In extreme situations of deprivation in the wild, birds would be a handy source of the badly needed sustenance to supply the body with proteins and energy to keep going. An easy method to trap them would involve putting a teaspoonful of flour on the ground. Them get a stick and tie it with a long string and place the stick on the ground. On top of the stick, a heavy container like a basin is placed. When birds come to eat the flour, just pull the stick and trap the birds inside. Extracting them should not be hard with a little imagination.