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Migration distances of shorebird species correlate with life history strategies. To assess agespecific migratory preparation and adult wing-molt strategies, we studied Western Sandpipers (Calidris mauri) and Semipalmated Sandpipers (C. pusilla) with different migration routes at the Paracas National Reserve in Perú, one of the most austral non-breeding areas for these sandpipers, from 2012 to 2015. Western Sandpipers breed near the Bering Sea, ~11,000 km from Paracas. Semipalmated Sandpiper populations at Paracas are a mixture of short-billed birds from western Arctic breeding sites, plus long-billed birds from eastern sites, -8000 km distant. Adults of both species arrive in October with primary feathers already partially renewed so wing molt starts at sites further north. Semipalmated Sandpipers with longer bills completed wing molt later than shorter billed birds. Adults of both species prepared for migration in February and March. No juvenile Western Sandpipers prepared for migration, confirming the \"slow\" over-summering life history strategy of more southerly non-breeding populations. Juvenile Semipalmated Sandpipers showed bimodality in strategies. Most showed no migratory preparation, but, during three non-breeding periods, from 27% to 31% fattened, molted, and partially replaced outer primaries during the pre-migratory period. Juveniles with longer culmens were heavier and tended to have more alternate plumage. Juveniles that were partially molting primaries had longer culmens and more alternate plumage. Juvenile Semipalmated Sandpipers from eastern-breeding populations thus have a higher propensity for a fast life history strategy, and western birds a slow one, at this non-breeding site in Peru. Westernbreeding Semipalmated Sandpiper populations thus resemble Western Sandpipers, suggesting a common, possibly distance-related, effect on life history strategy. La distancia de migración de aves playeras esta correlacionada con las estrategias de la historia de vida. Para determinar la preparación para la migración relacionada con la edad y la estrategias de muda en los adultos, estudiamos individuos de Calidris mauri y Calidris pusilla que tienen rutas de migración diferentes en la Reserva Nacional Paracas en Perú, una de las áreas de migración más australes para estas aves, entre 2012 y 2015. Calidris mauri se reproduce cerca del mar de Bering, ~11,000 km de Paracas. Las poblaciones de Calidris pusilla en Paracas son una mezcla de aves con pico corto de los sitios de reproducción del Oeste del Artico y aves con pico largo de sitios reproductivos al este, distanciados por -8000 km. Los adultos de ambas especies llegan en Octubre con las plumas primarias parcialmente renovadas, lo cual indica que la muda de invierno comienza en localidades más al norte. Los individuos de Calidris pusilla con el pico más largo, completaron la muda en las alas más tarde que los individuos de pico corto. Los adultos de ambas especies se prepararon para la migración en Febrero y Marzo. Ninguno de los juveniles de Calidris mauri se preparó para la migración, lo cual confirma una estrategia de verano más \"lenta\" de las poblaciones no reproductivas más sureñas. Los juveniles de Calidris pusilla mostraron bimodalidad en las estrategias. La mayoría de los individuos no mostro preparación alguna para la migración, pero, durante tres periodos no reproductivos, entre 27 y 31% de los individuos acumularon grasa, mudaron y reemplazaron parcialmente las primarias externas durante el periodo pre-migratorio. Juveniles con cúlmenes más largos fueron más pesados y tuvieron la tendencia a tener más plumaje alterno. Juveniles que mudaron las jrimarias parcialmente tuvieron cúlmenes más largos y mayor cantidad de plumaje alterno. Consecuentemente, os juveniles de Calidris pusilla de las poblaciones reproductivas del Este tienen una mayor propensidad a tener una estrategia más rápida en las historias de vida y las aves del Oeste una más lenta, en estos sitios no reproductivos de Perú. Poblaciones reproductivas del Oeste de Calidris pusilla son similares a Calidris mauri, sugiriendo un posible efecto común de la distancia sobre las estrategias de historia de vida.

The extinct Laysan Rail or Crake (Zapornia palmeri) was a small, flightless rail endemic to Laysan Island in the northwestern chain of the Hawaiian Archipelago. I detail the collections made, including eggs, nests, juveniles, and numerous adults prior to its extinction. The juvenile plumage was seemingly well documented, but my study of a series of juvenile specimens collected in 1891 and 1896 provides hitherto undescribed molt changes, from downy chick to definitive plumage. Morphometric data show that sexual size dimorphism is present with males being slightly more robust in bill, legs, and feet. I provide a detailed review of the literature showing the chronology of events that led to the extinction of the species and how this easily could have been avoided.

