Energetic Consequences for a Northern, Range-Edge Lizard Population

Lizards at the northern, cool edge of their geographic range in the northern hemisphere should encounter environmental conditions that differ from those living near the core of their range. To better understand how modest climate differences affect lizard energetics, we compared daily feeding and metabolism rates of individual Sceloporus occidentalis in two populations during mid-summer. Chuckanut Beach (CB) was a cool, maritime climate in northern Washington State, and Sondino Ranch (SR) was a warmer, drier climate in southern, inland Washington. We found no difference between populations in daily energy expenditure (DEE), as calculated from doubly labeled water estimates. The CB population, however, had significantly higher prey availability and rate of daily energy intake (DEI) as estimated from fecal pellet masses. Consequently, CB lizards had higher size-adjusted body masses than lizards from SR. Within CB, during midsummer, DEE was similar to DEI. Within the SR population, DEE trended higher than DEI during midsummer, but was not significantly different. We found no population differences in lizard activity, active body temperature, or preferred body temperature. Hence, we infer the longer activity season for the SR population may compensate for the low food availability and high daily energy cost of midsummer. Moreover, for the CB population, we infer that cooler temperatures and higher food availability allow the lizards to compensate for the shorter activity. We also suggest the CB population may benefit from the predicted warmer temperatures associated with climate change given the similar activity-period body temperatures and DEE between these lizard populations assuming food availability is sufficient

The Impact of Social Interactions on Torpor Use in Hummingbirds

Measurements of metabolic rate and fat deposition were made on a three-species hummingbird guild in southeastern Arizona to determine if the energetic advantage gained by a dominant territorial species (Lampornis clemenciae) over subordinate competitors (Archilochus alexandri and Eugenes fulgens) resulted in less frequent use of torpor. Results showed that L. clemenciae was able to store enough fat during the day to avoid nocturnal torpor. Restricted access to food limited fat storage in both competitors, resulting in frequent torpor use. Avoidance of torpor by L. clemenciae supports the notion that use of nocturnal torpor by hummingbirds comes with a cost, and that the ability to avoid torpor is an important benefit to dominant species

Effect of Temperature and Humidity on Evaporative Water Loss in Anna\u27s Hummingbird (Calypte anna)

Evaporative water loss (EWL), oxygen concumption (V0 ), and body temperature (Tb) of Anna\u27s 2 Hummingbirds (Calypte anna; ca. 4.5 g) were measured at combinations of ambient temperature (T J and water vapor density (Qva) ranging from 20 to 37 °C and 2 to 27 g · m-3 , respectively. The EWL decreased linearly with increasing eva at all temperatures. The slopes ofleast squares regression lines relating EWL to Qva at different temperatures were not significantly different and averaged -0.50mg H20·m-3 ·g-2 ·h-1 (range: -0.39 to -0.61). Increased Qva restricted EWL in C. anna more than has been reported for other endotherms in dry air. The percent of metabolic heat production dissipated by evaporation (HJHm) was lower than that of other birds in dry air, but higher than that for other birds at high humidity when T.\u3c33 °C. When T.\u3e33 °C the effect of humidity on H0/Hm was similar to that in other birds. Calypte anna might become slightly hyperthermic at T.\u3e 37 °C, which could augment heat transfer by increasing the Tb-Ta gradient. Body temperature for C. anna in this study was 43 °C (intramuscular) at T.s between 25 and 35 °C, which is above average for birds. It is estimated that field EWL is less than 30% of daily water loss in C. anna under mild temperature conditions ( \u3c 35 °C)

Effects of Variation in Food Quality on the Breeding Territoriality of the Male Anna\u27s Hummindbird

Thirteen territorial male Anna’s Hummingbirds, Calypte anna, were observed during the 1981 and 1982 breeding seasons. Breeding territories were large, but size was not determined by energy availability. When a food source (sucrose solution in feeders) was present, the degree to which it was defended was a function of food quality. If a high-quality food source was absent, males did not exhibit the behaviors associated with defending a food source, but breeding territoriality remained intact. Territories were maintained for the entire breeding season even when food quality was varied. The lack of a relationship between the number of chases involving females and dive displays with variations in food quality, along with observations of long territory tenure, suggest that the primary function of the territory is reproductive and that an internal food sourcei s not necessaryfo r its maintenance

Diurnal Variation in Mass, Metabolic Rate, and Respiratory Quotient in Anna\u27s and Costa\u27s Hummingbirds

