Feather Regrowth Research Articles

Determinants and constraints of feather growth.

During the periodic moult of the plumage of birds, a fast regrowth of feathers would shorten the time of reduced plumage functionality. However, it has long been known that feather growth-rate is limited and that long feathers take disproportionally longer to grow than small feathers, which has severe consequences on moult duration and the completeness of moult in large birds. The reasons for the limitations of feather-growth must be related to the size and/or functions of the feather follicle, but are largely unknown. Here we measured the size of the feather follicle (taking calamus width as a proxy) and related it to parameters of feather growth (feather growth-rate by mass and by length) and feather structure (feather length, mass, massiveness [mass of feather material per mm feather-length]). We used three independent datasets which allowed for interspecific analyses, and for intraspecific comparisons of differently structured feathers within the framework of biological scaling. We found that the cross-sectional area of the calamus (as a proxy of feather follicle size) was directly proportional to feather growth-rate by mass. Hence, factors acting at a two-dimensional scale (possibly nutrient supply to the growing feather) determines feather growth rate by mass, rather than the linear arrangement of stem cells (in a circular configuration) as had previously been assumed. Feather follicle size was correlated with both feather length and massiveness, hence it seems to be adapted to some extent to feather structure. Feather growth-rate by length was dependent on both the feather material produced per unit time (growth-rate by mass) and the amount of material deposited per unit feather-length. Follicle size not only determines feather growth-rate by mass, but also directly the structural design (shape, number of barbs, etc.) of a feather. Therefore, feather growth-rate is severely constrained by the requirements imposed by the structural feather design.

Successful resection of an osteoma in a great horned owl (Bubo virginianus) with subsequent lack of regional feather regrowth

A free-living adult great horned owl (Bubo virginianus) was presented to a wildlife rehabilitation centre in Southern California with a firm, pedunculated mass arising from the caudal-dorsal border of the...

Moult location and diet of auks in the North Sea inferred from coupled light-based and isotopebased geolocation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 599:239-251 (2018) - DOI: https://doi.org/10.3354/meps12624 Moult location and diet of auks in the North Sea inferred from coupled light-based and isotope-based geolocation Katie St. John Glew1,*, Sarah Wanless2, Michael P. Harris2, Francis Daunt2, Kjell Einar Erikstad3,4, Hallvard Strøm5, Clive N. Trueman1 1Ocean and Earth Science, University of Southampton, Waterfront Campus, Southampton SO143ZH, UK 2Centre for Ecology & Hydrology, Bush Estate, Penicuik EH26 0QB, UK 3Norwegian Institute for Nature Research, Fram Centre, 9296 Tromsø, Norway 4Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway 5Norwegian Polar Institute, Fram Centre, Postbox 6606 Langnes, 9296 Tromsø, Norway *Corresponding author: katie.stjohnglew@soton.ac.uk ABSTRACT: Many pelagic seabirds moult their feathers while at sea, which is an energetically costly behaviour. Mortality rates during moult can be high, so spatial and trophic ecology during this critical period is important for understanding demographic patterns. Unfortunately, individual foraging behaviours specifically linked to at-sea moulting are commonly unclear. This paper combines 2 different approaches to geolocation: data from bird-borne geolocation loggers and stable-isotope assignment using carbon and nitrogen isotope maps (isoscapes). Coupling 2 geolocation processes allows some uncertainties associated with isotope-based assignment to be constrained. We applied this approach to quantify species-specific foraging locations and individual trophic variability during feather regrowth in 3 sympatric auk populations breeding on the Isle of May, Scotland (common guillemot Uria aalge, razorbill Alca torda and Atlantic puffin Fratercula arctica). Inferred foraging areas during moult differed between species and feather types. Guillemots likely underwent moult within the southern North Sea, razorbills along the east coast of England and into the southern North Sea and puffins off the east coast of Scotland. Estimates of individual trophic position varied considerably within feather types (up to 1 trophic level difference between individuals), among feather types grown during different time periods and across the 3 species, with guillemots consistently foraging at higher trophic positions than razorbills and puffins. Used in combination, these methods better constrain foraging areas during moulting, and provide a technique to explore individual differences and flexibility in foraging strategy, which is valuable information for both seabird conservation and marine spatial planning. KEY WORDS: Isoscape · Trophic ecology · Foraging · Moult · Atlantic puffin · Common guillemot · Razorbill Full text in pdf format PreviousNextCite this article as: St John Glew K, Wanless S, Harris MP, Daunt F, Erikstad KE, Strøm H, Trueman CN (2018) Moult location and diet of auks in the North Sea inferred from coupled light-based and isotope-based geolocation. Mar Ecol Prog Ser 599:239-251. https://doi.org/10.3354/meps12624 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 599. Online publication date: July 12, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Xenobiotic and essential metals biomonitoring by feathers: molting pattern and feather regrowth sequence in four dominant waterfowl

