Moult Strategies Research Articles

Molt Patterns, Biometrics, and Age and Gender Classification of Landbirds on Saipan, Northern Mariana Islands

Abstract Molt strategies and plumage development by age and gender are poorly understood for resident tropical landbirds. We used data from six banding stations on Saipan, Northern Mariana Islands, and examination of 267 museum specimens to describe patterns of molt and to establish criteria for assessing age and gender of nine native resident landbird species on the island. Feather replacement sequences in the majority of Saipan's resident landbirds were typical of related species. Preformative molts occurred in at least eight of the nine species; these and definitive prebasic molts were incomplete to complete, and prealternate molt appeared to be absent for all species. We developed criteria for classifying gender of sexually dimorphic species using plumage cues, presence of brood patch or cloacal protuberance, and biometrics. We confirmed whether or not both brood patch and cloacal protuberance were reliable indicators of gender during breeding in monomorphic species. Distinct periods or seasons of mol...

Status of migrant and resident waders, and moult strategies of migrant waders using African inland wetland habitats, at Barberspan Bird Sanctuary in South Africa

Status of migrant and resident waders, and moult strategies of migrant waders using African inland wetland habitats, at Barberspan Bird Sanctuary in South Africa MAGDALENA REMISIEWICZ* & JOEL AVNI Animal Demography Unit, Department of Zoology, University of Cape Town, Rondebosch 7701, South Africa Avian Ecophysiology Unit, Department of Vertebrate Ecology and Zoology, University of Gdansk, al. Legionow 9, 80-441 Gdansk, Poland Ecotone Africa, 16 Kimberley Rd, Observatory 7925, Cape Town, South Africa

Sex‐dependent response of primary moult to simulated time constraints in the rock sparrow Petronia petronia

There is growing evidence that moult speed affects plumage quality. In many bird species, males and females differ in terms of breeding effort, survival expectation and the relationship between fitness and plumage quality. Consequently, differences in moult strategies between the sexes can be expected. The aim of this study was to assess whether, under simulated time constraints and with no parental investment in the previous breeding season, males and females differed in: a) timing and duration of primary moult, b) growth rates of individual primary feathers, and c) number of concurrently growing feathers. We investigated the effect of time constraints generated by a treatment consisting of two decreasing photoperiods (slow changing photoperiod, SCP=2 min day−1 and fast changing photoperiod, FCP=8 min day−1) on the primary post‐nuptial moult of captive rock sparrows Petronia petronia. Females started to moult on average 14 and 15 days later than males in both experimental groups. Primary moult duration was 10 (FCP) and 24 (SCP) days longer in males than in females, and, within sex, 34 (females) and 48 (males) days longer in SCP birds than in FCP ones. Females renewed a larger number of primaries simultaneously (5.7% in FCP and 12.8% in SCP) and had a higher total daily feather mass grown (9.9% in FCP and 22.4% in SCP), even though daily growth rates of individual primaries did not differ between sexes. As a result, males and females completed their primary moult at the same time within treatment. The observed differences in timing, duration and energy allocation for primary moult between the sexes probably have a genetic basis, as birds did not engage in reproduction during the preceding breeding season.

Rapid or slow moult? The choice of a primary moult strategy by immature Wood Sandpipers Tringa glareola in southern Africa

Immature migrant waders have more complex patterns of primary moult than adults, but these have been described only fragmentarily. The Wood Sandpiper Tringa glareola breeds in the taiga region of the Palearctic and part of the population migrates to southern Africa. We selected this population for a study of the primary moult strategies of an immature wader. After analysing the moult formulae of 674 immatures, we discuss potential factors that influence the choice of moult strategy. All moulters replaced two to six outer primaries; 91% moulted four or five. We used the Underhill–Zucchini model to estimate the timing and duration of moult in immatures replacing different numbers of primaries. A slow moult of five or six primaries, adopted by 29%, lasted on average 98–111 days, beginning on average 8–16 December. Moult of four primaries (63%) began on 6 January and averaged 73 days. A rapid moult of three primaries (7%) began on 24 January and averaged 55 days. All groups ended their moult between 19 and 28 March. GLM models showed that heavier immatures were more likely to start moulting than leaner birds. This tendency was more pronounced in November–January than in later months. The later the moult started, the fewer feathers were replaced and the faster the process. Departure time set the limit for the end of moult. We suggest the ability to choose different strategies allows immature Wood Sandpipers to adjust their moult to the variable conditions they encounter at wetlands in southern Africa.

