Jelena Kralj

Birds of a feather winter together: migratory connectivity in the Reed Warbler Acrocephalus scirpaceus

To investigate migratory connectivity in the Reed Warbler Acrocephalus scirpaceus, we analysed (1) all available sub-Saharan ringing recoveries and (2) stable isotopes in feathers grown in Africa sampled at 17 European breeding sites across a migratory divide. A cluster analysis of ringing recoveries showed remarkable connectivity between breeding and non-breeding grounds. Two main clusters represented populations taking the two main migratory routes [southwesterly (SW) and southeasterly (SE)]. Stable isotope analysis confirmed the separation of wintering areas of SW- and SE-migrating populations. Higher δ15N values in feathers of SE-migrating birds indicated that they occupied more xeric biome types. Values of δ13C that did not differ significantly among populations were higher than those from feathers of known European origin and indicated a C4 biome. Three populations with an unknown migratory direction were assigned to the SE-migrating populations on the basis of δ15N values.

Intraspecific Variation in the Wing Shape and Genetic Differentiation of Reed Warblers Acrocephalus scirpaceus in Croatia

Abstract. n Wing shape plays a major role in determining the aerodynamics and performance of avian flight. Intraspecific variation in wing shape reflects different migratory strategies or distances between breeding and wintering areas. Differences in the wing morphology and genotypes between coastal and inland breeding populations of the Reed Warbler in Croatia were studied. A total of 105 adult birds were measured, while blood samples were taken from 59 individuals. The results showed that the two geographically close populations of Reed Warblers differ in wing morphology, with birds from the inland population having more pointed and more slotted wings than those from the coastal population. There was a slight but significant difference in microsatellite allele frequencies between the two populations (FST = 0.015), suggesting that gene flow between the two populations is partly restricted. The differences in wing morphology imply that the two populations use different migratory routes and/or winter in different areas. Consequently, this migratory pattern may have influenced the contemporary genetic differentiation of the two populations.

Migration of Central and East European Acrocephalus Warblers at the Eastern Adriatic Coast: An Analysis of Recoveries

Migration of Central and East European Acrocephalus Warblers at the Eastern Adriatic Coast: An Analysis of Recoveries Migration routes and origins of the Reed Warbler (Acrocephalus scirpaceus), Great Reed Warbler (A. arundinaceus) and Sedge Warbler (A. schoenobaenus) populations migrating through the eastern Adriatic coast were investigated by analysing recoveries of birds ringed or found at two eastern Adriatic wetlands during autumn migration. There were 75, 104 and 63 long-distance recoveries for these three species, respectively. Great Reed Warblers from central and eastern Europe and Sedge Warblers from countries surrounding the Baltic Sea use the eastern Adriatic wetlands as stopover sites and continue their migration across the Mediterranean. Some Great Reed Warblers use south-western route during their return migration. Reed Warblers of unknown origin, presumably from eastern Europe continue their migration through south-western route to Spain (mean distance - 1329.3 ± 118.0 km, n = 20; mean azimuth - 251.05 ± 4.91°, n = 20; mean velocity - 63.25 km/day, n = 16). Local breeding Reed Warblers migrate southeast along the eastern Mediterranean (azimuth 117.53°). Eastern Adriatic coast represents a crossroads for migratory warblers using south-western, south-eastern and central Mediterranean flyways.

Nest Site and Nest-Hole Characteristics Used by Great Spotted Woodpecker Dendrocopos major L. in Croatia

ABSTRACT: Great Spotted Woodpecker is the most abundant and widespread European woodpecker species, and it thus contributes the most to the number of excavated tree holes — an important habitat resource for secondary hole users. However, majority of nest site characteristics data comes from boreal and temperate forests, with lack of information from Southern Europe. In this article, nest sites of the Great Spotted Woodpecker have been investigated in the continental forests of Croatia — a previously understudied area of this species range. A total of 41 active nest-holes found in the breeding seasons 2003 and 2004 are described. Nest-holes were mainly positioned below the crowns, in injuries of branch abscission. Nesting tree species were not used randomly: wild cherry Prunus avium in hill and pedunculate oak Quercus robur in riverine forests were preferred while hornbeam Carpinus betulus and maples Acer sp. were avoided. While tree species used for nesting vary across the Great Spotted Woodpecker range, and thus cannot be used as a uniform nest site predictor, defected wood spots on a tree, like scars of branch abscission, are identified as an important nest site clue and a habitat feature that is spatially more consistent. Nestholes dimensions acquired in this research could not be clearly differentiated from those given for the other parts of the continent.

