Originally Posted by imFragrance
so the HL is at somewhere like eye level of the bird ?
Horizon Line and Eye Level are synonymous. Eye Level is how high your eyes are from the ground. It's not where the eye is looking, only its elevation off the ground plane. If a 5' person were standing and looking at their feet, the Eye Level would be 5' high, not where their feet are.
So, in the picture you posted the eye level is the camera's height from the ground, which is higher than the bird as we are looking down on it. If the photographer were on the 30th floor when she/he took this picture, the Eye Level would be at the 30th floor on the building across the way in the photo, which is much higher than the photo.
I also agree that you don't necessarily need to know this to make a convincing painting/drawing. But, a extra knowledge never hurts.... much.