Moult strategies of Cory’s Shearwaters Calonectris diomedea borealis: the influence of colony location, sex and individual breeding status

The replacement of old feathers is essential for birds, but it is also an energy-demanding task. As moult usually does not coincide with other stressful events in its annual cycle, such as reproduction and migration, the bird can optimise its use of time and energy allocated to different activities. There are very few studies comparing the moult strategies of populations with similar breeding calendars but occurring in areas of different habitat quality. Cory’s Shearwaters Calonectris diomedea have a partial moult–breeding overlap, an unusual phenomenon among pelagic seabirds. We have compared the moult schedules in Cory’s Shearwater colonies located in distinct environments (pelagic vs. coastal) and show that moult–breeding overlap is less extensive on Selvagem Grande, situated in deep oceanic waters, than on Berlenga, situated on the continental shelf. Colony attendance of failed breeders, most of which were moulting, was lower at Selvagem Grande than at Berlenga, which suggests that the feeding areas of birds from the former site are more distant from the colony. Failed breeders started to moult earlier than individuals still raising a chick, and breeding status had a stronger influence on determining the onset of wing-feather moult than colony location. Despite published evidence that internal circannual rhythms and external cues, such as variation in daylength, are important factors regulating moult schedules, it is clear that birds retain a considerable flexibility that allows them to respond to external factors in order to strategically manage time and energy in a way that is thought to maximise their fitness.

Introduction. Adaptation to the annual cycle

Most large organisms have an annual routine; that is to say they schedule activities in a regular way over the year. Like any behaviour, annual routines can be explained in terms of either their causation or their contribution to reproductive success, that is their evolutionary function. Previous

Effects of Size and Migratory Behavior on the Evolution of Wing Molt in Terns (Sternae): A Phylogenetic-Comparative Study

AbstractApproximately 60% of the 45 species of terns (Sternae) have an unusual form of wing molt in which a variable number of inner primaries and outer secondaries are replaced two or three times in a single year—a process that has been called “repeated molt.” Although several hypotheses have been proposed for the maintenance of repeated molt, few data exist regarding potential selective forces that may have favored the evolution of this molt strategy, and there are no explanations for the high degree of interspecific variation in the extent of repeated molt. Preliminary investigations indicated that large terns tended to have less repeated molt than small terns and that the presence of repeated molt appeared to be associated with migratory behavior. We examined these initial findings by combining data from the literature, from examinations of museum specimens, and from a recent molecular phylogeny of the terns to perform phylogenetic-comparative tests. First, we used independent contrasts to verify that the association between large terns and less repeated molt was significant and not a result of shared ancestry. Second, we used tests for binary character association to evaluate the apparent link between repeated molt and migratory behavior. The results of these tests, along with reconstructions of ancestral states, led to a potential explanation for the origin of repeated molt, in which a tropical, sedentary ancestor gave rise to several lineages that spread to temperate areas and adopted a migratory life history. With this shift to a more seasonal regime came shortened breeding periods and perhaps more time for molt, which could have led to modifications of the ancestral molting strategy and the origin of repeated molt.Efectos del Tamaño y del Comportamiento Migratorio en la Evolución de la Muda del Ala en los Gaviotines (Sternae): Un Estudio Filogenético Comparativo

EFFECTS OF SIZE AND MIGRATORY BEHAVIOR ON THE EVOLUTION OF WING MOLT IN TERNS (STERNAE): A PHYLOGENETIC-COMPARATIVE STUDY

