A lot of people come in for wing trims and ask us all the time about why feathers take so dang long to molt back in!
Birds rely on their primary feathers for flight. So if they molted all of those feathers within a few weeks time, like they do with their head and body, they wouldn’t be able to get away from predators or fly at all.
That is why the wing feathers will typically molt one at a time, when one feather is half way grown out the next will drop out and begin the growth process. So on and so forth you’ll get yourself a brand new wing of flight feathers!!
Here is a good example from Mandy’s wing! See if you can spot the feather that’s still growing in!