Class: Aves (Birds)
Body length: 11 inches (28 centimeters)
Shoulder height: 11 inches (28 centimeters)
Weight: 6 to 10.6 ounces (170 to 300 grams)
Life span: unknown
Incubation: 19 days
Number of eggs laid: 1 to 4
Age of maturity: 4 months
Conservation status: extinct in the wild; now found only in managed populations as part of an SSP.
• Guam rails can fly only about 3 to 10 feet (1 to 3 meters)
at a time!
• In their native Guam, the birds are called Ko'Ko'.
Animal Bytes: Guam Rail
Betcha can't find me!
Little is known about the secretive and territorial Guam rail. Why? Because there are so few of them in the wild! We do know that rails are very good at walking, or even running, without making any noise, even when moving through thick vegetation. Besides being able to move silently, they seldom vocalize, although a bird will respond to other rails, loud noises, or other disturbances with a loud, piercing whistle or series of whistles.
Fly? Sorry, I'm afraid of heights!
The Guam rail, like other island rails, is virtually flightless. This is probably because there were no natural predators on its native island to bother them. While they do not have much in the way of flight muscles, they do have well-developed leg muscles. They can swim, dive, and even sink, using their wings underwater.
Guam rails are year-round ground nesters, producing up to 10 clutches a year. Both parents build a shallow nest of grass and leaves, and the female lays one to four eggs. Chicks are able to leave the nest within 24 hours of hatching, although both parents continue to feed and care for them. They grow very quickly, reaching their adult weight at just seven weeks, and are able to become parents themselves at four months of age!
I'm so hungry, I could eat a gecko
Guam rails are omnivorous, although they do prefer animals instead of plants. Common menu items are skinks, geckos, fish, snails, insects, tomatoes, melons, seeds, and palm leaves. Rails at the Safari Park and the San Diego Zoo are offered crickets, mealworm larvae, mice, dog chow, and a specialized meat mixture for zoo carnivores.
A rail's worst enemy
Sometime between 1944 and 1952, the brown tree snake Boiga irregularis arrived on Guam, most likely on cargo ships. The snake's population rapidly increased because there was lots of prey (such as the Guam rails) and no natural predators. Prior to their arrival, there were no snakes on Guam, so the rail, like other native animals there, had developed no natural defenses against this predator. The tree snakes wiped out the native animal populations, and by the 1970s, 9 of the 11 native bird species had disappeared.
Prior to the 1960s, there were probably around 10,000 Guam rails living on Guam. The invasion of the brown tree snake is believed to be the chief reason for the decline of the species. The Guam rail had disappeared from southern Guam by the mid-1970s. Trying to save the species, the last few birds were removed from the island in the 1980s. In 1989, reintroduction of these birds began on the island of Rota, near Guam, as part of the Species Survival Plan for the species. The San Diego Zoo is participating in both the breeding programs and current reintroduction programs on Guam and nearby Rota Island.