Wildfires can destroy habitats but diversify bird song

Low-intensity wildfires cause bird populations to flee to new areas, which increases the diversity of bird song within a forest.

Researchers in California recorded the mating songs of over 1,500 Hermit Warblers, which are small grey and yellow birds found in a few Pacific Coast states. As the birds are spread over different forest types and areas, they have each developed their own unique mating song. The researchers found that originally, there were 35 different song dialects.

“The birds were generally isolated from each other,” said Brett Furnas, ecologist at the California Department of Fish and Wildlife and lead author of the paper published in The Auk: Ornithological Advances Journal.

“It’s a bit like how Darwin’s finches on the Galapagos became different, but of course I am talking about song here, a cultural trait which might happen quicker than with genetics.”

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The team’s research showed that after an area is hit by a wildfire, it is recolonised by a more diverse group of birds, which leads to more variation in bird song. The birds that have fled the wildfire will also find a new home, bringing their song to the area.

“These are two sides of the same coin; different dialects in different places (often called beta diversity) and more than one dialect in the same place (often called alpha diversity).” A balance of both is likely to be good for overall biodiversity, said Furnas.

“A low intensity fire can also potentially improve habitat conditions for this species by clearing out the understory,” said Furnas. “While a high intensity fire is a different story; it destroys the habitat so that there are no Hermit Warblers, and no song diversity.”

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The birds evolved in summer habitats naturally subjected to fire, but the pattern and intensity of the Californian wildfires has and continues to change dramatically. It’s unsure how this will affect the Hermit Warblers in the long-term.

These results may also be relevant to a wider understanding of how biodiversity of different species works, said Furnas. “Bird song usually changes much quicker than genetics, so it easier to study, but both are affected by the same evolutionary factors and pressures.

"Understanding how biodiversity (either genetic or cultural) changes over time may be important for helping us to make effective conservation decisions in light of climate change and other impacts.”