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ŠUMARSKI LIST 5-6/2021 str. 72     <-- 72 -->        PDF

sexes. All these factors (presumably more males in the population as in hilly areas, absence of long-distance migrations, higher roaming rate and larger home ranges in males) may together explain a male-biased mortality of red deer due to border fences in the study area.
Records of fence-related ungulate mortalities at the Hungary–Croatia border were concentrated in the first nine months (Fig. 2) after the implementation of the fence (49 carcasses; 83%). This may indicate that the behaviour of ungulates has altered in response to the border fence, which is consistent with previous findings of Pokorny et al. (2017) who also reported the highest mortality rate of red deer in initial days after the construction of the fence as a new and previously unknown obstacle for animal movements at the Slovenia–Croatia border.
It should be noted, however, that the real rates of mortality may be underestimated by our data, as ungulates may escape wounded, and then die elsewhere on the Croatian side (Fig. 3B). Indeed, out of the eight hunting grounds with registered mortality due to border fence, seven contained evidence of injured animals escaping, indicated through blood and hair that remained on razor-wired fencing. In addition, large sections of the Hungary–Croatia border fence remained unobserved, as game managers from some hunting grounds could not reach the border fence due to several obstacles (i.e., river, ravines, or the remaining minefields from the 1990s).
While our results are limited to the Croatian side of the border fence, the mortality on the Hungarian side is expected to be minimal or even non-existent. Indeed, the additional four-metre high solid mesh fence on the Hungarian side presents no direct mortality risk, as the layer of razor wiring is out of reach for ungulates, i.e. it is constructed at the top of the fence, while on the Croatian side razor-wired fencing is on the ground level (Fig. 3A). However, due to such design the border fence is completely impermeable for large mammals which may be, in comparison to direct mortality of wildlife, much more serious ecological risk as it affects the connectivity of populations (see Linnell et al., 2016b).
Fence structure may be very important factor affecting the mortality rate of ungulates. For example, no wild boar mortality was registered in the Slovenia–Croatia border fence, instead they were observed several times managing to pass successfully through the razor-wired fence (Pokorny et al., 2017). In contrast, three mortalities of wild boar were recorded when animals attempted to cross from Croatia to Hungary. We believe this could be due to differences in fencing as there is a second, four-meter high solid mesh fence beyond the razor wires (Fig. 3A) blocking movement through to Hungary, and therefore trapping the animal in between the two fences. It is clear when considering comprehensive ecological effects of border fences, i.e. both the direct impact on wildlife mortality and their indirect impact as a barrier in the ecosystem, razor-wired fences per se are not as strong negative factor as when they are combined with solid mesh fences. The latter, although not directly contributing to wildlife mortality, may importantly increase this risk when constructed together with razor-wired fences. Alone, these impermeable fences may seriously diminish the connectivity of populations, without having any direct and obvious negative effects, i.e. without causing the direct mortality of individuals. It should be mentioned that Slovenia has, at several locations, begun changing the fence type from razor-wired fences into a panel design, which may even have more pronounced negative impacts on large mammal populations in the future.
Short-term consequences of the border fences along Croatian border with Hungary are clear in terms of direct mortality, and as an obstruction to the movement of animals in the case of the dual-layer fences and/or solid mesh fences alone, which are impermeable. Regarding the observed species, it must be considered that both red deer and roe deer are known to perform regular movement within their distribution range under specific environmental characteristics (see Georgii, 1980; Georgii et al., 1983; Luccarini et al., 2006; Mysterud et al., 2011 for red deer; and Wahlstrom and Lieberg, 1995; Mysterud, 1999; Cagnacci et al., 2011 for roe deer): the impacts of fencing can be obviously more severe in such circumstances. Therefore, possible long-term and cumulative consequences of border fencing must also be of a significant largescale concern.
There are documented evidences that ungulate species in the region often cross state boundaries freely. Feulner et al. (2004), for example, stated that there are no movement barriers for red deer within the Carpathian region, and movement is known to take place between western Romania and the Banat (Serbia) as well as between Bačka (Serbia), Hungary and Croatia. This is confirmed by the reports by some of the interviewed game managers, whom observed red deer gathering in huge herds as they attempt to cross the border fence between Hungary and Croatia (Fig. 3C). This kind of behaviour of red deer in the area had not been previously recorded, and game managers attributed it to the border fence effect.
CONCLUSION
ZAKLJUČAK
64 ungulates and two large birds deceased due to the razor-wired fence along the Croatia–Hungary border in 28-month study period are strong evidence that border fences present important new manmade threat to wildlife. Therefore, in the case that current fences will remain or continue to expand along the northern boundary of the South-eastern Europe, it is likely that wildlife populations will suffer much more than just short-term damage (e.g. mortality due to attempts to cross the fence) as the effects on the genetic structure will become more prominent with time.