Optimal moult strategies in migratory birds

Avian migration, which involves billions of birds flying vast distances, is known to influence all aspects of avian life. Here we investigate how birds fit moult into an annual cycle determined by the need to migrate. Large variation exists in moulting patterns in relation to migration: for instance, moult can occur after breeding in the summer or after arrival in the wintering quarters. Here we use an optimal annual routine model to investigate why this variation exists. The modelled bird's decisions depend on the time of year, its energy reserves, breeding status, experience, flight feather quality and location. Our results suggest that the temporal and spatial variations in food are an important influence on a migratory bird's annual cycle. Summer moult occurs when food has a high peak on the breeding site in the summer, but it is less seasonal elsewhere. Winter moult occurs if there is a short period of high food availability in summer and a strong winter peak at different locations (i.e. the food is very seasonal but in opposite phase on these areas). This finding might explain why only long-distance migrants have a winter moult.     

Ecological correlates in the evolution of moult strategies in Western Palearctic passerines

Moult is an important process in the life cycle of birds. Passerines differ widely in the number, seasonality and extension of moult episodes, but the incidence of birds ecology on this variation remains largely uninvestigated. We analysed the patterns of moult in European passerines in relation to their distribution, migration and sexual dichromatism. Longer migrations and southern wintering quarters were characteristic of species with complete moults in summer and an additional moult in winter. The main moult in species with larger seasonal changes in sexual dimorphism tended to be scheduled just before the start of the breeding season, suggesting a link between sexual selection and the timing of moult. These patterns strongly support the importance of migration and dichromatism on the evolution of moult strategies.     

Frequency of complete moult in adult and juvenile Great Reed Warblers(Acrocephalus arundinaceus) in Spain

Summary We examined a large data set of adult and juvenile Great Reed Warblers (Acrocephalus arundinaceus), caught over five years, to study the occurrence of complete moult in a Spanish population. A total of 27 adults and 5 juveniles were in active moult. The proportion of birds moulting each year varied between 0.03 and 0.19. Nearly half the adults were finishing moult. At least one bird was certainly of local origin, rather than on passage, and four more were moulting when retrapped in subsequent years, suggesting that they too were resident breeders in the area. Some other birds were probably resident also, because they were in moult when caught at the beginning of August. Two of the five juveniles finished their moult in the area. In conclusion, our data seem to show that complete moult before departure to the wintering quarters is a regular process undertaken by some of the breeding population of Great Reed Warblers in north-east Spain.

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Das Vorkommen von Vollmauser bei Alt- und Jungvögeln des Drosselrohrsängers(Acrocephalus arundinaceus) in Spanien

Zusammenfassung Von 837 zwischen 1992 und 1996 im Ebro Delta gefangenen Drosselrohrsängern mauserten 27 Alt-und 5 Jungvögel. Der jährlichen Anteil mausernder Vögeln betrug zwischen 0,03 und 0,19%. Etwa die Hälfte der mausernden Altvögel und zwei der Jungvögel beendeten ihre Mauser im Untersuchungsgebiet. Diese Daten zeigen, daß Drosselrohrsänger in Spanien wenigstens teilweise auch schon vor Beginn des Wegzuges eine Vollmauser durchführen.

     

Adaptations to migration in birds: behavioural strategies, morphology and scaling effects

The annual life cycle of many birds includes breeding, moult and migration. All these processes are time and energy consuming and the extent of investment in any one may compromise the others. The output from breeding is of course the ultimate goal for all birds, while the investment in moult and migration should be selected so that lifetime fitness is maximized. In particular, long-distance migrants breeding at high latitudes face severe time pressures, which is a probable reason why natural selection has evolved efficient behaviours, physiological and morphological adaptations allowing the maximum possible migration speed. Optimal migration theory commonly assumes time minimization as an overall strategy, but the minimization of energy cost and predation risk may also be involved. Based on these assumptions, it is possible to derive adaptive behaviours such as when and at which fuel load a stopover site should be abandoned. I review some core components of optimal migration theory together with some key predictions. A review of accumulated empirical tests of the departure rule indicates that time minimization is an important component of the overall migration strategy, and hence gives support to the assumption about time-selected migration. I also briefly discuss how the optimal policy may be implemented by the bird by applying a set of simple rules. The time constraints on migrants increase with increasing body size. Some consequences of this are discussed.     

