Kenneth Nagy

University of California, Los Angeles | UCLA · Department of Ecology and Evolutionary Biology

1 Supplement Fig. S1 Figure S1. Relationship between shell hardness (SHI) and shell size (carapace length, CL) of one to 11 year old desert tortoises living in natural-habitat enclosures, and experiencing natural rainfall plus irrigation. The red curve represents the transformed linear regression equation calculated for a semilog analysis. The dash...

ABSTRACT: We measured survival, growth, and body condition of 8 hatchling cohorts of desert tortoises Gopherus agassizii (living in predator-resistant outdoor pens in the Mojave Desert, California, USA) over 11 yr to evaluate head-starting methods. At 11 yr of age, 7 times as many of the first cohort had survived than if they had been free-living t...

Covariation among behavioral and physiological traits is thought to enhance reproductive success and Darwinian fitness. Species that exhibit alternative mating strategies provide excellent opportunities to assess the relative contributions of physiological and behavioral traits to fitness. Male side-blotched lizards (Uta stansburiana) exhibit three...

Animals spend considerable time and energy acquiring food to meet their metabolic requirements, but if energetic or fitness costs are substantive, such as during winter, then some individuals may limit daily energy expenditure by reducing foraging duration. To date, the prevalence and magnitude of such compensatory foraging responses are poorly kno...

Head-starting of Agassiz's desert tortoise, a means to aid recovery of this threatened species, may adversely affect offspring sex ratios via temperature-dependent sex determination combined with possible unnatural thermal conditions in head-start facilities. We determined sex ratios in juvenile tortoises hatched from first clutches of 4 annual coh...

We released and monitored 53 juvenile Agassiz's Desert Tortoises (Gopherus agassizii), aged two to 15 y, that were hatched and head-started inside predator-resistant field enclosures. We set free these tortoises under a variety of conditions to evaluate effects of release distance, season of release, and age/body size on homing behavior and survivo...

We subjected neonate Desert Tortoises (Gopherus agassizii) that hatched inside fenced, predator-resistant field enclosures containing natural vegetation to either a natural rainfall regime or a regime of natural rainfall plus irrigation (supplemental precipitation) over a five-year period, to test the hypothesis that mimicking an above-average rain...

Field metabolic rates (FMR) and water influx rates (WIR) were measured in Gila Monsters (Heloderma suspectum) in the Mojave Desert of southern Nevada. Gila Monsters had rates of energy use that were less than half of those expected for lizards of their size, including species that live in arid habitats. Free-living Gila Monsters also had comparativ...

Field metabolic rates (FMR) and water influx rates (WIR) were measured in Gila Monsters (Heloderma suspectum) in the Mojave Desert of southern Nevada. Gila Monsters had rates of energy use that were less than half of those expected for lizards of their size, including species that live in arid habitats. Free-living Gila Monsters also had comparativ...

Short Communication / Field metabolic rate, water flux and food consumption... Abstract Wild silky anteaters (Cyclopes didactylus) were studied in Panama during the dry season using doubly-labeled water (DLW) to measure field metabolic rates (FMR) and water intake rates (WIR), and to es-timate feeding rates. Their daily requirements for energy, foo...

We used data from 17 to 20 microsatellite markers to investigate the incidence of multiple paternities in wild Agassiz’s desert tortoises, Gopherus agassizii. Neonates were sampled from clutches of eggs laid by wild mothers in nesting enclosures at Edwards Air Force Base and at the Marine Corps Air Ground Combat Center, California. We genotyped 28...

The steppe tortoise (Testudo horsfieldi) is probably the most widespread and abundant of all living terrestrial tortoises, but paradoxically, this chelonian as been studied only superficially. Steppe tortoise populations are declining rapidly as a result of massive harvesting for the pet trade and extensive disruption of their habitat by intensive...

Exotic plants can make up a major component of the diet for some Desert Tortoises (Gopherus agassizii) in the Mojave Desert. If introduced plants differ nutritionally from native plants, they may influence the growth and welfare of young tortoises. Minerals available from a native grass (Achnatherum hymenoides), an introduced grass (Schismus barbat...

The metabolic cost of growth in reptiles has been difficult to detect in many previous studies. We designed experiments to detect and quantify added costs of growth by comparing daily energy expenditures of young, growing Desert Tortoises (Gopherus agassizii) with similar-sized, but adult, Parrot-Beaked Tortoises (Homopus areolatus). We measured bo...

Shovel‐snouted sand dune lizards, Meroles anchietae, are reported to include much seed from grasses and fig marigolds in their diets year‐round. This diet is quite unusual for a reptile, and invites investigation. We had an opportunity to examine the diet and to measure seed digestibility for M. anchietae living on dunes near Gobabeb, Namibia. Stom...

