Variation In Body Mass Research Articles

Severe recent decrease of adult body mass in a declining insectivorous bird population.

Migratory bird species that feed on air-borne insects are experiencing widespread regional declines, but these remain poorly understood. Agricultural intensification in the breeding range is often regarded as one of the main drivers of these declines. Here, we tested the hypothesis that body mass in breeding individuals should reflect habitat quality in an aerial insectivore, the tree swallow (Tachycineta bicolor), along a gradient of agricultural intensity. Our dataset was collected over 7 years (2005-2011) and included 2918 swallow captures and 1483 broods. Analyses revealed a substantial decline of the population over the course of the study (-19% occupancy rate), mirrored by decreasing body mass. This trend was especially severe in females, representing a total loss of 8% of their mass. Reproductive success was negatively influenced by intensive agriculture, but did not decrease over time. Interestingly, variation in body mass was independent of breeding habitat quality, leading us to suggest that this decline in body mass may result from carry-over effects from non-breeding areas and affect population dynamics through reduced survival. This work contributes to the growing body of evidence suggesting that declines in migratory aerial insectivores are driven by multiple, complex factors requiring better knowledge of year-round habitat use.

Mechanistic drivers of flexibility in summit metabolic rates of small birds.

Flexible metabolic phenotypes allow animals to adjust physiology to better fit ecological or environmental demands, thereby influencing fitness. Summit metabolic rate (Msum = maximal thermogenic capacity) is one such flexible trait. Skeletal muscle and heart masses and myocyte metabolic intensity are potential drivers of Msum flexibility in birds. We examined correlations of skeletal muscle and heart masses and pectoralis muscle citrate synthase (CS) activity (an indicator of cellular metabolic intensity) with Msum in house sparrows (Passer domesticus) and dark-eyed juncos (Junco hyemalis) to determine whether these traits are associated with Msum variation. Pectoralis mass was positively correlated with Msum for both species, but no significant correlation remained for either species after accounting for body mass (Mb) variation. Combined flight and leg muscle masses were also not significantly correlated with Msum for either species. In contrast, heart mass was significantly positively correlated with Msum for juncos and nearly so (P = 0.054) for sparrows. Mass-specific and total pectoralis CS activities were significantly positively correlated with Msum for sparrows, but not for juncos. Thus, myocyte metabolic intensity influences Msum variation in house sparrows, although the stronger correlation of total (r = 0.495) than mass-specific (r = 0.378) CS activity with Msum suggests that both pectoralis mass and metabolic intensity impact Msum. In contrast, neither skeletal muscle masses nor pectoralis metabolic intensity varied with Msum in juncos. However, heart mass was associated with Msum variation in both species. These data suggest that drivers of metabolic flexibility are not uniform among bird species.

Geographic variation in body mass of first-year Reed Warblers Acrocephalus scirpaceus in Iberia

On their route to tropical Africa, European trans-Saharan migrants must cross two major geographical barriers, the Mediterranean Sea and the Sahara Desert, which necessitates the accumulation of large fuel loads.While northernAfrica is the chief region wheremost migrants gain fuel for the Sahara crossing, Iberia is a target area to gain fuel before the sea crossing existing between Europe andAfrica. Despite the large body of studies approaching the question of fuel accumulation before geographic barriers, it is still poorly known which factors apart from distance to a certain barrier shape the geographical pattern of fuel reserves. To investigate this question in detail we used data of first-year Reed Warblers from 12 localitieswithin Iberia during the autumnmigration period of 2009.We run linearmodels to analyze the effects of location in Iberia, date, and body size on bodymass variation at each migratory flyway (eastern, central and western Iberia). Flight ranges from each site were also calculated. Our results showed that ReedWarblers in Iberia had the necessary fuel needed to arrive in northernAfrica but not to tropical Africa. However, bodymass patterns varied depending on the geographical region (eastern, central or western Iberia).Date did not affect bodymass in central andwestern Iberia, but in eastern Iberia heavier birds tended to pass later. Thus, the factors shaping body mass of ReedWarblers in Iberia before the sea crossing to Africa seemed to be more complex than just the distance to this geographical barrier, with underlying stopover quality-associated factors possibly playing a relevant role.

