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Status and conservation of Yellow-headed Parrot Amazona oratrix “guatemalensis” on the Atlantic coast of Guatemala

  • Eisermann & Avendaño Bird Studies Guatemala

Abstract and Figures

In 2001 the abundance of Yellow-headed Parrot Amazonaoratrix at a roost site in Punta de Manabique, Guatemala was found to be 70 individuals. A comparison with a roost census in 1994 suggested a population decline. The largest threat to this form of Yellow-headed Parrot is nest-robbing for the pet trade. The rate of decline and the limited number of individuals living in the wild suggest the population is facing extinction. The core zone of reproduction is located in a palm savanna. Information on feather patterns of the head of this form of A.oratrix is provided.
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Bird Conservation International (2003) 13:361366. BirdLife International 2003
DOI: 10.1017/S0959270903003265 Printed in the United Kingdom
Status and conservation of Yellow-headed
Parrot Amazona oratrix ‘‘guatemalensis’’ on
the Atlantic coast of Guatemala
In 2001 the abundance of Yellow-headed Parrot Amazona oratrix ‘‘guatemalensis’’ at a roost
site in Punta de Manabique, Guatemala was found to be 70 individuals. A comparison
with a roost census in 1994 suggested a population decline. The largest threat to this form
of Yellow-headed Parrot is nest-robbing for the pet trade. The rate of decline and the
limited number of individuals living in the wild suggest the population is facing
extinction. The core zone of reproduction is located in a palm savanna. Information on
feather patterns of the head of this form of A. oratrix is provided.
Yellow-headed Parrot Amazona oratrix is endemic to northern Central America,
with several subspecies occurring in Mexico, Belize, Guatemala and Honduras
(Juniper and Parr 1998). While the taxonomic status of these subspecies is not
yet clear (Howell and Webb 1995), Lousada and Howell (1996) describe a form
named Amazona oratrix ‘‘guatemalensis’’ found on the Atlantic coast of Guatemala,
and emphasize the special threat to this population. The status of this population
and the threats it faces were described in Collar et al. (1992). A. oratrix is consid-
ered globally Endangered by IUCN (Hilton-Taylor 2000) and BirdLife Interna-
tional (2000).
In 2001 a basic study was undertaken on the local avifauna of the Punta de
Manabique protected area (hereafter Manabique) in Izabal, Guatemala
(Eisermann 2001). I attempted to evaluate the status of Yellow-headed Parrot,
using roost counts, and compared the results with previous estimates.
Study area and methods
The peninsula of Punta de Manabique is a marine and terrestrial protected area
on the Atlantic coast of Guatemala (15°50N 88°30W) (Figure 1). The terrestrial
area covers 670 km
and is characterized by palm swamp forests, coastal brush,
mangrove, and a mosaic of forest fragments and agricultural land. About 2,000
people live inside the limits of the protected area (INE 1994) and practise fishing,
charcoal-making, cattle farming and other agricultural activities for subsistence.
More than 320 bird species are known to occur in Manabique (Eisermann 2001).
In order to estimate the population size of Yellow-headed Parrot, I conducted
Knut Eisermann 362
Coast line
Limit of the protected area
10 km
Roost site and
principal flight direction
of arriving parrots
Area of reproduction
Gulf of Honduras
Figure 1. The Punta de Manabique protected area surveyed for Yellow-headed Parrot
Amazona oratrix.
counts on a traditional roosting site. According to interviews with local people
it was the only known night roost. Censuses with two observers took place before
and after the breeding season (8 January, 6 May, 14 June 2001). As they arrived
at the roost the parrots were readily observed since the roost was in an isolated
stand of tall mangroves surrounded by the sea and swamp shrub. Calling parrots
were clearly distinguishable from other large Amazon parrots Amazona spp. even
at dusk. Wind strength was classified according to the Beaufort Wind Scale.
I documented Yellow-headed Parrots nesting in palm savanna and mangrove
forest. During the reproductive period in April, A. oratrix were most abundant
in an open palm savanna dominated by Roystonea oleracea. The understorey con-
sisted of various species of grass, some up to 2 m tall. The area was used for low
intensity cattle grazing. This palm savanna is usually flooded during the rainy
season (June–January, L. Salgero, pers. comm.).
Most nest holes were found in snags of Roystonea, but were also found in
trunks of other trees with suitable cavities (e.g. Salix spp.). Three nest cavities
were located along the coastline of Manabique in old red mangroves
(Rhizophora mangle), some as high as 20 m tall. In April, when juveniles were
growing within the nest holes, I made an observation of feeding adults. The
majority of nest holes previously observed were destroyed by poachers.
