Kenneth A. Nagy

FIELD METABOLIC RATE AND FOOD REQUIREMENT SCALING IN MAMMALS AND BIRDS

Field metabolic rates (FMRs or HF), all measured using doubly labeled water, of 23 species of eutherian mammals, 13 species of marsupial mammals, and 25 species of birds were summarized and analyzed allometrically (log10-1og10 regressions). FMR is strong- ly correlated with body mass in each of these groups. FMR scales differently than does basal or standard metabolic rate in eutherians (FMR slope = 0.81) and marsupials (FMR slope = 0.58), but not in birds (FMR slope = 0.64 overall, but 0.75 in passerines and 0.75 in all other birds). Medium-sized (240-5 50 g) eutherians, marsupials, and birds have similar FMRs, and these are - 17 times as high as FMRs of like-sized ectothermic vertebrates such as iguanid lizards. For endothermic vertebrates, the energy cost of surviving in nature is enormous compared with that for ectotherms. Within the eutherians, marsupials, or birds, FMR scales differently for the following subgroups: rodents, passerine birds, her- bivorous eutherians, herbivorous marsupials, desert eutherians, desert birds, and seabirds. Equations are given for use in predicting daily and annual FMR and food requirement of a species of terrestrial vertebrate, given its body mass.

Field metabolic rate and body size.

SUMMARY The field metabolic rates (FMRs) of 229 species of terrestrial vertebrates, all measured using the doubly labeled water method in free-living individuals, were evaluated. Daily rates of energy expenditure were as low as 0.23 kJ per day in a small reptile (gecko), to as high as 52 500 kJ per day in a marine mammal (seal). This is a range of nearly six orders of magnitude. More than 70% of the variation in log-transformed data is due to variation in body size (expressed as body mass). Much of the remaining variation is accounted for by thermal physiology, with the endothermic mammals and birds having FMRs that are about 12 and 20 times higher, respectively, than FMRs of equivalent-sized, but ectothermic, reptiles. Variation in log(body mass) within each of these three taxonomic classes accounts for over 94% of the variation in log(FMR), and results from nonlinear regression analyses using untransformed data support this conclusion. However, the range of residual variation in mass-adjusted FMR within classes is still more than sixfold (ratio of highest over lowest). Some of this variation is associated with affiliations with lower taxonomic levels (Infraclass: eutherian vs metatherian mammals; Family: passerine, procellariform and galliform birds vs other birds), some is associated with habitat (especially desert vs nondesert), and some with differences in basic diet preference and foraging mode and season. The scaling slopes for FMR often differ from BMR slopes for the same Class of animals, and most differ from the theoretical slope of 0.75. Differences among slopes and intercepts that were detected using conventional regression analyses were largely confirmed upon reanalysis using Independent Contrasts Analysis to adjust for phylogenetic biases.

Energetics of Pregnancy and Lactation in Freeranging Little Brown Bats (Myotis lucifugus)

We combined field measurements of metabolic rate, made with doubly labeled water, with data from our previous studies to examine reproductive energetics in 24 female little brown bats (Myotis lucifugus). Including estimates of tissue or milk production, M. lucifugus required an average of 33.7 kJ d⁻¹ of assimilated energy in pregnancy compared to 41.3 kJ d⁻¹ during lactation. Predicted insect consumption was 5.5 g d⁻¹ for a 9-gpregnant female and 6.7g d⁻¹ for a 79-g lactating female. About 2% of total energy assimilated during pregnancy was stored as new tissue, whereas lactating females exported 32% as milk. Estimated assimilated energy demand on the first day of lactation was 33.8 kJ d⁻¹ and increased to 60.3 kJ d⁻¹ at peak lactation. By subtracting laboratory measurements of roosting costs from observed metabolized energy expenditure, we calculated that foraging flight by 9-g pregnant M. lucifugus required 4.46 kJ h⁻¹; this was 13% less than allometric predictions. Foraging fight accounted for the largest proportion of the daily metabolized energy budget during pregnancy (61%) and lactation (66%). The large amount of energy devoted to foraging by this aerial-feeding bat may partially explain the low proportion of energy it allocates to tissue production and milk export.