Post-juvenile molt of Common Snipe was investigated during 2004-05 at the Jeziorsko reservoir, central Poland. Body mass and mass of fat stores were dependent on the stage of post-juvenile molt. The body mass increased prior to the commencement of molt, but during the intensive stage of the process it decreased and returned to the previous level. Fat-free body mass increased during molt, which may be attributed to increased protein synthesis or the higher water content of growing feathers. Fat stores were similar in snipe before and in the initial stage of molt; however, they decreased significantly during the transition to the intensive stage of the process. In total, snipe lost approximately 57% of the mass of fat loads over the course of molt (4.9% of lean body mass). Being a highly energetic constraint, post-juvenile molt is suggested to affect certain life history traits of Common Snipe such as the length of the staging periods during the autumn migratory period.

Temporal overlap between parental care and molt occurs frequently in birds, but few studies have examined how individuals manage conflicts between these 2 demanding phases of the annual cycle. The potential for trade-offs between molt and parental care is especially high in the Hooded Warbler (Setophaga citrina) because (1) all rectrices are replaced simultaneously during primary molt, leaving birds temporarily without a functional tail; and (2) the tail plays an important role in foraging, as birds use their white tail spots and tail-flicking behavior to startle insect prey. I examined how simultaneous rectrix molt affected late-season parental care in a color-banded population of Hooded Warblers in northwest Pennsylvania, USA. Of 62 adults initiating rectrix molt before the end of parental care, 43 (69%) deserted their late-season nestlings and fledglings, leaving the mate to provide all remaining parental care. Because females initiate rectrix molt significantly later than males, most instances of uniparental desertion involved molting males abandoning fledglings or nestlings, but rare cases of postfledging desertion by females also occurred. Although most molting parents deserted, the probability of desertion decreased significantly with brood age, presumably because the costs of providing parental care during molt decline as fledglings approach independence. The probability of desertion by the male also decreased significantly with male age, suggesting that more experienced males can successfully balance the dual demands of molt and late-season parental care. In females, however, the only instances of desertion involved unusually old females ≥5 yr old, which suggests that rare cases of female desertion may occur as a mechanism to reduce reproductive effort late in life. My findings indicate that conflicts between parental care and molt, and the strategies that individuals use to manage those conflicts, merit increased attention from ornithologists seeking to understand the full annual cycle of migratory songbirds.

Ornithologists have largely embraced the molt terminology of Humphrey and Parkes (1959) as modified by Howell et al. (2003; the H-P-H system). In a recent commentary, Wolfe et al. (2014) summarized the derivation and benefits of H-P-H terminology, suggested slight modifications, and promoted analyses on the evolution of molts using H-P-H nomenclature. We appreciate the timeliness of Wolfe et al.'s review and agree with most of their conclusions and modifications. We disagree, however, with Wolfe et al.'s proposal for introducing a new and restricted use of the term “definitive” in H-P-H nomenclature. To avoid confusion, we recommend that definitive plumage and definitive molt cycle continue to be used as defined by Humphrey and Parkes (1959) and Howell et al. (2003), respectively, as terms indicating that plumage appearance and molt cycle have achieved stasis. We also recommend that the term “plumage” can be used more widely than the definition proposed by Humphrey and Parkes (1959), and that the term “juvenal” can henceforth be replaced by “juvenile” in molt and plumage literature.

The three modes of insect postembryonic development are ametaboly, hemimetaboly and holometaboly, the latter being considered the only significant metamorphosis mode. However, the emergence of hemimetaboly, with the genuine innovation of the final moult, represents the origin of insect metamorphosis and a necessary step in the evolution of holometaboly. Hemimetaboly derives from ametaboly and might have appeared as a consequence of wing emergence in Pterygota, in the early Devonian. In extant insects, the final moult is mainly achieved through the degeneration of the prothoracic gland (PG), after the formation of the winged and reproductively competent adult stage. Metamorphosis, including the formation of the mature wings and the degeneration of the PG, is regulated by the MEKRE93 pathway, through which juvenile hormone precludes the adult morphogenesis by repressing the expression of transcription factor E93, which triggers this change. The MEKRE93 pathway appears conserved in extant metamorphosing insects, which suggest that this pathway was operative in the Pterygota last common ancestor. We propose that the final moult, and the consequent hemimetabolan metamorphosis, is a monophyletic innovation and that the role of E93 as a promoter of wing formation and the degeneration of the PG was mechanistically crucial for their emergence. This article is part of the theme issue ‘The evolution of complete metamorphosis’.

