Location Of Molt Research Articles

Enriched feather hydrogen isotope values for Wood Thrushes sampled in Georgia, USA, during the breeding season: implications for quantifying dispersal

We used an analysis of deuterium values (δD) of 151 Wood Thrush ( Hylocichla mustelina (J.F. Gmelin, 1789)) feathers collected during the breeding season at the Piedmont National Wildlife Refuge in Georgia, USA, to determine fidelity to the study site. We compared δD values in feathers of birds with known molt locations and birds with unknown molt locations. Mean feather value of δD was –24.8‰ (SD = 10.5‰, range = –48.0‰ to –5.5‰), and we were unable to determine a site-specific signature to assess fidelity of breeders within our sample. We used an information criterion approach to evaluate multiple hypotheses to explain the high variation in δD, and the geographic location of sample sites within the study area was selected as the best model. Feather δD values were higher than expected from mean growing-season rainfall δD values predicted for our study site. We discuss possible explanations for the enriched δD values and postulate that heat stress during molt may have contributed to our results. We suggest that future stable isotope data collection consider the potential for small-scale variation in feather δD values; information on diet gathered simultaneously with feather samples may be valuable for future studies.

Prebasic Molt and Molt-Related Movements in Ash-Throated Flycatchers

AbstractWe describe the timing and location of the prebasic molt in the Ash-throated Flycatcher (Myiarchus cinerascens), a hawking insectivore with resident populations in Mexico and migrant populations that breed in the western United States. The timing of fall molt with respect to migration is of particular interest for Ash-throated Flycatchers from the United States because they breed in arid lowland habitats that are probably unproductive in late summer, and because time constraints on molt might force northern populations to leave their breeding grounds before molting. Adults and juveniles depart their breeding grounds to arrive and molt in the region of the Mexican monsoon shortly after the monsoon rains begin. Diminishing food on the breeding grounds and increasing food in the monsoon region seem more important than time constraints for explaining molt-related movements by northern populations, because more southerly breeding birds east and west of the monsoon region also move to the monsoon region to molt. We found age class differences in the timing and duration of molt. In adults the primary molt starts approximately 14 July and requires 76 days to complete, whereas in juveniles, primary molt starts approximately 1 August (18 days after adults) but requires only 50 days to complete. We found no evidence that juveniles molt more primaries simultaneously than adults, so we conclude that the daily growth rate of individual feathers must be higher in juveniles than adults.

PREBASIC MOLT AND MOLT-RELATED MOVEMENTS IN ASH-THROATED FLYCATCHERS

Abstract We describe the timing and location of the prebasic molt in the Ash-throated Flycatcher (Myiarchus cinerascens), a hawking insectivore with resident populations in Mexico and migrant populations that breed in the western United States. The timing of fall molt with respect to migration is of particular interest for Ash-throated Flycatchers from the United States because they breed in arid lowland habitats that are probably unproductive in late summer, and because time constraints on molt might force northern populations to leave their breeding grounds before molting. Adults and juveniles depart their breeding grounds to arrive and molt in the region of the Mexican monsoon shortly after the monsoon rains begin. Diminishing food on the breeding grounds and increasing food in the monsoon region seem more important than time constraints for explaining molt-related movements by northern populations, because more southerly breeding birds east and west of the monsoon region also move to the monsoon regio...

Evidence for Wing Molt and Breeding Site Fidelity in King Eiders

Fidelity of King Eiders (Somateria spectabilis) to breeding and wing molt sites was examined using satellite telemetry data obtained opportunistically when battery life of transmitters provided locations in a second year. Consecutive breeding locations were obtained for eleven female and 23 male King Eiders. All females exhibited breeding site fidelity by returning to sites within 15 km of first year breeding areas on the North Slope of Alaska. Breeding locations of males in a subsequent year were located on average >1000 km from their prior breeding sites and were primarily outside Alaska, on the coasts of Russia and Canada. Second-year wing molt locations were obtained for two female and six male King Eiders. Wing molt sites of males were located 6.2 ± 3.1 km apart on average in successive years, while female wing molt locations averaged almost 50 km apart. Our results demonstrate site fidelity of female King Eiders to a breeding area on the North Slope of Alaska, document the dispersal of male King Eiders between breeding seasons, and present the first evidence for wing molt site fidelity in males.

Reproductive Effort, Molting Latitude, and Feather Color in a Migratory Songbird

Toward the end of the breeding season, migratory songbirds face crucial tradeoffs between the timing of reproduction, molt, and migration. Using stable hydrogen isotopes, we show that male American redstarts investing in high levels of reproduction late in the season adopt a unique strategy of combining molt and migration. Tail feathers molted during migration also reflect less orange-red light, indicating reduced carotenoid concentration. Thus, we show how reproduction in a migratory animal can influence both life history strategies (location of molt) and social signals (feather color) during subsequent periods of the annual cycle.

