SPRING WEIGHTS OF SOME PALAEARCTIC MIGRANTS AT LAKE CHAD

A visit was made to Malamfatori, on the western shore of Lake Chad, Nigeria, from 22 March to 13 April 1967, with the principal aim of studying Palaearctic migrants in relation to the environment. About 2,400 Palaearctic migrants of 29 species were mist-netted in beds of bulrush Typha australis and thickets of saltbush Salvadora persica. Some 300 of these were collected for fat analysis; the remainder were released after measurement and ringing, and provided 275 retraps during the course of the study. Data were supplemented by further netting by A. J. Hopson in late April and May. Yellow Wagtails Motacilla flava, Sedge Warblers Acrocephalus schoenobaenus and Whitethroats Sylvia communis were abundant and were studied in greater detail than other species. Yellow Wagtails fed almost exclusively on midges, particularly the abundant Tanytarsus spadiceonotatus. Sedge Warblers fed on small insects and spiders, and Whitethroats on Salvadora fruits. Sedge Warblers and some other chiefly insectivorous species turned to a diet including berries shortly before emigrating. Changes in weight during the course of the day were difficult to investigate, but were probably bimodal. Good correlations of weights with wing-lengths were obtained for species for which many data were available. Pre-migratory fattening did not occur synchronously in all populations of a species, but once it started in an individual it proceeded at a constant rate of 0.2 g/day in Sedge Warblers and 0.6 g/day in Whitethroats. Predation pressure probably ensured that individuals emigrated immediately they attained their maximum pre-migratory weight, although some Sedge Warblers and Whitethroats left the area before attaining maximum weight. Differences between the mean weight curves of first-caught and retrapped birds are discussed, and it is concluded that in some species there were both through-migrant and temporarily-resident populations at Malamfatori. The mean weights per day of Whitethroats, Sedge Warblers and also Reed Warblers A. scirpaceus were falling in late March, and slight changes in the weather, particularly temperature, may have been responsible. In mid-April there was a “rush” of lean Whitethroats, which are thought to have originated to the SW in Nigeria. Yellow Wagtails, Sedge Warblers and Whitethroats deposited up to 40% fat/live weight; Sand Martins Riparia riparia had up to 28%, and a small sample of Ruffs Philomachus pugnax up to 17%. In the case of Sedge Warblers, fat reserves were sufficient for crossing the Sahara both to the north and to the northeast. Contrary to the findings in some previous lipid studies, the fat-free dry weight and water content increased during fattening. The fat-free dry weight increase was about 34% in Yellow Wagtails, 18% in Sedge Warblers, and 35% in Whitethroats. The tissues involved in this increase were not investigated, but a study of Yellow Wagtails at Malamfatori in 1968 (in prep.) suggests that the pectoral muscles hypertrophy during fat deposition sufficiently to account for nearly all of the increase in fat-free dry weight and water fraction.     

THE WINTERING AND MIGRATION OF PALAEARCTIC PASSERINES AT KAMPALA, SOUTHERN UGANDA

Palaearctic passerines were observed and trapped over three seasons near Kampala, in southern Uganda. Passage migration and wintering are described.
Only 11 species were encountered at all frequently. Three of these were common as passage migrants only, the rest remained in numbers throughout the northern winter. Most migrants reached Kampala during October and November, but the majority of Acrocephalus warblers appeared later. Spring departure commenced at the end of March, and continued throughout April. Autumn passage was in progress from late September to December, but appreciable spring movement was confined to a period of a few weeks only.
Ringing revealed that most wintering warblers were highly sedentary, and that a high proportion of surviving birds returned to the same site in successive winters. No fewer than 12–5% of the 220 Acrocephalus warblers ringed during 1966/67 were retrapped during the following season.
Wing measurements were recorded for most migrants trapped. Plumage details were noted, and representative specimens of several species were subsequently compared with museum series. It was concluded that most migrant passerines which occurred at Kampala were of eastern origin.
Migration times were compared with those recorded for some other areas. The spring movement from southern Uganda to the Middle East tends to be more rapid than the return journey. Some species apparently spend weeks or even months of the autumn in northeast Africa before reaching the equator,     

Habitat use and densities of co‐existing migrant Willow Warblers Phylloscopus trochilus and resident eremomelas Eremomela spp. in Zimbabwe

Capsule Migrant Willow Warblers occupy more woodland types and occur at higher densities than ecologically‐similar resident Afrotropical warblers.

