Today we are going to take a deep dive into the secret world of the dumbo rat, covering everything from history to genes and lifespan to health issues. We’ll explain why dumbos are dumbos and the specific ways the genetic mutation impacts the rat.
We’ll also lay some dumbo myths to rest and offer a definitive answer as to how dumbos differ from top eared rats. So let’s begin by discovering where the dumbos that we live with today actually came from.
The History of the Dumbo Rat
The dumbo rat is thought to have originated as a spontaneous mutation within the pet rat population in the USA. Sources vary as to the exact details but a breeder in North West America seems most likely.
The American Fancy Rat and Mouse Association (AFRMA) records this as happening in 1991. It is extremely likely that all of the dumbo rats around the world today are descended from this one individual.
Making More Dumbos
In keeping with breeding protocols for gene testing, the dumbo would then have been bred to a top eared rat. This mating would have resulted in a full litter of top eared babies, as we now know that a recessive gene causes the mutation.
All babies in the litter would have carried the dumbo gene (now called dmbo – or du in the UK fancy). It’s likely that at least one baby was then bred back to the dumbo parent – we don’t know whether this was the mother or the father – to produce more dumbos.
Being a recessive gene, both parents need to at least carry the gene to produce dumbos in the litter. Two siblings from this first litter may also have been bred together to produce more dumbos.
Why Dumbo x Dumbo May Not Be As Good As It Sounds!
A top eared carrier mated to a top eared carrier would be expected to produce 25% dumbo babies. Where a top eared carrier is mated to a dumbo the litter would be 50% dumbo, and two dumbos mated together will produce an all dumbo litter.
Of course, these are statistical probabilities and the actual outcome might be very different in practice, except in the dumbo x dumbo mating, which always produces 100% dumbos. However, mating dumbo to dumbo is not usually the best way to produce great dumbos!
This is because the genetic factors involved cause a reduction in the growth of the eye in late gestation. This creates a tendency in the variety towards having small eyes, but it can be overcome by regular crossing back to top eared rats with good eye size.
When Did Dumbos Reach Other Countries?
Dumbos were first exported to the UK in May of 1999, shortly after they were standardized for exhibition by the AFRMA. After initial suspicion within the UK fancy about other possible effects of the mutation beyond ear position, they have been widely accepted throughout the UK and Europe.
What Is a Dumbo Rat?
A dumbo rat is a variation of the standard top eared Norway rat (rattus norvegicus). Dumbos are essentially standard rats who have a genetic mutation (dmbo) on chromosome 14, which affects a number of physical characteristics:
- Ear placement – ears are displaced from the top to the side of the head.
- Ear shape and size – shape is rounded, almost circular and size is often somewhat larger than the top eared equivalent.
- Eye size – research has noted reduced growth of the eye during the later stages of gestation (achieving around 86% of normal size). If dumbo x dumbo matings are repeated over a number of generations this effect can produce extremely small eye size in the offspring.
- Facial bones – shortening of the cheekbone, micrognathia (undersized jaw) and microstomia (small mouth). These effects are also exaggerated when dumbos are continuously bred to dumbos.
Genetic analysis has revealed that the gene dmbo (commonly called ‘du’ in the UK) is likely to be a deletion mutation, that is, a mutation where genetic material is deleted from the normal sequence.
Researchers have concluded that the rat dumbo phenotype (the way the dumbo rat looks) is probably the result of the lack of an enhancer that regulates the Hmx1 gene – a gene that itself regulates the development of craniofacial (skull and face) structures.
How Long Does a Dumbo Rat Live?
Lifespan is unaffected by the dumbo mutation and a dumbo’s average life expectancy is the same as a top eared rat’s life expectancy – around 2 years.
The things that are more likely to affect lifespan are the quality of the breeding line, diet, exercise, feeding ad-lib, some coat deletion genes like blue, the quality of veterinary care and so on.
Good Breeding – The Key to Keeping Dumbos Healthy
Dumbo rats need to be bred thoughtfully and often crossed back to top eared rats to prevent problems arising from the cumulative effects of the gene.
With this caveat, the physical changes that affect dumbo rats are usually minor and not thought to cause unwanted symptoms. Reduced eye size can be limited by crossing back to top eared rats and selectively breeding from dumbos with good eye size.
Equally – with good breeding practices – the facial bones are rarely shortened enough to cause the rat any problems (like malocclusion where the teeth don’t connect).
Sadly, many pet rats are bred in rodent farms where this doesn’t always happen and dumbos do appear with tiny eyes and problems arising from their skull shape.
Is a Dumbo Physically Different to a Top Eared Rat in Other Ways?
