Diet and food availability of the greater bilby
(Macrotis lagotis), was examined at two sites and over
two summer and two winter seasons in Astrebla Downs National Park in
south-western Queensland. The presence of both invertebrate and plant material
in almost all faecal pellets (99.6% and 98.5%, respectively)
indicated that bilbies in south-western Queensland are omnivorous. The plant
component of the bilby diet consisted predominantly of
Dactyloctenium radulans seeds (frequency of occurrence:
94.4%). The major invertebrate prey items were Isop-tera (termites,
73.1%) and Formicidae (ants, 77.6%). The frequency of occurrence
of invertebrates in faecal pellets was higher during summer than winter, but
the frequency of occurrence of plants was relatively constant regardless of
season. Within the invertebrate categories, Isoptera and Acrididae
(grasshoppers) displayed the greatest seasonal difference, with a
significantly higher proportion of both categories in the diet during summer
than winter at both study sites. The availability of invertebrate prey items
also varied with season, and for most taxa, frequency of oc-currence was
significantly higher in summer than winter. In contrast, the frequency of
occurrence of seeds and bulbs (Cyperus bulbosus) varied
only slightly with season. Seasonal changes in food availability were
reflected by variation in dietary composition; however, relative proportions
of some dietary items differed from their proportional availability.
Therefore, bilbies were considered to be qualitatively opportunistic;
selecting more invertebrates when their apparent availability increased, but
continually exploiting the available seeds and bulbs. Additionally, although
bilbies appeared to have some preferences for particular food items, several
food items were selected almost randomly, and therefore bilbies were also
considered to be dietary generalists. Such an opportunistic feeding strategy
is advantageous to an arid-zone species as it permits the continuous
exploitation of food resources that are unpredictable in their availability
both spatially and temporally.
Seasonal Changes in Feeding Success, Activity Patterns, and Weights of Nonbreeding Sanderlings (Calidris alba)