Aims To compare population densities of Willow Warblers and eremomelas in adjacent acacia, mopane and miombo woodlands, and assess the abundance of potential invertebrate prey in each habitat type, in order to investigate whether Palearctic migrants use more open habitats and are more flexible in habitat use than their Afrotropical counterparts in the same feeding guild.

Methods Using distance sampling we carried out four replicated sets of point counts in acacia woodland and three sets of counts in miombo and mopane between December 1999 and February 2000. We noted the tree species in which we saw warblers foraging and took beating‐tray samples of potential arthropod prey present on tree foliage in each of the three habitats.

Results Willow Warbler density in acacia woodland increased from 1.80 ± 0.54 (se) birds/ha in early December to 7.15 ± 1.41 birds/ha in late January after influxes of later arrivals. Densities of Willow Warblers in miombo and mopane were much lower (1.14 ± 0.28 and 0.38 ± 0.23 birds/ha, respectively) and did not show significant changes. Burnt‐necked Eremomelas averaged 0.74 ± 0.34 birds/ha in acacia woodland, and in miombo densities of Green‐capped and Yellow‐bellied Eremomelas were 0.23 ± 0.17 and 0.34 ± 0.26 birds/ha, respectively. Densities in mopane were too low to estimate reliably. Willow Warblers and Green‐capped Eremomelas showed some apparent preferences in tree species used for foraging but differences in tree use were not obviously related to the abundance of arthropod taxa present as potential prey.

Conclusion Willow Warblers occupied more habitats at greater density than similar Afrotropical warblers. They appear to favour acacia, but their settlement patterns and the reasons for disparities between densities of immigrants and residents are unclear.     

Morphological sexing of passerines: not valid over larger geographical scales

Sex determination of birds is important for many ecological studies but is often difficult in species with monomorphic plumage. Morphology often provides a possibility for sex determination, but the characters need to be verified. We tested whether five passerine species can be sexed according to standard morphological measurements applying a forward logistic regression with sex determined by molecular analysis as the dependent variable. Furthermore, we tested whether the results can be used on a larger geographic scale by applying morphological sexing methods gained by similar studies from other regions to our data set. Of the five species of this study only Garden Warblers Sylvia borin could not be sexed morphologically. In the Robin Erithacus rubecula, 87.2% of all individuals were sexed correctly. For Reed Warblers Acrocephalus scirpaceus, Willow Warblers Phylloscopus trochilus and Reed Buntings Emberiza schoeniclus, the respective values were 77.6, 89.4 and 86.4%. When the logistic regression functions from similar studies on Robins and Reed Buntings in Denmark and Scotland were applied to the birds from south-western Germany, they performed less well compared to the original dataset of these studies and compared to the logistic regression function of our own study. The same was the case for Willow Warblers when a wing length criterion used in Great Britain was applied to the birds of our study. These discrepancies may have several explanations: (1) the models are optimised for the dataset from which they were extracted, (2) inter-ringer variation in measurements, (3) the use of different age cohorts, (4) different morphology due to different habitat availability around the study site, or, most likely, (5) different morphology due to different migratory behaviour. We recommend that morphological sex differentiation methods similar to this study (1) be only used population specific, (2) only with one age cohort and (3) to adjust the extracted equations from time to time.     

Migration strategies of sylviid warblers: chance patterns or community dynamics?

