Sylvia Borin Research Articles

Orientation of passerine trans-Sahara migrants: the directional shift (‘Zugknick’) reconsidered for free-flying birds

As most long-distance migrants leave their breeding ranges in Western Europe towards the southwest, they must change their migratory directions somewhere to reach their nonbreeding areas in Africa. Laboratory experiments have been the basis to suggest an endogenously controlled, abrupt directional shift in the south of the Iberian Peninsula, the so-called ‘Zugknick’. We compared own radar data gathered in Europe and the Western Sahara with this established theory. Radar tracks were filtered according to the wing beat pattern and migratory passage of garden warblers, Sylvia borin, and pied flycatchers, Ficedula hypoleuca, the species used in the former experiments. The flight directions were highly concentrated and the mean direction in the Western Sahara was only slightly more south than the southwesterly directions in central and southwestern Europe. At observation sites close to the southern edge of the Sahara, mean directions were south to east-southeast. We therefore conclude that an endogenously predetermined directional shift occurs towards the end of the Sahara crossing according to physiological or environmental triggers leading the birds towards their wintering ranges in the southeast.

Monitoring Passerine Reproduction by Constant Effort Ringing: Evaluation of the Efficiency of Trend Detection

The Dutch Constant Effort Site (CES) programme has been operating since 1994 and is especially designed for the analysis of demographic parameters. Currently, it works with 40 active mist-netting sites and has a database with more than 250,000 records at its disposal. Here, we ask whether the effort invested in the programme is appropriate to detect temporal trends of productivity of passerine bird populations across The Netherlands. We specifically ask if less effort would produce the same results or if the number of CESs should be augmented. To evaluate these questions we used a resampling approach in which we decreased sample size in steps of five and iterated resampling 1000 times for each step, thus simulating CES programmes in which fewer sites were operated. For the twenty most abundant species and for each sample size, linear regressions of the productivity index (a logistic generalized linear model of the proportion of captured juvenile birds) on year were compared with the regression obtained using the complete records. The proportion of samples that yielded significant positive or negative slopes was determined, as well. For the majority of species without significant temporal trends (18), the proportions of significant slopes at smaller sample sizes were lower than 20%, indicating a moderate risk of committing Type I errors (detecting a negative or positive trend although productivity did not change over time). For the Garden Warbler Sylvia borin, which showed a significant positive productivity trend, the probability of committing Type II errors (not detecting existing trends) increased rapidly with decreasing sample size. We conclude that the Dutch CES programme works with a sufficient number of sites to detect reliable temporal trends for most of the more abundant passerine species. However, increasing the number of sites would allow for a more secure determination of productivity trends for those species that currently show ambiguous results (Reed Warbler Acrocephalus scirpaceus, Willow Warbler Phylloscopus trochilus, Willow Tit Parus montanus).

Migratory Birds: Ecology and Conservation. A report on the BOU’s Annual Conference held at the University of Leicester, 5–7 April 2011

In April 2011, the British Ornithologist’s Union’s annual conference took place at the University of Leicester. The theme of this year’s conference was the ecology and conservation of migratory birds, and talks ranged from those focussed on either breeding, migration or wintering ecology, to those linking two or more of these and trying to build a more complete picture of the complex problems faced by long distance migrants. Talks also covered recent technological advances, which are increasingly allowing us intriguing new insights, particularly into the seasonal movements and wintering areas of some of the most declining species. Finally, talks examined the policy challenges associated with protecting migratory species and how best to tackle flyway-scale conservation of migratory birds.

