Bird song has been proposed as one measure for seeing how biodiversity is maintained within an ecological community. Song learning using imitation, related to cultural drift, frequently prompts the improvement of sets of geologically particular song variations wihin bird species.
Hermit Warblers sing a formulaic song to attract mates, in contrast with a repertoire of more complex songs they use to defend territories. There is often a single, dominant formulaic song within the same geographic area. In the United States, the summer range of Hermit Warblers is limited to the Pacific Coast states of California, Oregon, and Washington.
Hermit Warblers are quite sensitive to fire and other disturbances. They can have a negative impact on fires or selective timber harvests. On the other hand, the resulting changes in forest structure and increasing insect populations could positively impact them.
Scientists recorded the formulaic songs from 1, 588 males across 101 study sites during 2009 and 2014. The outcomes offer a detailed description and mapping of Hermit Warbler songs throughout California.
Scientists then classified the songs into 35 dialects. They modeled the effects of recent fire history at the local scale, the amount of breeding habitat at the regional scale, and the distance between territories to examine factors involved in song diversity.
Scientists found that the song dialects tended to be isolated from each other within different forest types, but that in contrast, local song diversity increased with the amount of local fire and regional habitat.
Based on the data from ten study areas revisited in 2019, scientists have shown that the diversity of song forms increased at locations that had been burned by wildfire between visits. Taken together, the results suggest that fires, the mass effects of dispersal of birds singing rival song forms, and time all disrupt the uniformity of songs locally.
The paper’s lead author, Brett Furnas, said, “Our surveys suggest that song dialects arose in sub-populations specialized to different forest types. Over the longer term, the fire caused some birds to flee and created a vacuum for other birds to fill. The net result is that some areas now have birds singing more than one dialect resulting in a complex diversity of songs throughout California.”
- Wildfires and Mass Effects of Dispersal Disrupt the Local Uniformity of Type I Songs of Hermit Warblers in California, The Auk: Ornithological Advances. DOI: 10.1093/auk/ukaa031