In cold, quiet forests in December, some people stand with binoculars and listen intently. It is a holiday
tradition for some bird-lovers to take part in the Audubon Christmas Bird Count. And maybe some of those long-time birders noticed the declining trend before the rest of the public did.
Using data similar to the Christmas bird counts along with cutting-edge radar and bird population estimates, researchers from the Cornell Lab of Ornithology recently revealed some harrowing news: since 1970, three billion birds have disappeared in North America. Thats across multiple species, biomes, and regions of the continent. The greatest losses came from the most common groups of birds, ones you would easily recognize in your backyard: sparrows, bluejays, blackbirds, and so on.
This news can seem surprising: there’s still an abundant flock at your bird feeder and a chorus in the early morning hours. But these daily observations don’t tell the story of how many birds there used to be: for some species, hundreds of millions more.
Why is this happening? The researchers point to habitat loss, pesticide use, and urbanization as culprits.
But, importantly, birds did not decrease in every habitat type in the study. Because of wide ranging efforts to conserve wetlands, wetland birds have actually increased in abundance over the time period of the study. This is good news, and it means that we already know that conservation works.
We already have the tools to restore what is lost, before it is too late.
Listen for a change
Restoring habitat, removing unnatural predators, and avoiding pesticides can all be valuable actions to bring birds back– but how can we tell if these actions are working? Environmental managers have to measure the outcome of their conservation efforts, and that means somehow measuring the number of birds.
Listening for birds can be one way to do this, but in a different way from the Christmas Bird Counts. Instead of having an expert on site to identify each call, technology is rapidly developing to identify animals by their sound– a field of study known as bioacoustics. This is especially useful in areas that are inaccessible by researchers but still key sites to study the impacts of bird conservation.
As an example, let’s say you, as a manager, have an island full of an invasive predator that eats birds. You could set up a recorder to figure out how many birds are there at the start– not too much noise on the recorder. Then you could remove all of said invasive predator from the island. Because this predator is gone, the birds should increase in abundance again, and you could set up the recorder again. This time you might collect a huge amount of data: hours and hours of calls, and hopefully you have a computer program to help the identification process go a little faster.
A team of researchers from multiple institutions led by Abraham Borker of UC Santa Cruz wanted to do just that to assess seabirds on the Aleutian Islands after removing Arctic Fox and Norway Rats. After collecting the data the hard way: recording, counting, and identifying birds by their calls, the researchers wanted to see if there was an easier way for future managers to assess their work. What might be easier, the researchers thought, would be to look at the soundscape of the calls. In other words, they could look at the shape of the data; its richness, complexity, the highest high notes, and estimate bird abundances from those numbers.
After putting out recorders at sites where predators were removed at different times in the past, the researchers listened for the seabirds. They matched all their soundscape data to the calls they had collected and identified previously. And finally, the researchers found their shortcut: by looking at the richness of the sound, they could estimate the abundance of birds much more easily.
Of course, by making the process quicker and easier by assessing soundscapes rather than individual calls, you lose some accuracy. Things other than birds can influence the richness of your sounds: weather and time of year. Even though assessing soundscapes might not get you the most accurate picture, having this potential tool is better than the other options: investing great time, money, and expertise into call identification, or not knowing the outcomes of your actions.
Supporting conservation and research are the steps forward to reverse the bird decline, and measuring the success or failure of these efforts is a key component of this. It’s going to take some work to bring back the birds that were lost. Until then, keep listening.
Rosenberg, K. V, Dokter, A. M., Blancher, P. J., Sauer, J. R., Smith, A. C., Smith, P. A., … Marra, P. P. (2019). Decline of the North American avifauna. Science, 366(6461), 120 LP – 124. https://doi.org/10.1126/science.aaw1313
Borker, A. L., Buxton, R. T., Jones, I. L., Major, H. L., Williams, J. C., Tershy, B. R. and Croll, D. A. (2019), Do soundscape indices predict landscape scale restoration outcomes? A comparative study of restored seabird island soundscapes. Restor Ecol. Accepted Author Manuscript. doi:10.1111/rec.13038
Feature Image: “Puffin’s Shout” from Latrabjarg, Westfjords, Iceland, by Luca Temporelli.