Quite a few of them have a substantial amount of HP stat.
Drifblim, Lugia, Yveltal, Ho-oh, Rayquaza, Noctowl, Braviary, Honchkrow, Shaymin-Sky, Gyarados, Salamence, Dragonite,Tropius all have above 100 base stats in HP, which is considered good and in some cases, impressive.
Also, flying types have ranked seventh in all types of Pokemon in terms of HP, which is pretty decent.
All this means that while many flying types do have a abysmal HP stat, quite a few do have a (deceptively) good amount of HP.
But not many of the bird Pokemon have a good HP stat, mostly because they have hollow bones and relatively shorter lifespans compared to other animals.
Flying types doesn't always mean bird Pokemon, Pokemon like Gyarados, Dragonite and Salamence are anything but bird Pokemon.
Hope I helped!