Efforts to preserve the Thick-Billed Parrot in North Western Mexico
By Tiberio Monterrubio PhD. (Mexico) ©
Thick-billed Parrot is one of the two species in the genus Rhynchopsitta. This species is a medium-size parrot that averages 38 cm in length and with its long and pointed tail and wings has a body form similar to a small macaw (falcon like shape). Forshaw (1989) considered the Rhynchopsitta genus to be related to the macaws because the body form is similar and the naked skin patch around the eyes in thick-bills resemble the naked skin patches in some macaw species. Thick-bill males and females are alike in coloration; adults are bright green and possess a yellow stripe on the under-wing coverts. Their superciliary, forehead, and "shoulders" are red (Juniper and Parr 1998). The life span of the species exceeds 30 years in captivity but life span in the wild is unknown. No information exist on survival rates of the different age groups in the wild (Forshaw 1989, Snyder et al. 1994). Adults are easily differentiated from juveniles that lack the red superciliary and "shoulders"; the bill coloration of inmatures is flesh that darkens with time and in adults it is black.
The Thick-billed Parrot (Rhynchopsitta pachyrhyncha) is considered endangered by the Mexican and U.S governments and is listed in appendix I of CITES (Birdlife International 2000). In the case of the Thick-billed Parrot, a decline of the species throughout its range is a consensus (Snyder et al.1999). The population was estimated at fewer than 5000 birds in 1992 and 1000-4000 in 1995 (Birdlife International 2000).
Most parrots live in tropical habitats at low elevation, are sedentary or short distance migrants, and are territorial (Juniper and Parr 1998). On the contrary, Thick-billed Parrots live in temperate forests at high elevations, are migratory, nomadic in winter to seek food, and specialists on a single food resource (conifer seeds), and are social at all seasons. The breeding range of the species is actually restricted to the states of Chihuahua and Durango in northwestern México. During the non-breeding season (late November to April), the species migrates to south-central portions of the Sierra Madre Occidental. The Sierra Madre Occidental is a range of rugged mountains extending from northwest Chihuahua and Sonora to the central part of Michoacán in Mexico. This mountain chain runs parallel to the pacific ocean. The sierra is 100 to 200 km wide and 1200 km long and consists of rugged terrain with some elevations reaching 3000 m (Lanning and Shiftlet 1983). The species is considered highly vulnerable to human disturbance because of its specialized diet, the specific nesting conditions and its limited geographic range. In an effort to prerserve the species, we have studied the parrot numbers, breeding activity, and nesting habitat requirements of the Thick-billed Parrot during the latest 6 years 1995-2000.
The parrots were mostly studied in 6 remaining nesting areas. The study sites are located in the northwest and central portion of the state of Chihuahua (Fig 1). High elevation conifer forests of the region consist of Mexican white pine, Durango pine, Douglas fir, White fir and Quaking aspen (Lammertink et al. 1996, Lanning and Shiftlet 1983). The characteristics of these high elevation areas varies from plateau-like tops with open pine and fir forests, to thick pine and fir stands in canyons and below high cliffs (Snyder et al. 1999).
Nests were found by daily searches following vocalizing pairs, during the pre-laying period (early in June), parrot activity involves cavity examination, loud vocalizations, and frequent small flock movement at a local scale. Once a nest-tree was found, Geographic Positioning System (GPS) readings of its location were taken and the tree was marked with flagging for a posteri recognition. Nest-trees found in any breeding season were re-examined in subsequent seasons. During the egg laying period (middle June-late July), we used climbing spikes, rappel rope and harnesses to determine nest content and activity status. Frequently, many nest cavities were only occupied early in the season; some others were only used as roosting places.
Accessible nests were examined weekly by climbing the tree and observing the cavity interior. Parrot chicks produce loud vocalizations and are heard at short distances from the nesting trees. During the Post hatching period (late July-mid August); individual trees were checked when adults were absent for foraging. Recently hatched chicks were weighed. Eggs and chicks were color marked with non-toxic paint for later identification.
