Assessing consumption of Curiosity[R] feral cat baits by Blotched Blue-tongued Lizards.
Feral cats Felis catus maintain self-sustaining populations in the wild in Australia where they impact wildlife through direct predation, disease transmission and resource competition (Department of the Environment 2015). The Curiosity[R] feral cat bait (Curiosity[R] Bait) has been developed to provide land managers of conservation reserves with a humane control tool that is attractive and palatable to feral cats but employs technologies to minimise impact on populations of native species. The bait contains a 78 mg para-aminopropiophenone (PAPP) formulation that is encapsulated in a tough acid-soluble polymer that forms a robust pellet. This is known as the Hard Shell Delivery Vehicle (HSDV) and is implanted within a moist meat food lure (Johnston et al. 2011; Johnston et al. 2014). Feral cats' foraging behaviour is based on identification of visual and auditory cues, but they will consume carrion, including baits, if encountered when hungry and the food is palatable. As feral cats rarely exhume buried food items, poison baits intended for this species must be surface-laid. This creates greater potential for exposure of non-target wildlife species than occurs in canid control programs, which typically use a buried baiting procedure.
Pen and field trials have demonstrated that the use of the HSDV in the meat lure is an effective technique to reduce the exposure of wildlife species to the toxicant (Marks et al. 2006; Hetherington et al. 2007; Forster 2009; Johnston 2010; Gigliotti 2011; Algar et al. 2017; Heiniger et al. 2018). This presentation technique exploits the differing dentition and feeding behaviour between feral cats and Australian native wildlife species. Feral cats are known to simply shear food items into manageable sizes before swallowing (Bradshaw 1992; Hilmer et al. 2010). It is common to find large, identifiable portions of prey species in their stomachs (Kutt 2012; McGregor et al. 2015; Johnston, pers. obs., 2012). In contrast, native wildlife species chew their food more thoroughly and tend to reject large hard items (Marks et al. 2006; Hetherington et al. 2007; Forster 2009; Johnston 2010; Gigliotti 2011; Algar et al. 2017; Heiniger et al. 2018). Buckmaster et al. (2014) assessed the potential for exposure to the encapsulated toxicant amongst all Australian native terrestrial vertebrate species. This study combined a desktop review along with results from in vivo observations for species considered to be likely to consume Curiosity[R] baits. Further studies were recommended to assess the hazard that the baits present to other non-target species outside the existing dataset where there was any uncertainty about their risk to consuming Curiosity Baits (Buckmaster et al. 2014). The current study was undertaken to inform the risk of bait consumption by Blotched Blue-tongued Lizards Tiliqua nigrolutea and potentially for other Tiliqua species.
Cage trapping programs for feral cats on French and Phillip Islands in Western Port, Victoria, have resulted in the capture of Blotched Bluetongued Lizards as a non-target species. Trapping records over the period 2010-2018 were reviewed, with the capture rate of Blotched Blue-tongued Lizards compared across seasons; summer (December-February), autumn (March-May), winter (June-August), spring (September-November) and used as an index of activity. Trapping methods were consistent throughout the study period in terms of trap design, food lure provided and locations used, but trapping effort was biased towards cooler months when it was expected that feral cats were more responsive to the food lure provided in traps.
Field observations of the interactions of Blotched Blue-tongued Lizards with non-toxic versions of the Curiosity[R] bait were conducted in February-March 2018 on Phillip and French Islands (Fig. 1). Traps were opened at 25 sites on Phillip Island each morning within three hours of dawn and then closed before dusk. Traps on French Island remained open throughout the study, being checked within two hours of dawn and again prior to dusk, as this study was conducted in parallel with a feral cat trapping program.
The meat lure component of the Curiosity[R] bait was prepared from minced kangaroo meat and chicken fat. The meat was pH buffered to 7.5 to prevent premature deterioration of the HSDV, then formed into skinless sausages and air-dried (Johnston et al. 2014). Each bait was implanted with a non-toxic HSDV that contained Rhodamine B dye and placed at the rear of the cage trap (Fig. 2). Rhodamine B dye leaves a readily discerned mark on contact with moisture and/or skin tissue (Fisher 1999). A sheet of fabric was placed under all traps so that any uneaten portions of food and/or HSDV were retained. Captured lizards were removed from the cage, measured and inspected for pink-coloured staining around the mouth that would indicate exposure to the Rhodamine B dye. A small identifying mark, located behind either front leg, was created with a felt tip pen to assist with the identification of recaptured individuals. The lizards were then released into nearby vegetative cover. The amount of bait material consumed by the lizards and the condition of the HSDV (intact/damaged/not found) were documented. A fresh Curiosity[R] bait (including non-toxic HSDV) was supplied when the trap was reset.
Historical trap records from both island sites, comprising 99 816 trap days, indicated 406 individual captures of Blotched Blue-tongued Lizards over the study period (2010-2018). The majority (63%, n=256) of these captures occurred in summer despite this season recording the least trapping effort (Fig. 3). During the winter season, three lizards were captured over a total of 50 620 trap days (0.005% trap success). Greater numbers of lizards were captured in autumn (65) and spring (82) achieving an equivalent trap success of 0.3%. By contrast, considerably less trapping was undertaken in summer (~8000 days), but resulted in significantly greater trap success (3.7%). A chi-square test of independence in R (R Core Team 2019) demonstrated a significant difference in capture rates of T. nigrolutea between seasons [X.sup.2] = 2073.3, df = 3, p<0.001.
