Body Mass In Spring Research Articles

The Feast and the Famine: Spring Body Mass Variations and Life History Traits in a Pulse Resource Ecosystem.

AbstractPhenotypic plasticity is the most immediate mechanism of adaptative response to environmental change. Studying plastic changes in response to fluctuating environments provides insights into how such adjustments may impact life history traits. Here, we used a 14-year data set of repeated body mass measurements in male eastern chipmunks (Tamias striatus) to assess the extent of plastic changes for this trait in a resource pulse ecosystem. We first determined the magnitude of variation in body mass at the population level in response to the drastic change in food resource availability from American beech tree seeds (Fagus grandifolia). Males that emerged in the spring from winter torpor following a nonmast year had a lower body mass than males emerging after a mast year, but they tended to recover this loss by mid-June. We found significant among-individual variation in spring body mass plasticity (i.e., individual-by-environment interaction). We then investigated the relationships between individual spring body mass plasticity, longevity, and lifetime reproductive success. Interestingly, heavier males lived longer than lighter males, but more plastic males had a lower longevity and lower lifetime reproductive success than less plastic males. The report of such plastic response in a stochastic resource system provides valuable insights into the interplay between the costs and benefits of phenotypic plasticity as an adaptation to environmental fluctuations.

Altered natal dispersal at the range periphery: The role of behavior, resources, and maternal condition.

Natal dispersal outcomes are an interplay between environmental conditions and individual phenotypes. Peripheral, isolated populations may experience altered environmental conditions and natal dispersal patterns that differ from populations in contiguous landscapes. We document nonphilopatric, sex‐biased natal dispersal in an endangered small mammal, the Mt. Graham red squirrel (Tamiasciurus hudsonicus grahamensis), restricted to a single mountain. Other North American red squirrel populations are shown to have sex‐unbiased, philopatric natal dispersal. We ask what environmental and intrinsic factors may be driving this atypical natal dispersal pattern. We test for the influence of proximate factors and ultimate drivers of natal dispersal: habitat fragmentation, local population density, individual behavior traits, inbreeding avoidance, competition for mates, and competition for resources, allowing us to better understand altered natal dispersal patterns at the periphery of a species’ range. A juvenile squirrel's body condition and its mother's mass in spring (a reflection of her intrinsic quality and territory quality) contribute to individual behavioral tendencies for movement and exploration. Resources, behavior, and body condition have the strongest influence on natal dispersal distance, but affect males and females differently. Male natal dispersal distance is positively influenced by its mother's spring body mass and individual tendency for movement; female natal dispersal distance is negatively influenced by its mother's spring body mass and positively influenced by individual tendency for movement. An apparent feedback between environmental variables and subsequent juvenile behavioral state contributes to an altered natal dispersal pattern in a peripheral population, highlighting the importance of studying ecological processes at the both range center and periphery of species’ distributions.

Seasonal Time Keeping in a Long-Distance Migrating Shorebird.

Because of the complications in achieving the necessary long-term observations and experiments, the nature and adaptive value of seasonal time-keeping mechanisms in long-lived organisms remain understudied. Here we present the results of a 20-year-long study of the repeated seasonal changes in body mass, plumage state, and primary molt of 45 captive red knots Calidris canutus islandica, a High Arctic breeding shorebird that spends the nonbreeding season in temperate coastal areas. Birds kept outdoors and experiencing the natural photoperiod of the nonbreeding area maintained sequences of life-cycle stages, roughly following the timing in nature. For 6 to 8 years, 14 of these birds were exposed to unvarying ambient temperature (12 °C) and photoperiodic conditions (12:12 LD). Under these conditions, for at least 5 years they expressed free-running circannual cycles of body mass, plumage state, and wing molt. The circannual cycles of the free-running traits gradually became longer than 12 months, but at different rates. The prebreeding events (onset and offset of prealternate molt and the onset of spring body mass increase) occurred at the same time of the year as in the wild population for 1 or several cycles. As a result, after 4 years in 12:12 LD, the circannual cycles of prealternate plumage state had drifted less than the cycles of prebasic plumage state and wing molt. As the onset of body mass gain drifted less than the offset, the period of high body mass became longer under unvarying conditions. We see these differences between the prebreeding and postbreeding life-cycle stages as evidence for adaptive seasonal time keeping in red knots: the life-cycle stages linked to the initiation of reproduction rely mostly on endogenous oscillators, whereas the later stages rather respond to environmental conditions. Postbreeding stages are also prone to carryover effects from the earlier stages.