Timing and Location of Wing Molt in Horned, Red-necked and Western Grebes in North America

Abstract We document timing and location of wing molt in the Horned Grebe (Podiceps auritus), Red-necked Grebe (Podiceps grisegena), and Western Grebe (Aechmophorus occidentalis). Horned Grebes left breeding ponds in late May to August and were observed on large ponds and lakes (near breeding locations) where they replaced remiges before progressing to wintering areas in September and October. Red-necked Grebes moved to much larger bodies of water such as the Great Lakes and the coast following breeding and prior to molt. On the Pacific Coast, Boundary Bay, British Columbia was identified as a major molt site. Freshwater molting areas were identified around Manitoulin Island in northern Lake Huron. On the Atlantic coast, molt sites were located in the Gulf of St. Lawrence. Western Grebes were found in wing molt at both large freshwater lakes and coastal locations (including Boundary Bay, British Columbia). Like the Great Crested Grebe (P. cristatus) and Eared Grebe (P. nigricollis), Horned, Red-necked and...

Molt-Migration in Western Tanagers (Piranga Ludoviciana): Age Effects, Aerodynamics, and Conservation Implications

AbstractWe describe timing and location of the prebasic molt in Western Tanagers (Piranga ludoviciana), focusing on age class differences in premolt movements. Most adults migrate south to the American Southwest where they stop to molt before moving on to their wintering grounds. Molting adults are found in southern mountain regions (Sierra Madres and southern Rockies) and in the Mexican monsoon region, where late summer rains cause a substantial increase in productivity. In contrast, juvenile Western Tanagers move to nearby montane habitats to molt before migrating, a previously undocumented strategy in western passerines that show molt-related movements. By molting in nearby montane habitats, juveniles avoid the aerodynamic cost of migrating in their “fluffy”, aerodynamically inefficient juvenal plumage. Western Tanagers are the fifth species known to use the Mexican monsoon region during the prebasic molt, further affirming the importance of that area to the conservation of Neotropical migrants that breed in western North America.

Abundance and Distribution of Harlequin Ducks Molting in Eastern Canada

Until recently, very little was known about the basic ecology of the Harlequin Duck (Histrionicus histrionicus) in eastern North America, including molting locations. A combination of aerial, ground and boat surveys were initiated in 1989 (Québec) and 1994 (Newfoundland and Labrador), and continued through 1999, to locate their molting areas. Molting Harlequin Ducks were found in Labrador, Newfoundland and the Gaspé Peninsula and Anticosti Island, Québec. Coastal areas of southern Labrador, Grey Islands, northern Newfoundland, and Bonaventure and Anticosti Islands, southern Québec, were the most important sites. The tip of northern Labrador and possibly sites along the Québec North Shore and Greenland are the most likely sites where the rest of the eastern population molts. Molting chronology for the ducks in Québec is similar to those on the east and west coast of North America. Now that these sites are known, monitoring and, if necessary, protection of these sites can be considered.

MOLT-MIGRATION IN WESTERN TANAGERS (PIRANGA LUDOVICIANA): AGE EFFECTS, AERODYNAMICS, AND CONSERVATION IMPLICATIONS

We describe timing and location of the prebasic molt in Western Tanagers (Piranga ludoviciana), focusing on age class differences in premolt movements. Most adults migrate south to the American Southwest where they stop to molt before moving on to their wintering grounds. Molting adults are found in southern mountain regions (Sierra Madres and southern Rockies) and in the Mexican monsoon region, where late summer rains cause a substantial increase in productivity. In contrast, juvenile Western Tanagers move to nearby montane habitats to molt before migrating, a previously undocumented strategy in western passerines that show molt-related movements. By molting in nearby montane habitats, juveniles avoid the aerodynamic cost of migrating in their “fluffy”, aerodynamically inefficient juvenal plumage. Western Tanagers are the fifth species known to use the Mexican monsoon region during the prebasic molt, further affirming the importance of that area to the conservation of Neotropical migrants that breed in western North America.

LOW FREQUENCY OF “DOUBLE MOLT” OF REMIGES IN RUDDY DUCKS REVEALED BY STABLE ISOTOPES: IMPLICATIONS FOR TRACKING MIGRATORY WATERFOWL

Ratios of the stable carbon (d13C) and hydrogen (dD) isotopes in newly grown remiges of Ruddy Ducks (Oxyura jamaicensis) are influenced by the isotopic character of food types and ambient water. Systematic isotopic foodweb and water differences between coastal wintering grounds and prairie breeding grounds of Ruddy Ducks provide the basis for using isotopic analyses of feathers to trace the location and timing of molt. Anecdotal evidence, based largely on captive birds, suggests that Ruddy Ducks replace their remiges twice each year (once each on the breeding and wintering grounds), but a recent literature analysis indicates that this phenomenon is rare. Thus, we investigated the extent to which a biannual molt of the remiges occurs in the wild and at the population level. We analyzed the stable isotopes of carbon (n 5 57 birds) and hydrogen (n 5 50 birds) in flight feathers to estimate the prevalence of the so-called ''double molt'' of remiges in free-living Ruddy Ducks. Our data showed that natural populations of Ruddy Ducks express an overwhelming unimodal distribution of isotope ratios in their remiges, suggesting that they undergo a single molt at or near the breeding grounds. Only 3 to 6 of 50 birds from Manitoba showed isotopic evi- dence consistent with growing remiges on the wintering grounds. Feathers from Ruddy Ducks harvested during the fall in the Mississippi Flyway had isotopic profiles consistent with growth on northern freshwater breeding sites. Thus, our results confirm that the re- placement of remiges twice each year by Ruddy Ducks is rare, and they suggest that this dual stable-isotope technique can be used to infer general molting origins of North American waterfowl. Received 6 October 1998, accepted 26 May 1999.

