I’ve always thought [name]Peregrine[/name] was rather gorgeous for a boy, and I do make the connection to the bird but I think it’s a really majestic connotation. I think it goes really well with [name]Caspian[/name], Zephan and [name]Eve[/name] (lovely set!). [name]Quillon[/name]'s interesting (though I prefer [name]Quillan[/name]), but I think [name]Peregrine[/name]‘s nicer. I agree about [name]Percival[/name]; I love [name]Hugo[/name], and don’t see it as gruff necessarily, but I can’t really see it with your other childrens’ names.
In short, I think [name]Peregrine[/name]'s a great choice, especially if you con’t have a problem with unusual names.
[name]Just[/name] noticed, [name]Peregrine[/name] and [name]Quillon[/name] both relate to bird ([name]Peregrine[/name] being a bird of prey, and [name]Quillon[/name] containing “quill”). For what it’s worth, you might like [name]Wren[/name], [name]Altair[/name], [name]Phoenix[/name], [name]Vireo[/name], Rook, Condor, [name]Heron[/name], [name]Sparrow[/name], [name]Efron[/name], Avocet, Swift, [name]Finch[/name], Kestrel, [name]Fowler[/name], [name]Talon[/name] or [name]Weaver[/name]? All of which relate to birds in some way. I also thing the following would go well with [name]Caspian[/name], Zephan and [name]Eve[/name] - Propsero, [name]Nemo[/name], [name]Olivier[/name], [name]Prospero[/name], [name]Orrin[/name], [name]Sherlock[/name], [name]Ezra[/name], [name]Atticus[/name], [name]Merlin[/name], [name]Roan[/name], [name]Cesar[/name], [name]Indiana[/name], [name]Sullivan[/name], [name]Cornelius[/name] or Aslan. I realise you’re probably nearing the final stages of naming now and aren’t looking for suggestions, but just thought I’d give you something to ponder 
EDIT: Having said that, I do hate the nicknames Perry and Reg. That’s just me though. I prefer Pen(n) or Rin(n), but those are more of a stretch.