Data from: Foraging plasticity and physiological adaptations enable hummingbirds to subsist on dilute nectars

Hummingbirds frequently feed on small volumes (< 30 µl) of
sucrose-rich nectars. Climate change is expected to affect both the
abundance and the concentrations of accumulated nectar. Using experimental
feeding trials and field-collected measures of daily energy expenditure
and floral nectar contents, we test the nectar dilutions at which
hummingbirds can no longer meet their daily energy needs. We found across
14 hummingbird species that they are limited in how much they can increase
their feeding rate (compensatory feeding) with decreasing nectar
concentrations: nectar consumption increased until dilutions of 4-6 %
sucrose, where birds fed at a maximum feeding rate (0.70 gNECTAR gBODYMASS
-1 hr-1), after which nectar consumption (and corresponding sucrose
intake) decreased. Integrating lab-tested maximum feeding rate with daily
energy expenditure estimated from free-living hummingbirds, we found most
species could meet daily energy needs while feeding on dilute nectars, but
there is an average dilution threshold (~7 % sucrose). Hummingbirds may
cope with energy deficits caused by variability in resources and
competition with other nectarivores by adjusting their time spent
foraging. Our energy budget models show that to meet average daily
energetic needs, hummingbirds could feed ~2 hours on concentrated nectars,
or an unattainable 19 hours feeding on dilute nectars. We show that
maximum feeding rates pose a physiological cap on hummingbirds’ ability to
use dilute nectars, which has implications for hummingbird survival and
ultimately pollination. Thus, nectars provided by trochilophilous plants
should be more concentrated than this dilution threshold. This mechanistic
understanding may inform future work on the impacts of changes in flower
phenology and nectar quality on hummingbirds.