Seasonal differences in energy requirements of Garden Warblers Sylvia borin migrating across the Sahara desert

The Sahara desert acts as an ecological barrier for billions of passerine birds on their way to and from their African wintering areas. The Garden Warbler Sylvia borin is one of the most common migrants involved. We used body mass of this species from Greece in autumn and spring to simulate the desert crossing and to assess how body mass relates to fuel requirement. The flight range estimates were adjusted to the seasonal extent of the desert, 2200 km in autumn and about 2800 km in spring. In autumn, with an average fuel load of about 100% of body mass without fuel, birds were not able to cross the desert in still air, but northerly winds prevail during September and with the average wind assistance only one in 14 was predicted to fail to make the crossing. Body mass data from spring, after the desert crossing, was used to estimate departure body mass from south of the desert. The average wind assistance in spring is close to zero and departure body mass of the average bird arriving at Antikythira, a small Greek island, under such conditions was estimated to be 34.6 g, which corresponded to a fuel load of 116%. Calculations based on 1% body mass loss per hour of flight showed slightly larger body mass loss than that calculated from flight range estimates. The results suggest that passerine birds about to cross the eastern part of the Sahara desert need to attain a larger fuel load in spring than in autumn.

Assessing breeding success in common woodland birds using a novel method

Capsule Repeated counts of fledged broods can provide a useful estimate of breeding success for most common woodland birds. Aims To assess the efficacy of comparing fledged-brood survey data with territory mapping using simple mark–recapture analysis techniques to provide an estimate of breeding success for common woodland birds that does not involve finding nests. Methods Three observers undertook territory mapping surveys of adults, followed by counts of fledged broods four times a week during May–July 2007 in two 15 ha woods each, both in southern England. Using known fledging to maturity periods, these counts were used to calculate daily detection probabilities for broods of ubiquitous species. These enabled fledged brood territory occupancy probabilities (i.e. brood to territory ratios) to be estimated that take account of the possibility that broods were present but missed by surveys. Results Of the 19 species found in all six woods, mean daily detection probability estimates for fledged broods of 17 species ranged from 0.17 to 0.50 with significant variation between woods for 12 species, but within region/observer for four species. The mean probability of detecting a brood at least once was over 75% using four visits per week and over 50% using two visits. Only for Great Spotted Woodpeckers Dendrocopos major and Garden Warblers Sylvia borin was the fledging period too short and the daily detection probability too low to provide a reasonable estimate of the territory occupancy probability. Conclusion Daily detection probabilities for fledged broods of most common woodland birds were sufficiently high to enable useable estimates of fledged-brood territory occupancy probabilities to be made based on a survey programme involving two or three visits per week between late May and the end June. The method used may have application as a means of providing a relatively easily derived productivity index for woodland bird monitoring programmes or for research studies.

Breeding and post-breeding responses of woodland birds to modification of habitat structure by deer

Birds in woodland can be affected by increasing deer populations through changes to vegetation structure and potential impacts on foraging resources; these effects need to be better understood. Effects of deer browsing are reported from a replicated split-plot exclusion experiment in English coppiced woodland. All stages of growth were examined up to eight years after felling. We used standardised mist-netting (totaling 1920 h) to sample birds in breeding and post-breeding periods. Deer browsing strongly altered vegetation structure by reducing canopy cover and shrub layer foliage density. However deer did not affect invertebrate density per unit of foliage, providing no evidence of an ungulate-mediated plant chemical response affecting forage quality for invertebrate herbivores. At avian guild level, significantly more ground and understorey foraging birds were captured where deer were excluded, and negative responses to browsing were more marked for pooled migrants than pooled residents. At the species level, especially pronounced negative effects were evident for dunnock ( Prunella modularis) and garden warbler ( Sylvia borin); approximately five times more dunnocks were captured in deer exclosures than in browsed vegetation. We also detected negative responses to browsing by nightingale ( Luscinia megarhynchos) and long-tailed tit ( Aegithalos caudatus). No significant positive responses to browsing were detected. For some species the use of young re-growth increased post breeding relative to the breeding period, including a marked shift by pooled residents that involved a disproportionate number of juveniles. Previous studies in North America have shown that, through vegetation modification, ungulate activity can alter woodland bird assemblages; as far as we are aware this is the first experimental demonstration of effects in Europe, and at low to moderate browsing intensity typical of the wider landscape scale.

