BTC - Technical Paper

TECHNICAL PAPER

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Automated operation. Finally, the system had to require little maintenance and be able to operate unattended for several months. We used a Psion Organiser II (model LZ, [Psion Plc, Concord, Mass.]) datalogger with 3 ports: I for the reader, I to download data and upload instructions from a portable laptop computer, and I for a temperature probe, to be deployed later. The datalogger contained all instructions for automated operation (i.e., ON/OFF times, duty cycle, and other reader setup parameters). For each detection, the datalogger stored PIT tag number, time of day, date, and duration of time the tag was within the read zone of the coil. Multiple readings <30 seconds apart were treated as a single event. If a given tag was read more than once within 30 seconds, the reading "event timer" was reset and the duration was incremented for as long as the recurring reading took place. This prevented overloading of the datalogger's memory by repeated readings of the same tag and provided the "duration" for the animal at the reader.

A cable (0.75-1 in) connected the reading coil to the reader. The reader was linked to a datalogger and the battery. The battery was connected to the solar panel via a 2-conductor, 12-gauge, 30-m long wire enclosed in 12-mm diameter PVC conduit and buried 250 mm.

Application and discussion

We attached 14- x 2-mm cylindrical (AVID 2003), 18- X 3-mm cylindrical (AVID 201.3), and 18- x I-mm disk (AVID 2017) PIT tags (AVID Inc, Norco, Calif.) to the carapaces of 172 tortoises within approximately 3 kin of 2 corrugated metal culverts 1.6-m diameter x 66-m long. Tag size depended on tortoise size. The 14- and 18-mm cylindrical , tags were attached vertically to the pygal scutes of small tortoises and to the tenth or eleventh marginals of medium-sized tortoises, respectively. The 18-mm disk tags were attached horizontally to I of the marginal scutes of large tortoises. Devcon Five-Minute Epoxy' (ITW Devcon, Danvers, Pa.) was used to attach tags.

Fig 2. Linkages between major components of the automated reading system used to detect and record identities of desert tortoises entering and exiting storm-drain culverts.

Installation of our system at 2 culverts was completed on 30 April 1995. Five tortoises (Nos. 24, 144, 192, 201, and 729) were recorded crossing readers on several occasions: No. 24, 27 times on 4 consecutive days in 1996; No. 144, 6 times on 2 days in 1995; No. 192, 9 times on 1 day in 1996; No. 201, 1 time in 1996; and No. 729, 29 times on 7 days in 1995, and 3 times on 2 days in 1996. Tracks, possibly of No. 729, based on timing and size of the tracks, were found crossing the same reader on 1 other day, but it was not detected by the reader. That animal, a large male (248-mm midline carapace length), had a 14-mm tag attached horizontally (the least effective combination of tag size and positions for effective detection distance). We saw no other tortoise tracks at the culverts while the readers were functioning.

The 1995 data from tortoise No. 729 exemplified the application of the ARS to assess use of culverts. Tortoise No. 729 was known to be on the south side of the highway on 15 August 1995. On 9 September 1995 it was recorded passing over the north reading coil of the first culvert at 1716 hours; the reader on the south side of the culvert had a blown fuse and was not working. The tortoise spent 25 minutes away from the reading coil, perhaps outside the culvert, then passed over it again, perhaps going into or through it for the night. The next morning it passed over the coil, probably exiting the culvert, at 0620 hours, and took 2 hours 57 minutes to arrive at the second culvert 460 in away. It took 7 hours 18 minutes to pass through to the south side of the 62.8-m long, 1.37-m diameter culvert. Nine minutes later it re-entered, spent the night inside, then exited the north end of the culvert at 0822 hours on 17 September 1995. After spending 1 night on the north side of the highway, it re-entered the first culvert at 1215 hours on 18 September 1995 and was next found south of the highway on 25 October 1995.

We made modifications to 4 new ARS units to improve performance. For example, 2 reading coils became wet when water leaked through a broken seal. In 4 new units deployed in spring 1996, we inserted the reading coil through the side of the housing, rather than the top. We also changed the type of seal and reduced its size. In the new units, we moved the reader module to a compartment inside the reading coil housing. This increased signal processing efficiency and reading distance by reducing noise signal pickup and reading coil detuning. Third, we replaced the vented lead acid batteries with sealed lead acid batteries (Panasonic' [Matsushita Electric Corp. of America, Secaucus, NJ.] No. LCL 12V20P 12 volt ' 18 Ah at 10-hr rate). Finally, we found that reading distances vary by approximately 50% because reader tuning varies with temperature and perhaps moisture content of the soil. The new readers are self-tuning, which allows better tracking of environmental conditions without affecting reading distance.

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