La cultura en el aprendizaje de lenguas extranjeras

Preliminary investigation of the study site to determine the most effective locations for the fixed radio triangulation sites began in late 1990. Initially, tracking possums to den sites and discussions with an experienced radio-tracker aided in defining possible sites. Changes in weather conditions, in particular temperature, as well as relative positions of the tracker and the radio transmitter were known to result in considerable variation in signal quality and apparent direction. Figures 1.4-1.6 show the bowl shaped topography of the study site, with a central spur which protrudes into the paddock from the northern ridgeline. The spur, with a base of the disintegrating greywacke rock common to the East coast hill country of the Wairarapa, has a steep eastern face dropping into the confluence of several creeks and caused a varying degree of signal reflection. The ridgeline around the perimeter of the site has a steep grade from the northern ridge down to the lower valley, with gentler slopes from the southern and south-eastern ridges, and seemed to be suitable for the placing of the tracking towers. Ideally triangulation of an area using two towers would have them placed so that the baseline between the towers is not within the study area, (White, 1985) as locations of animals on this line cannot be determined. The topography of the area meant this ideal was unlikely to be achieved. Also of concern were the damaging effects of strong winds from the north-west which funnelled directly into the valley. Strong to gale force winds (50-75 km/hr) were common throughout the year and often continued for 2-4 days. Gusts greater than 100 km/hr are regularly recorded during these nor’westerly ‘blows’ (Meteorological office data). It would have been impossible to handle the triangulation aerials on exposed ridges or other points during such winds. Potential sites were investigated by using one person to carry the transmitter through the site while the other took bearings with handheld aerials. Ease of access to the site and protection from the wind were factors considered as well as accuracy of bearings. The handheld aerials are far less accurate than the twin yagis used for triangulation but gave an indication of signal and bearing quality. Four sites were chosen as potentially suitable and several nights were spent tracking the signals from possums as they moved from their den areas to feed to determine if signal reception was similar to that experienced during the day. Only the two sites in the eastern end of the paddock gave adequate coverage, as possums spent considerable time close to the baseline between the other possible locations and there was signal reflection and distortion caused by the spur from the north ridge. The twin-yagi aerials were tested for accuracy using transmitters placed at surveyed points throughout the paddock as described in a later section. In all, 25-30 days spread over 6 months were spent developing a triangulation system in the area with another 15 days training operators, and gathering radio triangulation error data.

Radio triangulation was carried out at intervals from April 1991 to April 1992, with 6 animals tracked each night. Emphasis was placed on those possums known or suspected to have TB, possums which denned in the same areas as the TB animals, and in the latter stages of the study, immature animals. During the initial stages of the project there were up to 5 tuberculous animals in the area but not all were tracked during a session. All of the tuberculous possums died during 1991, hence there

are no complete 12-month records for these animals. At any one time, up to three steers carried radio collars. They were also tracked at intervals throughout the year. Achievement of the objective of the study - to determine home-ranges of individual animals and compare the patterns of use of these areas - was significantly affected by the building of a fenceline down the centre of the paddock, which prevented access by the cattle to the northern half of the study site.

2.4.2.1. Tracking procedures

Radio-tracking was targeted at 4 periods during the year: 1. Mating - April through May

2. When the joeys were back riding - August to October

3. When the joeys were becoming independent - November through December 4. Pre-mating - February to March

Each tracking session was over an average of 3 nights, and there were 2-3 sessions during each period. The aim was to track 3 tuberculous possums plus 2 clinically normal animals which denned in the same area. The 6th animal was either a steer, a juvenile possum or randomly selected possum. Tuberculous possums were tracked on each subsequent session, if possible, and 3 normal animals were also routinely tracked (at least 2 nights each session). As animals died, or radio signals were lost, other possums replaced them. Six to eight possums and 2 steers were selected as possible candidates before each tracking session. At dusk signals were rechecked and 6 of the animals chosen to work with that night. Animals were not tracked if the radio signal was unclear - possibly due to imminent radio failure or the position of the possum. Cattle were regularly tracked for 2-3 months but, after division of the paddock, only if feeding in the lower part of the paddock at dusk. On most nights the steers remained in 1 or 2 small areas, 700-800 m away from most of the radio-tracked possums.

Aerials and equipment in the field were checked for damage each day, and aerials recalibrated against fixed transmitters at known locations in the area. The settings were checked several times during the night. Radio triangulation began before dusk and continued until dawn, with each animal located once every 12 minutes. Two-way radios provided communication between trackers for support and consultation if subsequent bearings appeared unreasonable. As there were only 2 operators involved in the study bearings could not be mapped as they were taken, and any censoring of data was done later. Data from the check sheets was entered into a database and from there run through Telem88 (Telem88, 1990; Coleman and Jones, 1990), an analysis and mapping programme for radio-telemetry data. Results were checked for distances moved between observations and rejected if unreasonable (movement of more than 150 m between subsequent locations). Final (at dawn) den site locations were checked against daylight tracking locations, if available, as a further check on accuracy of the system. Data were summarised and analysed using Paradox version 3.5 (Borland Corporation, Scotts Valley, California, USA), Parastat (Financial Modeling Specialists, Arlington, Virginia, USA), Statistix version 4 (Analytical Software, St. Paul, Minnesota, USA) and

Telem88 (Coleman and Jones, Dept. of Fisheries and Wildlife, Virginia and State University, Blacksburg, Virginia, USA). Data was mapped and displayed in PCArc/Info version 3.4d (Environmental Systems Research Institute Canada Ltd., Don Mills, Ontario, Canada), and Idrisi version 4 (Clark University Graduate School of Geography, Worchester, Maine, USA),

2.4.2.2. Juveniles

A juvenile possums was fitted with a radio transmitter as routine if its mother was known to be tuberculous. Additionally, between September and December 1991, 25 juveniles were fitted with radio collars to determine their fate over the following 6-8 months. All of the possums had been tagged as joeys in the pouch and their mother’s were regularly caught in the area. Several of the juveniles were tracked by radio triangulation at night but, as the main aim was to follow dispersing immatures, most of these animals were only routinely checked to determine their denning areas in the paddock. If they were not caught during a trapping week, or their position remained constant over 2 weeks, they were tracked on foot to confirm that they were still alive or the radio had not been lost.