DISCUSSION
We tested the effect of fruit and insect deprivation on the body
condition of wild-caught captive Village weavers. First, we confirmed
that Village weavers prefer grains compared to fruits and insects as
indicated by observed foraging frequencies on diet types per unit time,
and GUD. Weavers fed with a diet of grains supplemented with insects
lost less body mass, maintained pectoral muscle, and accumulated higher
fat reserves during the eight weeks of the experiment compared to those
supplemented with fruits. PCV and HBC did not differ between diet
treatments but increased over time in both diet treatments.
The observed preference for grains is consistent with existing knowledge
that Village weavers are largely granivores despite being described as
omnivores (Collias & Collias, 1970; Adegoke, 1983). Grains and seeds
are richer in carbohydrates and fatty acids (which are highly
concentrated energy sources) than fruits and insects (Korasov & del
Rio, 2007; Dimiceli et al., 2007). Therefore, the consistently
higher number of Village weavers foraging on grains relative to fruits
and insects suggest that a diet of grains is more crucial for maximizing
their daily nutrient requirements relative to fruits and insects.
However, despite this preference for grains, weavers foraged on fruits
and insects because these food items contain specific vitamins and
minerals or nutrients such as carotenoids (a source of yellow, red, or
orange pigments), and proteins (Linville and Breitwisch, 1997; Bailein,
2002; Walker et al., 2014) which are unavailable in grains.
Fruits contain sugar and carotenoids and the latter the probable source
of the yellow plumage colour of the Village weaver as in other birds
(Ewen et al., 2006; Osinubi et al., 2018).
Relative diet preference may simply indicate the amount of each food
item intake, or effort required to meet daily nutrient/energy
requirements. For example, judging by the absolute mass of food items
consumed based on GUD estimates, the weavers consumed as much fruits as
grains weekly, but this was achieved over a shorter foraging time,
suggesting that they were much more efficient in handling the fruits
diet provided than grains or that they needed more time on grains to
obtain their requirement. Note however, that the observed similarity in
GUD between grains and fruits might be partly explained by evaporative
water loss from the fruits during exposure in the aviaries, so overall,
weavers consume more grains that fruits. The lower GUD of insects on the
other hand, may simply imply that the weavers only need to feed on a
small amount of insects for their daily dietary protein requirements
(Karasov & Levey, 1990; Klassing, 1998). Access to water and digestive
constraints may also determine how much of a food item is consumed in
the wild. For example, grain foraging may be restricted by water
availability especially during the dry season (Molokwu et al.,2010), but our ad libitum provision of water throughout this
experiment may have relaxed this constraint and improved the utilization
of grains.
Our observation that males fed more on fruits (and insects) than females
is consistent with the idea that colourful males target carotenoid rich
foods in the wild (Walker et al., 2014). We presume this is
because of the differential need for dietary carotenoids and protein to
be incorporated in moulting feathers since males are more brightly
coloured than females (Borrow & Demey, 2004) and were actively moulting
at the time of the experiment. The observed preference for fruits and
insects by the males in our study is unlikely due to dominance of males
over the females because both sexes fed equally on grains supplied