Relaciones teóricas de los cantos de aves de Colombia: un contraste entre hipótesis.

Abstract

Acoustic signals are one of the most important forms of communication for many animals. They can be subject to selective forces of abiotic and biotic nature. For instance, environmental conditions can affect the acoustic attributes of animal sounds, as the sound wave transmission is highly dependent on these conditions (according to the acoustic adaptation hypothesis). Similarly, species with larger body size or longer beaks may have lower acoustic frequencies due to restrictions in the sound-producing body structure or modulation during emission, respectively (according to the morphological adaptation hypothesis). Additionally, a greater number of species in a community could lead to increased interspecific competition, resulting in changes in the acoustic attributes of species competing for communication channels (according to the acoustic niche hypothesis). Despite this clear theoretical panorama, only a few studies have been conducted to contrast the hypotheses explaining acoustic expression. To better understand the potential theoretical responses of animal acoustic expression, I evaluated the relationship of different variables and the acoustic attributes of Colombian birds with important representation in the Instituto Humboldt's Environmental Sound Collection (IAvH-CSA) "Mauricio Álvarez-Rebolledo". Specifically, the peak frequency of each audio recording was contrasted with environmental attributes reflecting acoustic adaptation (precipitation, spatial human footprint index, vegetation index, and elevation), body size (average mass and beak length of each species), and the value of regional species richness expected (potential interspecific competition pressure) in each location where the recording was obtained. Additionally, the(statistical) interaction between some variables may represent ecogeographic rules that could affect the dominant frequency. For example, an interaction between elevation and body mass represents the Bergmann's ecogeographic rule (lower dominant frequencies at higher elevations, due to increased body mass in colder places), while an interaction between elevation and beak length represents the Allen's ecogeographic rule (lower dominant frequencies at lower elevations, where longer beaks predominate). To contrast these relationships, generalized linear models were performed, using the peak frequency as the response variable and controlling for taxonomic Family. Some families followed the predictions of the hypotheses, particularly the relationship between peak frequency and vegetation index (environmental adaptation), body mass (morphological adaptation), and the Bergmann's ecogeographic rule. However, when comparing the hypotheses, the latter interaction between elevation and body mass proved to be the most important relationship, highlighting the potential effect of thermoregulation within environmental gradients on the acoustic expression of Colombian birds. This study provides a holistic insight into theoretical postulates and available data from a megadiverse country, analyzing the relationship between acoustic characteristics of Colombian bird songs (peak frequency) with environmental and morphological variables. The findings emphasize the close connection between abiotic environmental filters (elevation) and morphological aspects (body mass) in empirically explaining the distribution of peak frequencies in Colombian birds. Thus, these results contribute to the general knowledge of avian acoustic communication and their adaptation to the environment, using the megadiversity of Colombian birds as a study case.