Savi's Warbler Research Articles

Better together? Assessing different remote sensing products for predicting habitat suitability of wetland birds

AbstractAimThe increasing availability of remote sensing (RS) products from airborne laser scanning (ALS) surveys, synthetic aperture radar acquisitions and multispectral satellite imagery provides unprecedented opportunities for describing the physical structure and seasonal changes of vegetation. However, the added value of these RS products for predicting species distributions and animal habitats beyond land cover maps remains little explored. Here, we aim to assess how metrics derived from different types of high‐resolution (10 m) RS products predict the habitat suitability of wetland birds.LocationNorth‐eastern part of the Netherlands.MethodsWe built species distribution models (SDMs) with occurrence observations from territory mapping of two selected wetland bird species (great reed warbler and Savi's warbler) and metrics from a Dutch land cover map, country‐wide ALS and Sentinel‐1 and Sentinel‐2 RS products. We then compared model performance, relative variable importance and response curves of the SDMs to assess the contribution and ecological relevance of each RS product and metric.ResultsOur results showed that ALS and Sentinel metrics improve SDMs with only land cover metrics by 11% and 10% of the Area Under Curve (AUC) for the great reed warbler and the Savi's warbler respectively. Assessments of feature importance revealed that all types of RS products contributed substantially to predicting the habitat suitability of these wetland birds, but that the most important variables vary among species.Main conclusionsOur study demonstrates that metrics from different high‐resolution RS products capture complementary ecological information on animal habitats, including aspects such as the proportional cover of habitat types, vegetation density and the horizontal variability of vegetation height. Land cover maps with detailed spatial and thematic information can already achieve high model accuracies, but adding metrics derived from ALS point clouds and Sentinel imagery further improve model accuracy and enhance the understanding of animal–habitat relationships.

Niche separation of wetland birds revealed from airborne laser scanning

Numerous organisms depend on the physical structure of their habitats, but incorporating such information into ecological niche analyses has been limited by the lack of adequate data over broad spatial extents. The increasing availability of high‐resolution measurements from country‐wide airborne laser scanning (ALS) surveys – a light detection and ranging (LiDAR) technology – now provides unprecedented opportunities for characterizing habitat structure. Here, we use country‐wide ALS data in combination with presence–absence observations of birds from a national monitoring scheme in the Netherlands to quantify niche filling, niche overlap and niche separation of three closely‐related wetland birds (great reed warbler, Eurasian reed warbler and Savi's warbler). We developed a workflow to derive LiDAR metrics capturing different aspects of vertical and horizontal vegetation structure and used a principal component analysis (PCA), niche equivalency and niche similarity tests to analyse the fine‐scale breeding habitat niches of these warbler species in the Netherlands. The widespread Eurasian reed warbler almost completely filled the available wetland habitat space (93%) whereas the two other species showed considerably less niche filling (64% and 74%, respectively). Substantial niche overlap occurred among all species, but each species occupied a distinct part of the habitat space. The great reed warbler mainly occurred in tall and vertically complex wetland vegetation and was absent in areas with large proportions of reedbeds. The Eurasian reed warbler occupied all parts of the wetland habitat space, whereas the Savi's warbler mainly occurred in large homogenous reedbeds with low vegetation height. Our results demonstrate that broad‐scale ecological niche analyses can incorporate the fine‐scale 3D habitat preference of species with unprecedented detail (e.g. 10 m resolution), and thus go much beyond quantifying the climate niche and 2D habitat information from land cover maps. This is important to identify habitat features and priorities for biodiversity conservation in wetlands and other habitats.

David Pearson (1941–2017)

David Pearson (1941–2017)

Dietary Characterization of Savi's Warbler Locustella luscinioides and Great Reed Warbler Acrocephalus arundinaceus in Eastern Spain

We are grateful to G. Assandri, D. Beneyto, M. Delandes, P. Lucio, M. Marin, C. Mompo, M. Morganti, R. Oliver, R. Piculo, E. Pons, R. Sanchez-Serrano and D. Vidal for their help with the fieldwork, and to S. Ano, N. Ibanez and J. Villarroya for their help in counting and classifying invertebrates. We would like to thank the authorities of the Marjal de Pego-Oliva Natural Park and the Servei de Conservacio de la Biodiversitat de la Generalitat Valenciana for providing the facilities to work in protected areas, and for providing the relevant permits. The present work has been partly financed by Projects CGL2005-02041 and CGL2010-21933/CO2-02 of the Spanish Ministry of Science and Innovation. FC was supported by an Atraent talent grant from the University of Valencia. Juan A. Amat and two anonymous reviewers contributed to improve an earlier version of the manuscript.

