shiV s,” in examine whether plants defended by birds were which the territory owner fl ew from one perch superior in nectar production to undefended to another within its territory, and “time gone,” plants, we selected plants in defended and unde- in which the bird leV its territory and was out of fended patches of Heliconia for comparison of sight of the observers. their nectar production over 24 h. We also recorded two other activities specifi c Lastly, to examine the benefi ts of territorial to our study, “mating chases” and “canopy defense by Purple-throated Caribs, we mea- time.” The dates of the study coincided with sured standing crops of nectar in fl owers of the end of the nesting period of Purple-throated the three Heliconia morphs on defended and Caribs (Wolf and Hainsworth 1971; Wolf and undefended areas over various intervals during Wolf 1971; Wolf 1975a, b; Schuchmann and which the birds defended fl owers (dawn to 1400 Schuchmann-Wegert 1984), and we observed hours; see below). females on the nest and copulations on or Time budgets.—We determined the boundaries near males’ territories in all three years. of each territory by observing the point at which Hence, some females, such as those on the territorial birds evicted intruders, which in our nest, may have intruded solely to steal nectar, study included neighboring and nonterrito- whereas others may have intruded to mate rial males, nonterritorial females, Bananaquits (Wolf and Hainsworth 1971). Wolf (1975a) and (Coereba fl aveola), Lesser Antillean Bullfi nches Schuchmann and Schuchmann-Wegert (1984) (Loxigilla noctis), and St. Lucia Orioles (Icterus described the mating behavior of Purple- laudabilis). The heterospecifi c intruders entered throated Caribs as being initiated by a series of male territories either to pierce Heliconia fl ow- chases, in which the female repeatedly returns to ers (Bananaquit) or to consume part or all of the male’s territory, only to be chased again and them (bullfi nch and oriole). We then measured again. We therefore classifi ed any interaction in January 2005] Hummingbird Territoriality 191 which a female was repeatedly chased by a male 52.416 cal g–1 h–1 and 31.2 cal g–1 h–1 as the costs of or returned to a male’s territory within a minute si ing and sleeping, respectively. We assume an or less of the previous intrusion as a “mating average temperature of 20°C, which falls within chase,” though Wolf and Hainsworth (1971) the range of night-time and daytime tempera- lumped such activities in their “chasing” cat- tures in the rainforest during our studies. egory. Hence, one source of error in our study In 2001 and 2002, we were able to obtain is that we may have erroneously classifi ed some weights for the territorial individuals studied multiple chases as mating behavior, when they by a racting them to a Heliconia infl orescence may in fact have been persistent intrusions a ached to the end of a dowel connected to by nonmating females; likewise, some single an electronic balance (Temeles et al. 2004), chases may have been mating, rather than feed- and we used those values in computations of ing, behavior. In addition, some of the time dur- energy budgets. We did not obtain weights for ing which birds were gone from their territories the males studied in 2000; we used an estimate involved instances in which birds were actively (10 g) based on the average weights of males seeking food or feeding at fl owers of trees in obtained in 2001 and 2002 for computations of the rainforest canopy (primarily Hibiscus elata). that year’s energy budgets. Although we could not observe the birds for the We assumed that all chasing, mate-chasing, entire time they were in the canopy, we none- and perch-shiV ing activities involved 100% theless observed them feeding at Hi. elata fl ow- forward fl ight; whereas all fl ycatching activi- ers on occasion, or inferred feeding visits if they ties involved 100% hovering fl ight. Calculations were observed wiping their bills aV er visits to of foraging costs were a bit more complicated, the canopy. We thus recorded such canopy vis- because birds’ movements included si ing to its as “canopy time” to diff erentiate them from feed, hovering at infl orescences, and fl ying “time gone,” and will address the signifi cance between infl orescences during foraging bouts. of canopy time below. To calculate foraging costs, we fi rst determined Energy budgets.—We used the time budgets the average amount of time a bird spent per to calculate energy budgets for the 7.5 h birds fl ower by dividing the number of fl owers the spent on territories (i.e. 0630 to 1400 hours) bird visited during each of its foraging bouts and for a 24-h day. Calculations of energy by the duration of each bout (in seconds) and budgets were based only on the proportions of then taking the average across all bouts for each time activities during which birds were under bird (n = 272 foraging bouts; n = 791 fl owers). observation (i.e. we excluded time gone and We also measured the average amount of time canopy time from those analyses). We con- a bird spent with its bill in each fl ower. Across verted time budgets to energy budgets using years, birds spent an average of 3 s per fl ower Wolf and Hainsworth’s (1971) measurements si ing with their bill in a fl ower, an additional of fl ying and resting metabolism of Purple- 1 s per fl ower si ing at the infl orescence, and an throated Caribs. On the basis of a measurement additional 3 s per fl ower hovering. The remain- –1 –1 of oxygen consumption of 43.4 mL O2 g h for ing time per fl ower was spent in forward fl ight 100% hovering fl ight, they estimated the cost of as the bird fl ew between fl owers. We therefore hovering fl ight for Purple-throated Caribs to assumed in our calculations of foraging costs be 208.32 cal g–1 h–1, assuming a caloric equiva- that a bird spent 4 s per fl ower si ing, 3 s per lent of oxygen of 4.8 cal mL–1 (RQ ≈ 0.8) and fl ower hovering, and the remainder of its aver- a temperature of 20°C. Wolf and Hainsworth age time per fl ower in forward fl ight, and used (1971) noted that the costs of forward fl ight are those proportions to calculate both total forag- likely less than the costs of hovering; accord- ing costs and foraging costs per fl ower. Lastly, ingly, we assumed that the cost of forward fl ight for calculations of 24-h energy budgets, we (177.07 cal g–1 h–1) was 85% that of hovering assumed that a bird had an 11-h day in which fl ight (Wolf et al. 1976). Hainsworth and Wolf to forage and spent the remainder of its time (1970) recorded a standard metabolic rate for (13 h) sleeping. –1 –1 Purple-throated Caribs of 6.5 mL O2 g h at Economics of defense.—Gill and Wolf (1975) 20°C and estimated their active metabolic rate presented two diff erent equations to examine while si ing to be 1.68× that value (Wolf and the relationship between time spent foraging Hainsworth 1971). We thus used values of and nectar volumes in their studies of sunbird 192 Tjrjqj, Gtqirs, si Kziq [Auk, Vol. 122 territory economics, one based on the observed transformed. Those analyses, as well as regres- 24-h daily energy budget of the birds and the sion analyses and t-tests, were performed using other based on a balance between calories MINITAB, release 12 (Minitab, State College, obtained and calories expended (see appendix I Pennsylvania). Below, we present means and in Gill and Wolf 1975). We used the la er equa- their corresponding standard errors (SE) for the tion, in which calories obtained are balanced by variables studied. calories expended, to examine the relationship between foraging time and energy costs and Rjzq nectar volumes for the three types of Heliconia morphs over the 7.5 h during which birds were Nectar production.—We observed no signifi - on territories. In that equation, caloric gains cant diff erences in nectar production over 24 h equal total costs expended: among Heliconia species and morphs (P = 0.70, n = 24 plants, one-way ANOVA). Over 24 h, H.

