Cozumel thrasher

Cozumel thrasher
Conservation status

Critically Endangered  (IUCN 3.1)[1]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Mimidae
Genus: Toxostoma
Species: T. guttatum
Binomial name
Toxostoma guttatum
(Ridgway, 1885)
Cozumel thrasher range

The Cozumel thrasher (Toxostoma guttatum) is a bird from the mockingbird family (Mimidae), which is endemic to the island of Cozumel off the Yucatán Peninsula, Mexico. It is believed to be the most critically endangered species of bird in Mexico - if it indeed still exists, which is probable but not certain.[2]

This bird is closely related to the long-billed and brown thrasher. It has been generally described as shy, but there have been descriptions to the contrary. It was once abundant throughout Cozumel before two hurricanes greatly affected its numbers. Invasive species are also thought to have impacted the population of the thrasher.

Taxonomy and Description

The Cozumel thrasher was first described as Harporhynchus guttatus by Robert Ridgway in 1885.[3][4] It has been described as a subspecies to its relative the long-billed thrasher, but was considered a separate species when it was determined in a 1998 study that it differed genetically more than five percent from both the long-billed and brown thrasher.[5] In the same study it was determined to be the basal member of the rufum group of Toxostoma thrashers.[5] The bird is monotypic.[3]

The thrasher is 21.5 to 24 cm in length. The adult has a brown crown, back, shoulders, and rump that becomes more red in its tint on its lower back and rump. Greater and lesser coverts are a warm brown with concealed white tips, preceded with a black bar. Primaries and secondaries are grayish-brown with warm rufous-brown outer webs. The retrices are also have a warm brown color. The lores and ear-coverts are a mottled grey brown. The chin and throat are an off-white color with a blackish partial malar stripe. The chest is a buffy-white in color with stark black teardrop shaped spots. The belly is off-white, and the flanks have larger black spots. Its vent is buffy and an underwing that is buffy-white with darker markings. The iris is yellow, the bill is grayish-brown, and the legs are brown with a dull tint. Juveniles' plumage have not been recorded, but presumably is similar in development to adulthood like the long-billed and brown thrasher.[3]

Similar species

The Cozumel thrasher is similar in appearance to the long-billed thrasher, but is smaller, darker in color, a blacker bill, and the markings are more sharply defined.[6] No other thrasher species co-exist on the island, but is most likely to be confused with the migratory wood thrush. The wood thrush differs in lacking wing bars, a shorter beak, and a different shape.[3]

Habitat

The habitat preferences for the thrasher is thought to be in low and medium deciduous and semideciduous forests.[3] It may have have once been most abundant in forest edges adjacent to clearings.[6]

Behavior

The thrasher is predominately terrestrial and elusive and as with all members of the Toxostoma genus, it may result to running instead of flying when startled. Ornithologists Ludlow Griscom and Raymond A. Paynter, Jr. have noted is secretive behavior, but James Bond did not.[6]

The song is described as a rich varied warbling, slightly scratchy with little repetition.[3] Bond described its alarm note being similar to the brown thrasher.[6]

Distribution

The distribution of the thrasher is restricted to Isla Cozumel which is 45km long and 20km wide.[3]

Decline and status

The numbers of this bird declined rapidly when Hurricane Gilbert hit this island on September 14, 1988. Until it was sighted in June 2004, this bird had last been seen in 1995, the same year that Hurricane Roxanne hit Cozumel on October 11, and it was widely believed to have become extinct.[2]

It is still unclear what damage the impact of Hurricanes Emily and Wilma in 2005 caused; it seems that the bird was not found anymore during a survey in December 2006[7]

Inquiry from the local population had suggested that the species would likely be encountered near the Mayan ruins of San Gervasio.[3]

The last - unconfirmed - sightings were in April 2006, where an apparent T. guttatum was sighted at the Cozumel Golf Club; in October and December 2007, thrashers were also seen but could not be reliably identified as T. guttatum. Relocation efforts continue; though at least a few birds seem to survive, the continuing existence of this species had not been verified as of January 2008.[8]

Some scientists believe that other factors must have contributed to the bird's decline, because the Cozumel thrasher likely survived hurricanes for millennia.[8] Introduced species, including predatory boa constrictors—which were released on the island in 1971 and are now abundant—may also have had a detrimental effect.[9]


Footnotes

  1. ↑ BirdLife International (2012). "Toxostoma guttatum". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
  2. ↑ 2.0 2.1 ENS (2004)
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Brewer, David (2001). Wrens, Dippers, and Thrashers. Yale University Press. pp. 232–33. ISBN 978-0-300-09059-8.
  4. ↑ The Ibis, Volume III, Fifth Series. 1885. p. 320.
  5. ↑ 5.0 5.1 Zink, Robert M.; Dittmann, Donna L. (1999). "Evolutionary Patterns of Morphometrics, Allozymes, and Mitochondrial DNA in Thrashers (Genus Toxostoma)". The Auk 116 (4): 1021–38. doi:10.2307/4089682.
  6. ↑ 6.0 6.1 6.2 6.3 "El cuitlacoche de cozumel: The endemic thrasher of Cozumel Island". Villanova University. Retrieved 8 March 2015.
  7. ↑ Surfbird News (2006)
  8. ↑ 8.0 8.1 Curry (2008)
  9. ↑ Martínez-Morales, Miguel Angel; Cuarón, Alfredo D. (July 1999). "Boa constrictor, an introduced predator threatening the endemic fauna on Cozumel Island, Mexico" (abstract). Biodiversity and Conservation 8 (7): 957–963. doi:10.1023/A:1008815004072.

References

External links