Socorro mockingbird

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Socorro mockingbird
Mimus graysoni (Museum de Geneve).jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Mimidae
Genus: Mimus
Species:
M. graysoni
Binomial name
Mimus graysoni
(Lawrence, 1871)
Mimus graysoni map.svg
Synonyms

Mimodes graysoni Ridgway, 1882

The Socorro mockingbird (Mimus graysoni) is an endangered mockingbird endemic to Socorro Island in Mexico's Revillagigedo Islands. The specific epithet commemorates the American ornithologist Andrew Jackson Grayson.

Contents

Mimus graysoni shows its close relationship to the northern and tropical mockingbirds rather subtly. It is a much stouter bird, resembling some thrashers in habitus. It also has a distinct juvenile plumage, more rufous above and has a heavy pattern, especially below. This uncannily resembles, e.g., the gray thrasher (Toxostoma cinereum) from Baja California, [2] but is apparently a case of convergent evolution. [3]

Systematics and taxonomy

This is a rather distinct Mimus mockingbird and was for some time placed into a distinct genus, Mimodes. This was revealed to be incorrect based on analysis of mtDNA NADH dehydrogenase subunit 2 sequences. [3]

Rather, the present species is closely related to the northern and tropical mockingbirds. Its distinctiveness is the result of the strong selective pressure on its island home, which enforced the evolution of conspicuous adaptational autapomorphies. The juvenile plumage might also have been the result of genetic drift enforced maybe by resource partitioning in this aggressive bird. The standard model of molecular clocks cannot be applied for mimids as their rates of mutation seem to vary much over time. [4] While it is the most phenotypically distinctive bird on Socorro, it also has the strongest ecological change from its ancestors; therefore its distinctiveness is not informative except supporting the theory that it is one of the older Socorro endemics. [2]

Thus, and because the adaptation to the peculiar conditions on Socorro may even have accelerated not only morphological but also molecular evolution  – see also founder effect   it cannot be said with any certainty whether or not among Mimus, the Socorro species is a quite recent island offshoot of either of the mainland species. In any case, the three taxa are very close relatives.

Ecology and status

The Socorro mockingbird today lives mainly in unmodified low forest above 600 m (2000 ft), where it prefers groves of Oreopanax xalapensis and the endemic Guettarda insularis , with an understorey dominated by Triumfetta socorrensis and the endemic Eupatorium pacificum . [1] As late as March 1953 it was still "common" at lower elevations, foraging in arid open shrublands of Croton masonii and prickly pear [note 1] . [2] In November of the same year, the birds had retired to the more humid forest in the uplands and were busy singing and defending territories. [2] Today, they mainly remain in Ficus cotinifolia stands when visiting the lower elevations. [1] The breeding season is extended, with nests in attendance between November and July, with the peak laying occurring in March and April. [1] Three eggs are laid, which take no more 15 days to hatch. [1]

The birds are generally reluctant to fly and as late as the mid-20th century were still fatally unwary; if pressed they will rather hop away than fly and if they take wing, it is usually for a few meters only. [2] This may be an adaptation to the fact that Socorro has no native terrestrial predators, but red-tailed hawks and great frigatebirds that not infrequently prey on mockingbird-sized birds.

This species feeds on small invertebrates, the remains of land crabs ( Johngarthia planata ) [2] and fruit, namely of the endemic shrubs Ilex socorrensis and Sideroxylon socorrense , the latter of which has also become rare. [1] Flies are pecked up but do not seem to be snatched out of the air. [2] Like many Mimidae, the Socorro mockingbird is an aggressive, solitary species living alone or with its partner. When they come together at a plentiful food source – e.g. blowflies on a carcass – there is a marked social hierarchy between birds and rarely are more than two or three actively feeding; the less dominant birds hang around nearby, waiting for their turn. [2]

The call is two medium followed by one lower whistle. Less often, a full song is given, consisting of a variable warbling tune, repeated several times as in many mockingbirds. It is not clear whether this species imitates other birds like its relatives do; in any case only the Socorro tropical parula, Socorro towhee and Socorro wren would seem to possess songs that might serve as models for the mockingbirds, and except the parula these are not often found in the mockingbird's core habitat. [2]

Status and conservation

This species numbers fewer than 400 individuals altogether and is considered Critically Endangered by the IUCN. Mimus graysoni is mostly threatened by habitat loss caused by feral sheep and the locust Schistocerca piceifrons , and predation by feral cats which became established after 1953, probably in the early 1970s. It is not believed that the northern mockingbird which has colonized Socorro in the late 20th century is limiting the recovery of its relative; the two Mimus do not occupy the same habitat and even if they did, the native bird is larger and more powerful and would probably simply outcompete its mainland relative in native vegetation at least. The extermination of the sheep is underway in the hope of restoring the island ecosystem. [1]

