What happens to rainforest birds when Amazonian forest is destroyed?  The simple answer is that forest birds don't persist in pastures or clearcuts, but the actual landscape is more complicated in space and time.  Economic drivers, government programs, road construction, and other forces have created a mosaic of forest fragments and regenerating vegetation throughout the Amazon.  One of the only sites with a long-term focus on accompanying bird populations and communities in these dynamic landscapes is the Biological Dynamics of Forest Fragments Project, north of Manaus, Brazil.  We've been sampling birds there since the 1970s.  In our current NSF-funded project, we worked with birds in small forest fragments and 20-30 year old regenerating forest that grows naturally when pasture or cutover forest is abandoned.  We wanted to know where the birds are in this landscape, and how forest birds are faring when they occur outside of old-growth forest. 

Our main long-term sampling method has used fine nets, called mist nets, deployed in the understory to catch birds passively.  This is the most standardized approach for sampling birds.  A big advantage of birds in the hand is that we don't have a problem of observer experience- each bird can be identified with 100% accuracy.  This is also a great tool for training aspiring ornithologists, as we've done with many students from Brazil, the US, and elsewhere.  Netted birds can be aged, weighed, measured, sampled for DNA or hormones via blood or feathers, and given a uniquely numbered band before being released unharmed.  Erik Johnson and Jared Wolfe, two students who got their PhDs on the project, took advantage of capture data to write a book on how to identify, age, and sex Amazonian birds.  This product is a big advance for research and education with the world's most complicated avifauna.  PhD student Cameron Rutt spearheaded a major analysis from the net results to show the vulnerability of forest birds in the network of small fragments and second growth, resulting in a robust assessment for 64 species.  Unfortunately, only a handful of species thrive in the disturbed landscape.  On the other hand, PhD student Angelica Hernandez-Palma's work showed that as second growth develops, birds grow their feathers faster, suggesting that time improves habitat quality.  We also observed these results from the other direction- if regenerating forest is cut, condition of birds in adjacent forest declines.

Nets are great for standardized sampling, but they do a poor job for >100 species that almost never descend low enough to be captured.  We surveyed these groups by looking and listening (mostly listening) throughout the landscape.  This work has revealed some encouraging news about the future of forest birds as forest regenerates.  First, we don't see a problem of colonization by non-forest or invasive birds.  Second, regenerating forest includes a significant proportion of primary forest species, even if many are at lower abundance than in primary forest.  Third, bird communities in secondary forest are starting to include complex social organization of mixed-species flocks and army-ant-following birds.  Finally, we see evidence that some forest birds are breeding in regenerating forest.  Taken together the netting plus observational data suggest that regenerating forest is moving in the right direction for supporting forest birds, even if it remains an incomplete substitute after 30 years of growth.

Our research has left unanswered questions to be addressed beyond this NSF grant's support.  When we run the same analysis for continuous forest samples from the past 10 years compared to the early 1980s, we see declining abundance for a broad swath of forest birds, particularly those that use the forest floor and the very lowest vegetation.  PhD student Vitek Jirinec has been sampling birds and the characteristics of these microhabitats to assess the drivers and implications of changes within what we thought to be undisturbed forest.  Even as regenerating forest provides opportunities for forest bird communities, we are concerned that the primary forest baseline has shifted in the absence of landscape change, with the result that bird communities we knew from the early 1980s have been permanently diminished.

Last Modified: 04/30/2019
Modified by: Philip C Stouffer