Variation of the Savi's Warbler (Locustella luscinioides) Leucocyte Profiles and Body Condition in Relation to Age, Sex and Moult

Birds of different sex and age are known to differ in morphology and physiology. We investigated leucocyte profiles and body condition of the Savi's warbler (Locustella luscinioides) in relation to sex, age and moulting status. We caught birds during the post-breeding period at the stopover site in northern Poland. Of the leucocyte profiles, we examined the heterophil/lymphocyte ratio (H/L), and the number of leucocytes, lymphocytes and heterophils per 10 000 red blood cells (RBC). We found a significant effect of the pentad × age interaction on the H/L ratio. In adults, body condition (BC, size-adjusted body mass) was similar in both sexes. Among adults, females had higher numbers of leucocytes and heterophils per 10 000 RBC and a lower relative number of lymphocytes compared to males. It is possible that subtle sex differences in parental care at the end of the breeding period account for these differences. They may be too subtle to affect BC, but are visible at some leucocyte variables. Moreover, BC of...

Factors Affecting Post-Breeding Moult in the Savi's WarblerLocustella luscinioidesin Northern Poland

A majority of Eurasian short-distance migrants moult after breeding and before autumn migration, while most long-distance migrants perform a winter moult in the tropics after autumn migration. Another strategy among long-distance migrants is a partial moult on the breeding grounds, suspended moult and then completion of moult on the wintering grounds. The Savi's Warbler Locustella luscinioides is a small passerine adopting such a ‘suspended moulting’ strategy. Here, we investigate the sequence and extent of the post-breeding moult in Savi's Warblers breeding in and migrating through northern Poland in relation to sex, body mass and date. We analysed 65 molecularly sexed adult Savi's Warblers (32 females and 33 males) caught during autumn migration in 2010–2011. Adult Savi's Warblers from the studied populations were found to suspend moult. Exchange of wing feathers started at the third primary (P3) and progressed in both directions. The onset of secondary moult began with S1 and occurred when P6 was shed....

Ticks of the Hyalomma marginatum complex transported by migratory birds into Central Europe

Hyalomma ticks are well-known vectors transmitting infectious agents, which can result in severe and potentially fatal diseases in humans. Migratory birds may carry infected ticks over long distances. Here, we report on records of ticks of the H. marginatum complex in birds from Central Europe during the spring migration in 2008–2012. A total of 1172 birds belonging to 32 species, 16 families, and 3 orders was examined for ticks. Sixteen individuals of 6 passerine species were found to transport 30 ticks, identified as individuals belonging to the H. marginatum species complex (consisting of H. isaaci, H. marginatum sensu stricto, H. rufipes, H. turanicum, and H. glabrum) during 5 spring seasons. Infested bird species included the great reed warbler Acrocephalus arundinaceus, the Eurasian reed warbler A. scirpaceus, the marsh warbler A. palustris, the sedge warbler A. schoenobaenus, Savi's warbler Locustella luscinioides, and the common nightingale Luscinia megarhynchos. All of these Central European breeders are migratory species wintering in Africa. To our knowledge, this is the first study to record ticks of the H. marginatum complex on the great reed warbler and Savi's warbler.

Sex discrimination in the Savi’s Warbler (Locustella luscinioides) using morphometric traits

Determining an individual's sex is often difficult in species with monomorphc plumage. but it is important in many ecological studies. This study proposes a logistic function for sexing the Savi's Warbler, Locustella luscinioides, based on standard body measurements. Nine measurements (wing length, tail length, head to bill length, bill length, bill width, billheight, tarsus width in two dimensions and hind-claw length) were selected via logistic regression using AIC (Akaike's information criterion for small sample size). with sex (determined by molecular analysis) as the dependent variable. In total, 224 Savi's Warblers (161 immatures and 64 adults) caught in northern Poland during autumn migration in 2010 and 2011 were examined. The function applied to immatures identified wing length, bill length, head to bill length and hind-claw length as the best measurements for sexing, with 91% of birds correctly classified (90% of females and 92% of males). A second function, applied to adults, included only wing length and bill length as the best predictor variables to identify sex, and it correctly classified 94% of individual (93% of females and 94% of males).

