Density and habitat use of a reintroduced population of the Red-billed Curassow (Crax blumenbachii), an endangered species of the Brazilian Atlantic forest

Resumen

Abstract Human activities significantly threaten wildlife, especially large-bodied vertebrates. As their populations decline and local extinctions occur, active conservation efforts, such as reintroductions into historical ranges, become essential. The Red-billed Curassow (Crax blumenbachii), a large bird from the Cracidae family (Galliformes), has been the focus of multiple reintroduction programs over the past 35 years. Here, we investigate the population density, abundance, and habitat use of a reintroduced population in the Atlantic Forest, a hotspot for tropical biodiversity. Data were collected from April to October 2014 across 15 line transects evenly spread throughout the study area. Density and abundance were estimated using Distance sampling, while habitat use was analyzed through occupancy modeling, dividing transects into 250-meter segments (n = 49). We combined Cracidae species encounter data to fit the detection function and derived estimates for the focal species from this. In occupancy modeling, detection (p) and occupancy (ψ) refer to the frequency and probability of use, respectively. The population density was estimated at 2.54 individuals per square kilometer (95% CI = 1.72 to 3.75), and the total abundance was around 36 individuals (95% CI = 24 to 53). The probability of use (ψ) declined steadily with increasing distance from the release site (β = -2.69, CI = -5.13 to -0.26). Our density estimate aligns with data from wild populations of the species and other cracids. However, the higher use of areas near the release site may relate to supplementary food provisions and limited dispersal movements, though other factors could also influence these patterns. Although limited to the reintroduction period from 1991 to 2014, these findings provide valuable insights that could inform future management and deepen our understanding of this endangered cracid species.