Hirundo 1/1999

Edula, E.
Breeding biology of the birds in artificial nests in the surroundings of Viljandi, 1968-1987
Summary: Nest-boxes have been put in the gardens and woods near Viljandi. Since 1970 there have been permanently about 200 boxes: three large for owls, 20 for starlings and the remaining for small passerines. The area and bird population dynamics have been described in Edula (1998), and the earlier (1956-1967) results about breeding biology in Edula (1969).
In different years 45-87% of the boxes were occupied, altogether by 14 bird species. Regular breeders were the Starling, Pied Flycatcher and Great Tit; also the Wryneck (no breeding records in the latest years), Marsh Tit and Tree Sparrow often nested in boxes. Occasional breeders were the Tawny Owl, Robin, Willow Tit, Crested Tit and Blue Tit, Nuthatch, Treecreeper and House Sparrow. The recorded clutch sizes are summarized in Table 1.
Tawny Owl. Out of nine breeding attempts (breeding was considered to begin with laying) seven were successful, producing on the average 2.3 young per breeding attempt.
Wryneck. The eggs were usually layed between 21 May and 6 June (earliest 18 May 1975, latest 20 June 1971). In addition to 25 successful attempts which produced on the average 6.6 young, the breeding failed in ten cases.
Starling. Laying starts mainly in the late April or early May (Figure 1). Long-term dynamics in the clutch size and breeding success are presented on Figure 2. The largest clutches (8 eggs) were observed in 1968 and 1969. In 1970-1987 208 breeding attempts (189 successful) produced on the average 3.7 young per attempt.
Pied Flycatcher. This species is the most numerous in the nest boxes. It arrives between 23 April and 9 May, and starts to breed in the second half of May (Figure 3). Long-term dynamics in the clutch size and breeding success are presented on Figure 4. The average clutch size was similar to that in 1956-67. The largest clutch (13 eggs) was probably layed by more than one female. Average measurements of 201 eggs were 17.71×13.35 mm, weight of 102 eggs 1.53 g. The incubation period lasted usually 13-14 (12-18) days (n=31), the whole period between the laying of the first egg and the
leaving of young was 32 days. Altogether 3.8 young fledged per breeding attempt (n=1352; out of these 953 were successful).
Robin. The breeding in nest boxes was confirmed in 16 cases. Ten successful attempts produced on the average 5.4 young per successful attempt.
Marsh Tit. Laying started usually between 23 April and 7 May; the incubation lasted 14 days (one observation), and the nestling period 20 days (two observations). 28 nests out of 42 were successful, producing on the average 6.2 young per successful nest.
Willow Tit. Most nests were situated in snags, nest-boxes were inhabited in 15 cases. Laying started between 1 and 24 May, incubation lasted 12-14 days (n=4). Ten nests were successful, the average number of young per successful nest was 5.3.
Crested Tit. Usually nests in snags, but 25 nests were found also in nest boxes. Usually laying started in the third decade of April; incubation lasted 14-15 days (n=3). Only nine nests were successful and on the average 4.8 young fledged per successful attempt. The average measurements of 13 eggs were 16.02×12.39 mm.
Blue Tit. Only 15 nest-box breedings have been recorded. Laying started between late April and mid-May. Nine attempts were successful, on the average 8.3 young fledged per successful nest. Great Spotted Woodpecker predated three clutches completely and one partly.
Great Tit. Many birds lay two clutches (Figure 5). Incubation starts differently in first and second clutch; it lasted 9-16 days (n=37), usually (n=21) 12-13 days. The long-term dynamics in the clutch size and breeding success are presented on figures 6-8. The average measurements of 152 eggs were 17.92×13.44 mm, weight of 86 eggs 1.64 g. On the average, 5.9 young fledged per first (n=552) and 5.5 young per second clutch (n=301); per successful attempt 7.3 (n=427) and 6.3 (n=258), respectively. The eggs of the first clutch tended to fail more often, possibly because of more intensive predation by Great Spotted Woodpecker.
Treecreeper. Has nested in nest boxes only twice.
Nuthatch. Six out of nine clutches were successful, producing on the average 4.29 young per successful attempt.
Tree Sparrow. Breeds up to three times in a season, clutches have been found from April to late July. In the first half of the study period the nests were persecuted systematically. 30 successful clutches yielded 4.6 young per successful attempt. The average measurements of 176 eggs were 19.66×14.75 mm.
House Sparrow. One breeding case (in 1968).

