Duration Of Moult Research Articles

Age differences in primary moult of the Black-headed Gull Chroicocephalus ridibundus

Flight feather moult is an energetically expensive stage of the annual cycle of birds. Its timing is adjusted to other important time- and energy-demanding activities, including migration. In the vast majority of migratory birds, primary moult occurs before or after migration or moulting is suspended during migration. The Black-headed Gull is an exception: it starts moulting flight feathers at the onset of the autumn migration. The course of primary moult in this species is still poorly understood due to the difficulty in obtaining sufficient data from the entire period of flight feather replacement. In this paper, we employed digital photos taken in the field to estimate the start, variation in the start date and duration of primary moult in adult and immature Black-headed Gulls, by using the Underhill–Zucchini likelihood moult model. On average, immatures started their moult on 7 June, 25 days earlier than adults, but their moult lasted 5 days longer. Consequently, there was a 20-day difference in the end of moult – that is, on average it occurred on 16 September and 6 October in immature and adult gulls, respectively. Adults showed greater variability in the mean primary moult start date than immatures, as the beginning of flight feather replacement may depend on breeding success (earlier after breeding failure) and on breeding phenology. The overlap of primary moult and migration produces a trade-off in resource allocation between those two processes, which leads to a low number of simultaneously growing primaries and a decrease in the growth rate of the two external, heaviest flight feathers. Existing reports of a later completion of primary moult in the first half of November in this species are based on the faulty assumption that the outermost primary is always the longest, which is not the case in 34% of individuals.

Effects of sublethal methylmercury and food stress on songbird energetic performance: metabolic rates, molt and feather quality.

Organisms regularly adjust their physiology and energy balance in response to predictable seasonal environmental changes. Stressors and contaminants have the potential to disrupt these critical seasonal transitions. No studies have investigated how simultaneous exposure to the ubiquitous toxin methylmercury (MeHg) and food stress affects birds' physiological performance across seasons. We quantified several aspects of energetic performance in song sparrows, Melospiza melodia, exposed or not to unpredictable food stress and MeHg in a 2×2 experimental design, over 3 months during the breeding season, followed by 3 months post-exposure. Birds exposed to food stress had reduced basal metabolic rate and non-significant higher factorial metabolic scope during the exposure period, and had a greater increase in lean mass throughout most of the experimental period. Birds exposed to MeHg had increased molt duration, and increased mass:length ratio of some of their primary feathers. Birds exposed to the combined food stress and MeHg treatment often had responses similar to the stress-only or MeHg-only exposure groups, suggesting these treatments affected physiological performance through different mechanisms and resulted in compensatory or independent effects. Because the MeHg and stress variables were selected in candidate models with a ΔAICc lower than 2 but the 95% confidence interval of these variables overlapped zero, we found weak support for MeHg effects on all measures except basal metabolic rate, and for food stress effects on maximum metabolic rate, factorial metabolic scope and feather mass:length ratio. This suggests that MeHg and food stress effects on these measures are statistically identified but not simple and/or were too weak to be detected via linear regression. Overall, combined exposure to ecologically relevant MeHg and unpredictable food stress during the breeding season does not appear to induce extra energetic costs for songbirds in the post-exposure period. However, MeHg effects on molt duration could carry over across multiple annual cycle stages.

Individual variation in life-history timing: synchronous presence, asynchronous events and phenological compensation in a wild mammal.

Many animals and plants have species-typical annual cycles, but individuals vary in their timing of life-history events. Individual variation in fur replacement (moult) timing is poorly understood in mammals due to the challenge of repeated observations and longitudinal sampling. We examined factors that influence variation in moult duration and timing among elephant seals (Mirounga angustirostris). We quantified the onset and progression of fur loss in 1178 individuals. We found that an exceptionally rapid visible moult (7 days, the shortest of any mammals or birds), and a wide range of moult start dates (spanning 6-10× the event duration) facilitated high asynchrony across individuals (only 20% of individuals in the population moulting at the same time). Some of the variation was due to reproductive state, as reproductively mature females that skipped a breeding season moulted a week earlier than reproductive females. Moreover, individual variation in timing and duration within age-sex categories far outweighed (76-80%) variation among age-sex categories. Individuals arriving at the end of the moult season spent 50% less time on the beach, which allowed them to catch up in their annual cycles and reduce population-level variance during breeding. These findings underscore the importance of individual variation in annual cycles.