Wild Desert Tortoises, Gopherus agassizii, are eating different foods now than they were decades ago, because exotic plant species have invaded and flourished in the Mojave Desert over the last century. Reservations about the nutritional quality of exotic vegetation compared to native vegetation led us to conduct feeding experiments with growing, j...

Mediciones precisas del consumo de alimento en aves jóvenes presentan un gran valor para una serie de estudios ecológicos, pero los métodos tradicionales de medición son problemáticos y altamente propensos a errores. En animales que obtienen el agua principalmente a través del alimento, es posible estimar el consumo de alimento mediante mediciones...

Introduction, The acquisition and allocation of energy can be two of the most critical processes in an organism's life. The amount of energy an individual obtains from the environment can determine not only its survival, but also whether it can engage in reproduction, a very evolutionarily important activity. Among vertebrates, there exists a fairl...

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 s...

The metabolic cost of growth in reptiles has been difficult to detect in many previous studies. We designed experiments to detect and quantify added costs of growth by comparing daily energy expenditures of young, growing Desert Tortoises (Gopherus agassizii) with similar-sized, but adult, Parrot-Beaked Tortoises (Homopus areolatus). We measured bo...

Deserts are relatively dry and dehydrating places, by definition, but desert animals are composed of 65–75% water, just like non-desert animals. Do desert animals maintain water balance and body hydration level by conserving water better (decreasing output, as compared with non-desert species) or by getting more water each day (increasing input), o...

Plasma concentrations of sex steroids (testosterone and progesterone), proteins (total protein and albumin), lipids (phospholipids, cholesterol, and triglycerides), and minerals (calcium and phosphorus) were measured in wild Testudo horsfieldi in Uzbekistan, during the short, 3-month activity period (March-May, 1998). Testosterone concentration in...

Herbivorous vertebrates of arid regions are frequently faced with inadequate food quality, quantity or both. The time and energy devoted to foraging is vital to balancing their energy budgets. For desert ectotherms, a low metabolism should be advantageous, reducing their total energy requirement, but extreme ambient temperatures can strongly constr...

In animal species without parental care, the fitness of males should increase with the number of females en- countered, court, and fertilise, and the fitness of females depends strongly on the quantity and quality of resources acquired. This should ,translate into ,a marked sex differences in the ,patterns of space ,utilisation. We analysed the ,se...

Desert tortoise (Gopherus agassizii) populations have experienced precipitous declines resulting from the cumulative impact of habitat loss and human and disease-related mortality. Diagnosis of disease in live, free-ranging tortoises is facilitated by evaluation of clinical signs and laboratory test results but may be complicated by seasonal and en...

Abstract: In animal species without parental care, the fitness of males should increase with the number of females encountered, court, and fertilise, and the fitness of females depends strongly on the quantity and quality of resources acquired. This should translate into a marked sex differences in the patterns of space utilisation. We analysed the...

Accurate measurements of food consumption by young birds are of great value in a variety of ecological studies, but traditional measurement methods are problematic and prone to high error. In animals that obtain their water primarily through food, it is possible to estimate food consumption from measurements of water influx rate, using radioactivel...

Abstract. - We measured body masses and shell dimensions of free-ranging adult desert tortoises (Gopherus agassizii) through two years of above-average rainfall (1992-93) in the Mojave Desert of California. A condition index (CI), simulating a physical density value, was calculated as the ratio of body mass to estimated shell volume (carapace lengt...

Animals accommodate to environmental change in several ways, depending on the time scale involved. Over short periods of time, such as hours or days, animals faced with an increase in environmental temperature may use behavioral means to escape into cooler local microhabitats. Or, they may use physiological or morphological means, such as increased...

Age and size at maturity are determined through complex interactions among size at birth, growth rate, mat- uration, and survival. We studied sexual size dimorphism and growth rate and maturation patterns in a long-lived or- ganism, the steppe tortoise (Testudo horsfieldi), using the scute lamina number and width as age and growth measures. There w...

Hypothesizing that emperor penguins (Aptenodytes forsteri) would have higher daily energy expenditures when foraging for their food than when being hand-fed and that the increased expenditure could represent their foraging cost, we measured field metabolic rates (FMR; using doubly labeled water) over 4-d periods when 10 penguins either foraged unde...

Selective forces shape sexes differently, with male body proportions facing strong selection to enhance mate searching and male-to-male combat traits, and female fitness being influenced by the ability to assimilate large amounts of nutrients necessary for vitellogenesis (and/or gestation), and their ability to carry the eggs or embryos. We evaluat...

Selective forces shape sexes differently, with male body proportions facing strong selection to enhance mate searching and male-to-male combat traits, and female fitness being influenced by the ability to assimilate large amounts of nutrients necessary for vitellogenesis (and/or gestation), and their ability to carry the eggs or embryos. We evaluat...