The variations of some metals including nickel, iron, copper, zink, mercury, lead, and cadmium were examined in wing primaries of dominant wintering waterfowl in international wetlands near the Caspian Sea’s southern basin, including graylag goose (Anser anser), mallard (Anas platyrhynchos), pintail (Anas acuta) and common teal (Anas crecca). The core question of this study is the determination of primary feathers arrangement in molting, growth pattern effects and its performance on the bioaccumulation of contamination and determining the best growth feather location for biomonitoring purposes. The metals content, overall trend lines, and correlations among the 10 primary wing feathers were compared, and molting effects and feather regrowth were investigated. The metals were measured by AMA 254 Advanced Mercury Analyzer and inductively coupled plasma atomic emission spectroscopy. In all the species, almost all primaries have simultaneous regrowth, but their growth continues irregularly. There were significant differences in metal differences with juvenile waterfowl that did not experience molting compared to adults that do. The results showed that all of the species (except common teal) have experienced molting due to the difference of Hg concentration between adults and juveniles. It seems unplanned or random selection of bird’s feathers to achieve pollutants monitoring purposes by previous studies’ methods can now be challenged. In order to examine the linear changes of some elements (mercury, copper, and zink), it is recommended to collect samples of middle primaries, while samples of the feather growth locations to study the linear changes of nickel, iron, lead, and cadmium are necessary.

FORCED MOLT IN FOUR JUVENILE YELLOW-EYED PENGUINS (MEGADYPTES ANTIPODES).

Penguins are dependent on waterproof plumage for survival. The molt in sub-Antarctic penguin species is a seasonal and catastrophic process during which the animals go through periods of fasting and high levels of stress. Their entire plumage is usually replaced in 3 wk. Attempts at consistent hormonal induction of molt in penguins have been unsuccessful. Four Yellow-eyed Penguins ( Megadyptes antipodes ) were referred for treatment at Wildbase, Massey University, Palmerston North, New Zealand, in late April 2014, following loss of waterproofing, feather breakage, increased body weight, pododermatitis, and damage to caudal feathers from hock sitting. Feather plucking of damaged areas to stimulate feather regrowth was attempted with poor results. Waiting 10-12 mo for a natural molt was not tenable. Catastrophic molt was induced by treatment with 10 g/kg of fresh beef thyroid gland orally once a day. The molt was complete in 18-26 d during which the animals regained full plumage and waterproofing after feather regrowth. The forced molt feathers had abnormal pigmentation but were of sufficient quality to allow release of the birds back to the wild.

Malaria infection negatively affects feather growth rate in the house sparrow Passer domesticus

Birds often face various stressors during feather renewing, for example, enduring infection with blood parasites. Because nutritional resources are typically limited, especially for wild animals, when an individual allocates energy to one physiological system, there is subsequently less for other processes, thereby requiring a trade‐off. Surprisingly, potential trade‐offs between malaria infection and feather growth rate have not been experimentally considered yet. Here, we conducted three studies to investigate whether a trade‐off occurs among feather growth rate, malaria infection and host health conditions. First, we explored whether naturally infected and uninfected house sparrows differed in feather growth rate in the wild. Second, we asked whether experimental inoculation of malaria parasites and/or forcing the renewal of a tail feather. Lastly, we evaluated whether individual condition was affected by experimentally‐induced feather regrowth and/or malaria experimental infection. Our findings showed that feather growth rate was negatively affected by natural malaria infection status in free‐living birds and by experimental infection in captive birds. Furthermore, birds that did not increase body mass or hematocrit during the experimental study had slower feather growth. Together our results suggest that infection with blood parasites has more negative health effects than the growth of tail feathers and that these two processes (response to blood parasite infection and renewal of feathers) are traded‐off against each other. As such, our results highlight the role of malaria parasites as a potential mechanism driving other trade‐offs in wild passerines.

