There seems to be a special habit of Barnacle geese (Branta leucopsis) when rearing the offspring: one often observes a few adult animals looking after the hatchlings and fledgelings; several other flocks are separate and consist exclusively of adults like the one shown here
<a href="//commons.wikimedia.org/wiki/User:AWeith" title="User:AWeith">Andreas Weith</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>