No abstract

Opportunistic predator like the long-eared owl is able to respond to population fluctuations of its main prey. The composition of the winter diet of this owl species was investigated during the period of 13 winters (1992-2000, 2006-2011) in agricultural areas in Slovakia. In total, we found 23 mammal species and 33 bird species (H′ = 0.82) in pellets. The frequency of the dominant prey species, the common vole, varied from 57.7% to 92.4%. Our data show that the abundance of the common vole: (i) had biggest impact on the food niche breadth of the long-eared owl; (ii) when in decline, it was significantly compensated by the increase in the amount of 15 other accessory species (subject to the specific diet offered during the study winters); (iii) was positively correlated with the number of owls in the winter-roost, which varied during the 13 studied winters.

Temperature and precipitation are amongst the most important characteristics of local climatic conditions affecting the breeding biology of birds. Many bird species experiencing higher temperatures lay their eggs earlier and/or have bigger clutches. Higher precipitation can lead to a decrease in food availability and/or an increase of the costs of thermoregulation, which consequently may result in lower breeding success. In this paper we present differences in the breeding biology of two collared flycatcher (Ficedula albicollis) populations experiencing different temperatures and precipitation conditions associated with the different altitudes of their localities. We found differences in clutch size and nest success, as well as small differences in dates of egg laying. The population breeding at a higher altitude, and thus harsher conditions, was characterized by smaller clutches and lower nest success. In addition, this population was significantly affected by local weather, and showed correlation between both the beginning of egg laying and the local temperature, as well as between nest success and precipitation. Conversely, the population inhabiting the lower elevation locality with milder conditions showed no relationships with temperature or precipitation. These results suggest that severe conditions, such as high altitude, enhance the effect of local climatic conditions on collared flycatcher breeding ecology.

No abstract

In the period between the years 1976 to 2016 we monitored the nesting site distribution of two populations of saker falcon (Falco cherrug) concentrated in the highlands and adjacent lowlands of western and eastern Slovakia. In western Slovakia we recorded nesting by 56 pairs and 514 nestings, and in eastern Slovakia we observed nesting by 32 pairs and 245 nestings. There were similar nesting success rates in both regions, with pairs producing on average 3.2 young in every successful nest. During the monitored period as a whole a total of 1,788 young saker falcons were raised. At the same time all the pairs gradually resettled in the lowlands, and in the new environment the nesting success rate significantly improved (81.1% compared with 57.1 % in the highlands). This change of nesting biotopes was caused by the impacts of intensive exploitation and environmentally inappropriate forest management, with the accompanying excessive disturbance of nesting birds, but at the same time the disappearance of ground squirrel (Spermophilus citellus) colonies led to a change in the food spectrum for the observed saker falcon pairs. We evaluated the falcons’ feeding habits in western Slovakia between the years 1977 and 2016 (49 pairs; 1–17 pairs/year) and in eastern Slovakia between 2009 and 2016 (12 pairs; 1–3 pairs/year). Altogether 17,669 prey items were identified. From 1976 onwards mammals (Mammalia, 19.8%, 24 species) became gradually less represented as a component in the falcons’ diet compared with birds (Aves, 79.9%, 58 species). In areas of western Slovakia we found stable and predominant proportions of domestic pigeons (Columba livia f. domestica) ranging from 52% to 62%. The proportion of pigeons was distinctly lower in eastern Slovakia (31.5%), compensated for by larger shares of common vole (Microtus arvalis), common starling (Sturnus vulgaris), Eurasian magpie (Pica pica) and hooded crow (Corvus cornix). The common starling (9.5%) was a significant prey species in the lowlands of western and eastern Slovakia alike. Mammals were mostly represented by common voles (9.8%), European hamsters (Cricetus cricetus, 5.3%), ground squirrels (2.1%) and hares (Lepus europaeus, 1.6%). Changes over time in the composition of falcons’ prey were also evaluated over five periods in western Slovakia.