Sound Recorders Track Seabirds by the Seashore
(Inside Science) – The wavy gray lines on a graph called a spectrogram turn the sounds of the seashore into a picture. To Abe Borker, a seabird biologist at the University of California, Santa Cruz who has an eye for nature’s music, these waves reveal the language of animals communicating with each other.
Recently, Borker has turned his attention to the unique calls and sounds of seabirds. He is developing new ways to monitor bird populations and behavior with audio recordings -- a method that could give biologists an important window on threatened species, while saving them time and money.
For example, the tern, a seabird related to a gull, uses an “advertisement call” when it approaches other terns.
“It’s basically them saying, ‘Hello,’ to their mate and chicks as they approach the colony,” said Borker. These calls encode information about bird abundance. “There is a consistent relationship between the number of times the tern says hello and the number of terns that are breeding on the island.”
Seabirds, like albatross or petrel, are birds that spend most of their life at sea. Many come to shore only to raise their young on isolated islands or cliffs. Seabirds play a major part in the ocean food web, consuming a significant amount of fish or other animals. And they are used as indicators to help scientists understand how the climate is changing.
Seabirds are highly endangered. According to the International Union for Conservation of Nature, about one-third are threatened by extinction. The good news is that conservationists have developed effective strategies for bolstering seabird populations. One strategy capitalizes on the fact that birds like to be around other birds of the same species to lure the animals to desired locations. For example, the Audubon Project Puffin used wooden decoys to attract puffins to Egg Rock, an island off Maine's coast. The US Fish & Wildlife Common Murre Restoration Project played calls in addition to using decoys to attract the black-and-white birds to Devil’s Slide Rock, California, where the population had been wiped out by the 1986 Apex Houston oil spill. Other conservation methods include reducing predators like rats and cats from islands where seabirds breed.
These conservation strategies are highly effective, but require extensive resources. That’s where Borker comes in. His efforts to monitor changes in seabird populations and the impact of restoration efforts will help conservationists know where to best direct their time and money.
Seabirds are difficult to monitor. They spend most of their lives at sea and nest on remote islands or cliffs. Many are secretive, only coming out at night or nesting in burrows in the ground. Typical monitoring efforts require trained specialists spending onerous time listening to and interpreting bird calls. Borker thinks there is a better way.
In 2011 Borker hopped aboard a small boat to a group of remote islands off the coast of California. His team of seven people hiked ashore loaded with camping and scientific equipment. They set up microphones and recorders all over the island. A few months later, when breeding season had ended, they collected the recorders and downloaded the data. Borker is now using a computer program to help identify bird calls and decipher the events on the noisy island.
“We also have a way of converting sounds into pictures and using image processing tools that are probably not too different from the way Google image finds faces,” Borker said. His tools can reveal the frequency, timing, duration, and intensity of different bird calls. That information can help explain the soundscape in more detail, such as the number of bird calls happening at any moment of the recording.
Borker is on the leading edge of acoustic monitoring of seabirds, but it is a well-established method for studying marine mammals, something David Mellinger, an Oregon State bioacoustician, has been doing since the early 1990s.
“I’m excited about what [Borker] is doing,” he said, “I’ve long thought it might be useful to use acoustics to study seabirds.”
According to Mellinger, acoustic monitoring presents some challenges, such as dealing with wind noise or converting acoustic data to population estimates. But the increased efficiency is worth it, he said. “It takes one person to do what five or ten people could do before.”
Mellinger believes this is especially beneficial in the current funding climate for biology and conservation research. If scientists develop new analysis methods over time, they could reprocess old data to reveal new information. Additionally, audio recorders and software programs don’t get tired, the way a researcher might. “If you are sitting there for hours [counting birds] your attention tends to wander. A computer it is more consistent. Computers don’t get bored,” Mellinger said.
Borker said that acoustic monitoring will help conservationists determine the most efficient way of allocating resources for seabird protection and restoration. It can also lead to new discoveries. For example, recent work by the company Conservation Metrics and the National Park Service helped scientists confirm breeding grounds for the ashy storm petrel -- Borker’s favorite bird -- on California's Channel Islands.
“It’s a rare bird that breeds almost entirely in California and a little bit of northern Baja,” said Borker, “So it’s a unique species that is totally ours to protect and ours to lose.”