Biologists using poo to track tropical wildlife must account for busy beetles
Scat. Dung. Droppings. Feces. Call it what you will, excrement is often treasured by wildlife biologists. It can tell scientists what an animal is eating, if it is healthy or sick, and each load carries a trove of identifying DNA. Tracking turds is also a longstanding, non-invasive method for monitoring rare, secretive species, such as carnivorous cats. But beware the dung beetle, a new study warns researchers working in the tropics. The busy insects can beat biologists to the droppings, skewing data and creating results that don’t mean squat.
The study, in the current issue of Oryx: The International Journal of Conservation, may be the first — and last — to focus on the ultimate fate of refrigerated lumps of human and jaguar doo placed in the Brazilian Amazon. The researchers – consulting biologist Darren Norris and Fernanda Michalski of the University of Sao Paulo – wanted to see just how reliable scat surveys might be in the tropics. Past research, mostly in temperate climates, has shown that the surveys can be skewed by animals that eat feces, a behavior called coprophagy. If researchers can estimate the removal rates in different kinds of habitats, however, they can use some standard methods and clever statistical tricks to correct their data.
To conduct their experiment, the researchers collected and froze scat from five captive-bred jaguars kept in a zoo in Rio Grande do Sul. They also gathered feces from two unidentified (and apparently free-ranging) human donors. Then, they thawed the feces and prepared 50-gram samples that each “had the same consistency and composition.” They placed 108 samples along 18 50-meter-long transects that ran through three types of habitat: pasture, forest, and corridors connecting forest patches. Half the samples were simply placed on open ground; the other half were protected from insects by plastic-covered “towers.” Finally, they regularly checked the droppings over the next 24 hours.
Overall, nearly half (44%) of the “open” samples were gone within 24 hours, although feces left in the pasture transects were left untouched. In contrast, two-thirds of the open samples in forested areas quickly disappeared. Dung beetles were the most common culprit associated with disappearing doo. The insects feed on and sometimes live in dung; some have earned the name “tumblebugs” for their practice of creating small balls of dung that they roll away with their hind legs. In the study, the beetles – and some ants too – showed a distinct preference for human scat, which accounted for 62.5% of the removed samples.
The high removal rates mean tropical scat surveys “may not be cost effective for species that occur at low densities,” the authors conclude. Still, they say the surveys could be useful for more common species, if they are carefully designed and take busy scavengers into account. – David Malakoff
Source: Norris, D., & Michalski, F. (2010). Implications of faecal removal by dung beetles for scat surveys in a fragmented landscape of the Brazilian Amazon. Oryx, 44 (03), 455-458 DOI: 10.1017/S0030605309990809
Image © Ockra | Dreamstime.com