The field observations comprised 502 and 511 trap days on Phillip and French Islands respectively. A total of 30 adult Blotched Bluetongued Lizards were trapped, with four individuals caught twice (Table 1). Baits were either wholly or partially consumed in 73% of presentations, with the HSDV consumed in 86% of these (Table 2).
Blotched Blue-tongued Lizards are known to be generalist omnivores, consuming invertebrates, snails, soft plant material such as flowers, and carrion (Ehmann and Strahan 1992; Shea 2006; Robertson and Coventry 2019). Our data demonstrates that Blotched Blue-tongued Lizards will consume the Curiosity[R] bait including the HSDV when they encounter it. The dentition and masticatory behaviour in Blotched Blue-tongued Lizards does not lead to similar HSDV rejection behaviour that has been observed in mammals (Marks et al 2006; Hetherington et al. 2007; Forster 2009; Johnston 2010; Gigliotti 2011; Algar et al. 2017; Heiniger et al. 2018) and birds (Gigliotti 2008). Other Tiliqua have similar diets and behaviours (Shea 2006), and will consume Curiosity[R] baits if they encounter them.
There is limited data on the susceptibility of Australian reptiles to PAPP, with small-scale pen trials conducted only with Lace Monitors Varanus varius and Rosenberg's Goanna V. rosenbergi, indicating a high susceptibility to the compound (summarised in McLeod and Saunders 2013). No data exist describing the tolerance of Tiliqua to PAPP. We assume that Tiliqua have a similar tolerance to the varanids tested and that one Curiosity[R] bait would contain a lethal dose if ingested. In this case, we suggest that the lizards that consumed the HSDV would have died had toxic PAPP doses been provided.
The seasonal difference in the activity of reptiles such as Blotched Blue-tongued Lizards in the south-east of Australia is well known (Cogger 2014; Robertson and Coventry 2019). This is reflected in the variable capture rate of Blotched Blue-tongued Lizards during feral cat trapping programs undertaken on Phillip and French Islands. These programs have mostly been undertaken during the cooler months as this is when feral cats are more likely to demonstrate interest in the food lure provided in the cage traps.
The exposure hazard of T. nigrolutea to Curiosity[R] baits can be largely mitigated by exploiting the observed seasonal behaviours of this species at this latitude. Restricting the application of Curiosity[R] baits to cooler months when these animals are minimally active is recommended. In south-east Australia, this would typically be during late May-July. It is unlikely that baits laid at this time would subsequently present a hazard when Blotched Blue-tongued Lizards become more active as daily temperatures increase in Spring, due to natural degradation and consumption by other species, particularly invertebrates.
Previous work by Jessop et al. (2013) monitored removal of non-toxic Curiosity[R] baits from stations using trail cameras during summer 2010-11 in eastern Victoria. In that study, Lace Monitors Varanus varius were responsible for removing 7% of the 1686 supplied baits. Greater bait take was observed on days of elevated temperature, but notably Monitors were active and removed baits during cooler summer days of 17 [degrees]C (Jessop et al. 2013).
A precautionary approach is recommended for land managers who intend to use Curiosity[R] baits, to avoid application of baits during periods when non-target reptile species, such as Tiliqua sp., are expected to be active and consume baits. A hazard assessment considering potential impacts on populations of non-target species is recommended during the planning stages of Curiosity[R] baiting programs.
The Phillip Island Nature Parks Animal Ethics Committee approved the use of animals in this research under protocol 4.2017. The Department of Environment, Land, Water and Planning issued research permit number 10008436 under the National Parks Act (1975) and Wildlife Act (1975). Ross Holmberg, Duncan Sutherland and two anonymous referees provided valuable improvements to the manuscript.
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Michael Johnston (1), Frank Gigliotti (2) and Julie Trezise (3)
(1) Scientec Research Pty Ltd. Email: email@example.com, PO Box 122, Warrandyte, Victoria 3113.
(2) Conservation Department, Phillip Island Nature Parks, PO Box 97, Cowes, Victoria 3922.
(3) French Island Landcare Group, Tankerton Post Office, French Island, Victoria, 3921.
Table 1. Summary of capture records. Species Phillip Island Blotched Blue-tongued Lizard Tiliqua nigrolutea 18 Cat Felis catus nil Echidna Tachyglossus aculateus 5 Long-nosed Potoroo Potorous tridactylus nil Rabbit Oryctolagus cuniculus nil Species French Island Total Blotched Blue-tongued Lizard Tiliqua nigrolutea 12 30 Cat Felis catus 5 5 Echidna Tachyglossus aculateus 3 8 Long-nosed Potoroo Potorous tridactylus 1 1 Rabbit Oryctolagus cuniculus 1 1 Table 2. Summary of Curiosity[R] bait consumption and HSDV recovery in Blotched Blue-tongued Lizard trials. No. of HSDV presentations recovered Whole bait consumed 14 2 Partial bait consumed 8 1 No bait consumed 8 8
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|Author:||Johnston, Michael; Gigliotti, Frank; Trezise, Julie|
|Publication:||The Victorian Naturalist|
|Date:||Dec 1, 2019|
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