To keep their centre of balance when walking birds have evolved to have their equivalent of our thigh held permanently close to the body. The leg does not start to extend out from the body until after the knee joint which is never seen**. The backward bending leg joint that you see in bird's legs when they are walking is the equivalent of our ankle. A bird's foot is the equivalent of the tips of our toes. Thus the part of a bird's leg that looks like its shin is actually the equivalent of the arch of our foot.
**As we have seen, Seagull knees are visible.
As for the expression Bee's knees ~
Somewhere else I found this: Bees do have segmented legs, consisting of parts called a coax, a trochanter, a femur, a tibia and a tarsus, the joints between which must be considered to be 'knees'.
This is one of the dozy bees I've seen stumbling about after bumbling around the purple crocus pollen.
My first open daffodil was looking prettier than ever today:
I found my first Grape Hyacinth of the year:
and sweet Violets:
More buds opening on the Rhodo:
Shoots coming up from a Peony I planted last fall:
and two birds in a tree next door ~ I think, because of the pinkish hue on the bird at the right, these two might be a pair of House Finch.
All photos taken today were from my front and back garden, as I am not ready to wander far as yet.
After checking Nic's photos and video link, I see that a Heron sports visible knees too! If you haven't already, please check out his remarkable photos.