Scientists have long been trying to understand why the Neotropical region holds the highest diversity of birds on Earth. Recently, there has been increased interest in morphological variation between and within species, and in how climate, topography, and anthropogenic pressures may explain and affect phenotypic variation. Because morphological data are not always available for many species at the local or regional scale, we are limited in our understanding of intra‐ and interspecies spatial morphological variation. Here, we present the ATLANTIC BIRD TRAITS, a data set that includes measurements of up to 44 morphological traits in 67,197 bird records from 2,790 populations distributed throughout the Atlantic forests of South America. This data set comprises information, compiled over two centuries (1820–2018), for 711 bird species, which represent 80% of all known bird diversity in the Atlantic Forest. Among the most commonly reported traits are sex (n = 65,717), age (n = 63,852), body mass (n = 58,768), flight molt presence (n = 44,941), molt presence (n = 44,847), body molt presence (n = 44,606), tail length (n = 43,005), reproductive stage (n = 42,588), bill length (n = 37,409), body length (n = 28,394), right wing length (n = 21,950), tarsus length (n = 20,342), and wing length (n = 18,071). The most frequently recorded species are Chiroxiphia caudata (n = 1,837), Turdus albicollis (n = 1,658), Trichothraupis melanops (n = 1,468), Turdus leucomelas (n = 1,436), and Basileuterus culicivorus (n = 1,384). The species recorded in the greatest number of sampling localities are Basileuterus culicivorus (n = 243), Trichothraupis melanops (n = 242), Chiroxiphia caudata (n = 210), Platyrinchus mystaceus (n = 208), and Turdus rufiventris (n = 191). ATLANTIC BIRD TRAITS (ABT) is the most comprehensive data set on measurements of bird morphological traits found in a biodiversity hotspot; it provides data for basic and applied research at multiple scales, from individual to community, and from the local to the macroecological perspectives. No copyright or proprietary restrictions are associated with the use of this data set. Please cite this data paper when the data are used in publications or teaching and educational activities.

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.

Acoustic signal production is affected by allometric relationships, by which the larger the animal, the lower its call frequency. In this paper, three evolutionary acoustic hypotheses were tested: the Signal-to-Noise Ratio Hypothesis (SNRH), in which evolution maximizes call ranges by increasing the signal-to-noise ratio; the Stimulus Threshold Hypothesis (STH), in which evolution maximizes the range of a specific signal threshold; and the Body Size Hypothesis (BSH), in which the emission of long wavelengths is enabled by body size. Three spectral metrics were measured, Dominant Frequency (FDOM), Minimum Fundamental Frequencies (FFMIN), and Maximum Fundamental Frequencies (FFMAX) of Neotropical Parrots, New World Doves, Woodcreepers, Tinamous, and Thrushes. A Ranged Major Axis (RMA) regression showed that body mass is significantly correlated with all of the spectral parameters in Parrots, Doves, and Woodcreepers, but only with the fundamental frequencies of Tinamous. The FDOM of Parrots corroborated the SNRH. The FFMIN of Woodcreepers and Tinamous corroborated the SNRH and BSH. The FFMAX of Parrots corroborated the STH and BSH. Those acoustic hypotheses could shed light on the evolutionary processes involved in avian communication, although results indicate that these depend on the taxa and spectral parameters considered.