Ranging behaviour of yellow necked-mouse Apodemus flavicollis in an endemic area for TBE in Trentino, Italian Alps

This research is part of a long-term study on the host-vector-pathogen system of some tick-borne diseases, mainly tick-borne encephalitis (TBE), an emerging pathology transmitted in Europe by the tick Ixodes ricinus. The yellow-necked mouse Apodemus flavicollis, extensively distributed in the beech woodlands in Trentino (Eastern Italian Alps), plays a crucial role in the ecology of TBE as reservoir host of the immature stages of the vector of the causative agent of this disease; in particular, this species can amplify the TBE virus both through viremic and non-viremic transmission (i.e. between co-feeding ticks). Our previous results indicated sexually mature males as the functional group most accountable for disease transmission, due to their tick burden, in average higher than in females. The aim of the present study is therefore to assess the ranging behaviour of both sexes and evaluate if it could account for this difference. A telemetry study was carried out in a TBE focus (Valle dei Laghi - Trentino, National grid reference: 1651959E, 5093546N). The field trial was based on capture-mark-recapture and radio-tracking techniques. We set up a 6.7 ha trapping grid (18x18 traps, 15 m spaced) with Ugglan live traps, which were activated 5 nights/month, from May to November. Some of the yellow-necked mouse individuals captured between July and October were fitted with radio-collars (BD-2C transmitter, Holohil System Ltd., Canada). The weight of radio-collars (1.8g, power: 3.3 mA, average life span: 53 days) never exceed 6% of the mice body weight. Only resident animals were marked with radio-collars, as determined by the number and localisation of recaptures. After capture, mice were anaesthetized, fitted with the collar and then allowed to rouse from sleep and adapt to the radio-collar in a terrarium, to be released in the capture point the following morning. Four radio-tracking sessions of three weeks were completed from July to October 2005. Individuals were radio-tracked by homing-in, aiming at a precision of localisation of 3.5 m; animal movements were recorded from dusk to dawn, so that the interval between successive fixes was not less than 60 minutes. One fix/day/animal was also recorded in daylight, to localise burrows. Date, time, meteorological conditions, activity and, when possible, position below or above ground and behaviour were recorded along with the localisation. A total of 746 diurnal and 3256 nocturnal fixes from 39 mice, 26 males and 13 females, were recorded. From a minimum of 11 to a maximum of 18 individuals were simultaneously monitored during each radio-tracking session. The mean number of localizations per animal per session was 12,41 ± 0,84 for diurnal and 57,81 ± 8,00 for nocturnal fix. Home range were calculated as minimum convex polygon (MCP 95%) and Kernel probability distribution (Kernel 95%) by the software R, package Adehabitat; spatial analyses were performed by means of ArcGis 9.0. The mean size of male’s home range was 9057.01 m2 ± 1624.75 and 6530.94 m2 ± 1207.16 for kernel 95% and MCP 95% respectively; for females, it was 5143.39 m2 ± 782.21 and 3627.10 m2 ± 665.93 for kernel 95% and MCP 95% respectively; the mean home range size, both for Kernel and MCP, highly differed between sexes (Mann-Whitney U-Test: Z= 3.14, p< 0.01; Z= -3.03, p< 0.01).