Supernatural abilities effecting creatures of the same kind

[Cato Taldinius]

2 Shadow Angels are using their howl ability:

Howl (Su)

Once per day, the shadow angel can produce a shriek of heart rending sorrow and soul chilling fear. All creatures within 100 feet of the shadow angel must succeed a DC 26 Fortitude save or be paralyzed with dread and sadness for 1d4 rounds. The save DC is Charisma-based.

Does one angel's howl effect the other?

[Drejk]

"All creatures" - yes it affects the other shadow angel. If some creatures were excluded from the effect it would be noted in the description.

[deuxhero]

Well firstly it's a third party monster so...

Anyways, I think so. Only with poison is a creature immune to its own species's special ability without otherwise being stated.

The monster's special abilities are pretty weird though aside from that, the text uses various synonyms for fear, but doesn't state what happens to creatures immune to fear.

[Kayerloth]

Personally if they are immune to fear effects, mind-effecting magic or paralysis I'd say they couldn't be effected by the Howl or given its a 3rd party material simply edit the material for clarity and to suit my purposes something I wouldn't hesitate to do for the most part with any material regardless of source if its my campaign anyway (particularly where it concerns a creature).

Also since the Howl always originates from the creature I'd tend to say it is immune to the effects of its own Howl and by extension at minimum immune to the Howl by another Shadow Angel of equal or less HD. But that is strictly how I'd do it.

Edit: I'd probably also say anything that couldn't hear the Howl could not be effected, i.e. give it a sonic descriptor essentially.