Assessment of regrowth of flight feathers after manual removal in American kestrels (Falco sparverius).

The objective of this study was to evaluate if extraction of broken feathers outside the molting period was an efficient method to induce growth of new flight feathers as part of the rehabilitation process of raptors with damaged plumage. Primaries, secondaries, and rectrices (four of each) were removed under general anesthesia from 10 American kestrels (Falco sparverius) using two different protocols: with and without filling the follicle with bismuth subnitrate (Orbeseal) to prevent it from sealing. Birds were kept in large aviaries under natural daylight and outdoor temperatures. Rate and quality of growth of new feathers were assessed regularly for 4 mo. Results were significantly different between the types of feathers: 100% of rectrices, 58% of secondaries, and 8% of primaries started to grow within the 4 winter months, and 95% of rectrices, 30% of secondaries, and 0% of primaries completed their growth normally within this period. The use of Orbeseal did not improve the outcome. The tail feathers began to grow between the second and third weeks at about 2.7 mm/day, and growth was completed within 7 wk. Rate, starting time, and duration of remigial growth were less predictable and varied widely among individuals. Although the exact impact of these extractions on the natural molt is still unclear, most of the primaries that were plucked during this study failed to regrow normally during the following molt. In conclusion, plucking damaged tail feathers in kestrels can successfully decrease the duration of rehabilitation. However, this procedure would not be recommended for wing feathers.

Central place foraging and feather regrowth rate in bridled terns (Onychoprion anaethetus): an insight from stable isotopes

In this study, the stable isotope ratios of δ13C and δ15N of bridled terns’ (Onychoprion anaethetus) tail feathers were used to investigate changes in the food sources assimilated by the birds on Penguin Island, Western Australia, during different phases of the breeding season. Samples were taken immediately after they arrived on the island returning from migration (BM), before egg-laying (BEL), after egg-laying (AEL), after hatching (AH) and from fledglings (F). A one-way MANOVA (excluding the BM phase) and two one-way ANOVAs (including all phases), showed that the δ13C and δ15N values differed significantly between the stages of the breeding season, with the greatest differences between the BM and BEL stages. The mean δ13C values were higher and those for δ15N were lower for BM birds than all other stages, indicating that the food source assimilated by the birds, and their foraging locations, changed during the breeding season. These results support the hypothesis of the Central Place Foraging Theory, i.e. that adult breeding birds adjust their foraging strategies when they are bound to a central place to care for their young. Induced feathers were regenerated over ~70 days and their regrowth rates were similar before and after egg-laying.

Dietary protein level affects iridescent coloration in Anna's hummingbirds, Calypte anna

Many animal displays involve colorful ornamental traits that signal an individual's quality as a mate or rival. Brilliant iridescent ornaments are common, but little is currently known about their production cost and signaling value. One potential cost of colorful ornaments is the acquisition of limited dietary resources that may be involved, directly or indirectly, in their production. Protein, the primary component of bird feathers and of many nanostructural components of iridescent traits, is naturally restricted in hummingbird diets (comprised mostly of sugars), suggesting that iridescent coloration may be especially challenging to produce in these animals. In this study, we experimentally investigated the effect of dietary protein availability during molt on iridescent color expression in male Anna's hummingbirds (Calypte anna). We fed captive birds either a 6% (high) or a 3% (low) protein diet and stimulated molt by plucking half the gorget and crown ornaments on each bird as well as the non-ornamental iridescent green tail feathers. We found that birds receiving more protein grew significantly more colorful crown feathers (higher red chroma and redder hue) than those fed the low-protein diet. Diet did not affect gorget coloration, but regrowth of feathers in captivity affected both gorget and crown coloration. Additionally, birds on the high-protein diet grew yellower (higher hue) green tail feathers than birds on the low-protein diet. These results indicate that iridescent ornamental feathers are sensitive to diet quality and may serve as honest signals of nutrition to mates or rivals. Further, because both ornamental and non-ornamental iridescent coloration were affected by conditions during their growth, iridescent color in these birds appears to be generally condition dependent.

