“And God created great whales, and every living creature that moveth, which the waters brought forth abundantly, after their kind, and every winged fowl after his kind: and God saw that it was good.”
There are quite a number of birds that cannot fly. This sometimes surprises us, but it shouldn’t. We tend to wonder how they “lost” the ability to fly, but, although there are some species that might possibly have lost an ability to fly (as losing such an ability usually involves loss of information, not spontaneous creation), there is no reason to suppose that many have lost an ability. After all, we do not wonder at mammals that fly (i.e., bats), and we accept that these were created on Day Five, whereas most mammals were made on Day Six. In the same way, most flightless birds seem to be perfectly designed the way that they are. Ratite birds, for example, have no keel on their sternum. The keel is what anchors muscles to the wings, to enable flight. But birds like ostriches, rheas, emus and kiwis show no evidence, either in extant species or in the fossil record, to suggest that they ever had a structure. Therefore, they have not evolved into such a state – they were designed like that by God because that is the best design for us.
Other birds are flightless for other reasons. Penguins, for example, do not fly, but they do sort-of fly through water! Again, this requires a particular type of design that could not arise by itself. God designed penguins just perfectly for their habitat and their lives.
Flightless birds do not support evolutionary ideas. God created them as He saw fit.