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.     

WEIGHTS OF SOME PALAEARCTIC MIGRANTS IN SOUTHERN UGANDA

Between March 1966 and May 1968 Palaearctic passerines were mist-netted in thick bush and lightly wooded savannah habitats near Kampala, on the northern shore of Lake Victoria. This paper reports weights of the seven principal species involved. Most migrants appeared to be in a lean condition during the winter months, when weights were relatively low and varied little in each species. Birds were not particularly light on arrival. In fact, autumn Garden Warblers Sylvia borin and Willow Warblers Phylloscopus trochilus were sometimes markedly heavy, and for the former species there was some evidence that the individuals concerned were passage migrants. Autumn weights of Swallows Hirundo rustica, Reed Warblers Acrocephalus scirpaceus and Yellow Wagtails Motacilla flava were similar to those recorded in winter. The mean weight of all species rose during late March or early April. Although most Garden Warblers and Willow Warblers trapped at the time of spring migration were within the normal winter weight range, many Acrocephalus warblers and the majority of Sand Martins Riparia riparia and Yellow Wagtails were rather heavy. Spring weights 40% or more above mean winter weight were not uncommon in the Sedge Warbler Acrocephalus schoenobaenus, but were recorded only occasionally in other species. Although most passerine migrants evidently left Kampala with substantial fat reserves, it was concluded that a considerable number of warblers departed at rather low weight. High spring weights were mainly confined to a period of two or three weeks in each of the warbler species. Locally wintering Acrocephalus warblers must have attained full premigratory weights within three weeks, and a number of spring retraps showed substantial gains at minimum mean rates of between 0–1 and 0–35 g per day. Most heavy Garden Warblers were probably on passage. Significant correlations between weight and wing-length were obtained for all species investigated, regressions of weight on wing-length being in the range 011-0-25 g/mm. Spring weights are briefly compared with data from Nigeria, and the northward migration of passerines from Lake Victoria is discussed.     

Inability to regain normal body mass despite extensive refuelling in great reed warblers following the trans‐Sahara crossing during spring migration

Migratory birds wintering in Africa face the challenge of passing the Sahara desert with few opportunities to forage. During spring migration birds thus arrive in the Mediterranean area with very low energy reserves after crossing the desert. Since early arrival to the breeding grounds often is of importance to maximize reproductive success, finding stopover sites with good refuelling possibilities after the Saharan passage is of utmost importance. Here we report on extensive fuelling in the great reed warbler Acrocephalus arundinaceus on the south coast of Crete in spring, the first land that they encounter after crossing the Sahara desert and the Mediterranean Sea in this area. Birds were studied at a river mouth and due to an exceptional high recapture rate (45 and 51% in two successive years), we were able to get information about stopover behaviour in 56 individual great reed warblers during two spring seasons. The large proportion of trapped great reed warbler compared to other species and the large number of recaptures suggest that great reed warblers actively choose this area for stopover. They stayed on average 3–4 d, increased on average about 3.5 g in body mass and the average rate of body mass increase was 4.8% of lean body mass d^–1. Wing length affected the rate of increase and indicated that females have a slower increase than males. The results found show that great reed warblers at this site regularly deposit larger fuel loads than needed for one continued flight stage. The low body mass found in great reed warblers (also in birds with high fat scores) is a strong indication that birds staging at Anapodaris still had not been able to rebuild their structural tissue after the strenuous Sahara crossing, suggesting that rebuilding structural tissue may take longer time than previously thought.     

Flight-range estimates for small trans-Sahara migrants

Arguments in support of the non-stop and the intermittent strategies for crossing the Sahara have been based on data on the fat reserves of birds before the crossing and of birds grounded in the desert. In this paper, flight-range estimates were calculated and the necessary assumptions about air speed, energy input during flight, and energy equivalent of body reserves were evaluated. As examples, Willow Warblers Phylloscopus trochilus and Garden Warblers Sylvia borin were investigated during autumn migration from two study sites north of the Sahara and two study sites in the desert. In still air, the flight-range for both species at all study sites was too short to reach the Sahel zone without refuelling. It is concluded that birds depend on tailwinds for a successful crossing, independent of a non-stop or an intermittent migratory strategy, and that weather conditions in autumn allow them to rely on tailwinds.     