Forage-mediated density and climate effects on body mass in a temperate herbivore: a mechanistic approach.

The interplay between density and climate in shaping the dynamics of herbivore populations is widely acknowledged, and current research is fueled by the identification of mechanisms underlying their effects on individuals and populations. We assessed whether forage availability mediated the effects of density and winter climate on body mass of white-tailed deer (Odocoileus virginianus) yearlings by experimentally reducing deer density to 7.5 and 15 deer/km2 during eight growing seasons, and by using causal (graphical) hierarchical models and Bayesian hierarchical modeling to assess relationships. The abundance of preferred forage decreased with deer density and varied quadratically (positive parabola) with winter North Atlantic Oscillation (NAO), whereas the fall mass of yearlings increased with forage abundance and spring mass. Fall mass did not differ between experimentally reduced deer densities, yet experimental yearlings were 30% heavier than yearlings harvested at ambient densities. Hence, forage abundance simultaneously mediated the effects of density and climate on fall body mass, which was also influenced by carry-over effects of spring body mass. Our findings increase our ability to anticipate how temperate large herbivores will respond to ongoing changes in intrinsic (e.g., large-herbivore density) and extrinsic (e.g., climate) factors.

Reproduction in North American elk Cervus elaphus: paternity of calves sired by males of mixed age classes

Our objective was to examine effects of groups of mixed numbers and ages of male North American elk Cervus elaphus on the reproductive performance of females. We conducted research at the Starkey Experimental Forest and Range in northeastern Oregon, USA, during 1993‐2000. Each spring in late March, we released 40 female elk, eight yearling (9‐month old) male elk and 2‐8 branch‐antlered elk (i.e. ≥ 2 years of age during rut the following autumn) into a 622‐ha fenced pasture. Elk were gathered during autumn and early winter, and were brought to winter feeding grounds where blood samples were drawn to determine pregnancy status. The following spring, females were released into an 80‐ha pasture prior to parturition. We searched for and captured newborn calves and obtained ear‐punch samples for genetic analysis. We used 18 microsatellite loci to establish paternity of each calf. We varied the ratio of mature males (i.e. ≥ 3 years old) to female ratio from 0.03 to 0.21. As expected, mature males (older and heavier) were more successful in siring calves than were younger males. Within age classes, however, body mass in spring did not accurately predict mating success in autumn. Reproductive rates were not affected by season of grazing by cattle, yearling male to female ratio or mature male to female ratio. Sire age had no effect on mean dates of calf births or on calf weights. Neither sire age nor season of grazing by cattle had significant effects on calf weights; however, mean date of birth was significantly earlier when cattle grazing occurred during the previous autumn than when cattle grazed during the preceding spring. Furthermore, the number of calves sired by yearling males was greater when cattle grazing occurred during autumn, than when grazing occurred during spring. In the years with disruptive cattle grazing during rut, females mated not only with yearling males, in general, but often with those who were lighter in body mass during the previous spring than others in the same cohort. The extent to which those yearling males are untested in combat with older, dominant herd bulls may have genetic consequences leading to differences in fitness and subsequent reductions in calf survival.Please note that the supplementary information, including Appendix SI mentioned in this article, is available in the online version of this article, which can be viewed at www.wildlifebiology.com

SEASONAL BODY MASS AND HABITAT SELECTION OF SOME MIGRATORY PASSERINES OCCURRING IN ISRAEL

ABSTRACT Migratory passerines were mist-netted during the spring and autumn migrations at two localities in Israel: Ein Fashkha, a desert oasis near the Dead Sea, and Elon, a maquis vegetation area in the western Galilee. In both localities, mean body mass of the blackcap (Sylvia atricapilla) was significantly heavier in autumn, and heavier in the Galilee than in the oasis. More blackcaps were netted in spring at both sites. The robin (Erithacus rubecula) had heavier body mass in spring, and its capture rate was higher in autumn. In autumn, the blackcap passes through Israel loaded with fat on its way south to its winter quarters in East Africa. In spring, it arrives in relatively poor body condition after crossing the Sahara. A higher capture rate during springtime could be explained by the poor condition of the birds. The robin winters in Israel, and birds captured in autumn have just completed their migration, and carry little fat reserves, while those caught in spring are loaded with fat for their nor...