On one hand, it seems that the Socorro mockingbird is a prolific species and would be able to increase in numbers quickly if habitat improves. On the other hand, its terrestrial habits make it vulnerable to cat predation and this may limit its recovery even if sheep are contained; it is not known for example in how far foraging in the lowlands – now cat-ridden – was important for robust breeding success. In addition, it can be expected that predation on this species by both the native red-tailed hawk as well as the feral cats has increased since the Socorro dove – formerly a preferred prey item – has become extinct in the wild. Cerro Evermann, Socorro's main volcano, is still active and erupts on a limited scale every few decades; [5] as the mockingbirds seem to depend on upland forest habitat, a major eruption could place the species in jeopardy (see also San Benedicto rock wren). This threat is not considered significant compared to the problem of introduced species however. [1]

Notes

  1. Probably Engelmann's Prickly Pear (Opuntia engelmannii): Brattstrom & Howell (1956)

Related Research Articles

<span class="mw-page-title-main">Mimid</span> Family of birds

The mimids are the New World family of passerine birds, Mimidae, that includes thrashers, mockingbirds, tremblers, and the New World catbirds. As their name suggests, these birds are notable for their vocalization, especially some species' remarkable ability to mimic a wide variety of birds and other sounds heard outdoors. They are commonly referred to as mimic thrushes but are not, in fact, thrushes.

<span class="mw-page-title-main">Mockingbird</span> Family of birds

Mockingbirds are a group of New World passerine birds from the family Mimidae. They are best known for the habit of some species mimicking the songs of other birds and the sounds of insects and amphibians, often loudly and in rapid succession.

<span class="mw-page-title-main">Thrasher</span> New World group of passerine birds

Thrashers are a New World group of passerine birds related to mockingbirds and New World catbirds. Like these, they are in the family Mimidae. There are 15 species in one large and 4 monotypic genera.

<span class="mw-page-title-main">Northern mockingbird</span> Species of bird

The northern mockingbird is a mockingbird commonly found in North America. This bird is mainly a permanent resident, but northern birds may move south during harsh weather. This species has rarely been observed in Europe. This species was first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae as Turdus polyglottos. The northern mockingbird is known for its mimicking ability, as reflected by the meaning of its scientific name, "many-tongued mimic". The northern mockingbird has gray to brown upper feathers and a paler belly. Its tail and wings have white patches which are visible in flight.

<span class="mw-page-title-main">Gray catbird</span> Species of bird

The gray catbird, also spelled grey catbird, is a medium-sized North American and Central American perching bird of the mimid family. It is the only member of the "catbird" genus Dumetella. Like the black catbird, it is among the basal lineages of the Mimidae, probably a closer relative of the Caribbean thrasher and trembler assemblage than of the mockingbirds and Toxostoma thrashers. In some areas it is known as the slate-colored mockingbird.

<span class="mw-page-title-main">Catbird</span> Group of birds

Several unrelated groups of songbirds are called catbirds because of their wailing calls, which resemble a cat's meowing. The genus name Ailuroedus likewise is from the Greek for 'cat-singer' or 'cat-voiced'.

<span class="mw-page-title-main">Revillagigedo Islands</span> Volcanic archipelago in the Pacific Ocean

The Revillagigedo Islands or Revillagigedo Archipelago are a group of four volcanic islands in the Pacific Ocean, known for their unique ecosystem. They lie approximately 458 kilometres (285 mi) from Socorro Island south and southwest of Cabo San Lucas, the southern tip of the Baja California Peninsula, and 698 to 1,092 kilometres west of Manzanillo. Historically linked to the Mexican state of Colima, to which they were granted in 1861 to establish a penal colony, the islands are under Mexican federal property and jurisdiction.

<span class="mw-page-title-main">Socorro Island</span> Small volcanic island off the west coast of Mexico

Socorro Island is a volcanic island in the Revillagigedo Islands, a Mexican possession lying 600 kilometres (370 mi) off the country's western coast. The size is 16.5 by 11.5 km, with an area of 132 km2 (51 sq mi). It is the largest of the four islands of the Revillagigedo Archipelago. The last eruption was in 1993.

<span class="mw-page-title-main">Sage thrasher</span> Species of bird

The sage thrasher is a medium-sized passerine bird from the family Mimidae, which also includes mockingbirds, tremblers, and New World catbirds. It is the only member of the genus Oreoscoptes. This seems less close to the Caribbean thrashers, but rather to the mockingbirds instead.