αTf = cfTf + csTs + C caribaea produced 98.3 ± 9.6 µL per fl ower, the red-green morph of H. bihai produced 90.3 ± where Tf is foraging time in hours, Ts is si ing 6.8 µL per fl ower, and the green morph of H. time in hours, cf is foraging costs per unit of bihai produced 92.5 ± 7.1 µL per fl ower. Nectar –1 time, cs is si ing costs per unit of time (524 cal h from fl owers of the green-bracted morph of H. and 419 cal h–1 for a 10-g male and an 8-g female, bihai (28.2 ± 2.7% sucrose weight:weight) was respectively, at 20°C), C is other costs (i.e. mis- signifi cantly more concentrated than nectar cellaneous costs, such as perch-shiV ing, which from fl owers of either the red-green-bracted are 125 cal for males and females), and α is calo- morph of H. bihai (25.6 ± 6.1% sucrose) or H. ries gained per hour of foraging. caribaea (25.1 ± 4.4% sucrose; P < 0.05, one-way In Gill and Wolf’s (1975) model, α was ANOVA with Tukey multiple comparisons). obtained by multiplying the number of microli- We observed no signifi cant diff erences in nec- ters of nectar (N) by the number of calories per tar volumes or nectar concentrations between microliter of nectar and the number of fl owers defended and undefended areas over 24 h (P > visited per hour, which is the number of seconds 0.50, two-way ANOVAs). per hour (3,600 s) divided by the number of sec- Rates of nectar production did not diff er onds of foraging per fl ower. We used values for signifi cantly among the three Heliconia morphs N of 1.09 cal µL–1 of nectar for H. caribaea and the (P > 0.20, n = 72 plants, two-way ANOVA), were red-green morph of H. bihai, and 1.24 cal µL–1 highest in the early morning, and progressively of nectar for the green morph of H. bihai. As we declined into early aV ernoon. At dawn (0600 will discuss in more detail below, the average hours), fl owers of the three Heliconia morphs number of seconds of foraging per fl ower dif- contained ~50 µL per fl ower (~50% of nectar fered among the three Heliconia morphs, and production over 24 h) and produced nectar thus we used values of 10.8 s, 15.0 s, and 23.87 s at the rate of 5–6 µL h–1 per fl ower. By 1000 per fl ower for H. caribaea, red-green H. bihai, and hours, rates of nectar production had declined green H. bihai, respectively. Those values corre- to 4 µL h–1 per fl ower; by 1400 hours, rates of –1 spond to foraging costs per hour (cf) of 1,397 cal nectar production had declined to 2 µL h per h–1, 1,497 cal h–1, and 1,601 cal h–1 for a 10-g male; fl ower (~2% of nectar production over 24 h). and 1,118 cal h–1, 1,198 cal h–1, and 1,281 cal h–1 Territory characteristics.—Territory areas and for an 8-g female. Heliconia fl ower densities defended by male Statistical analyses.—We used one- and two- Purple-throated Caribs ranged from 96 m2 and way analyses of variance and Tukey multiple 1.1 fl owers per square meter to 696 m2 and 0.07 comparisons to examine diff erences in terri- fl owers per square meter (Fig. 1). Areas of male tory areas, fl ower densities, percentage of time territories did not diff er signifi cantly between and energy costs of foraging and defense, years, but fl ower densities were signifi cantly 24-h energy costs, and 24-h energy produc- lower in the drought year of 2001 as compared tion among the three years of the study and with 2000, but not as compared with 2002 (Table among Heliconia morphs. For those analyses, 1; P < 0.006, two-way ANOVA and Tukey mul- year and Heliconia species were treated as tiple comparisons). Across years, H. caribaea fi xed eff ects, and all percentages were arcsine- territories defended by males were signifi cantly January 2005] Hummingbird Territoriality 193