Density‐dependence vs. density‐independence – linking reproductive allocation to population abundance and vegetation greenness

1. Recent studies have shown that optimal reproductive allocation depends on both climatic conditions and population density. We tested this hypothesis using six years of demographic data from eight reindeer (Rangifer tarandus) populations coupled with data on population abundance and vegetation greenness [measured using the Enhanced Vegetation Index (EVI)]. 2. Female spring body mass positively affected summer body mass gain, and lactating females were unable to compensate for harsh winters as efficiently as barren ones. Female spring body mass was highly sensitive to changes in population abundance and vegetation greenness and less dependent on previous autumn body mass and reproductive status. Lactating females were larger than barren females in the spring. Moreover, female autumn body mass was positively related to female autumn body mass and reproductive success and was not very sensitive to changes in vegetation greenness and population abundance. 3. Offspring autumn body mass was positively related to both maternal spring and autumn body mass, and as predicted from theory, offspring were more sensitive to changes in vegetation greenness and population abundance than adult females. A lagged cost of reproduction was present as larger females who were barren, the previous year produced larger offspring than equally sized females that successfully reproduced the previous year. 4. Reproductive success was negatively related to female autumn body mass and positively related to female spring body mass. Moreover, females who successfully reproduced the previous year experienced the highest reproductive success. The fact that negative density-dependence was only present for females that had successfully reproduced the previous year further support the hypothesis that reproduction is costly. 5. This study shows that female reindeer buffer their reproductive allocation according to expected winter conditions and that their buffering abilities were limited by population abundance and a lagged cost of reproduction and enhanced by vegetation greenness.

Experimental evidence of cost of lactation in a low risk environment for a long‐lived mammal

In a previous experiment we have documented that organisms adopt a risk‐sensitive reproductive allocation when summer reproductive investment competes with survival in the coming winter (Bårdsen et al. 2008). This tradeoff is present through autumn female body mass, which acts as an insurance against unpredictable winter environmental conditions. We tested this hypothesis experimentally on female reindeer experiencing stable and benign winter feeding conditions. Additional supplementary feeding and removal of newborns represented two sets of experimental manipulations. Females in the supplementary feeding group increased more in winter body mass relative to control females. This manipulation, however, did not have any effect on summer body mass development for neither females nor offspring, but we found a positive effect of feeding on offspring birth mass for smaller females. In contrast, offspring removal did have a positive effect on summer body mass development as females in this group were larger in the autumn relative to control females. In essence, we documented two immediate effects as: (1) supplementary feeding did have a positive effect on spring body mass for smaller females; and (2) offspring removal did increase the female summer somatic growth as this had a positive effect on female autumn body mass. Additionally, we tested for lagged effects, but we could not document any biologically significant effects of neither manipulation in the coming spring. The fact that we only found rather weak effects of both manipulations was as expected for risk sensitive individuals experiencing benign environmental conditions over many years.

Expression of annual cycles in preen wax composition in red knots: constraints on the changing phenotype

Birds living in seasonal environments change physiology and behavior in correspondence to temporally changing environmental supplies, demands and opportunities. We recently reported that the chemical composition of uropygial gland secretions of sandpipers (Scolopacidae, order Charadriformes) changes during the breeding season from mixtures of monoesters to diesters, which fulfill specific functions related to incubation. A proper temporal match between the expression of diester preen waxes and incubation requires a flexible organization of the trait. Here we analyze the possible degrees of flexibility with reference to the functionality of better-understood molt and body mass cycles of free-living and captive red knots (Calidris canutus). The relative flexibility of seasonal cycles in preen wax composition was examined by two experimental perturbations: (1) giving birds restricted access to food and (2) monitoring them long-term under a constant photoperiodic regime. We found that wax type cannot change instantaneously, but that changing the type of wax is under similar organizational time constraints as the replacement of feathers. Just as molt and mass cycles, the seasonal rhythm of diester secretion appeared to be under endogenous control: most birds placed in a constant photoperiod still maintained seasonally changing preen waxes. Diester preen wax secretion was synchronized with the peak in body mass in spring, but became less well expressed under constant photoperiodic conditions and when food availability was limited.

