have a preponderance ofshort wavelength sensing (blue-sensitive) cones and
relatively few long wavelength sensing (red-sensitive)
cones. Other taxa of birds, such as galliformes and
columbiformes, have a much higher percentage of long
wavelength sensing cones (Hart et al., 1999). Hart et al.
(1999) further demonstrate that the evolutionary selection
for color sensitive vision may reflect factors such
as diet, behaviors, and environment (e.g., land vs. water
dwelling). These observations of retinal physiology
make sense in terms of the respective birds’ natural history.
Galliformes, such as chickens and turkeys, utilize
red pigmentation of the skin and feathers as a measure
of developing social hierarchies and mating, whereas,
Mallards (anseriformes) do not contain red pigments
but rather utilize the blue–green plumage during the
reproductive season. Thus, if ducks’ retinas have relatively
more surface area devoted to seeing blue wavelengths,
it is possible under blue lighting that most
of the visualized details that aid in object recognition
are lost. Our study did not investigate the green wavelengths
as our focus was on the 2 spectral extremes,
red and blue; green either alone or in combination with
blue may have either elicit beneficial or further detrimental
results; these possibilities will be the focus of
future studies. Regardless of the proximate cause for
the increased stress in ducks under blue light, the observed
increase in circulating corticosterone may have
impacted carcass parameters.