I'm of the opinion that the best feathers for making kulmusim come from the first five feathers on either wing of the wild Canada goose which have been naturally molted from a mature bird. They're strong, have much longer barrels than turkey quills, need much less resharpening and one such quill, properly tempered, can last for months of full-time writing. These quills do however require a much lighter touch than say turkey quills.
Next best, I think is the Toulouse goose. These birds often reach 25 lbs or more and produce very large feathers. Because they're raised in captivity their feathers seem to be not as strong as those of birds which fly. Nonetheless, their quills are highly desirable and make fine, long wearing pens.
The average white domestic goose has potential, but seldom is allowed to reach a size, or an age where it's quills are large, or hard enough.
Most common of all for use as kulmulsim are the feathers of the turkey, mostly white domestic, but increasingly also those of the wild turkey.
Turkey feathers are good, but stiff, very much like writing with a stick. However, if you cut the shoulder back and leave a good long nib, they're very serviceable particularly when a large ksav is needed, for example when writing the aseres. These quills are also softer, even when tempered, and require frequent resharpening, say every ten to twelve lines. The usable section of the barrel is also quite short making each feather somewhat short lived. I've noticed many people tend to hold them with a grip of iron as though they might otherwise escape and consequently to press very hard on them when writing. It seems to me that such a tight grip would swiftly lead to hand cramps and the onset of various tendon related conditions.
I have a number of Lubavitcher friends who hold the Turkey is not a kosher species and that therefore its quills should not be used for writing STAM. I think this is a minority opinion though.
Until this week, I'd never actually thought of venturing beyond the traditional goose, or turkey quill for making kulmusim. Recently however, some well-meaning individual sent me an enormous box of some 6 dozen peacock wing feathers, thinking I could use them in my work. They are some sixteen inches long and look like they could make very good kulmusim.
I am aware that in a sort of hypothetical sense the peacock is kosher at least according to Rashi and the OU. However, others hold that it is completely treif. Does anyone have any clear information about the status of the peacock?
To complicate matters, at the bottom of the box were some four dozen, iridescent blue macaw feathers.
I suspect that because so few people have actually entertained the idea of eating a parrot that few rabbis have felt the need to pasken on the kashrus of the genus psittacidae. Although I like experiments, I'd prefer to keep them solidly within bounds of the halakha. My assumption is that macaw feathers are better suited for Purim costumes than kulmusim, but would anyone happen to know whether they are actually considered treif, or kosher?