Sex-Specific Seasonal Change in Body Mass in Two Species of Vespertilionid Bats

In most mammals, reproductive cost differs between males and females in timing and duration because of the different sex-specific energy allocation strategies to maximize fitness. The differences in reproductive strategy adopted by sexes may result in differences in seasonal variation of body mass. Here seasonal variations in body mass are discussed for two species of vespertilionid bats: Daubenton's bat (Myotis daubentonii) and Savi's pipistrelle (Hypsugo savii). Both species were observed to have a seasonal variability in body conditions, which was sex dependent. In late spring and for a given forearm length, females were heavier than males, but differences were small in late summer. Furthermore, female'’s body mass decreased during late spring and summer likely to support the energy requirement for lactation, while male's mass did not change (H. savii) or slightly increase (M. daubentonii) over the same period. On the contrary male M. daubentonii depleted body fat reserves during early autumn, likely because of the energy expenditure to increase mating opportunities. Our results suggest that seasonal changes in body condition in hibernating bats may reflect the differences in reproductive strategies between sexes.

Ecology of Aquatic WarblersAcrocephalus paludicolain a Fall Stopover Area on the Atlantic Coast of France

The Aquatic Warbler Acrocephalus paludicola is the only endangered songbird in continental Europe. This trans-Saharan migratory bird significantly transits along the French Atlantic coastline during post-breeding migration and the right bank of the Gironde estuary has been identified as an important stopover site. We studied the spatial occupancy strategies of stationing individuals during August of three successive years (2010–2012). We characterized habitat use by radio-tracking individuals revealing relatively small foraging ranges (6.6 ± 2.6 ha on average) with only 1 ha actually exploited (core area), and a relatively high habitat fragmentation rate. Capture-mark-recapture analyses assessed the average stopover duration of individuals and body-mass variations during their stopover. The estimated average stopover duration was 6.46 ± 0.46 days (95% confidence interval: 4.4–9.6). Lean birds tended to forage significantly more than stout birds: on average, they gain 2.81 ± 0.89% of their initial mass each day whereas stout birds only gain 0.12 ± 0.56%. Analyses of droppings characterized the local diet. We noticed that Aquatic Warbler preferentially used partially-flooded or flooded habitats with heterogeneous and rather low vegetation, such as bulrush beds or bulrush beds mixed with reed beds. Orthoptera, Araneae and Hymenoptera represented the largest contributions to the consumed biomass (64.7%, 13.4% and 8.9% respectively). The importance of the fuel deposition rate of lean birds reflects the importance of the estuary as a stopover site for the species. It means that the available resources allow birds to replenish and continue their migration route. However, the sustainability of the site's functionality is questioned because of the evolution of habitats (erosion, rise in water levels and changes in food web).

Use of a morphometric method and body fat index system for estimation of body composition in overweight and obese cats.

To develop morphometric equations for prediction of body composition and create a body fat index (BFI) system to estimate body fat percentage in overweight and obese cats. Prospective evaluation study. 76 overweight or obese cats ≥ 1 year of age. Body condition score (BCS) was determined with a 5-point scale, morphometric measurements were made, and dual-energy x-ray absorptiometry (DEXA) was performed. Visual and palpation-based evaluation of various body regions was conducted, and results were used for development of the BFI system. Best-fit multiple regression models were used to develop equations for predicting lean body mass and fat mass from morphometric measurements. Predicted values for body composition components were compared with DEXA results. For the study population, prediction equations accounted for 85% of the variation in lean body mass and 98% of the variation in fat mass. Values derived from morphometric equations for fat mass and lean mass were within 10% of DEXA values for 55 of 76 (72%) and 66 of 76 (87%) cats, respectively. Body fat as a percentage of total body weight (ie, body fat percentage) predicted with the BCS and BFI was within 10% of the DEXA value for 5 of 39 (13%) and 22 of 39 (56%) cats, respectively. The BFI system and morphometric equations were considered accurate for estimation of body composition components in overweight and obese cats of the study population and appeared to be more useful than BCS for evaluation of these patients. Further research is needed to validate the use of these methods in other feline populations.

Use of a novel morphometric method and body fat index system for estimation of body composition in overweight and obese dogs.