Molecular Systematics of the Malagasy Babblers (Passeriformes: Timaliidae) and Warblers (Passeriformes: Sylviidae), Based on Cytochrome b and 16S rRNA Sequences

The phylogenetic relationships of the Timaliidae (babblers) and Sylviidae (warblers) have long challenged ornithologists. We focus here on three Malagasy genera currently assigned to the Timaliidae, Mystacornis, Oxylabes, and Neomixis, and on their relationships with other babblers and warblers using the sequences of two mitochondrial genes (cytochrome b and 16S rRNA). Maximum parsimony analyses show that the Malagasy “babblers” are not related to any of the other African and Asian babblers. The genus Mystacornis is neither a babbler nor a warbler. The other Malagasy “babblers” are members of warbler groups (the monophyly of the Sylviidae is not demonstrated). Oxylabes madagascariensis and Hartertula flavoviridis (we recognize Hartertula as a genus for the species flavoviridis, previously Neomixis flavoviridis) constitute, with two presumed sylviine taxa, Thamnornis chloropetoides and Cryptosylvicola randrianasoloi, a warbler radiation endemic to the island of Madagascar. The other Neomixis species (tenella, striatigula, and viridis) belong to another warbler group comprising cisticoline taxa. These results show that the Timaliidae did not disperse to Madagascar. Rather, the island has been colonized, independently, by at least two clades of warblers, probably originating from Africa, where the Sylviidae radiation has been the most extensive.     

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

Summary 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.

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Körpermassen von sechs Arten von Langstreckenziehern entlang des Herbstzugweges

Zusammenfassung Wir analysierten Körpermassen- und Mauserdaten von sechs Singvogelarten auf dem Herbstzug entlang ihres Zugweges von Nordeuropa bis Nordafrika. Die Körpermassen von 46 541 diesjährigen Vögeln, die auf 34 Beringungsstationen im Rahmen eines internationalen Projektes gesammelt wurden, sind die Grundlage dieser Untersuchung. Neben der Entwicklung der Körpermassen entlang des Zugweges untersuchten wir den Einfluss der Mauser, des Fangdatums, der Tageszeit und der Körpergröße auf die Körpermasse. Mausernde Vögel waren schwerer als nichtmausernde mit der gleichen Fettmenge. Die Körpermasse nahm im Laufe der Saison und im Verlauf des Tages zu. Große Vögel (mit einer längeren 8. Handschwinge) waren schwerer als kleine. Gartengrasmücken (Sylvia borin) und Trauerschnäpper (Ficedula hypoleuca) wurden entlang des Zugweges kontinuierlich schwerer. Beide Arten machten die Jugendteilmauser hauptsächlich noch im Brutgebiet durch. Schilfrohrsänger (Acrocephalus schoenobaenus) wurden nach Süden ebenfalls etwas schwerer, aber sie begannen mit einem Reiseabschnitt ohne weiteren Fettaufbau schon in Mitteleuropa und mauserten ihr Kleingefieder hauptsächlich erst in Afrika. Die Körpermassen von Teichrohrsängern (Acrocephalus scirpaceus) und Dorngrasmücken (Sylvia communis) blieben nach Süden weitgehend konstant. Beide Arten lagerten die nötigen Energiereserven zum Überfliegen der Sahara erst kurz davor an. Sie trennten Jugendteilmauser und Zug nicht vollständig. Ähnlich verhielten sich Grauschnäpper (Muscicapa striata), doch im Gegensatz zu den zwei vorherigen Arten, wurden sie auch im Mittelmeergebiet nicht wesentlich fetter. Sie scheinen daher regelmässig in der Wüste zu rasten und zu fressen.

