Estimating density, population size and dynamics of Common Buzzard (Buteo buteo) in the West Carpathian region by a new method

In the Hornr Ponitrie Region (central Slovakia) during 1991-2001 we conducted a regular survey of Common Buzzard nests. In 2002-2006 our sampling effort increased and within the selected areas we studied buzzard dispersion/distribution, density and population dynamics using a new method of large-scale thorough search for nests with multiple nest check. The method is designed to estimate the dispersion/distribution, density and population size of target species (particularly raptors) at an absolute scale of abundance in large tracts of heterogeneous landscapes for studies of population fluctuations, trophic dynamics, reproductive success, habitat selection and use. It consists of systematic search for nests with extent of several tens of km2 and grain of c. 3000 m2, identifying and positioning the nests, and subsequent 1-3 nest checks during the each of three or more consecutive breeding periods. Further essential features include correct record of nest positions and other variables, combination of nest checks with ringing and marking, proportional sampling in apparently suitable and less suitable areas and proper timing and spacing of nest visits. In 2007 the sampling focused on DSF (Databank of Slovak Fauna) grid square 7377 covering c. 135 km2. We searched 71 km2 in total and estimated the density at 129 pairs/100 km2. Within the district of Prievidza (959 km2) we found 150 active buzzard nests. In 2008 we sampled the grid square 7377 more extensively, including higher altitudes (800-1200 m a. s. l.). Sampling of 82 km2 in total yielded the density estimate of 93 pairs/100 km2. Within the district of Prievidza we found 110 active buzzard nests. The reproductive success over four year period averaged 1.2 fledgling per active nest (n = 310 nests). Our sample enabled us to estimate the minimum population size in the whole grid square 7377 at 130 breeding pairs, i.e. 96 pairs/100 km2. Minimum population size for the whole district of Prievidza can be estimated approximately at 500 breeding pairs (52 pairs/100 km2), c. 350 of which breed in mountain forests, c. 80 in agricultural woodlots, and c. 70 in riparian vegetation. Rough estimate of minimum breeding population in the whole Slovakia is c. 15 000 pairs, i.e. on average 31 pairs/100 km2. V oblasti horného Ponitria sme v rokoch 1991-2001 vykonávali rámcový monitoring hniezd myšiaka hôrneho Buteo buteo. V rokoch 2002-2006 sa výskum zintenzívnil a na vybraných plochách sme zisťovali disperziu, denzitu a pop