To develop morphometric equations for prediction of body composition and create a body fat index (BFI) to estimate body fat percentage in overweight and obese dogs. Prospective evaluation study. 83 overweight or obese dogs ≥ 1 year of age. Body condition score (BCS) was assessed on a 5-point scale, morphometric measurements were made, and visual and palpation-based assessments and dual-energy x-ray absorptiometry (DEXA) were performed. Equations for predicting lean body mass, fat mass, and body fat as a percentage of total body weight (ie, body fat percentage) on the basis of morphometric measurements were generated with best-fit statistical models. Visual and palpation-based descriptors were used to develop a BFI. Predicted values for body composition components were compared with DEXA-measured values. For the study population, the developed morphometric equations accounted for 98% of the variation in lean body mass and fat mass and 82% of the variation in body fat percentage. The proportion of dogs with predicted values within 10% of the DEXA values was 66 of 83 (80%) for lean body mass, 56 of 83 (68%) for fat mass, and 56 of 83 (67%) for body fat percentage. The BFI accurately predicted body fat percentage in 25 of 47 (53%) dogs, whereas the value predicted with BCS was accurate in 6 of 47 (13%) dogs. Morphometric measurements and the BFI appeared to be more accurate than the 5-point BCS method for estimation of body fat percentage in overweight and obese dogs. Further research is needed to assess the applicability of these findings to other populations of dogs.

Optimal lamellar arrangement in fish gills.

Fish respire through gills, which have evolved to extract aqueous oxygen. Fish gills consist of filaments with well-ordered lamellar structures, which play a role in maximizing oxygen diffusion. It is interesting that when we anatomically observe the gills of various fish species, gill interlamellar distances (d) vary little among them, despite large variations in body mass (Mb). Noting that the small channels formed by densely packed lamellae cause significant viscous resistance to water flow, we construct and test a model of oxygen transfer rate as a function of the lamellar dimensions and pumping pressure, which allows us to predict the optimal interlamellar distance that maximizes the oxygen transfer rate in the gill. Comparing our theory with biological data supports the hypothesis that fish gills have evolved to form the optimal interlamellar distances for maximizing oxygen transfer. This explains the weak scaling dependence of d on Mb: d ∼ Mb(1/6).

Linking body mass and group dynamics in an obligate cooperative breeder.

Social and environmental factors influence key life-history processes and population dynamics by affecting fitness-related phenotypic traits such as body mass. The role of body mass is particularly pronounced in cooperative breeders due to variation in social status and consequent variation in access to resources. Investigating the mechanisms underlying variation in body mass and its demographic consequences can help elucidate how social and environmental factors affect the dynamics of cooperatively breeding populations. In this study, we present an analysis of the effect of individual variation in body mass on the temporal dynamics of group size and structure of a cooperatively breeding mongoose, the Kalahari meerkat, Suricata suricatta. First, we investigate how body mass interacts with social (dominance status and number of helpers) and environmental (rainfall and season) factors to influence key life-history processes (survival, growth, emigration and reproduction) in female meerkats. Next, using an individual-based population model, we show that the models explicitly including individual variation in body mass predict group dynamics better than those ignoring this morphological trait. Body mass influences group dynamics mainly through its effects on helper emigration and dominant reproduction. Rainfall has a trait-mediated, destabilizing effect on group dynamics, whereas the number of helpers has a direct and stabilizing effect. Counteracting effects of number of helpers on different demographic rates, despite generating temporal fluctuations, stabilizes group dynamics in the long term. Our study demonstrates that social and environmental factors interact to produce individual variation in body mass and accounting for this variation helps to explain group dynamics in this cooperatively breeding population.

The metabolic determinant underlying the rate of energy use during prolonged fasting for the diamondback watersnake, Nerodia rhombifer (1101.4)

During prolonged bouts of fasting, tissues and organs lose mass as a function of their metabolic expenditure and differences in the allocation of endogenous energy. We previously observed considerable variation in the rate at which individual diamondback watersnakes (Nerodia rhombifer) lose body and fat mass during extended fasts. It has also been found that these snakes exhibit variation in their standard metabolic rate (SMR). We therefore hypothesized that individual variation in SMR is responsible for the observed variation in body mass and body fat loss with fasting. Predictably, snakes with relatively high SMR would metabolize fat stores at a greater rate (therefore loss body mass faster) than snakes that possess relatively low SMR. We explored the causal relationships between SMR and body and fat loss during extended bouts of fasting for the diamondback watersnake by examining variation in SMR and differential loss of body, fat, and organ mass over six months of fasting. Baseline SMR and body mass was measured from 55 snakes and organ masses from 10 snakes. For each following month, 5 snakes were dissected, with 10 snakes sampled on the 6th month. SMR of individuals was measured at 2‐month intervals. On average snakes lost 0.1 grams of fat per day while fasting, with a 5‐fold range in daily fat loss among snakes. After 5 months of fasting, variation in body fat loss ranged from 25% to 90%. There was a 2.5‐fold variation in SMR among these same individuals. As predicted, snakes with higher SMR experienced a greater rate of body fat loss. We have demonstrated that basal rates of metabolism can significant determine rates of body fat loss and therefore impact an individual’s capacity to survive long episodes of fasting.

