Hirundo 2/1998

Lõhmus, A., Kuresoo, A., Leibak, E., Leito, A., Lilleleht, V., Kose, M., Leivits, A., Luigujõe, L. & Sellis, U.
Status and numbers of Estonian birds
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 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 other 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 1950-1997. Irregular and regular breeders etc. were however determined by occurrence pattern in the last 20 years (1979-98) or (if status considerably changed during this period) according to the most recent years (e. g. Citrine Wagtail is a regular breeder although its first breeding dates back only to 1991).
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 recent years) and inaccuracy of estimate. If numbers had changed unidirectionally in recent years, the estimate reflects the latest known situation (preferably in 1998).
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 method using the previous estimate (Lilleleht & Leibak 1993) and the 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 (mainly Southern Finland).
Breeding estimate reliability is divided into three classes:
A – reliable quantitative data from recent years; B – generally well known, but quantitative data incomplete; C – very poor or missing (recent) quantitative data.
The changes in breeding 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 (1971-90) trends were corrected if previously unknown data were available.
Winter numbers (individuals) are given according to January data, excluding years with extraordinary weather conditions. Most estimates are obviously very rough and (except for waterfowl) with unknown reliability.
Results
The estimates are shown in Table 1 (270kb). Some exotic and tamed species have been excluded from analyses.
As of 1.1.1998, 339 bird species have been recorded in Estonia (categories A-D), 222 of these are breeders (209 regular, 7 irregular and 6 occasional), 150 species have been observed in winter (94 regularly) and 212 species on migration (194 regularly).
329 species have occurred naturally, four of these (Gavia immer, Tetrax tetrax, Syrrhaptes paradoxus, Athene noctua) only before 1950. Three more species have occurred naturally in earlier times but recent records concern either escapes (Tadorna ferruginea) or birds with unknown origin (Gyps fulvus, Aegypius monachus). Seven species have probably always been escapes from captivity and two regular species (Columba livia, Branta canadensis) belong to category C. Four species (Pelecanus onocrotalus, Phoenicopterus ruber, Bucephala islandica, Bucanetes githagineus) are of unknown origin, as previously also Anser caerulescens (recent records concern escapes).
According to this study 7.9-15.7 million pairs of birds breed in Estonia, ten most common species making up 56-57% of this. Only 13 breeding species have been counted highly reliably, most of species with B-level reliability, and as many as 60 species with C-level reliability.
Recent addition rate of new breeding species seems lower than previously: in 1971-90 altogether 6 regular and 3 irregular new breeders settled in Estonia, compared to one species (Citrine Wagtail) in 1991-97. In 1971-90 69 species decreased and 77 species increased, in 1991-97 those numbers were 55 and 57, respectively. In this decade Falco columbarius, Charadrius dubius, Philomachus pugnax and Jynx torquilla have shown strong decrease, while Phalacrocorax carbo, Ciconia ciconia, Cygnus cygnus, Branta leucopsis, Haliaeetus albicilla, Tringa nebularia, Locustella luscinioides and Panurus biarmicus have shown strong increase.
Altogether, 2.4-8.6 million individuals were estimated to occur in midwinter, ten most numerous species making up 57-68% of this.
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