This is irrelevant, because we don't know how many "some" is. If this were stronger, it might even weaken the argument by suggesting that health isn't a concern for female grouse.

Did the illness or the treatment have any effect on the male grouse's air sacs? We don't know, so this has no effect on the argument.

Are these males still chosen by females? Is there another way that the grouse demonstrate their health? This isn't enough information to do anything to the argument.

This supports the hypothesis by affirming the scientists' assumption that there's a way for female grouse to determine males' health based on their air sacs—simply by looking for parasites.

Without knowing whether this strain of malaria has any effect on the male grouse's air sacs, this just isn't relevant to the argument.