pellets. Since rates will typically vary with diet, values from zoo animals are often unreliable
estimates of this parameter. An alternative approach is to calibrate dung counts with live-trapping
estimates of population size on the same area, and thus derive an empirical relationship between
dung counts and population size (Krebs et al. 2001).
Advantages and disadvantages
Life produces dung, and consequently the presence of a species in an area can be as certained
by dung counts. In habitats where dung persists this method can be used very effectively to
index population abundance with a minimum of effort. As techniques for identification of individuals
from DNA in dung are developed, fresh dung can also potentially become a way of
estimating population size by mark–recapture of dung from specific individuals (Eggert et al.
2003).
If a long-term study is needed, it is important to have permanent quadrats that are cleared at each
sampling so that the issue of dung age does not arise. If no independent estimate of population
abundance is available, all of the cautions about using indices need to be considered carefully.
For some species of larger mammals the type of dung produced varies between the growing
and non-growing seasons, and this can be used to advantage to index seasonal habitat
use.
364 Mammals
Biases
The main problem in sampling dung is that it is typically not randomly distributed in the landscape,
and that it can decompose at quite different rates in various micro-habitats.
Feeding signs for herbivores
If a herbivorous species leaves characteristic marks on their food plants, these feeding marks or
scars can be used both to determine presence and absence and to index the relative abundance of
a population.
Method
Counting feeding signs depends on detailed knowledge of the natural history of the species and
the food plants it utilises. Since diets of most mammals change seasonally, there may be one
season in which the feeding signs are most easily counted.
Voles in grasslands cut tillers of grasses and leave these fresh cuttings in their runways. A
census of these clippings was used over 80 years ago to index vole numbers in Britain (Chitty