By Alex Marinelli
Another successful small vertebrate trapping week has come and gone at Arid Recovery, with many positives from the 2021 survey. These surveys are important for Arid Recovery as they help us to gain an understanding of the population sizes and distributions of smaller animals and contribute to our long-term database, which spans all the way back to 1998. With the significant increase in rainfall in 2020 following two years of severe drought, there was much excitement to see how each species’ population has responded.
The survey was conducted over four eventful trapping nights between the 9th and 13th of March, which included some hot weather and a very swift pack up on the final morning due to rain. The week started off with an enjoyable barbeque the night before the survey, where we met all the wonderful volunteers with whom we’d be spending the next week. After a great bonding session, we set off bright and early the next morning to dig our pitfall lines. At Arid Recovery, surveys are conducted in two habitat types, dunes and swales. These habitats are surveyed in alternating years and this year it was time to survey the swales. Defined by hard-packed clay substrates, the swales provide a challenging morning of digging trenches, due to rocks in the soil. However, all teams persisted with no complaints and we managed to complete all our lines just after lunch. The mammoth effort that morning was worth it, as we knew it would provide us an opportunity to see the amazing smaller creatures of the reserve over the coming days.
There were two pitfall lines at each site, with six pits per line, alternating between large and small pits. Each pit contained small tubes, such as toilet rolls and plastic pipes, which acted as shelter for the animals inside the pits. Seed and a small amount of water were also added to pits, hopefully providing the animals with some relief once they had fallen in. Three false floors were also randomly assigned to pits in each line. The purpose of these false floors is to provide an area for reptiles to hide under and to escape predation from mammal species when they fall into the same trap.
Well, the rain provided the goods, with a total of 759 captures from 22 reptile species and 9 mammal species. This was 74 more individuals than the last 2 years combined and made for a very busy lab space, with buckets and bags of animals everywhere.
This increase in captures is likely due to the rapid resurgence (“boom”) of the small mammal populations on the reserve following rain. In 2019, 23 mammals were captured in the swales and, in 2020, 26 were captured in the dunes. This year saw a dramatic jump with 279 captures, and the number of species caught increased from 4 to 9. This is a great example of a boom-bust cycle and shows the effect an increase in rain can have on an arid ecosystem. The most common mammal species found were the Spinifex Hopping Mouse (Notomys alexis), Plains Mouse (Pseudomys australis), Forrest’s Mouse (Leggadina forresti) and Fat-tailed Dunnart (Sminthopsis crassicaudata). The capture of a Desert Mouse (Pseudomys desertor) had staff excited as this was only the 8th time ever (and the first time in 10 years) that this species has been recorded during annual pitfall trapping at Arid Recovery.
While there were fewer reptile captures this year, than in the 2020 dune survey, captures increased greatly from 126 individuals in the 2019 swale survey to 480 this year. Species numbers also increased from 17 in 2019 to 22 in 2021. The most common reptile species recorded this year were the Central Netted Dragon (Ctenophorus nuchalis), several skink species such as Ctenotus schomburgkii and Ctenotus leonhardii, and the Gibber Earless Dragon (Tympanocryptis intima). There were several gecko species recorded, including the Sand-plain Gecko (Lucasium stenodactylum), Bynoe’s gecko (Heteronotia binoei) and a Three-lined Knob-tail gecko (Nephrurus levis). There was also an Interior Blind Snake (Anilios endoterus) and, strangely, a Sand Goanna (Varanus gouldii) managed to find itself stuck in a pit.
The 2021 trapping survey would not have been possible without the help of dedicated staff and volunteers. To the staff, thank you for all your tireless work throughout the survey and for passing your knowledge onto us. For me personally I have learned loads from you and I’m sure all the volunteers feel the same. A big thank you must also go to the volunteers for taking time out of your busy schedules to come and help with the survey. I hope you all gained tonnes of valuable experience and have many fond memories of the trapping week. All the best for your future endeavours and hopefully see you all again soon!