Put on your thinking caps and attempt to think outside the norm. Why is the spring foliage on most deciduous plants fluorescent green of one shade or another?
What effects do the spring fluorescent green foliage have on the human psyche?
What effects do the fluorescent greens of spring flowers have on the rest of the animal kingdom that has visual contact with it?
Do you think every deciduous plant species has its own unique spring green color?
Do you think its possible that every deciduous plant within a given species has its own unique spring green even though its difference would be very, slight? Example: 50 different individual box elder trees, each one having a spring green slightly different from the others, though the difference would be imperceptible to us.
Could birds that have excellent color vision and may have even sharper vision in the green area of the color spectrum perceive this difference?
Could migrating birds be master perceptors of spring green foliage enough to discern their select habitat niche from the air? Could this perception be sharp enough to pinpoint the unique spring greens of the exact location where they spent the breeding season the year before or the location they were raised in? Could this be found from an aerial approach?
Much research has gone into bird migration, and its believed that migrating birds use the earths magnetic poles and the stars to navigate to the home place, i.e., their unique breeding ground. Night migrants, of course, use the combination of the two methods. However, the magnetic poles and the sun could be used in the daytime, but most birds show up in the spring only when the habitats allow it. That is, only when the plantscape is far enough along in development to allow insect life, which feeds and/or reproduces on the developing plants. This allows plentiful insects as food for the birds.
Birds arrive in waves of millions as spring expands along a timeline from south to north. For example, you would expect bird migrants to appear first in southern Illinois, a week later in central Illinois, etc. Their arrival is contingent on the progression of leaf development stages in the plantscape, which is contingent on warm weather. Arriving too early would be fatal. Every year, bird migrants arrive predictably by given dates if the spring foliage is on schedule. But, spring sometimes arrives late, and if it does, what keeps the birds from fatally over-migrating before the plantscape is ready?
Day migrants would hit the brakes when the appropriate spring greens stop, but what would night migrants do? Could night-migrating birds using the stars and the magnetic poles find an exact breeding location at a precise window of time without using the spring color codes of vegetation? What keeps these birds from hitting the spring green zones at night too early?
Do you believe spring greens are visible at night perceived in another end of the spectrum called infrared? All living things give off heat, and produce infrared light in some degree. Birds that are brave enough to migrate at night must have some night vision. If these same species are flushed from their nests at night, they usually return shortly, and that takes good vision.
Owl eyes are designed to work with very little light, but diurnal birds that migrate at night or are forced into night flight for other reasons may depend somewhat on infrared sight, at least in a minimal sense.
Theres no evidence to substantiate that birds use infrared vision or that spring greens are color codes, but you have to admit they sound appealing. Isnt theory construction fun?