Locomotor capacity and foraging behaviour of kalahari lacertid lizards

Abstract Closely related lacertid lizards (Eremias, Nucras) in the Kalahari desert differ in patterns of foraging behaviour. Some species are relatively sedentary (‘sit-and-wait’) whereas others are more active (‘widely-foraging’) predators. We determined whether whole-animal locomotor capacities (cruising endurance on a treadmill, initial speed and maximum burst speed in a racetrack, and sprint endurance in a torus-shaped track) correlated with interspecific differences in foraging behaviour. Two of three widely-foraging species had greater cruising endurance, graater sprint endurance, but lower burst speed than did a sit-and-wait species. However, the two species that sprinted quickly also had limited endurance, and vice versa. Pre-feeding negatively influenced endurance but not sprint capacity. Theoretical models of foraging behaviour should recognize that ectotherms have limited endurance, that there can be a trade-off between speed and endurance, and that pre-feeding can reduce some aspects of locomotor capacity.

TRANSMITTER LOADS AFFECT THE FLIGHT SPEED AND METABOLISM OF HOMING PIGEONS

Eight homing pigeons (Columba livia) were flown distances of 90 and 320 km with and without transmitters (weighing either 2.5% or 5.0% of the pigeons body mass, M,) mounted on a back harness. Flight times in April through June for the 90-km distance were 60 min without a transmitter or harness, 69 min with a harness alone and about 76 min with a harness and transmitter (weighing either 2.5% or 5.0% of M,). Flight times for the 320-km distance were 4 hr 16 min for the controls and 5 hr 35 min for the two fastest pigeons wearing a harness and transmitter weighing 2.5% of M,. The results show that on 90-km flights harnesses alone slow birds by 15% and harnesses and transmitters (5 5%M,) slow birds 25 to 28%; on 320-km flights harnesses and transmitters slow birds >31%. Moreover, on the 320-km flights, CO, production of the pigeons (measured with the doubly- labeled water method) was 41 to 52% higher per hour when encumbered with a transmitter and harness. Thus, encumbered pigeons produced 85 to 100% more total CO, covering the 320-km distance. Therefore, high performance homing pigeons work substantially harder and longer during a long distance flight when wearing harnesses and transmitters.

Energetics and Water Flux of Free-Ranging Big Brown Bats (Eptesicus fuscus) during Pregnancy and Lactation

We used doubly labeled water to measure carbon dioxide production and water flux during pregnancy and lactation in free-ranging big brown bats, Eptesicus fuscus. Mean (± SE ) carbon dioxide production was 1,749 ±144 ml/day during pregnancy ( n = 16) and 2,770 ±351 ml/day during lactation ( n = 5). Including estimates of tissue production and milk export, we calculated that the average requirement for assimilated energy was 48.9 and 105.1 kJ/day for pregnant and lactating females, respectively. About 2% of the total energy required during pregnancy was placed into fetal tissue; milk energy accounted for 28% of the energy assimilated during lactation. Daily water flux was 8.47 and 17.07 ml/day for pregnant and lactating females, respectively. We calculated that E. fuscus obtained >66% of its water preformed in the diet, but 20–22% of daily water intake was from drinking. Urinary water was the largest component of water efflux during pregnancy (72%) and lactation (56%); water exported in milk represented 22% of daily water efflux during lactation. Calculated evaporative losses for free-ranging E. fuscus were half those predicted from laboratory measurements.

Reference intervals and physiologic alterations in hematologic and biochemical values of free-ranging desert tortoises in the Mojave Desert.

