Molt Status Research Articles

Diet of moulting Swainson's Thrushes (Catharus ustulatus) and Tennessee Warblers (Leiothlypis peregrina) at a stopover site during fall migration measured with fecal DNA metabarcoding

Moult and migration are energetically demanding and require adequate nutrition. In some species, individuals may interrupt their fall migration to moult at discrete stopover locations outside of their breeding grounds (i.e., moult-migration) leading to competing nutritional demands for moult and migration. Here, we use DNA barcoding of fecal samples to compare the diet of moulting and actively migrating (post-moult) Swainson’s Thrushes (Catharus ustulatus) and Tennessee Warblers (Leiothlypis peregrina) during their fall migration stopover at a large urban greenspace in Montreal, Canada. Diet differed according to moult status, species, and seasonality. Swainson’s Thrushes had a broad diet with frequent detections of both insects and berry-producing shrubs; while detections in Tennessee Warblers’ diets were mainly arthropods. For both species, more actively migrating individuals consumed fleshy-fruiting plants than moulting individuals. A higher proportion of moulting birds consumed arthropods compared to active migrants, due to either arthropod availability or a dietary preference for proteinaceous foods to grow feathers. Both species and moult classes consumed more native plants than non-native plants later in the season. We show the importance of managing urban greenspaces with native plants and diverse food sources that can provide for the different dietary needs of migratory birds.

Colony attendance and moult pattern of Cory's Shearwaters (Calonectris borealis) differing in breeding status and age

Migratory birds must fit three costly life‐history events within the annual cycle, reproduction, moult and migration, to minimize their overlap and maximize survival and breeding success. However, some seabirds, such as Cory's Shearwater Calonectris borealis, overlap body moult and breeding, with flight feather renewal occurring in late chick‐rearing. In contrast, the moult patterns of non‐breeding adult (sabbatical) and immature Cory's Shearwaters, which also attend the colony during the breeding season, remain poorly understood. Furthermore, the potential implications of life‐stage and breeding status trade‐offs on moult status and colony attendance in non‐breeders has rarely been investigated. Surveying different areas within one colony between June and September 2013 and 2014, we studied the age and breeding status composition of birds attending the breeding colony and scored moult of their body (breast and upper‐neck), wing and tail feathers. We found that in addition to breeders (n = 165), 57.6% of the birds (n = 389) attending the colony were 4‐ to 10‐year‐old immatures (n = 132) and adult sabbatical shearwaters (n = 92). Sabbaticals and 8‐ to 10‐year‐old immatures (n = 28) were present at the colony during incubation, whereas only three sabbatical birds and no 8‐ to 10‐year‐old immatures were captured in late chick‐rearing. Conversely, 4‐ to 7‐year‐old immatures arrived later in the season but were still present in late chick‐rearing. Sabbatical and 8‐ to 10‐year‐old immatures were moulting body feathers at the same time as adult breeders, whereas, among 4‐ to 7‐year‐old immatures, older birds moulted earlier than younger birds. A larger proportion of sabbatical birds were replacing tail feathers compared with adult breeders. However, there was no evidence that sabbaticals or 8‐ to 10‐year‐old immatures differed in wing moult from adult breeders until August. Overall, our study shows that colony attendance by non‐breeding adults and immatures is widespread in this population. The synchronous moult schedule of flight and body feathers across age groups at different life‐history stages may suggest that this aspect of moult is controlled by environmental conditions.