Phenology and duration of remigial moult in Surf Scoters (Melanitta perspicillata) and White-winged Scoters (Melanitta fusca) on the Pacific coast of North America

By quantifying phenology and duration of remigial moult in Surf Scoters ( Melanitta perspicillata (L., 1758)) and White-winged Scoters ( Melanitta fusca (L., 1758)), we tested whether timing of moult is dictated by temporal optima or constraints. Scoters (n = 3481) were captured during moult in Alaska, British Columbia, and Washington, and remigial emergence dates were determined. We provide evidence for a pre-emergence interval of 7.3 days that occurs after old primaries are shed and before new ones become visible. All age and sex classes of both scoter species exhibited a wide range of emergence dates (Surf Scoters: 26 June to 22 September; White-winged Scoters: 6 July to 21 September) suggestive of a lack of strong temporal optima for remigial moult. For both species, timing of moult was influenced by site, year, age, and sex. Relative to other waterfowl species, scoters have typical remigial growth rates (Surf Scoters: 3.9 mm·day–1; White-winged Scoters: 4.3 mm·day–1) but a long flightless period (34–49 days), in part because their relatively high wing-loading requires a greater proportion of feather regrowth to regain flight. Our data suggest that moulting scoters are not under strong selective pressure to complete moult quickly.

RED CROSSBILLS COPE WITH MOULTING AND STRESS

No matter how much effort a bird puts into preening, there is always a time when its feathers need replacing. However, feather regrowth is a costly process. Jamie Cornelius from the University of California Davis, USA, is intrigued by the metabolic trade-offs that animals make between competing physiological processes. `Trade-offs are a very potent evolutionary force in forming the behaviour and physiology of animals,' she says. Knowing that animals divert resources from non-essential to critical processes, Cornelius and her colleagues wondered how resource-intense moulting impacts on the ability of some songbirds to deal with stress. She explains that most songbirds only moult after the breeding season and they free up resources for feather regrowth by suppressing their stress response. But how do nomadic songbirds that moult over a longer period and depend on unreliable food sources juggle the competing demands of their stressful lives versus feather regrowth? Knowing that corticosterone is the key hormone triggering a stress response in birds, Cornelius and her supervisor, Thomas Hahn, decided to measure levels of the hormone in red crossbills and zebra finches to find out how well they prepare for stressful encounters while replacing their plumage (p. 2768).Unfortunately, capturing moulting red crossbills was far from easy. `The tricky thing is that red crossbills are nomadic so you don't know where they are going to be in a given year,' explains Cornelius. However, by tracking the bird's favourite food source – pine cones – as they ripened, Cornelius eventually located flocks of the elusive birds and was able to trap them by luring them into mist nets with captive red crossbill decoys. Then Cornelius had to work fast. Knowing that being trapped was stressful for the birds, she had to collect the first tiny blood sample from each bird within 3 min: before its corticosterone levels began rising. Next, she gently placed the bird in a cloth bag and collected three more blood samples over the course of an hour as the bird coped with the stressful situation. Finally, she assessed how far each individual's moult had progressed before releasing it back into the wild.Meanwhile, down in Australia, Nicole Perfito was also trapping zebra finches, collecting blood samples and checking how may feathers they had replaced. `Zebra finches show a very slow moult that takes nearly a whole year,' explains Cornelius, who adds that the birds living in the deserts around Alice Springs are also dealing with very unpredictable conditions, so a strong stress response would be very beneficial.Next, Cornelius travelled to Creagh Breuner's lab at the University of Montana to find out how the birds had handled the stress. Measuring the concentration of corticosterone in the trapped birds' blood, Cornelius found that the level of the stress hormone had rocketed and she also found that the zebra finches from the harsh desert around Alice Springs produced the highest corticosterone levels.The nomadic birds with extended moults were able to maintain their costly stress responses for protection from their stressful lifestyle, unlike other songbirds that suppress the response while replacing their plumage rapidly. Having found that some songbirds do make the trade-off while others don't, Cornelius and her colleagues suggest that instead of being hardwired, songbirds may be able to adjust their moult/stress response trade-off to match their circumstances.

