@LazurURH - Thanks for your comment on the matter
As for the Inkscape filters, you're right - they totally slow my computer down. I often try them out, out of curiosity, but in the end I never use them.
The background still isn't there, as you can see, but thanks to you I had another idea. You suggested a paperlike background and I thought I could try to make the bird stand out not by coloring it, but making it into a papercut.
Something like this:
@Brynn - The bird COULD be a young fieldfare but I'm not sure, as I've already returned the book with the photo. (Why would anyone want to ring a fieldfare? It's so common) About visibility of the bird - I guess making it into a papercut somewhat helps (I'll add some shadows when I decide on the background at last); thanks to that I was able to put in the original version, not the vectorized one. Still I need to polish all the rough-wip-edges. Background. Did I mention it? Oh yeah.
This particular piece is really taking ages. That's what happens when you don't know what you want from the start, when you can just alter the main idea in the process if something's obviously wrong.