The effects of community dynamics in birds on the optimisation of their migratory strategies is a neglected area. For three years, we captured migrating warblers on autumn passage at a coastal site in western Britain. We used canonical correspondence analysis (CCA) to assess spatio‐temporal patterns of occurrence, and principal components analysis (PCA) to assess morphological variation. We calculated Euclidean distance in ordination and morphological space to assess separation between species pairs, and used Monte‐Carlo simulations to assess the probability of pattern occurring by chance.
Ordination revealed five species‐groups separated by habitat type and time of passage. Reed Warbler Acrocephalus scirpaceus and Sedge Warbler A. schoenobaenus (Group 1) occurred in wet habitats and peaked simultaneously. In drier habitats with scrub, a first wave of Blackcap Sylvia atricapilla (Group 2) significantly preceded Grasshopper Warbler Locustella naevia, Willow Warbler Phylloscopus trochilus, Whitethroat Sylvia communis and Lesser Whitethroat Sylvia curruca (Group 3), which in all but one case (Lesser Whitethroat) significantly preceded Garden Warbler Sylvia borin (Group 4); peak numbers of Chiffchaffs Phylloscopus collybita and a second wave of Blackcaps (Group 5) occurred later still. Age effects were found only in Acrocephalus, with adults peaking before juveniles.
For seven out of eight pairings within genera, separation in time of passage increased significantly in species that were morphologically similar. The only exception was Blackcap and Lesser Whitethroat which differed substantially in both passage time and morphology. Monte‐Carlo simulations showed that chance was unlikely to be responsible for ordination patterns, nor for inter‐specific variation in passage time and its relationship with species morphology.
These data provide annually consistent evidence that migrating sylviid warblers are separated ecologically by habitat use, time of passage and morphology: we cannot refute the hypothesis that community dynamics have influenced niche use and autumn migratory strategy. We call for further tests of the ‘migrant interaction’ hypothesis in other geographical locations and taxa, particularly where migrants are allopatric and interact ecologically only on migration.     

Brutzeitliche Beutewahl beim Seggenrohrs?ngerAcrocephalus paludicola

Summary Aquatic Warblers inhabitCarex Marshes (Magnocaricia) exceptionally rich in arthropods. Contrasting with the otherAcrocephalus species their mating system is some form of polygyny resp. promiscuity and the female alone feeds her nestlings. At 17 nests females fed large prey items compared with the arthropod fauna of the vegetation. Food was collected close to the nest and feeding rate proved to be high. Therefore richness of arthropods in the vegetation seems to form a prerequisite to this mating system untypical amongAcrocephalus warblers.     

Stable isotope ratios in winter‐grown feathers of Great Reed Warblers Acrocephalus arundinaceus,Clamorous Reed Warblers A. stentoreus and their hybrids in a sympatric breeding population in Kazakhstan

Analyses of the stable isotope composition of feathers can provide significant insight into the spatial structure of bird migration. We collected feathers from Great Reed Warblers Acrocephalus arundinaceus, Clamorous Reed Warblers A. stentoreus and a small sample of their hybrids in a sympatric breeding population in Kazakhstan to assess natural variation in stable isotope signatures and delineate wintering sites. The Great Reed Warbler is a long‐distance migrant that overwinters in sub‐Saharan Africa, whereas the Clamorous Reed Warbler performs a short‐distance migration to the Indian sub‐continent. Carbon (δ¹³C), nitrogen (δ¹⁵N) and deuterium (δD) isotope signatures were obtained from winter‐grown feathers of adult birds. There were highly significant differences in δD and less significant differences in δ¹³C between Great and Clamorous Reed Warblers. Thus, our results show that the stable isotope technique, and in particular the deuterium (δD) signal, resolves continental variation in winter distribution between these closely related Acrocephalus species with sympatric natal origin. The isotope signatures of hybrid Great × Clamorous Reed Warblers clustered with those of the Great Reed Warblers. Hence, a parsimonious suggestion is that the hybrids undergo moult in Afrotropical wintering grounds, as do the Great Reed Warblers. The observed δD values fell within the range of expected values based on available precipitation data collected at precipitation stations across the wintering continents of each species. However, the power to predict the winter origin of birds in our study system using these data was weak as the expected values ranged widely at this broad continental scale.     

