Hirundo 2/2004

Lõhmus, A.
Causes of death of raptors and owls in Estonia, 1985-2004
Summary: Mortality of raptors and owls has not been specifically studied in Estonia (but see Randla & Tammur 1996b; Lõhmus 1994a, 2001, for data on some species) and this paper summarizes their causes of death in 1985-2004. The material has been collected all over the country (Fig. 1) by (1) the participants of national monitoring projects; (2) two wildlife-rehabilitation centres; (3) ecologists studying raptor diets and population ecology. The causes of death of full-grown birds were classified into 20 categories of four main types (Table 1); for nestlings, some additional categories were used. Yet, the frequencies of disease, poisoning and exhaustion are obviously underestimated, since autopsies have been seldom made and other proximate causes (traffic, predation) may have concealed the ultimate ones.
Most deaths of full-grown birds (n = 615; Tables 3-4) were directly or indirectly caused by man (47%; notably traffic, powerlines and other collisions and injuries) and predators (34%; mostly the Goshawk, Golden Eagle and Eagle Owl). The frequency distributions of causes of death did not differ significantly between first-year juveniles and older birds, which implies that mortality-reduction measures could be roughly the same for both age groups. In winter, the main causes of death for owls (n = 27) were traffic (15) and exhaustion (7); no specific causes dominated for raptors (n = 17).
An intensive study in northwestern Tartumaa revealed manyfold overestimation of the frequency of man-induced mortality among smaller species and Goshawks in the remaining material. Considering this bias, I suggest that antropogenic deaths are particularly important for eagles, the Osprey and the Eagle Owl, and possibly for the Goshawk and the Tawny Owl in Estonia. There were 27 cases of persecution (44% of these were eagles or the Osprey). In general, however, persecution is not likely to influence the Estonian raptor and owl populations significantly any more (probably, some tens of full-grown raptors and a few nestlings are killed annually).
The death of nestlings (n = 128) was mostly related to food shortage and disease (46%, incl. cannibalism) or nest predation (30%); in tree-nesting species, nestlings often fell down from the nest (19%).
In general, natural causes of death were more frequent in Estonia than in most other European countries, and no alarming trends for conservation were detected.

Erit, M.
How many counts are needed for efficient bird census on floodplain meadows?
Summary: Mapping of breeders’ territories (see Koskimies & Väisänen 1991, Gilbert et al. 1998, Bibby et al. 2000) is often used for censusing birds. Usually, mapping is based only on 2-3 counts, but the efficiency of such a small number of counts is unknown. In 2001-2003, breeding birds were mapped on floodplain meadows of River Emajõgi in the Alam-Pedja Nature Reserve. Territorial birds and ducks were mapped on two study plots seven (or eight) times per season (including 1-2 night counts). The aim of the current study was to estimate the apparent visit efficiency (ratio between the results obtained from a single count and all counts; Svensson 1978) of 1-4 morning counts compared to counts performed five times, and to find a minimum number of counts for correct estimation of breeding territories. In 5-visit counts, breeding pair was defined as a cluster formed of at least two observations. In ducks Anas sp., maximum number of individuals (excl. nonbreeding individuals in flocks) per count was considered as the number of breeding pairs.
Four species or species groups (table 1) were included to analysis. To estimate apparent visit efficiency, I used all possible combinations of counts from six datasets (two study plots, three years). The abundance, relative to 5-times-counts, was calculated using species maps. Average apparent visit efficiency for all breeding birds was 55% (SD 14%) for a single count, 80% (11%) for double counts and 97% (9%) for 3-visit counts (Figure 1). For 4-visit-counts, the efficiency was 109% (8%) if all registered territories were considered, and 83% (7%), if territory was defined by at least two observations. The efficiency of counts increased and their variance decreased significantly along with growing number of counts. Efficiency was smallest and most variable in non-passerines, especially in ducks. In three cases, I was able to analyse the efficiency of 5- compared with 6-visit counts, the efficiency was 90% (SD 4%). In the Common Snipe and Sedge Warbler, efficiency of single and double counts in their main breeding time was 7-10% higher than the average efficiency, but the variation did not differ significantly.
Consequently, birds of floodplain meadows should be mapped at least three times during a breeding season. Four counts per season gives more precise estimates if all observation clusters are defined as breeding territories, whatever the number of observations is. To estimate the numbers of particular species, two counts during the time of species’ maximum activity may be sufficient. When one is interested in the numbers of all birds breeding on a floodplain, the census should include also night counts.

Laurits, M., Erit, M., Kuresoo, A. & Luigujõe, L.
Is it necessary to describe vegetation composition and structure while mapping birds on floodplain meadows?
Summary: We analysed distribution of bird species on a floodplain meadow in relation to 1) general landscape structure elements (at microhabitat scale) and 2) vegetation type, which distinguishes vegetation associations by species composition and vegetation structure. By comparing the two approaches, we looked for an optimal method to follow bird-habitat relationships in bird monitoring.
Breeding birds were mapped according to Koskimies & Väisänen (1991) in a floodplain meadow of River Emajõgi in the Alam-Pedja Nature Reserve in 2001-2003. Seven counts (including two at night) were performed in 2001 and 2003, and five counts (incl. one at night) in 2002. During the counts, we described also the landscape elements (Table 1), where individual birds were recorded. Vegetation types (Table 2) were mapped in 2001; later only substantial changes were recorded.
Using the general approach, non-passerines and open-landscape passerines were distinguished as sedge-preferring (open floodplain) birds, but occurence of bushes or reedbed patches was important too (Table 1). The number of bird species and breeding density was higher in diverse areas. The detailed analysis of vegetation types distinguished the same taxa (Table 2), but enabled to determine the preference in more detail (vegetation density, height and lush, soil humidity).
Consequently, the two approaches gave similar results on relationships between birds and the vegetation, although the detailed vegetation mapping was more informative. Considering the increased cost of time and labour of the latter approach, we suggest to describe the basic structure of habitat as well as soil moisture during bird mapping.

Eenpuu, R. & Elts, J.
Invasion of the Fieldfare to Estonia in winter 2002/03
Summary: The overview of a Fieldfare Turdus pilaris invasion to Estonia in winter 2002/03 is based on ornithophenological data collected by the members of the Estonian Ornithological Society. In autumn 2002, rowanberries were extremely abundant. Invasion of fieldfares started in the last decade of November and lasted till the beginning of March. Largest flocks (up to 2500 birds) were seen in January and in the first half of February (Figure 1). According to the monitoring of winter land birds in Estonia, the 2002/03 invasion was the largest during the last decades (Figure 2). The numbers of breeding Fieldfares did not increase in 2003.

Lilleleht, V.
Changes in avian systematics
Summary: The article reviews the latest proposals in avian systematics, and the attempts of the Association of European Records and Rarities Committees (AERC) to standardise their implementation in Europe. The Estonian Rarities Committee (at the Estonian Ornithological Society), decided at 26.02.2004 to follow the recommendations of AERC also in the list of Estonian birds. The new Estonian list is available at www.eoy.ee

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