Hamster adolescence: nipping, territory and why dwarf pairs break up

Quick answer

The friendly, sleepy hamster you brought home changes when it matures, and the change catches almost every new owner out. It becomes more nocturnal, more territorial about its nest and its hoard, more likely to object when a hand appears from above, and in some cases it starts to bite.

That is normal development rather than lost taming, and it is not something the hamster forgets and needs reminding of. What has changed is the animal's priorities, and the handling has to change with them.

The second half of this is the one that costs lives. Dwarf hamsters that lived happily together as juveniles frequently turn on each other at maturity, usually at night, usually silently. Separating at the first warning sign is the whole intervention.

An adult hamster comes to a still, low, open hand. It defends itself against a hand that reaches down over it.

• Never wake a sleeping hamster to handle it. Almost all defensive biting starts there.
• Syrian hamsters must live alone from a young age. Housing two together will end badly.
• Dwarf pairs that were fine as juveniles can fight at maturity. Separate at the first sign, permanently.
• Wash your hands before handling. A hand that smells of food gets bitten by an animal with poor eyesight.
• Sudden aggression in a previously settled adult is a medical question, not a behavioural one.

:::danger
Never throw, flick or shake a hamster that has bitten you.

The reflex is almost impossible to suppress and it kills hamsters. A dropped hamster falls a long way relative to its size onto a hard floor, and head injuries, spinal injuries and fractures follow. If a hamster latches on, lower your hand to a flat surface and stay still. It will let go within seconds once it is not suspended in the air. Pulling your hand away tears its teeth through the skin and makes the wound far worse.
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Decide in 60 seconds

What actually changes at maturity

Hamsters go from dependent juvenile to reproductively mature adult very quickly. Everything that follows is downstream of that.

Territory. An adult hamster has a nest, a hoard and a set of routes, and it defends them. A hand entering the cage is entering territory. Cleaning the whole cage at once removes every scent marker the animal has placed and it will spend the following nights re-establishing them, often frantically.

Scent marking. Syrians have flank glands, visible as dark patches on the hips, which become prominent and are rubbed against surfaces. Dwarf species have a ventral gland on the belly. Increased marking is a sign of maturity, not of a skin problem.

Nocturnality. Juvenile hamsters potter about at odd hours. Adults consolidate their activity into the night, so daytime handling attempts increasingly mean waking a sleeping animal.

Hoarding. Pouching and caching intensify. A hamster with full cheek pouches is not in a mood to be handled, and reaching into a hoard is one of the more reliable ways to get bitten.

The oestrous cycle. Females come into season every few days. It is accompanied by a distinct smell and sometimes a small amount of discharge, both of which are normal. Owners frequently present this as an infection.

A related point worth knowing: a female in oestrus who is stroked along the back may suddenly freeze with her back dipped and her tail raised, completely rigid. That is the receptive posture. It is not a seizure and it is not paralysis, and it resolves on its own.

Independence. Adult hamsters simply want to be handled less than juveniles do. That is not a deterioration in the relationship, and the goal shifts from cuddling to cooperative, hamster-initiated contact.

The dwarf pair problem

This is the part of hamster adolescence that has real consequences.

Syrian hamsters are strictly solitary. Two Syrians housed together will fight, and the fight is frequently fatal. There is no enclosure size and no introduction technique that changes this. If you have two Syrians in one cage, separate them today.

Dwarf species are different but not safe. Roborovski, winter white and Campbell's hamsters can live in same-sex pairs or small groups, and many do so successfully for life. Many others do not. The failure point is almost always maturity, when a hierarchy has to be established in a space that does not allow the loser to leave.

The fight usually happens at night. It is often silent. Owners find the outcome in the morning.

Warning signs that come before the fight:

One hamster sleeping outside the nest, or in a separate nest.

One hamster monopolising the wheel, the food bowl or the sand bath while the other waits.

Chasing, pinning, or one animal repeatedly climbing over the other.

Squeaking heard at night.

One hamster losing weight.

Fur loss or small wounds, particularly on the rump, the tail base or the genital area.

One hamster becoming reluctant to come out at all.

If you see any of those, separate them permanently. Not for a cooling-off period, and not into a divided cage. Hamsters that have fought do not reconcile, and each subsequent attempt is more dangerous than the last.

If you keep dwarfs in a pair, give them a far larger enclosure than the minimum, with duplicated everything: two wheels, two water sources, several food stations scattered rather than one bowl, multiple hides with more than one entrance each, and deep bedding they can build separate burrow systems in. Have a second complete setup ready before you need it, because the day you need it you will need it immediately.

Duplicated resources and space to avoid each other is the only thing that keeps a dwarf pair working, and it stops working anyway in many cases.

