Many people mistakenly believe that for religious Jews with milk, unlike with meat, everything is simple: it is sufficient to make sure that it is produced from the kosher animal and a required amount of time as passed after having a meal that contained meat – and that’s it – you can drink it for your pleasure. However, Jews would not be Jews if such important issue would be so easy.
Unlike mammals and fish, it is not mentioned in Tora any formal factors which woulld allow to distinct between kosher birds and non-kosher. Pentateuch only limits by specifying 24 species of birds which are prohibited for Jews to eat. (Vayikra, 11:13-19; Devarim, 14:12-18). What is more, over time Jews had forgotten what are these birds and as a result were forced to limit themselves with a small number of birds concerning which existed a stable kosher tradition.