Bioacoustics of Birds
Many animals rely on sound for communication, especially birds. Human generated noise can have a large impact on bird numbers and productivity. Science Moab talks with Skip Ambrose, a wildlife biologist who specializes in the bioacoustics of birds. We talk about the specialized methods of recording the sound of birds and how this data helps define how much the birds are affected by human noise.
Meet the Scientist: Skip Ambrose
I worked for the US Fish and Wildlife Service in Alaska for 30 years, from about 1973-2003, studying endangered species, primarily Arctic and American peregrine falcons. Part of this work involved studying the impacts of military aircraft on nesting falcons. In 2003, I went to work for the National Park Service in Fort Collins, CO, to help the Park Service their Natural Sounds Program. We studied sound levels in many national parks, trying to establish background sound levels prior to air tours. I worked for the NPS for 5 years, and then retired, and formed my own company and currently study the impacts human-caused sounds on Greater Sage-Grouse.
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Interview Transcript - Impacts of Human Noise on Wildlife
All species of wildlife are affected by human noise in some way. This column will feature methods used to determine how much birds, in particular, are affected by human noise.
Many animals rely on sound for communication, especially birds. Wildlife biologist Skip Ambrose dedicates his work to understanding the bioacoustics of birds. Bird numbers and their ability to thrive depend a great deal on communication by way of birdsong. As human noise has become louder, some birds have been able to adapt their volume to compete. Some have not.
Ambrose: My name is Skip Ambrose. I’m a wildlife biologist. I specialize in acoustics. I have worked for the Fish and Wildlife Service for about 30 years and in park service for about five. I now have my own company called Western Bioacoustics. We study the impacts of human-caused noise on wildlife.
Science Moab: Could you explain what bioacoustics is?
Ambrose: Bioacoustics is the study of the impact of acoustics, or sound, on wildlife.
Science Moab: Why study the bioacoustics of birds in particular?
Ambrose: In Alaska, while working for the Fish and Wildlife Service, I studied peregrine falcons. Peregrine falcons eat almost exclusively other birds. A large part of that is pasturing songbirds. My goal originally was to study peregrine falcons and their prey species. The populations of songbirds are really important to peregrine falcons. Songbirds rely on vocal communication so much that human-caused noise can have a negative impact on those birds.
To meet my original goal, we had to understand the survey techniques for the primary prey species, which was the songbird. So we used bird surveys. About 80% of bird surveys are strictly acoustic.
Science Moab: How do you physically measure and record the birds?
Ambrose: We survey birds, for example, by walking a 1-kilometer line. Every 100 meters, we stop and record the birds that you see or hear. You hear more than you see. So for 10 stations on a 1-kilometer line, you would do 10 points and listen to birds for 5 minutes, then move on to the next point. Now, digital recorders’ memory and battery life have gotten much better. We can now place recorders and collect data for a whole breeding season, which we can study and also archive. We use about 1 terabyte for one season.
Science Moab: In general, what are you listening for with the birds?
Ambrose: There are two primary focuses of our study. One is to study the presence or absence of birds and the relative abundance of these birds. This is the main use of the recordings. But another use is to understand the potential negative impacts these birds experience due to man-made noise.
For these recordings, we have kind of a code system. Every bird species has a code. Every human cause sound has a code. During these sample recordings, we write down everything that we hear. For example, in a 10-second period, we might hear 2 or 3 birds and 2 or 3 human-caused sounds like distant aircraft, vehicles, or cattle. We will write down everything that we hear. When we record for multiple years, we see these trends of airplane noise going up, airplane noise going down. We note that the yellow warblers are going up or that the yellow warblers are going down.
It’s difficult to measure exactly how the birds are being affected. Some birds will increase their amplitude to overcome human-caused sounds. But at some point, birds can only increase their volume by so much. We measure the amplitude of the man-made noise with a sound level meter. The bigger questions we look to answer are: did the bird populations go up or down? Was the sound a large part of that?
We’ve learned that even if birds can hear each other, they don’t necessarily hear distress or alarm calls of other birds. If they hear something like a red tailed hawk or a peregrine falcon and issue an alarm call, they might not know why they can’t hear each other.
Science Moab: Is there anything further you would like to talk about?
Ambrose: I tell people, “when you go out, listen and think about what you hear. You and I can turn up the volume, or talk louder. But many wildlife species don’t have that option.” I hope people will not ignore this, which is difficult because we’ve grown up making noise. Sound is a really important resource for wildlife. We don’t have to be noisy. We have the ability to know what causes issues. We just need the political courage to address it.
