Changes in the density and spatial distribution of red fox dens and ...

Acta Theriologica 53 (2): 121–127, 2008.PL ISSN 0001–7051Changes in the density and spatial distribution of red foxdens and cub numbers in central Poland following rabiesvaccinationJacek GOSZCZYÑSKI, Magdalena MISIOROWSKA and Sebastian JUSZKOGoszczyñski J., Misiorowska M. and Juszko S. 2008. Changes in the densityand spatial distribution of red fox dens and cub numbers in central Polandfollowing rabies vaccination. Acta Theriologica 53: 121–127.Increases in red fox Vulpes vulpes (Linnaeus, 1758) numbers and densitieshave been found in all European countries involved in the rabies vaccinationprogram. In Poland, the number of foxes has increased steadily since the1990s. Between 1999–2000, the average density of foxes reached 1.3–2 ind./km 2in some parts of the country. The aim of the study was to estimate the changein fox population densities in central Poland during 1980–2006, and to assessthe effect these changes have had on the spatial distribution of natal dens,mean numbers of cubs observed at occupied dens and the sedentary/nomadicfox ratio. Estimations of fox population density and numbers were based onthree methods: (1) counts of tracks in snow, (2) locations of natal dens andcounts of cubs, and (3) the battue (driving) method. The three methods ofassessment were used continuously in our study area over a period of 25years. Average yearly results were analysed and comparisons made betweenthe periods before and after implementation of the anti-rabies vaccination.The results obtained with all three methods show a significant increase in thefox population, when the two analysed periods are compared. Increases in foxpopulation densities correlated with increased numbers of breeding sitesbeing located outside forests, from only single ones in the 1980s to 24% of thetotal in 2005. The average number of cubs per occupied den decreased significantly(by 11%) in comparison with before the anti-rabies vaccinationperiod. The great increase (more than 100%) in fox numbers observed usingthe battue (driving) method suggest, that nomadic animals can form animportant part of winter population in our study area.Department of Forest Protection and Ecology, Warsaw University of Life Sciences, Warsaw, Poland,Nowoursynowska 159 Str., 02-776 Warsaw, Poland, e-mail: Magdalena.Misiorowska@wl.sggw.plKey words: Vulpes vulpes, density, distribution of breeding dens, cub numbers,rabies vaccinationIntroductionThe elimination of rabies via a nationwidevaccination program is likely to have major impactson the dynamics of red fox Vulpes vulpes(Linnaeus, 1758) populations. An increase in foxnumbers and population densities has beenfound in all European countries participating in[121]

Response of red fox to rabies vaccination 1231. Counting of tracks on snowIn winter, indices of fox abundance were obtained fromsnow tracking conducted on transects. The first half ofFebruary, when mating season occurs, was excluded fromtracking. These transects were walked by observers within1–2 days of new falls of snow. The index of fox density usedwas the number of fox trails crossing 1 km of transect perday (n tracks/1 km/24 hrs) calculated as a mean for thewinter season. The yearly mean length of transects in thefirst period (1979–1995) was 90 km and in the second(1996–2006) was 54.6 km.2. Estimation of natal densAt the beginning of spring, an attempt was made to locateall dens present in the study area. Although the locationsof the majority of dens were already known due toearlier investigations, several new dens were found everyyear. Information obtained from hunters, farmers and foresterswas also checked. The identification of natal denswas based on the presence of animal tracks at the entrancesand in close proximity to burrows. Other signs of animalpresence taken into account were: carrion remains and remnantsof prey, faeces of cubs and the typical odour. Thecounts of cubs were performed at natal dens in May andJune. An attempt was made to observe dens for long enoughto count all cubs appearing at the surface. If necessary, observationswere repeated over subsequent days. In case ofabsence of cubs in a den, irrespective of unquestionablesigns of animal presence, neighbor dens were also checkedto register the facts of carriage of young.3.ThebattuemethodIn late autumn (October, November) and early spring(March), driving censuses (aimed at estimating the densityof roe deer and hare populations) were undertaken in localforests by the staff of the Department of Zoology and GameManagement and students of Warsaw Agricultural University.Each forest compartment to be censused was surroundedby observers who stationed themselves 50–100 mapart (to maintain visual contact). The observers alongthree sides of an estimated compartment remained stationary,while those along the fourth side moved inward andwent through the entire area. The observers (both stationaryand moving) noted animals passing through the line ofobservers and the closed area being censused. This methodof animal counting excluded duplication of measurements(Pucek et al. 1975). Apart from hares and roe deer, the foxespresent in an area were also noted.The three methods of fox density assessment presentedhave been used continuously on our study area for the last25 years. Average yearly results were compared betweenthe periods before and after the anti-rabies vaccination programwas implemented.Student’s t-test and test for comparison of two percentages(Bailey 1995) were applied in statistical analyses.Results and discussionThe results obtained with all three studymethods showed a significant increase in the foxpopulation, when the two analysed periods wereTable 1. Changes in density indices of the fox populations before (1980–1995) and after (1996–2005) the onset of the rabiesvaccination program, as calculated by the three different methods (Rogów, central Poland). 1 – Goszczyñski 1989, J. Goszczyñski,unpubl.; 2 – Data from Department of Forest Protection and Ecology, Agricultural University of Warsaw; 3 –Goszczyñski 1989, Lach 1991; 4 – Jackowski 1999, Juszko 2005 and this paper.Mode of estimation and estimated areaParametersCompared periods1980–1995 1996–2005tpSnow trackings – whole terrain Number of seasons analyzed 14 7Total length of snow tracking (km) 1244.70 383.00Mean density (n tracks/km/24 hrs) 5.86 1 11.01 4.85 < 0.001SD 1.78 2.82Driving censuses – forests only Number of seasons analyzed 12 9Total surface of driving censuses (km 2 ) 21.04 29.87Mean density (n inds./km 2 ) 1.22 2 2.58 2 2.86 < 0.05SD 1.08 1.28Number of dens with cubs – whole terrain Number of seasons analyzed 12 7Total number of dens with young 112 105Yearly mean of dens with young 9.33 3 15.00 4 4.41 < 0.001SD 1.70 3.55

