Hirundo 1/1997

Special issue on raptors and owls

Lõhmus, A.
Population changes of raptors and owls in north-western Tartumaa
Summary: The paper analyses the occurrence of raptors and owls during the last 100 years by publications, archive materials and author’s own data. The study area (900 km²) is situated in east-central Estonia (ca 58°25’N, 26°20’E). Forests covered ca 20% of the area in the beginning of the century and 40% in 1990s.
In 100 years 14 Accipitriformes, 5 Falconiformes and 8 Strigiformes species have been recorded as breeders. Their present population sizes are presented in Table 1. Additionally, 4 raptor or owl species have occurred as transit migrants, winter visitors or vagrants. Both in 1894-1904 and 1987-1996, 26 species were recorded. The Peregrine disappeared and Montagu’s Harrier appeared as regular breeders in 100 years. Among breeders another 7 species have decreased and 8 species increased in number, while all winter visitors have become more rare.
The present frequency compared to the situation 100 years ago is probably:
a) similar in Pernis apivorus, Milvus migrans, M.milvus (very rare vagrant), Circus cyaneus, Accipiter gentilis, Bubo bubo, Asio flammeus, Aegolius funereus;
b) lower in Circaetus gallicus, Accipiter nisus (ca 5 times), Buteo lagopus, Pandion haliaetus, Falco tinnunculus (ca 3-4 times), F.columbarius (10-20 times), F.peregrinus (extinct), Nyctea scandiaca, Surnia ulula (ca. 10 times), Glaucidium passerinum (at least 3-5 times), Strix aluco (at least 3 times);
c) higher in Haliaeetus albicilla, Circus aeruginosus (doubled), C.pygargus (newcomer), Buteo buteo (3 times), Aquila pomarina, A.chrysaetos, Falco subbuteo, Strix uralensis (5-10 times), Asio otus (5-10 times).
However, because of persecution the numbers of P.apivorus (?), Circus aeruginosus, A.gentilis, A.nisus and B.buteo decreased significantly to the 1920-1950s and have recovered since then. Compared to the present situation the frequency of Milvus migrans was higher in the middle of the century, and of Bubo bubo and Asio flammeus in 1950s-1970s.
The trends are unknown for Circus macrourus, Aquila clanga and Falco vespertinus.

Evestus, T.
Raptors in the surroundings of Otepää
Summary: The author has studied numbers and breeding success of raptors near Otepää (Valga district). Up to 1991, 150 sq. km-s were investigated, instead of 190 sq. km-s since 1992. Forests cover 50% of the area, nemoral forests and boreal pine forests dominate.
Nine raptor species were detected in 1988-1996, two of them (Montagu’s Harrier and the Osprey) as non-breeders. The number of occupied breeding territories of other species is shown in Table 1. The dominating species is the Common Buzzard (on average 17.3 territories per 100 sq. km-s).
The brood size was almost stable in the Common Buzzard contrasting to the declining trend in the Goshawk (Fig. 1).

Ojaste, I.
Observations at Palivere raptor plot
Summary: The plot (100 km²) is situated at the territory of Taebla and Oru parishes (Lääne district), ca 59°02’N, 23°52’E. Regular observations are carried out since 1992, some occasional data has been gathered earlier. Main attention is paid to numbers of breeding raptors and owls.
A total of 14 species of Accipitriformes (including 9 breeders), 4 (3) of Falconiformes and 5 (5) of owls have been recorded. Number of occupied territories has fluctuated between 32 and 41 (Table 2). From vagrants the Pallid Harrier was observed.
In 1987-96 arrival or departure of raptors has been recorded in 33 cases (Table 1). In autumn 1993 raptors were regularly counted by a 25 km road. 329 observations of 13 species were made (Fig.1).