Abstract Approximately 60% of the 45 species of terns (Sternae) have an unusual form of wing molt in which a variable number of inner primaries and outer secondaries are replaced two or three times in a single year—a process that has been called “repeated molt.” Although several hypotheses have been proposed for the maintenance of repeated molt, few data exist regarding potential selective forces that may have favored the evolution of this molt strategy, and there are no explanations for the high degree of interspecific variation in the extent of repeated molt. Preliminary investigations indicated that large terns tended to have less repeated molt than small terns and that the presence of repeated molt appeared to be associated with migratory behavior. We examined these initial findings by combining data from the literature, from examinations of museum specimens, and from a recent molecular phylogeny of the terns to perform phylogenetic-comparative tests. First, we used independent contrasts to verify tha...

Using stable isotope analysis to determine the winter moult extent in migratory birds: the complex moult of Savi's warblers Locustella luscinioides

Patterns of feather wear in birds captured in spring have traditionally been analysed to describe the extent of winter moult in long‐distance migrants. However, the interpretation of feather wear may be rendered extremely difficult due to long moult periods, by the progress of the season, and by the existence of complex moult patterns. Here, stable isotope analysis is used to determine the origin of the wing feather generations present in Savi's warblers Locustella luscinioides captured in Portugal. Carbon, nitrogen and hydrogen isotope ratios of feathers of known European origin differed significantly from those known to have grown in Africa. A discriminant analysis, in which 91.1% of the cross validated samples were correctly classified, was used to determine the origin of tail and wing feathers collected from birds caught when they returned to the breeding quarters. The interpretation of feather‐wear generally agreed with the stable isotope analysis, but some inconsistencies were identified. The extent of winter moult in Savi's warblers is described and its moult strategy discussed.

Molt Strategies and Age Differences in Migration Timing Among Autumn Landbird Migrants in Southwestern Idaho

AbstractIntraspecific patterns of autumn migration timing are not well known, particularly in the western United States. Here, we (1) describe autumn migration timing and age ratios of landbird migrants in southwestern Idaho, (2) examine differences in timing among age and sex classes, and (3) demonstrate how prebasic molt strategies affect migration timing differences between age classes. As a group, Neotropical migrants were most common from late July through early September, whereas temperate migrants were most common from mid-September into early October. Proportion of hatch-year birds was 74.5% for all migrants combined and ranged from 33.3% to 100% for individual species. Timing differences between sex classes were detected in only a few species and no general patterns emerged. In 22 of 31 Neotropical and temperate migrants examined, there were significant differences in timing between adults and hatch-year birds. In species in which adults begin fall migration before replacing flight feathers, adults migrated earlier than hatch-year birds. Conversely, in species in which adults molt flight feathers on or near the breeding grounds before departing on fall migration, hatch-year birds migrated earlier than adults in all but one case. Therefore, it appears that molt strategy is a powerful determinant of intraspecific migration timing differences and, to our knowledge, this is the first study to document this pattern among migrant passerines of North America.Estrategias de Muda y Diferencias en el Momento de Migración Otoñal en Migrantes Terrestres en el Suroeste de Idaho

Unravelling the migration and moult strategies of a long‐distance migrant using stable isotopes: Red Knot Calidris canutus movements in the Americas

For long‐distance migrants, such as many of the shorebirds, understanding the demographic implications of behavioural strategies adopted by individuals is key to understanding how environmental change will affect populations. Stable isotopes have been used in the terrestrial environment to infer migratory strategies of birds but rarely in marine or estuarine systems. Here, we show that the stable isotope ratios of carbon and nitrogen in flight feathers can be used to identify at least three discrete wintering areas of the Red Knot Calidris canutus on the eastern seaboard of the Americas, ranging from southeastern USA to Patagonia and Tierra del Fuego. In spring, birds migrate northwards via Delaware Bay, in the northeastern USA, the last stopping point before arrival in Arctic breeding areas, where they fatten up on eggs of spawning Horseshoe Crabs Limulus polyphemus. The isotope ratios of feather samples taken from birds caught in the Bay during May 2003 were compared with feathers obtained from known wintering areas in Florida (USA), Bahia Lomas (Chile) and Rio Grande (Argentina). In May 2003, 30% of birds passing through the Bay had Florida‐type ‘signatures’, 58% were Bahia Lomas‐type, 6% were Rio Grande‐type and 7% were unclassified. Some of the southern wintering birds had started moulting flight feathers in northern areas, suspended this, and then finished their moult in the wintering areas, whereas others flew straight to the wintering areas before commencing moult. This study shows that stable isotopes can be used to infer migratory strategies of coastal‐feeding shorebirds and provides the basis for identifying the moult strategy and wintering areas of birds passing through Delaware Bay. Coupled with banding and marking birds as individuals, stable isotopes provide a powerful tool for estimating population‐specific demographic parameters and, in this case, further our understanding of the migration systems of the declining Nearctic populations of Red Knot.