Fuel Load and Potential Flight Ranges of Passerine Birds Migrating through the Western Edge of the Pyrenees

The estimation of fuel load and the potential flight ranges of migrant birds are crucial to understanding the ecological and evolutionary significance of bird migration strategies. The movement of migrant birds between Iberia and the rest of Western Europe is thought to be shaped by the Pyrenees and nearby seas. Because of this area's unique geography, the routes of migrants that move to (autumn migration) or from (spring migration) Iberia tend to pass through the western and eastern edges of the Pyrenees. Fuel-load analyses and the assessment of potential flight ranges from these edges can provide insights about the extent of Iberia's use as a consistent stopover and fuelling area. Using data obtained over a period of six years (2004–2009), we calculated fuel load and potential flight ranges for ten common passerines (pre-Saharan, i.e. that overwinter mainly within the circum-Mediterranean region: Robin Erithacus rubecula, Bluethroat Luscinia svecica, Chiffchaff Phylloscopus collybita, Blackcap Sylvia atricapilla; sub-Saharan, i.e. that overwinter in tropical Africa: Sedge Warbler Acrocephalus schoenobaenus, Reed Warbler Acrocephalus scirpaceus, Melodious Warbler Hippolais polyglotta, Willow Warbler Phylloscopus trochilus, Garden Warbler Sylvia borin, Common Whitethroat Sylvia communis that stopover at Txingudi marshlands, at the western edge of the Pyrenees. The fuel load for the 25% heaviest fraction of caught birds ranged from 10.6% over lean body mass to 25.5% (mean: 18.3%) in spring and from 6.7% to 39.7% (mean: 25.2%) in autumn. Thus, potential flight ranges tended to be longer during autumn than during spring, particularly for the sub-Saharan species. All pre-Saharan species except one (Bluethroat) had sufficient fuel to arrive in southern Iberia or northern Africa, and three sub-Saharan species (Sedge Warbler, Garden Warbler, Common Whitethroat) had sufficient fuel to reach the north of the Sahara Desert but not its southern border. The potential flight ranges in spring were rather similar among species (ca. 1000 km from Txingudi).

Pollen Couriers Across the Mediterranean: The Case of Migrating Warblers

Cecere J.G., Cornara L., Mezzetta S., Ferri A., Spina F. & Boitani L. 2011. Pollen couriers across the Mediterranean: the case of migrating warblers. Ardea 99: 33–42.At stopovers sites in the Sahara and on Mediterranean islands, European warblers may feed on nectar. As a consequence of this behaviour the pollen of exploited plants often sticks on the birds' bill or plumage. We analyzed pollen samples carried by migrating warblers staging at Ventotene Island (Italy), a stopover site located in the Central Mediterranean and reached by large numbers of birds after a direct flight from North Africa. We discuss the possible role of migrants as pollen vectors. A total of 38 plant taxa were recorded in the pollen samples collected on 147 migrants. Pollen of Brassica sp., Ferula communis, Citrus sp. and Eucalyptus sp. were most commonly found. The nectar of the first two plants is largely exploited by warblers on Ventotene and the presence of their pollen on plumage is principally due to nectar feeding in situ. On the contrary, Citrus sp. and Eucalyptus sp., which are scarce and absent on the island respectively, were mainly collected on dried and agglutinated samples and their presence is likely to be due to nectar feeding at other sites than Ventotene. The other 34 plant taxa were recorded with low frequencies. Overall, the data suggest that nectar feeding migrants could play a role as pollen vectors only for Citrus sp., Eucalyptus sp., F. communis and Brassica sp. However, the other less common plant taxa could also be useful markers of migration routes. We found species-specific relationships between bird species and the plants used for nectar feeding: short-distance migrants (mainly Eurasian Blackcap Sylvia atricapilla and Subalpine Warbler S. cantillans) land on Ventotene when Brassica sp. flowers are more abundant and they mainly carry the pollen of this species. On the contrary, long-distance migrants (Garden Warbler S. borin and Common Whitethroat S. communis) principally transport the pollen of F. communis, whose flowering period takes place at the same time as their staging period on the island. The study underlines the tendency of warblers towards nectar feeding during migration.

