Changes in nesting habitat of the saker falcon (Falco cherrug) influenced its diet composition and potentially threatened its population in Slovakia in the years 1976–2016

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.

Distribution, abundance, and breeding of the imperial eagle (Aquila heliaca) in Western Slovakia in 1977–2022

“…Generally higher breeding successes have been recently observed in Central Europe for other species in the same environment, especially at agrocenoses, such as the saker falcon (Falco cherrug) (Chavko 2019), the great bustard (Otis tarda) (Nagy 2018), the red-footed falcon (Falco vespertinus) (Slobodník et al 2021), and the European roller (Coracias garrulous) (Repel et al 2022). Measures to manage these species may have had a positive impact on their population (e.g., , Palatitz et al 2015.…”

Overview of raptor and owl ringing in Slovakia in 2020

“…Eurasian hobby has been ringed in Slovakia sporadically, compared to the past, when more attention had been paid to it (Lipták 2007) as shown in the number of ringed individuals (Formánek 1977, Slobodník et al 2009). Even though its population is low, the saker falcon belongs to the species ringed the most (Chavko 2010, Chavko et al 2014, Chavko et al 2019). Just as in the case of the red footed falcon, all the chicks were ringed in their nests.…”

Post-fledging dependence period, dispersal movements and temporary settlement areas in saker falcons (Falco cherrug)

“…Populations from Austria, Hungary and Slovakia are interconnected, as evidenced by movements, especially of young birds, and the nesting of birds from other countries in neighbouring countries (Slobodník 2008; Slobodník & Jenčo 2020. The population, for instance, in Ukraine and east Slovakia, after its recent increase, shows currently a slightly declining trend again (Chavko et al 2019), which is related to the reclassification within the IUCN Red List from the category "vulnerable" to the category "endangered" (BirdLife International 2022). On the contrary, the population in Slovakia is slowly growing (Černecký et al 2020), which is mainly due to its positive population trend in the western part of the country (Chavko & Deutschová 2012; Chavko et al 2014.…”