Seasonal, Age, and Sex Differences in Weight, Fat Reserves, and Plasma Corticosterone in Western Sandpipers

Western Sandpipers (Calidris mauri) were followed throughout their annual cycle along the Pacific Coast of North America. Changes in body condition and corticosterone were tracked at two overwintering sites (Ensenada, Mexico, and San Diego, California), four migration stopover sites (Bodega Bay, California, Grays Harbor and False Bay, Washington, and Hartney Bay, Alaska), and a breeding site (Nome, Alaska). Adult males and females had elevated weight and fat scores during spring migration, breeding, and autumn migration relative to lean levels during winter. Although elevated mass and fat reserves may hinder escape from predators and are not necessary at wintering sites with benign conditions, the cost-benefit trade-offs with weight and agility shift during migration and breeding. Extra fat and muscle are necessary for fueling the long flight to and from the breeding grounds and serve as a hedge against unpredictable food and weather conditions on the breeding grounds. First-year birds weighed less and had lower fat reserves at smaller stopover sites than migrants at a large stopover site. Plasma levels of corticosterone revealed seasonal differences in the adrenocortical response to stress, although initial levels were fairly consistent across seasons. The highest stress response of the annual cycle in males was during autumn migration, in contrast to the lowest levels during early spring migration, breeding, and overwintering. Late-spring migrants and autumn premigrants had intermediate stress responses. An emerging pattern from this and other shorebird studies is that migrants with imminent flights of more than 1000 km have elevated corticosterone levels

Defining the Degree of Seasonality and its Significance for Future Research

Seasonality describes cyclic and largely predictable fluctuations in the environment. Such variations in day length, temperature, rainfall, and resource availability are ubiquitous and can exert strong selection pressure on organisms to adapt to seasonal environments. However, seasonal variations exhibit large scale geographical divergences caused by a whole suite of factors such as solar radiation, ocean currents, extent of continents, and topography. Realizing these contributions in driving patterns of overall seasonality may help advance our understanding of the kinds of evolutionary adaptations we should expect at a global scale. Here, we introduce a new concept and provide the data describing the overall degree of seasonality, based on its two major components—amplitude and predictability. Using global terrestrial datasets on temperature, precipitation and primary productivity, we show that these important seasonal factors exhibit strong differences in their spatial patterns with notable asymmetries between the southern and the northern hemisphere. Furthermore, our analysis reveals that seasonality is highly diverse across latitudes as well as longitudinal gradients. This indicates that using a direct measure of seasonality and its components, amplitude and predictability, may yield a better understanding of how organisms are adapted to seasonal environments and provide support for predictions on the consequences of rapid environmental change

The relationship of telomere length to baseline corticosterone levels in nestlings of an altricial passerine bird in natural populations.

BackgroundEnvironmental stressors increase the secretion of glucocorticoids that in turn can shorten telomeres via oxidative damage. Modification of telomere length, as a result of adversity faced early in life, can modify an individual's phenotype. Studies in captivity have suggested a relationship between glucocorticoids and telomere length in developing individuals, however less is known about that relationship in natural populations.MethodsIn order to evaluate the effect of early environmental stressors on telomere length in natural populations, we compared baseline corticosterone (CORT) levels and telomere length in nestlings of the same age. We collected blood samples for hormone assay and telomere determination from two geographically distinct populations of the Thorn-tailed Rayadito (Aphrastura spinicauda) that differed in brood size; nestlings body mass and primary productivity. Within each population we used path analysis to evaluate the relationship between brood size, body mass, baseline CORT and telomere length.ResultsWithin each distinct population, path coefficients showed a positive relationship between brood size and baseline CORT and a strong and negative correlation between baseline CORT and telomere length. In general, nestlings that presented higher baseline CORT levels tended to present shorter telomeres. When comparing populations it was the low latitude population that presented higher levels of baseline CORT and shorter telomere length.ConclusionsTaken together our results reveal the importance of the condition experienced early in life in affecting telomere length, and the relevance of integrative studies carried out in natural conditions

Baseline and Stress-Induced Plasma Corticosterone during Long-Distance Migration in the Bar-Tailed Godwit, Limosa lapponica

The specific roles of corticosterone in promotion of avian migration remain unclear even though this glucocorticosteroid is elevated in many migrating bird species. In general, glucocorticosteroids promote metabolic homeostasis and may elicit effects on feeding and locomotion. Because the migratory stages of refueling and flight are characterized by distinct behaviors and physiology, the determination of corticosterone levels during each stage should help identify potential processes in which corticosterone is involved. We measured baseline levels of corticosterone in bar-tailed godwits (Limosa lapponica) during two distinct stages of migration: (1) immediately after arrival at a false stopover site just short of theWadden Sea and (2) throughout the subsequent 4-wk refueling period on the Wadden Sea. Plasma corticosterone was higher in arriving than in refueling birds. In addition, corticosterone increased with size-corrected body mass during the refueling phase, suggesting that corticosterone rises as birds prepare to reinitiate flight. Therefore, elevated corticosterone appears associated with migratory flight and may participate in processes characterizing this stage. We also performed a capture stress protocol in all birds and found that corticosterone increased in both arriving and refueling godwits. Therefore, the normal course of migration may be typified by corticosterone concentrations that are lower than those associated with stressful and life-threatening episodes.