SPRING-TO-FALL MASS GAIN IN A NORTHERN POPULATION OF NORTH AMERICAN PORCUPINES

Mammalian herbivores from northern environments often store fat in summer to decrease the energetic stress of winter. We measured mass gain during the spring-to-fall season in a Quebec population of North American porcupines (Erethizon dorsatum) and determined how it is affected by the age, sex, and reproductive status of individuals.Porcupinesgainedmasswithoutinterruptionfrommidspringtolatesummer, butmassgainsweremore important in mid- to late spring and late summer than at other times. This likely reflected local variations in the nutrient content of forage. Adult males lost mass during the rutting period of early fall. All age‐sex classes except lactating females gained about 3 kg, or 40% of their spring body mass. This is not markedly different from mass gains observed in other nonhibernating mammalian herbivores. We generate the hypothesis that in this population some ecological, behavioral, or physiological mechanism limits the rate of mass increase to about 21 g per day.

Contrast in adaptive mass gains: Eurasian golden plovers store fat before midwinter and protein before prebreeding flight.

Before predictable periods of high nutritional demand and little or no intake, vertebrates store fuel mainly composed of energy-dense lipids or energy-poor but protein-rich muscle tissue. Documenting contrasts in fuel composition and storage patterns within species, or even within individuals, would greatly help to elucidate the functional significance of the variety of storage strategies demonstrated in birds. We show here that the 40-50 g mass gain of 200 g in Eurasian golden plovers (Pluvialis apricaria) in autumn in The Netherlands consists of fat only, but that the similar gain in body mass in spring consists of proteinaceous tissue (pectoral and other skeletal muscle and possibly skin tissue). That the same golden plovers store energy in autumn and store protein in spring suggests that they face energy deficits in early winter and risk protein deficits in spring, especially perhaps after arrival on the breeding grounds in late April and early May. In autumn and winter their diet consists largely of protein-rich earthworms, but upon arrival on Low Arctic and montane tundras, golden plovers tend to eat berries which are rich in sugars but notably poor in proteins. We therefore propose that the build-up of proteinaceous tissue in spring reflects a strategic storage of a nutritional resource that is likely to be in short supply somewhat later in the year.

Interspecific competition in tree squirrels: do introduced grey squirrels ( Sciurus carolinensis ) deplete tree seeds hoarded by red squirrels ( S. vulgaris )?

Red squirrels (Sciurus vulgaris) and introduced eastern grey squirrels (S. carolinensis) scatterhoard seeds of broadleaf trees. Scatterhoarded seeds are an essential resource in spring and their consumption increases red-squirrel fitness. We examined whether grey squirrels partly deplete the high-energy food resources cached by red squirrels, reducing their consumption, in two ways: (1) at the population level, comparing energy intake of feeding on cached seeds between a study site with red and grey squirrels and one with only red squirrels present; and (2) at the individual level, in the study site where species co-exist, relating hoard recovery of red squirrels to the amount of core-area overlap with grey squirrels. There were no significant site differences in the mean daily energy intake of red squirrels feeding on seeds recovered from caches. However, in the red-grey site, during spring, red squirrels that had a high percentage of their home-range core area overlapped by grey squirrels had a lower daily energy intake than low-overlap red squirrels. Body mass of red squirrels in spring was negatively correlated with the percentage of interspecific core-area overlap, but not with core-area overlap with other red squirrels. Our data suggest that interspecific competition for scatterhoarded seeds, with grey squirrels pilfering red squirrels' food caches, caused a reduced energy intake in red squirrels with a high degree of interspecific core-area overlap, and reduced body mass in spring. Therefore, cache pilfering is likely to reduce reproductive output in red squirrels, and thus play a role in the replacement of red by grey squirrels.

