Coyotes have been nocturnal for a very long time. It hasn't just started to happen. However coyotes get conditioned into specific behavior. During deer season, any vehicle that starts to slow down and coyotes take off. However, farmers in tractors can often drive very close to coyotes.

You will still see coyotes out during the day, but by the time you see them, they probably heard/saw your vehicle and take off. I still call and kill a lot of daytime coyotes in ND, so they will move during the day as well as the night.
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Korey Kirschenmann
Night Goggles Product Specialist