Trunks were either chopped down, their entrance considerably widened, or a
hole made at nest height, when the nest cavity bottom was considerably
below the entrance.
A traditional roosting site was situated in a stand of tall (20 m), mostly dead
mangrove stands on the beach. Parrots were observed using trees 1050 m from
Yellow-headed Parrot in Guatemala 363
the waterline, with the wind strength 7. It is unknown if parrots use the same
trees in nights with stronger winds. Local people report the roost has existed for
more than 10 years (C. Palencia, pers. comm.). The distance between the core
area of reproduction and the roost site was approximately 13 km.
Abundance and status
In order to estimate the abundance of parrots, repeated censuses were con-
ducted at a traditional roosting site. Parrots arrived soon after sunset within
45 and 80 min, in pairs or groups of three individuals, congregating in the
upper canopy of 710 mangrove trees. Between January and June, five Brown
Pelicans Pelecanus occidentalis and a pair of Red-lored Parrot Amazona autum-
nalis roosted in the same trees. During January 2001 and before the breeding
season, 60 individuals of Yellow-headed Parrot were counted, and in May
and June, after fledging of juveniles, 68 individuals were recorded, suggesting
low reproductive success.
I recorded the distribution pattern of yellow head feathers of six parrots
(Figure 2) to further document exterior features of the Manabique population
as provided by Lousada and Howell (1996) since the taxonomic status of the
intermediate form A. oratrix ‘‘guatemalensis’’ is still unclear. Three wild indi-
viduals (a, b, c in Figure 2) were observed clearly on 8 May 2001 at the roosting
site after sunrise. Photographs were taken of these and also of three captured
individuals in huts of local Guatemalans. Table 1 provides a characterization of
the unfeathered parts of the three captured individuals.
Semideciduous and deciduous forests, moist forest, gallery forests, pine sav-
annas, mangroves and coastal shrub have been reported as habitat of A. oratrix
(Collar et al. 1992, Howell and Webb 1995, Lousada and Howell 1996, England
2000). The use of Roystonea palm savanna has not been described previously and
seems to be a unique trait of the Manabique population. However, the structure
of this vegetation is similar to pine savanna.
Lousada and Howell (1996) counted about 100 individuals in Manabique at
the traditional and only known roosting site in 1994. The difference in counts
between 1994 and 2001 could indicate a population decline of some 30%. These
results underlie the dramatic decline of the species in most of its range (Snyder
et al. 2000). Due to habitat destruction and natural barriers, the Manabique popu-
lation of A. oratrix ‘‘guatemalensis’’ is isolated from other populations (Lousada
and Howell 1996). It may be therefore, that Yellow-headed Parrot is seriously
threatened in Manabique.
The primary threats to Yellow-headed Parrot throughout its range are nest-
robbing for the pet trade and loss of habitat (Snyder et al. 2000). The Manabique
population suffers from this illegal trade, which is organized from Honduras,
but only three parrots were seen in huts of local Guatemalans during 10 months
in the field. Nest-robbers cross the border armed and carrying machetes, axes
and ropes (L. Salgero pers. comm.). Nest cavities and trees are almost always
destroyed when poaching juveniles or eggs. Therefore, the population faces a
Knut Eisermann 364
Figure 2. Distribution pattern of yellow head feathers (drawn in black) among different
individuals of Amazona oratrix in Punta de Manabique according to photos by K. Eiserm-
ann. (a, b) wild-living couple, (c) wild-living individual, (d) captive individual at the age
of 1 year, (e) captive individual at the age of 3 years, (f) captive individual at the age of
4 years.
Table 1. Exterior features (referring to Lousada and Howell 1996) of three captive individuals of
Amazona oratrix.
4-year-old bird 3-year-old bird 1-year-old bird
Claws Dark Pale Dark
Mandibles Very pale Very pale Pale
Cere/bristle Pale/pale Pale/pale Grey/pale
Orbital ring/eyelid edge Pale/dark Pale/dark Pale/dark
loss of productivity, not only due to the loss of individuals, but also due to the
declining number of potential nesting sites. An additional threat to A. oratrix is
hunting, evidenced by the discovery of parrot wings beside a fireplace in a local
fishing camp near the roosting site. Available suitable habitat is further
Yellow-headed Parrot in Guatemala 365
threatened by intensive cattle grazing, which is practised even within the pro-
tected area.