     

Behavioural changes are related to moult regulation in the cockroach, Periplaneta americana

Abstract. Larval holometabolous insects show changes in behaviour (e.g. start of wandering and spinning) in specific periods of the moulting cycle in relation to definite ratios of juvenile hormone and moulting hormone (ecdysone). In hemimetabolous insects no such changes in behaviour are known. It should be investigated whether the cockroach Periplaneta americana shows changes in locomotor activity and in food and water consumption in relation to periods of ecdysone production during the last larval stage. Within a mean duration of the last larval stage of 30 days there were two periods of reduced locomotor activity: on day 9 and between days 13 and 17. From days 12–13 food consumption decreased by c . 40% up to the day 18. Water consumption decreased between days 9 and 18 by about 55%. Peaks of ecdysone production appeared after these changes of behaviour in each case. Therefore in larval Periplaneta ecdysone seems not to trigger these behavioural changes.     

Spring phenology of ecological productivity contributes to the use of looped migration strategies by birds

Migration is a common strategy used by birds that breed in seasonal environments. The patterns and determinants of migration routes, however, remain poorly understood. Recent empirical analyses have demonstrated that the locations of two North America migration flyways (eastern and western) shift seasonally, reflecting the influence of looped migration strategies. For the eastern but not western flyway, seasonal variation in atmospheric circulation has been identified as an explanation. Here, we test an alternative explanation based on the phenology of ecological productivity, which may be of greater relevance in western North America, where phenology is more broadly dictated by elevation. Migrants in the western flyway selected lower-elevation spring routes that were wetter, greener and more productive, and higher-elevation autumn routes that were less green and less productive, but probably more direct. Migrants in the eastern flyway showed little season variation but maintained associations with maximum regional greenness. Our findings suggest the annual phenology of ecological productivity is associated with en route timing in both flyways, and the spring phenology of ecological productivity contributes to the use of looped strategies in the western flyway. This fine-tuned spatial synchronization may be disrupted when changing climate induces a mismatch between food availability and needs.     

Notes on the moult of red-backed shrikes ( Lanius collurio ) in their non-breeding range

Moult data from 302 museum skins and 11 trapped birds from sub-Saharan Africa show the course of flight feather moult. Most birds seem to start flight-feather moult soon after arrival in their southern African non-breeding ranges. About 75% of the birds had started before mid-December, i.e., during the main arrival time of the species. The mode of moult scores 1 and 2 was reached on 7 December; the last birds with a score of zero occurred in the first days of January. The mode of moult scores 5 and 6 was reached on 27 February. Thus, the time elapsed between the days when 50% of the population had reached the first and last stages of recorded moult was about 82 days; nine days later 75% had reached this last stage before moult was completed. Thus, individual moult may be estimated to cover about 80–90 days. The main moulting period is between mid-November and mid-March, thus covering about four months. No temporal difference was detected between males and females. A tendency for an advancement of adults compared to young birds was not statistically significant. According to the progress of the moult, sexing of young birds in the field is possible for 50% of the birds towards the end of January and for most birds before mid-February.     

A special moult after the release of the embryo from the brood pouch of Anomopoda (Branchiopoda,Crustacea): a return to an old question

In the past there were doubts about the existence of a especialmoult after the release of an anomopod embryo from the maternalbrood pouch. This moult occurs in all studied anomopods and marksthe beginning of the first juvenile instar. The term neonata (orneanate) must be applied to the unexpanded animal (the terminalphase of embryogenesis) before this moult, and not to the earlyphase of the first postembryonic instar. The latter is the nextstage of development. Using knowledge of the presence of thismoult, it is possible to understand and explain the contradictionsin the periodization of postembryonic development as described bydifferent authors. Under normal conditions males of bosminids andevolutionarily advanced chydorids have only two juvenile instars(with specific morphology) in the course of development. This is anadditional argument to support the idea of close relationship ofthe families Chydoridae and Bosminidae.