I know only that it is not a bird and an insect. I am really interested in from what it is.
That's the gladius (also known as pen) of a cephalopod, probably a squid. The gladius is an internal remnant of the originally external shell of cephalopods.
According to University of California Museum of Paleontology:
Members of the Coleoidea are probably the best known of the Cephalopoda, as this group contains the squids (Teuthoidea) and octopuses (Octopoda) [...] The majority of coleoids are squid species, and most of these animals are torpedo-shaped, fast moving, and have a thin, flexible internal shell called a pen.
And according to the Tree of Life project:
Other cephalopods have other types of shell remnants. The gladius lies within a sac, the shell sac, which secretes it and to which various muscles attach. The gladius has a variety of shapes and thicknesses, is composed mostly of chitin and is located in the dorsal midline and generally extends the full length of the mantle.
Here is one similar to yours:
I concur with the answer of Gerardo Furtado. I sometimes go fishing and this looks exactly like the gladius (Fig. 1) of a loligo vulgaris (Fig. 2). The gladius is a hard internal structure in cephalodopds. In French we call that a "plume", as it has the appearance of a feather.
Fig. 1. The gladius, or squid pen. source: Oceans of Kansas
Fig. 2. loligo vulgaris. source: wikipedia