The Belem Curassow (Crax fasciolata pinima) is one of the most endangered birds in South America, without sightings of birds in the wild for 40 years. This subspecies is nationally and internationally classified as critically endangered and close to extinction, suffering from poaching and deforestation in its range. Here we present new records of free-living individuals made on three indigenous lands in Pará and Maranhão states: in part of Terra Indígena Mãe Maria, Bom Jesus do Tocantins, Pará; in locations within the Reserva Biológica do Gurupi/Terra Indígena Alto Turiaçu, Centro Novo do Maranhão, Maranhão; and around the Terra Indígena Rio Pindaré, Alto Alegre do Pindaré, Maranhão. We also provide recommendations to protect this bird via a dedicated conservation program which includes finding new individuals in non-sampled areas (north of BR-222), estimating population size, enhancing taxonomic and natural history knowledge, capturing wild animals in order to start urgent ex situ conservation programs, and developing environmental awareness programs with the local and indigenous populations.

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Communication among birds constitutes the foundation of social interactions, and acoustic signals should evolve based on their efficiency to convey information. We examined the acoustic signals of an Amazonian bird assemblage by testing whether vocal allometry was the main driver in song evolution. We expected the acoustic parameters of the songs to follow general allometric rules, as the size of the vocal apparatus limits the vibration capacity of the syrinx. We tested whether smaller species use lower than expected frequencies due to environmental filtering by examining deviations from allometric relationships. Alternatively, small species could use higher than expected frequencies as a consequence of competitive processes that promote the use of vacant portions of the acoustic spectrum. We recorded birdsongs between 2013 and 2018 and measured three spectral parameters: the dominant frequency (FDOM), the minimum fundamental frequency (FFMIN) and the maximum fundamental frequency (FFMAX). We created an allometric model based on the acoustic pattern of the larger species and used it to predict the frequencies of the smaller species. We compared the frequency values expected by allometry with the observed parameters of the avian assemblage. We found that FDOM and FFMIN were higher than expected by allometry alone, supporting competition structuring in the acoustic ecology of the assemblage. The successful insertion of many species into the acoustic space is the result of long processes of natural selection, with our data highlighting the importance of competition in the vocal structuring of the community.

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