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Wildfire shapes diversity of hermit warbler songs in California

small gray bird with yellow head with black beak in a tree with branches and bushes

small gray bird with black beak, wings and chest, yellow head with mouth open in a tree with branches and leaves
Hermit warblers spend much of their time in forest canopy. They are rarely seen but very vocal and easily heard. Photo by Dr. Brett Furnas.

's arm holding a recording device to record songs of small gray birds
Scientists record songs of hermit warblers and use the data for surveys that support conservation efforts. Photo by Russ Landers.

illustration of drawn trees with musical notes
Hermit warblers flee wildfires which ultimately creates opportunities for new birds to take over a habitat. This may explain why some areas have multiple mating dialects. Illustration by Sarah Noll..

New research shows that fire history seems to be shaping the diversity of bird songs throughout the state. The new paper, published in leading bird journal The Auk: Ornithological Advances, addresses the diversity of song dialects sung by hermit warblers – birds which get their name because they are rarely seen and spend much of their time in forest canopy. They are, however, very vocal and easily heard.

Interestingly, the paper’s lead author, CDFW Senior Environmental Scientist Dr. Brett Furnas, never set out to study the hermit warbler, which is a migratory songbird that breeds in California, Oregon and Washington.

Dr. Furnas’ journey studying the bird began a decade ago while he and his colleagues were doing surveys on songbirds in northern California. They noticed that songs from one species of songbird – the hermit warbler – were so complex that it was difficult to identify the species.

“We ultimately compiled a list of 35 different song dialects from the hermit warbler throughout California,” said Dr. Furnas

The team also noted, as had been confirmed in prior research, that all of the hermit warblers’ songs in a particular area sounded the same -- and they believed those songs to be the males’ mating calls.

“Females in that area were probably raised to recognize that one type of call. The males have to sing it perfectly,” said Dr. Furnas, noting that the birds do have a repertoire of other songs that males use to announce their territories to other males.

Then the team made a surprising find: In some areas they surveyed, there was more than one mating dialect. For example, two males singing different mating songs.

That finding led to Dr. Furnas’ hermit warbler research. He traveled throughout California and recorded and analyzed mating songs from more than 1,500 male hermit warblers during mating season, April through July, from 2009 to 2014.

What appeared to be causing the mixing of songs, he found, was wildfires.

“Hermit warblers are very sensitive to fire in the short term, and they typically abandon an area shortly after a fire. This creates a little bit of a vacuum, and other birds fill in that gap. The net result is that you get some areas with more than one dialect,” he said.

The new study also provides the first comprehensive description of hermit warbler mating song variants throughout California.

Results from the study have several uses:

  • Now that scientists have a library of the hermit warblers’ complex songs, they can use that data to better survey the hermit warblers and other species.
  • Although the hermit warbler is abundant in California, it does have some potential conservation concerns. In summer, the hermit warbler is only found in three states, and in Oregon and Washington the bird is hybridizing with a closely related but more aggressive species. One possible outcome is that California could ultimately be the only home to non-hybridized hermit warblers. The research could help with conservation efforts.
  • The findings could improve scientists’ understanding of how song diversity functions, helping them disentangle the complex relationships involved with biodiversity.

Read Dr. Furnas’ paper “link opens in new tab or windowWildfires and Mass Effects of Dispersal Disrupt the Local Uniformity of Type 1 Songs of Hermit Warblers in California.”

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CDFW Photos: Top Photo: Hermit_1: Hermit warblers are a migratory songbird that breeds in California, Oregon and Washington. Photo by Dr. Brett Furnas.

Media Contact:
Ken Paglia, CDFW Communications, (916) 825-7120