Hirundo 1/2002

Mägi, E.
The Ruff on the meadows of Matsalu
Summary: Numbers of the Ruff (Philomachus pygnax) have decreased in whole Europe. In Estonia, the Ruff was a widely distributed breeding bird some decades ago, occupying areas islands, western and northwestern coast as well as alluvial meadows on bigger rivers. In the beginning of the 1990s the breeding number was estimated at about 2000 pairs, and the trend for 1971–90 was stable (Lilleleht & Leibak 1993). Ten years later the estimate was only 100–200 (Lõhmus 2001). Given that Kasari floodplain meadows and the surroundings of Matsalu Bay (Fig. 1) have continuously held the highest number of Ruffs in Estonia, this article (1) gives a historical overview about the status of the subpopulation, (2) describes its breeding habitats, and (3) reviews the history of grassland management and its possible impact on Ruff numbers in the area. Most of the data (incl. about 150 nest descriptions) comes from the systematic censuses of breeding birds since 1958. Earlier data have been collected by Eerik Kumari and some other researchers.
In the 1870s, the Ruff was among the most numerous non-passerines around the Matsalu Bay. In the 1930s, drainage of the Kasari Delta had started, and E. Kumari stated the Ruff as a common breeder (at least 85 pairs) on the Kasari meadow, eastern part of the coastal hay meadows of Matsalu Bay and on larger islands of the bay (Sits 1937, see Fig. 2). In the 1950s, the species had (again) spread widely on the meadows around Matsalu, Topi and Topu Bays, as well as on islands in the bay and in hay-islands in Moonsund. Its numbers reached 940 pairs (Table 1). After such a big increase, decrease started. First, the Ruff disappeared from juniper-rich coastal meadows, then – after grazing was stopped, and open water areas between reedbed and meadows were lost – also from traditional breeding sites in the inner part of Matsalu Bay. In Kasari floodplain meadows, the number of breeding Ruffs started to decrease since 1986–1987. In the last few years, no breeding Ruffs have been detected there but some pairs might still breed. A few pairs breed almost annually in the middle part of Matsalu Bay meadows. The total population estimate for 1997–2001 is 0–15 pairs in Matsalu, and the total Estonian population is obviously much smaller than the last estimate of 100–200 pairs. On migration, the Ruff is still numerous (although less numerous than in top periods) and approximately 12,000 specimens have been counted during migration peak in Kasari meadows, reedbed and on the coast.
In the 1930s, when Ruff numbers were low, they bred only in coastal hay-meadows and in the Kasari flood-plain meadows. Pastures were occupied during population increase; this also coincided with the period when many previously mowed areas were changed to pastures. Most nests have been found from wet meadows with short grass, particularly areas with small ditches. Usually, the nests were in small grass-tufts.
Obviously, there are many reasons for the disappearance of Ruffs. One reason could be global warming and northward shift of its distribution range. However, also habitat change is likely to have big impact. For example, Kasari meadow, from which Ruffs almost disappeared, has been continuously used as hay meadow. However, modern mechanised mowing has resulted in (1) the decrease of mowing area (to 2 500 ha); (2) higher grass – the lowest 15 cm remains now untouched; (3) dense stub-cover of willows (only upper part of is cut down). These changes alter the insect fauna, and old grass and scrub make foraging harder for short-billed birds (e.g. Lapwing and Ruff) and nestlings. From a distance, the meadow looks well managed but for birds, it could be like any other poorly mowed area.

Tuule, E., Tuule, A. & Elts, J.
Numbers and population dynamics of the Lapwing in the surroundings of Saue, 1963–2001
Summary: Breeding Lapwings (Vanellus vanellus) were counted in an approximately 100-km² area in the surroundings of Saue (northern Estonia, near Tallinn), 1963–2001. The landscape is mosaic and the share of open agricultural habitats has increased during the study years. Lapwings were counted in 50 m wide transects. The average annual density (pairs per 1 km²) for the 39 years was 22.1±14.6 (S.D.) pairs in fields, 20.5±19.7 (S.D.) pairs in meadows, 11.0±9.0 (S.D.) pairs in pastures, and 1.5±1.5 (S.D.) pairs in wooded and bushy meadows. Population trends were negative in all biotopes, but particularly strong decrease took place in fields (r= –0.71, p<0.001). Very sharp decline was detected between 1984 and 1985, when Lapwing density dropped 4.7 times in fields, 2.7 times in meadows, and approached zero in pastures and wooded meadows (declines 13 and 16 times, respectively). The most probable reason for this catastrophic decline was high mortality in wintering grounds.

