Territory of Guam

Guam Kingfisher Todirhamphus cinnamominus ©D W Ross (Creative Commons) Website
Birding Guam

Guam, officially the Territory of Guam, is an island in the western Pacific Ocean and is an organized, unincorporated insular area of the United States. It is one of five U.S. territories with an established civilian government. The island’s capital is Hagåtña (formerly Agana). Guam is the largest and southernmost of the Mariana Islands.

Guam lies between 13.2°N and 13.7°N and between 144.6°E and 145.0°E, and has an area of 209 square miles (541 km2), making it the 32nd largest island of the United States. It is the southernmost island in the Mariana island chain and is the largest island in Micronesia. This island chain was created by the colliding Pacific and Philippine tectonic plates. The Mariana Trench, a deep subduction zone, lies beside the island chain to the east. Challenger Deep, the deepest surveyed point in the Oceans, is southwest of Guam at 35,797 feet (10,911 m) deep. The highest point in Guam is Mount Lamlam, which is 1,332 feet (406 m). The island of Guam is 30 miles (48 km) long and 4 mi (6 km) to 12 mi (19 km) wide. The island experiences occasional earthquakes due to it being on the western edge of the Pacific Plate and near the Philippine Plate. In recent years, earthquakes with epicenters near Guam have had magnitudes ranging from 5.0 to 8.7. Unlike the Anatahan volcano in the Northern Mariana Islands, Guam is not volcanically active. However, due to its proximity to Anatahan, vog does occasionally affect Guam.The northern part of the island is a forested coralline limestone plateau while the south contains volcanic peaks covered in forest and grassland. A coral reef surrounds most of the island, except in areas where bays exist that provide access to small rivers and streams that run down from the hills into the Pacific Ocean and Philippine Sea. The island’s population is most dense in the northern and central regions.

The climate is characterized as tropical marine. The weather is generally hot and very humid with little seasonal temperature variation. The mean high temperature is 86 °F (30 °C) and mean low is 76 °F (24 °C) with an average annual rainfall of 96 inches (2,180 mm). The dry season runs from December through June. The remaining months constitute the rainy season. The months of January and February are considered the coolest months of the year with night time temperatures in the mid to low 70’s and generally lower humidity levels. The highest risk of typhoons is during October and November. They can occur, however, year-round.

An average of three tropical storms and one typhoon pass within 180 nautical miles (210 mi/330 km) of Guam each year. The most intense typhoon to pass over Guam recently was Super Typhoon Pongsona, with sustained winds of 125 miles per hour, which slammed Guam on December 8, 2002, leaving massive destruction.

Ecological issuesFrom the seventeenth through nineteenth centuries, the Spanish introduced pigs, dogs, chickens, the Philippine deer (Cervus mariannus), black francolins, and water buffalo. Water buffalo, known as carabao locally, have cultural significance. Herds of these animals obstruct military base operations and harm native ecosystems. After birth control and adoption efforts were ineffective, the U.S. military began cullling the herds in 2002.

Other introduced species include cane toads imported in 1937, the giant African snail (an agricultural pest introduced during WWII by Japanese occupation troops) and more recently frog species which could threaten crops in addition to providing additional food for the brown tree snake population. Reports of loud chirping frogs, known as coquí, that may have arrived from Hawaii have led to fears that the noise could threaten Guam’s tourism. An infestation of the coconut rhinoceros beetle (CRB), Oryctes rhinoceros, was detected on Guam on September 12, 2007.

Number of Species
  • Number of bird species: 95

    The avifauna of Guam includes a total of 95 species, of which 2 are endemic, 2 have been introduced by humans, and 1 is rare or accidental. 6 species are globally threatened.
  • Number of endemics: 2

    Guam Rail Gallirallus owstoni is only extant in captivity and the re-introduction on Cocos and Rota Islands.
    There is also a captive population of Guam Kingfisher Todiramphus cinnamomius

  • iGoTerra Checklist

    iGoTerra Checklist
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Trip Reports

Click on WAND to see Fatbirder’s Trip Report Repository…

  • 2010 [01 January] - Jon Hornbuckle

    …Golden and Bridled White-eyes, White-throated Ground-Dove, Mariana Fruit-Dove and Rufous Fantail. Taped out Nightingale Reed-Warbler a little lower down at the entrance to the Hadderantanki Trail…
  • 2012 [03 March] - Gail Mackiernan - Western Pacific Cruise (New Zealand to Japan)

    …The Statendam docked at Guam at about 8.00 a.m giving us the whole day to explore the island. The island is virtually devoid of land birds except Drongos and Pacific Doves, thanks to the brown tree snake. Despite this we had rented a car and decided to tour around and see what birds we could find. We had a surprisingly enjoyable day seeing a good variety of migrant shorebirds and other wetland species. Yellow Bitterns were very common in the coastal marshes. We managed to find ten species of waders including beautiful spring plumage Sharp-tailed Sandpipers and Long-toed Stints. Most of these birds were on a small tidal creek that is part of the Sasa Bay Reserve and only a short drive along the coastal road south from the dock…
  • 2023 [04 April] - Doug Whitman

    PDF Report
    Northern Mariana Islands: Rota, Saipan, Tinian Guam Federated States of Micronesia: Chuuk, Pohnpei, Kosrae
Other Links
  • Checklist

    The avifauna of Guam includes a total of 95 species, of which 2 are endemic, 2 have been introduced by humans, and 1 is rare or accidental. 4 species listed are extirpated in Guam and are not included in the species count. 6 species are globally threatened
  • Guam Broadbill Myiagra freycineti

    Species profile
  • Guam Rail

    The Guam rail (Gallirallus owstoni) is a species of flightless bird, endemic to the United States territory of Guam.
  • Guam Rail Rallus owstoni

    Guam rails Rallus owstoni are a small flightless bird that lived only on the island of Guam in the Mariana Archipelago in the Pacific. They are omnivorous, eating leaves, seeds, fruits, small lizards, bird eggs, small mammals, and carrion
  • Native Forest Birds of Guam

    The limestone and ravine forests of Guam have historically supported fourteen species of terrestrial birds. Two of these fourteen birds are endemic to Guam at the species level. Five bird species are endemic at the sub-species level. One of the endemic species is now extinct. Seven have been extirpated from the island.

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