Distribution maps of Pan Amazonian Birds

The Amazon is the largest and most biodiverse tropical forest on the planet. However, the distributions of its species are still poorly understood, even for well-known vertebrate groups such as birds. Available distribution maps for Amazonian birds often lack precision in delimiting the range of each species. Existing information on the distribution of Amazonian birds is often limited to species-level taxonomy, although many Amazonian bird subspecies represent biological species. 

I investigated the geographic distributions of 4,148 bird taxa (species and subspecies), using scientific museum specimens as the primary data source. To construct the database, I used over 600,000 geographic records of specimens, with their geographic coordinates. I reviewed locality information from museum specimens and the literature to draw the distribution boundaries for each taxon in the form of distribution polygons. I then used the distribution polygons of each taxon to define Amazonian zoogeographic regions based on bird distribution patterns. I found that Amazonian bird distribution maps at the subspecies level best capture the regional diversity of birds in the Amazon. This new Amazonian bird distribution dataset allows biodiversity studies (e.g., macroecology, evolution, conservation) to be conducted at the subspecies level. This will facilitate biogeographic, ecological, evolutionary, and conservation research on birds in the most biodiverse region in the world.

I used the database to map bird contact zones throughout the Amazon and its adjacent regions. By grouping taxa into phylogenetically related groups, I was able to map regions where these taxa replace each other, possibly forming hybrid zones. I found regions where replacement of closely related taxa accumulates, thus forming suture zones. These suture zones are distributed throughout the Amazon region, and most are associated with large rivers. In the Amazon lowlands, rivers clearly coincide with the location of most suture zones, acting as physical barriers to bird dispersal, despite being permeable barriers. My results corroborate the observation that Amazonian rivers tend to have a diminished effect as a barrier to dispersal near their headwaters.

I also assessed the conservation status of 3,320 bird taxa in the Amazon and its periphery. I used the distribution polygons I created as a proxy for the extent of occurrence (EOO) of Amazonian birds. I integrated the EOO of each taxon with its distribution records (locality points) to generate models of environmental suitability under current and future climate scenarios. I also incorporated information on current and future deforestation into the different projected scenarios. Based on the range size of each taxon in each modeled scenario, I classified 3,320 taxa into one of the IUCN Red List categories using the B1 criterion (i.e., geographic range extent). I found that birds in all Amazonian regions will be affected by future environmental conditions, but to varying degrees. Birds living along the eastern slope of the Andes will face the greatest reduction in their range. In the southern and eastern Amazon, high rates of deforestation combined with more extreme future climate conditions will also strongly affect birds in this region. My conclusions based on subspecific taxa provide greater granularity to the current IUCN conservation classifications.