Guam: Can forests that have lost all of their birds still function normally?
Can forests that have lost all of their birds still function normally?
This is an important question for the now bird-less forests on the
island of Guam, an island in the western Pacific. How did Guam lose
its birds? In the mid-1940s, the brown tree snake was accidentally
introduced to what was then snake-free Guam. This snake became Guam’s
new top predator and ate its way through a buffet of the island’s bird
community. As a result, 10 of the island’s 12 forest bird species are
now extinct on Guam and the two surviving forest bird species remain
only in tiny, localized populations where snakes are controlled.
Guam’s now silent forests currently hold about 13,000 snakes per
square mile.
I started to think about the potential ecological impacts
of bird loss in 2002, when two years out of college, I was hired by
the U.S. Geological Survey to develop a “Rapid Response Team” that
would identify and eradicate new populations of brown tree snakes on
U.S.-associated Pacific Islands. Although I had heard the snake story
in my college conservation biology course, I did not know where Guam
was when I applied for the job. Yet, three weeks later, I was on a
plane headed there. As I worked on Guam during the next three years, I
often wondered why no one was studying how Guam’s bird losses impacted
the forests’ remaining organisms. So in 2005, I began a Ph.D. program
in biology at the University of Washington to investigate how bird
loss changes the movement of seeds around Guam’s forests.
This spring, I, along with my co-advisers Joshua Tewksbury and Janneke Hille Ris
Lambers, our collaborator at the University of Guam Ross Miller, and
my field assistant Theresa Feeley-Summer, began to examine whether the
loss of birds had caused changes in how the seeds they typically eat
are distributed. The study is funded by the Budweiser Conservation
Scholarship and the National Science Foundation (NSF) Integrated
Graduate Education, Research, and Training (IGERT) and Graduate
Research Fellowships. In this study, we set seed traps at various
distances from fruiting False Elder (Premna obtusifolia) trees in the
forests of Guam and Saipan, a nearby island with birds, and then
counted the number of seeds that fell into each trap.
This shows us
how far the seeds of fruiting trees are traveling in Guam’s bird-less
forests as compared to Saipan’s forests with birds. Although our study
is still ongoing, we have already produced some important results: we
found that all of the seeds from the fruiting trees on Guam remained
near their parent trees and maintained intact seed coats. By contrast,
many more of the seeds from the fruiting trees on Saipan were found
without seed coats away from their parent tree. The differences
between the distributions of the seeds on Guam and Saipan can be
attributed to the differences in their bird populations: In Saipan’s
forests, birds stop at fruiting trees, eat fruit, swallow the seeds
and then fly to the next tree, where they defecate, effectively moving
seeds away from where they are produced.
http://www.livescience.com/animals/090123-bts-birds-guam.html