Body Mass in Common Loons (Gavia immer) Strongly Associated with Migration Distance

Abstract. During 25 field seasons between 1988 and 2012, Biodiversity Research Institute captured and uniquely color-banded 2,730 adult Common Loons (Gavia immer) on breeding territories in 11 States and seven Provinces throughout North America. Body mass was obtained from each individual; tarsus and bill measurements were obtained from more than half the birds banded. Clinal variation in body mass, tarsal width and bill length was observed. Body mass varied from 2,700 g to 7,600 g; loons from populations in the upper Great Lakes and central Canada were smallest, and size increased to the east and west. Examination of band return and satellite tracking data resulted in three migration distance groups: 20%) than associated females, and withinpair differences increased with decreasing migration distance (i.e., males from coastal States were proportionally larger than their ma...

Do digestive contents confound body mass as a measure of relative condition in nestling songbirds?

ABSTRACTRelative nestling condition, typically measured as nestling mass or as an index including nestling mass, is commonly purported to correlate with fledgling songbird survival. However, most studies directly investigating fledgling survival have found no such relationship. We weighed feces and stomach contents of nestling golden‐winged warblers (Vermivora chrysoptera) to investigate the potential contribution of variation in digestive contents to differences in nestling mass. We estimated that the mass of a seventh‐day (near fledging) nestling golden‐winged warbler varies by 0.65 g (approx. 9% of mean nestling mass) depending on the contents of the nestling's digestive system at the time of weighing, and that digestive contents are dissimilar among nestlings at any moment the brood is removed from the nest for weighing. Our conservative estimate of within‐individual variation in digestive contents equals 72% and 24% of the mean within‐brood and population‐wide range in nestling mass, respectively. Based on our results, a substantive but typically unknown amount of the variation in body mass among nestlings is confounded by differences in digestive contents. We conclude that short‐term variation in digestive contents likely precludes the use of body mass, and therefore any mass‐dependent index, as a measure of relative nestling condition or as a predictor of survival in golden‐winged warblers and likely in many other songbirds of similar size. © 2014 The Wildlife Society.

Modern diet and metabolic variance--a recipe for disaster?

ObjectiveRecently, a positive correlation between alanine transaminase activity and body mass was established among healthy young individuals of normal weight. Here we explore further this relationship and propose a physiological rationale for this link.DesignCross-sectional statistical analysis of adiposity across large samples of adults differing by age, diet and lifestyle.Subjects46,684 19–20 years old Swiss male conscripts and published data on 1000 Eskimos, 518 Toronto residents and 97,000 North American Adventists.MeasurementsSerum concentrations of the alanine transaminase, post-prandial glucose levels, cholesterol, body height and weight, blood pressure and routine blood analysis (thrombocytes and leukocytes) for Swiss conscripts. Adiposity measures and dietary information for other groups were also obtained.ResultsStepwise multiple regression after correction for random errors of physiological tests showed that 28% of the total variance in body mass is associated with ALT concentrations. This relationship remained significant when only metabolically healthy (as defined by the American Heart Association) Swiss conscripts were selected. The data indicated that high protein only or high carbohydrate only diets are associated with lower levels of obesity than a diet combining proteins and carbohydrates.ConclusionElevated levels of alanine transaminase, and likely other transaminases, may result in overactivity of the alanine cycle that produces pyruvate from protein. When a mixed meal of protein, carbohydrate and fat is consumed, carbohydrates and fats are digested faster and metabolised to satisfy body’s energetic needs while slower digested protein is ultimately converted to malonyl CoA and stored as fat. Chronicity of this sequence is proposed to cause accumulation of somatic fat stores and thus obesity.

High frequency body mass measurement, feedback, and health behaviors

We analyze weight and fat percentage measurements of respondents in an online general population panel in the Netherlands, collected using wireless scales, with an average frequency of 1.6 measurements per week. First, we document the existence of a weekly cycle; body mass is lowest on Fridays and highest on Mondays, showing significant (p<0.01) differences of, on average, 0.2kilogram in weight, 0.06 in BMI value, and 0.03 in fat percentage. Second, we find that in the general population fat-based measures of obesity point at a three times larger prevalence of obesity (53%) than BMI-based measures (17%). Third, we find that feedback that includes a recommended weight range increases the temporal variation in individual body mass by almost ten percent (sd for weight increases from 1.13 to 1.22; sd for BMI increases from 0.37 to 0.41; sd for fat percentage increases from 0.55 to 0.61.

