Did a bit of digging on the web and found references in a couple of sources that refer to nectar as serving energy needs of the bees. Also said both nectar and pollen are used to supply nests for the young.
Here is what one article says:
"Similarly to honeybees, Orchard Mason Bees gather nectar in their Ã¢â‚¬Ëœhoney sacÃ¢â‚¬â„¢ while foraging. The nectar is used as energy source and to provision the tubular nest.
Unlike honeybees, Orchard Mason Bees do not have specially modified hind legs called corbicula to store and carry pollen. Instead, pollen is packed underneath rows of stiff hairs called scopa under the abdomen."
This second article is really informative, also mentions favorite food sources.
"Females mate soon after emerging, then begin nesting in 3 to 4 days. The bees forage on a number of different flowers. In wooded areas, they seem to prefer ballhead waterleaf. In urban areas, dandelion and Oregon grape are commonly visited, in addition to cherries and apples."
Many small bees visit our yard. Many look like miniature bumblebees. Are those likely to be Mason bees? We have several dead trees and and old barn with lots of cavities that should provide shelter and nesting sites for these bees. I notice large amounts of activity on the breath of spring and blue berry bushes in early to mid spring. We also have a pretty good crop of dandelions. Our yard back up to a forest area, and that transition of woods to open area probably works to our advantage of attracting many different species here.
I noticed in one article that you can easily build nesting cavities by taking a pine or fir block and drilling nesting chambers in it. I think I'll make a couple this week.
"The native eastern species of Orchard Mason Bee will nest in holes drilled in a wooden block. Untreated 4" x 6" lumber works great. Holes can be drilled in the wood on 3/4 inch centers. They should be 4-8" deep (depending upon the size lumber used), smooth, and a 5/16" diameter hole is important"