Seasonal Variation in Thermogenic Capacity of Migratory Warbling Vireos

-Seasonal physiological adjustments are similar for migration and winter acclimatization in passerine birds, as both involve endurance muscular activity. Consequently, migratory disposition should elevate maximal thermogenic capacity (VO,,m) under cold stress, as winter acclimatization does for most temperate-wintering passerines. This hypothesis was tested with a Neotropical migrant, the Warbling Vireo (Vireo gilvus), during migration and summer residency in southeastern South Dakota. Vireos were subjected to cold stress in an atmosphere of 79% He/21% 02 (helox), with concurrent measurement of oxygen consumption during spring, summer and fall. In the spring, vireos had a significantly higher VO,,,m (17.7%) and tolerated colder temperatures in helox than either summer or fall birds. Standard metabolic rate was 0.643 ? SD of 0.133 ml 02 min-' (n = 6) in summer, but could not be measured in spring and fall as vireos were nocturnally active and failed to attain steady-state conditions, presumably as a result of Zugunruhe. The increment of VO,tum in spring, apparently, was not a function of higher body mass in spring, given that mass did not vary significantly between seasons. Elevated thermogenic capacity in spring may be adaptive as chances of encountering cold weather during spring migration in the northcentral United States are greater than at other seasons. Alternatively, enhanced thermogenic capacity in spring may be related to differential migratory speeds between spring and fall, which might select for increased endurance (with thermogenic capacity increasing as a byproduct) in spring birds. The ubiquity of this pattern among migratory passerines is unknown. Received 12 May 1994, accepted 27 January 1995. SHIVERING THERMOGENESIS in cold temperatures and long-distance migration are energetically expensive endeavors for small birds. Since both sustained shivering and long-distance flight represent forms of endurance muscular activity, adaptation for flight might be expected to influence thermogenic performance, or viceversa. Indeed, such coupled changes in maximal capacity for thermogenesis and exercise (locomotion) have been detected for some mammals (Hayes and Chappell 1986), although this apparently is not universal (Conley et al. 1985). Similar studies have not been performed on birds, probably because convincing measurements for maximal metabolism during flight are nonexistent (Marsh and Dawson 1989). An indirect test for such coupled changes in maximal metabolism associated with flight and thermogenesis is to measure thermogenic capacity in birds in migratory disposition. These birds are presumably adapted for sustained flight, but are not exposed to the cold-temperature extremes faced by Temperate Zone residents during winter. Nevertheless, a number of physiological and biochemical adjustments associated with improved cold tolerance and migratory disposition are similar. Fat is the major fuel for shivering (Marsh and Dawson 1989) and winter-acclimatized passerines often show increased levels of stored fat relative to summer-acclimatized birds (Blem 1990), especially in species exploiting unpredictable winter food resources (Rogers and Smith 1993). Stored fat also increases markedly before migration in most small migrants, especially in those migrating long distances (Blem 1990), and fat serves as the major fuel for migration (Dawson et al. 1983). Winter-acclimatized passerines exhibit elevated pectoralis-muscle activities of enzymes involved in lipid and carbohydrate catabolism, particularly the former (Marsh and Dawson 1982, Yacoe and Dawson 1983), suggesting an increased reliance on fat during shivering thermogenesis relative to summer birds. An increase in activities of enzymes involved in fatty acid oxidation is also a component of migratory disposition in several migrants (Marsh 1981, Lundgren and Kiessling 1985, 1986, Driedzic et al. 1993). In addition, plasma-free fatty acids and triglycerides, as well as pectoralis lipids, increase during premigratory fattening in some migrants (Driedzic et al. 1993); plasma-free fatty acids, glycerol and triglycerides, in addition to

The Importance of Body Reserves Accumulated in Spring Staging Areas in the Temperate Zone for Breeding in Dark-Bellied Brent Geese Branta b. bernicla in the High Arctic

