General Question on Tying Supplies

Obviously, the bird its from.

Also, the color, texture, and stems. In short, they're two totally different materials, similar only in name, the part of feather they're from, and how they're used (usually wrapped about the shank as a body material, occasionally, bound by one end, as on some streamers).

Also, peacock herl quills/stems are stripped and used as bodies for dry flies like the quill gordon. I'm not aware of a similar use for ostrich herl...I'd think the quills are unsuitable for this.

For cheap ostrich herl, check out craft stores.

It would depend on what you are using them for. As an overwing, I would think either would work fine. Ostrich has a lot more movement than Peacock and comes in a lot more colors. If you are tying something that calls for a Ostrich herl tail then Peacock wouldn't give you as much movement. If you are tying something that call for Peacock herl to be wound around the hook the I suppose you could use Ostrich as a substitute although in this application I wouldn't think it would have the same appeal to fish as Peacock which tends to be darker and multi-colored with a little sparkle.