Of 18 species of native Guamanian birds, seven are extinct, two are extinct in the wild (the Guam Rail, pictured left, and the Micronesian Kingfisher survive only in captivity), six are rare, and three are uncommon.n Guam, brown tree snakes found dense forests that were teeming with the birds and small lizards that are their natural foods. No enemies slowed their spread, and their numbers mushroomed. The snake populations moved steadily north at a rate of a mile per year from their southern landfall.