Hirundo 16: 58–83 (2003)

Jaanus Elts , Andres Kuresoo, Eerik Leibak, Aivar Leito, Vilju Lilleleht, Leho Luigujõe, Asko Lõhmus, Eve Mägi & Margus Ots

Status and numbers of Estonian birds, 1998-2002

Summary

The paper gives an updated list of Estonian bird species, their status and numbers in breeding season and midwinter.
Methods. The estimates were evaluated as follows (hereafter the abbreviations are same as in Table 1).
Categories: A - species which has been recorded in an apparently wild state at least once since 1.1.1950; B - species which has been recorded in an apparently wild state only before 1950; C - released or escaped species which has established a self-supporting breeding population in the own country, also birds coming from category C population of another country; D - every species unless it is almost certainly a genuine vagrant or almost certainly an escape from captivity; E - escapes from captivity.
Status: H - regular breeder; S - summer visitor; L - passage migrant; T - winterer; ( ) - irregular (breeder etc.); [ ] - occasional (breeder etc); E - vagrant; int - introduced. A species was considered occasional breeder/winterer etc. if its occurrence fitted in this pattern in 1971-2002. Irregular and regular breeders etc. were however determined by occurrence pattern in the last 20 years (1983-2002) or (if status considerably changed in the period) according to the latest years.
No. of breeding pairs was taken as the common term of breeding population size, although in several species (e. g. gallinaceous birds, waders, raptors) pairs, in fact, were not counted. The minimum-maximum values consider both year-to-year variation (in some latest years) and inaccuracy of estimate. If numbers had changed unidirectionally in the latest years, the estimate reflects the latest known situation.
Winter numbers (individuals) are given according to January data, excluding years with extraordinary weather conditions. Most estimates are obviously very rough and with unknown reliability.
Evaluation methods are shown for breeding estimates: 1 - complete count (a full or near-full census); 2 - expert estimate (the best estimate in the opinion of experts studying the population of the species); 3 - compilation (an estimate derived from a number of sources); 4 - extrapolation from sample surveys in different habitats and/or random plots; 5 - a rough estimation from the previous estimate using known recent trend for correction (the previous method is indicated before character '/', e. g. 2/5= previously expert estimate); 6 - a rough estimate from few quantitative data and densities in neighbouring countries (Latvia, Southern Finland).
Reliability of estimate is divided into three classes: A - reliable quantitative data from several latest years; B - generally well known, but quantitative data incomplete; C - very poor or no (recent) quantitative data.
The changes in populations (trends) are expressed as follows: e = extinct as a regular breeding bird during the study period; - - = strong decrease (more than 50%); - = moderate decrease (10-50%); (-) = probable decrease (verification lacking); 0 = stable, no detectable change; (0) = probably stable; f = widely fluctuating, without steady trend; (+) = probable increase (verification lacking); + = moderate increase (10-50%); ++ = strong increase (more than 50%); (n) = newcomer with a few sporadic breeding records; n = newcomer as a regular breeding bird; ? = status largely unknown. In several cases also earlier trends were corrected if previously unknown data were available.

Results. The estimates are shown in Tables 1 and 2. Up to 01.01.2003 357 bird species have been recorded in Estonia, out of these 344 belong to categories A-C, five to category D and eight to category E (species which cannot survive in Estonia are, however, excluded). Breeding is confirmed in 221 species (207 regular, 4 irregular and 10 occasional), 153 species have been observed in winter (102 regularly) and 212 species on migration (202 regularly). Only 8% of breeding and 12% of wintering species have been counted highly reliably (Fig. 1).
According to this study 13.3-20.5 million pairs of birds breed in Estonia (0.6-1.0 million pairs of Non-Passeriformes and 12.7-19.5 million pairs of Passeriformes). Altogether, 3.0-9,3 million individuals were estimated to occur in midwinter, out of these 3.0-7.5 millions are Passeriformes.
Data collected in recent years enabled to improve earlier estimations (Lilleleht & Leibak 1993, Leibak et al. 1994, Lõhmus et al. 1998) for several species. The previous numbers for Anas clypeata, Columba palumbus, Pica pica, Acrocephalus scirpaeus and Motacilla flava were probably overestimated and those for the Tachybaptus ruficollis, Botaurus stellaris, Anas penelope, Bucephala clangula, Mergus merganser, M. serrator, Circus pygargus, Bonasa bonasia, Rallus aquaticus, Porzana porzana, P. parva, Numenius arquata, Streptopelia decaocto, Apus apus, Dendrocopos major, D. leucotos, D. minor, Picoides tridactylus, Alauda arvensis, Riparia riparia, Hirundo rustica, Delichon urbica, Prunella modularis, Acrocephalus schoenobaenus, A. dumetorum, and Sturnus vulgaris were apparently underestimated.

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