Moulting and Wintering Grounds of Marsh Warblers Acrocephalus palustris : Evidence from Stable Isotopes and Ring Recoveries

Abstract. n We analysed stable carbon (&dgr;13C) and nitrogen (&dgr;15N) isotope ratios in Marsh Warbler Acrocephalus palustris feathers sampled in Europe and Africa to assess non-breeding habitat selection and location of wintering grounds of different breeding populations. Feather &dgr;13C values showed that Marsh Warblers occupy a biome dominated by C4 vegetation during the stopover in northeastern Africa, whereas C3 habitats are used during the complete moult in southern Africa. East European Marsh Warblers differed in their stable isotope profiles from other European regions, suggesting a certain level of population segregation in southern Africa. A dual-isotope assignment approach confirmed this difference and helped us restrict the autumn staging areas to lower elevations of the Ethiopian Highlands west of the Rift valley. Available ring recoveries, however, suggested high levels of population mixing both on migration through East Africa and in the final wintering grounds.

The late-Holocene avifaunal assemblage from the island of Palagruža (Croatia): The earliest record of the Northern Gannet in the Adriatic Sea

The late-Holocene bird remains retrieved during archaeological excavations on pelagic island of Palagruža, Croatia, were analysed. The results of the analysis revealed presence of representatives of nine families: Procellariidae, Sulidae, Ardeidae, Accipitridae, Phasianidae, Rallidae, Laridae, Strigidae and Corvidae. Among the bird remains, the most numerous were remains of the Northern Gannet, Morus bassanus, which were widely distributed in the Mediterranean during the late Pleistocene. The finding of the Northern Gannet bones on Palagruža represents the first fossil record of this species in the Adriatic Sea and indicates a possible breeding site on the island. The direct Accelerator Mass Spectrometry (AMS) radiocarbon dating on two gannet bones revealed the age of 2878 ± 34 and 2694 ± 45 yr BP. Gannet bones from Palagruža were some 6000 years younger than other fossil records of that species from the Mediterranean. It is possible that during the gannet’s northward distributional shift, probably caused by centennial climatic variability and human pressure, gannet colony on that remote island in the Adriatic lasted longer than in the rest of the Mediterranean and existed until the late-Holocene. Lower sea-surface temperatures compared with the eastern Mediterranean, higher nutritive productivity and remoteness of Palagruža provided adequate breeding opportunities during that period.

The eagle owl Bubo bubo (Aves: Strigidae) in the Eastern Adriatic (Croatia): the study case of a high-density insular population

Abstract The Croatian population of the eagle owl Bubo bubo (Linnaeus, 1758) is estimated at 800–1200 breeding pairs with the majority of population breeding in the Mediterranean region, along the eastern Adriatic coast. The main aims of this work were two-fold: (1) to determine the eagle owl territorial densities in the central part of Mediterranean Croatia; and (2) to examine landscape composition and configuration of the study plots and consider possible reasons for differences in recorded densities. The abundance of the eagle owl was surveyed from 2001 to 2006 within three plots of similar size (a total survey area of 246 km2): two plots were on the mainland and one on the archipelago at about 16 km from the coast. The playback method was used to stimulate eagle owl territorial behaviour and to determine the locations of their territories. Territorial densities ranged from 4.5 to 26.2 pairs/100 km2, with the highest density being recorded on islands. We suggest that this high density is a result of good foraging conditions, especially year-round availability and high abundance of the yellow-legged gull Larus michahellis J. F. Naumann, 1840 and the brown rat Rattus rattus (Linnaeus, 1758), together with low risk of human-induced mortality.

Factors Affecting the Goldcrest/Firecrest Abundance Ratio in Their Area of Sympatry

The goldcrest (Regulus regulus) and the firecrest (Regulus ignicapilla) are sympatric over a large part of Europe, but with different abundance ratios. We studied the effects of geographical location, vicinity of the species range boundaries, habitat and climate factors on the goldcrest/firecrest abundance ratio. At the continental scale, a weighted multiple linear regression model resulted in four significant covariates: temperature, precipitation, forest type and occurrence rate (representing the vicinity of the species’ range boundaries). The firecrest dominates in warmer and more humid areas and its dominance is more pronounced in mixed forests. The projection of the model showed that in any combination of temperature, precipitation and occurrence rate, the probability to encounter the goldcrest is higher in coniferous forests. Studies in Croatia and the Czech Republic showed regional differences in habitat preferences related to forest type. A significant effect of the seasonal dynamics of precipitation was confirmed in Croatia. Climate change and changes in forestry may influence the distribution and abundance of these two Regulus species in Europe.

