Geoscience Reference
In-Depth Information
limited to species that occupy open habitat (grassland, savanna, or tundra) and
forage during daylight periods. Consistently identifying the grasses and forbs
consumed by herbivores may limit the application of this technique to habitats
where forage diversity is limited or species are easily differentiated. For wide-
ranging animals, the observer must follow subject animals and thus may affect
their foraging behavior or prey availability (Mills 1992). Among carnivores,
observations are usually limited to identifying large prey that are not eaten
whole (Schaller 1972; Mills 1992).
LEAD ANIMALS
Concern about the suitability of direct observation has prompted some inves-
tigators to use tame, hand-reared animals to investigate food use. Subject ani-
mals are followed closely by the researcher, allowing accurate identification of
the foods consumed and those avoided (Gill et al. 1983). Lead animals provide
an opportunity to observe the consumption of items that are consumed whole
(e.g., fruits and small forbs) or where there is little evidence of consumption.
Although this approach may eliminate some of difficulties associated with
direct observations, the diet summaries reported for lead animals have been
criticized as being artificial (Wallmo et al. 1973). Physiological condition,
hunger, presence of conspecifics, and previous foraging experience may affect
food use by tame animals and result in erroneous conclusions. Although this
approach has had only limited application among carnivores, it may be useful
under unique circumstances (such as a falconer using a trained raptor) to
investigate differential vulnerability of prey if captured prey are compared to a
random sample of the target population (Temple 1987).
FEEDING SITE SURVEYS
Feeding site surveys are among the earliest approaches used to investigate food
habits and were initially developed to determine the foods of livestock. This
method relies on an inventory of plants consumed or identification of prey
remains.
Survey of food remains
Because of the limitations imposed by cover or nocturnal activity, the food
habits of many species cannot be observed directly. As a result, some investiga-
tors have relied on an examination of feeding sites. This technique obviously
depends on the ability of the investigator to locate sites where feeding has
