pecking order

/P EH1 K IH0 NG AO1 R D ER0/
noun
  1. 1

    The natural hierarchy of social status and dominance occurring in a group of birds.

  2. 2

    The usually informal hierarchy of authority or command, often partial or approximate, as determined by the especially natural propensity for domination of different members of a specific group over each other, such as older brothers and sisters over their younger siblings.

Source: https://en.wiktionary.org/wiki/pecking%20order