Body Composition and Flight Ranges of Bar-Tailed Godwits (Limosa Lapponica Baueri) From New Zealand

AbstractBody composition analysis was performed on 37 Bar-tailed Godwits (Limosa lapponica baueri) that had been illegally shot during migratory fueling in northern New Zealand in March 1992. Adults (n = 35) were heavy (442–721 g), with fat loads of 30–45% of body mass. Two first-year males had only 5.4% and 8.9% fat, respectively, and had 13% less lean (fat-free dry) tissue than the average adult male. Males and females scaled along the same size axes, with little overlap between the sexes (females were larger). Larger birds carried more fat, but fat loads did not differ systematically with size (and, therefore, sex). Fatter birds (after accounting for body size) had larger flight muscle and lung masses, implying premigratory hypertrophy. Males that were not in body molt were fatter, but less colorful, than molting birds. They were also longer-winged and had larger testes but smaller intestines and salt glands, which suggests that they may belong to a subpopulation with a different fueling and molt strategy. Comparison between L. l. baueri and a smaller subspecies (L. l. taymyrensis) indicated that although the two subspecies scaled along the same lean mass-size axes, L. l. baueri deposited much more fat for their body size (1.7 × more than the equivalent-sized L. l. taymyrensis). On the basis of estimated travel costs for L. l. taymyrensis, predicted flight ranges for L. l. baueri ranged from 6,000 to 8,600 km, depending on whether wind assistance is assumed. That suggests that direct flights from New Zealand to southeastern or eastern Asia are possible (e.g. Philippines, 7,200 km; Japan, 8,700; South Korea, 9,100 km).Composition Corporelle et Distance de Vol chez Limosa lapponica baueri de Nouvelle-Zélande

Correlates of timing of spring migration in birds: a comparative study of trans-Saharan migrants

The evolution of migratory strategies in birds is likely to have been influenced by ecological as well as socio-sexual factors in both wintering and breeding areas. In this comparative study, we analysed timing of spring passage of 38 long-distance migratory bird species that winter south of the Sahara desert and breed in Europe, in relation to wintering and breeding latitudes, moult strategy, nesting site (open vs. cavity), and sexual dimorphism in size and coloration, which may reflect intensity of sexual selection. We employed a large data set consisting of more than 190 000 individuals ringed during spring migration in the Mediterranean Sea. We found that the species that migrated earlier were those wintering farther north, nesting in cavities and showing the largest degree of sexual size dimorphism (SSD). However, sexual dichromatism was not related to migration date. Among passerine species, moulting wing-feathers in Africa delayed migration. We found no support for the energetic constraint hypothesis, which proposes that early arrival selects for large male size, since early arriving species were not larger than late arriving ones. Thus, the observed associations suggest that variation in migration schedules at the interspecific level may have evolved in relation to ecological factors and SSD, possibly reflecting the intensity of mating competition. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85, 199–210.