smaller (128 ± 11 m2) and had higher densities of fl owers (0.68 ± 0.12 fl owers per square meter) than H. bihai territories (330 ± 97 m2 and 0.32 ± 0.10 fl owers per square meter; P < 0.03 for area comparison and P < 0.005 for fl ower density comparison; two-way ANOVAs and Tukey multiple comparisons; the single female was excluded from those analyses). The one female territory observed was larger (851 m2) and had lower densities of Heliconia fl owers (0.05 fl owers per square meter) than any of the male territo- ries (Fig. 1). Energy rewards on males’ territories also diff ered between years and between Heliconia Fig. 1. Relationship between flower density morphs (Table 1). Territories in the drought year (flowers per square meter, log-transformed) of 2001 provided ~55% as much energy (5.4 ± and areas of Purple-throated Carib territories 0.7 kcal per territory) as territories in 2000 (9.4 ± (square meters, log-transformed). The regres- 1.4 kcal per territory) and in 2002 (9.3 ± 0.9 kcal sion statistics for this relationship are: log ter- per territory, P < 0.03, Tukey multiple compari- ritory area = 1.98 – 0.71 log flower density; r2 = sons). Similarly, H. bihai territories defended 91%; P < 0.001. The slope of this regression dif- by males provided ~75% as much energy as H. fers significantly from a slope of –1, the slope caribaea territories (H. bihai: 6.9 ± 0.8 kcal per that would be predicted if birds were defending territory; H. caribaea: 9.1 ± 1.2 kcal per territory; a constant number of flowers across territories P = 0.06, Tukey multiple comparisons). The differing in area (t-test, t = 4.3, P < 0.001). Solid one female territory we studied provided less circles = male H. caribaea territories; open circles = energy (4.3 kcal) than all but one of the male male red-green H. bihai territories; triangle = territories. female green H. bihai territory. Time budgets.—Purple-throated Caribs spent most of their time on territories si ing, and si ing accounted for 83–92% of the total time budget when time gone from territories was

Tqj 1. Characteristics of Heliconia territories defended by Purple-throated Caribs in May and June of 2000, 2001, and 2002, on St. Lucia, West Indies. RG = red-green-bracted morph of H. bihai, G = green-bracted morph of H. bihai, HC = H. caribaea.

Flowers Kilocalories Area per per territory Year Sex Heliconia Bracts Flowers (m2) m2 per day 2000 Male 64% RG, 36% G 251 75 117 0.64 7.9 Male 71% RG, 29% G 201 60 196 0.31 6.2 Male 100% HC 254 112 120 0.93 12.0 Male 100% HC 353 106 96 1.10 11.4 2001 Male 69% RG, 31% G 437 49 696 0.07 5.1 Male 56% RG, 44% G 270 48 560 0.09 5.1 Male 91% HC, 9% G 494 68 132 0.52 7.3 Male 100% HC 333 37 105 0.35 4.0 Female 26% RG, 74% G 243 39 851 0.05 4.3 2002 Male 44% RG, 38% G, 18% HC 390 98 182 0.54 10.4 Male 78% RG, 22% G 250 67 231 0.29 7.0 Male 100% HC 459 101 144 0.70 10.8 Male 63% HC, 37% G 370 82 170 0.48 9.0 194 Tjrjqj, Gtqirs, si Kziq [Auk, Vol. 122 excluded (Table 2). Males spent 6.4–13.1% of their observed time foraging at Heliconia fl ow- ers, but we observed no diff erences in the percentage of time spent foraging by territorial males among the three years of our study or ach species between the species of Heliconia defended (P > e. All birds were All birds were e. 0.295 0.090 0.20; two-way ANOVA). The one territorial 0.049 0.022 0.142 female we observed spent a greater percent- age of time foraging (15.6%) than any of the males (Table 2). Males spent 0.6–5.5% of their time in aggressive defense of their territories s gone gone (Table 2), and signifi cantly more time defend- ing their territories in 2000 than in either 2001 or 2002 (P < 0.009, two-way ANOVA with Tukey multiple comparisons). The percentage of time males spent in territorial defense did not dif- fer between the species of Heliconia defended (P > 0.30, two-way ANOVA). The one territorial

female observed spent a smaller percentage of M = male, F territories in the rainforest canopy. its time budget in defense (0.3%) than any of the males. Although the percentage of time that males spent foraging on their territories did not diff er among years or between the species of Heliconia they defended, the percentage of time males spent “gone” in the canopy diff ered signifi cantly Proportion of time spent among years and between Heliconia species. Males spent a signifi cantly greater percentage of the time in the rainforest canopy in 2001 (11.1 ± 3.3%) as compared with 2000 (2.3 ± 0.9%) but not as compared with 2002 (5.6 ± 2.2%, P < 0.003; two-way ANOVA with Tukey multiple compari- sons). Across years, males on H. bihai territories spent signifi cantly more time in the canopy than males on H. caribaea territories (H. bihai: 9.4 ± 2.7%; H. caribaea: 3.2 ± 1.2%; P < 0.003; two-way ANOVA with Tukey multiple comparisons). The percentage of time males spent in the canopy was signifi cantly inversely correlated with the ). “Canopy gone” refers to time that the birds spent off

