Seabird Census by Sound Recording Sees Success

Estimating seabird populations has long been a struggle for researchers because the birds build nests in geographically inaccessible places and tend to hide their eggs in burrows. But a new, sound-based counting method is giving researchers the edge they need to estimate seabird populations.

Getting an accurate idea of how many seabirds are out there will give conservationists the data they need to ensure the protection and survival of seabirds. To date, it has been difficult to put a number on how fast seabird populations are declining.

Many of the remote island where seabirds nest are inhabited by feral cats and rats, which enjoy eating the birds and their eggs.

Seabird species that build their nests in burrows are particularly vulnerable to predation, easily trapped by a hungry predator. Many seabird species have disappeared from islands where cats and rats have been introduced.

"Those species that are most vulnerable to rats are often the ones that are the most difficult to count" said Steffen Oppel, a conservation scientist with the Royal Society for the Protection of Birds in England.

Oppel and his collaborators attempted a new method of counting seabirds that relies on sound recorders.

They set up their equipment on a remote island in the North Atlantic and recorded for two years. They were able to "count" the number of birds nesting on the island by recording their calls at night. Seabirds are quite noisy at night, and the nosier a night on one of these remote islands, the more seabirds are nesting there, the researchers said.

"Recording seabird calls for a few months is the easy part - but making sense of 1,000s of hours of sound recording is quite tricky" Oppel said in a statement.

The research team developed an algorithm that automatically counts the seabird calls in the recordings. Once the algorithm was run on the recordings, the results confirmed the researchers' suspicions: the higher concentration of bird calls was centered around the areas believed to have the most nests.

Using the data, the researchers were able to extrapolate the seabird population size for the entire island, a figure that had previously only been derived from pure guesswork.

"We can use this index over time to assess whether colonies are stable or decreasing - which is extremely important for many remote colonies about which we know very little," Oppel said.

The team published their work in the journal Nature Conservation.