Landscape and Patch Characteristics Affecting the Assemblages of Birds in Reedbeds in Terrestrial Matrix

We conducted an analysis of relationships between results of survey on breeding community of birds, including species richness, abundance of individual species and ecological groups of birds, and habitat features of 91 isolated reed patches in southwestern Poland. The approach to the reedbed habitat involves environmental differentiation at the patch level, landscape context and isolation, including the impact of man-made structures as potential constraints to the occurrence of birds. Generalized linear models have shown that 12 out of 14 analyzed environmental predictors had a statistically significant effect on birds. The results from individual species (sedge warbler, great reed warbler, bluethroat, Savi's warbler, water rail, moorhen and coot) models revealed that the number of territories was affected from two to four predictors. The number of reedbed specialists was affected positively by reed edge, water area and proportion of reed habitat within a 100-m radius, and negatively by railway. The numbe...

Phylogeography of a Habitat Specialist with High Dispersal Capability: The Savi’s Warbler Locustella luscinioides

In order to describe the influence of Pleistocene glaciations on the genetic structure and demography of a highly mobile, but specialized, passerine, the Savi’s Warbler (Locustella luscinioides), mitochondrial DNA sequences (ND2) and microsatellites were analysed in c.330 individuals of 17 breeding and two wintering populations. Phylogenetic, population genetics and coalescent methods were used to describe the genetic structure, determine the timing of the major splits and model the demography of populations. Savi’s Warblers split from its sister species c.8 million years ago and have two major haplotype groups that diverged in the early/middle Pleistocene. One of these clades originated in the Balkans and is currently widespread, showing strong evidence for population expansion; whereas the other is restricted to Iberia and remained stable. Microsatellites agreed with a genetic break around the Pyrenees, but showed considerable introgression and a weaker genetic structure. Both genetic markers showed an isolation-by-distance pattern associated with the population expansion of the eastern clade. Breeding populations seem to be segregated at the wintering sites, but results on migratory connectivity are preliminary. Savi’s Warbler is the only known migratory bird species in which Iberian birds did not expand beyond the Pyrenees after the last glaciation. Despite the long period of independent evolution of western and eastern populations, complete introgression occurred when these groups met in Iberia. Mitochondrial sequences indicated the existence of refugia-within-refugia in the Iberian Peninsula during the last glacial period, which is surprising given the high dispersal capacity of this species. Plumage differences of eastern subspecies seemed to have evolved recently through natural selection, in agreement with the glacial expansion hypothesis. This study supports the great importance of the Iberian Peninsula and its role for the conservation of genetic variation.

Low frequency of extra-pair paternity in Savi's Warblers (Locustella luscinioides)

AbstractAlthough the frequency of extra-pair paternity (EPP) has been described for many species, the relative importance of the various contemporary and historical factors explaining EPP variation is still the subject of debate. In this study, we found 11 polymorphic microsatellite loci in the Savi's Warbler (Locustella luscinioides), and used eight loci to analyze the paternity of 392 nestlings belonging to 102 broods of this little-known species. The frequency of EPP was 4.1% of nestlings and 5.9% of broods, which is surprisingly low given what is known about Savi's Warbler's life history and ecology, and among the lowest found of any socially-monogamous passerine bird. Comparisons with similar species indicate that this low frequency is unlikely to have been determined by the ancient evolution of life history strategies. Our observations suggest that the costs of engaging in extra-pair copulations might be high for the females. Larger males, particularly those with longer bill and tarsus, are more likely to be cuckolded; and the few possible comparisons between cuckolded males and extrapair sires reveal a similar pattern. We further show that bill and tarsus lengths correlate with arrival date, which is associated with individual quality in many migratory bird species.

Serologic Survey of Birds for West Nile Flavivirus in Southern Moravia (Czech Republic)

A serosurvey for West Nile virus (WNV) was carried out in 54 domestic birds (geese and ducks bred on fishponds) and 391 wild birds representing 28 migratory and resident species, using a plaque-reduction neutralization microtest with Vero cells and Egyptian topotype Eg-101 strain as test virus. The birds were sampled in the South-Moravian fishpond ecosystem between 2004 and 2006. Antibodies to WNV were not detected in domestic waterfowl, but 23 (5.9%) free-living birds of 10 species showed a positive response. These were the common coot (Fulica atra, 5 positive/18 examined), common kingfisher (Alcedo atthis, 1/1), reed warbler (Acrocephalus scirpaceus, 2/80), sedge warbler (A. schoenobaenus, 3/80), marsh warbler (A. palustris, 2/28), Savi's warbler (Locustella luscinioides, 3/12), reed bunting (Emberiza schoeniclus, 1/28), blackcap (Sylvia atricapilla, 2/11), penduline tit (Remiz pendulinus, 1/14), blue tit (Parus caeruleus, 1/1), and starling (Sturnus vulgaris, 2/4). The antibody titers were comparatively low (1:20-1:40), and the only high titer (1:160) was found in an adult marsh warbler. When 14 of the sera reacting with WNV were titrated in parallel with Usutu Flavivirus, 12 were interpreted as having specific antibodies to WNV, one coot had a higher titer against Usutu virus, and another one could not be attributed to either of the two viruses. In conclusion, 13 (3.3%) of 391 wild birds had specific antibodies to WNV. The results indicate that WNV activity in southern Moravia was limited during 2004-2006.

