My dissertation examined the dynamics of cloud forest bird communities
along an altitudinal gradient on the eastern slopes of the Ecuadorian
Andes. Specifically, I investigated the seasonality of breeding, compared
diets among groups of hummingbirds, and investigated a novel tool for
documenting altitudinal migrations. In Chapter 2, I compared the
prevalence of breeding condition in mist-netted birds among elevations and
months. I found a marked increase in breeding birds during Sept-Nov at
higher elevations, but little such "breeding season" at lower elevations.
I then shifted focus to diet among hummingbirds. I used N15 isotopes to
demonstrate that females and adults feed at higher trophic levels than
males and juveniles, respectively. Females captured during breeding
season were also feeding at higher trophic levels than those captured
outside of the breeding season, though the sample sizes were quite small
(Chapter 3).
I also examined a novel methodology for tracing annual altitudinal
migrations, which takes advantage of the natural variation in deuterium
abundance from the base to the peaks of the Andes (Chapter 4). Local
migrations by birds in the tropics pose conservation problems, in part
because the movements themselves are difficult to document. There is a
theoretical relationship between Deuterium (or O18) signature and
elevation, because of fractionation during precipitation events and
evapotranspiration. A previous study had suggested that if a bird had more
or less deuterium in its tissues than theory would suggest, such
discrepancy might be used to identify altitudinal migrants. Unfortunately,
when I refined their methodology, I found that the variation within species
and sites was too great to allow such applications.
In addition, during my field research I worked closely with the park guards
and communities along this altitudinal transect. I investigated the
changes brought by a new road bisecting the World Heritage Site with formal
survey methodologies. I also trained birds guides and park guards, and
found funding to ensure their having the basic equipment needed for
backcountry guiding.
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