West Nile Virus is a virus of the genus flavivirus. The West Nile virus is transmitted by several species of mosquitoes, while birds serve as reservoirs. As of February of 2005, the West Nile Virus had been detected in at least 60 species of mosquitoes, 18 species of mammals, including humans, and over 250 species of birds in North America.
West Nile Virus was first detected in the Americas starting in 1999. Hundreds of species of birds were being affected and were dying as the disease spread across the continental United States and South to the Caribbean. Consequently, serious concerns about endangered species and how they would be affected came up.
I will asses the risks faced by the endangered Costa Rican Scarlet Macaw in the face of West Nile virus. It is not a question of whether or not West Nile virus will eventually even come in contact with Costa Rican bird populations, but what will occur as a result thereof.
West Nile Virus is indeed an imminent, if not current, threat for the endangered Costa Rican Scarlet Macaw. It has been shown that West Nile virus is in countries surrounding Costa Rica and it is strongly suggested that it is the culprit for a tenfold drop in several bird species in Costa Rica. West Nile virus is also definitively considered a risk for macaws.
Costa Rican Scarlet Macaw populations are already considered at risk for extinction and are delicately maintaining sustainable levels in two disjunct populations, any further environmental stresses, such as West Nile virus, are seen as serious risks. Psittacines mortality from West Nile virus is generally considered to be low.
Table of Contents:
Where and what is West Nile virus?
-Brief history of West Nile virus
-Current state of West Nile Virus
-Are vectors present for WNV in Costa Rica?
Review of the Ava macao
-est. wild breeding populations in Costa Rica and in general
– currently sustainable, in decline or in recovery?
-genetic variation or experiencing bottleneck effects?
– how this could reduce the population’s ability to deal with WNV
The risks Scarlet Macaws face before and with WNV
– loss of genetic variation
– complete extinction
– set-back in current population conservation practices
How would West Nile Virus directly affect Costa Rican macaws?
– intro to possible risks
-how has WNV affected Macaws?
-how has WNV affected psittacines?
West Nile Virus is a virus of the genus flavivirus. Flaviviruses are often transmitted across species barriers when transmitted via arthropods. The West Nile virus is transmitted by several species of mosquitoes, but particularly by the Culex and Aedes mosquitoes, while birds serve as reservoirs (9). As of February of 2005, the West Nile Virus had been detected in at least 60 species of mosquitoes, 18 species of mammals, including humans, and over 250 species of birds in North America (10, 16).
West Nile Virus was first detected in the Americas starting in 1999 in New YorkState. This particular virus is endemic to the Old World, and especially to Africa. Serious human side-affects of the disease can be West Nile Meningitis, West Nile Encephalitis, West Nile Poliomyelitis and even death (10). In addition, hundreds of species of birds were being affected and were dying as the disease spread across the continental United States and South to the Caribbean. Consequently, serious concerns about endangered species and how they would be affected came up.
Naturally, the scientific community clamored about the possible affects of West Nile Virus on endangered bird species. Many different studies began to research every nuance of the virus, while scientists clamored to study its mode of transmission and affects on various endangered North American species.
Similarly, it is my goal to asses the risks faced by the endangered Costa Rican Scarlet Macaw in the face of West Nile virus. It is not a question of whether or not West Nile virus will eventually even come in contact with Costa Rican bird populations, but what will occur as a result thereof.
Where and what is West Nile virus?
The West Nile virus has been isolated or detected from more than 60 different species of mosquitoes in the United States (16). Yet, West Nile virus in the United States has been found primarily in mosquito populations which forage in the canopy (12). This is particularly important considering that the Scarlet Macaw also feeds in the forest canopy (13).
Studies have shown that mosquitoes known to be carriers of the West Nile virus are indeed present in Costa Rica. One such study found Aedes aegypti, Culex quinquefasciatus, Cx. restuans, and Cx. coronator in common mosquito breeding sites in San José, Costa Rica (15). All four of these mosquito species have been tested positive for West Nile in mosquito pools in the United States since 1999 (16).
Douglas Causey, senior biologist at the Harvard University Museum of Comparative Zoology, said the virus has spread into animals and birds in the Caribbean and is the leading suspect in a tenfold drop in several bird species in Costa Rica during the past year (14). It would be logical than to assume that acceptable vectors and reservoirs for West Nile virus are indeed present in Costa Rica.
Throughout my research I found multiple articles which stated that there is indeed a presence of West Nile virus in Central America (19), that West Nile Virus is suspected in Costa Rica (14), though I failed to find any studies for Costa Rica which have tested positive for West Nile Virus specifically.
Below is an illustration from PAHO/WHO of WNV circulation in Latin America and the Caribbean as of 2003.
Review of the Ava macao
The Scarlet Macaw, Ara macao, is a new world psittaciforme endemic to middle America: from the humid forests of Mexico to Eastern Bolivia, although disjunctly. The Scarlet Macaw is one of the 16 species of macaw from the American neotropical region currently in existence (6). The Ara macao is widespread in captivity but is rarely bred (Juniper and Parr, 1998).
