A budgie’s nose, also known as a cere, can turn brown due to a variety of reasons, including age, gender, and hormonal changes. In young budgies, both males and females have pink or purple ceres. As they mature, the cere of male budgies will typically turn blue, while the cere of female budgies will turn brown or tan.
In some cases, a budgie’s cere may turn brown due to hormonal changes. For example, female budgies that are in breeding condition may have a brown cere. Additionally, budgies that are sick or under stress may also have a brown cere.