Results

Trapping

Our effort consisted of 6,053 effective trap-nights between 06 August 2010 and 16 November 2010; we deleted 128 ineffective trap-nights during which a trap was considered mechanically non-functional or improperly baited. Water levels in portions of the trapping area rose steadily during early parts of the experiment, and traps in the southern tree islands were in 3 - 15 cm of water for much of the experiment.

Three Burmese pythons were captured in traps (Table 1), ranging in size from 1740 to 2240 mm SVL and 5840 - 7854 g body mass (Fig. 3). The pythons were captured on 13 Aug, 08 Sep, and 09 Oct; the first two (both males) were captured in traps equipped with round entrance flaps, and the third (a female) in a trap with a rectangular entrance. All three were captured in the trap grid of 40 traps.

We captured 69 non-target organisms in traps, for an overall incidental capture rate of 0.011 per trap-night. Most of these were rodents [native cotton rats (Sigmodon hispidus) and non-native roof rats (Rattus rattus)], but we also captured 4 species of frogs and 3 species of snakes (Table 2). Some of these 'captures' were of animals capable of entering and leaving the traps through the mesh at will, including small frogs and small native snakes. We observed no mortality of non-target organisms, all of which were released nearby.

Fig. 3. A Burmese python captured in a trap during the experiment. [larger image]

Visual searching

No pythons were observed during standardised morning visual searches, but two pythons were observed opportunistically while conducting field activities at the study site (Table 1). The first was observed on a canal bank along the west edge of the site, and the second was observed ~5 m from a trap but was not captured in that trap. Standardised visual searching resulted in observations of low numbers of non-target species (rats, hylid and ranid frogs, and native snakes; Table 2).

Post-trapping site treatment

Eleven P. molurus were discovered during vegetation management activities after the trap trial (0.136 pythons exposed/ha harrowed); ten of these were discovered by following behind the disc harrow, but one was found on the edge of the study site along an access road. These pythons averaged 1705 ± 481 mm SVL (range 970 - 2300) and 4712 ± 3074 g (range 718 - 9120; Table 1), and none were recaptures from trapping. Two pythons were killed outright by the harrow, and two more died shortly after capture from harrow-induced injuries. Of those remaining, a few sustained minor injuries (from which we judged they likely would have recovered) and the remainder escaped visible injury (all pythons were humanely euthanized after capture). Among non-target species, 27 live or dead snakes of six species were discovered during harrowing operations (Table 2). In addition, hundreds of rats (Rattus and Sigmodon, not identified to species) were seen fleeing from, or were killed by, the harrow each day.