Ten-year study in Costa Rica finds birds native to mature tropical forests are returning to relatively young secondary forests



Robin Weber, Senior Director of Marketing and Community Relations

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New research by scientists at the National Aviary provides hope for birds in tropical rainforests

September 8, 2017 (PITTSBURGH, Pa.) -- A new study by Dr. Steven Latta, director of conservation and field research at the National Aviary, and collaborators, demonstrates how young, recovering tropical forest fragments can be more valuable for bird conservation in tropical rainforests than once thought.  

While protecting pristine, un-logged forests has always been the cornerstone of rainforest conservation, the younger forests that regrow after coffee plantations and other farms are abandoned have been thought to play important but lesser supporting roles.  However Latta’s study in Costa Rica has found that over the course of a decade, the abundance of forest birds consistently increased in secondary forests that were only 50 years old.  

"When we began our research in 2005, we expected to witness declines in forest species," said Latta.  "Younger forests are known to buffer bird populations and stall their decline, but instead we found that although these forests lack the complex structure and old trees of mature forests, they kept getting more birds and more species.”

To carry out this long-term study Latta and his collaborator, Judy Richardson, from Connecticut Audubon, racked up thousands of frequent-flyer miles, returning to southwestern Costa Rica each fall and winter.  With the help of colleagues from the San Vito Bird Club they systematically counted all the birds they saw in three small secondary forests and unfurled mist nets to capture them.  Over 10 years they observed or captured almost 5,000 birds from 152 different species.   

On average, forest bird species in the young forest fragments increased about five percent each year.  Compounded over a decade, this resulted in a 50 percent increase in the abundance of many species.  For example, capture rates of species that prefer primary forest, such as the Green Hermit, White-ruffed Manakin, Sulpher-rumped Flycatcher, and White-breasted Wood-Wren, doubled over the course of the study.  Surprisingly, this occurred without substantial changes to the structure or composition of the forest habitats themselves.  Latta attributes these increases to growing populations of birds recolonizing the secondary forest fragments from the few remaining undisturbed forest plots in the region, such as the 750-acre forest at the nearby Las Cruces Biological Station.

Latta describes the process of birds recolonizing these younger forests as a “species credit” that was cashed in over the course of the study.  

“Environmental conditions in our study sites didn’t change, it’s just that over time as forests like ours regenerated across the landscape, more and more birds found the high-quality habitat in these younger fragments and began using them.”  

According to Latta, “These results are so encouraging for conservation because they suggest that if forests are allowed to recover, growing populations of birds will respond and return to these forests much sooner than we expected - as long as a remnant population still exists as a source for these new recruits.”

The consistent funding for this long-term study was provided by the Aviary’s Avian Conservation Endowment, Point Reyes Bird Observatory, and the Grace Jones Richardson Trust.  "An ecological study this long and thorough is truly exceptional," says National Aviary Research Associate Dr. Nathan Brouwer, the lead analyst of the huge dataset.  "Most field projects last two or three years, but Steve specializes in long-term efforts to monitor the status of these important bird habitats.”  According to Brouwer, such commitment is “the only way to understand what is really going on with the species and habitats we love.”

The paper, titled “Long-term monitoring reveals an avian species credit in secondary forest patches of Costa Rica”, is available through the open-access journal PeerJ.  



Latta SC, NL Brouwer, A Olivieri, J Girard-Woolley, JF Richardson.  2017.  Long-term monitoring 

reveals an avian species credit in secondary forest patches of Costa Rica. PeerJ 5:e3539


URL: https://peerj.com/articles/3539/


About the National Aviary

The National Aviary is America’s only independent indoor nonprofit zoo dedicated exclusively to birds. Located on Pittsburgh’s historic North Side, the National Aviary’s diverse collection comprises 500 birds representing more than 150 species from around the world, many of them threatened or endangered in the wild. The National Aviary’s large walk-through exhibits create an intimate, up-close interaction between visitors and free-flying birds, including opportunities to hand-feed and to meet many species rarely found in zoos anywhere else in the world. Hours