Ülo Väli

Sex− and species−biased gene flow in a spotted eagle hybrid zone

BackgroundRecent theoretical and empirical work points toward a significant role for sex-chromosome linked genes in the evolution of traits that induce reproductive isolation and for traits that evolve under influence of sexual selection. Empirical studies including recently diverged (Pleistocene), short-lived avian species pairs with short generation times have found that introgression occurs on the autosomes but not on the Z-chromosome. Here we study genetic differentiation and gene flow in the long-lived greater spotted eagle (Aquila clanga) and lesser spotted eagle (A. pomarina), two species with comparatively long generation times.ResultsOur data suggest that there is a directional bias in migration rates between hybridizing spotted eagles in eastern Europe. We find that a model including post divergence gene flow fits our data best for both autosomal and Z-chromosome linked loci but, for the Z-chromosome, the rate is reduced in the direction from A. pomarina to A. clanga.ConclusionsThe fact that some introgression still occurs on the Z-chromosome between these species suggests that the differentiation process is in a more premature phase in our study system than in previously studied avian species pairs and that could be explained by a shorter divergence time and/or a longer average generation time in the spotted eagles. The results are in agreement with field observations and provide further insight into the role of sex-linked loci for the build-up of barriers to gene flow among diverging populations and species.

Sex ratio of Lesser Spotted Eagle Aquila pomarina nestlings in good and poor breeding years

Capsule The ratio was female-biased in good years and male-biased in poor years, but did not differ from parity in the long term.

Factors limiting reproductive performance and nestling sex ratio in the Lesser Spotted Eagle Aquila pomarina at the northern limit of its range: the impact of weather and prey abundance

Abstract. Weather conditions and prey abundance impact many birds, but the influence differs between species and regions. I used 18-year data from Estonia, north-eastern Europe, in order to analyse the comparative effects of these factors on the breeding performance and nestling sex ratio in the Lesser Spotted Eagle. All studied reproductive parameters showed strong inter-annual fluctuations but no significant trends. Breeding frequency (proportion of pairs laying) was positively influenced by a warm pre-laying period (temperature in April) and a wet preceding season. These factors are probably associated with the higher occurrence and activity of amphibians that constituted important prey of the Lesser Spotted Eagle in spring. Breeding success (proportion of successful breeders) was determined mostly by the abundance of voles. Productivity (number of fledglings per nest) depended additively both on the spring temperature and abundance of voles in the breeding season; fledging of two nestlings was recorded regularly, mostly in years with high vole abundance. The total offspring sex ratio was slightly, though non-significantly, female-biased. Annual proportion of female nestlings was positively correlated with reproductive parameters and associated with rain in the preceding season, suggesting determination of fledgling sex ratio prior egg-laying. The results help to explain fluctuations in the reproductive performance of the Lesser Spotted Eagle and should be taken into account when monitoring and managing for conservation of this species.

Migration patterns of the Osprey Pandion haliaetus on the Eastern European–East African flyway

We analysed migration strategies of the Osprey Pandion haliaetus on the poorly studied Eastern European–East African flyway. Four adult birds were equipped with GPS-based satellite-transmitters or data-loggers in their breeding sites in Estonia (north-eastern Europe) and tracked to their wintering grounds in Africa and back, during up to six migration cycles. Departure times, migration routes, as well as wintering and stopover sites varied remarkably between individuals but not much between years. Stopovers (2–30 days) were made mostly in Europe and less in the Middle East (Turkey) and north-eastern Africa (Egypt). The Ospreys did not avoid flying long distances over the sea, and the sea was crossed four times during the night. The current study adds to current knowledge on Osprey migration and should help to concentrate actions on protecting important flyways and stopover locations.

Apparent survival rates of adult Lesser Spotted Eagle Clanga pomarina estimated by GPS-tracking, colour rings and wing-tags

ABSTRACT Capsule: In the migratory Lesser Spotted Eagle Clanga pomarina, colour rings and Global Positioning System transmitters indicated annual survival rates similar to other large raptors, but the rate suggested by wing-tags was significantly lower due to the higher rate of tag loss.

Successful Breeding of a Ten-Year-Old Hybrid Spotted Eagle Aquila clanga × A. pomarina Retaining Immature Plumage Characters

Greater Spotted Eagle Aquila clanga and Lesser Spotted Eagle Aquila pomarina are hybridising Eurasian raptors, but our knowledge of hybrid fertility is poor. Here, I present a case of interbreeding between a F1 hybrid spotted eagle male and a Lesser Spotted Eagle female in Estonia. The hybrid was first studied and ringed as a nestling in 1999, showing characters of both species. In 2009, the same bird was caught and, surprisingly, this ten-year-old individual had retained several immature characters. Again, characters of both species were recorded in the hybrid, as well as in his backcross-offspring. At the nest site level, the habitat of the hybrids hatching site was intermediate but its nesting site was typical of A. pomarina. At the landscape level hatching and breeding sites resembled habitat typical of A. clanga in Estonia.