THE SOUTHWARD MIGRATION OF PALAEARCTIC BIRDS OVER NGULIA, KENYA

Since 1969 remarkable numbers of night migrants have been attracted during misty conditions in November and December to three 1 kW floodlights at a game viewing lodge on the northeastern side of the Ngulia ridge, a small range of hills in the Tsavo National Park (West), southeast Kenya. The main species involved have been Palaearctic passerines, principally the Marsh Warbler Acrocephalus palustris, the Whitethroat Sylvia communis and the Sprosser Luscinia luscinia. Data were collected at the Lodge in the late autumns of 1969–71, and in particular between November 1972 and early January 1973, when over 2500 Palaearctic passerines were caught and ringed. Large falls have depended on mist or rain during the latter part of the night, at any time during the month except around full moon. Highest numbers have occurred in late November and the first half of December. In 1973 falls continued into the second week of January. Grounded birds move on quickly, extremely few having been retrapped. During 1972–73, the species prominent in falls at the Lodge were abundant as transit migrants in Tsavo only from mid-December to early or mid January, at which time retrap rates were highest. The high weights and considerable fat deposits of many birds caught suggested they were grounded some distance north of their destination. Forty-two migrants analysed had a mean lipid content of 12·9% of their live weight; none was appreciably dehydrated. In 1972–73, highest weights were found at the beginning and end of the season. Individual species are discussed, and in several cases their African status reviewed. Several species were encountered at Ngulia in numbers far larger than those previously reported from elsewhere in Africa. In 1972–73, for instance, over 1000 Marsh Warblers were caught and many thousands of others seen, hundreds of River Warblers Locustella fluviatilis occurred, and White-throated Robins Irania gutturalis, Basra Reed Warblers Acrocephalus griseldis, Rufous Bush Chats Cercotrichas galactotes and Olive-tree Warblers Hippolais olivetorum were caught regularly. Most of the Basra Reed Warblers, Upcher's Warblers Hippolais languida and Olivaceous Warblers H. pallida, and many of the Whitethroats (apparently all of the eastern race icterops) handled during late December and early January were in fresh plumage, although these species are not known to moult north of the Sahara. They are presumed to have renewed their plumage in northeast Africa earlier in the autumn. In many Basra Reed Warblers and Whitethroats moult was only partly completed; in almost all such cases it was arrested. Itinerancy south of the Sahara is discussed. It seems clearly established that a regular southward migration, in the usually accepted sense of the word, occurs across Tsavo, of Palaearctic species which have already been in tropical Africa up to three months. Most species involved in this migration cross the equator on a remarkably narrow front, and are rarely recorded in Kenya west of Nairobi.     

Foraging behavior of migrant warblers in mixed‐species flocks in Venezuelan shade coffee: interspecific differences,tree species selection,and effects of drought

Shade coffee has been identified as an important habitat for Nearctic‐Neotropical migrants during the non‐breeding season, including species of conservation concern such as Cerulean Warblers (Setophaga cerulea). To better understand habitat features important for migrants in shade coffee, we studied the foraging behavior of migrants in mixed‐species flocks at six shade‐coffee farms in the Cordillera de Merida, Venezuela, in 2008–2009 and the El Niño drought year of 2009–2010. We examined interspecific differences in foraging behavior and tree species selection of three foliage‐gleaning migrants, Blackburnian (Setophaga fusca), Cerulean, and Tennessee (Oreothlypis peregrina) warblers, and aerial‐foraging American Redstarts (Setophaga ruticilla). For morphologically similar Blackburnian and Cerulean warblers, we also examined factors influencing foraging rates (attack and movement rates), capture of large prey, and maneuver/substrate type. We found that aerial‐foraging American Redstarts foraged lower, used more aerial maneuvers, showed no tree species selection, and were less likely to forage in flocks than foliage‐gleaners. Although foraging rates were similar for Blackburnian and Cerulean warblers, the three foliage‐gleaners differed in foraging height and use of maneuvers. Cerulean Warblers foraged lower than the other two species, whereas Blackburnian Warblers used the greatest proportion of woody gleans. All three foliage‐gleaners selected Inga spp. (a commonly planted shade tree in shade‐coffee farms) for foraging, and Blackburnian and Cerulean warblers captured a greater proportion of large prey in Inga spp. than in other tree species. During the drought year, Blackburnian and Cerulean warblers captured half as many large prey and used a greater proportion of woody‐gleans. We found that interactions among behavioral, floristic, and environmental drivers influenced the foraging behavior of migrants wintering in shade coffee. Our results support those of previous studies suggesting that migrants partition resources behaviorally during the non‐breeding season, that foliage‐gleaners may benefit from the presence of shade trees, especially Inga spp., in agroforestry systems, and that drought may influence the foraging behavior of foliage‐gleaning migrants, presumably due to reduced prey availability.     