A. oratrix ‘‘guatemalensis’’ is considered an intermediate form between the
recognized subspecies A. oratrix belizensis and A. oratrix hondurensis (Lousada and
Howell 1996, 1997). My characterization of clearly observed individuals matches
closely the description in Lousada and Howell (1996) and further documents the
exterior features of this small population.
Punta de Manabique is a designated wildlife refuge. In order to preserve the
Manabique population of Yellow-headed Parrot, planning and conservation
administered by FUNDARY (Fundacio
n Mario Dary), should be focused in the
short term on preventing nest-robbing.
I thank FUNDARY for the technical support and Cesar Paz, Edy Troches and
Lucio Salgero for the field assistance. I appreciate critical and helpful comments
on the manuscript made by James D. Gilardi, Seb Buckton, Dylan Stearns, Jessica
Eberhard and Francisco Villela, who also improved the English usage provided
through the Association of Field Ornithologists’ programme of editorial assist-
ance. Results presented here are part of a study supported by the National Fish
and Wildlife Foundation and USAID.
Bird Life International (2000) Threatened birds of the world. Barcelona and Cambridge, U.K.:
Lynx Ediciones and Bird Life International.
Collar, N. J., Gonzaga, L. P., Krabbe, N., Madron
o Nieto, A., Naranjo, L. G., Parker, T. A.
III and Wege, D. C. (1992) Threatened birds of the Americas: the ICBP/IUCN Red Data Book.
Washington, D.C. and Cambridge, U.K.: Smithsonian Institution Press, and Interna-
tional Council for Bird Preservation.
Eisermann, K. (2001) Caracterizacio
n de la avifauna del Ν
rea de Proteccio
n Especial Punta
de Manabique, Izabal, Guatemala. Unpub. Report FUNDARY, Guatemala.
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assessment. Cotinga 13: 3243.
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Cambridge, U.K.: IUCN.
Howell, S. N. G. and Webb, S. (1995) A guide to the birds of Mexico and northern Central
America. New York: Oxford University Press.
INE (1994) Censo de poblacio
n, municipio Puerto Barrios. Guatemala: Instituto Nacional de
Juniper, T. and Parr, M. (1998) Parrots: a guide to parrots of the world. New Haven, CT: Yale
University Press.
Lousada, S. A. and Howell, S. N. G. (1996) Distribution, variation, and conservation of
Yellow-headed Parrots in northern Central America. Cotinga 5: 4653.
Lousada, A. S. and Howell, S. N. G. (1997) Amazona oratrix hondurensis: a new subspecies
of parrot from the Sula valley of northern Honduras. Bull. Brit. Orni. Club 117: 205
Snyder, N., McGowan, P., Gilardi, J. and Grajal, A. (2000) Parrots: status survey and conser-
vation action plan. Gland, Switzerland and Cambridge, U.K.: IUCN.
Knut Eisermann 366
n Mario Dary (FUNDARY), 5a avenida 962, 3er Nivel Apto. 2, Zona 1, Guatemala
Ciudad, Guatemala. Present address: P.O. Box 098 Perife
rico, Guatemala Ciudad, Guate-
Received 18 May 2002; revision accepted 4 June 2003
... Sunrise surveys lasted until 1030 h and afternoon counts were initiated 90 min before sunset. A minimum of 2 observers made observations at each survey site, with each watching 1808 of the view (Bibby et al. 2000, Eisermann 2003, Téllez-García 2008, Berkunsky and Reboreda 2009. ...
... Historically, the species was reported as uncommon or local along the Pacific coast (Schaldach 1963, Binford 1989, without specific abundance estimates among forest types (Ridgely 1981). One abundance estimate for a local population comes from the Punta de Manabique protected area (670 km 2 ) in Guatemala, where the entire population used a single communal roost of about 70 individuals (Eisermann 2003). This corresponds to a density of 0.1 individuals per km 2 ; however, we found no updated information concerning the Given the paucity of preexisting data, we are unable to compare our densities to historical data from the study area. ...
... Although communal roosts provide estimates of population abundance for Amazona parrots in a variety of habitats (Howell 1999, Eisermann 2003, Cougill and Marsden 2004, Vaughan et al. 2005, Matuzak and Brightsmith 2007, Lee and Marsden 2012, Kiacz et al. 2020, it is difficult to determine the effective area used by congregated parrots and to transform counts into density. ...