Two main breeding areas reported in the literature twenty years ago, continue to be the major breeding strongholds for the species. These areas are called Cebadillas and Madera and accounted combined for 74% of the nests respectively. I assessed reproductive success of 123 accessible nests. Overall, 81% of the nests were successful and 200 chicks fledged. In the 5-year period, clutches averaged 2.73 and 1.62 young parrots fledged/nest. Causes of total nest loss included: nest desertion, mammal predation, and parasite infestation. During the study, nests were found in 187 trees and snags of seven tree species. Nests occurred preponderantly in snags (59%). Nests averaged 75.2 cm diameter at breast height (dbh), and only 2 nests out of the total of 187 were in trees under 40 cm. dbh. Most nests occurred in Douglas fir (32.6%), and Mexican white pine (21.9%).
Some nesting persisted in areas under heavy commercial harvest, but trees and snags used for nesting were frequently logged and many nest sites were lost. Decline of the species seems to be related to large-scale logging of historical breeding and wintering range. Timber harvesting is affecting nest site availability in breeding areas and probably also food supply in breeding and wintering areas.
Thick-billed Parrot historically seem to have nested in mature and old growth forest at high elevations; they shared their habitat with the extinct Imperial Woodpecker (Campephilus imperialis). No large fragments of old growth forests remain at Thick-billed Parrot nesting elevation today, and it caused the Imperial woodpecker's extinction (Lammertink et al. 1996). Cebadillas and Madera, do not have the pristine conditions found in an old growth forests, but these are areas with higher densities of large snags, pines, and firs than most of the surrounding forests and functionally resemble mature forests and benefit parrot nesting.
Thick-billed Parrots do not seem to have reproduction problems at the current breeding areas in most years. Clearly Thick-billed Parrots do not require old growth forests exclusively for nesting. However, they do require large trees or snags for nesting, besides of the fact that large trees produce more seeds and are more beneficial for feeding. These conditions are now found in very few areas which are urgently needed for official protection. The cause of the species decline may be primarily due to a low survival rate of the parrots, specially juveniles during non-breeding time and probably may be related to habitat loss in wintering and stop-over habitats. Unreliable food supplies increased by the fragmentation and impoverishment of the pine forests in the wintering areas, breeding areas or both may now be the responsible for the species decline.
A recovery plan for the species it's under development with assistance from participating land owners, government officials and academic groups. Mechanisms to preserve the nesting habitat and restore the degraded areas must be found.
Where cavity availability is minimal, artificial nests may be placed and their use and suitability should be evaluated. Additional research on food availability in nesting and wintering areas and how it relates to success rates and reproduction should start soon. The research on the key factors regulating parrot abundance, productivity and survival should continue. If protected areas are designated, protection of breeding habitat and food supply may both be required. Finally, the establishment of a network of protected areas in the entire Sierra Madre should be considered not only to protect breeding habitat but to preserve food supply in the wintering areas as a strategy to preserve the Thick-billed Parrot and the associated bird communities in high elevation forests of the Sierra Madre Occidental.
Birdlife International. 2000. Threatened birds of the world. Barcelona and Cambridge, UK:Lynx Edicions and Birdlife International Insertar cita Birdlife International
Forshaw, J. M. 1989. Parrots of the World. Lansdowne Editions, Australia.
Lammertink, J. M., J. A. Rojas-Tome, F. M. Casillas-Orona., and R. L. Otto. 1996. Status and Conservation of Old-Growth Forests and Endemic birds in the Pine-Oak Zone of the Sierra Madre Occidental, Mexico. Institute for Systematics and Population Biology (Zoological Museum) University of Amsterdam. Amsterdam.
Lanning, D. V., and J. T. Shiflett. 1983. Nesting ecology of Thick-billed Parrots. Condor 85:66-73.
Snyder, N. F. R., E. C. Enkerlin-Hoeflich., and M.A. Cruz-Nieto. 1999. Account # 411: Thick-billed Parrot, Rhynchopsitta pachyrhyncha. The birds of North America. (F. B. Gill and A. Poole. Eds.) The American Ornithologists' Union and The Academy of Natural Sciences of Philadelphia. Philadelphia.
Send correspondence to:
Tiberio Cesar Monterrubio R. PhD.
Universidad Michoacána de San Nicolás de Hidalgo
Facultad de Biología Phone: (43) 16-74-12.
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