energy reward from their territories, which sug- ing Foraging catching Chasing chases shiV gests that males may have been compensating for low energy availability on their territories by H. bihai foraging in the canopy (Fig. 2). The one female we observed likewise spent all of its “time gone” or F 0.709 (0.827) 0.134 (0.156) 0.009 (0.010) 0.002 (0.003) 0.000 (0.000) 0.004 (0.004) M 0.735 (0.860) 0.085 (0.099) 0.003 (0.004) 0.020 (0.024) 0.007 (0.008) 0.004 (0.005) 0.146 0.037 M 0.725 (0.832) 0.089 (0.102) 0.002 (0.002) 0.035 (0.041) 0.018 (0.019) 0.004 (0.004) 0.127 0.008 M 0.705 (0.907) 0.055 (0.072) 0.002 (0.002) 0.006 (0.008) 0.004 (0.005) 0.004 (0.006) 0.224 0.155 M 0.761 (0.900) 0.071 (0.084) 0.001 (0.001) 0.008 (0.009) 0.001 (0.002) 0.004 (0.004) 0.154 0.067 M 0.603 (0.854) 0.081 (0.114) 0.002 (0.003) 0.014 (0.021) 0.002 (0.003) 0.003 (0.005) M 0.852 (0.894) 0.066 (0.070) 0.009 (0.010) 0.009 (0.010) 0.011 (0.012) 0.004 (0.004) in the canopy (Table 2). Sex Si Males spent between 0.1% and 1% of their time foraging for insects, primarily by fl ycatching H. caribaea

(Table 2). The single female we observed spent ( Heliconia bihai caribaea bihai caribaea bihai caribaea 1% of its time foraging for insects, also by fl y- bihai catching. We observed no signifi cant relationship

between percentage of time birds spent feeding Heliconia female. on insects and energy reward from their territo- males at e for the two been averaged time budgets have years, Within AST. 0700 to 1300 hours for 300 min (5 h) between observed of

Fly- Mating Perch Total Canopy Total Perch Mating Fly- Year Tqj 2. Time budgets of territorial Purple-throated Caribs. Values in parentheses are proportions of total time minus gon 2. Time budgets of territorial Purple-throated Caribs. Values Tqj 2000

2001

2002 ries (r = 0.16, P > 0.60, Pearson correlation). 2002 January 2005] Hummingbird Territoriality 195 ). M = expended H. bihai ” and “Canopy or H. caribaea ( s Sleeping 7.5 h 24 h Heliconia Fnl. 2. Relationship between “time gone” (i.e. time spent in the rainforest canopy [percentage of time budget in Table 2]) and energy reward (kilocalories) from territories of 12 male Purple- throated Caribs (r = –0.67, P = 0.017; percentage data arcsine transformed). Solid circles = male H. caribaea territories; open circles = male red- green H. bihai territories.

Energy budgets.—Across the three years of our study, 24-h energy expenditures of male Purple- throated Caribs averaged 11.20 ± 0.15 kcal (Table 3). The 24-h energy expenditure of the ter- ritorial female was 9.5 kcal. The four territorial males studied in 2001 expended signifi cantly less energy over 24 h (10.70 ± 0.30 kcal) than the four males studied in 2000 (11.5 ± 0.08 kcal) and 2002 (11.5 ± 0.05 kcal, P < 0.03, two-way ANOVA with Tukey multiple comparisons). The lower 24-h energy expenditures of males in 2001 were a consequence of less time invested in territorial defense and, to a lesser extent, in feeding on their territories; however, as noted above, much of the time those males spent off their territories involved feeding in the forest canopy, so their realized 24-h energy expenditures were likely greater than those reported in Table 3. Costs for only the time males spent on territories (0630 to ing Foraging catching Chasing chases shiV 1400 hours) averaged 4.89 ± 0.09 kcal (Table 3). Again, the 7.5-h daytime cost for the territorial female (4.3 kcal) was less than the 7.5-h daytime costs for males, and males in 2001 expended less F 0.605 (0.399) 0.348 (0.230) 0.029 (0.019) 0.007 (0.005) 0.000 (0.000) 0.010 (0.007) (0.340) 4,299 (9,549) energy during those daytime hours than males in M M 0.678 (0.435) M 0.632 (0.412) 0.211 (0.136) M 0.763 (0.479) 0.197 (0.128) M 0.013 (0.008) 0.768 (0.480) 0.177 (0.111) M 0.004 (0.003) 0.662 (0.428) 0.065 (0.042) 0.185 (0.116) 0.007 (0.004) 0.735 (0.466) 0.107 (0.070) 0.254 (0.165) 0.021 (0.014) 0.005 (0.003) 0.023 (0.014) 0.160 (0.102) 0.049 (0.031) 0.009 (0.006) 0.012 (0.008) 0.026 (0.016) 0.015 (0.010) 0.034 (0.022) 0.011 (0.007) 0.054 (0.035) (0.357) 0.006 (0.004) 0.015 (0.010) 0.026 (0.017) (0.349) 0.008 (0.005) 4,990 (11,374) 0.010 (0.006) (0.372) 0.032 (0.020) 5,174 (11,643) 0.013 (0.008) (0.375) 4,707 (10,980) 0.013 (0.008) (0.353) 4,433 (10,401) (0.365) 5,103 (11,561) 4,953 (11,462) 2000 and 2002 (Table 3). Sex Si Foraging costs of males ranged from 9.6% to 18.9% of the 24-h budget and from 15.2% to 29.1% caribaea bihai caribaea bihai caribaea bihai bihai of the 7.5-h daytime energy budget, and did not Heliconia diff er signifi cantly among years or between male, F = female. the species of Heliconia defended (Table 3, males at each species of for the two been averaged energy budgets have years, 2). Within gone” (see Table Fly- Perch Mate Proportion of calories spent calories Total Year Year 2001 2002 2001 Tqj 3. The 7.5-h daytime and 24-h (in parentheses) energy budgets of territorial Purple-throated Caribs, excluding “Time gone Tqj 2000 196 Tjrjqj, Gtqirs, si Kziq [Auk, Vol. 122

