Leafcutting bees gather pollen, carrying it on the abdomen or face, (unlike honey bees, which carry pollen in a sort of basket on their legs). The dense pollen-carrying hairs are called a scopa, from the Latin for broom.
The large yellow flowers in these images are Entire-leaved Gumweed (Grindelia integrifolia). The bees in these photos are remarkable for the pollen covered brush of hairs on the face.
The bee shown in image 5, has Nootka rose pollen on the abdominal scopa and another species of pollen on the back.
Megachilids lay eggs in holes they dig in the ground. Some species separate egg chambers with small leaf circles. The movie (6) shows a megachilid digging. Also see Leafcutter and Cuckoo in the menu.
I don’t know if this is true of many megachilids, but on a few occasions, I’ve been able to follow a single megachilid from flower to flower for many minutes, sometimes following it by its distinctive buzz.