Monitoring of spotted eagles in Estonia in 1994–2014: Stability of the lesser spotted eagle (Aquila pomarina) and decline of the greater spotted eagle (A. clanga)

Abstract Population trends of the lesser and greater spotted eagle in Estonia were comparatively estimated using data obtained in 1994-2014 from the monitoring scheme of common raptors and from special plots for monitoring of spotted eagles. Both approaches had pros and cons, but resulted in similar population trends. The numbers of the lesser spotted eagle have had minor fluctuations over the last two decades but the overall trend is stable; the current population size is estimated as 600-700 pairs. The number of greater spotted eagle breeding territories (pure-species and mixed pairs pooled) have significantly decreased, for example by 14% per year in 2004-2010, though in recent years the numbers seem to be stabilised at a critically low level. The decline of pure-species pairs was somewhat steeper than that ofmixed pairs, their proportion decreasing from a third to a quarter of the greater spotted eagle breeding territories. Altogether 5-10 breeding territories of the greater spotted eagle may be found nowadays in Estonia. Abstrakt Populacné trendy orla kriklavého a hrubozobého v Estónsku boli odhadnuté z údajov získaných v rokoch 1994 - 2014 v rámci monitoringu bežných druhov dravcov a tiež zo špeciálnych plôch na monitoring týchto dvoch druhov orlov. Oba metodické prístupy majú svoje klady a zápory, avšak z ich údajov vypocítané populacné trendy sú si podobné. Pocetnost orla kriklavého v posledných dvoch desatrociach mierne kolísala, celkový trend je ale stabilný; velkost jeho populácie sa v súcasnosti odhaduje na 600 - 700 párov. Pocet hniezdnych teritórií orla hrubozobého (cisté aj zmiešané páry) významne poklesol, napr. v rokoch 2004 až 2010 o 14 % za rok, v posledných rokoch sa ich pocet zdá byt stabilizovaný na kriticky nízkej úrovni. Pokles pocetnosti cistých párov bol prudší než u zmiešaných párov, ich podiel sa znížil z tretiny na štvrtinu z hniezdnych teritórií orla hrubozobého. Dnes je v Estónsku možné nájst 5 - 10 hniezdnych teritórií tohto druhu orla.

Short-distance migration of Estonian Common Buzzards Buteo buteo

The Common Buzzard Buteo buteo is a widespread species whose migration pattern differs by subspecies and regionally. Ring recoveries indicated that Buzzards originating from Estonia move southwest and winter in central and western Europe. This suggests that Estonia is occupied by the nominate subspecies of the Common Buzzard, which is a short-distance migrant.

Movements of the Goshawk in Estonia: an analysis of ring recoveries

The Goshawk Accipiter gentilis is a partially migrating raptor species, but its movement patterns differ between regions. In this study we have analysed ring recoveries of hawks ringed or recovered in Estonia (northeastern Europe) to identify the origin, direction and age structure of moving Goshawks. The vast majority of the foreign-ringed birds recovered in Estonia were juveniles or immature birds arriving in late autumn from Finland but no movement was detected in the opposing direction. Finnish birds have also been found in Estonia at breeding age, suggesting gene flow across the Gulf of Finland. The lesser number of birds originating from the south (Latvia) suggests some integrity in the Baltic Goshawk population. Recoveries of Latvian birds were dominant in the first half of the 20th century, but almost ceased later. This probably reflects the very strong impact of persecution on the Goshawk before the protection of the species, also indicated by the higher ring-recovery rate in the past. Movements within Estonia occurred in various directions while a small proportion of birds were involved in long-distance southward migration. This study suggests that movement patterns in the Estonian Goshawk population are similar to those in Fennoscandia.

Genetic determination of migration strategies in large soaring birds: evidence from hybrid eagles

The relative contributions of genetic and social factors in shaping the living world are a crucial question in ecology. The annual migration of birds to their wintering grounds and back provides significant knowledge in this field of research. Migratory movements are predominantly genetically determined in passerine birds, while in large soaring birds, it is presumed that social (cultural) factors play the largest role. In this study, we show that genetic factors in soaring birds are more important than previously assumed. We used global positioning system (GPS)-telemetry to compare the autumn journeys and wintering ranges of two closely related large raptorial bird species, the greater spotted eagle Clanga clanga and the lesser spotted eagle Clanga pomarina, and hybrids between them. The timing of migration in hybrids was similar to that of one parental species, but the wintering distributions and home range sizes were similar to those of the other. Tracking data were supported by habitat suitability modelling, based on GPS fixes and ring recoveries. These results suggest a strong genetic influence on migration strategy via a trait-dependent dominance effect, although we cannot rule out the contribution of social interactions.