P > 0.15, two-way ANOVA). By contrast, the P < 0.0002; t-test with log + 1 transformation; n = foraging cost of the territorial female was 23% 29 plants; samples from the diff erent Heliconia of its 24-h energy budget and 34.8% of its 7.5-h species and morphs were pooled because of daytime budget. Defense costs of males com- the lack of signifi cant diff erences in their 24-h prised 1.1–9.2% of their 24-h energy budget and and hourly nectar production). By 0900 hours, 1.6–14.2% of their 7.5-h budget, and were signifi - standing crops of nectar in defended fl owers cantly lower for males in 2001 than in 2000 (P < had declined to only 18.7 ± 4.2 µL per fl ower 0.05, Tukey multiple comparisons; Table 3). As (n = 14 plants) but were still signifi cantly greater compared with males, the one territorial female than standing crops of nectar in undefended spent a lower percentage of its 24-h energy bud- fl owers (6.3 ± 3.1 µL per fl ower, n = 9 plants, get in territorial defense (0.5% over 24 h and P < 0.0075, t-test with log + 1 transformation). 0.7% of the 7.5-h budget; Table 3). By late morning and early aV ernoon (1100–1400 Costs per fl ower.—The morph or species of hours), defended areas had nearly 10× as much Heliconia defended had a pronounced eff ect on nectar per fl ower (19.3 ± 5.4, n = 18 plants) as the time and energy costs per fl ower of territo- undefended areas (2.1 ± 0.8, n = 23 plants; P < rial birds (Fig. 3). Across the three years of the 0.0001, t-test with log + 1 transformation). study, males’ time and energy costs per fl ower Economics of defense.—The presumed benefi t were signifi cantly less at H. caribaea (time costs: of an accumulation of nectar in fl owers on a 10.8 ± 0.9 s per fl ower; energy costs: 4.2 ± 0.5 cal territory is that it greatly reduces the amount per fl ower) than at the red-green morph of H. of time a territorial bird must forage to meet its bihai (time costs: 15.0 ± 1.2 s per fl ower; energy energy requirements, as compared with birds costs: 6.3 ± 0.6 cal per fl ower; P < 0.005, two-way foraging on undefended sites. We examined ANOVAs and Tukey multiple comparisons). the hypothetical relationship between territorial Time and energy costs per fl ower for the ter- males’ time and energy costs and nectar avail- ritorial female at green H. bihai (time cost: 23.9 s ability using Gill and Wolf’s equation where per fl ower; energy cost: 8.5 cal per fl ower) were calories expended are balanced by calories considerably higher than time and energy costs obtained (see above and Gill and Wolf 1975). per fl ower of any of the males. To a great extent, For both H. caribaea and the red-green diff erences in time and energy costs per fl ower morph of H. bihai, foraging time and energy among the three Heliconia morphs were a func- costs increase rapidly at low nectar volumes; tion of territory area and fl ower density (Fig. whereas at high nectar volumes, foraging 3). Because territories of H. caribaea had signifi - time and energy costs show li le change with cantly higher fl ower densities than territories of changes in volume (Fig. 4). Estimated forag- either morph of H. bihai, territories were conse- ing times at high nectar volumes may slightly quently smaller. As a result, foraging time and underestimate real foraging times if the average energy costs per fl ower were reduced because licking time per fl ower increases at high nectar distances between fl owers were less. volumes. Nectar availability.—Gill and Wolf (1975) The energy savings derived from territorial hypothesized that the benefi t of territorial defense of patches of H. caribaea or the red- defense for a nectar-feeding bird is an accumu- green H. bihai are considerable for the observed lation of standing crops of nectar in defended standing crops of nectar per fl ower on defended fl owers resulting from exclusion of intruders. and undefended areas and easily support an Accordingly, we examined whether standing investment in defense of 5% of the 7.5-h energy crops of nectar were greater on defended patches budget (Table 4). Benefi ts from defense lessen of Heliconia than on undefended patches of at high nectar volumes (>30 µL), though such Heliconia. At all time intervals surveyed, stand- nectar volumes are probably not realized on ing crops of nectar were signifi cantly greater undefended areas, except immediately follow- on defended territories than on undefended ing dawn. patches. In the early morning (0800 hours), When the time and energy costs of foraging defended areas contained ~4× as much nectar at patches of H. caribaea and red-green H. bihai per fl ower as undefended areas (39.4 ± 8.8 µL are compared, it is clear that territorial males per fl ower on defended areas, as compared with would derive a distinct time and energy cost 10.8 ± 2.3 µL per fl ower on undefended areas; benefi t from defense of H. caribaea as compared January 2005] Hummingbird Territoriality 197