Flight muscle shape reliably predicts flight muscle mass of migratory songbirds: a new tool for field ornithologists

The pectoral muscle is the biggest organ within a passerine bird. It provides flight locomotion and is known to act as a protein source during periods with increased protein demands or decreased protein availability. The mass of the flight muscle is dynamic and changes during juvenile growth, reproduction, seasonal acclimatization, fasting and migration. Thus, a tool that accurately and non-invasively quantifies this phenotypic flexibility in flight muscle mass is of interest to ornithologists. We provide a calibration and validation of a "muscle meter" device designed to accurately measure the shape of the flight muscle. For two species of different size, the European starling (Sturnus vulgaris) and the garden warbler (Sylvia borin), we compared the accuracy and precision of different linear regression models for predicting flight muscle mass. The multifactorial linear regression model with the most support for both species included “muscle meter score” (mmscore), tarsus length and body mass (m b), although a simpler model with mmscore and m b had as much support for predicting flight muscle mass of European starlings. A validation exercise revealed that flight muscle mass of these two species could be estimated with a relative error of about 3%. The muscle meter is a simple device, easy and quick to handle, that can reliably and non-invasively estimate flight muscle mass of captive and wild birds when used in conjunction with standard measurements of tarsus length and m b.

The stopover behaviour of the Garden Warbler Sylvia borin in Obudu, southeast Nigeria

The Garden Warbler breeds in the Palaearctic and migrates to sub-Saharan Africa for the non-breeding season. We studied its passage, body mass and moult at the Obudu Plateau in southeast Nigeria in October–December 2005 and December 2007–January 2008. In Nigeria, Garden Warblers in the Guinea savanna have been shown to increase body mass in October–November, preparing for migration to wintering sites further south. They begin to arrive at Obudu from mid-October and the numbers gradually increase with time; median date of passage was 3 December. This influx is clearly different from that which has been recorded for other sites in West Africa. The patterns in wing length and size-corrected body mass of individuals suggest a difference in the migration time of individuals of different sizes in the two years. Average fuel loads were lower at Obudu than has been reported in Central Nigeria. This, and the capture of moulting individuals, suggests that Garden Warblers may not embark on a longer journey southwards in mid winter, and possibly may even winter at Obudu.

Chewing Lice (Phthiraptera: Amblycera, Ischnocera) From Some Wild Birds in the Kizilirmak Delta (Turkey)

We present the results of the studies on the chewing lice collected during the period 2009-2010 from 32 wild birds belonging to 11 species, in the Kizilirmak Delta of Turkey. From the 13 chewing louse species identified in the studied material, six of them are new records for the parasitological fauna of Turkey, namely: Ricinus fringillae De Geer, 1778 ex Fringilla coelebs; Cuculicola latirostris (Burmeister, 1838) ex Cuculus canorus; Brueelia domestica (Kellogg & Chapman, 1899) ex Hirundo rustica; Brueelia merulensis (Denny, 1842) ex Turdus merula; Brueelia turdinulae Ansari, 1956 ex Turdus philomelos; and Penenirmus affectator (Zlotorzycka, 1976) ex Sylvia borin. Also, the following two new chewing louse - bird species associations are reported for the first time all over the world: Quadraceps anagrapsus (Nitzsch (in Giebel), 1866) ex Sterna albifrons; and Penenirmus sp. ex Sylvia melanocephala. The presence of a chewing louse species is reported on S. melanocephala for the first time in the world . And not the least, it is reported, for the first time, the presence of three chewing louse species - bird species associations in the Turkish parasitological fauna: Menacanthus curuccae (Schrank, 1776) ex Acrocephalus scirpaceus and Sylvia borin; and Menacanthus eurysternus (Burmeister, 1838) ex Turdus merula.