Rapid flight feathers moult and fat stores in the Common Snipe Gallinago gallinago in the early stage of autumn migration

We analysed primary and secondary feather moult and fat reserves in 539 Common Snipes captured in the middle Pripyat River Valley, an important stopover site for waders in Central Europe, between 2002 and 2022. The average daily rate of feather growth was 1.89% in primaries and 2.27% in secondaries, being one of the highest documented in waders. The estimated duration of growth for a single flight feather varied from 11 to 21 days in primaries and from 8 to 11 days in secondaries. Moreover, multiple flight feathers (up to 14) were replaced simultaneously. As a result, the wing moult in Common Snipes was rapid with the mean primary moult duration estimated at 53 days (28 June–20 August) according to the Underhill–Zucchini model, and only 20 days in secondaries (31 July–20 August) based on moult estimates of individual secondaries. Hence, although secondary feathers began to grow when primary moult was already advanced, moulting of both flight feather groups was completed in most birds at almost the same time. Our study shows that Common Snipe in the middle Pripyat River Valley exhibit very rapid wing moult with large wing gaps. Fat reserves and thus body mass of Common Snipes were the lowest when the wing gap was greatest, compensating for their reduced wing area. Late and slow movement towards wintering grounds, allows them to moult rapidly at the early stage of autumn migration, which is likely to occur only in sites with abundant food resources.

Extended molt phenology models improve inferences about molt duration and timing

Abstract Molt is an essential life-history event in birds and many mammals, as maintenance of feathers and fur is critical for survival. Despite this molt remains an understudied life-history event. Non-standard statistical techniques are required to estimate the phenology of molt from observations of plumage or pelage state, and existing molt phenology models have strict sampling requirements that can be difficult to meet under real-world conditions. We present an extended modelling framework that can accommodate features of real-world molt datasets, such as re-encounters of individuals, misclassified molt states, and/or molt state-dependent sampling bias. We demonstrate that such features can lead to biased inferences when using existing molt phenology models, and show that our model extensions can improve inferences about molt phenology under a wide range of sampling conditions. We hope that our novel modelling framework removes barriers for modelling molt phenology data from real-world datasets and thereby further facilitates the uptake of appropriate statistical methods for such data. Although we focus on molt, the modelling framework is applicable to other phenological processes that can be recorded using either ordered categories or approximately linear progress scores.

Highland and lowland forest birds differ in their feather growth rates: a multispecies test in the southwestern Palaearctic

Mountain birds face numerous challenges caused by altitude‐dependent environmental seasonality. Although elevation gradients may affect bird morphology, migration strategy and/or phenology of seasonal events (breeding and moulting), the life histories of highland compared with lowland birds have been little explored. In this study we compared the growth rate and mass of the tail feathers of six forest passerine species sampled at different elevations in the Iberian Peninsula (north) and the Maghreb (south) to assess potential differences in moult duration and feather quality between highland and lowland bird populations. As timing is crucial in seasonal environments, we also explored seasonal changes in temperature in the different study areas as a proxy for the duration of the optimal temporal windows available in summer for breeding and moulting. In addition, we compared wing configuration between highland and lowland populations, which could reflect differences in their migration strategy (migratory versus sedentary). The results showed that highland birds had less time available for breeding and moulting, longer and more concave wings, and faster feather growth rates than lowland populations, but we found no consistent patterns of variation in feather mass. These results suggest that selection might have favoured an accelerated moult and a more migratory behaviour in highland populations to cope with the reduction in the optimal temporal window as elevation increases. These patterns are similar to those observed in migratory populations moving along latitudinal gradients to breed in highly seasonal northern environments. We therefore hypothesize that elevational gradients at the southern limit of the Palaearctic could be an important driving force promoting variation in feather growth rate and wing configuration, and probably also other avian life‐history characteristics.