To examine how hummingbirds that do not enter torpor at night store and utilize energy, open-circuit respirometry and a strain gauge were used to measure daily variation in 0 2 consumption (Vo2 ), C02 production, respiratory quotient (RQ), and body mass in Anna\u27s hummingbird, Calypte anna, and Costa\u27s hummingbird, Calypte costae. During the day, Vo2 was highly variable primarily because of dif ferences in activity among individuals. At night Vo2 varied little between individuals, but mean Vo2 was more than two times that predicted from body mass for resting, postabsorptive birds. F0.85), indicating the use of carbohydrate as a metabolic substrate. Predicted crop volumes of the hummingbirds are sufficient to store the amount of feeder solution (0.25 g sucrose per ml) required to account/or the observed nighttime RQs. This suggests that hummingbirds in this study were using their crop as a supplemental energy storage depot at night

Rivoli\u27s Hummingbird: Eugenes fulgens

Rivoli\u27s Hummingbird was named in honor of the Duke of Rivoli when the species was described by René Lesson in 1829. Even when it became known that William Swainson had written an earlier description of this species in 1827, the common name Rivoli\u27s Hummingbird remained until the early 1980s, when it was changed to Magnificent Hummingbird. In 2017, however, the name was restored to Rivoli\u27s Hummingbird when the American Ornithological Society officially recognized Eugenes fulgens as a distinct species from E. spectabilis, the Talamanca Hummingbird, of the highlands of Costa Rica and western Panama. Rivoli\u27s Hummingbird is found from the southwestern United States to northern Nicaragua, and is the second-largest hummingbird species in the United States. It exhibits sexual dimorphism, primarily in coloration, body mass, and bill length. The species typically occurs at middle to high elevations throughout much of Mexico and Central America. Birds migrate north in early spring to breed, some of them reaching forested mountains at the northern limit of the breeding range in Arizona and New Mexico. Throughout its range, Rivoli\u27s Hummingbird occurs in a variety of habitats, but it is most frequently found in dry pine–oak (Pinus–Quercus) forests. Breeding is often associated with cool canyons and drainages in the mountain ranges of southern Arizona and New Mexico, where nests are often constructed high up in trees that overhang streams. Despite the extensive range and abundance of the Rivoli\u27s Hummingbird, its basic life history is largely unknown, with most information coming from studies in central and southern Mexico. The transient nature of males and the secretive habits of females have made research in the U.S. difficult, although it appears that northern males may forage more by traplining (see Behavior: Agonistic Behavior) than by being territorial and aggressive. Additional information is needed on migration and movement ecology, breeding biology (courtship, nest construction, number of broods, nestling development, parental care), breeding success, feeding behavior (dietary importance of insects; role of bill dimorphism in feeding efficiency), and the function of vocalizations

Take-off mechanics in hummingbirds (Trochilidae)

Initiating flight is challenging, and considerable effort has focused on understanding the energetics and aerodynamics of take-off for both machines and animals. For animal flight, the available evidence suggests that birds maximize their initial flight velocity using leg thrust rather than wing flapping. The smallest birds, hummingbirds (Order Apodiformes), are unique in their ability to perform sustained hovering but have proportionally small hindlimbs that could hinder generation of high leg thrust. Understanding the take-off flight of hummingbirds can provide novel insight into the take-off mechanics that will be required for micro-air vehicles. During take-off by hummingbirds, we measured hindlimb forces on a perch mounted with strain gauges and filmed wingbeat kinematics with high-speed video. Whereas other birds obtain 80–90% of their initial flight velocity using leg thrust, the leg contribution in hummingbirds was 59% during autonomous take-off. Unlike other species, hummingbirds beat their wings several times as they thrust using their hindlimbs. In a phylogenetic context, our results show that reduced body and hindlimb size in hummingbirds limits their peak acceleration during leg thrust and, ultimately, their take-off velocity. Previously, the influence of motivational state on take-off flight performance has not been investigated for any one organism. We studied the full range of motivational states by testing performance as the birds took off: (1) to initiate flight autonomously, (2) to escape a startling stimulus or (3) to aggressively chase a conspecific away from a feeder. Motivation affected performance. Escape and aggressive take-off featured decreased hindlimb contribution (46% and 47%, respectively) and increased flight velocity. When escaping, hummingbirds foreshortened their body movement prior to onset of leg thrust and began beating their wings earlier and at higher frequency. Thus, hummingbirds are capable of modulating their leg and wingbeat kinetics to increase take-off velocity

The Effect of Food Availability on Time and Energy Expenditures of Territorial and Non-Territorial Hummingbirds