While some unscrupulous pet shops and breeders may try to sell dumbos as special ultra-exotic rats, they are – in all other ways – the same as top eared rats. So, whatever you may hear, dumbos are standard rats with changes that only affect their skull and eye development.
This means that dumbos have the same average body size, limb and tail length as other rats, as well as the same brain and organ development. They are renowned for being “stockier” than top eared rats, but this is related to breeding choices.
It is perfectly possible to breed lines which produce dumbos that are lean and racy, just as it is possible to breed lines of top eared rats who are chunky and prone to being overweight. So, what should the ideal dumbo rat look like?
The Ideal Dumbo Rat
The dumbo is now a standardized variety, which can be exhibited at rat shows across many countries including the USA and UK. The dumbo is judged as a standard rat with the following differences:
- The ears to be set low on the sides of the head, their base at the back of the cheeks wider and more open than a standard rat. The ear is slightly furled at the top and should stand out at a prominent angle from the head. The ear may appear to be rose petal-shaped but should be perfectly rounded and as flat as possible.
- Head shape to follow the standard for normal eared rats, though may appear to differ due to the ear position. A prominent occiput (back of the skull) is normal but should not present a ‘hunchback’ appearance.
- Faults: creased, bent and wrinkled ears, ears being too narrow, pointed, and tubular rather than rounded.
- Serious faults: Dome skulls, foreshortened head, misplaced or small eyes.
- Color to conform to a recognized color or pattern variety.
From NFRS standards of excellence – formatting ours
Other Differences Between Dumbo and Top Eared Rats
It’s not uncommon to hear all kinds of claims made about dumbo rats as being rare, special, different to fancy rats, larger, smaller, more docile and so on. These claims have no foundation.
Dumbo rats are essentially just rats who have their ears on the side of their head, a predisposition to smaller eye-size and somewhat shortened cheek and jaw bones.
Despite some early claims of dumbos having more docile temperaments, this does not appear to be a dumbo trait. Some dumbos are extremely docile and some are active and spirited. The same is true for top eared rats.
The temperament of any individual dumbo depends on genetic and environmental influences in exactly the same way that the temperament of a standard rat is determined.
When on heat, female top eared rats communicate their willingness to mate with displays of darting, jumping and vibrating their ears. Female dumbo rats do not seem to vibrate their ears when on heat.
However, thousands of dumbo females have successfully communicated their receptiveness, been mated and become pregnant. So, the lack of this trait does not seem to affect the male rat’s willingness to mate when a dumbo female is on heat.
Despite a similar genetic mutation in humans (probably more severe) called Treacher Collins Syndrome being associated with deafness, this does not appear to be a feature of dumbo rats. They do, however, sometimes have a smaller opening into the ear canal.
Without further research and auditory testing, it is not yet possible to say that dumbo rats have the normal – extremely sensitive – hearing of a top eared rat. Hopefully, someday laboratory studies will give us this information.
Injury and Illness
The low set ears of the dumbo rat seem to be more prone to injury, especially during rat fights, than their standard eared friends and relations. Most injuries are minor and heal quickly without intervention, but nicks and gaps in the ear can remain after healing.
Ear infections and zymbal gland tumors are the two main rat illnesses to affect the ear and related glands. These conditions affect top eared rats and dumbos alike, and a survey of cases mentioned in a large rat care facebook group shows no difference in the rate of occurrence between the two varieties.
Deciding Whether a Dumbo Rat Is for You
The decision as to whether or not to home a dumbo rat as one (or more) of your mischief is really down to personal preference about the appearance of the dumbo. The lower ear position and wider forehead can soften the facial features making the rat look both kind and cute.
This can be very appealing to some people, while others prefer the sharper, natural features of the top eared rat. Dumbo rats are potentially available in all of the color, pattern and coat types of the standard rat.
So, a dumbo can be any color variety, marked variety, or shaded variety and can come in a standard coat, rex, satin, and so on. They can even be hairless!
The important thing to remember is that a dumbo is not more exotic than a standard rat and in some areas are actually more commonplace. Be suspicious of anyone who tries to charge more for a dumbo – a dumbo is a standard rat with a different ear set and should cost the same.
No special care or attention is needed to own a dumbo rat. They require the same housing, diet, care and attention as a standard eared rat and, as with all other varieties, can live in a mixed variety group.
In fact, litter siblings are often homed in dumbo/ top eared pairs. It’s one way of easily telling your rats apart if they are the same color variety.
Dumbos, like all rats, usually make affectionate, inquisitive, endearing companions and often have a notably cute appearance, which many humans enjoy.
Rest assured that a well-bred dumbo rat is not disadvantaged as a pet rat and will enjoy life with all the usual rattie enthusiasm that standard rats are renowned for.