Abstract
The Humboldt penguin (Spheniscus humboldti) is native to the Peruvian and Chilean coast and is one of the world’s most endangered penguin species. It is listed in Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), and currently it is one of two species of penguins in North American zoos and aquaria to be managed under an Association of Zoos and Aquaria (AZA) Species Survival Plan. Although the population in the wild has decreased dramatically over the past several decades, and the species has been in captivity for many years, review of the literature revealed that very little has been published about the natural biology and behavior of the Humboldt penguin.
In 1994, the Milwaukee County Zoo initiated a 5-year study of the natural ecology of the Humboldt penguin residing on Ex-islote de los Pajaros Ninos near Algarrobo, Chile. The team of field researchers originally included members of the veterinary, curatorial, and keeper staff of the Milwaukee County Zoo; a Chilean graduate student; and a field assistant. Contact with a well-known Chilean ornithologist had been established during an earlier study of the colony and continues; he obtains the necessary permits, and he functions both as a liaison between the field team and the Chilean government, and as a guide. Although several of the original co-investigators have left the zoo, they remain active members of the project and field team (they are supported by their institutions, the Riverbanks Zoo and Denver Zoo, through paid leave and small monetary contributions). Researchers from the United States are able to spend approximately 8–10 weeks annually in the field, while the graduate student and field assistant monitor the research site approximately every 2 weeks during the rest of the year.
The study is multifaceted, investigating nest site tenacity, pair-bonding, incubation time, weight loss of eggs during incubation, longevity, morphometrics for sex determination, causes of mortality, chick growth rates, and prevalence of disease as determined by serologic assays.
Establishing the prevalence of disease in an apparently healthy, free-ranging population is valuable for several reasons. First, if the population were to experience a significant increase in mortality in the future, comparisons between the serologic prevalence of diseases in the ill population and those established previously may help elucidate the pathogenic agent and source of disease. Second, comparison of the prevalence of disease in wild versus captive populations may indicate those diseases that occur primarily in captivity and lead to improved husbandry. Finally, knowledge of the diseases affecting a free-ranging population is useful if it becomes necessary to import wild birds as new genetic stock for captive propagation.
During the first 2 years of the study, approximately 750 penguins were individually marked, and blood samples were collected. Plasma was removed, frozen, and transported to the United States for assay. To date, 200 plasma samples have been assayed for titers to paramyxovirus-1 (PMV-1 or Newcastle’s disease), PMV-2, PMV-3 (hemagglutination inhibition assays), and avian influenza (agar gel immunodiffusion). Ninety-nine samples have been assayed for Aspergillus titers (ELISA), and 99 for titers to Chlamydia (complement fixation). Preliminary results indicate that the percentage of samples with positive titers to PMV-1, Aspergillus, and avian influenza is low to none. Approximately 20% of the samples had positive titers to Chlamydia, nearly 50% were positive for PMV-2, and roughly 10% of the samples had titers to PMV-3.
The use of caution cannot be overstated when interpreting serologic results and using them to make assumptions about the overall health of the population. Except for the Aspergillus assay, none of these assays has been validated for Humboldt penguins. Production of humoral antibodies in response to the PMV-1 virus varies widely among taxonomic groups and individuals;2 the same may hold true for PMV-3. It is interesting to note that one reference states that antibodies to PMV-3 haven’t been documented in feral birds.1 The direct complement fixation (CF) test for Chlamydia detects only immunoglobulin G activity, and therefore is useful to detect past infection only. In addition, this test method may not be accurate in many bird species. Elementary body agglutination is more worthwhile for detecting current infection. However, CF may be useful epidemiologically to follow the status of a population.3 Serial sampling of individual penguins will be necessary to document changes over time and is in our research plan. Investigations into the Chlamydia titers using elementary body agglutination, as well as prevalence of diseases caused by Plasmodium spp. (avian malaria), Salmonella pullorum, and Mycoplasma spp. will ensue as funding allows.
Acknowledgments
We would like to thank the Zoological Society of Milwaukee for their contribution to this project, especially funds for stipends and for the serologic assays. We would also like to thank the Windway Foundation, of Sheboygan Wisconsin, for underwriting our airfare and other expenses. We wish to extend our gratitude to the Consejo de Monumentos Nacionales and the Corporacion Nacional al Forestal of Chile for their permission to do this study, and to the Cofradía Nautica del Pacífico at Algarrobo for allowing us access to the island. Finally, a special thank you goes to our Chilean colleagues: Dr. Braulio Araya, Alejandro Simeone, and Mariano Bernal.
Literature Cited
1. Gerlach, H. 1994. Viruses. In: Ritchie, B. W., G. J. Harrison, and L. R. Harrison, eds. Avian Medicine: Principles and Applications. Wingers Publishing, Inc., Lake Worth, Florida. P. 927.
2. Grimes, J. E. 1984. Direct complement fixation and isolation attempts for detecting Chlamydia psittaci infections of psittacine birds. Avian Dis. 29:873–877.
3. Grimes, J. E., and F. Arizmendi. 1996. Usefulness and limitations of three serologic methods for diagnosing or excluding chlamydiosis in birds. J. Vet. Med. Assoc. 209:747–750.