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A field test of attractant traps for invasive Burmese pythons (Python molurus bivittatus) in southern Florida

Results

Abstract
Introduction
Methods
>Results
Discussion
Acknowledgments
Literature Cited
Figures and Tables

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.
photo of a Burmese python captured in a trap during the experiment
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.

Table 1. Characteristics of 16 Burmese pythons (Python molurus bivittatus) captured or observed in the Frog Pond area east of Everglades National Park, Florida, during and immediately after the trap trial.

TRAP = captured in python trap, OVE = opportunistic visual encounter, DISC = collected by following disc harrow after trial. No pythons were observed during standardised visual surveys. SVL = snout to vent length

Date Method of capture Sex SVL (mm) Mass (g) Notes
13 Aug 2009 TRAP 1740 5840  
08 Sep 2009 TRAP 2240 7854  
09 Oct 2009 TRAP 1980 6160  
29 Oct 2009 OVE Unk. ~1250 Unk. Moving across transect
13 Nov 2009 OVE Unk. ~2000 Unk. Motionless in grass
17 Nov 2009 DISC 1690 4378 Live, died later
18 Nov 2009 DISC 980 718 Live
18 Nov 2009 DISC 1160 1196 Live
18 Nov 2009 DISC 2100 9120 Dead
18 Nov 2009 DISC 1570 2900  
19 Nov 2009 DISC 2010 6990  
20 Nov 2009 DISC 970 882 Live, died later
20 Nov 2009 DISC 2300 8770 Dead
20 Nov 2009 DISC 1960 7344 Live, along access road
23 Nov 2009 DISC 2210 4984 Live

24 Nov 2009

DISC

1805

4546

Live


Table 2. Species composition and number of individuals of non-target vertebrates captured in python traps (all taxa), observed during visual surveys (exclusive of birds), or exposed by disc harrowing in the Frog Pond area east of Everglades National Park, Florida, between 06 August and 24 November 2010.
Species Common name Captured in traps Seen during visual survey Exposed by harrowing
Hyla cinerea Green Treefrog 7 5 0
Osteopilus septentrionalis Cuban Treefrog 12 0 0
Rana grylio Pig Frog 1 0 0
Rana sphenocephala Southern Leopard Frog 3 0 0
Rana sp. Frog sp. 1 1 0
Eumeces sp. Skink sp. 0 1 0
Nerodia fasciata Banded Watersnake 1 1 1
Thamnophis sirtalis Eastern Gartersnake 5 0 2
Pantherophis obsoleta Yellow Ratsnake 0 0 10
Pantherophis guttatus Cornsnake 0 0 8
Coluber constrictor Racer 0 2 3
Agkistrodon piscivorus Cottonmouth 2 0 1
Sigmodon hispidus Hispid Cotton Rat 28 2 >100
Rattus rattus Roof Rat 9 1 >100

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