Gerbil Behaviour
Thumping
There are two reasons gerbils thump: to warn other gerbils in their colony of danger or in sexual excitement. When alarmed or excited, gerbils will make a rhythmic thumping sound with their hind feet. Usually only one gerbil in an enclosure will do this while the others perk up their ears and listen. It's really amusing when you have several tanks of gerbils and one gerbil will thump an alarm, and another in another aquarium will thump back! It's their way of communicating danger. Gerbils produce this thump by stomping both their feet on the ground. It is amazing how loud and how long they can thump. While we may not be able to differentiate between the two types of thumps, gerbils can certainly tell the difference. While an alarm thump may produce a chorus of warning thumps, a mating thumps will often go ignored.
Grooming
Grooming is not only a way to keeps clean, but also it is a vital part of the social infrastructure of gerbils. Pairs, parents, and pups will spend a lot of time each day grooming each other. Regular daily grooming is a sign that all is well in the family group.
Fighting
There are two distinct types of fighting: play fighting, and serious fighting. Play fighting goes on frequently among gerbils, especially pups. It is what we always called 'roughhousing'. They will pounce and jump on each other. Then give a wild chase around the tank. In a gerbil-boxing match they will stand on their hind legs and hit at each other. (Much the way you may have seen kangaroos box.) Gerbils live in small family groups in the wild. There is one dominant pair that mates, and a number of their older offspring that help care for the young. When one of the subordinate gerbils is ready to start their own family they will move on. When kept in captivity gerbils cannot move on. They are forced to live as we, their humans, see fit. Much fighting can be avoided by following a few rules. Always introduce two strange gerbils using the split cage method. (details found under "Split Cage Introductions"). Young pups, sexually mature pairs, and an older male and young pup clan most easily.
Never keep more than two adult females together
Never keep more than four adult males together, though some have success with up to seven
Never, ever breed more than one female in a single tank
There are a few warning signs that trouble is brewing. Your gerbil may lose weight, have bit marks on their head or rump and tail, and most seriously of all stop sleeping in the nest. If you see these signs pressure may be building, and a fight imminent. One way to prevent gerbils from fighting is to keep the tank simple, with only open structures and with only one logical, enclosed box to nest in. When gerbils do fight, they are very violent and often fight to the death. Once blood has been drawn, reconciliation is unlikely.
Marking
If you look at your gerbil's stomach you will see a small patch of bearskin; this is their scent gland. It produces an oily secretion that they use to mark their territory. They will mark everything that is in their territory, as well as, family members. This is done by rubbing their stomach or mounting the object or other gerbil.
Digging Madly In The Corner
A lot of people mistake gerbils' habit of digging in the corner of their cages as an urge to get out. It isn't. This is known as "stereotyped digging" and is caused by the gerbils' natural instinct to burrow. It is perfectly normal.
Escapes
Gerbils, being the mad geniuses they are, are sometimes very good at escaping. It is vital that you have a lid on your aquarium and make sure there is no way your gerbils can escape. If they do escape, seal of all exits to every room in your home, put the cats/dogs out or in a small room (that you're SURE the gerbil isn't in!) and start looking. Escapees are not likely to travel far from their home, so start in the room where their tank is kept. Slowly move around the room; looking under and behind the furniture or in the back corner of the nearest closet. Once you have found them sit down quietly and wait for them to come out. They usually can't resist investigating. If they are very friendly, confident, and recognize you as the source of good food they may come near enough that you can carefully scoop them up. Often a gerbil will come right up to their tank; if it is placed on the floor, especially pups.
Keep a 1 - 2 foot section of PVC piping handy. Lay it on the floor near where they are hiding. Sit back a ways and be very quiet. Whey the gerbil investigates the PVC pipe quickly drop a towel over it; blocking both exits. Quickly, but carefully put your hands over the two ends. (You will only have a few seconds.) A shoebox with a small hole in one side can often work, too.
If you absolutely can't get your gerbil out of hiding, or can't find it, set out a number of sunflower seeds on the floor along with a dish of water in that room (or in each room if you can't find them). Count the number of seeds, and check back later. Often you'll find the husks of shells left over, which means the gerbil has been there. You might be able to set a high-sided trap with ramps leading up to the side, and a towel to climb down (the weigh of the gerbil should pull it into the trap). The idea is that the gerbil can get into it but not climb out.