Song structure and variability in the Black-headed Bunting ( Emberiza melanocephala )

Fighting and flirting are the main evolutionary forces behind the development of bird song and both contribute to different song characteristics. By comparison of vocalisations throughout bird taxa, we can help to reconstruct the evolutionary history of the song. In this study, we provide the first detailed analysis of song structure and song type variability in the Black-headed Bunting (Emberiza melanocephala). We quantify the fine structural characteristics of the song and describe the song and syllable repertoire size. Further, we describe intraindividual song variability over time and interindividual song variability over space, and we explore whether this species uses syntactic rules to create songs. Our analyses reveal that the Black-headed Bunting has a short yet rather complex song and that the syllable pool is extensive. Its song is constructed of three parts that differ in both complexity and rhythm, suggesting the use of syntactic rules in constructing a song. The male song is typically built of 9–13 syllables, with 7–12 that are non-repetitive. Each male sings only one stereotyped song, which remains identical throughout the male’s lifespan, providing evidence for age-limited song learning. Songs are individually distinct, suggesting the importance of song in individual recognition of males. Two spatial levels of song variation in the Black-headed Bunting are shown. On a microgeographical level, relatively small song neighbourhoods are formed with a handful of birds singing the same song type. On a macrogeographical level, dialects can be distinguished by the end part of a song. The most striking feature of the male Black-headed Bunting song is the immense variability of song types. Typically, only a small number of males shared the same song type, and males with unique song types occurred frequently as well. The high song complexity and single-song repertoire found in the Black-headed Bunting could reflect a high level of polygyny and a low level of parental care, therefore pointing to strong intersexual selection on the male song.ZusammenfassungAufbau und Variabilität des Gesangs männlicher Kappenammern (Emberiza melanocephala) Kämpfen und Flirten sind zwei wichtige Funktionen des Vogelgesangs und damit auch treibende Kräfte der Evolution, die zur Ausprägung von Vogelgesängen beitragen, dabei aber unterschiedliche strukturelle Merkmale fördern. Um die Evolution von Vogelgesängen zu rekonstruieren, ist unter anderem der Vergleich von Gesängen verschiedener Vogelarten eine wertvolle Methode. In dieser Studie präsentieren wir dazu die erste detaillierte quantitative Analyse und Beschreibung von Struktur und Variabilität des Gesangs männlicher Kappenammer (Emberiza melanocephala). Neben Gesangsaufbau, der Ausprägung von Gesangstypen und der Silbenrepertoiregröße werden intra- und interindividuelle Gesangsunterschiede sowie mögliche zugrundeliegende syntaktische Regeln untersucht. Unsere Analysen zeigen, dass männliche Kappenammern kurze aber komplexe Gesänge produzieren, die sie aus einem umfangreichen Silbenpool schöpfen. Der typische Gesang von Kappenammermännchen besteht aus drei Teilen, die sich in Komplexität und Rhythmus unterscheiden, was auf die Verwendung syntaktischer Regeln beim Gesangsaufbau hindeutet. Eine Gesangstrophe besteht typischerweise aus 9-13 Silben wovon 7-12 nicht wiederholt werden. Jedes Männchen produziert nur einen Strophentyp der über die gesamte Lebensdauer unverändert vorgetragen wird. Die Gesänge unterscheiden sich aber zwischen Männchen und dürften der individuellen Erkennung dienen. Bezüglich geografischer Unterschiede im Gesang zeigen sich gleiche oder ähnlichen Gesangstypen zwischen Nachbarn. Großräumig können Dialekte differenziert werden die sich durch den Endteil einer Strophe unterscheiden. Typisch für den Gesang männlicher Kappenammern ist eine Vielfalt an Strophentypen, wobei meist nur wenige Männchen denselben Strophentyp teilen, viele Männchen aber einzigartige Strophen produzieren. Die Tatsache, dass jedes Männchen nur einen Strophentyp produziert, die einzelnen Strophen aber relativ komplex sind, deuten auf eine hohe Neigung zu Polygynie und eine geringe Bereitschaft der Männchen, sich an der Brutfürsorge zu beteiligen hin. Intersexuelle Selektion dürfte also für den Gesang männlicher Kappenammern von großer Bedeutung sein.

Apparent survival rates of a long-lived partial migrant: the Yellow-legged Gull Larus michahellis

ABSTRACT Capsule: In Yellow-legged Gull Larus michahellis populations from the eastern Adriatic Sea, there are considerable differences in the ratio of migratory birds and apparent survival among the colonies. Survival was dependent on age, colony and area of dispersal. Aims: To identify the ratio of migratory birds within populations of Yellow-legged Gulls, and to compare apparent survival of gulls during migration in central and northern Europe and around the Adriatic Sea. Methods: We analysed 15 years of resighting data of Yellow-legged Gulls using a MARK multi-state model to calculate survival rates. The effects of age, natal colony and area of dispersal were examined. Results: Almost 60% of Adriatic Yellow-legged Gulls were migratory but the ratio varied among colonies (10.3–78.3%). Survival was dependent on age, colony and area of dispersal, with average values per group ranging between 0.599 (se 0.093) and 0.684 (se 0.084). Conclusion: The ratio of migratory and dispersive Yellow-legged Gulls from different Adriatic colonies might be affected by both inheritance and food availability.