Hematology and blood parasites of seabirds at Rocas Atoll, Brazil

Abstract

**Abstract:** Rocas Atoll (3°52′S 33°49′W) is the only atoll in the South Atlantic Ocean, located approximately 260 km off the Northeast coast of Brazil. Despite its small surface (two islets with a combined area of 0.36 km2), Rocas Atoll is home to approximately 150,000 seabirds. Five species breed on the atoll: Black Noddy (Anous minutus), Brown Noddy (Anous stolidus), Sooty Tern (Onychoprion fuscatus), Masked Booby (Sula dactylatra), and Brown Booby (Sula leucogaster). Additionally, small numbers of Red-footed Booby (Sula sula) and Magnificent Frigatebird (Fregata magnificens) also roost on the islets. In June 2017, blood was collected from the tarsus (Suliformes) or jugular vein (Charadriiformes) of 214 seabirds: 26 A. minutus, 42 A. stolidus, 46 O. fuscatus, 33 S. dactylatra, 27 S. leucogaster, 20 S. sula, and 20 F. magnificens. Thin blood smears were freshly prepared, fixed with methanol, stained with Rosenfeld-Giemsa, and examined under the microscope. Two blood parasites were detected: Babesia sp. in Brown Booby (prevalence = 44%) and Haemoproteus sp. in Magnificent Frigatebird (prevalence = 10%). Although a previous study had detected DNA of Haemoproteus sp. in the blood of Brown Noddy, this parasite was not seen in this species' blood smears. Leukocyte profiles were generally similar across species and age groups, with the following averages (mean ± S.D.): heterophils 40.3%±15.9%, lymphocytes 53.8%±15.9%, monocytes 4.2%±3.9%, eosinophils 1.7%±3.0%, and basophils 0%±0.1%. The proportion of eosinophils was highest in S. dactylatra and S. leucogaster, especially in adults, suggesting a higher exposure to helminth parasites. The heterophil-to-leucocyte ratio, an indicative of physiological stress, was higher in adults than in chicks and immatures in most species, with the exception of A. stolidus where an opposite pattern was noted. This is the first hematological study of seabirds at Rocas Atoll, and is part of a broader health survey program that aims to identify pathogens and health challenges that may bear significance for seabird conservation at Brazil's oceanic islands. **Authors:** Ralph Vanstreels¹, Daniela Mariani², Renata Hurtado¹, Veridiana Galizia³, Maurizélia Silva⁴, Jean Ramos Silva² ¹Institute of Research and Rehabilitation of Marine Animals, ²Universidade Federal Rural de Pernambuco, ³Autonomous veterinarian, ⁴Instituto Chico Mendes de Conservação da Biodiversidade