Gull-billed Terns in north-western Australia: subspecies identification, moults and behavioural notes

Two subspecies of the Gull-billed Tern (Sterna nilotica) occur along the coasts of north-western Australia: the large, pale Australian subspecies macrotarsa, and a smaller, darker migratory subspecies from northern Asia. On the basis of banding data we describe the measurements and moult strategies of both subspecies in north-western Australia and identify the Asian migrants as subspecies affinis. Asian migrants have a predictable plumage cycle including regular alternation between breeding and non-breeding plumage in adults. The moult strategy of Australian macrotarsa is more varied and we argue it is adapted to exploit unpredictable breeding opportunities. Plumage and structural characters described in this paper allow the two subspecies to be distinguished in the field, and field observations demonstrate some broad ecological differences between them. Adult affinis occur in Australia from August to April, with smaller numbers of immatures remaining during the dry season; they are strictly coastal, occurring in highest abundance over intertidal flats near mangrove systems where they pluck prey from the surface of mud while in flight. Subspecies macrotarsa uses the north-western Australian coast as a non-breeding area, but it does so mainly during the dry season and also uses grasslands and inland wetlands; unlike affinis, in Roebuck Bay it is regularly kleptoparasitic, stealing large crabs (Macropthalmus sp.) from Whimbrels (Numenius phaeopus).

Resistance of flight feathers to mechanical fatigue covaries with moult strategy in two warbler species

Flight feather moult in small passerines is realized in several ways. Some species moult once after breeding or once on their wintering grounds; others even moult twice. The adaptive significance of this diversity is still largely unknown. We compared the resistance to mechanical fatigue of flight feathers from the chiffchaff Phylloscopus collybita, a migratory species moulting once on its breeding grounds, with feathers from the willow warbler Phylloscopus trochilus, a migratory species moulting in both its breeding and wintering grounds. We found that flight feathers of willow warblers, which have a shaft with a comparatively large diameter, become fatigued much faster than feathers of chiffchaffs under an artificial cyclic bending regime. We propose that willow warblers may strengthen their flight feathers by increasing the diameter of the shaft, which may lead to a more rapid accumulation of damage in willow warblers than in chiffchaffs.

Sexing, ageing and moult of Buzzards Buteo buteo in a southern European area

In order to obtain a reliable method for sexing and ageing Buzzards Buteo buteo breeding in southern Europe, 115 birds from a wildlife rehabilitation centre and 43 trapped birds were measured, sexed and aged over four years (2000–2003). Dead birds were sexed by examining their gonads, and live birds by the presence of a brood patch. Wing length, minimum tarsus width and body weight were the only variables which differed significantly between the sexes, although there was much overlap for the wing length and weight. Buzzards with less than 7 mm minimum tarsus width were male and those greater than 7.9 mm were female. Birds did not complete moult in one year, moulting less than 60% of the flight feathers in one season. The first and the second moult followed a pattern, but afterwards moult was unpredictable and totally asymmetric. Also, half the females and 33% of males had started to moult within 30 days of their chicks hatching. These results differ from those published for Buzzards from northern Europe. The size and moult pattern depend on factors such as prey availability and migratory status, which in turn vary between areas. We therefore suggest caution when considering the moult strategies, ageing criteria and sexing criteria published for other countries.

MOLT STRATEGIES AND AGE DIFFERENCES IN MIGRATION TIMING AMONG AUTUMN LANDBIRD MIGRANTS IN SOUTHWESTERN IDAHO

Abstract Intraspecific patterns of autumn migration timing are not well known, particularly in the western United States. Here, we (1) describe autumn migration timing and age ratios of landbird migrants in southwestern Idaho, (2) examine differences in timing among age and sex classes, and (3) demonstrate how prebasic molt strategies affect migration timing differences between age classes. As a group, Neotropical migrants were most common from late July through early September, whereas temperate migrants were most common from mid-September into early October. Proportion of hatch-year birds was 74.5% for all migrants combined and ranged from 33.3% to 100% for individual species. Timing differences between sex classes were detected in only a few species and no general patterns emerged. In 22 of 31 Neotropical and temperate migrants examined, there were significant differences in timing between adults and hatch-year birds. In species in which adults begin fall migration before replacing flight feathers, adu...