Currently the Scarlet Macaw is listed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora under Appendix I (Juniper and Parr, 1998), and has been since 1985 (6): species listed as such are considered endangered. The CITES is an international agreement between governments aiming to protect animals involved in international trade, so as to not threaten their survival (5).
Under the CITES Appendix I, it is considered that any removal of species with this listing from the wild would be “disastrous for the overall survival of that species (Bennu, D.A.).” Consequently, absolutely no trafficking is allowed for species listed under Appendix I, not even accredited organizations/agencies and zoos, unless the individual offered for sale is proven to be the offspring of captive breeding stock.
Scarlet Macaws in general have been declared as declining throughout their range, namely around developing centers, due to habitat loss, trade and hunting for food and plumes. Any additional environmental stress to the already struggling Ara macao population, such as the introduction of West Nile virus, could create a snowball affect and encourage subsequent continued deterioration of the specie’s outlook for survival.
The total Middle American Scarlet Macaw population has been estimated as less than 4,000 (Juniper and Parr, 1998). In Costa Rica, there are only two viable Scarlet Macaw populations in existence. In these two Costa Rican populations there are an estimated 700 macaws in the Osa Conservation Area and 330-400 in the Central Pacific Conservation Area. Even as such, the Costa Rican Scarlet Macaw population is currently at sustainable levels (Vaughan et. al., 2005).
The risks Scarlet Macaws face before and with WNV
When discussing the population of Scarlet Macaws in Costa Rica, it is also beneficial to look at population trends. It has been observed in a study by Vaughan that the Costa Rican Scarlet Macaw population fluctuates both seasonally and has fluctuated in long-term scales. From 1990- 1994 there was a 4% reduction in the population of Scarlet Macaws annually in Costa Rica. Yet, after two years of “high”-recruitment of young macaws into the Costa Rican Macaw population, therefore upping population counts in 1995 and 1996, the population has leveled out. These years of higher than previous annual recruitment levels were possibly attributed to intensive management of the Scarlet Macaw populations. Yet in regression, management since 1997 has been inconsistent and the Costa Rican Macaw population has merely sustained itself (Vaughan et al., 2005). With continued mismanagement as Costa Rica begins to feel the affects of West Nile virus, it is my opinion that the Scarlet Macaw will suffer and begin to experience a population reduction.
To focus on what changes in management have been responsible for impacting the Scarlet Macaw population in Costa Rica, we will also look to Vaughan’s study. He mentioned that, “management practices included creation of a local conservation organization that coordinated environmental education, artificial nest construction, networking among stakeholders and with governmental authorities, and artificial and natural nest protection (Vaughan et. al., 2005). This is in response to the more specific issues that Costa Rican Scarlet Macaws are facing, such as their illegal capture, nest destruction, deforestation and the subsequent fragmentation of populations and habitat (6). These destructive activities need to be addressed more seriously in the following years as the Scarlet Macaw populations undergo any repercussions of West Nile virus.
In addition, deforestation profoundly affects Scarlet Macaw populations due to the fact that this species is found exclusively in forests at water’s edges. In general, the ideal habitat of the Scarlet Macaw is lowland tropical forest and savanna. More specifically, in Costa Rica the Ara macao is present in deciduous and humid forests as well as more open areas and edges with non-contiguous stands of tall trees (Juniper, T., Parr, M., 1998). In addition, the Scarlet Macaw nests in hollowed out trees, living or dead, in the months from December to June (6). Without suitable habitat, this species will most certainly be quickly wiped out. As continued deforestation occurs concurrently with the spread of West Nile virus, possible affects may be compounded.
Deforestation has already led to habitat fragmentation for the Costa Rican Ara macao. Currently there are two separate Scarlet Macaw gene pools in Costa Rica: one in the Osa peninsula in the CorcovadoNational Park and one in the Central Pacific Conservation Area (6, 1). Some of the issues that can result from habitat fragmentation are bottleneck affects, inbreeding depression, genetic drift and general loss of genetic variation.
An issue resulting from isolation of small populations of individuals is a genetic bottleneck. Bottlenecks are an effect common to populations in which there has been a dramatic reduction in numbers. Bottlenecks essentially reduce genetic diversity, even though the population may recover (Klug, W., Cummings, M., 2005). The Costa Rican Scarlet Macaw has already experienced reduction in numbers; though there still are a significant number of individuals within the two Costa Rican populations of Scarlet Macaws, it is possible that some genetic diversity has been lost due to a possible mild genetic bottleneck.
A cause of loss of genetic variation is genetic drift leading to allele fixation and loss of heterozygosity; this may happen in genes which are not critical to the species survival, as well as in critical genes. Should a disease enter a population that targets individuals of one phenotype or another, a heterozygous population may be the saving grace for that gene pool. Unfortunately though for populations which have experienced allele fixation due to genetic bottleneck, a particular disease could completely devastate what is left of a struggling species. One can only hope that the Costa Rican Scarlet Macaws have not yet undergone allele fixation for critical genes involved in immune response for the West Nile virus. With the recent introduction of West Nile virus this will soon be made clear.