Automatic detection of short time periodic bird calls in realistic monitoring scenarios

In this contribution, we propose a method for the automatic detection and localisation of bird calls featuring simple as well as highly repetitive structures. Reporting from a research project focused at computer aided acoustical monitoring, a detector for Locustella luscinoides (Savi's Warbler) is presented, performing reliably even on highly distorted recordings. In cooperation with the Animal Sound Archive at the Humboldt University, Berlin, this detector was incorporated into a multimodal censusing method combining GPS-data and automatically annotated audio recordings to perform line mapping. An evaluation of the proposed techniques for unsupervised monitoring purposes was also performed on 20 hours of multichannel recordings from Lake Parstein, a cane brake area in Germany. Finally, exemplifying the discriminative potential of the underlying features, we will point out the application to other members of the Warbler family as well as the detection of cricket and toad sounds.

Autumn migration of Savi's Warblers Locustella luscinioides in Portugal: differences in timing, fuel deposition rate and non-stop flight range between the age classes

Capsule The autumn migration strategy of Portuguese Savi's Warblers differs between age classes in timing, fuel deposition rate and flight range. Aims To describe the autumn migration strategy of Savi's Warblers, and compare the age classes. Methods Data from 533 first captures and 149 retraps, held by the Portuguese Ringing Centre, were analysed, and potential non-stop flight ranges were estimated. Results Juveniles started migrating in early August whereas adults departed at the end of August and both vacated the breeding quarters in early October. In contrast to juveniles, adults showed a marked increase in mass and fat from the end of August and had a significantly greater fuel deposition rate. Accordingly, in adults, the average potential still-air flight range increased dramatically from 600 km in August to 1500 km in September, whereas in juveniles it remained approximately the same (about 150 km). The fattest adults had an average flight range of 2750 km, and so were able, theoretically, to reach the winter quarters without refuelling. Conclusions The autumn migration strategy of Portuguese Savi's Warblers differs between age-classes in timing, fuel deposition rate and flight range. Adult Savi's Warblers are time-selected migrants in autumn. The early departure of juveniles with smaller fuel stores is consistent with their lower fuel deposition rates, as expected under time-minimizing migration models, as is the fuel-overloading and by-passing of potential staging sites seen in adults. However, energy-selected migration cannot be excluded as a possible explanation for the juvenile migration pattern, as these birds left the breeding quarters with only enough fuel to reach the next staging site.

Nest-site selection and predation in Savi's Warblers Locustella luscinioides

Capsule Savi's Warblers preferred sites dominated by high and dense Juncus and Rubus with thick litter, and avoided pure reeds; predation was higher in sites with less litter. Aim To describe nest-site selection and identify which habitat and nest features influence predation risk. Methods Comparisons were made between habitat characteristics measured at nest-sites and random points, and between predated and successful nests. Results Total vegetation cover, litter thickness, habitat type, undergrowth height and undergrowth cover, which were higher or denser at nest-sites, were the most important variables influencing the distribution of Savi's Warbler nests. Nests were most often predated in sites with low litter thickness. Conclusion Savi's Warblers are dependent on the presence of dense low vegetation and litter for nesting, which should be maintained close to or within reed-beds for their benefit.