Fnl. 3. Relationships between seconds of foraging time per flower and energy expended per flower (in calories) and territory area or flower density. Solid circles = male H. caribaea territories; open circles = male red-green H. bihai territories; triangle = female green H. bihai territory. Excluding the one female, the regression statistics for these relationships are: (A) seconds per flower = 9.7 + 0.014 territory area, r2 = 68%, P = 0.001; (B) calories expended per flower = 3.65 + 0.007 territory area, r2 = 64%, P = 0.002; (C) seconds per flower = 16.7 – 7.45 flowers per square meter, r2 = 49%, P = 0.011; (D) calories expended per flower = 7.1 – 3.7 flowers per square meter, r2 = 47%, P = 0.014. with defense of the red-green morph of H. bihai 1,100 cal, as compared with males defending (Fig. 4). Across a range of observed standing the red-green morph of H. bihai. Those savings crops of nectar per fl ower (10–40 µL), males in time and energy result from higher densities defending H. caribaea would spend 0.3–1.5 h less of H. caribaea than of the red-green morph of H. in foraging and would save approximately 150– bihai, which resulted in smaller territory areas of 198 Tjrjqj, Gtqirs, si Kziq [Auk, Vol. 122

Fnl. 4. Relationships between (A) foraging time budgets and (B) associated total cost budgets and nectar availability for territorial male Purple-throated Caribs at flowers of H. caribaea (solid circles) and the red-green morph of H. bihai (open circles). Foraging times are presented as percentages of 7.5 h during which birds were on territories during daytime (0630–1400 hours) and were computed using the equation for balanced costs and benefits from Gill and Wolf (1975) (see text). For these calculations, a 10-g male was assumed to spend 10.8 s per flower at H. caribaea and 15 s per flower at red-green H. bihai. Arrow indicates that calculated foraging time exceeds the time available.

Tqj 4. Energetic benefi ts (in calories) of territorial defense resulting from decreases in foraging time caused by accumulation of standing crops of nectar on territories (Fig. 4). Gross savings refl ect energy saved for given diff erences between standing crops on defended and undefended areas. Defense levels refl ect energetic costs of defense possible by gross savings as percentages of the 7.5-h time budget. Negative values refl ect costs in excess of benefi ts. Cost of defense is 133 cal for 1% of the 7.5-h daytime budget for a 10-g male.

Standing crop (µL) Net defense level Heliconia Undefended Defended Gross savings 1% 2% 3% 4% 5% caribaea 30 40 94 –39 –172 –305 –438 –571 20 30 201 68 –65 –198 –331 –464 20 40 295 162 29 –104 –237 –370 15 20 220 87 –46 –179 –312 –445 10 20 730 597 464 331 198 65 10 15 510 377 244 111 –22 –155 5 15 2,984 2,851 2,718 2,585 2,452 2,319 bihai (red-green) 30 40 158 25 –108 –241 –374 –507 20 30 352 219 86 –47 –180 –313 20 40 510 377 244 111 –22 –155 15 20 410 277 144 11 –122 –255 10 20 1,471 1,338 1,205 1,072 939 806 10 15 1,061 928 795 662 529 396 5 15 10,376 10,241 10,108 9,975 9,842 9,709 January 2005] Hummingbird Territoriality 199 males defending H. caribaea and, hence, shorter territories was economical, with energy gains traveling times between fl owers (Figs. 1 and exceeding metabolic costs (Tables 1 and 3). 3). At extremely low nectar volumes (2.5 µL Similar temporal variation in defense and per fl ower for H. caribaea and 2.5–5.0 µL per maintenance of territories has been observed fl ower for red-green H. bihai), foraging time and for other species of nectar-feeding birds (e.g. energy costs greatly exceeded available time Gill and Wolf 1975, Co on 1994). If costs are and energy, which suggests that use of only extrapolated to 24 h, however, only 2 of 13 these fl oral resources by males is uneconomical Heliconia territories met or exceeded estimated at extremely low nectar volumes (Fig. 4). 24-h energy expenditures of the birds. Wolf and Sexual dimorphism.—In comparison to H. Hainsworth (1971) studied the territorial behav- caribaea and the red-green morph of H. bihai, ior of Purple-throated Caribs on Dominica and the green morph of H. bihai fl owers at much noted that densities of H. caribaea fl owers were lower densities (see Table 1), which increases usually insuffi cient to provide territory sites. travel time between fl owers and, hence, forag- Our observations are consistent with theirs, ing time and energy costs per fl ower (Fig. 3). As but we caution that our study was conducted a result, the hypothetical relationship between during periods when Heliconia fl owering was nectar volumes and foraging time and energy past its peak, with only ~20% of bracts bearing costs over 7.5 h is shiV ed to the right (Fig. 5), fl owers. At times of peak fl owering, with ≥50% which means that at any given nectar volume, of bracts bearing fl owers, all Heliconia territo- the time and energy costs of foraging would ries defended by males would meet their 24-h be higher for the green morph of H. bihai than energy demands of 11.2 kcal. Moreover, at peak for the red-green morph or H. caribaea. For both fl owering, males’ 24-h energy demands would males and females, foraging time and energy likely be less than the 11. 2 kcal reported here if costs at volumes per fl ower of ≤5 µL would territory sizes became smaller because of higher exceed the time available, which suggests fl ower densities; that would reduce foraging that foraging solely at the green morph of H. costs per fl ower, assuming that defense costs bihai at those nectar volumes is uneconomical. did not increase dramatically as a result of Across the range of observed standing crops of increased intruder pressure at higher fl ower nectar per fl ower (10–40 µL), a female Purple- densities. throated Carib would spend ~0.6 h less time and Many of the birds we studied supplemented ~1.7 kcal less energy in foraging than a male their nectar intake from Heliconia fl owers by (Fig. 5). Females’ time and energy savings foraging at fl owers in the rainforest canopy, would be much reduced, as compared with and time spent in the canopy was inversely males’, over the same range of nectar volumes correlated with nectar production on Heliconia per fl ower at the red-green morph of H. bihai territories (Fig. 2). Trombulak (1990) also noted (0.3 h less foraging time, at 1.2 kcal less), and an inverse relationship between amount of even more reduced at H. caribaea (0.1 h less time that Blue-vented Hummingbirds (Amazilia foraging time, at 1.0 kcal less; Fig. 5). Expressed saucero ei) were absent from territories of another way, the time and energy savings males Combretum farinosum and the energetic value gain by foraging on H. caribaea or the red-green of territories, which suggests that much of the morph of H. bihai (~50% time savings and ~15% “time gone” is actually time spent foraging. energy savings) rather than the green morph Hence, foraging time and energy costs of nec- of H. bihai, at volumes per fl ower of 10–40 tar-feeding birds are likely higher than reported µL, would be much greater than the time and if time gone is actually time spent foraging, energy savings realized by females (~40% time but such additional costs may be balanced by savings and ~10% energy savings). energy gained from foraging off territories. A negative consequence of leaving the territory to Dnznts forage elsewhere is that the territory’s resources become available to intruders, but our observa- Economics of defense.—With the exception of tions suggest that territorial Purple-throated one male, territorial defense by Purple-throated Caribs may incur li le nectar loss to intruders Caribs over the period of the day (0630 to 1400 by leaving their territories to forage in the hours) during which they maintained Heliconia canopy. On many territories, especially during 200 Tjrjqj, Gtqirs, si Kziq [Auk, Vol. 122

