- Incomplete
digestion by the nestlings leaves some residual food in their fecal
sacs, providing some
nutrition for the adult
- In one study, fecal
sacs provided as much as 10% of the daily requirements of
adult White-crowned
Sparrows (Morton 1979)
- Normally the fecal
sacs are eaten when the nestlings are young and carried away
when they get older,
as the size of fecal sacs increased
- This could be because there is less nutritional value or
energy content as the
nestlings digestive
system becomes more efficient
- Or, that the cost
of eating so many increases with the volume and number eaten
-
- Energy density of
fecal sacs remain constant with water content about 75%
-
- Food for Thought?
Recycling nutrients in this way maybe an important time and
energy-sparing habit as
opposed to being beneficial energy content