Post-juvenile Moult Research Articles

Fuel deposition and speed of early autumn migration of juvenile Bluethroats Luscinia s. svecica leaving their natal area in Swedish Lapland

The period between independence and the early phase of autumn migration is a difficult period for juvenile birds and a relatively poorly known part of the annual cycle. We present data on post-juvenile moult, fuel deposition and speed of early autumn migration of "red-spotted" Bluethroats Luscinia s. svecica, studied during 14 years (1984—1997) in Ammarnäs, Swedish Lapland. The juvenile Bluethroats leave their natal site from early August onwards, while still being in active post-juvenile moult. They do not put on any noticeable fuel stores, probably because foraging conditions are generally poor. This is reflected in a very slow initial speed of migration (11–21 km/d) between the natal area and stopover sites in eastern Sweden.

Photoperiodic response to early hatching in a migratory bird species.

A considerable number of bird species of the northern hemisphere have been breeding earlier over the last few decades, most probably in response to global warming. In migratory birds, there is also a trend towards later departure from the breeding grounds in autumn. Yet it is not known whether this trend in the timing of migration reflects an evolutionary process or is just an immediate phenotypic response to global environmental change. We conducted an experiment with migratory blackcaps (Sylvia atricapilla) to investigate how the photoperiodic conditions experienced by birds hatching earlier in the season affect the timing of post-juvenile moult and the onset of autumn migration. In a split-brood experiment, we reared 30 nestlings from six different families and kept them either under a photoperiodic regime simulating conditions 6weeks before their actual hatching date or under simulated natural photoperiods. Time-shifted birds started moulting at an earlier age compared to controls and showed an early phase of nocturnal migratory activity. Under the influence of long day lengths moult was prolonged and migratory activity was interrupted. However, the termination of moult and the reinitiation of migratory activity were not delayed to the extent that birds compensated for the simulated early hatching date. Thus, we suggest that extant physiological responses to the photoperiod are maladaptive under the novel environmental conditions imposed by a global increase in temperature, leading to earlier autumn migration in juvenile birds with earlier breeding.

Body mass of six long-distance migrant passerine species along the autumn migration route

We analysed body mass and moult data of six passerine species along their autumn migration route from northern Europe to North Africa and derived hypothetical models of the organisation of their migration in terms of fuel store accumulation. We analysed data of 46,541 first-year birds from 34 trapping sites, sampled in a network of collaborating European and African ringing stations. After accounting for effects of time of day and size, there were marked differences between the six species examined in the change of body mass along the migration route and in the timing of moult. Garden Warblers (Sylvia borin) and Pied Flycatchers (Ficedula hypoleuca) underwent their postjuvenile moult prior to migration and increased their average body mass along the migration route. Sedge Warblers (Acrocephalus schoenobaenus) also increased body mass towards the south, but started the migration bout without further refuelling well before the Sahara and moulted mainly in the wintering grounds. Reed Warblers (Acrocephalus scirpaceus) and Whitethroats (Sylvia communis) migrated while still moulting and did not increase average body mass towards south. They accumulated the energy needed to fly over the Sahara just before it. Spotted Flycatchers (Muscicapa striata) behaved in the same way, but contrary to Reed Warblers and Whitethroats they did not accumulate much fat stores in North Africa, which might urge them to stop and fuel up regularly in the Sahara. In the course of the season average body mass of all species increased slightly, which enabled them to migrate faster. In general, average body mass of first-year birds in northern and central Europe during the migration period was comparable to that of adults during breeding.

Dependence of Postjuvenile Moult on Hatching Date, Condition and Sex in the Great Tit

We examined the influence of hatching date, nestling condition (body mass), size and sex on the age at the onset, and on the duration and extent of postjuvenile moult in a Great Tit population in southern Finland. Date of hatching explained most of the variation in moult parameters. Onset of moult was closely connected with hatching date: Great Tits from first broods started moulting in July and birds from second broods started in mid-August. The age at the start of moult decreased from 56 to 42 days from first to repeat and second broods and the duration of moult decreased from 67 to 59 days. Variation of moult parameters with date of hatching and the timing of moult are in concordance with experimental data on photoperiodic control of moult. Females started to moult older and moulted less extensively than males, especially in first broods. Residual body mass during moult reflected the state and intensity of moult, but did not correlate with the final extent of moult. This contradicts the recent protein stress and condition hypotheses.

