During the morning (8:30 AM DST) on a bright summer day in Chapel Hill, NC, USA my garage doors were open and four ceiling fixtures, each with four five-foot fluorescent bulbs behind plastic diffusers, were on. After a few minutes a ruby-throated hummingbird (Archilochus colubris) arrived, actively pushing his beak around the upper portion of the fixtures. The hummingbird calls, usually faint and squeaky, were intense, prolonged, and seemed through my anthropomorphic filter to be alarmed, agitated or ecstatic.
This continued for an hour until the lights were turned off; the hummingbird almost immediately flew from the garage (which faces 53 degrees NE) to the back yard, where a hummingbird feeder and butterfly bushes (Purple Buddleia) reside.
[I realize this reads like an original report from an eighteenth century English clergyman (except for the part about the electric lights).]
A Google search returned a small number of reports from birders describing similar incidents, and I was interested in the mechanism.
Birds have a retinal cone visual receptor for ultraviolet (UV) light, peaking at 370 nm. Two review papers in the vision literature are of interest (Goldsmith, 1994 (no relation)); and Bennett and Cuthill, 1994). Many bird species, insects (e.g., bees), and rare mammals (some rodents) can see in the UV spectrum. UV Light can be phototaxic for bees. Functions for UV light for birds fit into three main categories: 1) Orientation, using atmospherically scattered polarized UV light, suggesting a role in short and long migrations; 2) Foraging, due to portions of plants reflecting UV light; and 3) Detecting mates. Mating with a large fluorescent light seems a heroic task for a hummingbird; perhaps this explains the squealing.
More remarkable to me was that when the light was turned off the bird returned almost immediately to its ambient environment.
The amateur backyard biologist morphed into those with special scientific interests, e.g., groups of birders collecting data for activities in the Audubon Christmas bird count, and similar citizen-scientists who are participating in scientific experiments through crowd-sourcing.
This is a call for citizen-scientists to share their experiences with birds, especially hummingbirds, who may be attracted to intense light sources so that we may all learn together. Please report?
Are all bird species attracted to lights?
Type of light and intensity of light (e.g., size, watts).
I look forward to your comments. Data will be compiled and shared in this space.
Goldsmith, TH (1994) Ultraviolet receptors and color vision: Evolutionary implications and a dissonance of paradigms. Vision Res 34: 1479-1487
Bennett, ATD and Cuthill, LC (1994) Ultraviolet Vision in Birds: What is its Function. Vision Res. 34:1471-78