Reedbed structure and habitat preference of reed passerines during the post-breeding period

Post-breeding habitats of nine passerine species were studied in the permanently flooded reed beds of ponds near the village Puste Uľany (SW Slovakia) in 2002. Structural features of reed beds and the abundance of all birds studied were sampled at two sites and eight study plots. The reed bed structure and abundance of four passerines differed considerably between the individual study plots. The variations in vegetation structure were also caused by winter reed burning in the SE part of study area. Stems in burnt reed beds were smaller and thinner than unburnt. Abundance of the reed warbler and to a lesser extent sedge warbler was higher in tall reed beds, while the bearded tit preferred thick reed stems. Position of reed beds along the shore - open water gradient was an important factor in terms of abundance at the study plots in the case of the reed bunting. This species showed a strong preference for the reed bed edge with open water. Horizontal distribution of other species seems to be random, however, the birds with the exception of Savi's warbler preferred the upper stratum of reed bed in vertical distribution. Our field data corroborate with those found in experimental studies concerning with ecomorphological characteristics of birds. Some inconsistencies, however, could also be caused by other factors (e.g. foraging preferences). Comparison of breeding and post-breeding habitat requirements of the studied bird species confirmed a more or less random distribution of the majority of species in the post-breeding period. Some variation was found in the cases of only the reed warbler and bearded tit.

Post‐juvenile and post‐breeding moult of Savi's Warblers Locustella luscinioides in Portugal

We describe the sequence and extent of the complex and little understood post‐juvenile and post‐breeding moults of Savi's Warblers Locustella luscinioides. In contrast to previous studies, the post‐juvenile moult occurred in at least 44% of the birds, 5% of which moulted some or all tertials and greater coverts. The timing of overlap between the filling and the post‐juvenile moults, and the fact that later‐moulting birds had no post‐juvenile moult, strongly suggests that the moult extent is dependent on fledging date. From July onwards, all adult males overlapped breeding and moult, whereas only 11% of the females did so. The start of moult varied from 6 June to 25 August, and was significantly earlier in males. Only 18% of the birds completed the moult, whereas the remaining individuals retained a variable number of inner primaries and/or secondaries. Interestingly, not only was the number of retained primaries positively associated with the date of moult, but so too was the primary number of birds in which the moult started. We view this as an adaptation allowing the replacement of the most important feathers for flight when the time available for moult is short. Body condition did not vary with the progress of moult when date was taken into account, but fat reserves still tended to decrease and then increase. The body condition was correlated positively with the wing raggedness, so Savi's Warblers do not compensate for an increasing wing load during moult.

Using stable isotope analysis to determine the winter moult extent in migratory birds: the complex moult of Savi's warblers Locustella luscinioides

Patterns of feather wear in birds captured in spring have traditionally been analysed to describe the extent of winter moult in long‐distance migrants. However, the interpretation of feather wear may be rendered extremely difficult due to long moult periods, by the progress of the season, and by the existence of complex moult patterns. Here, stable isotope analysis is used to determine the origin of the wing feather generations present in Savi's warblers Locustella luscinioides captured in Portugal. Carbon, nitrogen and hydrogen isotope ratios of feathers of known European origin differed significantly from those known to have grown in Africa. A discriminant analysis, in which 91.1% of the cross validated samples were correctly classified, was used to determine the origin of tail and wing feathers collected from birds caught when they returned to the breeding quarters. The interpretation of feather‐wear generally agreed with the stable isotope analysis, but some inconsistencies were identified. The extent of winter moult in Savi's warblers is described and its moult strategy discussed.

Using stable isotope analysis to determine the winter moult extent in migratory birds: the complex moult of Savi's warblers Locustella luscinioides

Using stable isotope analysis to determine the winter moult extent in migratory birds: the complex moult of Savi's warblers Locustella luscinioides

Variation of morphometric parameters within the Savi's Warbler (Locustella luscinioides) population in eastern Poland

Variation of morphometric parameters within the Savi's Warbler (Locustella luscinioides) population in eastern Poland Characteristics of the intra-populational variation of morphological parameters in the Savi's Warbler is based on measurements of 512 individuals caught in the breeding seasons of 1989-1998 in the Bagno Ławki peatbog (the southern basin of the Biebrza river valley). In the studied population, adult Savi's Warblers had longer and more rounded wing, longer tail and larger body mass than young individuals. Moreover, significant differences in the length of allula and 1st primary were found between these age classes. The range of wing length noted in this population, with the maximum value of 78 mm, distinctly exceeded the range of this parameter described for European populations of the Savi's Warbler. The average lengths of wing, tail allula and tarsus were distinctly higher in males than in females. Sexes did not differ in body mass, Kipp's distance and wing pointedness index. In the studied population, a distinct long-term variability of tail length, Kipp's distance, wing-tip pointedness index and tarsus length was found in young birds. In adults such variability was found only in tarsus length. The paper discusses possible reasons for the long-term variability of studied parameters.