Reproductive success, selected nest characteristics and the effectiveness of establishing protection zones of the lesser spotted eagle (Aquila pomarina) population in Slovakia

Abstract 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. Abstrakt V rokoch 2011 – 2014 sa realizoval monitoring hniezdnej populácie orla krikľavého (Aquila pomarina) v ôsmich chránených vtáčích územiach na Slovensku. U 149 hniezdnych párov z celkových 272 úspešných hniezdení počas 4 hniezdnych sezón vyletelo 277 mláďat. Priemerná reprodukčná úspešnosť predstavovala 0,51 juv./prítomný pár, 0,69 juv./hniezdiaci pár a 1,37 juv./100 km2. V uvedenom období bolo okolo hniezd orlov krikľavých ustanovených celkom 151 ochranných zón, ktoré zabezpečili ochranu 119 hniezdnych teritórií, čo predstavuje cca 17 % hniezdnej populácie orla krikľavého na Slovensku. Testovaním účinnosti ochranných zón sa zistilo, že v hniezdach s vyhlásenou ochrannou zónou je vyššia pravdepodobnosť úspešného odchovania mláďat v porovnaní s hniezdami bez takejto zóny. Pravdepodobnosť, že hniezdenie bude úspešné v hniezdach hniezdiacich párov bez ochrannej zóny bola 48.1% (95% confidence intervals (CIs): 37.4–59.0%), v hniezdach s ochrannou zónou 64.8% (95% CIs: 59.8–69.6%). Medzi 5 najčastejšie využívaných hniezdnych stromov na hniezdenie A. pomarina na Slovensku patrí Picea abies 61× (28,4%), Pinus sylvestris 45× (20,9%), Quercus sp. 36× (16,7%), Fagus sylvatica 25× (11,6%) a Abies alba 18× (8,4%). Medzi zriedkavejšie druhy hniezdnych stromov patrí Larix decidua 12× (5,6%) a Alnus glutinosa 3× (1,4%), ďalších 11 druhov hniezdnych stromov nedosiahli 1 %. Najvyšší počet hniezdnych stromov (n = 215), tj. 34 hniezd (15,8%) sa nachádzal v intervale nadmorskej výšky 401 – 450 m a 29 hniezd (13,5%) v intervale 351 – 400 m n. m. Ostatné výškové pásma boli pod hranicou 10%. 54% zistených hniezd (116 hniezd) sa nachádza vo výškovom pásme 301 – 600 m n. m., 71 hniezd (33%) v pásme 600 – 900 m n. m. Najnižšie situované hniezdo bolo v nadmorskej výške 150 m a najvyššie 950 m, priemer bol 595,01 m. Najvyšší počet hniezd (n = 209) bol na strome umiestnený v rozmedzí 15,1 – 20,0 m (n = 92, 44,02%). Najnižšie zistené hniezdo bolo vo výške 5 m a najvyššie 30 m nad zemou.