Annual cycle of the Helmeted Honeyeater Lichenostomus melanops cassidix, a sedentary inhabitant of a predictable environment

The annual cycle of breeding, moult and weight variation in the Helmeted HoneyeaterLichenostomus melanops cassidix, a sedentary bird of temperate southeast Australia, is documented. Breeding and moult were sequential unimodal annual events, whose timing was highly consistent between years. However, overlap of breeding and moult was frequent, and some individuals even commenced primary moult before laying their final clutch. The timing of the post‐juvenile moult was coincident with that of adults. Early‐hatched young moulted within a few months of hatching, but late‐hatched young deferred moult for a year. Helmeted Honeyeaters were heaviest in autumn and early winter, and lightest in spring and early summer, a cycle most consistent with the redirection of all available resources to reproduction. The long breeding season (seven‐and‐a‐half months) of the Helmeted Honeyeater, extensive overlap of breeding and moult, and other life‐history attributes including small clutch size, are more consistent with the described bio‐rhythmic patterns for birds in the humid tropics than the temperate zone. However, the Helmeted Honeyeater has a fairly rapid primary moult rate, unusual amongst species that overlap moult and breeding. This combination of attributes reflects the stable, somewhat seasonal environment occupied and the resource monopoly established by this tightly territorial subspecies. We speculate that extension of the breeding season, by overlapping breeding and moult, is one of the few options available to vary life‐history strategies amongst ‘old‐endemic’ Australian birds of the temperate zone.

Post-juvenile body moult in the Blue Tit Parus caeruleus: influence of age and nestling history

The influence of sex, age and nestling history (viz. brood size, hatching date and nestling condition) on the progress of post-juvenile body moult in the Blue Tit Parus caeruleus was investigated. The stage of body moult advanced with increasing age in both sexes, but was independent of hatching date, experimental brood size and nestling condition. The estimated age at the onset of post-juvenile moult was 23–46 days and the average estimated age at moult completion was 113 days. After controlling for age differences, females were on average more advanced in moult than males, although the magnitude of this sex effect differed in different study years. The results suggest that in juvenile Blue Tits, an individual's age and sex are more important determinants of the progress of the post-juvenile moult than nestling condition, brood size or hatching date.

Behavioural and morphological correlates of variation in the extent of postjuvenile moult in the SiskinCarduelis spinus

Siskins Carduelis spinus show great variation in the acquisition of adult plumage, so that yearling birds can be classified as either “delayed” (i.e. still showing yearling plumage) or “advanced” (i.e. with an adult plumaged appearance). The extent of moult in males is related to the size of their black bib, which in turn is highly correlated with their social dominance rank. Autumn male body mass is higher in advanced than in delayed moult birds, but by winter the relationship is reversed, suggesting a trade‐off between investment in moult and subsequent body condition. Results were similar in Spain and Britain. A possible cost of advancing moult is suggested by an analysis of aggressive interactions at bird feeding tables which showed that adult males discriminate between delayed and advanced birds, directing most aggression towards adult‐looking yearling males. The results suggest that the variation in the extent of postjuvenile moult is not only related to energetic constraints but has other important behavioural and ecological implications.