We studied the time and energy allocations related to territorial behavior in male Blue-throated Hummingbirds (Lampornis clemenciae; about 8.3 g) under conditions of unlimited and restricted food availability. When food was unlimited. territorial males avoided inter-specific aggression, chasing only 11% of the inter-specific intruders (Black-chinned Hummingbirds, Archilochus alexandri; about 3.5 g). Thus, when food was unlimited, inter-specific intruders were able to forage efficiently, meeting their estimated daily energy requirement with ease (27 kJ/day). Conversely, 81% of intraspecific intruders were chased, and intra-specific intruders were able to feed at territorial feeders only when the territorial male was away. Chases of intra-specific intruders were longer and appeared to be more intense than chases of inter-specific intruders. When food was restricted territorial activity, including the total number of chases engaged in by the territory owner, was significantly reduced, although the basic characteristicso f territorial behavior (e.g., chasesa nd displays) did not change. Territory owners chased a higher proportion of inter-specific intruders when food was restricted (48%), suggestinga n increasei n inter-specific competition. A high proportion of intra-specific competitors continued to be chased (80%), although the total number of intra-specific intruders was lower. We believe that variations in the cost of territoriality are dependent primarily on the level of intra-specific competition. This is supported by the fact that when food was restricted to an amount that could support a maximum of 1.4 L. clemenciae(basedo n doubly labeledw ater measurementso ffield metabolic rate in a previous study), energy intake by the territory owner decreased from 114 kJ/day to 64 Id/day, with the primary difference being number of intra-specific chases. These data also suggest that the exclusion of other hummingbird species might be based strictly on the amount of available food (energy). When food is restricted, inter-specific competition is more costly to the territory owner causing the exclusion of a higher proportion of inter-specific intruders. The high proportion of intra-specific intruders that are chased in either experimental condition suggestst hat territorial behavior in L. clemenciaem ight have functions other than resource protection per se, such as social functions related to their mating system

Field Metabolic Rate and Food Consumption of Two Sympatric Hummingbird Species in Southeastern Arizona

We compared the field metabolic rate (FMR) and behavior around sugar-water feeders of sympatric territorial and non-territorial hummingbirds in the Chiricahua Mountains of southeastern Arizona during July 1987 and 1989. The territorial species was the Blue-throated Hummingbird (Lampornis clemenciae; mean mass 8.77 g) and the non-territorial species the Black-chinned Hummingbird( Archilochusa lexandri; mean mass 3.67 g). FMR (CO2p roduction)a nd watert urnoverw erem easuredu singt he doublyl abeledw ater technique. FMR averaged 81.7 kJ/day (n = 4) in L. clemenciae and 29.1 kJ/day (n = 4) in A. alexandri. Mean mass-specific FMR was higher in L. clemenciae (18.36 ml CO2 g-\u27 hr-\u27) than in A. alexandri (15.58 ml CO2 g-\u27 hr-\u27). This might be due to higher activity costs associated with the aggressive territorial behavior of L. clemenciae.Water influx averaged 1,734 ml kg-\u27 day-\u27 in L. clemenciae (n = 5) and 1,728 ml kg-\u27 day-\u27 in A. alexandri (n = 6). These values represent turnover rates equivalent to 185% and 245% of body mass per day respectivelya nd arec onsistentw ith measurementsm ade on otherh ummingbirds pecies. Where these species coexist in the Chiricahua Mountains, L. clemenciae is a dominant territorials pecies whereasA . alexandria ppearst o be non-territoriala, cquiringe nergy by robbing nectar from L. clemenciae territories. Lampornis clemenciae is highly aggressive againstc onspecifics,b ut appears to ignore intruding A. alexandri. Lack of territorial defense behavior in A. alexandri might reduce field energy expenditures and contribute to a lower FMR than L. clemenciae. We hypothesize that the lack of territorial aggression by L. clemenciae against A. alexandri is due to the high quality, abundance, and predictability of their food source which eliminates the profitability of such aggression. We also suggest that the intense aggression exhibited by L. clemenciae towards conspecifics might be motivated by factors relating to fitness other than defense of a food source

Field Metabolic Rate and Food Consumption by Free-Living Anna\u27s Hummingbirds (Calypte Anna)

We measured C02 production and water flux using doubly labeled water in wild Anna\u27s hummingbirds living in the Santa Ana Mountains of Southern California during autumn (September) of 1981. The estimated field metabolic rate (FMR) of a hummingbird maintaining a constant body mass (mean 4.48 g) is about 32 kl/day, which is 5.2 times basal metabolic rate (BMR). Metabolic rates during daylight hours were about 6.8 X BMR, less than one-half that expected for an Anna\u27s hummingbird in continuous hovering flight. We estimated nighttime metabolism to be near 2.1 X BMR, which is about what would be expected for a normothermic, resting bird experiencing cool air temperatures (as low as 15 C) but much higher than expected if torpor were employed. Water influx was about 164% of body mass per day in birds maintaining a constant mass. Most of this water intake was in the form of sucrose solution from feeders in the area, but some probably came from insects eaten by the birds. Hummingbirds probably did not drink liquid water from streams or ponds during the measurement period