I don't use the mod but you could try opening the sh3.sdl file with S3D, about the third page down you should see the section:
Animations.Seagulls.Seagull
just make sure the Min & max Radius are set to 200 & 400, if there is no fault here then check the actual sound files (7 of) Seagull_0.wav (from 0 to 6) in the Sound folder, play them to see that they play ok, they maybe blank!

Hope this helps.