ABSTRACT—The Yellow-headed Parrot (Amazona oratrix) is considered globally endangered due to intense poaching pressure and extensive tropical forest loss. We examined the relationships among nesting pair density, survey area, tropical forest type, and forest conservation conditions to estimate the potential population size in central-western Mexico. The surveyed areas constitute a representative sample of forest types, property ownership, and land use in the region. We estimated the overall surveyed area and the nesting pairs in general and by each forest type. Data were analyzed in multiple and single linear regression models.We used a high-resolution vegetation model to measure the extent of each forest type and land use in the area with suitable climatic conditions for nesting. We recorded 111 nesting events in 77 distinct nest trees during the 2002–2013 study period in an area of 185.3 km2. Overall nesting density was 0.59 6 0.28 pairs per km2. Individual areas surveyed showed a broad variation in nest densities (0.14–1.5 per km2). Primary tropical semi-deciduous forest held 64% of the nesting pairs and the highest nesting density (1.98 6 0.82 per km2). Tropical dry deciduous forest contained 11% of nesting pairs and 0.20 6 0.19 pairs per km2. Single linear regression models by forest type performed better and are more practical for abundance calculations than multiple regression models. We estimate the size of the nesting population in the region at 701 pairs (95% CI: 526–876), which corresponds to about 1,399–2,330 parrots, using the mature/ immature ratio used by the IUCN. The results suggest that central-western Mexico may hold about 27% of the species’ global population.
... The Yellow-headed Parrot (A. oratrix) is a Neotropical species found in Mexico and northern Central America. This species is classified as "Endangered" on the IUCN Red List and thought to be declining across its range Ornithological Applications 124:1-14 © 2022 American Ornithological Society (Eisermann 2003, Monterrubio-Rico et al. 2010, BirdLife International 2020. Population declines are attributed to the pet trade and to habitat loss, resulting in small remnant populations scattered throughout its historical range (Lousada andHowell 1996, Monterrubio-Rico et al. 2010). ...
Full-text available
The endangered Yellow-headed Parrot (Amazona oratrix) has experienced a considerable reduction in abundance and distribution. Identifying natural and anthropogenic causes of nest failure is a critical step towards developing conservation actions that increase nest survival. In this study, we examined daily nest survival in relation to temporal, habitat, and anthropogenic factors, as well as nest site properties. We monitored nests (n = 124) across 6 study sites in Belize during 2017 and 2018 and independently modeled the effects of predation, abandonment and poaching on daily nest survival rates. Overall, the estimated cumulative nest survival probability was 0.18 (95% CI: 0.12–0.25). Predation was the main cause of nest failure, followed by abandonment, and poaching. Our results showed that nest predation and abandonment usually occurred early in the nesting cycle. Day within the nesting season negatively influenced daily survival for abandoned nests and had a quadratic effect on survival for poached nests. Poaching events occurred at a specific date range later in the season, with nests farther from the nearest human settlement having higher daily survival. Findings from this study highlight the additive mortality effect that nest poaching is having on Yellow-headed Parrot populations in Belize and show that managers can anticipate the timing and location of nests most vulnerable to poaching.
... When possible, we also recorded with video in main flyways and/or colonial roosting areas. In secure areas, additional evening counts were conducted at sites where the birds congregated as in Jaumave, Tamaulipas, where macaws forage on nut trees (Eisermann 2003, Cougill and Marsden 2004, Vaughan et al. 2005, Bonilla-Ruz et al. 2007b, Matuzak and Brightsmith 2007. ...
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The preservation of Military Macaw Ara militaris in Mexico required the implementation of a nationwide assessment evaluating its vulnerability using IUCN criteria. With the combined effort of several institutions, the abundance, location, dispersion, habitat availability, and climatic conditions of areas occupied by the species were determined. Although the species’ extent of occurrence is extensive (263,919 km2) only 29% of this constitutes area of occupancy. Published estimates indicate a series of isolated populations containing from four macaws to 215. Macaws occurred in 35 populations in four regions of 16 states containing an estimated 1,563–3,263 macaws; lower than required for long-term viability. Within regions, neighbouring populations were separated by an average of 68 km. The extent of occurrence is heterogeneous, and macaws inhabit areas that differ in elevation, precipitation, temperature, and forest cover. Higher local abundances occur in landscapes where annual precipitation is ≥1,100 mm, and primary forest availability ≥1,800 km2. Although the existence of undetected macaw groups in Mexico is possible, these are likely to contain only small numbers of individuals, as most detected areas with macaws contain less than 40 individuals, and larger concentrations are more likely to be noticed due to their conspicuous behaviour. The species is threatened primarily by its low overall abundance, fragmented distribution, and forest loss around populations with the highest abundance. With the information generated, it is possible to design and implement specific management and conservation strategies at different geographic scales for the recovery and maintenance of the species in Mexico. It is necessary to strengthen collaborative programmes among conservation organizations, government agencies, and local communities in each region of the country to organize and finance community-based actions such as monitoring, habitat restoration, protection from poaching and the creation of a network of conservation corridors and macaw reserves focused on conservation.
