A GRAIN DIET SUPPLEMENTED WITH INSECTS RATHER THAN FRUITS SUPPORTS A
MORE ROBUST BODY CONDITION IN AN OMNIVOROUS TROPICAL SONGBIRD
Abstract
1. Omnivores utilise dietary sources which differ in nutrients, hence
dietary restrictions due to environmental change or habitat alteration
should cause nutrient limitations; and thus, deterioration of body
condition if omnivory is obligate. 2. We investigated how the body
condition of the Village weaver Ploceus cucullatus (weavers), which
forages predominantly on grains, responds to insects and fruits
deprivation. 3. Forty wild-caught weavers held in aviaries were fed a
combination of grains and fruits, or grains and insects ad libitum for
eight weeks. We confirmed diet preference by recording the number of
foragers on each diet option per minute for one hour and the amount of
food left-over after 3 hours of foraging. Fortnightly, we assessed
indices of body condition including body mass, pectoral muscle, and fat
scores, Packed Cell Volume (PCV) and Haemoglobin Concentration (HBC). We
modelled the number of foragers, food left-over and body condition as
functions of diet, while accounting for time (weeks) and sex effects. 4.
We confirmed grains as the preferred diet and found that males ate more
fruits and insects than females. Weavers fed on grains and fruits lost
body and pectoral muscle mass and accumulated less fat than those fed on
grains and insects. This effect was sex-dependent: females deprived of
insects lost more pectoral muscle mass than males of the same group and
males but not females, deprived of fruits accumulated more fat reserve
than those deprived of insects. PCV and HBC did not differ between diets
but increased over the eight weeks. 5. Weavers are likely obligate
rather than facultative omnivores, with insects as being a more
nutritive supplement than fruits. We conclude that nutrient limitation
arising from environmental change or habitat alteration can impair body
condition and affect physiological response to environmental seasonality
in other obligate omnivores like the weavers.