<span class="mw-page-title-main">Andrew J. Grayson</span> American ornithologist and painter

Andrew Jackson Grayson (1819–1869) was an American ornithologist and artist.

<span class="mw-page-title-main">Socorro dove</span> Species of bird

The Socorro dove or Grayson's dove is a dove that is extinct in the wild. It was endemic to Socorro Island in the Revillagigedo Islands off the west coast of Mexico. The last sighting in its natural habitat was in 1972 and it only survives in captivity. A reintroduction program is being prepared.

<span class="mw-page-title-main">Tropical mockingbird</span> Species of bird

The tropical mockingbird is a resident breeding bird from southern Mexico to northern and eastern South America and in the Lesser Antilles and other Caribbean islands.

<span class="mw-page-title-main">Tropical parula</span> Species of bird

The tropical parula is a small New World warbler. It breeds from southernmost Texas and northwest Mexico (Sonora) south through Central America to northern Argentina, including Trinidad and Tobago. This widespread and common species is not considered threatened by the IUCN.

<span class="mw-page-title-main">Clarion Island</span> Westernmost of the Revillagigedo Islands

Clarion Island, formerly Santa Rosa, is the second largest, westernmost and most remote of Mexico's Revillagigedo Islands. The island is located 314 kilometres (195 mi) west of Socorro Island and over 700 kilometres (430 mi) from the Mexican mainland.

<span class="mw-page-title-main">Pearly-eyed thrasher</span> Species of bird

The pearly-eyed thrasher is a bird in the thrasher family Mimidae. It is found on many Caribbean islands, from the Bahamas in the north to the Grenadines in the south, with an isolated subspecies on Bonaire.

<span class="mw-page-title-main">Trembler</span> Genus of birds

Tremblers (Cinclocerthia) are a genus of perching birds in the family Mimidae that are endemic to the Lesser Antilles. They are medium-small, mostly brown or grey birds with long beaks and tails that typically are held cocked. Most recent authorities recognize two species in the genus, but some split each into two species, bringing it to four species:

<span class="mw-page-title-main">Socorro parakeet</span> Species of bird

The Socorro parakeet, known in aviculture as the Socorro green conure or Socorro conure, is a species of bird in subfamily Arinae of the family Psittacidae, the African and New World parrots. It is endemic to Socorro Island in the Revillagigedo Islands, Mexico.

<i>Mimus</i> Genus of birds

Mimus is a bird genus in the family Mimidae. It contains the typical mockingbirds. In 2007, the genus Nesomimus was merged into Mimus by the American Ornithologists' Union. The genus name is Latin for "mimic".

<span class="mw-page-title-main">Socorro wren</span> Species of bird

The Socorro wren is a species of bird in the family Troglodytidae. It is endemic to Socorro Island, Mexico. It was formerly placed in Thryomanes but was moved to Troglodytes considering "manners, song, plumage, etc." and by biogeography and mitochondrial DNA sequence analysis of the MT-NADH dehydrogenase protein 2 gene.

Sideroxylon socorrense is a plant species in the family Sapotaceae. It is endemic to Mexico, native to Socorro Island in the Revillagigedo Islands and to the Pacific coast states of Sinaloa and Nayarit on the Mexican mainland.

References

  1. 1 2 3 4 5 6 7 8 BirdLife International (2020). "Mimus graysoni". IUCN Red List of Threatened Species . 2020: e.T22711084A179825007. doi: 10.2305/IUCN.UK.2020-3.RLTS.T22711084A179825007.en . Retrieved 12 November 2021.
  2. 1 2 3 4 5 6 7 8 9 Brattstrom, Bayard H. & Howell, Thomas R. (1956). "The Birds of the Revilla Gigedo Islands, Mexico" (PDF). Condor . 58 (2): 107–120. doi:10.2307/1364977. JSTOR   1364977.
  3. 1 2 Barber, Brian R.; Martínez-Gómez, Juan E. & Peterson, A. Townsend (2004). "Systematic position of the Socorro mockingbird Mimodes graysoni" (PDF). Journal of Avian Biology. 35 (3): 195. doi:10.1111/j.0908-8857.2004.03233.x. Archived from the original (PDF) on 2008-09-07.
  4. Hunt, Jeffrey S.; Bermingham, Eldredge & Ricklefs, Robert E. (2001). "Molecular systematics and biogeography of Antillean thrashers, tremblers, and mockingbirds (Aves: Mimidae)" (PDF). Auk . 118 (1): 35–55. doi:10.1642/0004-8038(2001)118[0035:MSABOA]2.0.CO;2. S2CID   51797284.
  5. Global Volcanism Program (2007): Socorro. Version of 2007-JUN-10.