Below the line are three sets of images, each comparing a sketch to a final print(s):
The second comparison is of the Omaos, also for the Living Endemic Birds of Hawaii series. Again it would seem that the sketch very accurately laid out the birds for the final painting, but not the foliage, which is not really sketched at all.
Finally, the third compoarison is for the extinct Nukupu'u. It seems there is a pattern in that again the sketch is quite accurately rendered in the painting (middle image), but the foliage has been changed. The painting of the Nukupu'u with an artifact (right image) shows a similarly posed bird, though obviously not the close match of the left and middle imnages.
Bottom line: Marian appears to use sketches to get a general layout of bird paintings she will render, with an emphasis on the birds; the foliage seems to either be missing from her sketches, or changed significantly in her final work.
Akiapola'au
Omao
Nukupu'u