Low Frequency of “Double Molt” of Remiges in Ruddy Ducks Revealed by Stable Isotopes: Implications for Tracking Migratory Waterfowl

Abstract Ratios of the stable carbon (δ13C) and hydrogen (δD) isotopes in newly grown remiges of Ruddy Ducks (Oxyura jamaicensis) are influenced by the isotopic character of food types and ambient water. Systematic isotopic foodweb and water differences between coastal wintering grounds and prairie breeding grounds of Ruddy Ducks provide the basis for using isotopic analyses of feathers to trace the location and timing of molt. Anecdotal evidence, based largely on captive birds, suggests that Ruddy Ducks replace their remiges twice each year (once each on the breeding and wintering grounds), but a recent literature analysis indicates that this phenomenon is rare. Thus, we investigated the extent to which a biannual molt of the remiges occurs in the wild and at the population level. We analyzed the stable isotopes of carbon (n = 57 birds) and hydrogen (n = 50 birds) in flight feathers to estimate the prevalence of the so-called “double molt” of remiges in free-living Ruddy Ducks. Our data showed that natural populations of Ruddy Ducks express an overwhelming unimodal distribution of isotope ratios in their remiges, suggesting that they undergo a single molt at or near the breeding grounds. Only 3 to 6 of 50 birds from Manitoba showed isotopic evidence consistent with growing remiges on the wintering grounds. Feathers from Ruddy Ducks harvested during the fall in the Mississippi Flyway had isotopic profiles consistent with growth on northern freshwater breeding sites. Thus, our results confirm that the replacement of remiges twice each year by Ruddy Ducks is rare, and they suggest that this dual stable-isotope technique can be used to infer general molting origins of North American waterfowl.

Annual Survival and Site Fidelity of Steller's Eiders Molting along the Alaska Peninsula

Populations of Stellers eiders (Polysticta stelleri) molting and wintering along the Alaska Peninsula have decliued since the 1960's. We captured and marked a large sample of Steller's eiders molting in 2 lagoons along the Alaska Peninsula between 1975-97. We used mark-recapture analysis techniques to estimate annual survival and movement probabilitics within and among lagoons for male and female eiders. Estimates of annual survival (±SE) were 0.899 = 0.032 for females and 0.765 = 0.044 for males. Both sexes showed high rates of fidelity to specific molting locations (>95%) within lagoons: yet we found no evidence that aunual probability of survival differed among groups molting in different locations either within or among lagoons. We found weak evidence that annual survival decreased between the periods 1975-81 and 1991-97. The lower survival of males compared to females is unusual for waterfowl and may result in a female-biased sex ratio. We conclude that a decrease in adult survival may have mitiated the long-term population decline. Further, a shortage of males may be limiting reproductive potential.

Ecological Segregation of Adelie, Gentoo, and Chinstrap Penguins at King George Island, Antarctica

Ecological segregation among Adelie, Gentoo, and Chinstrap penguins during summer results from differences in breeding chronology, foraging behaviors, and life history tactics. To determine the importance of these factors in segregating the niches of the three species, we collected data on their population size, breeding success, breeding chronology, feeding frequency, and foraging range. Gentoo Penguins feed inshore and are deep divers. Their small populations probably reflect the comparatively large amount of food they need to rear chicks and the small foraging range that is dictated by short nest relief schedules and nonfasting behaviors. Their deep diving ability enables them to exploit a niche that is unavailable to their more abundant congeners. Adelie and Chinstrap penguins are shallow—diving, offshore foragers that avoid competition by differences in breeding chronology, prebreeder behaviors, and molting strategies. Adelie chicks fledge just as Chinstrap chicks reach creche age. Different migration times and molting locations further reduce niche overlap. The ultimate factors responsible for this tropic segregation may be unrelated to these proximate factors, however. Nonmigratory behavior, short nest reliefs, nonfasting, and slow growth of chicks may be adaptations to the mild conditions experienced by Gentoo Penguins in their sub—Antarctic range. The differences in Adelie and Chinstrap breeding time may reflect adaptation of Adelies to early breeding in the harsh, short summer of the continental Antarctic, and adaptation of Chinstraps to later breeding in the milder Maritime Antarctic. We found no evidence to suggest that the niches of the Pygoscelis penguins were influenced by competition for food, and suggest that adaptation to conditions in the center of their respective distributions is the primary cause affecting ecological segregation in areas of sympatry.