Reproduction and agonistic behavior of black skimmers (Rynchops niger) in a mixed-species colony in the Brazilian Pantanal

Abstract

ABSTRACTBlack skimmers (Rynchops niger) are colonial waterbirds in Nearctic and Neotropical regions. They often breed in mixed colonies with terns. This work analyzes the reproductive biology of skimmers within a colony including large-billed terns (Phaetusa simplex) and yellow-billed terns (Sternula superciliaris), located along the Cuiabá river in the Brazilian Pantanal, during July–September 2015. We focused on nesting parameters, timing of reproduction, nest survival, predation risk, and agonistic behavior. Skimmer nests (n = 31) were not aggregated (R = 0.40); mean nest distance was 6.91 ± 3.39 m. Incubation lasted on average 21.6 ± 1.6 days. Nest survival was low (3.2%) due to predation and abandonment, with the green iguana (Iguana iguana) as major predator of eggs. Aggressive behavior included chase and turn-off flights and mainly involved birds of prey (26.5%) followed by jabirus (Jabiru mycteria; 18.2%). The low number of nesting terns (n = 3), which can act as protector species, may have negatively impacted the fledging success of R. niger. Reproductive parameters and the complexity of behavioral interactions in such mixed colonies should be further studied in the Pantanal as model cases for ecological/ethological adaptations of colonial breeders under the impact of a seasonally fluctuating water regime.