We examined evaporative water loss of neonate (<1 yr old) tortoises in laboratory experiments designed to evaluate the dependence of evaporation on humidity, and of juvenile (1-4 yr old) tortoises in field experiments designed to reveal the influence of burrow microclimate on water gain and loss. In controlled laboratory conditions, rates of body m...

Selective forces shape sexes differently, with male body proportions facing strong selection to enhance mate searching and male-to-male combat traits, and female fitness being influenced by the ability to assimilate large amounts of nutrients necessary for vitellogenesis (and/or gestation), and their ability to carry the eggs or embryos. We evaluat...

Rates of field metabolism and water influx of 6 endangered species of marsupials living on Barrow Island, Western Australia, were measured using doubly labeled water. Field metabolic rates (FMRs) of these arid-habitat species are related to body mass according to the following equation: FMR (kJ/day) = 9.58 g0.539 (r2 = 0.935). The allometric equati...

Lizards in the family Xantusiidae (the night lizards) are known to have resting metabolic rates that are only half those of other lizards of comparable size. We evaluated whether xantusiids also have low field metabolic rates (FMR) and food requirements by measuring FMR and water flux rates with doubly labeled water in three xantusiid species in th...

Do young reptiles avoid paying the metabolic costs of rapid growth? Growing mammals and birds must spend extra energy, beyond the metabolic costs they have when not growing, to pay the cost of synthesizing new tissues. lis synthesis cost is in addition to the other costs that growing animals pay to forage for, consume, digest and allocate the extra...

Several factors have combined with an upper respiratory tract disease (URTD) to produce declines on some population numbers of desert tortoises (Gopherus agassizii) in the western USA. This study was designed to determine the seroepidemiology of URTD in a population of wild adult tortoises at the Desert Tortoise Research Natural Area (DTNA) study s...

We studied egg production in two Californian populations of desert tortoises, (Gopherus agassizii) in 1992 and 1993. One population inhabited the Desert Tortoise Research Natural Area (DTNA) in the western Mojave Desert, where most of the rain falls in the winter. The second population lived near Goffs, in the eastern Mojave, where annual precipita...

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...

We summarize the recent information on field metabolic rates (FMR) of wild terrestrial vertebrates as determined by the doubly labeled water technique. Allometric (scaling) relationships are calculated for mammals (79 species), reptiles (55 species), and birds (95 species) and for various taxonomic, dietary, and habitat groups within these categori...

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 threate...

Digestibilities of dry matter, energy, water, and nitrogen were determined for four foods of desert tortoises (Gopherus agassizii) that were kept individually in outdoor pens where food intake and feces output could be measured quantitatively. Two native plants, the forb Malacothrix glabrata and the grass Achnatherum (Oryzopsis) hymenoides, and two...

To investigate constraints on males associated with maintenance of harems, we used a time-energy approach to explore the relationship between temporal occupancy of roosts and nightly foraging activity in male and female greater spear-nosed bats, Phyllostomus hastatus. Harem males and females differed significantly in frequency and duration of night...

This chapter explores the composition of animals' body, and that water is the most important substance in terms of composition, whereby animals contain 70% water by mass and 99% water by number of molecules. It also shows that the transition from Anamniotes to Amniotes is a soft-tissue transition of the postcranial skeleton and the evolutionary pre...

1. Desert gerbilline rodents consume mainly plant material, in particular seeds. However, seeds are less available following winter rains than in summer and many rodents shift their diets from predominantly seeds to ones containing more vegetation. This shift results in a proportionately greater preformed water intake and, as these rodents do not d...

Many natural history characteristics of agamid and iguanian lizards suggest that these closely related groups occupy similar kinds of niches in the Old and New World, respectively. Do these similarities also include physiological properties? We measured field metabolic rates and water flux rates, with doubly labeled water, in Bibron's agama (Agama...

Doubly-labeled-water measurements of field metabolic rates and water influx rates in free-ranging honey possums (mean mass = 9.9 g) during late winter in Western Australia indicated that these nectarivores had lower daily energy expenditures than did insectivorous, dasyurid marsupials of similar body mass. Honey possums are capable of using torpor,...

We describe a method for measuring metabolic rates (MRs) of ectotherms using successive measurements of radionuclide body burdens, which may provide an alternative means of measuring field metabolic rate (FMR). Although MRs can be measured in the laboratory, variability in food supply and quality, temperature, activity, and other factors preclude t...

The ecophysiology of the agamid lizard Ctenophorus nuchalis was studied near Shark Bay, Western Australia, during three seasons, over four years, in order to evaluate seasonal and year-to-year variation in energy and material balance, and to compare this agamid with similar-sized iguanid lizards. We measured water influx and efflux rates and field...

Free-living Merriam's kangaroo rats in the Mojave Desert did not drink, even when abundant rainwater was available for short periods in winter and summer, but they still obtained much more water than expected from a diet of dry seeds alone. Year-round measurements of water influx rates and field metabolic rates (via doubly labeled water), diet comp...