Meta‐analytic assessment of physiological markers for decapod crustacean welfare

AbstractDecapod crustacean welfare is not only an ethical consideration for legislative purposes. Under culture and fishery settings, poor environmental conditions and operator practices can cause stress, which compromises the immune system and increases the risk of disease. For finfish, there are established environmental and animal (group, individual) welfare indicators. This is not the case for crabs, lobsters or shrimp. While environment‐based indicators like temperature, pH and oxygen levels are easily transferable, there is no consensus for a common measure of stress to monitor welfare in decapod crustaceans. To address this shortcoming, we conducted a meta‐analysis of the primary literature to test for relationships between haemolymph (blood) condition, for example, levels of glucose, L‐lactate, haemocytes (n = 8), and sources of physical stress, for example, handling, trawling, emersion and transport (n = 12). Despite variations in effect sizes (n = 459), generalised linear mixed models repeatedly ranked L‐lactate (followed by urea and glucose) as the most significant physiological predictor of stress in the haemolymph, with trawling followed closely by emersion as the most impactful stressors. Duration post (stress) exposure, sex (male, female), water temperature and moult stage (pre‐, inter‐, post‐moult) were not associated significantly with stress prediction using the selected biochemical and cellular parameters, however, moult status was undefined in ~48% of literature sources and should be interpreted with caution. We present evidence that quantitating L‐lactate levels in the haemolymph represents a physiologic operational welfare indicator of decapod crustaceans, which complements existing condition/vigour indices.

Validation of the water content of the digestive gland as an indicator of nutritional condition in the American lobsterHomarus americanus(H. Milne Edwards, 1837) (Decapoda: Nephropidae)

AbstractSimple nutritional condition indicators are needed to provide information on the influence of ecosystem changes on the populations of the American lobster Homarus americanus (H. Milne Edwards, 1837) on various timescales. This study validates the use of the water content (% wet mass) of the digestive gland as an indicator of nutritional condition in the lobster (carapace length 65–127 mm) by assessing its capacity to estimate digestive-gland lipid reserves under variable environmental and physiological conditions. The validation was completed using samples from wild lobsters dissected shortly after being captured during different seasons and in various locations in the St. Lawrence Estuary and Gulf of St. Lawrence (GSL), and data from an environmentally realistic laboratory study on post-ovigerous females from the southern and the northern GSL sampled at different stages of their molt cycle. In both wild and experimental lobsters, water content was the best predictor of lipid reserves compared to other condition indicators (i.e., condition factor, various digestive-gland indices, and hemolymph Brix index). A strong linear relationship was found between lipid and water contents. Lipid content and interrelated molting status were identified as two important factors leading to the variations in water-fat regression equations among groups of wild or experimental lobsters. As lipid content could vary spatiotemporally in unexpected ways in a changing environment, it is recommended to use a sampling event-specific regression line to estimate digestive-gland lipid content from measured water content in field monitoring programs. Combining water content with molt status indicators such as Brix index is recommended to support interpretation of the observed variations in condition.

Maintaining control: metabolism of molting Arctic seals when hauled out and in water.

Seals haul out of water for extended periods during the annual molt, when they shed and regrow their pelage. This behavior is believed to limit heat loss to the environment given increased peripheral blood flow to support tissue regeneration. The degree to which time in water, particularly during the molt, may affect thermoregulatory costs is poorly understood. We measured the resting metabolism of three spotted (Phoca largha), one ringed (Pusa hispida), and one bearded (Erignathus barbatus) seal during and outside the molting period, while resting in water and hauled out. Metabolic rates were elevated in spotted and ringed seals during molt, but comparable in water and air for individuals of all species regardless of molt status. Our data indicate that elevated metabolism during molt primarily reflects the cost of tissue regeneration, while increased haul out behavior is driven by the need to maintain elevated skin temperatures to support tissue regeneration.

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Application of a global age-coding system (“WRP”), based on molts and plumages, for use in demographic and other studies of birds

Abstract Determination of a bird’s age or cohort is critical for studies on avian demography, occurrence patterns, behavior, and conservation management. Age designations have largely been developed in north-temperate regions and utilize calendar-based or seasonally based codes; however, in tropical regions and in the southern hemisphere, these coding systems have limited utility at best. To address these issues, we had previously devised the “WRP system,” based on the nomenclature of Humphrey and Parkes (H–P) and Howell et al., which defines molts in an evolutionary context applicable to birds globally. Here we refine and build upon core concepts and definitions of the WRP coding system, resolving key limitations that were identified during its first decade of use. The WRP system employs a three-letter alpha code in which each letter describes a different aspect of H–P terminology: the molt cycle (which informs a bird’s age) and molt and plumage status within the cycle (each of which can also inform age). Here we recommend the continued use of most of the original (“core”) WRP coding while augmenting the system with an optional adjunct-code entry for comprehensiveness, clarity, and flexibility, and we clarify a few additional codes to cover less common molting and plumage strategies. For most users, from 7 to 13 core and 1 adjunct WRP code will be sufficient to describe all plumages and provide molt status and ages for demographic studies or other purposes. The revised WRP system is flexible enough to be adapted to the specific goals of programs while also providing core codes that can facilitate the comparison of avian age, molt, and plumage status on a global basis. We anticipate that our revised and standardized version of the WRP system will be easily adopted and could eventually replace calendar-based and seasonally based coding.