Age and food deprivation affects expression of the glucocorticosteriod stress response in Magellanic penguin (Spheniscus magellanicus) chicks

We examined how the glucocortical stress response in free‐living Magellanic penguin (Spheniscus magellanicus) chicks changes with age and whether adrenocortical function of chicks within a brood varies in relation to food provisioned by adults. Chicks showed little corticosterone response to capture stress shortly after hatching, an intermediate response around 45‐d posthatch, and a robust stress response near fledging. However, in response to an adrenocorticotropic hormone (ACTH) challenge, hatchlings were capable of secreting corticosterone at adult‐like levels. The larger sibling in broods of two showed a similar gradual stress‐response development pattern. In contrast, by day 45, when differences in body condition were well established between siblings, the smaller, food‐deprived chicks significantly increased baseline levels of corticosterone but showed normal stress‐induced levels. Near fledging, baseline levels had returned to normal, but stress‐induced levels were lower than expected. Similar to altricial species, normally developing semialtricial Magellanic penguin chicks do not express a robust corticosterone stress response until near fledging. Chronic stressors such as food deprivation cause corticosterone use to be up‐regulated earlier than expected. However, in cases of extended chronic stress, down‐regulation may ensue, thus avoiding the negative effects of chronically elevated levels of corticosterone

Physiological condition in Magellanic Penguins: Does it matter if you have to walk a long way to your nest?

Colony edges, as opposed to interiors, are often considered less advantageous nesting places in colonial species. For temperate-breeding penguins, inland colony edges should be less desirable than other edges, as there are added costs of walking farther inland, and ambient temperatures are higher. During settlement and incubation, we compared body condition and baseline and stress-induced levels of the hormone corticosterone in male Magellanic Penguins (Spheniscus magellanicus) nesting on the sea edge of a colony with those nesting on the inland edge, \u3e800 m from shore. Body condition in both groups was significantly lower during settlement than during incubation, but was similar in both groups within breeding stages. Corticosterone levels were similar between breeding stages and for groups within each breeding stage. While body condition can vary over time, penguins appear to be well buffered to physiological extremes, as they do not show modification of corticosterone levels with variations in nesting conditions

Metabolic profile of long-distance migratory flight and stopover in a shorebird

Migrating birds often complete long non-stop flights during which body energy stores exclusively support energetic demands. The metabolic correlates of such long-distance travel in free-living migrants are as yet poorly studied. Bar-tailed godwits, Limosa lapponica taymyrensis, undertake a 4500 km flight to their single spring stopover site and thus provide an excellent model in which to determine the energy fuels associated with endurance travel. To this end, we evaluated plasma concentrations of six key metabolites in arriving godwits caught immediately upon landing near their stopover site. Initial metabolite levels were compared with levels after 5 h of inactive rest to determine how flight per se affects energy metabolism. Birds refuelling on the stopover site were also examined. Arriving godwits displayed elevated plasma free fatty acids, glycerol and butyrate, confirming the importance of lipid fuel in the support of extended migratory activity. Furthermore, elevated plasma triglycerides in these birds suggest that fatty acid provisioning is facilitated through hepatic synthesis and release of neutral lipids, as previously hypothesized for small migrants with high mass-specific metabolic rates. Finally, elevations in plasma uric acid suggest that protein breakdown contributes to the support of long-distance movement, to possibly maintain citric acid cycle intermediates, gluconeogenesis and/or water balance

Stress Responses in Tropical Sparrows: Comparing Tropical and Temperate Zonotrichia

Seasonal modulation of the adrenocortical response appears to be ubiquitous in mid- to high- latitude vertebrates but has not been investigated in tropical vertebrates. Previous studies demonstrate that temperate passerines show seasonality in corticosterone secretion and corticosteroid binding globulin capacities. We examined seasonal and sex differences in the stress response in an equatorial population of Zonotrichia capensis, the only Zonotrichia that breeds in the tropics, and compared the results with those of northern Zonotrichia. Seasonal differences in tropical Zonotrichia would presumably be independent of photoperiod and thus directly related to such activities as reproduction and feather molt. In addition, we investigated the possible role of binding globulin as a sex steroid binding globulin, as suggested for temperate passerines. Similar to northern congeners, Z. capensis show seasonal modulation in total corticosterone and binding globulin capacity with higher levels during breeding than molt. However, unlike many temperate passerines, there are no sex differences in corticosterone secretion or binding globulin capacity. Furthermore, the seasonal differences in total corticosterone diminish when the free levels are calculated. The contrast between equatorial and northern congeners indicates factors such as breeding environment and life-history strategy may play important roles in shaping stress response in these species

Experimental chronic noise is related to elevated fecal corticosteroid metabolites in lekking male greater Sage-Grouse (Centrocercus urophasianus).

There is increasing evidence that individuals in many species avoid areas exposed to chronic anthropogenic noise, but the impact of noise on those who remain in these habitats is unclear. One potential impact is chronic physiological stress, which can affect disease resistance, survival and reproductive success. Previous studies have found evidence of elevated stress-related hormones (glucocorticoids) in wildlife exposed to human activities, but the impacts of noise alone are difficult to separate from confounding factors. Here we used an experimental playback study to isolate the impacts of noise from industrial activity (natural gas drilling and road noise) on glucocorticoid levels in greater sage-grouse (Centrocercus urophasianus), a species of conservation concern. We non-invasively measured immunoreactive corticosterone metabolites from fecal samples (FCMs) of males on both noise-treated and control leks (display grounds) in two breeding seasons. We found strong support for an impact of noise playback on stress levels, with 16.7% higher mean FCM levels in samples from noise leks compared with samples from paired control leks. Taken together with results from a previous study finding declines in male lek attendance in response to noise playbacks, these results suggest that chronic noise pollution can cause greater sage-grouse to avoid otherwise suitable habitat, and can cause elevated stress levels in the birds who remain in noisy areas