Primary moult in the annual cycle of adult African Oystercatchers Haematopus moquini

African Oystercatchers Haematopus moquini are sedentary, intertidal foraging birds, range-restricted to Namibia and South Africa. Their annual cycle has two components: breeding and moult. The Underhill–Zucchini model estimated a primary moult duration of 154 days, and mean start and completion dates of 1 April and 2 September. Most eggs (90%) are laid between mid-November and mid-February; thus, on average, oystercatchers have 2–3 months between moult completion and egg laying. The completion date confirms an overlap between moult and the period of post-fledging dependence of juveniles on their parents. The 154-day primary moult duration spreads the energetic demands of feather production to cope with this overlap and with the fact that primary moult extends through winter when storms make intertidal areas inaccessible for days. There are approximately 50 quantitative studies of primary moult for migrant waders (suborder Charadrii); this is the third for a resident species. The other two species of resident waders studied are in south-eastern Australia: the Hooded Dotterel Thinornis cucullatus and Sooty Oystercatcher Haematopus fuliginosus. The Hooded Dotterel has one of the longest estimated moult durations (203 days) and its moult and breeding overlap. The annual schedules for the Sooty Oystercatcher and African Oystercatcher are similar, as is the estimated moult duration: 149 and 154 days, respectively. Preliminary studies of the primary moult of the Eurasian Oystercatcher H. ostralegus indicate the duration to be 100 days, which is two-thirds that of the two sedentary oystercatchers. This is likely a consequence of Eurasian Oystercatchers having migration and harsh winter conditions as additional components of their annual cycle, and thus a limited period for primary moult. This study was based largely on photographic records of African Oystercatchers in flight, with contributions by citizen scientists. We make two key conclusions: the need for more studies of the moult strategies of the Haematopidae and resident waders; and digital photography of free-ranging birds can be used to study primary moult.

The primary moult of adult Red-headed Finches Amadina erythrocephala

Little is known about the biology of the Red-headed Finch Amadina erythrocephala. This study investigates its primary moult, the first aspect of its life history to be looked at in depth. Additionally, we used a modified Cook’s distance algorithm to explore the influence of individual years on the moult parameter estimates. Lastly, the primary moult of Red-headed Finches is compared to that of other passerines resident in the Highveld region of South Africa. Red-headed Finches breed through the Highveld winter, and start moult on 22 August, on average. Moult extends through spring and most of the summer, reaching completion on 22 February, on average. However, the moult started unusually early in the years 1988, 2005, 2008 and 2019, whereas in 2017 moult started unusually late. The duration of moult was estimated to be 185 days. The majority of other passerines resident in the central Highveld breed through summer, undergo primary moult in autumn, and complete moult before the regular frosts start to occur during the Highveld winter. The moult duration of the Red-headed Finch is substantially longer than that of other resident passerines.

Primary moult of adult Laughing Doves Spilopelia senegalensis: introduction of the relative duration index and a comparison of moult indices

A new moult index, the relative duration index (RDI), was developed to quantify progress through moult using the Underhill–Zucchini model of primary avian moult, with the Laughing Dove Spilopelia senegalensis as a case study. The RDI weights individual primaries in accordance with their estimated relative moult durations in the same way that proportion feather mass grown (PFMG) weights primaries in accordance with their relative masses. A sample of 1 893 moult records of adult Laughing Doves was used to study their primary moult. Moult parameters were estimated for three moult indices: the traditional moult score (TMS), PFMG and the RDI, and for each of the 10 primaries. Comparing the moult parameter estimates of each of the three indices to their respective cumulative growth curves obtained from the progression of moult of individual primaries, PFMG had the closest fit. However, any of the three moult indices would give satisfactory results for the Laughing Dove. Laughing Doves had an estimated primary moult duration of 215 days, with mean start and end dates of 3 November and 6 June, respectively. The standard deviation parameter was 66 days, which implies a lack of synchronisation of moult in adult doves. It was hypothesised that the RDI might be an appropriate moult index for species that moult one feather at a time and for which the individual moult durations are not proportional to their mass, as seen in Laughing Doves. However, this was not the case as PFMG provided the best fit. The RDI might also prove to be an appropriate moult index for species that moult multiple feathers simultaneously during part of the moult period and these feathers grow more slowly than when fewer feathers are moulting simultaneously.

