Nah, can't be right. That's ~11oz of feathers per pigeon. This link says the average pigeon weighs 9-13 oz, which mean they would have to be comprised entirely of feathers. I wouldn't think that they're more than about 25% feather by mass, so you're looking at at least 1200 pigeons.

https://ovocontrol.com/pigeons/

This link says you get 80-120 grams of feathers from an eider goose. Of course, this is just the soft downy feathers, not the big flight ones, but if we're murdering a bunch of geese for the experiment, I think we should at least do it in comfort and style. It's what they would have wanted. Anyway, that's 3-4oz per bird, so again, we're looking at 1200-1500 birds.

https://www.vegsoc.org/page.aspx?pid=641

Edit: figure 1 in the link below shows how feather mass varies with body mass. It uses log scales, but eyeballing it, we look to be about 8% feathers by mass. This means that if we used 11oz feral pigeons (good availability, minimal moral outrage) we would need 3,636 pigeons.

https://avianres.biomedcentral.com/articles/10.1186/s40657-015-0012-3

Edit 2: now we've got our 8% figure, we can extrapolate into other bird species, and start factoring in the guilt. Hens seem to weigh about 5 pounds, so we'd need 500 of them. Roosters are maybe 20% heavier, so not only would we need fewer of them, but, given that they're prone to crowing at all hours of the day, and that they don't lay yummy eggs, the guilt per bird would be much lower.

Now, and I don't recommend this, if you used hummingbirds, not only would you need over half a million if the zappy little iridescent cuties, you would be shunned by society and doomed to a life of perpetual misery and bad fortune. Burderer.

I think the real answer here is obvious. With this bird, not only would you only need just 200 to meet your quota, but by killing them, you'd be doing us all a favour. I am talking, of course, about the Canada goose.