Lethal and sublethal effects of the anti‐sea lice formulation Salmosan® on the Pacific spot prawn (Pandalus platyceros)

AbstractThe effects of the aquaculture chemotherapeutant Salmosan® (active ingredient [a.i.]: azamethiphos) were examined in Pacific spot prawns (Pandalus platyceros) at three temperatures (5, 11, and 17°C). Post‐molt prawns were more sensitive to Salmosan® than intermolt prawns; repeated (3x) 1‐hr LC50 values for post‐molt prawns ranged from 17 (9.3–31 95% confident intervals) to 40 (25–63) μg/L a.i. while intermolt prawns survived 3 × 1‐hr exposures up to 100 μg/L a.i. Using LC50 values, Salmosan® was approximately 2.4 times more toxic at 17 versus 5°C. Temperature significantly altered chemosensory and locomotory behaviors in intermolt prawns with the highest activity at the intermediate temperature. Significant decreases in antennule flicking (84 and 104% over controls) were seen at 17°C after 3 × 1‐hr pulse exposures to 50 and 100 μg/L a.i., respectively. Temperature, but not Salmosan®, affected molting success: at 17°C significantly lower survival was seen during ecdysis (60% of those at 5°C) and at 5°C, molt time was longer (41 ± 3 days) compared to 11°C (34 ± 4 days) or 17°C (21 ± 4 days). Life stage (molt status) and environmental parameters (temperature) alter the effects of Salmosan® to non‐target spot prawns.

Melanin-based ornament darkness positively correlates with across-season nutritional condition.

Sexually dimorphic ornamental traits are widely regarded as indicators of nutritional condition. However, variation of nutritional condition outside the reproductive and the ornament production seasons has rarely been considered, although it affects the generality of information content, especially for ornaments that may be used across the year. We measured several indicators of migratory and molt condition in male and female blackcaps (Sylvia atricapilla) during their autumn migration, and quantified their crown reflectance. We detected robust correlations between migratory and molt condition indices, and the correlation structure was similar in the two sexes. Furthermore, the across‐season measure of body condition was positively related to the darkness of the black crown in males, while being unrelated to reflectance traits of the reddish crown in females. Our results reinforce the possibility that some melanin‐based ornaments may be year‐round indicators of individual quality via their dependence on nutritional condition.

Body Mass and Primary Molt Patterns of Greater Sage-Grouse in Colorado

Patterns in body mass and molt provide useful information about how birds interact with their environment and act as potential explanatory variables in behavioral and demographic differences among sex and age classes. We collected population data for Greater Sage-Grouse (Centrocercus urophasianus) in Jackson and Moffat counties, Colorado, from 1973 to 1993 prior to consideration of federal listing of the species under the Endangered Species Act. Using spotlights and long-handled nets, we located and captured Greater Sage-Grouse while they roosted (primarily at night). Each captured bird was banded and released near the site of capture. We recorded the molt status of the primary flight feathers (1–10) and measured body mass. Most birds were captured prior to and during breeding (March–May) and during the brood-rearing period (July–September). Replacement of primary (P) flight feathers was initiated in May, starting with the first primary (P1), and was completed at the last primary (P10) by late September for adult (ASY) and subadult (SY) males, and by October for hatch-year males (young of the year, HY). Adult and subadult females did not replace primary flight feathers until after nesting was completed, starting in June. Primaries 1–3 were replaced within a week of the hen leaving the nest site, with or without chicks. Primary replacement then was similar to that of adult and subadult males and was completed before early October. A few late-nesting hens retained P10 and P9 into early October. Young of the year rarely replaced juvenal P9 and P10 in the year of hatching. Body mass of males peaked (x = 3000 g for adults, and 2200 g for yearlings) in March–April when birds were primarily feeding on sagebrush and then decreased to late May and reached seasonal lows (x = 2200 g) in July–August. Mass of females peaked in April (x = 1640 g) and decreased to 1250 g in August.

