Using Multiple Survey Methods to Detect Terrestrial Reptiles and Mammals: What Are the Most Successful and Cost-Efficient Combinations?

1. What they did

People planning wildlife surveys have to choose methods that will find the species they want, often on a tight budget. Earlier studies had compared survey methods, but the authors could find none that compared their costs in numbers. They set out to compare six methods for detecting ground-dwelling reptiles and small to medium mammals (under 3 kg) in the bushland fragments of Brisbane City, Queensland, by how many species each found and what each cost.

• Sites. 59 sites (20 m by 45 m) in scribbly gum woodland, each with three parallel transects 10 m apart. All sites were surveyed over three nights in 2004, and 51 again in 2005; nine were not resurveyed because of recent fire or human interference.
• Methods. At each site they set 8 wire cage traps, 10 Elliott traps (aimed at small-bodied mammals), 5 dry pitfall traps (10 litre buckets, no drift fences, because of dense vegetation and fallen wood) and 3 hair funnels. Cage traps, Elliott traps and hair funnels were baited with peanut butter, rolled oats, honey and vanilla essence, with apple added in the live traps. Direct observations and scat collection were done opportunistically on every visit.
• Identification. Live-caught animals were identified with a field guide, photographed, weighed, sexed and released where caught. Hair and scats were sent to one of two independent experts (Michiala Bowen for the initial surveys, Barbara Triggs for the repeat surveys). Only “definite” identifications were used.
• Costs. For each method they worked out the cost of surveying one site for one three-night survey: equipment, bait and sample analysis, wages for two people, and travel. They then compared the average number of species and captures per site per dollar.

2. What they found

What was detected

• 28 target species from 11 families: 19 reptiles and 9 mammals. Every method found at least two target species and at least one species no other method found.
• Each method mainly found either reptiles or mammals; none found both in equal numbers.

Method by method

• Cage traps: 2664 trap nights gave 277 captures, but only 19 were target species (mostly northern brown bandicoots, plus bush rats, swamp rats and one carpet python). Most captures were common brushtail possums (124) and introduced black rats (100).
• Elliott traps: 3330 trap nights gave 55 captures; 19 were target mammals (common dunnarts and yellow-footed antechinus), found by no other method.
• Pitfall traps: 105 of 568 pitfall traps caught target species: 12 small or young reptiles and one mammal, the common planigale. Four reptiles and the planigale were found only this way.
• Hair funnels: 84 of 341 wafers held hair, but only 17 could be definitely identified to species, seven of them target species. They gave three mammals: brown antechinus, northern brown bandicoot and long-nosed bandicoot (the antechinus and long-nosed bandicoot only by this method).
• Direct observations and scats: together these found 14 reptiles and two mammals. Direct observation found six large or active reptiles (such as snakes, dragons and the lace monitor) that no other method found. Scats added a melomys that could not be identified beyond genus.

Costs per site (three nights)

• Hair funnels were cheapest ($178.86) and cage traps dearest ($925.66), followed by Elliott traps ($815.18). Pitfall traps ($626.37), direct observation ($655.52) and scat analysis ($660.52) cost about the same. Equipment and travel made most of the difference.

Value for money

• Overall and for reptiles: pitfall traps found the most species and captures per dollar, then direct observations.
• For mammals: hair funnels gave the most species and captures per dollar, then Elliott traps, then cage traps. Scats and pitfall traps were the costliest per mammal detection, and direct observation found no target mammals.
• Overall, scat detection and analysis gave the lowest detection success for the money spent.

3. What they concluded

• No single method finds all species, so surveys of a community need a combination of methods.
• Reptiles: pitfall traps as the main method for small reptiles (with drift fences where habitat and budget allow), and time-limited active searches for large reptiles. Together, these are likely the best combination, and running them together roughly halves travel costs.
• Mammals: cage traps plus hair funnels for medium-sized mammals, Elliott traps plus hair funnels for small mammals, and pitfall traps added only for planigales or similar shy species.
• Hair funnels are cheap and catch hair from animals of many sizes, but they cannot tell individuals apart, and hair is hard to identify to species. The authors considered their own definite identifications accurate.
• Scat detection is best used as an extra method when funds allow; it may work better where ground cover is sparse. Costs will differ between studies depending on how many traps are used, how long searches last and how many samples are analysed.

4. How tracking was or was not used

No footprints or trailing were used. Two of the six methods relied on signs: scats found opportunistically during site visits, and hair caught on sticky wafers in hair funnels. Both were identified away from the field by independent experts, and only “definite” identifications were used. The scats added one mammal, a melomys, that no other method detected, but it could not be identified to species.

5. Tracker or observer certification

Reported but not validated. Hair and scat samples were identified by “independent experts” (Michiala Bowen and Barbara Triggs); no test of their skill is reported. The authors note a study (Lobert et al. 2001) in which almost half of the hair samples analysed by two independent experts involved some identification error. Who searched for scats in the field is not reported.

6. Other technologies, skills or innovations

• Hair funnels (Faunatech) with a single large opening tapering to a closed bait chamber, and a wafer coated with a sticky substance (“faunagoo”) in place of the double-sided tape used in earlier designs.
• A simple costing framework (equipment, bait and analysis, personnel at $19 an hour plus 15.5% on-costs for two people, and vehicle travel at $0.50 per km) that turns detection results into species and captures per dollar.

7. Implications for conservation (from the paper)

• Brisbane has cleared about two-thirds of its pre-European woody vegetation, and Brisbane City Council needs to know where species occur across the urban landscape to plan, manage and restore its bushland.
• The choice of survey methods affects how accurate and complete the results are; relying on one method gives a biased picture of the community.
• Matching methods to the target species’ body size and behaviour, and to the budget, gives the most detections for the money.