Reduced body mass gain in small passerines during migratory stopover under simulated heat wave conditions

For birds that migrate long distances, maximizing the rate of refueling at stopovers is advantageous, but ambient conditions may adversely influence this vital process. We simulated a 3-day migratory stopover for garden warblers (Sylvia borin) and compared body temperatures (Tb) and rates of refueling under conditions of a heat wave (Ta=40°C by day, and 15°C at night) with those under more moderate conditions (Ta=27°C by day, and 15°C at night). We measured Tb with implanted thermo-sensitive radio transmitters. Birds had significantly lower rates of body mass gain on the first day of stopover (repeated measures mixed model ANOVA, p=0.002) affecting body mass during the entire stopover (p=0.034) and higher maximum Tb during the day when exposed to high Ta than when exposed to moderate Ta (p=0.002). In addition, the birds exposed to high Ta by day had significantly lower minimum Tb at night than those exposed to moderate daytime Ta (p=0.048), even though Ta at night was the same for both groups. We interpret this lower nighttime Tb to be a means of saving energy to compensate for elevated daytime thermoregulatory requirements, while higher Tb by day may reduce protein turnover. All effects on Tb were significantly more pronounced during the first day of stopover than on days two and three, which may be linked to the rate of renewal of digestive function during stopover. Our results suggest that environmental factors, such as high Ta, constrain migratory body mass gain. Extreme high Ta and heat waves are predicted to increase due to global climate change, and thus are likely to pose increasing constraints on regaining body mass during stopover and therefore migratory performance in migratory birds.

Food availability but not melatonin affects nocturnal restlessness in a wild migrating passerine

A large number of passerine species migrate at night, although most of them are diurnal outside the migratory seasons. This diurnal-to-nocturnal transition is a major life-history event, yet little is known about its physiological control. Previous work showed that during the migratory periods captive birds showing nocturnal migratory restlessness (Zugunruhe) have reduced concentrations of circulating melatonin at night compared to non-migratory periods. This suggested that the hormone melatonin, a main component of the avian circadian system, is involved in the expression of Zugunruhe. Other studies demonstrated that the relationship between low melatonin levels and Zugunruhe is not a seasonal correlation. When Zugunruhe was interrupted by exposing birds to a fasting-and-refeeding protocol, melatonin levels increased. Here we studied whether melatonin and food availability influence the intensity of Zugunruhe in wild migrating garden warblers (Sylvia borin) at a stopover site. Birds were held in recording cages overnight, with or without food available, and either bled to determine melatonin concentrations or treated transdermally with melatonin. We found that melatonin levels at night were correlated with the intensity of diurnal locomotor activity and with condition, but were not correlated with Zugunruhe. Similarly, the melatonin treatment did not have effects on Zugunruhe, whereas food availability increased it. Our study shows that the nocturnal melatonin levels in migrating warblers depend on food availability and are correlated with condition. In addition, it suggests that melatonin does not control Zugunruhe and might rather be involved in energy conservation and/or clock synchronization during migration.

Carbon Turnover in Tissues of a Passerine Bird: Allometry, Isotopic Clocks, and Phenotypic Flexibility in Organ Size

