Guam rails are omnivorous, although they do prefer animals instead of plants. Common menu items include skinks, geckos, fish, snails, slugs, insects, tomatoes, melons, seeds, and palm leaves. The rails generally eat food that is on the ground but are known to catch low-flying insects, including butterflies. They do most of their foraging at dawn and dusk.
Guam rails are year-round ground nesters, producing up to 10 clutches a year. Both parents build a shallow nest of grass and leaves hidden in dense grass. The female lays one to four eggs. The downy black 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, getting their juvenile feathers at four weeks and reaching their adult weight at just seven weeks. They are able to become parents themselves at four months of age!
Although Guam rails seldom vocalize, they do respond to other rails, loud noises, or other disturbances with a loud, piercing whistle or series of whistles. During breeding season, the birds make loud, penetrating screeches and short kips.