Timing of events on the breeding grounds for five species of sympatric warblers

ABSTRACT On the breeding grounds, migratory birds have limited time to breed and molt before autumn migration. However, few studies of long‐distance migrants have examined the phenology of these events to determine what life‐history trade‐offs might result if these activities overlap. From 2000 to 2007, I used banding data to determine the timing of migration, breeding, and primary molt for Yellow Warblers (Dendroica petechia), Yellow‐rumped Warblers (D. coronata coronata), American Redstarts (Setophaga ruticilla), Ovenbirds (Seiurus aurocapilla), and Canada Warblers (Wilsonia canadensis) at a study site in Alberta, Canada. Hatching date did not differ among species (P= 0.63), with means ranging from 27 June to 3 July. All species began primary molt between 12 July and 18 July, near the expected fledging date of offspring, and therefore all species exhibited overlap between postfledging parental care and molt. The duration of primary molt ranged from 28 d for Canada Warblers to 69 d for Yellow‐rumped Warblers. Yellow Warblers, Yellow‐rumped Warblers, and American Redstarts began autumn migration having completed about 50% of their primary molt. However, Ovenbirds departed when 21% of molt was complete, and Canada Warblers departed 2 d after completing molt. For all five species of warblers, molt did not overlap with nest‐bound breeding activities. However, molt did overlap with both postfledging care and migration. This suggests that initiating migration as soon as possible is important, possibly because earlier arrival on the wintering grounds may improve access to high quality winter habitat. Overall, warblers may maximize individual fitness by combining life‐history events that result in overlapping portions of the breeding cycle, molt, and migration.     

Intraspecific variation of wing pointedness index in juvenile Acrocephalus warblers in the southeastern Baltic

Variation of wing pointedness index between groups of juveniles captured in different months (July, August, and September) and at different stages of juvenile moult was studied in three Acrocephalus warbler species captured on the Courish Spit on the Baltic Sea. Sedge warblers (Acrocephalus schoenobaenus) captured in July had less pointed wings than sedge warblers captured in August or September. Marsh warblers (A. palustris) showed no significant difference between birds in early and in late moult. No differences in wing pointedness were found between different cohorts of reed warblers (A. scirpaceus), including known locally hatched birds and late migrants captured in September. It is hypothesised that reed warbler populations in the northeastern Baltic are too evolutionarily young to have evolved a different wing shape as compared with the local Courish population.Communicated by F. Bairlein     

SPRING WEIGHTS AND PASSAGE OF SEDGE WARBLERS ACROCEPHALUS SCHOENOBAENUS IN CENTRAL KENYA

Weight and other data were collected on over 1300 Sedge Warblers Acrocephalus schoenobaenus in central Kenya, mainly during spring (April-May). The weight, fattening rate and length of stay of spring passage birds varied from one site to another. In scrub and thicket at Kariobangi, Nairobi, passage and new arrival continued each year into May; few birds stayed to fatten, and weights over 16 g (40% above mean winter weight) were practically never recorded. At Lake Nakuru, thousands of birds were present during late April-early May 1972; many stayed to fatten for 1–3 weeks, and weights over 16 g (maximum 215 g) were not uncommon; new arrivals of lean birds continued into May. At Athi River, in 1971, many of the birds present during mid-late April stayed 1–2 weeks and fattened rapidly; 20% of all late April weights were in the range 16–21 g. Mean fattening rates at Nakuru and Athi River were 0.31 and 0.64 g/d respectively. The migration strategy and potential flight range of Kenyan spring birds is discussed. Active wing moult was rarely recorded. Most locally wintering birds and spring passage birds were judged to have renewed their plumage during the preceding October-January.     

