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An infographic describes the increase in bird biodiversity as forests regrow in northwestern Costa Rica.An infographic describes the increase in bird biodiversity as forests regrow in northwestern Costa Rica.

UWindsor biologists show bird diversity grows when tropical forests grow

If birds sing in a tropical forest, and no one is around to hear them, do they make a sound? Yes they do, according to a new bioacoustic study from a University of Windsor biology team.

Working in one of Earth’s most imperiled ecosystems, the dry forests of Central America, researchers Kiirsti Owen and Dan Mennill used automated recorders to sample the sound of biodiversity.

“It’s really quite impressive what they’ve done in Costa Rica,” says Owen, a Master’s student in the Department of Integrative Biology and the lead author of the new study. “Through an ambitious effort to protect this forest, they managed to save some of the last remaining patches of these unique forests. Not only that, but they’re regrowing forests that were cleared.

“We wanted to know how birds are using those regrowing forests, and we collected recordings of their sounds to answer this question.”

Using the tools in Dr. Mennill’s bioacoustic lab, Owen deployed devices in forest patches of different ages, recording the distinctive sounds of almost 5,000 birds from more than 80 species. She combined the acoustic data with vegetation measurements collected by a team of collaborators.

“Our data show that older patches of re-growing forest provide homes to an increasingly diverse community of birds, including some birds that will only use old-growth forests,” said Owen.

Tropical dry forests are special ecosystems that harbor plants and animals not found elsewhere. However, these forests have been greatly reduced because they are easily converted to pastureland.

“This unique ecosystem experiences two seasons each year,” explained Mennill, who has been working with his students and collaborators in the Guanacaste Conservation Area in northwestern Costa Rica every year since 2003.

“There is not a drop of rain from November to April, but between May and October the forest receives torrential rainfall. We found that bird diversity increases in these recovering dry forests both during the dry season and the wet season.:

The article “Bioacoustic analyses reveal that bird communities recover with forest succession in tropical dry forests” appeared online this week in the open-access Canadian journal Avian Conservation and Ecology.

“This is really great news for birds and tropical dry forests,” concluded Owen, who will defend her Master’s degree this summer before beginning doctoral studies at the University of New Brunswick in the fall. “We have been able to show that conservation and restoration are working. It’s very rewarding to listen to bird communities and hear evidence of birds returning to these forests as they regrow.”