Investigating Food Habits of Terrestrial Vertebrates
175
comparison with a local reference collection or through the use of reference
books (Musil 1963).
Among herbivores, esophageal- and rumen-fistulated animals have been
used instead of sacrificed animals. Fistulating involves installing a permanent
device in the digestive tract of a living animal, allowing samples to be taken as
food passes that point in the digestive process (Torell 1954; Short 1962;
McManus 1981). Fistulation has been used extensively in describing the diets
of domestic animals (Vavra et al. 1978), but rarely has this approach been applied to wild ruminants (Rice 1970). Taming and hand-rearing fistulated animals are the only ways a researcher can approach them to collect samples. But
as with using domesticated “wild” herbivores for bite count data collection, the
time and money required are generally prohibitive and tame animals may not
reflect the true food habits of their wild counterparts.
Emetics, flushing tubes, and manual expression of the gullet have been also
been used, primarily on birds, to purge the upper portion of the digestive tract
without harming the animal (Errington 1932; Vogtman 1945). More recently,
nonlethal sampling of stomach contents has been successfully done on small
vertebrates, especially reptiles (Shine 1986; Henle 1989).
Evaluating the Importance of Specific Foods and Prey
USE, SELECTION, OR PREFERENCE?
Use, selection, and preference have been applied interchangeably when discussing food use patterns, resulting in some confusion. Use simply indicates
consumption of a specific food. Selection implies that an animal is choosing
among alternative foods that are available. Use is selective if foods are consumed disproportionally to their availability in the environment ( Johnson
1980). Preference is independent of availability. For example, animals can be
provided different foods on an equal basis (cafeteria experiment) to determine
preference among the foods provided.
AVAILABILITY VERSUS ABUNDANCE
As I have just indicated, any evaluation of the selection of foods can be accomplished only with information on food availability. Unfortunately, the availability of forage or prey species can be difficult to estimate. Physical access to
forage plants may be constrained by the reach of a herbivore or snow coverage
175
comparison with a local reference collection or through the use of reference
books (Musil 1963).
Among herbivores, esophageal- and rumen-fistulated animals have been
used instead of sacrificed animals. Fistulating involves installing a permanent
device in the digestive tract of a living animal, allowing samples to be taken as
food passes that point in the digestive process (Torell 1954; Short 1962;
McManus 1981). Fistulation has been used extensively in describing the diets
of domestic animals (Vavra et al. 1978), but rarely has this approach been applied to wild ruminants (Rice 1970). Taming and hand-rearing fistulated animals are the only ways a researcher can approach them to collect samples. But
as with using domesticated “wild” herbivores for bite count data collection, the
time and money required are generally prohibitive and tame animals may not
reflect the true food habits of their wild counterparts.
Emetics, flushing tubes, and manual expression of the gullet have been also
been used, primarily on birds, to purge the upper portion of the digestive tract
without harming the animal (Errington 1932; Vogtman 1945). More recently,
nonlethal sampling of stomach contents has been successfully done on small
vertebrates, especially reptiles (Shine 1986; Henle 1989).
Evaluating the Importance of Specific Foods and Prey
USE, SELECTION, OR PREFERENCE?
Use, selection, and preference have been applied interchangeably when discussing food use patterns, resulting in some confusion. Use simply indicates
consumption of a specific food. Selection implies that an animal is choosing
among alternative foods that are available. Use is selective if foods are consumed disproportionally to their availability in the environment ( Johnson
1980). Preference is independent of availability. For example, animals can be
provided different foods on an equal basis (cafeteria experiment) to determine
preference among the foods provided.
AVAILABILITY VERSUS ABUNDANCE
As I have just indicated, any evaluation of the selection of foods can be accomplished only with information on food availability. Unfortunately, the availability of forage or prey species can be difficult to estimate. Physical access to
forage plants may be constrained by the reach of a herbivore or snow coverage