Aspectos ecológicos de dois rapinantes, Bubo virginianus (Strigidae) E Geranoaetus melanoleucus (Accipitridae), no Pampa brasileiro.

Abstract

Raptors are considered a group of birds that indicate environmental quality and are naturally rare in the places where they live, as they need large areas to live and many species have a specialized diet. The Great horned Owl (Bubo virginianus) has a wide distribution across America, extending from Alaska and Northern Canada, to central Argentina and Uruguay. Black-chested Buzzard-Eagle (Geranoaetus melanoleucus) is distributed from Venezuela to Tierra del Fuego. Different aspects of the natural history of these two species still remain unknown, especially in the Neotropical region. Thus, this study describes data regarding the eating habits and reproductive biology of both species, in addition to obtaining information regarding the home range used by B. virginianus. Monitoring with B. virginianus was carried out over a period of 37 months between 2015 and 2018, while with G. melanoleucus it was 23 months between 2021 and 2023. The study area focused on the region central region of the Brazilian Pampa, with the monitoring of a couple of B. virginianus in the municipality of Santa Margarida do Sul, while for G. melanoleucus four couples were monitored, two in Santana do Livramento, one in Rosário do Sul and another in Alegrete. Data collection consisted of a fortnightly observation during the non-reproductive period, and at least a weekly observation during the nest use period, for B. virginianus. However, for G. melanoleucus, monitoring consisted of bimonthly observations during the non-reproductive period, and at least one monthly observation from the beginning of use of the nest, until the chicks left. The individuals' resting perches were checked, as well as below the nest, and the egagropylae and prey remains were collected, in addition to predation observations, for diet analyzes of both species. The home range used by the B. virginianus couple was estimated at 0.35 km² using the MCP method, or 0.41 km² based on estimates using the Kernel method. Individuals showing interest in places bordering the home range during the night, and remaining in the central part of it for shelter/rest during the day. Regarding reproductive data, the time of use of the nest was three months in all reproductive periods of B. virginianus, with the reproductive season related to the peak of winter, with one to two chicks being born near the end of this season. The cubs remained in their parents' home range for a period of seven to ten months, dispersing during the autumn of the following year. For G. melanoleucus, activities in the nests took place between the months of August and December, with the young being born between the months of September and October, and the dispersal of juveniles occurring between the months of June and September. 9 The diet of B. virginianus was based on rodents, especially Holochilus vulpinus and birds, following a pattern already known for the species. For G. melanoleucus, birds represented 48.4% of individual prey and mammals represented 34.4% of identified prey. The most common prey of these eagles was Lepus europaeus, an exotic and invasive species in the Brazilian Pampa.