Extinctions and Loss of Species from Guam: Birds
Beginning in the mid 1960's, the brown Treesnake decimated Guam's native avifauna. The birds of Guam evolved in the absence of snake predators. They had no experience with such a predator and lacked protective behaviors against the brown Treesnake. Consequently, they were easy prey for these efficient, nocturnal predators. As the snakes spread across the island, the number of snakes began to grow exponentially and bird populations declined. Nine of the 11 species of native forest-dwelling birds have been extirpated from Guam. Five of these were endemic at the species (*) or subspecies (**) level and are now extinct on Guam. Two of these species, the Guam rail and the Micronesian kingfisher, are being captively bred in zoos in the hope that they can eventually be released back into the wild. Several other native species exist in precariously small numbers, and their future on Guam is perilous.
The history of this decline starts shortly after the introduction of the brown Treesnake, although appreciable losses were not evident until the 1960s. By 1963, several formerly abundant species of native birds had disappeared from the central part of the island where snakes were most populous. By the late 1960s, birds had begun to decline in the central and southern parts of the island and remained abundant only in isolated patches of forest on the northern end of the island. Snakes began affecting the birds in the north-central and extreme northern parts of the island in the 1970s and 1980s, respectively. Most native forest species were virtually extinct when they were listed as threatened or endangered by the U.S. Fish and Wildlife Service in 1984.
Native Species
Aerodramus vanikorensis
Island swiftlet
Chachaguak (CNMI)
Yayaguak (Guam)
Nesting and roosting in caves, the island swiftlet has persisted in at least one refuge on Guam. The one active colony in south-central Guam is in a cave where they roost and nest, apparently out of reach for brown Treesnakes, so the young are able to reach maturity. At one time, there were perhaps a dozen swiftlet caves on Guam harboring thousands of these insectivorous birds. These populations have nevertheless declined along with the other forest birds.
Aplonis opaca
Micronesian starling
Sali (CNMI and Guam)
Although its numbers have been greatly reduced, the Micronesian starling is the only native forest bird that may survive into the future on Guam. The starling is a cavity nester and has been able to colonize a few urban areas using artificial nest sites and thus avoiding predation by the snake. A small population of starlings also resides on Cocos Island, an islet 3 km south of Guam.
Corvus kubaryi
Mariana crow
Aga (CNMI and Guam)
The only native forest bird to persist in snake-infested habitat, the Mariana crow has probably managed to persist on Guam due to its large size, long life span, and human intervention. However, its survival is now extremely tenuous. The population on Guam is believed to number only 12 individuals, including 4 birds recently translocated from Rota. Little or no successful recruitment into the adult population has occurred since 1986. Intensive efforts have been made by the Guam Division of Aquatic and Wildlife Resources to protect nests in trees from snakes and monitor lizards with electrical barriers on Andersen Air Force Base, but the numbers of nests available for such efforts have declined considerably over the last decade.
Egretta sacra
Pacific reef-heron
Chuchuko atilong (CNMI and Guam)
A native to the wetland and coastal areas of Guam, the Pacific reef-heron is uncommon on Guam but still nests on the nearby island of Cocos. It is equipped with a long bill and defensive manner that have probably helped it combat the brown Treesnake in confrontations. The reef-heron typically nests on rocky, offshore islets where it is protected from snakes.
Gallinula chloropus
Common moorhen
Pulattat (CNMI and Guam)
The common moorhen is now rarely seen on Guam, although effects of the brown Treesnake on this population are poorly documented. Fairly large in size and aggressive, moorhens would be difficult prey for most snakes and may be able to defend their nests against snakes. Also, the moorhen usually nests in wetland areas, which are not prime habitat for the snakes. Losses to snake predation most likely are concentrated on eggs or young birds.
Halcyon cinnamomina **
Micronesian kingfisher
Sihek (CNMI and Guam)
Once found throughout Guam's forests, the Micronesian kingfisher has been extirpated from the wild by the brown Treesnake and now exists only in captive populations at several mainland U.S. zoos. As experimental deterents progress and barrier technology improves, it is hoped that these populations will be introduced back into Guam's environment as the rail has been. Since this subspecies of kingfisher has a relatively soft beak and selects only soft, rotting trees in which to burrow nesting sites, it is possible that these trees could be protected in ways similar to those used for the Mariana crow. The existence of appropriate nest sites in areas where snakes have been controlled will be critical to the success of future introductions.
