Supplementary data for: Hummingbird ingestion of low-concentration ethanol within artificial nectar

Both frugivores and nectarivores are potentially exposed to dietary
ethanol produced by fermentative yeasts which metabolize sugars. Some
nectarivorous mammals exhibit preference for low-concentration ethanol
solutions compared to controls of comparable caloric content, but
behavioral responses to ethanol by nectar-feeding birds are unknown. We
investigated dietary preference by Anna's Hummingbirds (Calypte anna)
for ethanol-enhanced sucrose solutions. Via binary-choice experiments,
three male hummingbirds were exposed to sucrose solutions containing 0%,
1%, or 2% ethanol; rates of volitional nectar consumption were measured
over a 3-hour interval. Hummingbirds did not discriminate between 0% and
1% ethanol solutions but exhibited significantly reduced rates of
consumption of a 2% ethanol solution. Opportunistic measurements of
ethanol concentrations within hummingbird feeders registered values
peaking at about 0.05%. Ethanol at low concentrations (i.e., around 1%) is
not aversive to Anna's Hummingbirds and may be characteristic of both
natural and anthropogenic nectars from which they feed. Given high daily
amounts of nectar consumption by hummingbirds, chronic physiological
exposure to ethanol may thus be substantial, although naturally occurring
concentrations within floral nectar are unknown.