Thermoregulatory costs in molting Antarctic Weddell seals: impacts of physiological and environmental conditions: Themed Issue Article: Conservation of Southern Hemisphere Mammals in a Changing World.

For polar marine mammals, the energetic cost of thermoregulation depends on ambient conditions in the highly variable surrounding environment. Heat conservation strategies used by pinnipeds to reduce total heat loss include small surface area to volume ratios, the ability to limit perfusion and thick subcutaneous blubber layers. There are limits to how cool the skin surface may remain without compromising function, especially during the annual pelage molt, when hair and skin are replaced. To determine if actively molting seals incur higher thermoregulatory costs, surface temperature (ST) and heat flux (HF) were measured in 93 adult female Weddell seals (Leptonychotes weddellii) both prior to and during the active molting period using direct sensors and infrared imaging. Linear mixed-effect models revealed that ST increased significantly with increased ambient temperature and decreased wind speed (contributing 44.6 and 41.7% of the attributed variance, respectively). Seal STs were not impacted by molt status, but were maintained at 11.2 ± 0.3°C warmer than the ambient temperature. Infrared imaging results averaged 15.1 ± 1.4°C warmer than direct ST measurements. In contrast, HF was significantly higher in seals in early molting stages compared to the pre-molt season ( P < 0.001) and molt status accounted for 66.5% of the variance in HF. Thermoregulatory costs calculated from estimated basal metabolic rate and measured HF were more than double for molting seals as compared to those in pre-molt. This suggests that perfusion is increased during molt to support follicle development, despite the increased energetic costs associated with higher HF rates. Because ST, HF and thermoregulatory costs are strongly influenced by ambient conditions, molt timing is likely under selective pressure to occur during the warmest period of the year. Shifts in environmental conditions that delay molt phenology or increase HF rates could negatively impact seal populations by further increasing thermoregulatory costs.

Roseate Terns Sterna dougallii on the southeast coast of South Africa: information on moult and migratory status

Determining the migratory status of seabird populations is crucial for addressing conservation concerns. The Roseate Tern Sterna dougallii is considered endangered in South Africa in view of its small breeding population and the threats to eggs and chicks. Earlier works based on capture-recapture data suggest that this population adopts a partial migratory strategy. Updated capture-recapture data were combined with new data on moult and stable isotopes of scapular feathers to determine whether subpopulations could be identified in the South African breeding population. Moult data on 404 individuals failed to identify subpopulations, but two groups were identifiable with the stable isotopes: one group of four individuals exhibiting low carbon and nitrogen stable isotope ratios and a second group (comprising the remaining 152 individuals) with significantly higher ratios. The isotope data suggest that birds from the two groups moulted in different areas. Comparisons with published studies showed that the 152 individuals had likely moulted their scapulars in South African waters, but the moulting area for the remaining four individuals could not be ascertained due to the absence of detailed isoscapes in the southern part of the Mozambique Channel. Further work investigating the genetic differentiation between South African and Madagascan Roseate Terns may bring new insight into the migratory behaviour of the South African population.

The effect of short-term feed-deprivation and moult status on feeding behaviour of the Pacific white shrimp (Litopenaeus vannamei)

