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ABSTRACTThis is the first annual study of a Eurasian magpie communal roost in Bulgaria. The roost is situated in the Dendrological Park of the University of Forestry—Sofia. The study was carried out in 2007–2008. We ascertained that magpies used to visit the communal roost all year round. The maximum number of birds recorded on one visit was 1405 birds (December 2007) and the minimum number was 139 birds (July 2007). The number of birds sleeping in the communal roost declined in the beginning of the breeding season because the birds started sleeping in their nests or near to them. The average number of birds sleeping in the communal roost during the summer was 32,33% from these in winter. We suggest these were non-breeding and birds whose breeding territory overlapped with the area of the communal roost. Despite significant fluctuation in the number of roosting birds during different seasons, the arrival dynamics of magpies were markedly uniform across all seasons with the exception of spring. The number of birds increased gradually in the first intervals of the study and they reached their peak in the interval 30–15 minutes before sunset and then decreased similarly. However, in spring proportionally more birds arrived on the roost in the interval 15 minutes before to 15 minutes after sunset without any decrease after sunset. Having arrived on the communal roost before sunset, the magpies perched in the crowns of the tallest trees and concentrated in the highest NE part of the roost (altitude 591 m). In the twilight period the birds were shifting their place to the lowest parts (altitude 587 m) which were highly overgrown with dense shrubs. We suggest that the Park has become important for the magpie because of lack of exploitation and we think that returning the intensive exploitation might force the birds to change the roost.

ABSTRACTThe population status of bleak (Alburnus alburnut (L.) in sand-pit lake Chepintsi near Sofia by using some biological factors as growth rate, condition and fecundity was investigated. The maximum age, length and body mass of bleak were 3 years, 12.7 mm and 20 g, respectively. The first, second and third age group were 5.77%, 63.46%, 30.77% respectively. The linear and body mass growth rate were described by the equations: SL=1.3487+2.6601R (r=0.88); W=0.1499L1.8499(r=0.95), respectively. The condition coefficient of bleak (k) was the lower than that for other populations from different water bodies. Also the populations from different water basins were compared by the body mass at the same length. Fecundity was 7 168 eggs, the average was 1 707–12 284 eggs. The fecundity-length and fecundity-weight relationship were described by the equations: F=387.32L+4365.7 (r=0.46); F=1368.4W-3151.9 (r=0.59) respectively.

This work explores the potential of laser excited luminescence for the study of type and concentration of rare-earth (RE) luminescence centres in CaF2. A comparison with X-ray excited luminescence is made. The luminescence spectra of several natural and synthetic samples are obtained at low and room temperatures using different Ar+ and Kr+ laser lines for excitation. Tentative assignment of the luminescent lines to different RE2+ and RE3+ ions is made. The excitation is shown to take place predominantly through the emission of one phonon. The possibilities for concentration measurements of luminescent centres are discussed.

Results on the synthesis and the electrical and magnetic properties of BiSrCaCu2OxHTS with Tc=78K are presented. The preliminary structure analysis suggests an orthorombic symmetry with possible slight monoclinicity. Raman spectra of single microcrystals also support this conjecture.