Background In many insect species, fitness trade-offs exist between maximizing body size and developmental speed. Understanding how various species evolve different life history strategies requires knowledge of the physiological mechanisms underlying the regulation of body size and developmental timing. Here the roles of juvenile hormone (JH) and insulin/target of rapamycin (TOR) signaling in the regulation of the final body size were examined in the tobacco hornworm, Manduca sexta . Results Feeding rapamycin to wild-type larvae decreased the growth rate but did not alter the peak size of the larvae. In contrast, feeding rapamycin to the JH-deficient black mutant larvae caused the larvae to significantly increase the peak size relative to the DMSO-fed control animals by lengthening the terminal growth period. Furthermore, the critical weight was unaltered by feeding rapamycin, indicating that in Manduca , the critical weight is not influenced by insulin/TOR signaling. In addition, post-critical weight starved black mutant Manduca given rapamycin underwent metamorphosis sooner than those that were fed, mimicking the “bail-out mechanism”. Conclusions Our study demonstrates that JH masks the effects of insulin/TOR signaling in the determination of the final body size and that the critical weights in Drosophila and Manduca rely on distinct mechanisms that reflect different life history strategies. Our study also suggests that TOR signaling lengthens the terminal growth period in Manduca as it does in Drosophila , and that JH levels determine the relative contributions of nutrient- and body size-sensing pathways to metamorphic timing.

Several species of passerines leave their nest with unfinished feather growth, resulting in lower feather insulation and increased thermoregulatory demands compared to adults. However, feather insulation is essential for avian species breeding at northern latitudes, where cold conditions or even snowstorms can occur during the breeding season. In altricial arctic species, increased heat loss caused by poor feather insulation during growth could be counter-adaptative as it creates additional energy demands for thermoregulation. Using flow-through respirometry, we compared resting metabolic rate at thermoneutrality (RMRt), summit metabolic rate (Msum) and heat loss (conductance) in adult and juvenile snow buntings on their summer and winter grounds. In summer, when buntings are in the Arctic, juveniles had a 12% higher RMRt, likely due to unfinished growth, and lost 14% more heat to the environment than adults. This pattern may result from juveniles fledging early to avoid predation at the cost of lower feather insulation. Surprisingly, an opposite pattern was observed at lower latitudes on their wintering grounds. Although they showed no difference in RMRt and Msum, adults were losing 12% more heat than juveniles. We suggest that this difference is due to poorer insulative property of plumage in adults stemming from energetic and time constraints encountered during their post-breeding molt. High plumage insulation in first-winter juvenile buntings could be adaptive to reduce thermoregulatory demands and maximize survival in the first winter of life, while adults could use behavioral strategies to compensate for their greater rate of heat loss.

For adult Common Ground Doves from Sinaloa we demonstrate that the primaries are a single molt series, which sometimes feature two (in one case three) waves of feather replacement. Such stepwise primary replacement is found in many large birds but, at 40 g, this dove is much the smallest species reported to have multiple waves of replacement proceeding through its primaries simultaneously. Pre-breeding juvenile Common Ground Doves never feature two waves of primary replacement. Juveniles usually have more than two adjacent feathers growing simultaneously and replace their primaries in about 100 days. In contrast adults, which extensively overlap molt and breeding, usually grow just a single primary at a time, and require at least 145 days to replace their primaries. Molt arrests are thought to drive the generation of new waves of primary replacement in a diversity of large birds. For adult Common Ground Doves, we found molt arrests to be strongly associated with active crop glands, suggesting that the demands of parental care cause arrests in primary replacement in this dove. For those adults with two primary molt waves, initiation of an inner wave was most frequently observed once the outer wave had reached P10. Thus, unlike reports for large birds, Common Ground Doves usually suppress the initiation of a new wave of molt starting at P1 when the preceding wave arrests before reaching the distal primaries. This assures that relatively fresh inner primaries are not replaced redundantly, overcoming a serious flaw in stepwise molting in large birds (Rohwer, 1999).