West Nile virus could also affect long-lived species such as the Scarlet Macaw more seriously than shorter-lived species; a reason for this is how quickly a population can rebound after a significant reduction in population. Since Scarlet Macaws only lay one clutch every other year on average, with only one to two fledglings, annual reproduction rates are around one. Yet, this is before taking into account chick poaching, death due to disease, starvation or any other adverse effects. Since West Nile is often more severe in both old and young macaws (18), success rates of fledglings and each reproductive effort of older established Scarlet Macaws may be further reduced.
How would West Nile Virus directly affect Costa Rican macaws?
Macaws are indeed capable of coming down with West Nile virus. A 38 year old hybrid male macaw from a Miami zoological park died after a 3-week course of illness. He was subsequently tested and was, “seropositive by SN test for West Nile antibodies. Histopathology revealed vague neurological lesions. Virus isolation was negative (18).” West Nile virus has been declared a health risk for psittacine birds in very preliminary observations (18).
On the whole, I found very little information concerning Macaws and the West Nile Virus. Therefore, I strove to first establish that the Costa Rican Scarlet Macaw as a whole was already surviving with a delicate balance of sustainability. With this information, it is logical to assume that any added stress to the Costa Rican Scarlet Macaw populations would be detrimental; the population would consequently decline and possibly reach extinction.
On a more positive note, mortality rate for psittacine birds affected by West Nile virus appears to be low, with older birds seeming to be more severely affected. Isolation of the WNV has been unrewarding, suggesting that transient infections may occur in psittacines. It is also suggested that psittacines may react similarly to chickens in the face of WNV; chickens are not as severely affected as most North American birds. This has been due to several cases which exhibited acute onset of clinical signs and were seropositive. This would possibly indicate rapid seroconversion (18).
In conclusion, West Nile Virus is indeed an imminent, if not current, threat for the Costa Rican Scarlet Macaw. It has been shown that West Nile virus is in countries surrounding Costa Rica and it is strongly suggested that it is the culprit for a tenfold drop in several bird species in Costa Rica. West Nile virus is also definitively considered a risk for macaws in general, though older birds are most at risk.
With the Costa Rican Scarlet Macaw populations already considered at risk for extinction and delicately maintaining sustainable levels in two disjunct populations, any further environmental stresses, such as West Nile virus, are seen as serious risks. The populations are already facing multiple setbacks to recovery.
And yet, psittacines mortality from West Nile virus is generally considered to be low. We can only hope that the Costa Rican Scarlet Macaws can weather West Nile virus, and that management of their populations can improve to counteract any foreseeable losses.
Vaughan, C., Nemeth, N.M., Cary, J., Temple, S. (2005) Response of a Scarlet Macaw Ara macao population to conservation practices in Costa Rica. Bird Conservation International 15:119-130
Pan American Health Organization website
Environmental risks page from CornellUniversity
Juniper, T., Parr, M. (1998) Parrots: a guide to parrots of the world.YaleUniversity Press, New Haven and London.
Convention on International Trade in Endangered Species of Wild Fauna and Flora website
CITES seventeenth meeting of the Animals Committee in Hanoi, Viet Nam, 30 July-3 August 2001, periodic review of animal taxa appendices.
Klug, W.S., Cummings, M.R. (2005) Essentials of Genetics: fifth edition. Pearson Education, Inc., Upper Saddle River, NJ.
Beissinger, S.R., Snyder, N.F. (1992) New World Parrots in Crisis: solutions from conservation biology. Smithsonian Institution Press, Washington and London.
Merck Source resource library powered by Dorland’s Illustrated Medical Dictionary website:
AnimalWelfareInformationCenter’s WNV URL:
SAGARPA Mexican governmental health website:
Anderson, J.F., Andreadis, T.G., Main, A.J., Kline, D.L. (2004) Prevalence of West Nile virus in tree canopy-inhabiting Culex pipiens and associated mosquitos. The American Society of Tropical Medicine and Hygiene 71:112-119
Stotz, D.F., Fitzpatrick, J.W., Parker, T.A.III., Moskovitis, D.K. (1996) Neotropical Birds. The University of Chicago Press, Chicago and London.
Causey, D. (2003) Migratory birds and the spread of West Nile. PubMed- indexed for MEDLINE, Science. 2003 Feb 7;299(5608):821, PMID: 12575705
Scientific Electronic Library Online- Chili
Calderon-Arguedas, O., Troyo, A., Solano, M.E. (2004) Diversidad larval de mosquitos (Diptera: Culicidae) en contenedores artificiales procedentes de una comunidad urbana de San José, Costa Rica. Parasitol. latinoam. jul. 2004, vol.59, no.3-4, p.132-136. ISSN 0717-7712
Center for Disease Control and Prevention website:
Bennu, D.A. (1999) Rare and endangered Loriinae species. The American Museum of Natural History website.
Clubb, S.L., DVM (2002) West Nile virus infections in psittacine birds and preliminary findings on vaccination. ABVP Avian, Old World Aviaries website.
West Nile Virus in the Tropics. Smithsonian: Spotlight on Science website