Strategies of passerine migration across the Mediterranean Sea and the Sahara Desert: a radar study

Radar observations of the diurnal timing of bird migration in the Sahara Desert are presented for autumn migration. Study sites were on a transect along the north-south migratory direction. Three groups of birds migrating either during day, evening or night in the northern part of the Western desert in Egypt were identified. The maximum of day and night groups occurred later the further south the study sites were. Based on the distance between sites and the timing of peak migration, birds were flying at an estimated ground speed of about 20 m/s. The maximum of the evening group was at about 21:00 h at all sites. The three groups were classified according to three different strategies of migration across the Mediterranean Sea and the Sahara Desert: (1) the day group of birds performed a non-stop flight across the sea and at least the northern part of the desert; [2] the night group performed an intermittent migratory strategy with stopover at the coast of Egypt to continue migration the next evening; (3) the evening group birds were also intermittent migratory fliers, but they stopped somewhere in the desert after a continuous flight across the sea and part of the desert. About 20% of all migrants are involved in non-stop migration and 80% in intermittent migration with stopover at the coast (70%) or with stopover in the desert (10%). It is argued that any species of small passerine has the option to use any of the three strategies.     

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.     

Migrating songbirds on stopover prepare for,and recover from,oxidative challenges posed by long‐distance flight

Managing oxidative stress is an important physiological function for all aerobic organisms, particularly during periods of prolonged high metabolic activity, such as long‐distance migration across ecological barriers. However, no previous study has investigated the oxidative status of birds at different stages of migration and whether that oxidative status depends on the condition of the birds. In this study, we compared (1) energy stores and circulating oxidative status measures in (a) two species of Neotropical migrants with differing migration strategies that were sampled at an autumn stopover site before an ecological barrier; and (b) a species of trans‐Saharan migrant sampled at a spring stopover site after crossing an ecological barrier; and (2) circulating oxidative measures and indicators of fat metabolism in a trans‐Saharan migrant after stopovers of varying duration (0–8 nights), based on recapture records. We found fat stores to be positively correlated with circulating antioxidant capacity in Blackpoll Warblers and Red‐eyed Vireos preparing for fall migration on Block Island, USA, but uncorrelated in Garden Warblers on the island of Ponza, Italy, after a spring crossing of the Sahara Desert and Mediterranean Sea. In all circumstances, fat stores were positively correlated with circulating lipid oxidation levels. Among Garden Warblers on the island of Ponza, fat anabolism increased with stopover duration while oxidative damage levels decreased. Our study provides evidence that birds build antioxidant capacity as they build fat stores at stopover sites before long flights, but does not support the idea that antioxidant stores remain elevated in birds with high fuel levels after an ecological barrier. Our results further suggest that lipid oxidation may be an inescapable hazard of using fats as the primary fuel for flight. Yet, we also show that birds on stopover are capable of recovering from the oxidative damage they have accrued during migration, as lipid oxidation levels decrease with time on stopover. Thus, the physiological strategy of migrating songbirds may be to build prophylactic antioxidant capacity in concert with fuel stores at stopover sites before a long‐distance flight, and then repair oxidative damage while refueling at stopover sites after long‐distance flight.     

Reservoir water levels do not influence daily mass gain of warblers at a riparian stopover site

ABSTRACT Hydroelectric dam operations that lead to fluctuations in the water levels of reservoirs can influence the amount of riparian habitat available for migrating songbirds and may impact the use and quality of remaining habitat. Our objective was to determine if use of riparian habitats and mass gain by five warbler species at the Columbia River‐Revelstoke Migration Monitoring Station in British Columbia, Canada, were influenced by water levels in the surrounding Arrow Lakes Reservoir. We analyzed fall migration data collected from 1998 to 2006. Capture rates of American Redstarts (Setophaga ruticilla), Common Yellowthroats (Geothlypis trichas), Orange‐crowned Warblers (Vermivora celata), Wilson's Warblers (Wilsonia pusilla), and Yellow Warblers (Dendroica petechia) varied between years and weeks of the migration period, but were not affected by annual or weekly variation in water levels. Annual variation in capture rates was driven by hatch‐year birds (>80% of individuals captured were juveniles) and could reflect conditions on the breeding grounds that influence productivity. We found that mass gain by the five species of warblers varied between 0.32% and 0.98% of lean body mass/hour. Mass gain did not vary between years or across weeks of the migration period and was not influenced by annual or weekly variation in reservoir water levels. Although the amount of available riparian habitat was reduced when reservoir water levels were high, we found no evidence that this loss of habitat influenced either the number of warblers or the mass gain of warblers using the riparian habitat that remained. Body mass at the time of first capture varied between years and across weeks for all five species. For American Redstarts and Orange‐crowned Warblers, body mass declined as average weekly water levels increased, a pattern that could arise if water levels influenced either their settlement decisions or length of stay.     