Woodpeckers have unique molting patterns in which primaries and rectrices are replaced during all molt cycles but primary coverts and secondaries can be retained during prebasic molts. Details concerning replacement sequences and extents, however, are poorly known. We investigated molt patterns in 5 sapsucker (Sphyrapicus) taxa through the examination of 675 museum specimens and additional analysis of digital images. Sapsuckers replace fewer feathers per molt than most other North American woodpeckers. All individuals in 3rd basic plumage (3rd/4th calendar years) and a proportion of sapsuckers in 4th basic plumage (4th/5th calendar years) can retain juvenile feathers and be aged, a novel finding among woodpeckers and most bird species with the exception of some owls and larger flighted birds. Primary coverts and secondaries are replaced convergently from the outsides of each feather tract and Staffelmauser-like molting patterns can ensue. Asynchronous replacement of primary coverts and primaries (which are replaced distally) is unique to woodpeckers and kingfishers and may indicate that it evolved prior to the split of Piciformes and Coraciiformes. Juvenile body feathering and secondary coverts are retained longer into the fall and winter in the more highly migratory Yellow-bellied (S. varius) and Red-naped (S. nuchalis) sapsuckers, adding crypsis for migration and due to time constraints for molting. The extent of prebasic molts correlated positively with migration distance, being greater in Yellow-bellied and Williamson's (S. thyroides) sapsuckers and lowest in the nearly resident nominate subspecies of Red-breasted Sapsucker (S. ruber ruber), perhaps as related to the effects of solar exposure on an annual basis. Modeling of age structure through the 3rd and later basic plumages can inform conservation management related to salvage logging, climate-affected burn regimes, and the restoration of more favorable habitats. Los carpinteros tienen patrones de muda únicos, en los que las primarias y las rémiges son reemplazadas durante todos los ciclos de muda pero las coberteras primarias y secundarias pueden ser retenidas durante las mudas prebásicas. Sin embargo, no se tiene mucho conocimiento de los detalles de las secuencias de reemplazo y extensiones. Investigamos patrones de muda de 5 taxa de chupasavias (Sphyrapicus) examinando 675 especímenes de museo y analizando imágenes digitales adicionales. Los chupasavias reemplazan menos plumas por muda que la mayoría de los carpinteros norteamericanos. Todos los individuos en su plumaje básico 3rio (3ro/4to año calendario) y una proporción de los chupasavias en su plumaje básico 4rio (4to/5to año calendario) pueden retener plumas juveniles y ser de edad, un hallazgo nuevo entre los carpinteros y entre la mayoría de especies de aves, con la excepción de algunas lechuzas y aves voladoras de gran tamaño. Las coberteras primarias y secundarias son reemplazadas convergentemente a partir del exterior de cada canal de plumas, que a veces puede ser seguido de un patrón de muda tipo Staffelmauser. Un reemplazo asincrónico de coberteras primarias y de primarias (las cuales son reemplazadas distalmente) es único de carpinteros y martines pescadores y podría indicar que evolucionó previo a la separación de Piciformes y Coraciiformes. El plumaje corporal juvenil y las coberteras secundarias son retenidos durante más tiempo entrados el otoño e invierno en las especies de chupasavias más altamente migratorias Sphyrapicus varius y S. nuchalis, sumando camuflaje a la migración y debido a restricciones temporales para la muda. La extensión de las mudas prebásicas tuvo una correlación positiva con la distancia de migración, mayor en los chupasavias S. varius y S. thyroides y menor en la subespecie S. ruber ruber que es prácticamente residente, posiblemente relacionado a efectos de la exposición solar anual. El modelado de la estructura etaria utilizando el plumaje 3rio y plumajes básicos posteriores puede ayudar a tomar decisiones de manejo de conservación relacionadas con tala de rescate de maderas, regímenes de quemas afectados por el cambio climático y restauración de hábitats más favorables. Palabras clave: carpintero, determinación de edad, ecología, evolución, martín pescador, muda.