Micromineral Source Affects Intestinal Morphology but not Feather Formation in Pigeons

During 7weeks, two groups of eight pigeons received Zn, Cu, Mn and Se either as inorganic salts or organically bound to investigate the effect of micromineral source on two fast processes in avian metabolism: feather regrowth and intestinal renewal. Increased plasma Zn with reduced hepatic Cu in the organically bound minerals group suggests improved Zn bio-availability with a net antagonistic effect on Cu. Micromineral source did not affect feather regrowth, organ weight or intestinal pH, but the increased villus height with similar crypt depth pointed to increased absorptive surface.

Indications of phenotypic plasticity in moulting birds: captive geese reveal adaptive changes in mineralisation of their long bones during wing moult

Bone is continually undergoing cycles of apposition and resorption referred to as adaptive remodelling. We tested the hypothesis that captive moulting Barnacle Geese (Branta leucopsis) would show adaptive bone mineralisation during the flightless period of their annual flight feather moult, despite having never flown. The three leg bones showed selective changes in mineralisation in terms of mass and mineral content, while the wing bones did not change in mass or mineral content. The tibia/fibula was the only bone to also undergo significant changes in mass, increasing as moult progressed then decreasing significantly towards the end of moult. This was not a response to changing body mass. Instead, we propose that this is a response to the requirement for increased strength brought about by the significant increase in the force producing muscles that attach to the tibia. The femur and tarsometarsus showed the opposite trend, with mineral content decreasing significantly during mid-moult before increasing again at the end. These changes were also independent of changing body mass, suggesting instead that the calcium, or rather calcium derivatives, were mobilised for feather regrowth. This study demonstrates significant and selective adaptive natural changes in bone mass and mineralization that have not been previously demonstrated. That they should also occur in captive birds which show a decrease in locomotion during the wing moult period, suggests a high endogenous capacity for these changes.

Do captive waterfowl alter their behaviour patterns during their flightless period of moult?

Many different behavioural changes have been observed in wild waterfowl during the flightless stage of wing moult with birds frequently becoming inactive and reducing time spent foraging. Increased predation risk, elevated energetic demands of feather re-growth and restriction of foraging opportunities are thought to underlie these changes. By studying captive populations of both a dabbling and a diving duck species at the same site, we determined whether captive birds would reflect the behavioural responses of wild waterfowl to moult. The time-budgets of 42 Common Eiders, Somateria mollissima, (a diving duck) and 18 Garganeys, Anas querquedula, (a dabbling duck) were recorded during wing moult (July–August) and non-moult (January) with behaviour recorded under six categories. Despite captivity providing a low predation risk and constant access to food, birds altered their behaviour during the flightless period of wing moult. Time allocated to foraging and locomotion decreased significantly during moult compared to non-moult periods, while resting time increased significantly. Moulting Eiders underwent a greater reduction in time spent foraging and in locomotion compared with Garganeys, which is likely to be in response to a higher energetic cost of foraging in Eiders. It is possible that increased resting in both diving and dabbling ducks reduces their likelihood of detection by predators, while allowing them to remain vigilant. We demonstrate that there is much potential for using captive animals in studies that can augment our knowledge of behaviours of free-living conspecifics, the former being a hitherto under-exploited resource.

