Hornbill diets at San Diego Zoo Global: a review


Schlegel ML, Howenstein S. 2013. Hornbill diets at San Diego Zoo Global: a review. In Ward A, Coslik A, Mahan K, Treiber K, Reppert A, Maslanka M, Eds. Proceedings of the Tenth Conference on Zoo and Wildlife Nutrition, AZA Nutrition Advisory Group, Salt Lake City, UT.


Hornbills (Bucerotidae) are a family of birds that include 14 genera and 54 species spanning sub-Saharan Africa and Southeast Asia.7 They are easily identified by their long decurved bill and casque.7 The smallest hornbills range in body weight from 83-135 g (Black dwarf-hornbill, Tockus hartlaubi; Red-billed dwarf hornbill, Tockus camurus) while the largest can reach body weights of 2230-4580 g (Northern, Bucorvus abyssinicus, and Southern, Bucorvus leadbeateri, ground-hornbills).7 Additionally, hornbills span the range of feeding ecology from highly frugivorous to highly carnivorous.6

San Diego Zoo Global (SDZG) currently houses 15 species of hornbills at the San Diego Zoo and San Diego Zoo Safari Park with representative African and Asian species and those that span from highly frugivorous to highly carnivorous. Gamble et al., reviewed 486 hornbill necropsy records and documented 12% with iron storage diseases as the cause of death.5 A recent mortality review of 14 hornbill species in the SDZG collection identified 10 species which had individuals with iron storage disease as a contributing factor or the cause of death of 14-60% of the individuals (Burns, personal communication). With this incidence of iron storage disease a review of the SDZG hornbill diets was warranted.

Of the 15 hornbill species housed at SDZG, seven unique diets were identified (Table 1). The nutrient composition of those diets were determined using an in-house diet evaluation program (Table 3) and compared to recommended nutrient concentrations for psittacines and passerines.1

Comparing the diets fed to the most frugivorous hornbills at SDZG to the survey information by Foeken et al. (Table 2), the SDZG Diets 1-3 contained less in fruit and vegetables and greater in concentrates, meat, rodents and insects.3 All seven diets (Table 3) had adequate crude protein (CP) content compared to psittacines and passerines requirements and greater than the 10.8% dietary CP determined to be sufficient to meet nitrogen balance.1,2 The predominantly carnivorous diets (Diets 6 and 7) had more than 150% of the protein requirement of cats at maintenance, gestation and lactation.9

Iron content in all seven diets (Table 3) was greater than the suggested 50-100 ppm DM for hornbills to prevent iron storage diesese.4 Manganese of all diets was below the recommended 65 ppm for psittacines and passerines.1 Vitamin K was below the recommended concentrations in Diets 6 and 7 (Table 4). Vitamin K can be synthesized in the intestines and birds that have access to their feces decreases the dietary need.8 Choline was deficient in Diets 1 and 3. The majority of the choline in the other diets was being supplied by the Zoo Carnivore Diet. Biotin was deficient in Diet 3. This is in part due to the lack of information on the biotin concentration of the produce items in the diet. There are some fruits that are particularly good sources of biotin.8 Folic acid was deficient in Diet 3. The other diets are adequate in folic acid due to the addition of the Zoo Carnivore Diet in the diets.

For the diets that are being fed to the most frugivorous birds (Diets 1-3), reformulation of the diets need to be done to reduce the iron content to less than 100 ppm. Although dietary iron is important to reduce the risk of iron storage disease, there is a need to improve manganese concentrations in all diets and ensure that all nutrient requirements are met.

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