THE INUNDATION ZONE OF THE NIGER AS AN ENVIRONMENT FOR PALAEARCTIC MIGRANTS

Of at least 350 species so far recorded within the boundaries of the Niger Inundation Zone, no less than 108 (31%) are wholly or partially of Palaearctic origin. Five main habitats are recognized in the region: wetland, hygrophilous grassland, transition zone, non-flooded areas and aerial. The habitats, the Palaearctic migrants and their possible Ethiopian competitors are described and discussed. The annual Niger flood regime enables Palaearctic waterbirds to find suitable habitats somewhere within the region during all seasons, but most widely during the autumn and winter months of the flood recession. Non-aquatic species inhabiting flood plain grassland are scarce during the Palaearctic autumn, when the growth of vegetation reaches its maximum, becoming commoner and more diverse during the winter months. Wetland warblers of the genera Acrocephalus and Locustella have not been recorded on autumn passage. It is suggested that in some years at least, these and other trans-Saharan migrants from the West Palaearctic overfly the Sahelian latitudes of mid-West Africa. Species inhabiting the transition zone (which increases in area during years of below average rains and floods) are most in evidence at the end of the winter period and during the spring hot dry season, prior to northward trans-Saharan migration. Habitats and species encountered in the non-flooded areas are similar to those recorded in the Sahel zone elsewhere in West Africa. Aerial habitat is utilized by Common Swifts arriving en masse in early August, at the maximum development of the south-westerly monsoon airstream. Several aquatic species and the first few trans-Saharan migrants also occur during the summer rainy season. Some species (e. g. Whiskered Tern, Lesser Kestrel, Turtle Dove, Short-toed Lark and Sand Martin) are most numerous during the late winter and spring hot seasons, when conditions provided by the Inundation Zone may be more suitable for pre-migration feeding than in other parts of the Sahel zone. As yet there is virtually no information available to determine any effects that drought seasons or flood variation may have on the migrant populations.     

Estimating fat and protein fuel from fat and muscle scores in passerines

Fat is the prime energy source for birds during prolonged exercise, but protein is also catabolized. Estimates of the amount of catabolizable fat and protein (termed fat and protein fuel) are therefore important for studying energetics of birds. As fat and protein fuel can only be measured by sacrificing individuals or by use of technically complex methods, scoring systems were invented to estimate fat and protein fuel of birds in the field. The visible subcutaneous fat deposits and the thickness of the flight muscles are each scored on an ordinal scale but these scales do not correspond linearly to fat and protein fuel within species, which is needed for analyses such as flight range estimates. We developed an anova ‐type model to estimate fat and protein fuel from fat scores (FS) and muscle scores (MS) along with total mass and a size measurement. Using data from 11 337 individuals of eight passerine species (Common Nightingale Luscinia megarhynchos, Eurasian Reed Warbler Acrocephalus scirpaceus, Melodious Warbler Hippolais polyglotta, Willow Warbler Phylloscopus trochilus, Orphean Warbler Sylvia hortensis, Garden Warbler Sylvia borin, Common Whitethroat Sylvia communis, Subalpine Warbler Sylvia cantillans) mist‐netted in Mauritania, West Africa, we tested for independence of FS and MS and for variation in the relationship between scores and associated mass in response to physiological state. FS, MS and third primary length (size) explained variation in body mass of all eight species analysed (R²: 0.56–0.77). The parameter estimates of the model showed that fat and protein fuel increased monotonically with increasing fat and muscle scores. In two species we found small differences in the estimates between physiological states (seasons). We evaluated our model by comparing the predicted body mass of birds with both FS and MS equal to 0 with the mean body mass of individuals mist‐netted with both scores equal to zero. The values were very close. The amount of fat extracted from dead Garden and Willow Warblers was within the range of predicted fat fuel derived from the model. We conclude that our model is a useful non‐invasive method to estimate simultaneously mean fat and protein fuel of small passerines and we provide recommendations on its use.     

Nectar consumption of warblers after long-distance flights during spring migration

The consumption of nectar by European passerines has been reported only occasionally. In this study we investigated the occurrence and significance of nectar consumption of small passerine birds on spring migration after crossing the Mediterranean Sea. On Ventotene Island in the Tyrrhenian Sea, four migrating species of Sylvia warblers [Garden Warbler S. borin , Subalpine Warbler S. cantillans , Whitethroat S. communis , Blackcap S. atricapilld ) regularly foraged on the two most common flowering species at that time of year, Brassica fruticulosa (Cruciferae) and giant fennel Ferula communis (Umbelliferae), while other species visited flowers only occasionally or not at all. Feeding behaviour, pollen traces on the head, and the examination of pollen and sugar remains in droppings indicated that nectar was the main target of the Sylvia warblers, rather than pollen or insects on the flowers. This was confirmed by food choice experiments indicating a clear preference by Garden Warblers and Whitethroats for nectar from artificial flowers over mealworms. Although conclusive experiments are not available, we hypothesize that nectar might be a diet easy to obtain and to absorb for birds after a long-distance flight in which they have incurred a depletion of energy stores and a reduction of the digestive tract.     

