The burrow is part of the home
When evaluating a gerbil setup, ask what happens below the surface as well as on it. Substrate depth, secure containment and the position of heavier equipment all belong in the housing discussion. Read current guidance and obtain species-aware advice about construction and stability. A little decorative bedding under an attractive tunnel does not necessarily provide a usable burrowing environment. Avoid changing the habitat simply to make the animals easier to photograph.
Stable companionship needs a careful plan
Gerbils are social, but that does not make a new animal an automatic addition to an established group. Ask a reputable rescue or species-experienced professional about the existing group and any proposed change. This site does not offer a bonding protocol. Record which animals belong together in a sitter handover and make clear that a helper should not improvise introductions or move animals between groups.
Give appropriate materials a clear job
Suitable plain cardboard can support shredding and investigation; it is not a reason to add every packaging material you have. Check for ink, coatings, glue, staples and damage, and read the full welfare guidance on suitable nesting materials. Use the enrichment shelf as a starting prompt, then assess the particular material and animal. Remove anything that becomes unsafe rather than trying to complete a planned activity.
Learn what you can observe
Gerbils can be active at different points through day and night. A short observation is a sample, not a complete account of their routine. Write the time and context with anything you notice. If the animals are resting out of sight, let them rest; absence from the visible surface is not an invitation to dismantle the burrow. Concerns about wellbeing belong with a vet, not a social-media interpretation of one clip.