Seasonal changes in body mass of Arctic-nesting Brent Geese are characterized by a depression in early April, followed by a sharp increase during pre-migratory fattening. Both male and female Brent Geese increased their body mass by 25-35% in the Wadden Sea in April/May. Paired females reach on average higher body masses than single females. Female Brent Geese that returned with offspring to the wintering quarters in western Europe had on average been heavier at spring departure from the staging grounds in the Wadden Sea, than those failing to raise offspring. This difference remained significant after correcting for body size (i.e. wing length). In males, corrected spring body mass had no effect on subsequent breeding success. Measurements of changes in body mass of incubating female Brent Geese, coupled to estimated flying costs (based on data on body mass, wing span and total wing area) showed that body reserves stored in the Wadden Sea were insufficient to accomplish both migration and successful breeding. Presumably the geese refuelled in the White Sea, in order to complete their spring migration and arrive on the breeding grounds in Taymyr in the condition necessary for successful breeding.

Spring Body Condition, Fecundity and Survival in Female Willow Ptarmigan

1. We examined variation in spring body mass (adjusted for structural size and number of days before clutch initiation) and its relationship with measures of fecundity and survival for populations of female willow ptarmigan at La Perouse Bay, Manitoba (Lagopus lagopus albus Gmelin) and Chilkat Pass, British Colfumbia (Lagopus lagopus alexandrae Grinnell) in northern Canada. 2. Adult and yearling hen ptarmigan showed an increase in body mass during spring at both La Perouse Bay (LPB) and Chilkat Pass (CP). Although hens at LPB had greater body mass than hens at CP there were no differences in patterns of body mass gain attributable to either years, age-classes, or sites. 3. No differences were found in measures of fecundity or survival between yearlings (1 year of age) in good and poor condition at both sites. At CP, adult (2+ years of age) hens in good condition produced heavy chicks, were more likely to be monogamous, and were more likely to return to the study area in subsequent years than hens in poor condition. Hens in good condition at LPB had higher return rates the following year than those in poor condition but showed no differences in fecundity. 4. As measures of fecundity were not related to a hen's spring body condition, hens in poor condition probably invest relatively more in reproduction than those in good condition. Return of yearling hens was not related to their body condition in spring; however, we did observe low return rates of adult hens in poor condition. Thus, we suggest that the 'cost' of reproduction may be cumulative over years for female willow ptarmigan.

Adaptations of Peromyscus for Winter Survival in an Appalachian Montane Forest

Both Peromyscus leucopus and P. maniculatus had slightly higher body mass in spring and summer than in autumn and winter. Mean resting metabolic rates of both species were highest in September and November. For both species, maximum nonshivering thermogenesis following norepinephrine dosage increased markedly in early autumn, declined in October and January following unseasonably warm periods, peaked in February during the coldest portion of the winter, and declined throughout the spring. Neither length of photoperiod nor minimum ambient temperature correlated with the variation in resting metabolic rates; however, both environmental factors correlated strongly with capacity for nonshivering thermogenesis.

Energy Utilization by Free‐Ranging Sceloporus Virgatus Lizards

Seasonal and sexual differences in daily energy allocation were evaluated for the striped plateau lizard (Sceloporus virgatus, Sauria: Iguanidae) from field measurements of metabolic rates (doubly labeled water), time—activity budgets, body temperatures, and energy storage rates, along with laboratory measurements of resting metabolism (gas exchange) and food utilization efficiency. In spring, males had higher field metabolic rates (FMRs) than females, but females consumed food factor while abroad and used the extra energy for producing eggs. Females were abroad about half as long as males (3.6 vs. 7.6 h/d) but an estimate of their energy metabolism while abroad was much higher than that of males (8.3 vs. 3.6 times resting metabolic rate). Males did not eat enough food to satisfy their energy and they lost body mass in spring. During summer, both sexes maintained constant body masses and steady—state energy budgets, but females had much higher FMRs and feeding rates than mules because females were abroad and active longer than males. Daily energy expenditure was positively correlated with duration of daily activity period. A lizard that was active 8 h/d had an FMR about 8 times higher than if it had remained inactive in a retreat all day. Thus S. virgatus can change its daily cost of living by nearly an order of magnitude by varying the time it spends abroad. Field behavior patterns are consistent with the hypothesis that these lizards regulate their activity in a manner that enhances survival and reproduction.