... Yellow-headed Parrots in Guatemala of the race A. oratrix guatemalensis are found in Punta de Manabique and northwestern Honduras. They experienced a decline of 30% to 70 individuals from 1994 to 2001 primarily because of nest poaching (Eisermann 2003, Eisermann in litt. 2007). ...
Technical Report
Full-text available
A collaborative effort was undertaken in 2016 by members of the Yellow‐headed Parrot Working Group (and supporters) to assess the status of the globally endangered Yellow‐headed Parrot (Amazona oratrix) across Belize. This included transect surveys, roost searches and counts, and nest searches and monitoring across the pine savannahs. Transect surveys revealed a higher density in protected areas, both dense and open, than found in unprotected areas. This is likely related to higher quality habitat present as logging is rampant in the pine savannahs across and wildfire is also problematic. However, unprotected dense savannahs may be an important habitat type as well. Roost searches and counts were challenging and largely unsuccessful for assisting with the assessment of the population. They ranged from permanent and seasonal roosts in southern Belize to dynamic roosts in the north where repeated counts at the same sites were not possible. There were 89 known active nests, of which 76 were monitored; primarily in three protected areas. Twenty‐nine were successful producing 58 fledglings. 13 at‐risk chicks were extracted from 7 nests and later soft‐released. Poaching was the largest known reason for nest failure.
... These exceptional areas notwithstanding, our results should serve as a clear warning that this species is increasingly vulnerable to extinction in the southern portion of its range, an area typically thought of as its stronghold (BirdLife International 2016b;. It now appears that populations here are following the path towards decline and local extirpation already seen in more northern parts of its range, including El Salvador, Guatemala, Honduras and Mexico (Eisermann 2003, Marin-Togo et al. 2012, BirdLife International 2017. ...
Full-text available
Accurate assessments of population sizes and trends are fundamental for effective species conservation, particularly for social and long-lived species in which low reproductive rates, aging demographic structure and Allee effects could interact to drive rapid population declines. In the parrots (Order Psittaciformes) these life history characteristics have combined with habitat loss and capture for the pet trade to lead to widespread endangerment, with over 40% of species classified under some level of threat. Here we report the results of a population survey of one such species, the Yellow-naped Amazon, Amazona auropalliata , that is classified as ‘Endangered’ on the IUCN Red List. We conducted a comprehensive survey in June and July of 2016 of 44 night roosts of the populations in contiguous Pacific lowlands of northern Costa Rica and southern Nicaragua and compared numbers in Costa Rica to those found in a similar survey conducted in June 2005. In 2016 we counted 990 birds across 25 sites surveyed in Costa Rica and 692 birds across 19 sites surveyed in Nicaragua for a total population estimate of only 1,682 birds. Comparisons of 13 sites surveyed in both 2005 and 2016 in Costa Rica showed a strong and statistically significant decline in population numbers over the 11-year period. Assessment of group sizes approaching or leaving roosts indicated that less than 25% of groups consisted of three or more birds; there was a significantly higher proportion of these putative family groups observed in Nicaragua than Costa Rica. Taken together, these results are cause for substantial concern for the health of this species in a region that has previously been considered its stronghold, and suggest that stronger conservation action should be undertaken to protect remaining populations from capture for the pet trade and loss of key habitat.
... Roost counts are an effective method for estimating population size (Casagrande and Beissinger 1997;Eisermann 2003). They took place between 2010 and 2015 before (January-March) and after (October-December) the breeding season (several roost counts for each period and year, but not on a regular basis) when the roost trees were without foliage. ...
Although many parrot species are decreasing in their native range, introduced parrot populations can be found in urban areas around the globe. We thus need to understand how they adapt to this novel environment and to assess the possibility of a range expansion that might threaten native species. We studied population growth, nest site requirements, as well as limiting factors like reproductive output and mortality of the only European population of Yellow-headed Parrots (Amazona oratrix) in the city of Stuttgart, southwest Germany, to assess the risk of a possible range expansion. Although offspring could be seen on a regular basis, parrot numbers hardly increased during the last 5 years (51 individuals in spring 2015, including 12 breeding pairs). Ten accessible nest cavities were studied in detail: they were located exclusively in large, old London Plane (Platanus × acerifolia) trees in an area of less than 1 km2 in the city’s public parks and were at least 65 cm deep. Average reproductive output was 1.3 fledglings/pair, which is high in comparison to data from birds in their native range. Mortality, especially of young parrots, appears to be high due to risks in urban areas such as collisions with vehicles and windows and could partly explain slow population growth. This slow population growth in combination with the need for sufficiently large nest cavities may hinder a range expansion of this species in future years.
