Abstract

From the 54 extant hornbill species, 30 species, represented in 6–8 genera, are native to Asia in the areas of India, Thailand, Indonesia, and adjacent island countries.⁶ Many of the Asian hornbill genera have overlying natural territories, notably for this presentation Aceros, Rhyticeros, and Buceros.^5-7,9 In AZA-accredited facilities (www.aza.org), five hornbill genera and nine species are exhibited most typically and have managed programs; of these taxa, two genera and nine species are Asian hornbills. Hornbills are diverse in their dietary preferences ranging from predominant carnivores and insectivores (African) through non-seasonal omnivores (e.g., Buceros) to nearly exclusive frugivores (e.g., Aceros).^3,5-7,9 However, all Asian hornbill species have increased protein consumption as animal matter and calcium from figs during the breeding season.⁶

Frequently, Asian hornbills are represented as at risk for iron storage disease (ISD) or secondary hemochromatosis.^2,8 To define ISD for this presentation, it is the histopathologic presence of iron accumulation within the hepatic parenchyma and concurrent presence of hepatopathy. As a problem identified in primarily frugivorous avian taxa, ISD has been described with exceptionally high incidence in species such as toco toucan (Ramphastos toco) and Bali mynah (Leucopsar rothschildi). In these birds, it is considered highly unusual for adult bird histopathology to not present some degree of iron accumulation and a cause of death attributable to ISD (K. Benson, T. Norton, J. St. Leger, personal communications).¹ However, for hornbills, the program managers and veterinary and nutritional consultants have asserted the presumption of uniform ISD risk for their taxon as inaccurate. This disagreement first was based on lack of sufficient pathology data on which to conclude the issue. Additionally, documented nutritional assessment for the primarily displayed Asian hornbill genera (Buceros and Aceros) did not demonstrate differences in protein requirements and usage.² However, through recent collaboration of a leading private pathology service (Northwest ZooPath) and accumulated Coraciiformes TAG pathology data which now spans 20 years, new trends have been documented.

A comparison of the two databases is provided for overall data quality and context (Table 1). A total of 486 birds were available in the combined databases: individuals of African species (n=237) and Asian species (n=210), and those birds undesignated to species (n=39) which were eliminated from the total count. A further 113 birds were eliminated from analysis as incomplete necropsies were available; many of these were in-nest chick deaths or related to traumatic causes of death so histopathology was not performed. A final count of 185 Asian hornbills was available with complete histopathologies, including four genera of Asian hornbills with greater than 10 individuals per genus: Aceros (n=54), Anthracoceros (n=19), Buceros (n=79), and Rhyticeros (n=23).

Table 1. Comparison of two pathologic databases representing 20 years of accumulated data (1990–2012) for evaluation to determine risk of iron storage disease in Asian hornbill species

^a Database originating with NorthWest ZooPath and inclusive of 1994–2012
^b Database originating from Coraciiformes TAG advisor and inclusive of 1990–2007

For each individual bird that entered the final data set, complete gross necropsy and histopathology reports were reviewed to determine primary cause of death that was attributed to one of three categories: hepatic ISD; primary hepatic, but non-ISD, disease; non-ISD and non-hepatic cause. These groupings then were evaluated at both the genus and species level for analysis of ISD risk.

Overall, ISD was categorized as the cause of death in 58 individual hornbills, or 12% of the complete data set including African species. Asian hornbills (n=43) represented 74% of the total number of individuals so affected. Analysis by each Asian hornbill genus with consideration of ISD cases against all deaths (2–5%) and against only Asian species (4–8%) did not distinguish the groups from one another or the same calculations for African hornbills as a group (5% and 10% respectively). Analysis by Asian hornbill genera against the cases of ISD as a denominator were higher [Aceros (26%), Anthracoceros (17%), Buceros (16%), and Rhyticeros (12%)] than African hornbills overall. However, by species evaluation, an increased incidence of ISD was attributed as the primary cause of death in wrinkled (Aceros corrugatus) (24%) and wreathed (Rhyticeros undulatus) (30%) hornbills. In this database, no other individual species with greater than 10 individuals had such high presence of ISD.

The presence of ISD in Asian hornbills is not as prevalent as in the uniformly affected species such as Bali mynah or toco toucans. However, this database assessment has concluded that the more frugivorous Asian hornbill species, specifically in the Aceros and Rhyticeros genera, indeed should be considered susceptible to ISD. Routinely, it will be encouraged that they be managed with low iron content diet, restrictions on provision of ascorbic acid, and perhaps provision of chelating agents (i.e., tannins) as is routine for other ISD-sensitive species.^1,3,8 However, these dietary restrictions should be lifted during breeding season for dam and chick well-being, and are not considered necessary for other Asian hornbill genera.⁹

Acknowledgments

Woodland Park Zoo’s Kelly Helmick, DVM, MS, DACZM, Darin Collins, DVM, and Mark Myers are thanked for raising the question of iron storage disease from a 2012 death in their collection. Coraciiformes TAG colleagues Lee Schoen (chair, and Buceros advisor), Eric Kowalczyk (Aceros advisor), and Ellen Dierenfeld, PhD (nutrition advisor) are thanked for their review of this abstract and ongoing support of the veterinary advisor within the TAG and Buceros SSP.

Literature Cited

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