Moult performance varies in relation to colour patterns in crossbills

Carotenoid-based ornamentation can vary greatly among individual birds of the same population. This variability might consider the timing and duration of moult. Crossbills (genus Loxia) show large variation in their colour patterns, ranging from dull yellow to red. Thus, they provide an excellent avian model for testing whether the timing and duration of their moult are associated with their dominant colour patterns. Using a dataset of more than 1900 crossbills captured in the Pyrenees (Spain), we observed that individuals with red feathers started their primary moult early, while those with yellow feathers started moult on an average of 18 days later. We also found that yellow crossbills were more likely to suspend moults (i.e. temporally interrupt moult), postponing a part of the moult until September. These differences in the moulting process may be related to plumage colour, which reflect individual condition.

Plumage dimorphism and moult patterns of weaverbirds – a review

The colourful plumages of weaverbirds (family Ploceidae, with 118 species recognised) provide a well-known and in part iconic showcase of sexual selection, with widespread sexual dimorphism (93 species) as well as seasonal dimorphism (62 species). The tremendous diversity in both the type and degree of plumage dimorphism is poorly known, which calls for a better and extended understanding of the highly variable moult patterns in this group. Here, we lay a foundation for this by reviewing and discussing what is known of the timings and patterns of moult in the Ploceidae. The extent of post-juvenile moult is poorly known in weavers: it is known to be complete in 10 species, partial in two species, and either complete or partial in six species. However, it is likely that there is more variation than previously thought. Weavers typically have a complete moult after breeding, and before breeding a partial prenuptial moult, restoring the male (and, in some species, female) breeding plumage; this usually involves only body feathering, one exception being the Seychelles Fody Foudia sechellarum, which has a complete prenuptial moult. We compiled primary moult data based on the proportion of feather mass grown, for 11 weaver species, three of which are newly reported on. Timing of primary moult is discussed in relation to sex, location and annual timing. The duration of primary moult varies widely between and within species, from 46 days (1.5 months) in a widowbird to 215 days (7 months) in an arid species. Weavers in arid regions have longer moult durations than weavers in other regions. Examples of the overlap of primary moult and breeding are presented.

Identification and profiling of long non-coding RNAs during molt cycle: An involvement of lnc1182 in the molt of white shrimp, Litopenaeus vannamei

Molt is an essential physiological process for crustacean growth. It is known to be controlled by factors such as hormones and steroids, but the role of long non-coding RNA (lncRNA), a potential regulatory molecule, has not been studied. In this study, we investigated the role of lncRNA in the molt process of white shrimp, Litopenaeus vannamei. The 9437 of 58,142 unigenes of de novo assembled transcriptome were identified as putative lncRNAs, and 768 lncRNAs were differentially expressed during molt cycles. Five differentially expressed lncRNAs were selected to determine their expressions in different tissues and molt stages. Most were expressed more in gills and epidermis than other tissues. Expressions of lnc1182 and lnc336 significantly decreased during premolt stages and increased at postmolt in gills and epidermis, while lnc179 expression increased during premolt stages. RNA interference was used to investigate the role of lnc1182 in the molt process. The molt of lnc1182 knockdown shrimp progressed to early premolt faster than shrimp injected with dsGFP, and also shortened molt duration. In addition, total sugar level in hemolymph was higher in the lnc1182 knockdown shrimp than the control shrimp, whereas gill Na+/K+ ATPase activity, total hemocyte count, and expression of molt-inhibiting hormone (MIH) were not changed. These suggested that lnc1182 is likely involved in the control of sugar metabolism during molting but not in ion exchange activity and MIH expression. Furthermore, lnc1182 and 20-HE probably regulated each other. RNA sequencing was used to investigate the set of genes associated with lnc1182. Fifty-five transcripts were differentially expressed in gills of lnc1182 knockdown shrimp. Expressions of candidate metabolism and immune-related genes were validated for their differential expressions in lnc1182 knockdown shrimp. Our work produced lncRNA profiles and indicated possible functions of lnc1182 in metabolism and immunity during the molt cycle in shrimp.

Erratum: Eyestalk Ablation to Increase Ovarian Maturation in Mud Crabs.