Fnl. 5. Comparisons of foraging time and energy cost budgets for male (circles) and female (tri- angles) Purple-throated Caribs at flowers of green H. bihai (A and B), red-green H. bihai (C and D), and H. caribaea (E and F). Foraging times are presented as percentages of 7.5 h during which birds were on territories during daytime (0630–1400 hours) and were computed as in Fig. 4. For these calculations, females were assumed to weigh 8 g, and both males and females were assumed to spend 23.87 s per flower at green H. bihai, 15 s per flower at red-green H. bihai, and 10.8 s per flower at H. caribaea. Arrow indicates that calculated foraging time exceeds the time available. Foraging time and energy cost budgets for males and females at fl owers of green H. bihai at nectar volumes of 5 µL greatly exceeded time available and are not illustrated in graphs (A) and (B). January 2005] Hummingbird Territoriality 201 the drought year of 2001, rates of intrusion were proportions of time spent foraging by territorial low (<1 h–1). In addition, all territorial birds leV birds were much higher on territories of Inga their territories to forage in the canopy aV er spp., Hi. elata, or species of Myrtaceae than on bouts of feeding on Heliconia plants. Ewald and territories of H. caribaea or M. sapientum, because Orians (1983) observed similar behavior in birds feeding on the fl owers of the former species defending artifi cial, depressible food sources. required more fl ying. Assuming that these territorial birds drained On the basis of per-fl ower time and energy all the nectar from Heliconia fl owers during costs of foraging, our results suggest that Purple- foraging bouts, nectar losses to intruders would throated Caribs should perceive H. caribaea as a be low during brief (5-min) absences from ter- more-rewarding food source than either morph ritories. Whether territorial birds fed at fl owers of H. bihai. In support of that hypothesis, intru- prior to departure to deliberately reduce losses sion pressure was higher on H. caribaea than on to intruders (Ewald and Orians 1983) or leV ter- H. bihai territories in all three years of our study. ritories because nectar obtained from the feeding Time and energy costs of defense, however, bout did not meet their energy needs, or both, did not diff er signifi cantly among the Heliconia requires additional study, though the inverse species and morphs; the time and energy costs relationship we observed between time in the associated with increased intrusion pressure canopy and energy reward from the territory is on H. caribaea territories may have been off set more consistent with the la er explanation. by the time and energy costs associated with Lastly, all the territorial Purple-throated defense of larger H. bihai territories. Our mea- Caribs we studied foraged for insects, and our surements of foraging times per fl ower did not observations suggest that birds were opportu- control for variation in nectar concentration and nistic when foraging for insects. Nonetheless, volume between fl owers, however, and more insects may supplement nectar intake from precise measurements of birds’ foraging times territories (Chavez-Ramirez and Dowd 1992, at fl owers of the three Heliconia morphs are Chavez-Ramirez and Tan 1993) and may enable needed to accurately assess their preferences. birds to maintain defense of a site even when Resource partitioning and sexual dimorphism.— nectar rewards from the site are low. The critical factor for partitioning of the three Heliconia use.—In all three years of our study, Heliconia morphs between sexes of Purple- territories of H. caribaea were smaller and had throated Caribs seems to be the numbers of higher densities of fl owers than territories of bracts and fl owers per infl orescence, which either morph of H. bihai (Fig. 1 and Table 1). The result in diff erences in fl ower densities and, higher densities of fl owers decreased territory hence, time and energy costs per fl ower (Table owners’ travel times between fl owers and infl o- 1 and Fig. 3). Although we were able to fi nd rescences of H. caribaea as compared with either only one female on a territory during the three morph of H. bihai (Fig. 3), and theoretically years of our study, its territory was larger and would decrease the foraging time needed per had a lower density of fl owers than any of the day for territory owners to meet their energy territories defended by males and was the only demands (Figs. 4 and 5). Although we observed territory to consist primarily of fl owers of the no signifi cant diff erences in percentages of green-bracted H. bihai. During the study, most time males spent foraging on either H. caribaea females either foraged on Hi. elata fl owers in or red-green H. bihai territories, that