There is increasing recognition of the need to understand behaviours of species important in aquaculture to facilitate their production, however to date there has been limited focus in this area. The Pacific white shrimp (Litopenaeus vannamei), for example, is the most cultivated species in crustacean aquaculture globally, yet there are few studies that have addressed its feeding behaviour in detail. The objective of the present study was to evaluate the feeding behaviour of L. vannamei in response to feed-deprivation and moult status. Twenty-four juvenile shrimp (10.51 ± 2.17 g) were divided across three different feed-deprivation conditions (+0 h (control), +24 h or +48 h; n = 8 per treatment). Shrimp in all treatment groups were provided with their last food intake at 19.00 and subsequently experienced 14 h feed-deprivation. Those in the control group were recorded for behaviour at 09.00 the following day and were not feed-deprived for any additional time (+0 h), whereas the other treatments were feed-deprived by one (+24 h treatment) or two (+48 h treatment) extra days. Moult status was constantly monitored as it changed in all shrimp throughout the course of the experiment. Shrimp, provided with food, were observed individually via video in test arenas for 20 min where behaviours (e.g. inactivity, detection, feeding, attraction-to-feed) were recorded. Each shrimp was observed five times across different days with three days between recordings to obtain information on within-individual in addition to between-individual variation. Shrimp feed-deprived for +24 h and +48 h showed significantly increased feeding activity compared to the control group, which spent more time inactive and performing detection behaviours. Shrimp deprived of food for +48 h also had higher attraction-to-feed score, which were positively correlated with feeding activity. Shrimp in the inter-moult stage displayed increased feeding activity and a higher attraction-to-feed score. Longer periods of feed-deprivation reduced within- and between-individual variation across the majority of the behaviours measured. The results of this study highlight the relevance of feed-deprivation and moult status in nutritional trials and provide important baseline information for developing the use of behaviour to improve L. vannamei production.

Prey Selection in the Queen snake, Regina septemvittata, in Streams of the Northern Panhandle of West Virginia, U.S.A.

Regina septemvittata (Queen snake) is a semi-aquatic snake occurring throughout central and eastern North America that exhibits extreme dietary specialization, feeding almost exclusively on freshly molted crayfishes. Though it is known R. septemvittata forage on crayfishes, little is understood about prey preferences at the species and genus level. Because different crayfish species have varying life history patterns, and molting frequency is allied to life history attributes, it is not clear whether there is a preference based on crayfish species or prey availability based on molt state. To determine if R. septemvittata has preferences for species, we surveyed four streams in the northern panhandle of West Virginia for R. septemvittata and completed seasonal life history studies on crayfish species occurring in those streams from March through October 2018. Over the collecting season 101 Queen snakes were captured. From these, we recovered 24 prey samples that were subsequently identified using either polymerase chain reaction (PCR) or visual identification. Monthly crayfish sampling was used to determine molting frequency of the two available prey species in the study streams: Cambarus carinirostris and Faxonius obscurus. Preliminary results seem to indicate that freshly molted crayfish availability dictates foraging behavior in R. septemvittata, and a lack of specialization at the taxonomic level occurs in this species.

Development of Thermoregulatory Capability in Weddell Seal Pups

One of the greatest metabolic costs for endotherms is the energy allocated to thermoregulation. Weddell seals (Leptonychotes weddellii) are the southernmost breeding mammals, and as such are born into one of the most challenging thermal environments on the planet. During their nursing period, Weddell seal pups must develop the capability to survive both on the ice and in the water. Pups also concurrently shift from the use of fur to a reliance on blubber for insulation. This study examined the thermal and energetic costs associated with development and thermoregulation in Weddell seal pups. Metabolic rate (MR) in air was measured longitudinally for 4 pups every 2 weeks, starting at 1 week of age through the transition to independence (7 weeks); MR in water was measured in the same pups beginning at 3 weeks. Additionally, we assessed the molt status of each pup, and estimated body composition (blubber vs. lean mass) based on an elliptical cones model. There was a high degree of individual variability in mass‐specific MR in air in 1 week old pups (5.96–10.87 ml O2 min−1 kg−1), though in general it remained stable or decreased slightly from 1–7 weeks of age. Mass‐specific MR in water declined from 3 weeks to 7 weeks of age for 2 of the 4 pups, and remained stable for 2 pups. The difference between mass‐specific MR in air and in water also decreased from 3 to 7 weeks for 2 pups and remained steady for 2 pups; but by 5 weeks of age the difference between MR in air and in water was marginal for all 4 pups. Timing of the initiation of the molt and molt duration was also variable; two pups had molted patches by 3 weeks of age, and all but 1 pup were fully molted by 7 weeks of age. All pups gained mass from 1 to 5 weeks of age at an average rate of 2.02 ± 0.09 kg day−1 and the proportion of blubber increased from 1–3 weeks (25% to 38% of body mass). Blubber proportion remained steady from 3–5 weeks (38% to 40% of body mass) because pups gained proportionally more lean mass (61% of total mass gained). By 7 weeks, 3 of the 4 pups had weaned and were losing mass. Timing of MR equivalence in air and water did not vary with molt status (amount of lanugo) or with estimated body composition. Overall, these results indicate that Weddell seal pups have developed their thermal capabilities by ~5 weeks of age to protect themselves against increased heat loss in water, independent of the amount of lanugo fur or body composition.Support or Funding InformationThis project was funded by the National Science Foundation, Office of Polar Programs (#1543539).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The relationship of blue crab (Callinectes sapidus) size class and molt stage to disease acquisition and intensity of Hematodinium perezi infections.

