Novelty items, particularly novelty toys, can provide mere seconds or endless hours of enjoyment, depending upon the level of enlightenment achieved by their owners. An important factor in the success of novelty items is their ingenuity. Science has a vital role in the drinking bird's ability to provide amusement to the inane and bored masses. While drinking straw glasses can make you look silly for a few minutes, a toy that can dumbfound those unaware of the principles behind it... well, it can make you look silly for an entire lifetime. And the drinking bird is one such toy.

As its name suggests, the drinking bird is a fascinating toy that perpetually 'drinks' from any glass of water you care to put in front of it. Its ingenuity lies in the fact that, aside from looking rather wet and bedraggled at its head, it does not appear to take on any of the water. So where does it all go and what on earth is it that can make an inanimate object so thirsty?

Anatomy of a Drinking Bird

The bird consists of four essential parts (although it could be argued that there is also a fifth part, the glass of water):

• Armature - body
• Pivot - hips and legs
• Wick - head
• Inner liquid - guts

The armature consists of a glass tube attached to two glass bulbs, one at either end. The top of the tube opens out into the upper bulb, while the bottom of the tube extends almost to the bottom of the lower bulb, similar to a straw in a drink. Usually, the very bottom of the tube is immersed in the liquid.

The pivot consists of a horizontal bar which is clamped about the middle of the armature by a piece of metal tubing and two upright stands. The stands are the legs, and have holes drilled into them at the correct height to allow the bar to fit loosely. The bar is bent backwards slightly (or for you whizzy scientists out there, concave dorsally!) at the points where it makes contact with the legs, causing it to lean forwards.

The wick consists of a fuzzy material that coats the upper bulb and beak of the bird. The liquid inside must be suitably dense and viscous (thick/sticky), and have a low latent heat of evaporation (evaporate easily) - together these properties are known as Lv. The Lv of some liquids are shown below (units are kJ/kg - kilojoules per kilogram):

• Water = 2250 kJ/kg
• Ethanol = 880 kJ/kg
• Methylene chloride = 406 kJ/kg
• Mercury = 281 kJ/kg

Although mercury would be ideal, efficient, and would look very pretty, it is dangerous and expensive. As such, methylene chloride is the preferred choice. Today, the modern drinking birds contain Freon-11, a chemical used to cool fridges and freezers.

How It Works

The bird is an example of a 'heat engine', where a difference in temperature is converted into cyclical motion. To start the bird in motion, the head must first be soaked in water. As the water evaporates, it draws heat from inside the head, causing the vapour within to cool and condense out. The loss of heat and the reduction in the amount of vapour caused by the condensation produces an imbalance of pressures between the head and the abdomen¹. The vapour in the abdomen expands and pushes down to compensate for the loss of vapour in the head. This forces liquid up the tube into the head, further reducing the volume of vapour in the head, while at the same time, decreasing the pressure in the abdomen. This causes evaporation of the liquid, creating more vapour and increasing the pressure in the abdomen, resulting in yet more liquid being forced up the tube into the head.

The rising liquid raises the centre of mass of the bird to the point where it can no longer stay upright and tips forwards into the glass. The level of liquid in the bulbs has been set so that when the bird 'dips', the bottom of the tube is exposed. The angle of dip allowed by the pivot has also been calculated so that a bubble of vapour can rise through the tube and allow the liquid to drain back into the abdomen, tilting the bird back. The head, now covered with more water from the glass, continues the seemingly never-ending cycle of bird-thirst.

The force from the liquid draining back into the abdomen tips the bird back and creates a pendulum-like rocking motion. As the liquid rises through the tube, the swinging motion slows due to the liquid being more evenly distributed throughout the armature. When the liquid level nears the point of overbalance, movement has all but stopped. The liquid continues to rise, and slowly but surely the head tips into the water. The head remains stationary until most of the liquid has drained back into the lower bulb (a few seconds at most). It is this pause that gives the bird the appearance of drinking, rather than merely ducking.

The length of a dipping cycle depends upon the heat and humidity of the surrounding air, and the amount of time a bird can continue drinking is also dependent on these factors. (Don't forget, if there is no water in the glass, evaporation cannot occur, and the bird will no longer dip into the glass.) Many painstaking minutes of research have led to the conclusion that Britain has a fairly good climate for drinking birds. However, studies carried out on drinking birds in many parts of America tend to be stifled by heat and humidity. In Britain, the average cycle of the drinking bird from dip to dip is approximately 50 seconds.

The Many Guises of the Bird

The drinking bird has no one patent on it, and so has been produced numerous times by several manufacturers with varying quality. It has acquired several different identities in the process. The instructions for this Researcher's model refer to it as a 'Miracle Toy'. Other aliases include 'Dippy Bird', 'Happy Dippy Bird' and 'Magic Bird'. Whatever the bird itself may be called, the characteristic 'look' is maintained regardless of the manufacturer. The bird usually has large feet (normally wearing boots for stability), a single, brightly coloured tail feather - anything else might insulates the lower bulb, and could affect the bird's performance - and a hat that falls somewhere between early 20th Century gentleman and hideously dressed tap dancer. In spite of this clear transgression in fashion sense, 'Dippy' has attracted quite a following. Type 'drinking bird' into an Internet search engine and be astonished by the amount of curiosity it generates in physics teachers and complete numbskulls alike.

Another topic that remains in question is the species of the bird. While many have suggested that they are ducks (due to their ability to 'duck'), it is believed that this is not the case. The lack of plumage means that the bird would not be recognised by other ducks, and makes 'Dippy' unsuitable for life in water. Second, the abundance of fuzz on the beak, essential to its survival - or at least its drinking habits - has not yet been reproduced by nature.

How to Stop the Madness

You now know who it is, what it is, how it works and why it is so compulsive. But what if you just can't stand it? If a friend or a loved one owns a drinking bird that drives you crazy, here's how to stop it in its fuzzy, wobbling tracks.

• Empty the glass - After a while the bird will stop. However, the threat still remains.

• Insulate the abdomen - Drinking birds are quite sensitive, so much so that natural human skin oil can affect their performance. Insulating the lower bulb may reduce its motion, thereby reducing damage to your sanity.

• De-fuzz the head - Removing the absorbent properties of the head may drastically reduce the bird's thirst.

• Just Get Rid of the Damn Thing - This verges on the criminal and may cause grief or arguments within the family. You have been warned.

Some Final Words of Warning

If you have or intend to purchase a drinking bird, always read the instructions carefully and handle with care. Remember, it is not just a toy, it is also a drinking companion.

The following precautions were advised by the makers of 'Miracle Toy':

• Beware of cats (this is absolutely true and in no way an attempt at humour)
• Do not keep in sunlight
• Be careful when assembling

If you wish to purchase a drinking bird, visit your local novelty toy store or contact a general scientific wares supplier.