Nellis, R., Nellis, R. & Tammekänd, I.
Numbers and habitat use of wintering Common and Rough-legged Buzzards, Hen Harriers, and Great Grey Shrikes in western Estonia
Summary: In winter 2000/2001, four species of wintering predatory birds were censused in the open landscapes of Saare and Pärnu counties, in order to estimate the size of wintering population in these areas and to explore habitat use of the species. The total numbers were mainly estimated from average population densities for different open biotopes. The mean density of the Common Buzzard (Buteo buteo) in the agricultural landscape of Saaremaa was 0.79±0.39 individuals per 100 ha, in Pärnu county 0.27 and in the other biotopes of Saaremaa 0.44±0.98 ind./100 ha. The average density of the Hen Harrier (Circus cyaneus) was 0.05 ind./100 ha in both counties; the density was 0.08–0.11 ind./100 ha in the Rough-legged Buzzard Buteo lagopus, and 0.32 ind./ha (only Saaremaa counted) in the Great Grey Shrike (Lanius excubitor)(Table 1). Considering the densities as well as potential biases and confusing factors, we estimated the wintering populations for the winter 2000/2001 in West-Estonia as follows: Hen Harrier 20–40 individuals, Common Buzzard 750–1000, Rough-legged Buzzard 40–60, and Great Grey Shrike 500–700 individuals. These numbers are considerably higher than the latest estimates for the whole Estonia, probably as a result of better methodological approach of the current study as well as the mild winter 2000/2001. Common Buzzards preferred to forage rather on set-aside fields (on average, 1.77 ind. per 100 ha) than arable fields (0.59) and wet meadows (0.58), while the Great Grey Shrike was most abundant in arable fields (0.59) and wet meadows (0.58). However, the differences between observed and expected (according to relative cover of habitat types) habitat distributions of these species were not statistically significant.

Väli, Ü. & Laansalu, A.
Numbers, reproductive success and diet of raptors and owls in Härjanurme, Tartu County, in 1992-2001
Summary: Breeding numbers, reproductive success and diet of raptors and owls were studied since 1992 in Härjanurme study area (100 sq. km.), east-central Estonia (58°20’N, 26°25’E). Mosaic agricultural landscape (57%) dominates in the plot; forests cover 22.5%, flood plains 12.5%, mires and water bodies both 3.5%. Breeding territories of raptors and owls were mapped according to their territorial behaviour, repeated observations, nests or fledglings. Reproductive success was estimated with standard methods (e.g. Lõhmus et al. 1997). General diet composition of Buteo buteo, Strix aluco and Asio otus was determined from pellets and prey remains, but insects and bird feathers were excluded from material (birds were initially classified only as non-passerines and passerines). For Accipiter gentilis we used equally bones and feathers. Diets were described by diet width DW = 1/Σpi2 and diet overlap O = Σpijpik / √ Σpij2 Σpik2, where pi is the share of prey species i in the diet, and j and k are raptor species.
Altogether, 13 species (7 Accipitriformes, 2 falcons and 4 owls) were found as breeders (Table 1). The total annual number of breeding territories was 30–55 (mean 44). Species of cultural landscape were most numerous, but also high numbers of Circus aeruginosus were characteristic. Accipiter gentilis and Falco tinnunculus disappeared as breeders during the study. A white morph individual of Buteo buteo bred in the area throughout the study period. Circus cyaneus, Pandion haliaeetus, Haliaeetus albicilla were recorded as vagrants, Buteo lagopus was seen in spring migration.
Reproductive success of five species is summarized in Table 2. In Buteo buteo, productivity (p<0.001) and number of fledglings per successful nest (p<0.001) varied annually but were generally similar to the average values in Estonia.
Out of four species studied, diet of Strix aluco contained the highest numbers of different prey species but diet width was greatest in Buteo buteo (Table 3). Diets of Buteo buteo and Asio otus overlapped by 70%, the diets of Buteo buteo and Strix aluco by 58%, but the diets of the two owl species by only 31%. Accipiter gentilis fed only upon birds (Table 4). Mean body mass of avian prey was different in Strix aluco (65 g), Buteo buteo (158 g) and Accipiter gentilis (375 g; p<0,0001).

Lõhmus, A.
Are estimates of distance to forest edge biased in the data of nest record schemes?
Summary: If birdwatchers tend to look for nests of forest-dwelling birds more often near forest edges than in forest interior, the occasional data in nest record schemes could give biased estimates about habitat use relative to forest edge. In this study, I compared distances to openings from the nests of three raptor species (Accipiter gentilis, A. nisus and Buteo buteo) according to the data of a systematic study in Tartumaa county (east-central Estonia) and the nest record scheme of the Estonian Ornithological Society. The definition of edge (incl. openings as well as forest rides and roads) and distance classes followed those of nest cards. Median tests did not show any significant differences between the two data sets; in A. nisus, the distance to edge tended to be even longer in the nest record data (p=0.12; Table 1). Hence, nest record schemes can give quite realistic estimates of distances to forest edges. A shortcoming of the Estonian card is its inability to distinguish between different edges (e.g. large openings are not separated from rides and narrow roads).

Notes
Leito, A. A white-tailed Eagle attacked a Common Crane

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