Previous article No AccessErratumCarbon Turnover in Tissues of a Passerine Bird: Allometry, Isotopic Clocks, and Phenotypic Flexibility in Organ SizeUlf Bauchinger and Scott R. McWilliamsUlf Bauchinger Search for more articles by this author and Scott R. McWilliams Search for more articles by this author Original articleCarbon Turnover in Tissues of a Passerine Bird: Allometry, Isotopic Clocks, and Phenotypic Flexibility in Organ SizePDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Physiological and Biochemical Zoology Volume 83, Number 6November/December 2010 Sponsored by Division of Comparative Physiology and Biochemistry, Society for Integrative and Comparative Biology Article DOIhttps://doi.org/10.1086/657659 Views: 14Total views on this site Citations: 3Citations are reported from Crossref © 2010 by The University of Chicago. All rights reserved.PDF download Crossref reports the following articles citing this article:Clara Cooper-Mullin, Wales A. Carter, Ronald S. Amato, David Podlesak, Scott R. McWilliams, Nicoletta Righini Dietary vitamin E reaches the mitochondria in the flight muscle of zebra finches but only if they exercise, PLOS ONE 16, no.66 (Jun 2021): e0253264.https://doi.org/10.1371/journal.pone.0253264Chad L. Seewagen, Daniel A. Cristol, Alexander R. Gerson Mobilization of mercury from lean tissues during simulated migratory fasting in a model songbird, Scientific Reports 6, no.11 (May 2016).https://doi.org/10.1038/srep25762Elizabeth Yohannes, Raymond Lee, Vladimir Popenko, Ulf Bauchinger Bone collagen and muscle δ13C in relation to the timing of the migration of Garden Warblers Sylvia borin during return migration from Africa, Journal of Ornithology 153, no.33 (Dec 2011): 783–791.https://doi.org/10.1007/s10336-011-0794-yRelated articlesCarbon Turnover in Tissues of a Passerine Bird: Allometry, Isotopic Clocks, and Phenotypic Flexibility in Organ Size19 Jul 2015Physiological and Biochemical Zoology

Change in migration phenology and biometrics of two conspecific Sylvia species in Hungary

The distribution area and the timing of migration of many bird species have recently changed, presumably due to climatic factors. In our study, we estimated the effect of climate change on migration phenology and biometrics of two sister Sylvia species: the medium-distance migrant Blackcap (Sylvia atricapilla) and the long-distance migrant Garden Warbler (Sylvia borin). We used the data of 52,440 Blackcaps and 6,943 Garden Warblers caught and ringed at the Ocsa Bird Ringing Station (47°15′N, 19°15′E) in Hungary between 1984 and 2008. The age and in case of Blackcaps the sex groups were handled separately. The timing of the spring migration of Garden Warblers shifted earlier, whereas it did not change in Blackcaps during the study period. We presume—in accordance with other observations concerning Blackcaps in West-Europe—that it probably has changed earlier than the 1980s. The timing of autumn migration shifted about 2 weeks later in all age and sex groups of Blackcaps. We found significant correlation in the timing of autumn migration of sex groups, the sign of the differences between the timing of males and females changed. Juvenile Garden Warblers shifted their autumn migration 13 days later, but adults did not. Mean body mass decreased while mean wing length increased suggesting a change in the composition of the trans-migrant population. We hypothesise that due to climate change the breeding range of these species expanded northwards, producing an increased ratio of long-winged northern individuals in the trans-migrant populations.

Fat stores in a migratory bird: a reservoir of carotenoid pigments for times of need?

Carotenoids are well known for their immune-stimulant function in birds and other vertebrates. Moreover, they have potential antioxidant capacity, scavenging free radicals and protecting cell compartments from oxidation. Most essential carotenoids are fat soluble and could be stored for times of need especially in adipose tissues, built up by migratory birds as the main source of energy on long-distance flights. In an exclusive diet experiment, garden warblers (Sylvia borin) were fed ad libitum with an experimental diet, enriched with two different dose rates of carotenoids, or with control food, during the period of their first autumn migration. Plasma carotenoid content was measured via HPLC and chroma of plasma and fat examined with a spectrophotometer. Birds were infected with Isospora spp. and intensity of infection determined by oocyst counts 3days post infection. Plasma lutein levels and chroma of subcutaneous fat stores were positively correlated and chroma values of these fat stores increased in the birds that got the higher dose rate, whereas they decreased significantly in the control group after infection with Isospora spp. Chroma of subcutaneous fat deposits in vivo and intensity of Isospora infection were negatively correlated. By measuring the chroma of fat deposits in vivo, we show that fat can be a reservoir for carotenoids. These colorful antioxidants are stored in the fat and taken from there in times of a higher demand, e.g. when mounting an immune response to parasites.