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 Comoé 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.Communicated by F.Bairlein     

Longer is fatter: body mass changes of migrant Reed Warblers (Acrocephalus scirpaceus) staging at Eilat,Israel

Ecological barriers are the riskiest phases of the annual migrations for migratory birds. Comparatively little field data exists pertaining to the ability of migratory birds to prepare for the challenges of crossing ecological barriers, or their ability to recuperate afterward. Migrating Reed Warblers (Acrocephalus scirpaceus) were captured in Eilat, Israel, during their spring and autumn migrations. Data on spring and autumn body masses, their inter-annual variation, and the pattern of body mass increase were analysed. The birds show a significant inter-annual variation in their body mass and body condition index in both seasons, which is consistent with the data from other sites and for other passerine species. During stopovers, mass gain occurred in both seasons. Birds in poor initial condition, and those that stop over for a longer period of time, gained more body mass faster. In spring, but not in autumn, the progress of the season was also an important factor; late-arriving birds gained more fuel faster. The average rate of fuel gain was 0,157g·day^?1 ± 0.018 SE.     

Changes in migration phenology and biometrical traits of Reed,Marsh and Sedge Warblers

Global environmental processes like climate change could severely affect population level migratory behaviour of long range migrant birds. We analyzed changes in migration phenology and biometrics of three closely-related long-distance migrant Acrocephalus species. We used the records of 12 063 Sedge, 12 913 Reed, and 5 409 Marsh Warblers caught and ringed between 1989–2009, at a Hungarian stopover site. Quantile regressions were used to analyse the changes in spring and autumn migration phenology. Median spring arrival date of Sedge and Reed Warblers shifted 6.5 and 7.5 days earlier, respectively. Autumn arrival of all species shifted one (Reed and Marsh Warblers) or two (Sedge Warbler) weeks later. Mean body mass of adult Reed and Marsh Warblers decreased in spring (by 0.3 and 0.2 grams, respectively) and in autumn (by 0.8 and 0.2 grams, respectively) while body mass of adult Sedge Warblers decreased only in autumn (by 0.4 grams). Mean wing length of all species increased significantly (range of change: 0.6–1 mm). Despite the fact that the studied species are closely related, all three have remarkably different migration strategies. However, similar patterns can be observed in the studied parameters, indicating that global processes may have general effects on these species, albeit through markedly different mechanisms.     

Foraging behavior of three species of songbirds during stopover in southeastern Morocco during spring migration

Investigators studying the stopover ecology of migrating birds typically use the capture–recapture method to examine important parameters such as fuel deposition rates (FDR) and stopover duration. However, such studies can be constrained by the number of recaptures. An alternative method is to calculate a regression of mass over time of day, but this method may not be reliable because patterns of mass change of individual birds through the day may not reflect that of the whole population. Given the potential constraints of these methods, using them in combination with other methods, such as behavioral observations of foraging birds, may improve our understanding of the patterns of fuelling in birds at stopover sites. We observed the foraging behavior of three songbird species, including Western Bonelli's (Phylloscopus bonelli), Subalpine (Sylvia cantillans), and Willow (Phylloscopus trochilus) warblers, from 15 March to 30 April 2011 at a small oasis at the northern border of the Sahara desert in southeast Morocco. Given the location of our study site at the northern edge of the Sahara desert, birds migrating north likely needed to replenish their energy reserves at this stage of their journey. We assessed foraging effort by determining the rate (number per unit time) at which birds pecked at substrates or made aerial forays after flying insects. Peck rates were higher for Western Bonelli's Warblers than for Subalpine and Willow warblers, suggesting either species‐specific adaptations to feeding in arid environments or differences in the motivation to feed. In addition, Western Bonelli's Warblers had FDRs that were negative or close to zero and, therefore, were apparently unable to refuel successfully (i.e., increase their fuel stores) despite greater effort, possibly indicating less efficiency in obtaining food (i.e., more unsuccessful pecks). The lower peck rates of Subalpine and Willow warblers suggest either that they were less efficient at finding prey or were simply foraging at lower rates. For all three species, peck rates were lower at higher wind speeds, suggesting that wind may alter prey availability and detectability, especially of flying insects. Interactions among species‐specific migration strategies, environmental conditions, and habitat quality ultimately define the success of migration. Our results suggest that using observational data in combination with capture data may improve our understanding of these interactions at migration stopover sites.