Diet and Foraging

Horned Screamers are herbivorous birds that feed on aquatic plants. They are most likely to be seen feeding in mid-morning while walking or wading (5 Naranjo, L. G. (1986). Aspects of the biology of the Horned Screamer in southwestern Colombia. Wilson Bulletin 98(2):243–256. Close ).

Food Capture and Consumption

Horned Screamers feed by two methods: grazing and digging, with grazing being the more common mode. During grazing, birds peck at leaves, vines, stems, and flowers with lateral movements of the head; swallowing the food items immediately. When digging, birds wade slowly in shallow water, moving their bills into the mud with rapid backward strokes of the head (5 Naranjo, L. G. (1986). Aspects of the biology of the Horned Screamer in southwestern Colombia. Wilson Bulletin 98(2):243–256. Close ).

Major Food Items

Documented to feed on at least nine different plants, including Hydrangea spp., Eichornia crassipes, Polygonum hispidum, Paspalum dilatatum, and Artemisa absinthium, among others. Juveniles or younger birds will also eat insects (5 Naranjo, L. G. (1986). Aspects of the biology of the Horned Screamer in southwestern Colombia. Wilson Bulletin 98(2):243–256. Close ).

Horned Screamers feed mainly on succulent parts of aquatic plants, including leaves, stems, roots, and flowers (5 Naranjo, L. G. (1986). Aspects of the biology of the Horned Screamer in southwestern Colombia. Wilson Bulletin 98(2):243–256. Close ).

The digestive tract of the Horned Screamer is specialized for plant digestion: the proventriculus and gizzard are both relatively large, with the proventriculus bigger than the gizzard. The proventriculus is conical, with tubular and gastric glands that aid in primary leaf digestion. The mechanical disintegration of the food takes place in the gizzard, which is thick and muscular, and covered by a gastric cuticle called the koilin layer. The small intestine is the largest portion of the digestive tract, which terminates at two small ceca followed by the large intestine (56 Rudolf, C. (2019). DESCRIPCIÓN ANATÓMICA E HISTOLÓGICA DEL TRACTO DIGESTIVO DEL ARUCO (Anhima cornuta; LINNAEUS, 1766): UNA ESPECIE DE AVE FOLÍVORA. undergraduate thesis, Universidad Central de Venezuela. Caracas, Venezuela Close ).

The Horned Screamer's microbiota is similar to that reported for other herbivore vertebrates (57 García-Amado M. A., Rudolf C. A., Fuentes-Fuentes M. dM., Chorna N., Martínez L. M. and Godoy-Vitorino F. (2023). Bacterial composition along the digestive tract of the Horned Screamer (Anhima cornuta), a tropical herbivorous bird. PeerJ 11:e14805 Close ). The bacterial community of the digestive tract is composed of Firmicutes and Bacteroidetes that are specialized in fermenting complex plant carbohydrates. Complete degradation of cellulose occurs in the gastrointestinal tract, resulting in the end-products acetate, propanoate, butanoate, and acetoacetate.

Studies on the Horned Screamer's metabolism and temperature regulation are lacking. Given its physiology (see Nutrition and Energetics; 56 Rudolf, C. (2019). DESCRIPCIÓN ANATÓMICA E HISTOLÓGICA DEL TRACTO DIGESTIVO DEL ARUCO (Anhima cornuta; LINNAEUS, 1766): UNA ESPECIE DE AVE FOLÍVORA. undergraduate thesis, Universidad Central de Venezuela. Caracas, Venezuela Close , 57 García-Amado M. A., Rudolf C. A., Fuentes-Fuentes M. dM., Chorna N., Martínez L. M. and Godoy-Vitorino F. (2023). Bacterial composition along the digestive tract of the Horned Screamer (Anhima cornuta), a tropical herbivorous bird. PeerJ 11:e14805 Close ) and behavior (5 Naranjo, L. G. (1986). Aspects of the biology of the Horned Screamer in southwestern Colombia. Wilson Bulletin 98(2):243–256. Close ), it is possible that the Horned Screamer has a basal metabolic rate lower than expected based on body mass, as has been reported in other fermenting herbivores (58 López-Calleja, M.V. and Bozinovic, F. (2000). Energetics and nutritional ecology of small herbivorous birds. [Ecología energética y nutricional en aves herbívoras pequeñas]. Rev. Chilena Hist. Nat.. 73: 411-420. In English with Spanish summary. Close ); however, data are needed.

Naranjo (5 Naranjo, L. G. (1986). Aspects of the biology of the Horned Screamer in southwestern Colombia. Wilson Bulletin 98(2):243–256. Close ) observed Horned Screamers drinking while wading in shallow water; it dipped its bill into the water and lifted its head, swallowing the drink immediately.