A feeding experiment on migratory fuelling in whitethroats,Sylvia communis

The influence of food abundance on whitethroats' behaviour when preparing for autumn migration was investigated in a feeding experiment on the island of Gotland in the Baltic. Whitethroats attracted to a feeding site during post-juvenile moult attained a stable body mass 1.4g higher than birds in natural conditions. This fuel load is well below the maximum that whitethroats could deposit. After maintaining stable body mass during moult, the whitethroats started to gain mass and thereafter soon departed on migration. This shift was due to the birds increasing their gross food intake by about 70%. Both the average rate of fuel deposition (about 7% of lean body mass per day) and the average departure fuel load (over 50% of lean body mass) were much higher for birds at the feeding site than for birds in natural conditions. No correlation between rate of fuel deposition and departure fuel load was found at the feeding place. Larger departure fuel loads in late individuals suggest that departure decisions are affected by temporal cues. Comparisons with models of time-minimization during migration show that the lack of correlation between rate of fuel load and departure load contradicts the predictions in one model. In another model, where a finite distance is included, the relationship between rate of fuel deposition and departure fuel load is predicted to be step-wise. This means that within certain ranges of rate of fuel deposition the departure fuel load should not change, which is consistent with the result found in this study.

The autumn migration of Willow Warblers Phylloscopus trochilus in Sweden: results from a nation-wide co-operative project

The result of a nation-wide co-operative project studying the autumn migration of Willow Warblers Phylloscopus trochilus in Sweden is presented. This involved 18 bird observatories and private ringers during 1988–1990, at both coastal and inland sites, with data on more than 36,000 birds analysed. Data on age, wing length, fat and body mass were collected in a standardised way, as was scoring of post-juvenile moult (used as a measure of juvenile age). Each bird observatory made a basic compilation of data into weekly averages, upon which the present analysis builds. The proportion of juveniles (93%) was much higher than expected (c. 75%), at both inland and coastal sites. Adults migrated a few days later than juveniles. There was no sex difference in the timing of migration in adults. Juveniles of Ph. t. acredula started migration at an earlier age (35–40 days old) than juveniles of Ph. t. trochilus (50–55 days old). Average wing length increased during the season at many sites, suggesting that birds belonging to the longer-winged Ph. t. acredula passed later in season. Juvenile energy stores were small during mid post-juvenile moult, but higher in the last moult stage, especially at coastal sites. Generally, Willow Warblers in Sweden in autumn carry only small to moderate fat loads, which supports earlier findings that the commencement of migration involves short flights. Conclusions on energy stores were based on data from visual fat score. Because both moulting and migrating birds occurred at most sites, and moulting birds have a different composition of their lean body, body mass does not reflect the seasonal changes in fat loads. Body mass averages of 8.2–9.3 g were similar to averages from other parts of northern Europe, but below the values reported for birds prior to trans-Sahara flights and maximum masses of birds in captivity.

Evidence for partial prenuptial moult in adult and first-year Penduline TitsRemiz pendulinus

Contrary to earlier accounts, this paper suggests that both first-year and adult Penduline Tits undertake a partial prenuptial moult. This moult is more extensive in first-year birds than adults and includes the replacement of body feathers, marginal and median wing coverts and a variable number of greater coverts, rectrices and inner remiges. Most flight feathers and greater coverts renewed during the first prenuptial moult are probably replaced from the point that the previous post-juvenile moult had finished and the subsequent moult occurs sequentially. This complementarity between post-juvenile and prenuptial partial moult seems exceptional among European passerines. Males tend to renew more of their plumage between the summer and winter moult periods. The extent of the first prenuptial moult was negatively correlated with the extent of the previous post-juvenile moult. It is suggested that this is due to the small advantages provided by a more extensive prenuptial moult after a given level of plumage...

The timing of post-juvenile moult and fuel deposition in relation to the onset of autumn migration in Reed Warblers Acrocephalus scirpaceus and Sedge Warblers Acrocephalus schoenobaenus

The extent of post-juvenile moult and fuel deposition prior to migration in Reed Warblers Acrocephalus scirpaceus and Sedge Warblers A. schoenobaenus were analysed using 11 years ringing data from Lake Kvismaren in South Central Sweden. Re-trap data showed that Reed Warblers acquired their first winter plumage in 34 days, compared to 22 days in Sedge Warblers. The moult pattern of the two species differed due to Sedge Warblers only undertaking a fill-in moult of bare body areas. Fuel deposition rates for the two species were similar, 0.38 g/day for Reed Warblers and 0.34 g/day for Sedge Warblers. The estimated average fuel stores at departure from Lake Kvismaren differed, with Reed Warblers found to leave with a fuel store of 21% (in relation to lean body mass) compared to 6.2% in Sedge Warblers. The median date of departure from Lake Kvismaren was estimated to 30 August for Reed Warblers and 12 August for Sedge Warblers. The earlier departure of Sedge Warblers, with smaller fuel stores, may reflect different migration strategies between the species.

