Analysis of beaver (Castor fiber L.) mortality in Croatia and Serbia

Abstract

Population monitoring of beavers in Croatia and Serbia is being continuously run since the first release of beavers in 1996. in Croatia(Grubešić iKrapinec, 1998, Grubešić, 2014). Serbia has started with monitoring in 1999. When the first beak has been registered in the north of Vojvodina and it has been intensified since 2004. when they started with inhabitation - reintroduction (Ćirović, 2010). As a part of monitoring beavers in Croatia and Serbia since their reintroduction, beaver losses are being recorded by place and time of death, cause, sex and age of individuals. Information is being gathered with help of a network of associates, and by evidence of events. Based on the analysis of gathered information on beaver killings in the past 18 years a growth of killed beavers has been noticed, especially after the population growth and territorial expansion of beavers, and 10 years after the release in Croatia. In the observed period in Croatia a total of 111 beaver losses have been registered, while in Serbia this number is significantly lower and amounts to 36 individuals. Based on registered beaver losses a significant rise in beaver losses in the past 7 years has been noticed on the territory of Republic of Croatia. Actually the number of killed individuals has risen significantly when the beaver population has stabilized and increased its numbers and after 10 years since the inhabitation. In Serbia, despite the stabilization and territorial expansion, registered losses are relatively small, and stagnation or slight drop in killed or died animals has been noted. The main factor of mortality in Croatia and Serbia has been traffic. About one third of beavers (50 individuals) have been killed in traffic accidents. Traffic share in beaver mortality is equal or even somewhat smaller when compared to results from some parts of Germany, where this share is from 50% to even 86,5% (Pokorny and associates 2014., Muller 2014). Strangulation in fishing nets has been the second most significant beaver loss in populations on the territory of Posavina and Podravina (22 beavers - 15%). Autopsy unquestionably proved that 17 beavers (11.6%) died from illness. For 33 of them (22,4%), due to untimely findings or delivery to autopsy, a precise cause of death could not have been determined. When we look at beaver loss causes on the territory of Republic of Croatia traffic absolutely dominates, followed by unknown causes, and in third place illegal hunting and fishing (especially gillnets). In Serbia alongside unknown causes significant influences have diseases. From all 147 losses, only one beaver has been killed underneath a tree. Even though it has been noted he has been "killed at work"the position of the beavers body and tree points that the killing was not a consequence of knocking down the tree in question (Picture 1 and 2), but that the tree fell on the beaver as it has been passing by, most likely as a consequence of wind blowing the bitten tree down or exceptionally that an another individual knocked down the tree and it fell on the beaver passing by. Mostly adult individuals are being killed (Croatia 39, Serbia 14 beavers) which is linked to their increased activity in search for food and in moving about in general. Reasearch of other authors also shows that adult individuals are mostly being killed and mainly females (Pokorny and associates 2014). Sub adult individuals are being killed when exploring the territory (new locations) or when they inhabit a zone where the get killed easily, especially in traffic. This age group has mostly been killed in Serbia (15 beavers). In relation to sexual structure in Croatia and in Serbia a larger number of males were killed than females. Unfortunately, for half of killed beavers we were not able to tell the sex. If we look at beaver killing on a seasonal level, then two periods stick out, mostly spring then autumn. In spring beavers move more, especially the sub adult ones in search for foo and exploration of new habitats, while in autumn when they are more active in agricultural lands, they are being killed in traffic or in illegal hunting (this influence is most likely significantly bigger than the recorded one, but the prefix "illegal" points to unavailability of information and data on individuals killed this way). Illness for now are not a more significant cause of population loss, but in the future, especially in areas over-crowded by beaver, the might have a more significant role in the reduction of population, considering that we are dealing with a species (rodents) that are sensitive to certain diseases (leptospirosis, tularemia) (Parker and ass. 1951, Hopla 1974, Hörnfeldti sur. 1986, Mörneri sur., 1988, Wolli sur. 2012). Certain problems or flaws in delivering information on losses emerge due to associates not being educated; these are accidental findings by people who have seen this species most likely for the first time. Apart from that some information has been delivered without details that would give a clearer picture in determining a cause of death, age and sex. As a measure of protecting beavers first in line is respecting the legislation connected to illegal hunting and fishing, and the traffic killing might be decreased or somewhere completely prevented by setting up a wire fence alongside roads in troubling crosses. Also losses can be successfully prevented in watercourse construction in territories inhabited by beavers, that the personnel that is carrying out the construction is being educated and pointed to beaver protection measures while carrying out the work (lodge and animal protection from excavators). So called "dangerous" objects in which beavers can fall into and get hurt, can be adjusted in a way that beavers are enabled to get into such spaces but also to ensure the possibility of getting out from such a space. Beaver protection is being carried out by good media presentation and informing the public of beavers and their way of life, protection measures and citizen education. Such direct communication enables and simplifies information gathering on beavers, also including information on killed or died individuals. © 2015, Hrvatsko Sumarsko Drustvo. All rights reserved.