Methicillin-Resistant Staphylococcus aureus–Associated Dermatitis in a Congo African Grey Parrot (Psittacus erithacus erithacus)

A 2-year-old DNA-sexed female Congo African grey parrot (Psittacus erithacus erithacus) was evaluated for self-trauma of the feathers and skin of the tail base for a duration of more than 1 year. All rectrices and tail coverts were missing, the skin of the tail base was thickened and ulcerated, and the uropygial gland was swollen. Results of a complete blood cell count revealed relative monocytosis and basophilia. Survey radiographs showed truncation and lysis of the caudal vertebrae and pygostyle. Results of biopsy and bacterial culture of the tail base lesions revealed an ulcerative bacterial dermatitis positive for staphylococcal cassette chromosome mec (SCCmec) type IV (community-acquired) methicillin-resistant Staphylococcus aureus (MRSA). The bird was treated with oral trimethoprim-sulfamethoxazole, meloxicam, fluoxetine, topical lidocaine gel, and hydrotherapy. One month later, tail feather regrowth was evident; however, follow-up over 2 years found continued self-trauma to the rectrices in spite of repeated skin biopsies negative for MRSA or other bacteria. It is unknown if the MRSA cultured from this bird was commensal or acquired from either the environment or humans to which the bird was exposed.

Exogenous and endogenous corticosterone alter feather quality

We investigated how exogenous and endogenous glucocorticoids affect feather replacement in European starlings ( Sturnus vulgaris) after approximately 56% of flight feathers were removed. We hypothesized that corticosterone would retard feather regrowth and decrease feather quality. After feather regrowth began, birds were treated with exogenous corticosterone or sham implants, or endogenous corticosterone by applying psychological or physical (food restriction) stressors. Exogenous corticosterone had no impact on feather length and vane area, but rectrices were lighter than controls. Exogenous corticosterone also decreased inter-barb distance for all feathers and increased barbule number for secondaries and rectrices. Although exogenous corticosterone had no affect on rachis tensile strength and stiffness, barbicel hooking strength was reduced. Finally, exogenous corticosterone did not alter the ability of Bacillus licheniformis to degrade feathers or affect the number of feathers that failed to regrow. In contrast, endogenous corticosterone via food restriction resulted in greater inter-barb distances in primaries and secondaries, and acute and chronic stress resulted in greater inter-barb distances in rectrices. Food-restricted birds had significantly fewer barbules in primaries than chronic stress birds and weaker feathers compared to controls. We conclude that, although exogenous and endogenous corticosterone had slightly different effects, some flight feathers grown in the presence of high circulating corticosterone are lighter, potentially weaker, and with altered feather micro-structure.

The effects of chronic psychological and physical stress on feather replacement in European starlings ( Sturnus vulgaris)

Corticosterone (CORT) is seasonally modulated in many passerines, with plasma CORT concentrations lowest during the prebasic molt, when all feathers are replaced. Recent evidence indicating that CORT implants slow the rate of feather regrowth in molting birds suggests that plasma CORT concentrations are downregulated during molt in order to avoid the inhibition of feather growth caused by the protein catabolic activity of CORT. To further test this hypothesis, we examined whether endogenous CORT release, stimulated by exposure to either psychological stress or physical stress (food restriction), could inhibit feather regrowth rates or decrease feather quality in birds undergoing an induced molt (feather replacement after plucking). European starlings ( Sturnus vulgaris) were exposed to chronic psychological stress or food restriction for three weeks of the feather regrowth period. Throughout this time, the length of growing primary, secondary, and tail feathers was measured and blood samples were collected to measure baseline and stress-induced CORT concentrations. Upon completion of growth, feather quality was analyzed via measurements of mass, rachis length, feather area, and presence of fault bars. Both psychological and physical stress protocols elevated circulating plasma CORT but significantly less than implants from an earlier study did. Psychological stress had no effect on feather regrowth rates or feather quality. Food restriction had no effect on feather growth rate but caused asynchronous feather replacement. When combined with psychological stress, physical stress also resulted in smaller feather area. Results indicate that CORT implants may not accurately represent chronic stress physiology. Additionally, the purpose for downregulating CORT concentrations during molt appears to be more complicated than simply protecting feather production from CORT's catabolic effects.