Variation in the extent of postjuvenile moult in the Great Tit near Lake Ladoga (Russia)

We examined the extent of postjuvenile moult of rectrices, greater coverts, alula and tertials in the Great Tit Parus major during migration and feather replacement near Lake Ladoga. The moult of 16 hand%raised birds was also followed in experimental photoperiodic conditions simulating different hatching dates. The data from caged birds showed that the extent of moult in the Great Tit is photoperiodically controlled. Autumn short%light days reduce the extent of moult. The data from moulting birds trapped in the wild agreed with experimental results and revealed that the timing of feather replacement influenced the individual extent of moult. Annual variation in the extent of moult was influenced by the timing of breeding in the population. A possible explanation for the decline in the extent of moult during migration is discussed.

Fat Reserves and Health State in Migrant Goldcrest Regulus regulus

1. Although the importance of adequate fat deposits for migrating birds has long been recognized, little is known about causes of intraspecific variation in the size of energy reserves. 2. We studied individual variation in visible fat reserves, body size, state of health and nutrition among autumn migrating Goldcrests Regulus regulus. 3. Birds showing signs of infectious/inflammatory diseases (high red blood cell sedi- mentation rate) or anaemia (low packed red blood cell volume) had significantly smaller fat stores than birds lacking these signs. However, no differences in fat reserves or health state were detected in relation to stage of post-juvenile moult. 4. These results suggest that the ability to deposit fat in the face of an energetically demanding migration may be affected by an individual's state of health.

Behaviour, natural history, and annual cycle of the Henderson Island rail Porzana atra (Aves: Rallidae)

The little known endemic Henderson Island rail (or Henderson rail) Porzflna atra, inhabits forest on the coastal plain and upraised plateau of Henderson Island. Rails were studied for 15 months from January 1991 to March 1992. The population was estimated at c. 6200 individuals living in pairs or cooperative groups of 3–4 adults on territories averaging about 1 ha. Two or three eggs were laid in covered or open nests near the ground from mid-July to mid-February. Up to five consecutive nesting attempts were made in cases where eggs or young chicks were lost. Adults laid a second clutch when chicks were fully feathered at about one month of age. Both sexes incubated and helped rear the young. Older chicks sometimes helped feed younger siblings. Dispersal of juveniles from the natal territory took place in April. Adult birds underwent a rapid, simultaneous post-nuptial moult of the remiges in February-April; the post-juvenile moult involved body feathers only. Data on morphometries, breeding ecology, courtship behaviour and voice are compared with available information for the spotless crake P. tabuensis, the Henderson rail's closest relative and probable ancestor. These comparisons provide some information on how these two taxa have differentiated since rails arrived on Henderson Island some time in the last 380000 years.

Behaviour, natural history, and annual cycle of the Henderson Island rail Porzana atra (Aves: Rallidae)

The little known endemic Henderson Island rail (or Henderson rail) Porzflna atra, inhabits forest on the coastal plain and upraised plateau of Henderson Island. Rails were studied for 15 months from January 1991 to March 1992. The population was estimated at c. 6200 individuals living in pairs or cooperative groups of 3–4 adults on territories averaging about 1 ha. Two or three eggs were laid in covered or open nests near the ground from mid-July to mid-February. Up to five consecutive nesting attempts were made in cases where eggs or young chicks were lost. Adults laid a second clutch when chicks were fully feathered at about one month of age. Both sexes incubated and helped rear the young. Older chicks sometimes helped feed younger siblings. Dispersal of juveniles from the natal territory took place in April. Adult birds underwent a rapid, simultaneous post-nuptial moult of the remiges in February-April; the post-juvenile moult involved body feathers only. Data on morphometries, breeding ecology, courtship behaviour and voice are compared with available information for the spotless crake P. tabuensis, the Henderson rail's closest relative and probable ancestor. These comparisons provide some information on how these two taxa have differentiated since rails arrived on Henderson Island some time in the last 380000 years.

