How the Drinking Bird Science Toy Works

The drinking bird or sippy bird is a popular science toy that features a glass bird that repeatedly dips its beak into water. Here's the explanation for how this science toy works.

What Is a Drinking Bird?

Depending where you live, you may see this toy called a drinking bird, sipping bird, sippy bird, dippy bird or insatiable birdie. The earliest version of the device appears to have produced in China circa 1910-1930. All versions of the toy are based on a heat engine in order to function. Evaporation of a liquid from the bird's beak lowers the temperature of the head of the toy. The change in temperature creates a pressure differential inside the body of the bird, which causes it to perform mechanical work (dip its head). A bird that dips its head into water will keep dipping or bobbing as long as water is present. In fact, the bird works as long as its beak is damp, so the toy continues to function for a span of time even if it is removed from water.

Is the drinking bird a perpetual motion machine?

Sometimes the drinking bird is called a perpetual motion machine, but there is no such thing as perpetual motion, which would violate the laws of thermodynamics. The bird only works as long as water is evaporating from its beak, producing an energy change in the system.

What Is Inside a Drinking Bird?

The bird consists of two glass bulbs (head and body) that are connected by a glass tube (neck). The tube extends into the bottom bulb almost to its base, but the tube does not extend into the top bulb. The fluid in the bird usually is colored dichloromethane (methylene chloride), although older versions of the device may contain trichloromonofluoromethane (not used in modern birds because it is a CFC).

When the drinking bird is manufactured the air inside the bulb is removed so that the body will fill with fluid vapor. The "head" bulb has a beak that is covered with felt or a similar material. The felt is important for the functioning of the device. Decorative items, such as eyes, feathers or a hat may be added to the bird. The bird is set to pivot on an adjustable crosspiece fixed to the neck tube.

Educational Value

The drinking bird is used to illustrate many principles in chemistry and physics:

• boiling and condensation [dichloromethane has a low boiling point of 39.6 °C (103.28 °F)]
• combined gas law (proportional relationship between the pressure and temperature of a gas in a constant volume)
• ideal gas law (proportional relationship between the number of particles of a gas and the pressure in a constant volume)
• torque
• center of mass
• capillary action (wicking of water into the felt)
• wet-bulb temperature (temperature difference between head and body bulbs depends on the relative humidity of the air)
• the Maxwell-Boltzmann distribution
• heat of vaporization / heat of condensation
• functioning of a heat engine

Safety

The sealed drinking bird is perfectly safe, but the fluid inside the toy is not non-toxic. Older birds were filled with a flammable fluid. The dichloromethane in the modern version is not flammable, but if the bird breaks, it is best to avoid the liquid. Contact with dichloromethane can cause skin irritation. Inhalation or ingestion should be avoided because the chemical is a mutagen, teratogen and possibly a carcinogen. The vapor quickly evaporates and disperses, so the best way to deal with a broken toy is to ventilate the area and allow the fluid to disperse.