Stopover durations of three warbler species along their autumn migration route

In migrating birds, the success of migration is determined by stopover duration, the most important factor determining overall speed of migration, and fuel deposition rate. However, very little is known about stopover durations of small migrant birds, because appropriate methods for data analysis were lacking until recently. We used a new capture-recapture analysis to estimate stopover durations of 1st-year reed warblers Acrocephalus scirpaceus, sedge warblers A. schoenobaenus and garden warblers Sylvia borin at 17 stopover sites in Europe and Africa during autumn. Average stopover duration of non-moulting reed warblers was 9.5 days while moulting conspecifics stayed about twice as long. Average stopover duration of sedge warblers was 9.1 days and, in contrast to the other two species, differed between years at several sites. Garden warblers stayed 7.7 days on average. The long stopover duration of the reed warbler, resulting in slow overall migration speed, is related to its low fuel deposition rate. It can be explained by low, but predictable, food resources and an early departure during moult. Compared to the reed warbler, the stopover duration of the sedge warbler varies more between sites and probably also between years, as the supply of its preferred diet (reed aphids) is spatially and temporally unpredictable but can be superabundant. The short stopover duration of the garden warbler, leading to high overall migration speed, can be related to high fuel deposition rates, probably brought about by a change to an abundant, predictable and long-lasting fruit diet. Within species, stopover duration did not change significantly along the migration route. Hence, an increase of migration speed along the migration route, as suggested in the literature, may be caused by longer flight bouts in the south. However, it remains largely unknown which environmental and possibly endogenous factors regulate stopover duration.     

Detection range of songbirds using a stopover site by automated radio‐telemetry

A major uncertainty in automated radio‐telemetry studies of small birds is the detection range of receiving antennas. We compared simultaneous daytime detections (± 30 s) by automated and manual radio‐telemetry to assess detection probability and the proportion of transmissions detected for birds on migratory stopover as a function of distance, foraging guild (Black‐throated Blue Warblers, Setophaga caerulescens, and Yellow‐rumped Warblers, Dendroica coronata coronata, represented mid‐canopy foliage gleaners and White‐throated Sparrows, Zonotrichia albicollis, represented a ground forager), habitat type, meteorological variables, tower antenna number (1–4), and the position of a bird relative to the receiving antenna's bearing (offset angle). Our study was conducted at a migratory stopover site in southern Ontario, Canada. Most detections were in dense to sparse forest, and all individuals were within 1.03 km of the automated receiving station. Daily detection probability was near 100% for both foraging guilds. However, within 30 s before and after a manual radio‐telemetry location was made, detection probability and the proportion of transmissions detected by automated radio‐telemetry declined with distance, was higher for warblers than sparrows, and was lowest for 90° offset angles. Our results suggest that when research goals do not require detections with high temporal frequency, e.g., estimation of departure date or daily departure probability, our study design had an effective detection range of at least 1 km. However, where temporal precision is required, e.g., to investigate movements and changes in activity levels during stopover, detection range was ~300 m for ground‐foraging sparrows and 600 m for mid‐canopy foraging warblers, which is much lower than the presumed detection range of antennas under optimal conditions (15 km). This corresponds to a spatial area of coverage for forest‐dwelling birds of ~0.3–1.1 km². Our results suggest that to optimally configure an automated radio‐telemetry array at the regional scale, investigators should carefully consider detection range and its underlying covariates, including species type, the habitat matrix, and the orientation of antennas relative to preferred habitat.     

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.     

Different wintering strategies of two Palearctic migrants in West Africa – a consequence of foraging strategies?

The wintering strategies of Pied Flycatchers Ficedula hypoleuca and Willow Warblers Phylloscopus trochilus in their West African winter quarters were compared. Pied Flycatchers arrived early in the season (September) and stayed in the study area throughout the winter. They were territorial and showed a high return rate. Intraspecific relationships were mostly expressed by territorial behaviour. Interspecific relations seemed to be unimportant. Willow Warblers arrived relatively late (November) and were absent from the area for some weeks in January and February, a behaviour which was interpreted as itinerancy. Willow Warblers were non-territorial and never returned to a site. Willow Warblers usually moved through the area in monospecific or mixed-species flocks. Habitat and microhabitat choice of these species were similar but in feeding ecology they differed by the higher diversity of feeding substrates and feeding techniques of Pied Flycatchers. The differences in the winter strategies are explained by the ability of Pied Flycatchers to defend a territory because of their diversity in foraging behaviour, whereas Willow Warblers are more specialized and are therefore forced to be more mobile to find their patchily distributed food.     