Mass-change during moult in the Great TitParus major

Changes in mass during moult were investigated by analysis of data recorded on standard moult cards by members of the British Trust for Ornithology Ringing Scheme. In the analysis of post juvenile moult, all available cards that presented wing length, mass and time of capture were used. The analysis of adult post-nuptial moult was restricted to cards from a single year. Juvenile mass correlated strongly with body size, time of day and the number of greater coverts being replaced. After controlling for the effects of size and time of day, mass was found to increase with date except in those individuals in which all juvenile greater coverts were retained. In these birds residual mass declined with date. In adult males, mass increased with both date and moult scores of primary, secondary and tertial remiges and of rectrices but because of the strong correlations between moult scores and date, the true relationship was not clear. In adult females, mass declined with date before increasing again. Unlike the ma...

Postjuvenile moult in the Azure‐winged MagpieCyanopica cyanea cooki

Postjuvenile moult in Azure‐winged Magpies Cyanopica cyanea cooki was studied in free‐living and captive birds. Most natal primary (99.7%) and secondary (81.2%) feathers were retained, but only 50% of rectrices. Estimates of individual moult duration in free living birds in the following feather tracts gave: 65 days for tertials, 13 days for greater coverts, 97 days for rectrices, and 30 days for the alula. Wing coverts were the first to begin moult, followed by tertials. Alula feathers were the last to start moult. Tertial moult commenced at an average age of 97 days, regardless of hatching date. In captive birds, body moult was initiated in dorsal and upper tail coverts at the end of July and culminated in the interramal region by the end of November, with a mean moult duration of 122 days. Data on plumage growth and development are presented, and factors influencing the extent, timing and duration of moult are discussed.

The age of young Willow Warblers Phylloscopus trochilus estimated from different stages of post-juvenile moult

A scale for estimating the progression of post-juvenile moult in Willow Warblers is described. The scale was used on birds caught at Ammarnäs, Swedish Lapland in 1984—1991 . Two data sets were used to determine the average age (days since hatching) of birds in different stages of moult. First, 91 Willow Warblers with known hatching date were later retrapped and examined for state of moult. Most of these birds were caught in the earlier stages of moult. Second, birds first caught in one stage of moult were retrapped in later stages and this enabled an estimate to be made of the average age of juvenile Willow Warblers in the later stages of moult. The moult of juveniles commences at an age of 26 days, just after the outermost primaries reach full length. Few birds with completed moult were registered but data suggest that moult ends around 60 days of age. The scale is also applicable to juveniles of many other passerine species, but there are exceptions.

Sexual dimorphism in the post‐juvenile moult in the Azure‐winged MagpieCyanopica cyaneacooki

A sexual dimorphism in the postjuvenile moult of the Azure‐winged Magpie Cyanopica cyanea cooki is described. Males retain significantly fewer primaries, secondaries, upper greater primary coverts ...

Influence of Experience and Visual Stimulation in Japanese Quail Laying Site Selection Under Experimental Condition

We raised female Japanese quail until their post juvenile moult in “neutral” or simplified environments chosen according to features representative of natural habitats. At laying, we placed female quail individually in a choice situation with regard to environmental patterns. 9fiey took account of the visual factors of. their environment in selecting laying site. We found that female Japanese quail preferred a structured achromatic environment over a uniform achromatic environment. They showed a preference for vertical grey stripes over horizontal stripes and a clear preference for green over ochre. Green vertical and horizontal striping proved highly attractive but there was no preference for one or another. Juvenile experience does not affect laying site selection but it certainly does emphasize preference for green. Individual choice proved to be stable but, on the contrary, we found strong interin dividual variability within each one of the groups. The results taken as a whole are relevant to the choices faced by female quails seeking nest sites in their natural habitat.