Biology Reference
In-Depth Information
Figure 6.
Compensatory feeding in the white-bellied sunbird,
Nectarinia talatala
, feeding on
a broad range of sucrose concentrations. Values are means ± SE for volume consumption in
ml/day (
open squares
) and sucrose consumption in g/day (
solid circles
). At sucrose concentra-
tions below 0.25 M, the volume ingested is not sufficient to maintain energy balance.
(Redrawn from Nicolson & Fleming, 2003a.)
of sunbirds (
Nectarinia talatala)
and hummingbirds (
Selasphorus platycer-
cus
) have been compared across a range of sucrose and equicaloric hexose
solutions (Fleming et al., 2004). Both species preferred hexoses when of-
fered dilute diets (it may be difficult to hydrolyse sucrose under these
conditions), but otherwise showed no significant preference. This contrasts
with previous findings of sucrose preference in hummingbirds (Stiles, 1976;
Martínez del Rio, 1990). Most trials with birds have used 20% w/w sugar
solutions, and preferences can change when the nectars are more dilute (see
also Schondube & Martínez del Rio, 2003). Moreover, when sucrose and
hexose solutions of equal concentration are prepared on a % weight basis,
the sucrose has a 5% higher energy content, so that apparent sucrose prefer-
ence may in fact be a preference for the greater energy value of the sucrose
solutions used. Hummingbirds and frugivorous tanagers are known to be
remarkably sensitive to changes in sugar concentration: they can discrimi-
nate 1% differences at low concentrations (Blem et al., 2000) (Schaefer
et al., 2003). Rufous hummingbirds prefer 65% sucrose over other solutions