Väli, Ü.
Raptors and owls in southern Hiiumaa
Summary: The raptors and owls of Hiiumaa Island have been only scarcely studied earlier. The author counted breeding birds of prey at a 35 sq. km study area in southern Hiiumaa in 1995-96, by mapping the breeding territories and searching for nests. The results are presented in Table 1.
The earlier published data showed Accipiter nisus and Strix aluco as verified breeders of the area, but during this study the breeding of Pernis apivorus, Accipiter gentilis, Buteo buteo and Falco subbuteo was also detected. Circus cyaneus and Haliaeetus albicilla used the area in the breeding season only for feeding. Buteo lagopus, Circus aeruginosus, C. cyaneus, Falco tinnunculus and Strix uralensis have been observed as transit migrants, Haliaeetus albicilla, Buteo lagopus and Aquila chrysaetos as winter visitors.

Klein, A.
Raptors observed by Finnish birders in Pärnu district, 1996

Randla, T.
Eagle Owls at Nõva

Lõhmus, A.
How to study reproductive success in birds of prey?

Lõhmus, A., Evestus, T., Lauk, K. & Väli, Ü.
‘Reproductive success of raptors and owls in eastern and south-eastern Estonia*
Summary: We present data on eleven species of birds prey in four Estonian districts (Tartu, Valga, Võru and Põlva). The data were mainly gathered in 1986-1996 with standard methods (according to Lõhmus 1997, see this volume). The parameters were defined as follows. Breeding frequency – percentage of nesting territories where breeding started (eggs were layed). Successful breeding produced at least one fledging. Breeding success – number of succesful breedings / total number of breeding attempts. Productivity – mean number of fledgings per territory per year. Young birds were regarded fledgings if their age exceeded 80% of normal fledging age.
The main results are presented in Table 1. Compared with other European data, at least two species (Pernis apivorus and Bubo bubo, presumably also Strix uralensis) showed lower reproductive rate.
In three species (Buteo buteo, Circus aeruginosus, Asio otus) the reproductive success was normal. Falco tinnunculus showed normal reproductive output (2,62) in the 1970s – a time of population crash, which suggests that population decline was related to other reasons.
The results about Accipiter nisus, Falco subbuteo and especially Accipiter gentilis exceeded the average rates reported in Europe. All three last-mentioned species depend largely on avian prey. In A.nisus and A.gentilis the average productivity was much higher in highly fragmented south-eastern districts compared to less mosaic Tartu district.
Some other species (Pernis apivorus, Buteo buteo) were less productive in areas of wilderness (Alam-Pedja) compared to mosaic mineral land. However, the differences could not be seen in the mean number of fledgings per succesful nest. In Buteo buteo the average brood size differed between years (Fig. 1).
In Strix aluco and Asio otus the clutches and broods were smaller in 1986-1996 compared to earlier data (Table 3).

Lelov, E.
Notes on raptors and owls
Summary: The author presents some interesting observations on birds of prey in south-western Estonia.
Circus cyaneus. Three observations have been made in winter (Jan. 1967, 09.12.1984, 10.12.1996).
Circus pygargus. The flight speed of a foraging adult male was 30-35 km per hour. Two nests of the species have been found within 200 m distance from human settlement, but both broods failed.
Accipiter gentilis. An adult male brought prey to nestlings from a distance of 4.5 km. In winter, corvids feeding on carcasses are afraid and desert their feeding place when goshawk appears.
Buteo buteo has started to winter more often: of 33 winter observations in 1976-1996 even 29 have been made in 1990s. The nest-building of a Buzzard lasted five days. Pseudo-attacks (without physical contact) to the ringers and feeding on carcass are described. The distance between two occupied nests has been 550 m.
Aquila chrysaetos. Two pairs nested 9 km from each other.
Falco subbuteo. A nest was situated 60 m from the nest of Haliaeetus albicilla and twice brood has contained 4 nestlings. Wintering was observed in 1976 and 1992.
Strix uralensis. One nest is situated in a farmyard, the other in village oak alley (1.2 km away from the nest of Strix aluco).
Asio otus. Six times since 1976, young that have just left the nest have been observed late in summer (between 10 July and 27 Aug).

Project “Raptors and owls at permanent study areas”

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