The population of the red-footed falcon in Slovakia inhabits the north-western edge of the species' breeding range. This breeding population is relatively small and came near to extinction during the population decline of this species in central Europe in recent decades. Thanks to increasing numbers of breeding pairs in Hungary, the Slovak population began to grow again. Moreover, some differences in breeding biology associated with breeding in nest boxes were found. Here we describe the dependence of the small isolated breeding population in Slovakia on the core population in the more eastern parts of the Carpathian Basin, and the impact of supporting activities (nest boxes) on this raptor species in Slovakia.
In 2011–201 4 monitoring of the lesser spotted eagle (Aquila pomarina) breeding population was conducted in eight
special protection areas in Slovakia. From a total of 272 successful breeding attempts by 1 49 breeding pairs during 4 breeding
seasons 277 young birds were fledged. The average reproductive success ratio was thus 0.51 juv./pair present, 0.69 juv./breeding
pair and 1 .37 juv./1 00 km2. In the surveyed period a total of 1 51 protection zones were established around the nests in 11 9 breeding
territories, which provided protection for 1 7% of the breeding population of the lesser spotted eagle in Slovakia. By testing
the effectiveness of protection zones it was determined that in nests with an established protection zone the probability of successful
raising of young is higher in comparison with nests without such a zone. The probability that breeding will be successful in the
nests of breeding pairs without a protection zone was 48.1% (95% confidence intervals (CIs): 37.4–59.0%), and in nests with
a protection zone 64.8% (95% CIs: 59.8–69.6%). Among the five most frequent nest tree species used by A. pomarina in Slovakia
for breeding are Picea abies 61 × (28.4%), Pinus sylvestris 45× (20.9%), Quercus sp. 36× (1 6.7%), Fagus sylvatica 25× (11 .6%)
and Abies alba 1 8× (8.4%). Among the rarer nest tree species used are Larix decidua 1 2× (5.6%) and Alnus glutinosa 3× (1 .4%),
while a further 11 species of nest trees did not achieve even 1%. The highest number of nest trees (n = 21 5), i.e. 34 nests (1 5.8%),
was found in the altitude range of 401–450 m a.s.l. and 29 nests (1 3.5%) at 351–400 m a.s.l. Other altitude zones were all below
the 1 0% mark. A total of 54% of nests found (11 6 nests) are located in the altitude zone of 301–600 m a.s.l., and 71 nests (33%)
in the zone 600–900 m a.s.l. The lowest situated nest was at an altitude of 1 50 m and the highest at 950 m; the average was
595.01 m a.s.l. The highest number of nests (n = 209) were located on trees in a range 1 5.1–20.0 m above the ground (n = 92,
44%), while the lowest nest found was at a height of 5 m and the highest at 30 m above the ground.
Several estimates of the lesser spotted eagle breeding population in Slovakia were published in 1955-2002. In this study we estimate the breeding population of the lesser spotted eagle by 1997 and 2014. By 1997, the estimated size of the breeding population was 762 pairs. In 2002 an estimate of the population size by 2000 was published at 800-900 pairs. By 2014 we estimate the breeding population of the lesser spotted eagle in Slovakia at 600-800 pairs and the declining population trend in 2000-2013 at -23%. Our estimate is supported by the extrapolation from data obtained in 2011-2013 in eight selected Special Protection Areas (SPAs) within a framework of the project LIFE09 NAT/SK/000396 “Conservation of Aquila pomarina in Slovakia”. When analyzing abundance, density and trends in the species’ entire breeding range in Slovakia we first summarised the numbers of breeding pairs, their densities and trends within the selected SPAs and then explored the differences among them using ANOVA and cluster analysis. For the eight SPAs as a whole (n = 8) or partitioned by a grid of the Databank of Slovak Fauna (n = 119 squares) we calculated the interval estimates of the mean number of pairs (unweighted and weighted arithmetic means and medians). By summarising these estimates and extrapolating to the species’ entire breeding range in Slovakia (c. 28,935 km2) while increasing the sample size (n = 8, 9, 11 and 1 2 SPAs), the size estimates stabilise at a level of 670 (mean with 95%LCL = 507 and 95%UCL = 834) or 765 (median with 95%LCL = 393 and 95%UCL = 841 ) breeding pairs. The most reliable estimate of the breeding population of the lesser spotted eagle in Slovakia by 2014 is a median of 765 pairs with a 95% confidence interval from 393 to 841 pairs and an interquartile range from 418 to 835 pairs. We estimate a 23% decrease in the breeding population during 2000-2013, i.e. a small decrease -1 (20-49%). Three methods of estimating were used: 1 ) comparing the numbers of pairs in the selected SPAs between 2000 and 2014 - indicates a decrease of -26%; 2) comparing the numbers of pairs from long-term monitoring in five areas (orographic units Vihorlatské vrchy Mts, Laborecká vrchovina Upland, Volovské vrchy Mts, Orava and Horné Ponitrie Regions) by the 1990s and 2014 - indicates a decrease of -20%; 3) comparing the numbers of pairs by 1997 in selected areas within the boundaries of the current SPAs with the number of pairs in the same SPAs by 2014 - indicates a decrease of -23%. In the eight selected SPAs the estimated decline was even more pronounced, reaching a median trend of -35% in the 95% confidence interval from -54% to +25%. The estimate by 1997 fits in with an increasing trend of published breeding population estimates in Slovakia during 1955-2002. The estimate by 2014 is lower than the estimate by 2000, and for the first time ever a declining trend is recorded. By 2014 the breeding grounds of the lesser spotted eagle in Slovakia embrace an area of c. 28,935 km2. Taking an estimate of 600-800 breeding pairs, the mean density varies between 2.1-2.8 pairs.100 km-2.