Rebuilding handling with an adult hamster

The aim is a hamster that chooses to come to you. Nothing about that requires catching it.

Wash your hands. With unscented soap, before every session. Hamsters see poorly and identify by smell. A hand carrying the scent of your dinner is food.

Work at the hamster's schedule. Evening, when it has woken on its own and come out. Never open the nest to get it.

Sit down, and get low. A hand descending from above is what a bird of prey looks like. Place your hand flat on the floor of the enclosure or on a low surface and leave it there.

Let it come. Put a piece of food on your open palm and wait. Do not close your hand, do not follow the hamster, do not lift while it is eating.

Scoop with two hands from below once it will step on, cupping rather than gripping. Keep your hands low over a soft surface at all times.

Use a tube or a cup for moving it. Most hamsters walk into a cardboard tube or a mug readily, and it removes the catching problem entirely.

Keep sessions short. A few minutes. Finish while it is still going well.

Do not chase, corner or grab. Every one of those teaches the hamster that hands are a threat, which is the belief you are trying to change.

Give it somewhere to be handled. A large empty box or a bathtub with towels down, so out-of-cage time is not a chase around a room.

If a hamster is genuinely fearful rather than simply mature, go back to hand-feeding through the bars for a week or two before attempting contact at all.

When aggression is medical

An adult hamster that was settled and has become aggressive over days or weeks is a different problem from an adolescent finding its territory.

Pain. Dental overgrowth, an abscess, a tumour, a foot injury or a spinal problem all make an animal defensive. Handling hurts, so it objects to handling.

Ear or neurological disease. A hamster with a head tilt, circling, or loss of balance may lash out because it cannot orient.

Vision loss. Older hamsters and some with eye disease startle more easily because they see the hand later.

Torpor. In a cool room a hamster may enter a torpid state, becoming cold, stiff and slow to rouse. It looks alarming and is often mistaken for death. Warm the room gradually rather than the animal directly, do not shake it, and call the vet. A hamster roused abruptly from torpor is disoriented and may bite.

Full pouches. A hamster with impacted or infected cheek pouches is uncomfortable and defensive, and pouch impaction needs veterinary attention.

Pregnancy. An unexpectedly pregnant female becomes markedly defensive and should be left alone. Do not disturb a nest with pups.

Any hamster with a sudden change in temperament should be looked at rather than retrained.

A relaxed hamster grooms, stretches, and moves at its own pace. A tense one holds still with its weight back and its whiskers forward.

The problems that are not behavioural at all

A large share of what owners describe as adolescent problems are enclosure problems that happen to become obvious when the animal matures and becomes more active.

Bar chewing. Persistent, rhythmic bar chewing is a stereotypy. It is driven by an enclosure that is too small, too shallow or too plain, and it does not respond to bitter sprays or to being told off. More floor space, much deeper bedding, and things to do are the treatment.

Repetitive route running and backflipping. The same category.

Frantic digging in one corner. Usually not enough bedding depth to make a real burrow.

Escaping. An adult hamster tests the whole perimeter. Check lid clips, gaps around cable entries and the fit of any door every week.

Waking the household. A wheel with a bad bearing, a wheel that is too small so the back is arched, or a wheel mounted on cage bars transmitting sound. Fix the wheel rather than moving the hamster somewhere it will be disturbed during the day.

Getting these right removes a great deal of what looks like temperament.

What never to do

Do not house two Syrians together.

Do not wake a hamster to handle it.

Do not reach down over a hamster from above.

Do not throw, flick or shake a hamster that has bitten.

Do not pull your hand away from a hamster that has latched on.

Do not clean the entire enclosure at once. Keep some used bedding and nesting material so the scent map survives.

Do not reintroduce hamsters that have fought.

Do not put a hamster in a ball. They are stressful, poorly ventilated, cause foot and tail injuries, and the hamster cannot see where it is going.

Do not treat sudden aggression in a settled adult as a training problem.

When to get help

Immediately for a hamster that has been dropped or thrown, for wounds after a fight, for a hamster that is cold and unresponsive, and for a hamster with a head tilt or that is circling.

Same day for pouches that appear stuck full or swollen, for a lump, for blood, for laboured breathing, or for a sudden change in temperament in a previously settled adult.

Promptly for weight loss in either animal of a pair, for hair loss with scabbing, for a female with an abnormal discharge, and for persistent bar chewing that has not improved after the enclosure was made larger and deeper.

The realistic goal with an adult hamster: it comes out on its own, walks onto your hand, and leaves when it has had enough.

Bring the weekly weights for each animal, the species, the enclosure dimensions and bedding depth, how and when you handle, whether the animals are housed together, and a description of exactly when the biting happens. In hamsters, the circumstances of the bite usually explain it entirely.