Garden Warbler, Sylvia borin, detect carotenoids in food but differ strongly in individual food choice

The concept of optimal foraging has been used to show how animals can increase their fitness by actively regulating the ingestion of nutrients or by avoiding detrimental plant metabolites, such as alkaloids. There is, however, considerably less information available on whether and, if so, how animals actively select beneficial secondary compounds, such as dietary antioxidants. In the last two decades, carotenoids have been the most intensively studied dietary antioxidants in behavioural ecology, and the expression of carotenoid-based ornamentation has become a model for studying the condition dependence of sexually selected traits. In a series of experiments in which we offered individual Garden Warblers (Sylvia borin) a choice between two foods, one with and one without carotenoids, we found that individual birds did not select food for the maximum amount of carotenoids, rather they choose for a highly consistent carotenoid intake during the course of different dual-choice experiments in which the food offered differed in carotenoid content. However, it remains unclear whether the individual birds were able to optimise their carotenoid intake and, therefore, the expression of life history traits—even though individuals differed consistently in their carotenoid intake. In particular, females tended to avoid food with high carotenoid contents. Based upon the highly consistent carotenoid intake of individual birds, we conclude that our birds were able to perceive the presence of carotenoids in the food without the use of visual cues. We suggest that these results may shed new light on the mechanisms that birds may use to regulate the ingestion of these antioxidants and, consequently, possibly affect the expression of life history traits, such as immunocompetence or sexually selected traits.

Hypothermic abilities of migratory songbirds at a stopover site

Migratory birds use stopover sites for resting and feeding. Breaks after prolonged flights may allow cooling down the muscles and save energy through hypothermia. We measured hypothermic abilities in two long-distance migratory songbirds (garden warbler, Sylvia borin, and icterine warbler, Hippolais polyglotta) at a stopover site during spring migration selecting (1) birds just arrived after a prolonged flight (morning) (2) birds that had been resting in the vegetation for several hours (afternoon) and (3) birds caught in the late afternoon and kept overnight in standard conditions (night). In the first two samples, body temperature was measured immediately, 30 and 180 min after capture. In the night sample, it was measured at 1 a.m. in birds awake and asleep, and at 7 a.m., when all birds were awake. Morning birds showed the highest values (39.7°C), dropping of about 3°C after 180 min. In the afternoon birds (2), the time course was similar, but values (38.5°C) were lower than that of morning birds of about 1°C. At night, asleep birds had lower temperature than awake birds, reaching up to 10°C less than daytime values, but recovering in the early morning. Such remarkable plasticity in thermogenic abilities during migration could allow small migrants to economize energy in emergency situations.

Weather significantly influences the migratory behaviour of night-migratory songbirds tested indoors in orientation cages

Each year, millions of birds migrate from their breeding grounds to their overwintering sites and back. The success, duration and effort of such a long journey depend strongly on the meteorological parameters the birds encounter en route. The behaviour of free-flying migratory birds and those studied outdoors in orientation cages has been shown to be influenced by local weather factors. However, only a few, mostly descriptive, studies have analysed whether meteorological parameters should be considered when testing captive migratory birds indoors in orientation cages. Here, we used a statistical approach to analyse how meteorological parameters affect orientation performance in a night-migrating songbird, the garden warbler (Sylvia borin), when tested indoors in Emlen funnels. Our results show that the activity and directionality of the tested birds is influenced significantly by local atmospheric pressure. Together with previous studies, these results suggest that weather conditions have an impact on orientation behaviour even during indoor experiments. The findings emphasize the importance of mixing up and/or randomizing different conditions on any given night. Ideally, during any given test night, the same number of birds should be tested in each condition involved in a given study. Thereby, the documented weather effects will influence the results of all experimental groups equally.

The effect of celestial cues on the ontogeny of non-visual orientation in the garden warbler (Sylvia borin).

It was the aim of this study to find out whether additional information from the sun and the stars during early development leads to an improvement in the young birds' non-visual orientation performance during their first autumn migration period. The results indicate that the birds' ability to determine their migratory direction can mature independently of celestial information. Celestial cues, however, appear to be involved in the normal maturation process of migratory orientation, since the availability of celestial information during ontogeny tends to impair the birds' non-visual orientation.