In the blue crab, Callinectes sapidus, early studies suggested a relationship between smaller crabs, which molt more frequently, and higher rates of infection by the dinoflagellate parasite, Hematodinium perezi. In order to better explore the influence of size and molting on infections, blue crabs were collected from the Maryland coastal bays and screened for the presence of H. perezi in hemolymph samples using a quantitative PCR assay. Molt stage was determined by a radioimmunoassay which measured ecdysteroid concentrations in blue crab hemolymph. Differences were seen in infection prevalence between size classes, with the medium size class (crabs 61 to 90 mm carapace width) and juvenile crabs (≤ 30 mm carapace width) having the highest infection prevalence at 47.2% and 46.7%, respectively. All size classes were susceptible to infection, although fall months favored disease acquisition by juveniles, whereas mid-sized animals (31–90 mm carapace width) acquired infection predominantly in summer. Disease intensity was also most pronounced in the summer, with blue crabs > 61 mm being primary sources of proliferation. Molt status appeared to be influenced by infection, with infected crabs having significantly lower concentrations of ecdysteroids than uninfected crabs in the spring and the fall. We hypothesize that infection by H. perezi may increase molt intervals, with a delay in the spring molt cycle as an evolutionary adaptation functioning to coincide with increased host metabolism, providing optimal conditions for H. perezi propagation. Regardless of season, postmolt crabs harbored significantly higher proportions of moderate and heavy infections, suggesting that the process of ecdysis, and the postmolt recovery period, has a positive effect on parasite proliferation.

Leukocyte profiles indicate nutritional, but not moulting stress in a migratory shorebird, the Common Snipe (Gallinago gallinago)

The relative ratio of the two main leukocyte types, heterophils (H) and lymphocytes (L), is known to change proportionally to the concentrations of stress hormones in the circulating blood. Thus, analysis of leukocyte profiles serves as a reliable proxy of stress in vertebrates, as high H/L ratios indicate stronger stress response. Moult and migration are among the most energetically demanding and nutritionally stressful processes in the annual cycle of wild birds. Although most birds separate these two activities in time, a moult–migration overlap has been reported for several avian species. The aim of this study was to examine whether overlapping energy requirements of moult and migration produce an increased organismal stress in a shorebird species, the Common Snipe (Gallinago gallinago). For this purpose, we assessed leukocyte profiles and nutritional condition in more than 350 moulting and non-moulting snipe during autumn migration through central Europe. We found negative correlations between H/L ratios and different measures of condition, including size-corrected body mass, fat load, and plasma concentrations of triglycerides and total protein. However, no evidence was found for the effect of moult status on H/L ratios. Our study indicates that while migration in a poor nutritional state can be associated with elevated stress response, the process of feather replacement may not constitute a serious stress for migrating Common Snipe. We suggest that these results may help to explain the occurrence of moult–migration overlap in the Common Snipe and possibly in other avian species.