124 J. Goszczyñski et al.50Before vaccinationmean = 3.79, SD = 1.07, n = 5240301518Percentage of dens (%)2010050403061 2 3 4 5 6After vaccinationmean = 3.39, SD = 0.99, n = 592219103208810021 2 3 4 5 6Number of cubs at denFig. 2. Change in number of young foxes observed at natal dens before (1980–1995) and after (1996–2005) rabies vaccinationsprogram in Rogów (central Poland). Figures above columns denote the number of observed litters with given numbers of cubs.compared. The increase in the snow trackingindex was 88%, that in the average numberof natal dens was 66%, and that in fox numberscounted with the battue method of 110%(Table 1).In the period after the anti-rabies vaccinationprogram commenced, a decrease in the averagenumber of cubs per den was observed (Fig.2). The average number of cubs decreased significantlyby 11% (t = 2.03, df = 109, p < 0.05). Onlyoccasionally were litters with numerous cubsfound, and the numbers never exceeded five.This probably reflects increased competitionamong paired foxes for food and habitats. A decreasein reproductivity of foxes resulting fromincreased density was also found by Voigt andMacdonald (1984).The increase in fox population density correlatedwith numbers of breeding dens locatedoutside forests. Before the vaccination programstarted, nearly all breeding dens were in forests(with the exception of three out of 112). After thevaccination, the mean number of natal densoutside forests (in abandoned gravel pits, haystacks,railway scarps and orchards) increasedsignificantly to 13.3% of the total (t = 3.08,p < 0.01, test for comparison of two percentagesBailey 1995). This increase continued such that,

Response of red fox to rabies vaccination 125Table 2. Mean annual cull of red foxes in the study area and its vicinity (2001–2005).Monitoring districtArea (ha)Mean annual culln n/km 2Brzeziny 6000 11.8 0.20Regny 9000 34.4 0.38Cietrzew 8300 30.4 0.36Study area 8900 64.2 0.72in 2004–2005, 24% of all breeding dens wereoutside forest (Misiorowska 2005). In Poland atthe turn of the 1970s, the percentage of foxbreeding dens located outside forest was low,even in territories with limited forest cover(Pielowski 1976, Goszczyñski 1985, Go³dyn et al.2003). However, by the end of the 1990s, in theCzempiñ area, (where the level of afforestationdoes not exceed 6%), almost 83% of breedingsites were located outside the forest (Panek andBresiñski 2002). In another study, a high densityof foxes (2.2 ind./km 2 ) and a large number ofnatal dens were reported from a farmland areain Wielkopolska (Go³dyn et al. 2003). The increaseduse of breeding dens located in anagricultural landscape may indicate profoundchanges of habitat use by foxes, and adaptationto a human-modified environment (Bresiñskiand Panek 2000, Tryjanowski 2000, Panek andBresiñski 2002).During the last five years the average foxnumbers at the beginning of the hunting seasonwas approx. 80 ind. This number was estimatedon the basis of annual number of natal dens (15),mean number of cubs per den (3.4), and thenumber of adult foxes per occupied den (2). Thisvalue slightly exceeded an average annual huntingbag in the same period (approx. 64 per year).It could be expected that such a high huntingpressure resulted in a decrease in fox numbersand density in the following year. However, inevery subsequent winter, fox density remainedstable or even increased: from 12.7 tracks/km/24hrs to 13.49 in the 2000/2001 and 2004/2005hunting seasons respectively. Similarly, in everysubsequent spring, the number of occupied familydens showed an increasing trend (Misiorowska2005). This suggests that intruders fromneighborhood nearby formed an important partof the local population in our study area inautumn-winter. Probably, during the autumnand winter, young foxes dispersed from adjoiningterrains, where hunting pressure waslower (Table 2).Similar observations of compensation forpopulation wastage due to intensive shootingwere described by Reynolds et al. (1993), Côtéand Sutherland (1997) and Vos (2003). Intruderslead a nomadic life, and use forests as naturalshelter during the day. As a rule, these foxescirculate around and inside occupied territories,not using existing, occupied dens as temporaryrefuges. In effect, some of these animals stayabove ground during the day. The results withthe battue (driving) method applied in forestconfirm this suggestion: the greatest increase infox numbers, of more than 100%, was found forthis. The battue method is the best of the threeused to assess numbers of nomadic animals. Incases of high fox mortality (eg with intensiveshooting), some nomadic animals eventually occupyvacated territories and stabilize the wholepopulation (Jasja et al. 2001, Vos 2003).Our results may also have practical implicationsfor hunting management. An increased foxpopuation is regarded as the main reason for thedecrease in small game populations (Panek et al.2006). However, the successful reduction of thefox population over areas covering only severaldozen square kilometres, as in case of our studyarea, is not possible, if shooting pressure on adjoiningareas is low. From a game managementpoint of view, the goal should therefore lie in anintensive and coordinated increase in fox culling

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