Evaluation of attractants for non-invasive studies of Iberian carnivore communities

1. What they did

Carnivores live at low densities over large areas, so they are hard to detect in surveys. Attractants (baits, lures and scents) can raise the chance of detecting them, but most attractant studies have looked at single canid or cat species in North America and Australia, and choices are still mostly based on tradition. The authors set out to find which attractants work best for each Iberian carnivore and which combination works for the widest range of species.

• Enclosure trials (December 2008 to January 2009). Seven species were tested in two zoological facilities in Spain and Portugal: Iberian wolf (5 animals), European wildcat (3), common genet (2), stone marten (1), Eurasian badger (2), polecat (8) and red fox (1). Six attractants were offered at once, each on its own wooden stake about 30 cm above the ground: a commercial canid bait (Collarum Canine Bait), valerian-extract solution, fatty acid scent (FAS), Eurasian lynx urine, red-fox urine and a solution of stone-marten droppings. Each group was filmed for 3 hours at a time when they were known to be active, and every sniff, lick or bite, and rub was timed. Animals could not be told apart individually, so the authors standardised the times per animal per hour and used a selectivity index to see which attractants each species chose more than expected by chance.
• Field trials (July to October 2009). The best combination was then tested with camera traps in the Guadiana Valley Natural Park (Portugal) and Cabañeros National Park (Spain). Cameras were set on a grid about 1.4 km apart, after searching within 250 m of each point for carnivore paths. Lynx urine and valerian solution were placed side by side 2 to 3 m in front of each camera and topped up every 7 to 10 days, and the authors recorded how often each species sniffed, bit or marked them.

2. What they found

Enclosure trials

• Lynx urine was the most widely effective attractant: six of the seven species spent more time investigating it than expected by chance. Only the stone marten did not.
• Collarum bait came second (wolf, wildcat, badger and red fox), then FAS (wolf, genet and stone marten), valerian solution (two species) and red-fox urine (genets only). The stone-marten dropping solution attracted none.
• The stone marten was only drawn to FAS.
• Wolves and genets showed the strongest interest overall. Genets spent up to about 93 seconds per animal per hour on red-fox urine and 79 on lynx urine. Wildcats, stone martens, badgers and polecats showed the weakest overall interest, and wildcats ignored the stone-marten solution completely.
• Rubbing was rare except in wolves and genets. Wolves rubbed on all six attractants, most on FAS; genets rubbed most on FAS, lynx urine and red-fox urine. Wildcats and polecats rubbed only on valerian solution, badgers only on lynx urine, and the stone marten did not rub at all.
• Lynx urine plus FAS would have covered all seven species, but lynx urine plus valerian solution drew rubbing from more species (six), and earlier field work had shown lynx urine attracts stone martens. So lynx urine plus valerian was chosen for the field.

Field trials

• There were 472 carnivore detections of eight species (126 in Guadiana Valley, 346 in Cabañeros), including two species not tested in enclosures: the Egyptian mongoose and the least weasel. Red foxes made up 304 of them.
• Every species except the badger (18%) investigated the attractants on at least half of their visits. Red fox, wildcat, stone marten and Egyptian mongoose did so on 70% or more.
• Lynx urine drew more of the investigations than valerian for every species except the least weasel and the Egyptian mongoose.
• The authors observed red foxes urinating and rubbing on the lynx scent, and stone martens and genets defecating on it.

3. What they concluded

• No single attractant works for every species, but lynx urine combined with valerian solution should attract most species in Iberian carnivore communities.
• The lack of avoidance and the rubbing and marking suggest that carnivores read the scent of a predator or competitor as something to investigate, and even to mark over.
• Collarum bait and FAS suit studies of a few species (Collarum for canids such as the wolf and red fox; FAS for the wolf, genet and stone marten) rather than whole communities.
• Wildcats in the field showed more interest in lynx urine than valerian, possibly because the trials were in late summer, outside the breeding season.
• The stone-marten solution may have failed because the captive marten that supplied it behaved abnormally, and because a liquid gives no visual cue.
• Lynx urine meets the criteria for a good lure: consistent quality, available (lynx are kept in most zoos), cheap, easy to handle and attractive.
• Limitations stated by the authors: very few captive animals, the season of the field trials, possible effects of captivity on behaviour, and no “with versus without attractant” control in the field, so they cannot say for certain that attractants raise encounter rates.

4. How tracking was or was not used

Tracking played only a small part. Before placing each camera trap, the team searched a 250 m radius around the grid point for carnivore paths and set the camera where access was easy and detection was likely. The rest of the study relied on video and camera-trap photographs.

5. Tracker or observer certification

Not reported. The paper does not say who searched for carnivore paths. This does not affect the main findings, which come from video and photographs.

6. Other technologies, skills or innovations

• Cafeteria-style trials: six attractants offered at once in plastic tubes stuffed with cotton wool, filmed with a digital video camera (Velleman CAMCOLBUL2DC), with artificial lighting at night.
• Camera traps (Leaf River IR5) on a 1 km² grid.
• A selectivity index tested with bootstrap resampling, and a simple score (OMP) to rank attractants across species.

7. Implications for conservation (from the paper)

• The results give a baseline for choosing attractants in carnivore survey and monitoring programmes. Lynx urine is suggested as the preferred lure for whole carnivore communities like those in Iberia.
• Because several species rub on these attractants, they could improve rub-pad hair collection for genetic studies such as mark–recapture.
• Some of the other substances may still be useful for single-species monitoring.
• The authors stress replicating attractant studies, since the same lures give varying success.