Moult of three Palaearctic migrants in their West African winter quarters

Some theories about moult strategies of Palaearctic passerine migrants assume that birds adapt timing of moult to environmental conditions such as rainfall on their African wintering grounds. Species wintering in the northern tropics should limit moult to the period shortly after their arrival at the end of the rainy season. Passerine migrants wintering in West Africa should also moult more rapidly compared to related species or conspecific populations that moult elsewhere. We investigated the moult of melodious warblers Hippolais polyglotta, willow warblers Phylloscopus trochilus and pied flycatchers Ficedula hypoleuca wintering in Comoe National Park, Ivory Coast, between October 1994 and April 1998. In contrast to previous studies we did not restrict our analyses to moult of flight feathers but also included moult of body feathers. The results differed partially from the general assumptions of previous authors. Melodious warblers moulted twice: a complete moult shortly after their arrival, and a moult of body feathers and in some cases some tertials and secondaries in spring. Willow warblers moulting flight feathers were found between December and March with the majority moulting in January and February. Primary moult was not faster compared to populations moulting in central Africa and South Africa. Body feather moult varied strongly among individuals with birds in heavy moult between December and April. Pied flycatchers moulted body feathers and tertials between January and April. Birds with growing feathers were found throughout the whole period including the entire dry season. Moult strategies are thus not readily related to a few environmental factors in general and our results show that factors other than mere resource availability during certain times on the wintering grounds are likely to govern the timing of moult.

Phylogenetic analyses of the diversity of moult strategies in Sylviidae in relation to migration

Moult in birds is highly variable both within and among bird genera. The aim of the present study was to make an extended phylogenetic analysis of the diversity of moult strategies within Sylviidae in light of the recent phylogenies based on molecular data, and with the methodology of matched-pairs analysis. In the present study we analysed 141 sylviid taxa and, to improve character reconstruction, 22 outgroup taxa. The study could corroborate the earlier results that post-breeding moult is the ancestral state in Sylviidae. Migratory habits were found to be ancestral within Sylviidae but resident habits have evolved several times with a few reverse transitions back to migratory habits. Transitions in main moult strategy were significantly related to both migratory vs. resident habits and to migratory distance, giving support to the hypothesis that moult in the non-breeding season is related to migration as such and long-distance migration, respectively. Both resident and migratory taxa used minor alternative moult strategies besides the main moult strategy and such within-taxon flexibility might be a basal trait in Sylviidae. We investigated three variables that included minor strategies and found no relationship between these and migratory habits. However, two of these variables (the potential to interrupt moult and the occurrence of moult in both the post- and non-breeding seasons) were significantly related to migration distance. We conclude that migration patterns has some influence on the choice of moult strategy, and that flexibility in timing of moult is widespread within Sylviidae and might be a basal trait. We argue that such flexibility might be a prerequisite for changes in migratory strategies.

Molting and Salmonella enterica serovar enteritidis infection: the problem and some solutions

Induced molting is an important economic tool used by the egg industry to recycle an aging layer flock. It is estimated that approximately 70% of the flocks nationwide and almost 100% in California are molted annually. Considering that there are approximately 240 million hens in production in the U.S., a rough estimate of the numbers of hens molted every year would be between 144 and 168 million birds, a substantial number. There are many methods to induce molt, but feed removal until hens lose a specific weight is the most prevalent molt strategy in the U.S. However, experimental studies in our laboratory have shown that induced molting via feed removal depresses the immune system of hens and exacerbates a Salmonella enteritidis (SE) problem in a simulated flock situation. Molted hens excreted significantly higher SE numbers in the feces, had higher numbers of SE in internal organs, and exhibited more intestinal inflammation. Molted hens were 100- to 1,000-fold more susceptible to infection by SE and therefore more readily transmitted the organism to uninfected hens in neighboring cages. With the problems identified, solutions were sought, and several were successful in ameliorating the SE issue. Antibiotic therapy, vaccination, and use of low-energy, low-calcium diets to molt hens all dramatically decreased SE shedding during molt. All of the solutions provide the producer with many potential solutions to the SE food safety issue and still allow them to recycle their hens.