The Cornell Lab of Ornithology strongly recommends against using red dye in feeders: "There is no research that proves red dye is safe for hummingbirds, and very compelling anecdotal information from experienced, licensed rehabbers that hummers who have been fed dyed food have higher mortality and suffer tumors of the bill and liver."
Extremely High Dose
The concern about red dye comes not only from possible dangers of the chemical itself, but also from how the birds consume it. The amount of dye is not regulated, and the birds are so small that ounce for ounce they are exposed to levels that far exceed amounts known to be harmful. The Accepted Daily Intake (ADI) for Red #40 approved for human consumption by the World Health Organization is a maximum of 7 mg per kg (0.007 mg/g) of body weight (equivalent to 0.007 mg per g body weight).
Hummingbirds consume 10g of nectar solution per day. This means they ingest 17 times more red dye than the maximum daily limit recommended for humans.
@treeguy .... Is there really any need to be so rude and bolshy ?