A research team led by Hiroyoshi Higuchi, a professor of biological conservation at the University of Tokyo, has discovered that crows have the ability to see into transparent garbage bags when they scavenge for food.
It is already known that crows use their eyes when hunting for food, but the team believes it has systematically verified that crows are capable of processing visual stimuli. The group presented the results of the research to the Ornithological Society of Japan at a recent meeting in Tokyo.
The team placed meat at different times into one of three garbage bags — transparent, semitransparent and opaque — and observed how some 10 crows on a 2-meter perch in a large cage looked for the food, repeating the test about 80 times.
In most cases, the crows correctly spotted food within 30 seconds if the meat was inside the transparent garbage bag, the team said. But if the meat was in the opaque bag, about 30 percent of the crows did not leave the perch at all and those that did chose either the transparent or semitransparent bags without meat.
If a piece of meat was put in the semitransparent bag, the crows correctly selected it only if the meat’s shadow was visible, the team said, noting that the rate of correct selection dropped sharply if not.
The team also tested whether crows can detect ultraviolet radiation by putting a boiled egg and a piece of pork in one transparent bag, both of which reflect ultraviolet light, and a plastic food sample in another transparent bag.
As most of crows picked the bag with the real food, the team figures crows can also sense ultraviolet light. Team members said they will continue their research.
Team member Emiko Morishita believes using opaque bags will lead to fewer crows ripping up trash sites while scavenging for food.
She added, however, that once a crow decides that there is food inside a bag, it does not matter whether the bag is opaque or not.
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