 Birds
that nest in tree cavities interact in a ‘nest web’, analogous
to a food web. Some species (excavators) generate their own
cavities. Other species (secondary cavity nesters) depend on
cavities created by excavators or other processes. Secondary
cavity nesters can only reproduce if they can find and keep a
good cavity. Good cavities are often rare, especially in forests
subject to logging. The scarcity of good cavities might be one
of the factors that limits populations of the Vinaceous Amazon
and other birds of the Atlantic forest.
Research questions
- Under what conditions do tree cavities limit populations
of birds in the Paraná Pine forest?
- What are the biological processes that determine the
availability of cavities?
 Preliminary
results
- Selectively logged forest has fewer cavities suitable
for birds. Adding nest boxes led to more birds nesting
there, so cavities appear to be a limiting resource for
these birds in selectively logged forest.
- In contrast to North America, most cavities were not
made by woodpeckers but by falling branches or other
physical damage to trees. Most of the cavities used by birds
were in live branches or a live tree trunk.
What are we doing to help cavity-nesting birds?
-
 With
local farmers, we are monitoring nests to see what factors
affect their success (e.g., rain, predation).
- We made a poster to generate public awareness about the
importance of large live and dead trees for cavity-nesting
birds.
- In our school visits, we talk
with the children about the importance of keeping trees on
the farm, so that there are always cavities for birds to
nest in.
What else needs to be done?
On many farms, there are still large trees with cavities.
These trees remain in small patches of forest and in pastures.
They are key nest sites for threatened species like the
Vinaceous Amazon. It is important to
ensure that there will be cavity-bearing trees in the future,
too.
To do so, we need to encourage and help farmers to keep live
trees and forest patches on their farms. We need to find
strategies to improve the sustainability of lands currently
under cultivation. These strategies then need to be implemented
through technical support to farmers and incentives to keep
patches of forest on farms.
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