Getting accurate estimates on wildlife populations is difficult in any habitat, but especially tricky in tropical forests where even large mammals are capable of melting into the foliage like ghosts. If you’ve ever spent time in a tropical rainforest, you know you could walk within a couple meters of a jaguar and never even know. Therefore, scientists have to come up with creative ways—from camera traps to pawprints to studying feces—to estimate population size. In the new issues of mongabay.com’s open access journal Tropical Conservation Science, researchers look at the most accurate way to count white-tailed deer (Odocoileus virginianus) in central Mexican forests.
“The white-tailed deer is not considered an endangered species by the IUCN; however, local extinctions as a result of over-hunting and habitat loss are common in many sites in the Neotropics . Of the 38 recognized subspecies, at least 20 have a Neotropical distribution, but few [less than 6] have been studied, and population density data is not available for many sites. Therefore, suggestions on methods and field procedures to estimate population densities of the white-tailed deer are a crucial aspect for the conservation of this species,” the researchers write.
Accurate estimations of white-tailed deer populations in central Mexico are vital for sustainable management, given that the species is an important part of locals’ diets. Researchers tried four different methods of pellet counting to find the best way to compile population density: two ways to count pellet groups in circular plots known as FSC or FAR, strip transects, or line transects. They found that average density estimates were similar in all four counts, but recommend that line transects were the best method. Second was strip transect and last FSC.
The researchers write that in order to conduct any accurate count, “two crucial factors are required […]: pellet decomposition rate and daily defecation rate.”
The researchers caution, however, that every habitat is different.
“We strongly suggest replicating our study in other tropical areas in order to test these sampling methods. An important requirement is the comparison of these methods under different levels of white-tailed deer abundance.”
CITATION:
Angela A. Camargo-Sanabria and Salvador Mandujano. Comparison of pellet-group counting methods to estimate population density of white-tailed deer in a Mexican tropical dry forest. Tropical Conservation Science. Vol.4 (2):230-243, 2011.
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