Is there any reliable references giving a scientific answer to why bunnies like to chew on wires? What is the reason?
They have to chew. Rabbit teeth are constantly growing and the chewing activity actually serves to grind them down. Rabbits will chew pretty much anything "chewable" which includes wood, wires, and the like. If you give them lots of non-wire stuff to chew, like apple tree branches, then it does reduce the chance they'll go after your wires, but it doesn't stop it in my experience (we had two rabbits once).
One good option, by the way, is the plastic teething keys you can get for babies. Not only do rabbits like to chew on them, but they also toss them about for play. Our rabbits loved the plastic keys.
After 15 years of multiple rabbit ownership, I can assure you it is the smell draws them to the wire, and the texture keeps them coming back.
In fact, extremely rubbery remote control buttons are the one of the most sought after of all rabbit delicacies second only to sugar filled edibles:
A face up remote is a sure fire way to get a bunny that knows the taste of one onto a couch. However, the high number of reminate buttons seems to indicate, they while fun to chew on, rubber doesn't taste all that great to them, hence, my assertion that texture must play a part in it.
The above picture happened while I left my remote atop a 2.5 foot high stool and steeped away during a commercial break to use the bathroom. She had tasted a different remote a week prior and for months after any face up remote meant a lurking rabbit.
Because she was obstructed from seeing the remote was face up during this incident (and the fact rabbits have trouble seeing things up close), I am extremely confident that smell of rubbery like materials is strong factor in the attraction. If you think about it, this makes sense as rubber is a natural product that comes from trees, and thus rabbits might find the smell alluring.
You can also test your own rabbits "ability to see with it's nose", Have you ever left kibble on a counter out of sight to but within climbing reach to them? They will eventually (usually rather quickly) find there way there because their nose is what they use to identify things (food and each other and even us) with.
Similarly, in my years of experience, smelly rubber coated wires such as OEM usb cords are sought after preferentially over more plastic-y lamp cords or power wires, and I've lost 2 USB webcams because I thought I had all routes to the back of my computer covered.
This preference also seems to de-bunk the "buzzing wire" theory as USB cords carry DC power, so there is no current oscillating in them to make them buzz.
Another strike against the buzzing wire theory, while laying credence to the texture theory is that when the same wires are covered with hard plastic cord organizers such as these:
the rabbits leave the cords and the organizers alone. However, if you buy the cheaper, less softer plastic home-depot version, they will occasionally chew on the organizer. And if you get the extremely soft, almost rubbery kind of cord organizer form Ikea, they won't deter the rabbit at all and both your organizer and enclosed cables will be destroyed.
I once theorized it the location also had something to do with it as the rabbits might just be following their natural instinct to clear a runway though the briar patch to their hide away, but that was promptly debunked when the rabbit climbed to the back of a couch than traversed to a nearby desktop to take out a rubbery coated speaker wire that was hanging off the wall.
That said, not all rabbits are wire chewers (though I haven't met one that doesn't like rubber), but those same rabbits tend to be quite finicky about everything. For instance, my albino lion head and doesn't chew on wires, but he also won't eat most forms of leafy greens and hates our hardwood floors so he stays on the area rugs and thus has less exposure to wires to begin with.
If you have a finicky rabbit, you probably can train it not to chew wires with normal coatings, but I wouldn't push my luck with anything rubbery. In any case, it is easy enough to just cover every exposed wire with one of the above organizers.
There are several theories floating around as to why rabbits engage in this behaviour. One is that electricity in a live wire makes a noise that is audible to the rabbit and attracts them to it or they can feel the vibrations inside it. Another is that they might like the smell of the plastic or its rubbery feel. Also, if a rabbit is bored they will often chew just to pass the time. Based on my limited experience and what I was able to find, there doesn't exist a definitive reason as to why exactly, just speculative theories.
As John already mentioned in his answer, rabbits have to chew.
Chewing behaviour in rabbits is one that is not easily curbed. It is an instinctive behaviour as they need to chew in order to wear down their incisors which grow continuously throughout their lives. It is therefore important to understand the chewing behaviour of your pet rabbit and take the necessary precautions to protect your bunny and your belongings. (src)
Some preventative measures however are:
- Use flexible plastic tubing (like that used in fish tanks, but a larger diameter) is one of the easiest ways to protect cords. The tubing can be sliced length-wise with a utility knife and the cord pushed inside. A few rabbits will continue to chew on the plastic tubing, but this provides the time necessary to let the rabbit know (by clapping or stomping along with a verbal NO) that it is not appropriate to chew on the tubing. (src)
Give the rabbit something that is ok for him to chew on instead and something that it will enjoy more such as apples, willow, aspen branches, pine etc.
Use a deterrent such as spraying the rabbit with a water bottle or putting a nasty tasting substance such as bitter apple spray on things the rabbit likes to chew.
Also see some more additional tips on how you can bunny proof your home and electricals.
I can state that my rabbit can find a wire that has energy in it remarkably quick. An unplugged wire can sit in his cage for a week and be ignored. In less than a year, I have had to replace 3 lightening chargers but no mini USB. The digital antenna (indoor) was chased only when plugged in to power and only when the sockets that are on the wall switch are on, will he seek to destroy the lamps or fans that are plugged in.
As a trained electrician, I have repaired a lot of wires, and have found the car audio split sleeving to work best, though on some, he has tried to go for the plug part (laptop charger died this way.) He does not seem deterred by getting a shock, instead he seems to go after them even more ferociously.
I now keep him in a "playpen" and only after patrolling a room for any wire, do I allow him out. Now he is trying to dig through the carpet to get to the electrical wires under the flooring. I did go into the crawl-space to verify. Each area that he digs at, has a live circit running to a light or house appliance that is running. I would say it is sound or smell. At first I thought it was similar to the instinct of a cat with a cucumber/snake, but that does not explain the live wires only and the wires underneath in the crawlspace.