Ixobrychus sinensis
Yellow bittern
Kakkak (CNMI and Guam)
The Yellow bittern is now one of the most frequently sighted native birds on Guam. It moves between a mixture of habitats, preferring primarily wetland and grassy areas. The bittern is equipped with a long bill, and like the Pacific reef-heron, its tendency to defend itself probably has helped it survive on Guam. The bittern is also found on Cocos.
Myiagra freycineti *
Guam flycatcher
Chuguangguang (Guam)
Once widespread and relatively conspicuous, the Guam flycatcher was small in size and driven to extinction early by the brown Treesnake.
Rallus owstoni *
Guam rail
Ko'ko' (Guam)
A flightless bird, endemic to Guam, the Guam rail disappeared from southern Guam in the early 1970s and was extirpated from the entire island by the late 1980s. This species is now being bred in captivity by the Division of Aquatic and Wildlife Resources on Guam and at some mainland U.S. zoos. Since 1995, more than 100 rails have been introduced on the island of Rota in the Commonwealth of the Northern Mariana Islands in an attempt to establish a wild breeding colony. Although at least one chick resulted from these efforts, predation (largely by feral cats) and accidental deaths have been extremely high. A small number of birds potentially persist. A recent effort to introduce rails on Guam in a 22-ha forested area concentrated on protecting the rails by limiting snakes using a combination of trapping and a perimetereter barrier to reduce re-invasion by snakes. This endeavor allowed the tentative survival of several pairs of rails released into the area. Reproduction by the rails was reported in this control area on the basis of sounds attributed to chicks. The preliminary success constitutes one of the few bright spots in the conservation of Guam's native fauna in recent years and speaks to future opportunities to recover wildlife.
Rhipidura rufifrons *
Rufous fantail
Naabak (CNMI)
Chichirika (Guam)
Once widespread and relatively conspicuous, the Rufous fantail represents another small bird driven to extinction by the brown Treesnake.
Zosterops conspicillatus **
Bridled white-eye
Nosa' (Guam)
Once the most abundant bird on Guam, the bridled white-eye was probably the first species to be extirpated by the brown Treesnake, which constitutes extinction for the Guam subspecies. The smallest of the forest birds, high stress was placed on the white-eyes during the snake's irruption. The smaller birds such as white-eyes, fantails, and broad bills, as well as their eggs and young, were extremely vulnerable.
Non-endemic birds extirpated from Guam:
Acrocephalus luscinia
Nightingale reed-warbler
Gaga karisu (CNMI)
Ga'kaliso/Ga'karriso (Guam)
Found on Guam in low numbers prior to the spread of the brown Treesnake, the warbler has disappeared on Guam; however, its early disappearance could have been due to snake predation in combination with other factors.
Gallicolumba xanthonura
White-throated ground-dove
Paluman apaka (CNMI)
Paluman Apaka (male, Guam)
Paluman Fachi' (female, Guam)
A somewhat larger species, the ground-dove was able to persist while the smaller birds suffered heavy predation. However, in the last decade, it has been extirpated from Guam.
Ptilinopus roseicapilla
Mariana fruit-dove
Paluman totut (CNMI)
Totot (Guam)
Like the ground-dove, the Mariana fruit-dove was able to survive the initial snake irruptions on Guam but ultimately disappeared. It has not been seen on Guam since 1984.
Myzomela cardinalis
Cardinal honeyeater
Egigi (Guam)
A colorful and frequent urban resident on Guam, the Cardinal honeyeater was lost as the brown Treesnake population boomed.
Species extirpated from Guam prior to the introduction of the brown Treesnake:
Anas platyrhynchos
Mariana mallard
Nganga' palao (CNMI)
Nganga' (Guam)
The limited availability of open water habitats placed the Mariana mallard in jeopardy from over-hunting. It disappeared from Guam prior to World War II.
Megapodius laperouse
Micronesian megapode
Sasangat (CNMI and Guam)
The Micronesian megapode disappeared from Guam prior to the arrival of the brown Treesnake. The unusual bird's dependence on placing its nests in mounds of loose soil placed severe limitation on its numbers on Guam where such soils are scarce.