Field-metabolic rates and water-influx rates (both measured via doubly-labeled water) and diet composition (rumen contents, plant sample analyses) were measured in free-ranging male springbok antelope (Antidorcas marsupialis) during the three seasons of the Kalahari. Results from springbok that did not drink water during the hot, dry season indicat...

Foraging mode may influence an array of ecological and bioenergetic characteristics, several of which we compared between two snakes: sympatric sit-and-wait foraging sidewinders, Crotalus cerastes, and widely foraging coachwhips, Masticophis flagellum. During the majority of surface activity, the nocturnal C. cerastes were either coiled on or parti...

Field metabolic rates (FMRs) of 61 species of mammals, as measured with doubly labelled water, range from 29 kJ day-1 (0.34 W) in pipistrel bats to 49 MJ day-1 (570 W) in northern elephant seals, which is a range of 1678 times. Most of this variation is due to differences in body mass; the least-squares, log-log regression of mammalian FMR on body...

Both stressful and benevolent times of the year can be identified by measuring rates of water and energy use, diet and behaviour throughout a year. Jackrabbits Lepus californicus are strict herbivores. Most Mojave Desert individuals have no access to drinking water, and depend on their food for water. When vegetation dries up during the summer drou...

Aspects of chick-provisioning in Wilson' s Storm-Petrel were measured at Palmer Station, Antarctica. Chicks received meals averaging 9.2 g (21% of adult body mass) with a mean frequency of 1.1 feeds/chick' day. Feeding frequency decreased as chicks grew, but meal mass remained relatively constant throughout the fledging period. Free lipids accounte...

Studies of digesta transit in the desert tortoise (Xerobates agassizii, formerly Gopherus agassizii) voluntarily eating a succulent diet (green, growing Erodium cicutarium, red-stemmed filaree) or a dry diet (dead Schismus barbatus, split grass), indicated that digesta flow was determined primarily by a gut-fill effect. Total food consumed between...

We measured the field metabolic rate (FMR) and water influx rate (WIR) of the largest species of bird, the Ostrich (Struthio camelus), which lives in the Namib desert, one of the driest regions on earth. Along with doubly-labeled water (DLW) measurements of FMR and WIR, we examined the availability of plants in various habitats, the plants selected...

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We used the doubly-labeled water technique to measure the field metabolic rate (FMR) of free-ranging adult Black Guillemots (Cepphus grylle) during the chick-rearing period. The FMR was 3.63 +/-0.74 ml CO2 g-1 h-1, equivalent to a daily energy expenditure of 860 +/- 175 kJ d-1. The FMR was 3.17 times the resting metabolic rate (RMR) measured in a p...

water requirements, foraging behaviour, metabolism wild ostrich, Namibia

Northern Shrikes (Lanius excubitor) breed in a variety of habitats, including deserts. Deserts are characterized by unpredictable food supplies, which can lead to a slow growth rate of nestlings. However, given that Northern Shrike males use prey from their caches to augment freshly caught prey in providing food for their mates and nestlings, we hy...

Adelie penguins (mean body mass 3.81 kg) brooding small chicks bad field metabolic rates (FMRs, measured using doubly labeled water) averaging 1.64 mL CO2 g-1 h-1, equivalent to 3,896 kj d-1 and 3.8 times basal metabolic rate (BMR). Energy utilization while on the nest was 2.0 X BMR, and it was 5.4 X BMR when off the nest, including time spent fora...

We used the doubly labeled water method to measure rates of energy expenditure in free-living Southern Giant-Petrels (Macronectes giganteus, mean body mass = 3.89 kg) at Palmer Station, Antarctica. Despite superficial morphological and behavioral resemblances to the energetically efficient albatrosses, giant-petrels have high energetic costs while...

1. The Blanford's fox, Vulpes cana (Blanford 1877) is a small canid (mean body mass = 956 g) that inhabits rocky mountains and canyons in the deserts of Israel, where it feeds mainly on invertebrates and fruits. 2. We hypothesized that the energy expenditure of Blanford's foxes would be higher than that of a small canid that inhabits flat terrain,...

Free-living fat sand rats (Psammomys obesus) consumed only saltbush (Atriplex halimus), did not drink water, and maintained constant body mass in summer and winter. Rates of water influx and energy expenditure of adults were greater in winter than in summer. Daily intake of dry matter by adults ranged from 9.3 (summer) to 11.0% (winter) of body mas...

Gannets (genus Morus) are piscivorous seabirds with a breeding distribution restricted to the cool to temperate waters of the mid latitudes. Field metabolic rates of breeding Cape gannets M. capensis and their chicks were measured using doubly labelled water. Energy expenditures of adults incubating or brooding chicks at the nest were 2090 kJ d-1 (...