Use of Laser Ablation and Cryosurgery to Prevent Primary Feather Growth in a Pigeon (Columba livia) Model

Many species of birds kept in captivity must be rendered flightless to prevent escape from open enclosures. In this study, we evaluated the use of diode laser and cryosurgery as methods of ablating primary feather follicles in domestic pigeons (Columba livia). In group 1 birds (n = 6), primary feather 10 of both wings was treated with the diode laser (10 W, 2 seconds) and primary feather 6 was treated with the cryoprobe (5 seconds, 3 cycles). In group 2 birds (n = 6), primary feathers 10 and 6 were treated with the cryoprobe for 20 and 30 seconds, respectively, for 3 cycles. In all birds, primary feather 8 on both wings was manually pulled as the control follicle. Results showed that in group 1 birds, diode laser ablation prevented feather regrowth in 83% of follicles, however, freezing with the cryoprobe for 5 seconds did not prevent feather regrowth. In group 2 birds, treatment with the cryoprobe prevented feather regrowth at 100% and 42% of the treated sites (treatment times of 20 and 30 seconds, respectively). Significant tissue swelling and edema were observed in all group 2 birds. On histologic examination, follicle damage was most severe at the laser-treated sites in group 1 birds and at the 20-second freezing sites in group 2 birds, which correlated with the prevention of feather regrowth. The control follicles and follicles adjacent to treated areas in both groups were histologically normal. Feather follicle ablation with both the diode laser and the cryoprobe are effective in preventing feather regrowth; however, success with the cryoprobe depends on the ability of the probe to directly contact the feather follicle. Diode laser is a superior technique because it is faster, easier to perform, and causes minimal tissue damage.

Food supply controls the body condition of a migrant bird wintering in the tropics

The hypothesis that migratory bird populations are limited during the non-breeding season is increasingly supported by empirical studies that also suggest consequences that carry-over into subsequent seasons. Although variation in food supply is the best supported explanation for non-breeding season limitation, the ecological mechanisms and physiological consequences are not well understood. We both supplemented and reduced Ovenbird (Seiurus aurocapilla) food availability on replicate plots in Jamaica in each of 3 years to determine the direct role of food in limiting the physical condition of Ovenbirds. Annual variation in rainfall and food supply created a natural experiment in parallel with manipulations. Sex and age-classes of Ovenbirds did not respond differently in terms of body condition to either food manipulation or natural variation in environmental conditions, suggesting that this population is not structured by strong dominance relationships. Ovenbird body mass, fat, and pectoralis muscle shape were positively and predictably related to manipulated food availability. Feather regrowth rate also responded positively to food supplementation and negatively to food reduction in the drier of 2 years. Prior to manipulation, annual variation in body mass corresponded to annual variation in food supply and rainfall, providing additional, correlational evidence of food limitation. Since multiple intercorrelated body condition indices of Ovenbirds responded directly to food supply, and since food supply influenced body condition independently of other habitat features, we argue that food is a primary driver of non-breeding season population limitation. Moreover, since these effects were observed during the late non-breeding period, when individuals are preparing to migrate, we infer that food availability likely initiates carry-over effects.

Corticosterone inhibits feather growth: Potential mechanism explaining seasonal down regulation of corticosterone during molt

Corticosterone (CORT) is seasonally modulated in many passerines, with plasma CORT concentrations lowest during the prebasic molt when all feathers are replaced. To explain why, we proposed that the birds downregulate natural CORT release during molt in order to avoid CORT's degradative effects on proteins and its inhibition of protein synthesis. If CORT exerted these effects during molt, it could slow protein deposition during feather production and potentially result in a longer period of degraded flight performance. To test this hypothesis, either empty or CORT-filled silastic implants were inserted into captive European starlings ( Sturnus vulgaris) and white-crowned sparrows ( Zonotrichia leucophrys) undergoing induced (feather replacement after plucking) and natural molts. We then measured the rate of feather re-growth by regularly measuring the length of primary, secondary, and tail feathers. CORT implanted birds showed a significantly decreased rate of feather growth compared to control animals. Basal CORT concentrations of induced molt and non-molting birds were also compared but no difference was noted. The results suggest a tradeoff; a complete set of new feathers may be more important to the survival of a bird than the ability of CORT to respond maximally to a stressor.