Digestive response to restricted feeding in migratory yellow-rumped warblers

Smaller guts and slow initial mass gains at stopover sites have led to the idea that digestive physiology limits refueling rates in migrating birds. We tested the digestive-limitation hypothesis in yellow-rumped warblers using food restriction to simulate infrequent feeding during migration, which may cause a reduction in alimentary tract mass. Restricted birds had small intestine, pancreas, and liver masses 18%-22% lower than ad lib.-fed controls. Total activities of sucrase, maltase, aminopeptidase, and amylase were significantly lower in restricted birds, while those of trypsin and chymotrypsin were not. Only aminopeptidase mass-specific activity was significantly lower in restricted birds. Previously restricted birds were able to feed and digest at a high rate immediately following return to ad lib. feeding. Digestive efficiency did not differ between groups. These results suggest that before migration yellow-rumped warblers have some spare digestive capacity to compensate for declines in their digestive organ masses during migration.     

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.     

Skipping‐type migration in a small Arctic wader,the Temminck's stint Calidris temminckii

By using morphometric data and geolocator tracking we investigated fuel loads and spatio‐temporal patterns of migration and non‐breeding in Temminck's stints Calidris temminckii. Body masses in stints captured at autumn stopover sites from Scandinavia to northern Africa were generally not much higher than during breeding and did not vary geographically. Thus, we expected migrating stints to make several stopovers and either circumventing the Sahara desert with low fuel loads or fuelling at north African stopover sites before desert crossing. Geolocation revealed that birds (n = 6) departed their Norwegian breeding site in the last part of July and all but one migrated south‐west over continental western Europe. A single bird headed south‐east to the Balkan Peninsula where the geolocator died. As predicted, southbound migration proceeded in a typical skipping manner with 1–4 relatively short stopovers (median 4 d) during 10–27 d of migration before reaching north‐west Africa. Here birds spent 11–20 d before crossing the Sahara. The non‐breeding sites were located at or near the Niger River in Mali and were occupied continuously for more than 215 d with no indications of itinerancy. Spring migration commenced in late April/early May when birds crossed the desert and used stopover sites in the western Mediterranean basin in a similar manner as during autumn. The lowest body masses were recorded in spring at islands in the central Mediterranean basin, indicating that crossing the Sahara and Mediterranean barriers is exhausting to these birds. Hence, the skipping‐type pattern of migration revealed by geolocators is likely to be natural in this species and not an effect of instrumentation.     

The moult of Barred Warblers Sylvia nisoria in Kenya—evidence for a split wing-moult pattern initiated during the birds' first winter*

The moult of Barred Warblers Sylvia nisoria was studied during three winter seasons in southeastern Kenya at a southward passage site (Ngulia) and a wintering site (Mtito Andei). Most Barred Warblers migrating through Ngulia in November had yet to commence winter moult. These birds probably moulted subsequently in winter in northern Tanzania. In December, birds were found in heavy moult at Mtito Andei, and some of these birds were known to stay throughout the winter. By contrast, most birds reaching southeastern Kenya from late December onwards had already completed part or all of their winter moult, presumably at stopover sites in northern and eastern Kenya or in Ethiopia. Thus, winter moult in Barred Warblers takes place mainly in late November and December, either just before or soon after the final leg of autumn migration. In general, first-year birds renewed all tertials and tail feathers, about three to five secondaries per wing and commonly also the outer one to four large primaries per wing. Adults renewed all tertials and tail feathers, almost all secondaries and only occasionally an outer primary. The replacement of relatively fresh juvenile secondaries during the birds' first winter implies that the split moult pattern of this species (secondaries, tertials and tail moulted in winter; primaries and tertials in summer) is endogenously controlled.     

