In my opinion there are different definitions available here.
There is quantity of light vs quality of light.
Quality of light is like the different between a soft box and a parabolic. The soft box has a softer quality of light than the parabolic. The sun is like the parabolic, harsh and direct. The softbox is like the overcast day. Large diffused light source.
The quantity of light or the intensity of light is how much light there is. 400ws is more than 200ws. The bright sun is more intense than an overcast day.
These two factors do not affect the length of a shadow just the deepness( if you will) or darkness of the shadow. That is why on an overcast day there are almost no shadows visible. They are still there but the softness of the lightsource has wrapped around the subject and almost obliterated them.
The only thing that affects the length of the shadow is the angle of the light source in relation to the subject.
As for the rodent, my take on it was not on how long the shadow was, but whether the was a shadow at all, that determined the length of time until spring.