Draw the Clan as a Map
A list of names is not enough, because the risk is relational: the sitter needs to see the bonds. Write each group as its own block — the pair in the big tank, the trio in the second setup — with every gerbil's name, age, colour and one identifying detail that works at arm's length, like a white belly patch or a kinked tail tip. Under each block, one sentence states the rule for that group: these two are brothers and stay together always; this female lives alone since her sister died and must not be given a new companion by anyone but you. If two set-ups sit side by side, say explicitly that gerbils never move between tanks, not even "for a visit."
Ages and Why They Matter to a Sitter
Ages are not trivia here. An elderly gerbil in a clan needs gentler handling and may be the one the others groom most; a youngster introduced recently is still the clan's newest member and the first to check if squabbles start. Put an age beside every name, and flag the very old and very young. If one gerbil is on a vet's watch list or needs a daily once-over, the age column is where a sitter will connect that instruction to the right animal instead of the similar-looking brother.
The Introduction History, in Plain Words
Write down how the current clans came to be: who was born to whom, who was introduced as a pup, and whether a split-cage introduction was used and how long it took. Most importantly, record failures. If two gerbils were tried together and fought, name them and say the pairing is permanently off the table. Sitters improvise kindly — a lone gerbil looks sad, a spare tank looks empty — and the only thing standing between that kindness and a vet emergency is your written history saying these two already settled this question with their teeth.
Normal Clan Behaviour, So Nothing Is Misread
Describe what the sitter will actually see: the whole clan asleep in one heap, thumping at strange noises, scent-marking the tank glass, boxing play-fights between youngsters that end in grooming. Then describe the real warning signs in contrast — chasing that does not stop, a gerbil sleeping alone who always slept in the pile, blood, or one animal suddenly guarding the food. Declanning can begin quietly in an established group, and the sitter who knows the clan's normal is the one who will phone you at the right moment rather than after a fight.
Putting the Notes in the Sitter's Hands
Keep the clan sheet with the tanks, read it through with the sitter once before you leave, and make the never-separate rules the first thing on the page rather than the last. A KinsLe Care Pass carries exactly this kind of written-down clan knowledge to a sitter as temporary, clear access to each pet's routine and key details — so the bonds, ages and introduction rules you recorded are in their hands at the tank, not in a message thread they have to scroll for.