Lõhmus, A.
Monitoring of raptors and owls in Estonia, 1994-1998
Summary: Although in a few plots raptors and owls were studied already in the 1960s in Estonia, the monitoring has developed markedly only since 1989. In 1994 monitoring of raptors and owls at permanent study plots became a part of National Monitoring Scheme. This paper analyses the development and results of the project in five years (1994-98), and compares it with earlier data.
The project includes mapping the breeding territories (BT), checking potential nest sites and recording productivity of raptors and owls. At least 24 plots were studied in 1994-98 (Fig. 1). Although the locations are not randomly selected but determined by distribution of observers, the plots’ habitat composition is similar to Estonian average. Usually a plot follows UTM-grid square and covers 100 sq. km-s. If not studied for the first year, at least 150-200 work hours per 100 sq. km-s was needed to map the BT-s, and at least 250 hours to find 50% of nests (Fig-s 2-3).
The average breeding densities were calculated from average densities in every plot. Trends for most common species were reconstructed by comparing total numbers in plots studied in two subsequent years which were then standardized to the 1993 level. In general, potential nest sites were checked according to Haapala & Saurola (1986), the breeding results were recorded according to Lõhmus (1997a). Productivity is defined as number of fledglings per occupied nest.
The average breeding densities are presented in Table 1, occupancy of potential nest sites in Table 2, and average productivity in Table 3.
Coefficient of variation of densities in different plots gave the following order of distribution uniformity: Common Buzzard (35%), Honey Buzzard (43%), Sparrowhawk (48%), Hobby (52%), Goshawk (58%), Tawny Owl (80%), Long-eared Owl (82%), Ural Owl (100%), Montagu’s Harrier (104%), Kestrel (117%), Marsh Harrier (125%), Lesser Spotted Eagle (130%), Pygmy Owl (149%), Tengmalm’s Owl (173%), eagles (without Lesser Spotted) and the Osprey (186%), Hen Harrier (225%), Eagle Owl (231%), Short-eared Owl (387%), Merlin (400%).
The average densities in 1989-93 and 1994-98 were similar in most cases. The sharp decrease in Merlin, however, seems to have continued, and its present population in Estonia is estimated at 10-20 pairs (Lõhmus et al. 1998). Probably the numbers of Short-eared owl have decreased, too.
Evaluating trends by the samples of two subsequent years (Fig.-s 4-5) includes high risk of mistakes. When I eliminated the pair of largest change in every species, only decrease in the Goshawk and increase in Tawny Owl remained significant. In the first species also productivity has dropped, and I propose that it is mainly due to intensified forestry in the 1990s. The Tawny Owl population could have been restoring from impact of hard winter 1986/87.
The fluctuations in Long-eared Owl population are evident (Fig. 5). This overlaps with the three-year cycle of microtine voles which influenced productivity in several species, and occupancy of nest sites at least in two owl species. The top years in most of Estonia were 1990, 1993 and 1996, and minimum years 1989, 1992, 1995 and 1998 (or 1997). However, locally (e. g. near North-Estonian coast and in extreme south-eastern Estonia) the timing of cycles has been different.
In several aspects the productivity data overlaps with earlier results of a thorough local survey (Lõhmus et al. 1997). In this study, however, the productivity of Goshawk and Hobby was lower, and that of owls is overestimated as non-laying pairs were not taken into account.
The main conservation implications of the project were that 1) it allows monitoring of numbers of at least 16 and productivity of 11 species, and the further prospects for larger samples are good; 2) Merlin could have fallen into category of endangered species, there is a need for special survey and conservation plan for the species; 3) the Goshawk population will probably decrease significantly in the following years as possibly also the Lesser Spotted Eagle and Eagle Owl populations.

Elts, J. & Aua, J.
Roding of the Woodcock in Kuhjavere
Summary: On 3-12 April 1998 roding woodcocks were studied in a permanent station in Kuhjavere (Viljandi county). Every evening, between 20.30 and 21.30, the number of birds seen or heard (hereafter: contacts) was determined.
The timing of the roding flights is shown on Figure 1. The first five days were cold and no flights were detected at all. The first flight was observed on 8 April, followed by one day of no activity. The flights became regular since 10 April. A significant rise in roding intensity took place on 14 April, but on 17 April the number of contacts was again similar to that of 13 April. The following intensification turned to a continuous decline up to the end of the period.
In different evenings 0-20 contacts were counted. It is not known whether the woodcocks had arrived for the first count days, hence it is perhaps not correct to consider these days as unsuitable for roding. However, this conclusion could apply for 9 April, which was both preceded and followed by an active evening.
According to the number of contacts only one male could have been roding up to 12 April. It is supposed that on 13 April two, and on 14 April already 4-5 males could have been participated.
The frequency distribution of count results (Figure 2) indicates four clusters. The clusters suggest that a male, when it was alone, performed an average of 2.5 flight rings per hour; when one additonal male participated the number of rings was 3.7, and in the case of three males 4.2 rings per male per hour. The number of rings depends on many factors, of course, but the number of males seems to be among major impacts. The two evenings with maximum number of counts suggest on average 4.5 rings per male; this high intensity could have occurred because of participation of females.

Mikk, R.
When do birds stop singing?
Summary: Based on systematic observations during more than ten years near Tõrva (Valga county) the author presents data on annual last dates when singing or territorial calls were heard.

Mägi, E.
Birding towers in Matsalu

Note
Elts, J.
A clutch with five eggs in the Redshank

EOS chronicle