Erratum: Eyestalk Ablation to Increase Ovarian Maturation in Mud Crabs.

The relationship of moult timing, duration and sequence to the aerial lifestyle of the Little Swift (Apus affinis)

Feather moult is an important and energy‐demanding avian life‐history trait that is necessary to maintain the function of the plumage by replacing abraded feathers with new ones. However, during moult, aerodynamic capacity is temporarily impaired by the reduction and shape change of the flight surface. Therefore, among aerial birds, adaptations may evolve to reduce this impairment. Here, we studied the timing, duration and sequence of the annual complete moult of adult Little Swifts Apus affinis in northern Israel by examining the plumage of 55 individuals monthly in their colony. Primary moult occurs over 191.7 ± 24.0 days, representing 52.5 ± 6.6% of the annual cycle, and overlaps with the breeding season, a rare occurrence among small Palaearctic bird species. In addition, primary moult duration was significantly affected by its timing such that individuals that started to moult later had a shorter moult duration than those that started to moult earlier. This relationship is most likely to be a result of the time available for moult, which is limited by breeding and also by the cold season and the expected decline in food availability. Moult overlap with breeding or cold seasons may involve energetic and functional costs. Our results indicate two strategies that appear sequentially: (1) a slow and long moult that largely overlaps with breeding, and (2) a shorter moult that overlaps less with breeding (both strategies avoid moulting during the cold season). Most Little Swifts (85.7%) moulted their rectrices in a centripetal sequence starting with the outermost pair of rectrices inward. This moult was later in relation to wing feather renewal and had almost no overlap with primary moult. Finally, we tested a method for non‐invasively monitoring moult of small species by collecting and sampling shed feathers without the need to capture the birds themselves, as has been successfully used for larger bird species. This work demonstrates the importance of aerodynamic considerations in the evolution of life‐history traits. Moult‐related aerodynamic costs may be an important evolutionary factor shaping moult strategy, including timing, duration and sequence, mainly among species, like swifts, that are highly dependent on their aerodynamic ability.

Non-breeding behaviour in the Brown Skua (Stercorarius antarcticus lonnbergi): insights from modelling moulting patterns and stable isotope analyses

ABSTRACT Long-term changes in the life history and behaviour of seabirds during the non-breeding season can reflect shifts in environmental conditions. However, long-term marine studies are scarce, particularly on southern hemisphere seabirds. Here, we used moult scores from 86 Brown Skuas (Stercorarius antarcticus lonnbergi), a large predatory seabird breeding on the Chatham Islands, Aotearoa/New Zealand to model both the timing and duration of primary feather moult. In addition, we analysed stable isotope values (δ13C and δ15N) from 62 modern (2014–16) and ten museum tail feathers. These data provide insights into the non-breeding behaviour of Brown Skua. Interestingly, our results show that the primary feather moult occurred prior to birds departing the colony, starting on average on 2 January ± 5 days (SE). The average start of primary feather moult occurred five days prior to the end of breeding (7 January ± 10 days (SD)) and 42 days before the birds departed the colony (13 February ± 11 days (SD)). The average duration of primary feather moult was 189 ± 14 days (SE). Importantly, low δ13C values in four females suggested that tail feather moult might also occur while skuas are at the colony. There was no difference in tail feather δ13C and δ15N values between any pairwise comparison of modern and museum years. However, values of δ15N from tail feathers sampled in 2014 were different from those sampled in 2015 and 2016. This large annual variation in δ15N values from tail feathers over such a short period makes long-term comparisons difficult to interpret, particularly between years with low sample sizes. While the stable isotope analyses of tail feathers are informative, we recommend future studies of skuas sample the primary coverts rather than tail feathers.