Effects of the consumption of fish meals on the carotid IntimaMedia thickness in patients with hypertension: a prospective study.

The composition of dietary fat affects various modifiable cardiovascular risk factors and cardiovascular outcomes in the general population. We investigated the effects of the regular consumption of fish meals on the fatty acid composition of red blood cell (RBC) membranes and the relationship of this parameter with the carotid intima-media thickness (IMT), an early marker of atherosclerosis. In 56 hypertensive patients, we measured the carotid IMT using ultrasound imaging and the RBC membrane fatty acid composition using gas-chromatography and calculated the polyunsaturated to saturated fatty acid (PUFA/SFA) ratio. The patients received intensive nutritional counseling and three weekly meals of fish containing elevated amounts of PUFA, in order to increase the membrane PUFA content. The RBC membrane fatty acid composition and IMT were reassessed after one year. At baseline, the membrane PUFA/SFA ratio was inversely related to the carotid IMT, and the relationship was independent of all major cardiovascular risk factors. At follow-up, the PUFA/SFA ratio increased in the RBC membranes of 25 (45%) of 56 patients. The regular consumption of fish meals resulted in a decreased carotid IMT only in the patients with an increased membrane PUFA/SFA ratio. Changes in the PUFA/SFA ratio induced by the dietary intervention were inversely related to the changes in the IMT, independent of variations in body mass, blood pressure and plasma lipids. In hypertensive patients, a low RBC membrane PUFA/SFA ratio is associated with more prominent vascular damage, and the regular consumption of fish reduces the carotid IMT in patients in whom dietary intervention affects the membrane fatty acid composition.

Craniofacial variation, body size and ecological factors in aboriginal populations from central Patagonia (2000–200 years B.P.)

Previous studies have shown that ecological factors had a significant role in shaping the patterns of craniofacial variation among South American populations. Here, we evaluate whether temperature and diet contributed to facial diversification in small geographic areas. Facial size and shape of 9 osteological samples from central Patagonia (Argentina) were described using 2D landmarks and semilandmarks. Data on mean annual temperature, diet composition (δ13C and δ15N values) and femoral head maximum breadth, used as a proxy of body mass, were obtained for each sample. We then tested the association of body mass and the ecological variables with facial morphology using spatial regression techniques and a model selection approach. Akaike Information Criterion produced disparate results for both components of facial morphology. The best model for facial size included temperature and body mass proxy, and accounted for more than 80% of variation in size. Lower temperatures were related to larger facial sizes. Body mass was negatively associated with facial size and showed no relationship with the temperature. This suggests a relatively independent variation of cranial traits and body mass at the spatial scale studied here. Facial shape was not associated with the temperature or diet composition, contrasting with the patterns observed at larger spatial scales. Our results point out that the effect of climatic variables on cranial traits might be a source of morphological differentiation not only at large scales but also in small geographic areas, and that size and shape display a differential preservation of environmental signals.

Disentangling basal and accumulated body mass for cross‐population comparisons

Measures of human body mass confound 1) well-established population differences in body form and 2) exposure to obesogenic environments, posing challenges for using body mass index (BMI) in cross-population studies of body form, energy reserves, and obesity-linked disease risk. We propose a method for decomposing population BMI by estimating basal BMI (bBMI) among young adults living in extremely poor, rural households where excess body mass accumulation is uncommon. We test this method with nationally representative, cross-sectional Demographic and Health Surveys (DHS) collected from 69,916 rural women (20-24 years) in 47 low-income countries. Predicting BMI by household wealth, we estimate country-level bBMI as the average BMI of young women (20-24 years) living in rural households with total assets <400 USD per capita. Above 400 USD per capita, BMI increases with both wealth and age. Below this point, BMI hits a baseline floor showing little effect of either age or wealth. Between-country variation in bBMI (range of 4.3 kg m(-2) ) is reliable across decades and age groups (R(2) = 0.83-0.88). Country-level estimates of bBMI show no relation to diabetes prevalence or country-level GDP (R(2) < 0.05), supporting its independence from excess body mass. Residual BMI (average BMI minus bBMI) shows better fit with both country-level GDP (R(2) = 0.55 vs. 0.40) and diabetes prevalence (R(2) = 0.23 vs. 0.17) than does conventional BMI. This method produces reliable estimates of bBMI across a wide range of nationally representative samples, providing a new approach to investigating population variation in body mass.

