By Tori Wilson (Conservation Intern)
Above all else the theme for this year’s pitfall trapping should probably be perfect timing! We got stuck into our annual pitfall trapping this year in early March, lucking out on good weather and getting in before the COVID-19 situation had escalated in Australia, which allowed our team of volunteers to join us for the week from across multiple states. They hailed from Melbourne, Sydney, Canberra, Adelaide, and other parts of South Australia, all with a shared enthusiasm for ecology and conservation. We were also joined by Kate Taylor of Bon Bon Station (Bush Heritage Australia) and Glen Murray from SA Arid Lands NRM, who generously shared their knowledge and skills with the teams during the week-long pitfall survey.
Pitfall trapping is conducted each year at Arid Recovery to survey the small animals found on the reserve, providing a snapshot of how some of the species that are not commonly seen are going. The established pitfall sites are throughout dune and swale habitats (both inside and outside of the reserve), and are alternated each year to gather information on species across the different habitats. This year we’d be seeing what turned up in the dunes! We were also interested in seeing what effects the long running drought has had on the smaller species on the reserve. With significantly lower than average rainfall for the past three years there was a good chance we’d see signs of species struggling with the conditions, despite a brief reprieve in the form of a 60mm dump of rain a month before the pitfall survey. The only way to find out was to get stuck in and start surveying!
Day one saw our 17 staff and volunteers rise early and split into teams to set up the pitfall lines. Despite starting with the rising sun, it quickly became a warm day as we located pitfalls buried under sand or sticking well above the top of dunes, levelled them out, and built the pitfall lines around them. The pits themselves stay at their locations and are closed once the survey is finished, but the mesh fencing is erected just for the week and then packed down again. My team was keeping a running count of the number of flies each person had accidentally eaten (not a competition you want to win!) and there were plenty of drink breaks that saw team members returning the sand that had accumulated in their shoes back to the dunes. Still, the anticipation of what insights we might glean built with each line that went in.
All up we had 20 sites with two pitfall lines at each site. Each line had six pits, alternating between large and small diameters, and most pits had a wooden false floor allowing any smaller animals to evade larger ones if they ended up in the pit together. The pits themselves were furnished to be as comfortable and safe as possible for anything that ended up in them; A handful of sand covered the bottom of the pits allowing small reptiles to burrow, a cardboard loo roll was provided on top of the false floor as shelter, and a handful of seed was scattered into the pits to make sure no hungry mammals snacked on any reptiles during the night. Between the four teams of staff and volunteers, each pit was methodically checked twice daily to make sure no animals spent prolonged periods in the pits. Each individual animal was collected in a specifically labelled bag, so we could keep track of where and when we found them, and carefully transported back to the lab for processing.
The lab itself was a hive of excitement. You knew what your team’s bags held, but what did the other teams find? Staff and volunteers would rattle off their most interesting finds for the day and then processing would begin. Processing of the animals involves retrieving each one from its bag and collecting what we call morphometric data. That is age, sex, weight, length, and most importantly, species identification. Notes were also taken on tail regeneration (for the skinks and geckos) and other interesting observations (such as the ghostly-white Beaded Gecko we found that was mid-way through shedding its skin).
Once each animal had had its information taken, it was marked with a small dot on its underside so that we could tell any recaptured animals from new ones if they found themselves in the pitfalls again during the week. After processing each animal was returned to its temporary housing for a few hours and released in the evening when we went to check the pitfalls the second time for the day.
This year’s pitfall trapping turned up quite a number of animals, 510 reptiles and 26 mammals to be exact! Within these counts we also managed to get a reasonable diversity of species, which suggests that the animals are still faring well, despite the drought. We also noted that a number of the reptiles were juvenile or immature, suggesting that they have bred in response to the large rain event in February which is also a great sign. We also caught a couple of Sudell’s frogs (Neobatrachus sudellae), a burrowing frog species. These frogs can remain buried for extended periods of time, but return to the surface during rainy periods to breed and absorb water, so catching them in the pitfalls is another promising sign of life after the downpour in February.
Highlights included an elusive Giles’ Planigale (Planigale gilesi), a Southern Desert Banded Snake (Simoselaps bertholdi), and a Narrow-banded Shovel-nosed Snake (Brachyurophis fasciolatus); species that were new to many of the volunteers, and not so easy to come by. Despite initial fears that we might see some significant declines in species numbers or even species that should have been present but weren’t, the overall diversity of species and their apparent resilience to the drought conditions was the biggest takeaway of all.
Invertebrate species were collected from the pitfall traps too. Unlike the reptiles and the mammals, the invertebrates weren’t returned to the field. They are part of a larger research project into the diversity of invertebrates within the reserve. After the pitfall survey was completed the invertebrates from each pitfall line were logged by Order (i.e. Spiders belong to the Order Araneae) and stored in ethanol, a preservative that will keep them from breaking down.
The number of invertebrates collected was substantial, with over 2000 individuals counted. The majority of these were caterpillars (Order: Lepidoptera) and various species of beetles (Order: Coleoptera). Most of the caterpillars that were collected were Striped Hawk Moth (Hyles livornicoides) larvae that emerged in response to the rain in February.
The collection of the invertebrate species allows for long-term analysis to answer questions about the trends in abundance and diversity of some of the smallest creatures on the reserve. Short-term analysis can give us insights too. For example, this year we collected the highest number of scorpions (86 individuals) since invertebrates first started to be collected five years ago, and the data also tells us that scorpions are typically larger in the sites outside the reserve compared to inside. Why? Well that’s a question that would require some further research, but lucky for us that’s what we do here at Arid Recovery.