Moult intensity constraints along the complete moult sequence of the House Sparrow (Passer domesticus)

Sequence and intensity are two essential components of bird moult. While the moult sequences of remex tracts are highly homogenous across passerines, other tracts apparently show a high variability. Moreover, order of moult activation among tracts are insufficiently known. Likewise, dynamics of moult intensity as moult progresses remains poorly known. Here, we provide detailed quantitative description of moult sequence and intensity in the House Sparrow (Passer domesticus). To understand their role, we tested two hypotheses on the: 1) protection function of moult sequence, and 2) aerodynamic and physiological constraints on moult intensity. We scored percentage growth of 313 captured sparrows using the mass of the feathers of each tract (also length for remiges) to monitor moult intensity throughout the complete moult progress, which is defined as the fraction of new and growing feathers in a moulting bird relative to the total plumage. Moult sequence was highly variable both within wing coverts and among feather tracts, with moult sequence differing among all birds to some degree. We only found support for the protection function between greater coverts and both tertials and secondaries. Remex-moult intensity conformed to theoretical predictions, therefore lending support to the aerodynamic-constraint hypothesis. Furthermore, remex-moult speed plateaued during the central stages of moult progress. However, overall plumage-moult speed did not fit predictions of the physiological-constraint hypothesis, showing that the remex moult is only constrained by aerodynamics. Our results indicate that aerodynamic loss is not simply the inevitable effect of moult, but that moult is finely regulated to reduce aerodynamic loss. We propose that the moult of the House Sparrow is controlled through sequence and intensity adjustments in order to: 1) avoid body and wing growth peaks; 2) fulfil the protection function between some key feather tracts; 3) reduce detrimental effects on flight ability; 4) keep remex sequence fixed; and 5) relax remex replacement to last the whole moult duration.

Potential toxicity and dietary risk of tricyclazole to Chinese mitten crab (Eriocheir sinensis) in the rice-crab co-culture model

Tricyclazole is used as a common fungicide to control rice blast. However, studies on the toxicity of tricyclazole to crabs in the rice-crab co-culture system are still extremely rare. Here, the environmental dissipation of tricyclazole was monitored in this model, and the potential toxicity of tricyclazole to E. sinensis at environmental concentrations as well as the dietary risk was evaluated. The results showed that tricyclazole had no significant acute toxicity to E. sinensis (LC50 > 100 mg/L), while it promoted body weight gain. Tricyclazole in the hepatopancreas had a higher persistent bioaccumulation risk than in the muscle. Tricyclazole suppressed the immune response of E. sinensis under prolonged exposure and there should be gender differences, with females being more sensitive. Lipid metabolism enzymes were also significantly inhibited. While tricyclazole stimulated males molting but prolonged molting duration, both molting and duration of females were also disturbed. The dietary risk assessment indicated that tricyclazole intake from current crab consumption was low risk. This evidence demonstrated that tricyclazole may have potential risks to individual development, nutritional quality, and economic value on E. sinensis and should be used with caution in rice-crab co-culture system whenever possible.

Postbreeding movements and molting ecology of female gadwalls and mallards

AbstractThe wing molt is an important annual life‐history event that occurs in waterfowl and molt site selection can play an important role in determining survival. We tracked postbreeding movements of gadwall (Mareca strepera) and mallard (Anas platyrhynchos) females that bred in the Suisun Marsh (Suisun) of California, USA, to determine molt site selection and wing molt chronology. We attached backpack transmitters with global positioning system and global system for mobile communications (GPS‐GSM) technology to female gadwalls and mallards within Suisun and tracked the birds following the breeding season during 2015–2018. We determined molt locations for 52 female gadwalls and 112 female mallards. Thirty of the marked gadwall females selected 2 regions within southern Oregon‐northeastern California (SONEC) to undergo molt; 16 molted in the Upper Klamath Basin (southern OR) and 14 in the Lower Klamath Basin (northeastern CA). A large portion of female mallards molted in Suisun (n = 34) and the Sacramento Valley in California (n = 31) but also used the Upper Klamath Basin (n = 13), Lower Klamath Basin (n = 12), and the Yolo–Delta region in California (n = 12). On average, gadwalls departed Suisun on 30 July (±17.82 days [SD]), and mallards departed on 24 July (±22.69 days). Mean start date of molt for each species was similar: 27 August (±16.09 days) for gadwalls and 26 August (±21.03 days) for mallards. Molt end date was analogous for each species as well. Molt ended on average 1 October (±15.52 days) for gadwalls and on 5 October (±18.34 days) for mallards. Gadwalls and mallards showed intraspecific differences in average molt start and end date within the 3 main geographical zones: Suisun, Central Valley of California (Central Valley), and SONEC. Mean duration of wing molt for gadwalls was 34.72± 8.62 days and 41.09 ± 12.54 days for mallards. Both species primarily selected permanent marsh to undergo wing molt (gadwalls = 90.4%, mallards = 63.4%). Conservation and active management of these high‐use molting areas used by California's primary breeding waterfowl species could enhance postbreeding survival, leading to increased breeding waterfowl populations.