Effects of the February 2012 cold spell on terrestrial birds wintering in France

We document the mortality of terrestrial bird species wintering in France as a result of the 2012 February cold spell. We describe the range of species affected and how some of them reacted to the cold spell in term of movement and variation in body mass. Mortality records concerned 1,791 individuals from 42 species. Among terrestrial birds, Northern Lapwings Vanellus vanellus, Eurasian Woodcocks Scolopax rusticola and thrush species suffered the most from the cold spell. Among casualties, 56% of birds starved to death and 8.4% were predated. Collisions with vehicles accounted for 23.7% of deaths for all species, and reached 50% for Lapwings. Location of mortality records suggested that Lapwings and Woodcocks moved en masse towards the south and southwest of France to escape from the cold spell. Body mass of thrushes, Lapwings and Woodcocks birds was rapidly depleted because birds could not access food resources. On average, birds which were 30% lighter than birds weighed at the same period during normal winters had reached a lethal body mass. The results of this enquiry highlight the impact of such cold-weather events and the need, in particular for game bird species, to promote standardised enquiries on mortality when severe winter events occur.

Effect of water deprivation on baseline and stress-induced corticosterone levels in the Children's python (Antaresia childreni)

Corticosterone (CORT) secretion is influenced by endogenous factors (e.g., physiological status) and environmental stressors (e.g., ambient temperature). Heretofore, the impact of water deprivation on CORT plasma levels has not been thoroughly investigated. However, both baseline CORT and stress-induced CORT are expected to respond to water deprivation not only because of hydric stress per se, but also because CORT is an important mineralocorticoid in vertebrates. We assessed the effects of water deprivation on baseline CORT and stress-induced CORT, in Children's pythons (Antaresia childreni), a species that experiences seasonal droughts in natural conditions. We imposed a 52-day water deprivation on a group of unfed Children's pythons (i.e., water-deprived treatment) and provided water ad libitum to another group (i.e., control treatment). We examined body mass variations throughout the experiment, and baseline CORT and stress-induced CORT at the end of the treatments. Relative body mass loss averaged ~10% in pythons without water, a value 2 to 4 times higher compared to control snakes. Following re-exposition to water, pythons from the water-deprived treatment drank readily and abundantly and attained a body mass similar to pythons from the control treatment. Together, these results suggest a substantial dehydration as a consequence of water deprivation. Interestingly, stress-induced but not baseline CORT level was significantly higher in water-deprived snakes, suggesting that baseline CORT might not respond to this degree of dehydration. Therefore, possible mineralocorticoid role of CORT needs to be clarified in snakes. Because dehydration usually induces adjustments (reduced movements, lowered body temperature) to limit water loss, and decreases locomotor performances, elevated stress-induced CORT in water-deprived snakes might therefore compensate for altered locomotor performances. Future studies should test this hypothesis.

Moose body mass variation revisited: disentangling effects of environmental conditions and genetics

Large-scale geographical variation in phenotypic traits within species is often correlated to local environmental conditions and population density. Such phenotypic variation has recently been shown to also be influenced by genetic structuring of populations. In ungulates, large-scale geographical variation in phenotypic traits, such as body mass, has been related to environmental conditions and population density, but little is known about the genetic influences. Research on the genetic structure of moose suggests two distinct genetic lineages in Norway, structured along a north-south gradient. This corresponds with many environmental gradients, thus genetic structuring provides an additional factor affecting geographical phenotypic variation in Norwegian moose. We investigated if genetic structure explained geographical variation in body mass in Norwegian moose while accounting for environmental conditions, age and sex, and if it captured some of the variance in body mass that previously was attributed to environmental factors. Genetic structuring of moose was the most important variable in explaining the geographic variation in body mass within age and sex classes. Several environmental variables also had strong explanatory power, related to habitat diversity, environmental seasonality and winter harshness. The results suggest that environmental conditions, landscape characteristics, and genetic structure should be evaluated together when explaining large-scale patterns in phenotypic characters or life history traits. However, to better understand the role of genetic and environmental effects on phenotypic traits in moose, an extended individual-based study of variation in fitness-related characters is needed, preferably in an area of convergence between different genetic lineages.