Mallard (Anas platyrhynchos) Mortality and Recovery Rates Vary by Wing Molt Status at Time of Banding

Abstract. Recovery (i.e., shot, retrieved, and reported) rates and daily mortality risk of 52,330 adult Mallards (Anas platyrhynchos) leg-banded during pre-molt, in-molt, or post-molt during 1985–2011 were evaluated to better understand mortality during wing molt in dynamics of the Mallard population in California, USA. Recovery rates and non-hunting mortality risk varied by molt status at time of banding and California region where banded. Mallards banded during post-molt were 1.22 (95% credible interval = 1.10–1.32) times more likely to be recovered than Mallards banded pre-molt; recovery probability was similar for pre-molt and in-molt Mallards. Mallards banded post-molt had 0.43 (0.17–0.98) and in-molt 0.87 (0.51–1.49) times the daily risk of non-hunting mortality as Mallards banded pre-molt. Mallards were 0.92 (0.86–0.98) times as likely to be recovered, and daily risk of non-hunting mortality was 2.93 (1.79–4.94) times greater, if banded in Northeastern California than in California's Central Valley...

Altered expression of pectoral myosin heavy chain isoforms corresponds to migration status in the white-crowned sparrow (Zonotrichia leucophrys gambelii).

Birds undergo numerous changes as they progress through life-history stages, yet relatively few studies have examined how birds adapt to both the dynamic energetic and mechanical demands associated with such transitions. Myosin heavy chain (MyHC) expression, often linked with muscle fibre type, is strongly correlated with a muscle's mechanical power-generating capability, thus we examined several morphological properties, including MyHC expression of the pectoralis, in a long-distance migrant, the white-crowned sparrow (Zonotrichia leucophrys gambelii) throughout the progression from winter, spring departure and arrival on breeding grounds. White-crowned sparrows demonstrated significant phenotypic flexibility throughout the seasonal transition, including changes in prealternate moult status, lipid fuelling, body condition and flight muscle morphology. Pectoral MyHC expression also varied significantly over the course of the study. Wintering birds expressed a single, newly classified adult fast 2 isoform. At spring departure, pectoral isoform expression included two MyHC isoforms: the adult fast 2 isoform along with a smaller proportion of a newly present adult fast 1 isoform. By spring arrival, both adult fast isoforms present at departure remained, yet expression had shifted to a greater relative proportion of the adult fast 1 isoform. Altering pectoral MyHC isoform expression in preparation for and during spring migration may represent an adaptation to modulate muscle mechanical output to support long-distance flight.

Diurnal variation in corticosterone release among wild tropical forest birds.

BackgroundGlucocorticoids are adrenal steroid hormones essential to homeostatic maintenance. Their daily variation at low concentrations regulates physiology and behavior to sustain proper immunological and metabolic function. Glucocorticoids rise well above these baseline levels during stress to elicit emergency-state responses that increase short-term survival. Despite this essence in managing life processes under both regular and adverse conditions, relationships of glucocorticoid release to environmental and intrinsic factors that vary at daily and seasonal scales are rarely studied in the wild.MethodsThis study on 41 passerine species of the Ecuadorian Chocó applied a standardized capture-and-restraint protocol to examine diurnal variation in baseline and stress-related release of corticosterone, the primary avian glucocorticoid. Tests for relationships to relative body mass, hemoglobin concentration, molt status and date complemented this evaluation of the time of day effect on corticosterone secretion in free-living tropical rainforest birds. Analyses were also partitioned by sex as well as performed separately on two common species, the wedge-billed woodcreeper and olive-striped flycatcher.ResultsInterspecific analyses indicated maximum baseline corticosterone levels at the onset of the active phase and reductions thereafter. Stress-related levels did not correspond to time of day but accompanied baseline reductions during molt and elevations in birds sampled later during the September - November study period. Baseline corticosterone related negatively to hemoglobin in the wedge-billed woodcreeper and stress-related levels increased with body mass in the olive-striped flycatcher. There were no substantial sex-related differences.ConclusionsThe results of this study suggest a diurnal rhythmicity in baseline corticosterone release so robust as to emerge in pooled analyses across a highly variable dataset. While this detection in nature is singular, correspondent patterns have been demonstrated outside of the tropics in captive model species. Congruity in daily rhythms and links to physiological and life-history state across disparate taxa and environments may promote the yet unresolved utility of corticosterone release as a global metric for population health. However, certain results of this study also deviate from laboratory and field research at higher latitudes, cautioning generalization. Environmental distinctions such as high productivity and tempered seasonality may precipitate unique life-history strategies and underlying hormonal mechanisms in tropical rainforest birds.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-016-0151-3) contains supplementary material, which is available to authorized users.