Poliolimnas cinereus
White-browed crake
Bako (Guam)
Introduced Species
Of the approximately eight introduced species on Guam, five are uncommon or rare. Although some of these birds came from native ranges where snakes are abundant and are better adapted to resist predation by the brown Treesnake, extreme snake densities have caused even these species to encounter difficulty. Only three species are relatively common—the black francolin, the blue-breasted quail, and the Eurasian tree-sparrow—due primarily to their habitat selection. They persist in urban areas and developed sites, where snake density is limited by human activity and non-conducive habitat.
Coturnix chinensis
Domesticated quail
Bengbeng (Guam)
Many of Guam's residents who formerly raised quail in cages have abandoned the hobby due to problems and losses caused by snakes.
Francolinus francolinus
Black francolin
A native of India, the black francolin may have anti-predator defenses that provide some protection from brown Treesnake predation. The francolin is found throughout much of Guam but in highly variable numbers. Because of the francolin's large size, as adults they are not easy prey for any but the largest snakes. The francolin is a resident of open fields and savannas, areas that are not favorite habitats of the brown Treesnake.
Passer montanus
Eurasian tree-sparrow
Ga'ga' pale (CNMI)
The Eurasian tree-sparrow may have persisted only because it is so successful in urban areas surrounded by automobile traffic, predatory domesticated animals, and habitat discontinuities, all of which potentially reduce the abundance of the brown Treesnake. Yet the sparrow's abundance in many areas is quite low due to snake predation.
Rare or Uncommon Species on Guam:
Columba livia
Rock dove
Paluman mansu (Guam)
Once abundant in many urban and commercial sites, pigeons are rarely seen on Guam today.
Dicrurus macrocercus
Black drongo
Salin Taiwan (CNMI and Guam)
This native of Taiwan and eastern Asia harasses other birds and even humans that approach its nests. It prefers to perch in high open sites and is probably most successful when it nests on power poles, which are somewhat protected from intruding snakes. Even nests on power poles have declined since 1985.
Gallus gallus
Red junglefowl
Feral chickens are commonly found on Pacific Islands but declined drastically and then disappeared from Guam. Many Guam residents still raise fighting chickens and colorful diminutive chicken breeds, but a large number of eggs and chicks are lost to snakes.
Lonchura malacca
Chestnut mannikin
This diminutive flocking grassland bird has persisted in low numbers, but undoubtedly many fall prey to snakes.
Streptopelia bitorquata
Philippine turtle-dove
This habitat generalist was found to suffer nest losses of 74-93% attributed to snakes, but its high reproductive output and ability to use a wide spectrum of nest sites and feeding ranges have allowed it to persist on Guam. However, the poor nesting success demonstrated by studies done in 1984 and 1986 raise doubts as to this species' continued survival on Guam. Indeed, population levels have declined 80-90% or more throughout Guam.
Nesting Seabirds
While forest avian species have been conspicuously affected by the brown Treesnake, seabirds that nested on Guam prior to the snake's introduction have also declined drastically. Three species of seabirds nested on Guam prior to the entrance of the brown Treesnake in the environment. These birds are now absent or extremely rare on Guam, although the brown noddy and white tern can still be found on offshore islets where they are protected from snake predation. The cause of the disappearance of these nesting colonies is presumed to be snake predation on eggs and young.
Phaethon lepturus
White-tailed tropicbird
Fagpi-apa'ka (CNMI)
Fakpe, Utag (Guam)
This white bird is conspicuous on many Pacific Islands (e.g., Saipan, Rota, Tinian) that have prominent cliff lines like Guam. Nests in holes and crevices on limestone cliffs were vulnerable to predation by the brown Treesnake, ultimately leading to abandonment of Guam as a nesting site.
Anous stolidus
Brown noddy
dankolo (CNMI)
Fahang (Guam)
Brown noddys nest in numbers on nearby Cocos but have not successfully nested on Guam since snake populations peaked in the 1970s and 1980s.
Gygis alba
White tern
Chunge' (CNMI and Guam)
This widespread, common, and conspicuous seabird has abandoned Guam as a nesting site and is rarely seen except on Cocos where it nests in large numbers.
Species extirpated from Guam prior to the introduction of the brown Treesnake:
Puffinus pacificus
Wedge-tailed shearwater
Lifa'ru (CNMI)
Paya'ya (Guam)
The dependence of this species on loose soils appropriate for it to dig burrows and deposit eggs restricted its nesting to limited sites. Adults and young in nest burrows also tended to allow predators such as snakes and rats to come close instead of fleeing.