result is the forest canopy or trapline-foraged at unde- misleading, because males on H. bihai territories fended patches of H. caribaea and H. bihai. Those spent a greater percentage of their time in the undefended patches averaged 3.5 ± 0.8 plants canopy than males on H. caribaea territories (Fig. with 4.7 ± 0.9 infl orescences and 5.6 ± 1.4 fl owers 2 and Table 2). Hence, realized foraging time (n = 18 patches). In a previous study (Temeles et and energy costs are likely greater for males on al. 2000), we observed females, but not males, red-green H. bihai territories than on H. caribaea defending patches of the green-bracted H. bihai. territories, once time and energy spent foraging We have also observed females on H. carib- in the canopy are taken into consideration. Our aea and red-green H. bihai territories for brief interpretation receives some support from Wolf periods in early March; neither species was at and Hainsworth’s (1971) study of territorial peak fl owering, and females were subsequently Purple-throated Caribs on Dominica. There, displaced by males, which then defended and 202 Tjrjqj, Gtqirs, si Kziq [Auk, Vol. 122 maintained the sites from April through June. in the use of these Heliconia morphs may be even In 2003, we observed no birds on Heliconia ter- greater if each sex feeds most quickly at the ritories during late May and June. Densities of Heliconia species that matches its bill (Temeles et fl owers on Heliconia patches that had been terri- al. 2000), though diff erences resulting from feed- tories in previous years ranged from 0.00 to 0.03 ing with the bill in the fl ower (approximately 1–2 fl owers per square meter, below the densities of s) will have a lower eff ect on feeding time per fl owers on territories in previous years reported fl ower than diff erences in fl ower densities and here (Table 1). The low densities of fl owers on corresponding travel times between fl owers of Heliconia patches during 2003 suggest that such the three Heliconia morphs. sites could not be defended economically by Social dominance is common in humming- either males or females, though birds did tra- birds and has been off ered as a causal factor pline-forage at those sites. for the evolution of sexual dimorphism in bill As shown here, the time and energy sav- length observed in many species (Bleiweiss ings that females would theoretically gain by 1999). Under that scenario, dominant males switching from foraging on the green morph claim access to nectar-rich patches of short of H. bihai to foraging on either the red-green fl owers, whereas subordinate females are morph of H. bihai or at H. caribaea are less than relegated to nectar-poor, sca ered patches of the time and energy savings accruing to males fl owers. A longer bill would give an advantage (Fig. 5). Game-theoretic analyses of animal con- to females by allowing them to use a broader tests suggest that an individual’s investment in range of fl ower lengths than males (Temeles aggression depends on asymmetries between and Roberts 1993, Temeles 1996). The pres- itself and its opponent in the value of winning ent study and our previous ones (Temeles et (Parker 1974, Maynard Smith and Parker 1976, al. 2000, Temeles and Kress 2003) argue for Parker and Rubenstein 1981). The asymmetry that explanation: on both Dominica and St. in relative gains for males and females from Lucia, fl oral morphology and energy reward foraging on each of the three Heliconia morphs of Heliconia species and morphs correspond to off ers an explanation of resource partitioning bill morphology, body size, and energy needs between them in addition to size-related diff er- of male and female Purple-throated Caribs. ences in fi ghting abilities. Because males stand Whether social dominance similarly aff ects the to gain more than females from foraging on H. evolution of sexual dimorphisms in other hum- caribaea and the red-green morph of H. bihai as mingbird species requires further research, but opposed to the green-bracted morph of H. bihai, studies of Rufous Hummingbirds (Selasphorus they may be more motivated than females to rufus) suggest that it may (Kodric-Brown and contest the former resources more than the la er. Brown 1978; Carpenter et al. 1991, 1993a, b). By contrast, females trapline-forage at the green- In that species, however, subordinate females bracted morph of H. bihai by default, though are larger than males and compensate for their they may occasionally, as shown here, defend use of poorer patches of fl owers through lower territories of the green-bracted morph of H. bihai wing-disc-loading and cheaper costs of fl ight when fl ower densities are high enough to permit (Carpenter et al. 1991, 1993a, b). 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