Desert tortoise (Gopherus agassizii) populations have experienced precipitous declines resulting from the cumulative impact of habitat loss, and human and disease-related mortality. Evaluation of hematologic and biochemical responses of desert tortoises to physiologic and environmental factors can facilitate the assessment of stress and disease in tortoises and contribute to management decisions and population recovery. The goal of this study was to obtain and analyze clinical laboratory data from free-ranging desert tortoises at three sites in the Mojave Desert (California, USA) between October 1990 and October 1995, to establish reference intervals, and to develop guidelines for the interpretation of laboratory data under a variety of environmental and physiologic conditions. Body weight, carapace length, and venous blood samples for a complete blood count and clinical chemistry profile were obtained from 98 clinically healthy adult desert tortoises of both sexes at the Desert Tortoise Research Natural area (western Mojave), Goffs (eastern Mojave) and Ivanpah Valley (northeastern Mojave). Samples were obtained four times per year, in winter (February/March), spring (May/June), summer (July/August), and fall (October). Years of near-, above- and below-average rainfall were represented in the 5 yr period. Minimum, maximum and median values, and central 95 percentiles were used as reference intervals and measures of central tendency for tortoises at each site and/or season. Data were analyzed using repeated measures analysis of variance for significant (P < 0.01) variation on the basis of sex, site, season, and interactions between these variables. Significant sex differences were observed for packed cell volume, hemoglobin concentration, aspartate transaminase activity, and cholesterol, triglyceride, calcium, and phosphorus concentrations. Marked seasonal variation was observed in most parameters in conjunction with reproductive cycle, hibernation, or seasonal rainfall. Year-to-year differences and long-term alterations primarily reflected winter rainfall amounts. Site differences were minimal, and largely reflected geographic differences in precipitation patterns, such that results from these studies can be applied to other tortoise populations in environments with known rainfall and forage availability patterns.

ENERGY METABOLISM AND FOOD CONSUMPTION BY WILD HOWLER MONKEYS (ALOUATTA PALLIATA)

Rates of CO2 production in free-living and captive howler monkeys were measured using doubly labeled water, and assimilation of energy from natural foods was determined. Results permit construction of a field energy budget, and estimation of the feeding rate of these arboreal, plant-eating primates. Field metabolic rates averaged 355 kJ kg-1 day-1 (=2x basal metabolic rate). Assimilation of the energy in a fruit and leaf diet was =400o. Feeding rate in the field is estimated to be =54 g dry matter kg-1 day-1, or =90 kg dry matter ha-1 yr-1.

Temperature Regulation by the Inflorescence of Philodendron

The inflorescence of Philodendron selloum temporarily maintains a core temperature of 38� to 46�C, despite air temperatures ranging from 4� to 39�C, by means of a variable metabolic rate. The heat is produced primarily by small, sterile male flowers that are capable of consuming oxygen at rates approaching those of flying hummingbirds and sphinx moths.

Effects of climatic variation on field metabolism and water relations of desert tortoises

Abstract We used the doubly labeled water method to measure the field metabolic rates (FMRs, in kJ kg−1 day−1) and water flux rates (WIRs, in ml H2O kg−1 day−1) of adult desert tortoises (Gopherus agassizii) in three parts of the Mojave Desert in California over a 3.5-year period, in order to develop insights into the physiological responses of this threatened species to climate variation among sites and years. FMR, WIR, and the water economy index (WEI, in ml H2O kJ−1, an indicator of drinking of free water) differed extensively among seasons, among study sites, between sexes, and among years. In high-rainfall years, males had higher FMRs than females. Average daily rates of energy and water use by desert tortoises were extraordinarily variable: 28-fold differences in FMR and 237-fold differences in WIR were measured. Some of this variation was due to seasonal conditions, with rates being low during cold winter months and higher in the warm seasons. However, much of the variation was due to responses to year-to-year variation in rainfall. Annual spring peaks in FMR and WIR were higher in wet years than in drought years. Site differences in seasonal patterns were apparently due to geographic differences in rainfall patterns (more summer rain at eastern Mojave sites). In spring 1992, during an El Niño (ENSO) event, the WEI was greater than the maximal value obtainable from consuming succulent vegetation, indicating copious drinking of rainwater at that time. The physiological and behavioral flexibility of desert tortoises, evident in individuals living at all three study sites, appears central to their ability to survive droughts and benefit from periods of resource abundance. The strong effects of the El Niño (ENSO) weather pattern on tortoise physiology, reproduction, and survival elucidated in this and other studies suggest that local manifestations of global climate events could have a long-term influence on the tortoise populations in the Mojave Desert.