... New data from the Atlantic slope of the country suggest that, at least locally, the population of Yellow-headed Parrot Amazona oratrix may be in decline 14 . ...
Habitat loss and degradation are currently the main anthropogenic causes of species extinctions. The root cause is human overpopulation. This unique volume provides, for the very first time, a comprehensive overview of all threatened and recently extinct mammals, birds, reptiles, amphibians, and fishes within the context of their locations and habitats. The approach takes a systematic examination of each biogeographic realm and region of the world, both terrestrial and marine, but with a particular emphasis on geographic features such as mountains, islands, and coral reefs. It reveals patterns useful in biodiversity conservation, helps to put it all into perspective, and ultimately serves as both a baseline from which to compare subsequent developments as well as a standardization of the way threatened species are studied.
This datasheet on Roystonea oleracea covers Identity, Overview, Distribution, Dispersal, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
Full-text available
The primary lowland rainforest around the Mayan ruins of Palenque, in the state of Chiapas, Mexico, has been the focus of much study. The second growth and the mosaic of pasture and farmland surrounding the protected area of Palenque National Park also have received some attention by researchers and visitors. Until now though, a complete avifaunal list for this area had not been compiled. In our judgment, 353 species have been recorded reliably, a hundred more than previously reported. An additional 27 species have been reported at the site on multiple occasions but for which we feel there is no definitive evidence. There are 202 regular breeders, most of them resident, and 87 migrants that winter or pass through regularly. Relative capture rates for understorey birds indicate that Phaethornis longirostris and Henicorhina leucosticta are most often caught, and some rarely seen birds, such a Geotrygon montana, are less rare than previously thought. In a state in which habitat destruction is routine, in which national parks are increasingly becoming forested islands, we need baseline data such as these to get a clearer idea of what occurs there if we are to understand anthropogenic effects on forests.
This volume consist of eight main sections. Initially origins and evolutionary relationships are examined, followed by a brief section on the classification of the parrots. Next a section reviews the natural history of the parrots, briefly covering: general behaviour; distribution; habitat; movements; social behaviour; diet; breeding; and nocturnal species. Conservation status ics covered next. The main threats to parrots are then outlined and discussed: habitat loss; live bird trade; introduced species; persecution and hunting; and storms'climatic change. A brief section then looks at captive breeding. The mian body of the book is taken up with colour plates and a systematic section. The systematic section contains the following information, for each species: identification notes; voice; distribution and status (including distribution maps); ecology; description; sex/age; measurements; geographical variation; and references.
Distribution, variation, and conservation of Yellow-headed Parrots in northern
  • S A Lousada
  • S N G Howell
Lousada, S. A. and Howell, S. N. G. (1996) Distribution, variation, and conservation of Yellow-headed Parrots in northern Central America. Cotinga 5: 46-53.
Censo de población, municipio Puerto Barrios
INE (1994) Censo de población, municipio Puerto Barrios. Guatemala: Instituto Nacional de Estadística.
A guide to the birds of Mexico and northern Central America
  • S N G Howell
  • S Webb
Howell, S. N. G. and Webb, S. (1995) A guide to the birds of Mexico and northern Central America. New York: Oxford University Press.
Threatened birds of the world. Barcelona and Cambridge
Bird Life International (2000) Threatened birds of the world. Barcelona and Cambridge, U.K.: Lynx Ediciones and Bird Life International.
Threatened birds of the Americas: the ICBP/IUCN Red Data Book
  • N J Collar
  • L P Gonzaga
  • N Krabbe
  • A Madroñ O Nieto
  • L G Naranjo
  • T A Parker
  • D C Wege
Collar, N. J., Gonzaga, L. P., Krabbe, N., Madroñ o Nieto, A., Naranjo, L. G., Parker, T. A. III and Wege, D. C. (1992) Threatened birds of the Americas: the ICBP/IUCN Red Data Book. Washington, D.C. and Cambridge, U.K.: Smithsonian Institution Press, and International Council for Bird Preservation.