Carry‐over effects of winter habitat quality on en route timing and condition of a migratory passerine during spring migration

We examined how conditions prior to migration influenced migration performance of two breeding populations of black‐and‐white warblers Mniotilta varia by linking information on the migrant's winter habitat quality, measured via stable carbon isotopes, with information on their breeding destination, measured via stable hydrogen isotopes. The quality of winter habitat strongly influenced the timing of migration when we accounted for differential timing of migration between breeding populations. Among birds migrating to the same breeding destination, males and females arriving early to the stopover site originated from more mesic habitat than later arriving birds, suggesting that the benefits of occupying high‐quality mesic habitat during the winter positively influence the timing of migration. However, male warblers arriving early to the stopover site were not in better migratory condition than later arriving conspecifics that originated from poor‐quality xeric winter habitat, regardless of breeding destination. The two breeding populations stopover at the study site during different time periods, suggesting that the lower migratory condition of early birds is not a function of the time of season, but potentially a migrant's migration strategy. Strong selection pressures to arrive early on the breeding grounds to secure high‐quality breeding territories may drive males from high‐quality winter habitat to minimize time at the expense of energy. This migration strategy would result in a smaller margin of safety to buffer the effects of adverse weather or scarcity of food, increasing the risk of mortality. The migratory condition of females was the same regardless of the timing of migration or breeding destination, suggesting that females adopt a strategy that conserves energy during migration. This study fills an important gap in our understanding of the linkages between winter habitat quality and factors that influence the performance of migration, the phase of the annual cycle thought to be limiting most migratory bird populations.     

Blood parasites in migrating wood‐warblers (Parulidae): effects on refueling,energetic condition,and migration timing

Blood parasites can negatively affect energetic condition, arrival date, and reproductive performance of breeding birds, yet their impact on migrating birds is poorly understood. We quantified haematozoan infection and examined its relationship to migration timing, energetic condition, and refueling rate (plasma triglyceride concentration) for three species of wood‐warblers (Parulidae) migrating through northwestern Ohio, USA from 11 April–3 June of 2004 and 2005. Prevalence of infection for magnolia Dendroica magnolia (36.3%; n=383), yellow‐rumped D. coronata (58.3%; n=518), and yellow warblers D. petechia (12.7%; n=205) was approximately two times higher than reported in other migration studies and similar to infection rates found in breeding areas. Probability and intensity of infection were higher for later migrating yellow‐rumped warblers, especially in younger (second‐year) birds. Furthermore, we found a negative trend between intensity of infection and energetic condition for second‐year yellow‐rumped warblers. Haematozoan infection was not associated with refueling rate for any species. Our results indicate that for some migrants, especially younger birds, probability and intensity of haematozoan infection are related to later migration timing and reduced energetic condition during spring migration, and thus may be important determinants of subsequent reproductive performance in breeding areas.     

中国柳莺属鸟类分类研究进展

柳莺属(Phylloscopus)是广泛分布于旧大陆地区的小型食虫鸟类,目前全世界已知66种,其中约50种见于亚洲。该属鸟类外部形态十分相近且同域分布种数较多,历来是鸟类分类学中的研究难点及热点。2003年贾陈喜等介绍了20世纪90年代以来发表的分布于我国的柳莺属鸟类新种及相关分类学变动,涉及3个新描述种和9个由亚种提升的种,共计30种26亚种。2003年以来关于柳莺属鸟类的分类学研究取得了许多新的成果,同时我国境内也发现了一些新的分布记录。综合最新的文献及分布资料,整理得知我国现有柳莺属鸟类41种31亚种,与2003年的状况相比已有较大的变化。主要表现在:新描述种方面,德国学者Martens等2008年描述了黄腹柳莺(P.affinis)种组中的一新种———华西柳莺(P.occisinensis);2010年瑞典学者Alstrm等报道在越南和老挝地区新发现的灰岩柳莺(P.calciatilis)已被证实在我国有分布;亚种提升为种方面,如日本柳莺(P.xanthodryas)自极北柳莺(P.borealis)中独立,冠纹柳莺(P.claudiae)和西南冠纹柳莺(P.reguloides)分开等;分类地位再评议方面,如灰头鹟莺(Seicercusxanthoschistos)实为灰头柳莺(P.xanthoschistos)等;新分布纪录方面,如欧柳莺(P.trochilus)在内蒙古达里诺尔湖地区发现确切记录等。现今对柳莺属鸟类分类学方面的研究已明显呈现出传统形态学、分子遗传学、声谱分析及野外鸣声回放实验等新老技术手段相整合,多方面多角度地阐述问题的局面。中国是世界柳莺属鸟种分布最多的国家(其中有9种仅在或主要于我国境内繁殖),但我国鸟类学者关于该属鸟类的研究工作并不多见。柳莺属鸟类在分类学和进化生物学等领域具有重要的研究价值,我国鸟类学工作者应当引起足够的重视和关注。