The effects of feeding ration and cheliped autotomy on the growth and expression of ecdysteroid receptor in early juvenile mud crabs, Scylla paramamosain

This study investigated the combined effects of feeding ration and cheliped autotomy on the intermolt duration, molting success, molt increments in size and weight, and ecdysteroid receptor gene (SpEcR) expression of early juvenile mud crab Scylla paramamosain. Newly molted second stage juvenile crabs (C2) were subjected to four feeding conditions; optimal, suboptimal (1/2 optimal), low (1/4 optimal) ration and starvation, and autotomy (intact vs. cheliped autotomy) in a 4 × 2 factorial design until all crabs successfully molted or died. A significant interaction of feeding ration and cheliped autotomy on intermolt duration was identified. With reduced feeding ration, both intact and cheliped autotomized crabs showed increased time and desynchrony of molting, but decreased carapace size and body weight. Importantly, all crabs with different feeding rations even the low ration had high rates of molting success (> 95%), while the crabs subjected to starvation died without molting. When fed optimal ration, the mean intermolt duration of the cheliped autotomized crabs was significantly prolonged, while no such effect was found between autotomized and intact crabs subjected to suboptimal or low feeding ration. The qRT-PCR revealed that the expression of SpEcR showed a general trend of inhibited by reduced feeding ration, which was consistent with observed significantly increased intermolt duration. Interestingly, the transcript level of SpEcR was only significantly affected by cheliped autotomy under the optimal and suboptimal feeding rations but not for the low feeding ration. Together, the results of this study suggest that the S. paramamosain early juveniles have a strong tolerance for fluctuations in food availability. In addition, the availability of food and limb autotomy could significantly affect growth, molting duration and synchrony of the crabs, which appeared to reflect in SpEcR expression level that involved in the regulation of molting and limb regeneration process of the juvenile crabs.

Timing, duration and symmetry of moult in Cape Gannets

Little has been reported on moult in sulids, including gannets. The Cape Gannet Morus capensis is an endangered seabird endemic to southern Africa. We describe the timing, duration, symmetry and sequence of flight feather moult in Cape Gannets from two breeding colonies and assess whether moult can be used as an index of condition. Using the Underhill-Zucchini model, we estimate moult parameters based on the proportion of feather mass grown. Adult Cape Gannets began primary moult at the beginning of January (2–3 January ± 28 days SD) at both colonies. Primary moult is protracted, with multiple active centres (mean ± SD 1.8 ± 0.8, range 1–4) and 2.0 ± 0.9 feathers growing at the same time (range 1–5). Primary moult is suspended by early June at Malgas Island (estimated duration of moult ± SE, 153.9 ± 4.1 days) and late June at Lambert’s Bay (176.5 ± 5.5 days). Secondary moult commenced in late January and proceeded from two nodal points. Despite more secondaries (3.3 ± 1.9, range 1–8) being grown simultaneously than primaries, 8% of birds were still moulting secondaries at the start of the breeding season. However, it was not certain that these individuals were breeding. Tail moult also overlapped with that of the primaries, with multiple active centres (2.7 ± 1.2, 1–6) and 2.9 ± 1.3 feathers growing at the same time (range 1–8). Almost all primary (98%) and secondary moult (97%) was symmetrical, but there was little symmetry in tail moult (54%). Rectrix symmetry tended to be greater among gannets at Malgas Island (T1: 58%; T2–T6: 67–73%) than at Lambert’s Bay (T1: 50%; T2–T6: 55–66%). Differences in moult duration and perhaps asymmetry between locations may be linked to foraging conditions, given that Lambert’s Bay gannets are thought to be under greater food stress than Malgas birds.