Nathan
E. Thomas
Associate
Professor
Courses
- Even Fall
|
Odd Spring
|
| Animal
Physiology |
Principles
of Biology:
Organismal Diversity
|
Ornithology |
Environmental Biology
|
- Odd Fall
|
Even Spring
|
| Animal
Physiology |
Principles
of Biology:
Organismal Diversity
|
Comparative Environmental Physiology
|
Environmental Biology
| Capstone Seminar |
Research
Interests
The
broad scope
of my research is focused on the physiological aspects of vertebrate
organisms to provide information which can aid in their conservation
and management. Studies of habitat use and availability
paired
with the physiological response demonstrated by species utilizing those
habitats is paramount in understanding species requirements and overall
habitat health over both temporal and geographical scales. Research
from this field has become more sought after by wildlife managers and
government agencies in the face of global climate change and will
continue to be an invaluable asset as changes to current climate
patterns are altered in the coming years.
Current Research
Stopover habitat and
duration
A large amount of my research efforts thus far have been focused on
stopover biology of shorebird migrants. I have attempted to
cover
many of the major aspects of migratory timing and the physiology of
migrants to gain a greater understanding of what constitutes high
quality stopover sites for shorebirds. High quality habitats
in
the prairie pothole region were historically ephemeral with both strong
annual and seasonal variation. Due to anthropogenic
changes, primarily from agricultural practices, there have been drastic
declines in both the quantity and quality of available
habitats.
In recent times, several large federal or state managed sites have
begun to manage water levels with the intent of providing shorebird
habitat during the peak of migration. I have focused on the
use
of these habitats during fall migration by comparing several parameters
of both natural and managed stopover sites including macro- and
micro-habitat availability and use, as well as species composition and
abundance, at the two types of sites. Stopover duration as
measured via radio-telemetry also provided support for habitat quality
measures. Data from this work suggest that natural and
managed
stopover sites are equal in their attractiveness to migrants, though
certain species have affinities for habitat features that are only
found in one of the habitat types. The radio-telemetry work
demonstrates that stopover duration is different between habitats
suggesting that habitat quality differs despite the attractiveness to
migrants.
Blood
plasma studies
To further understand habitat differences, I examined several plasma
metabolites (which provide measures of fat deposition or breakdown),
creatine kinase (a measure of muscle breakdown), and plasma
corticosterone (a measure of stress) levels of three abundant
long-distance migrant species (Least, Semipalmated and Pectoral
sandpipers). Plasma assays only demonstrate metabolite levels
at
a snapshot in time, but data collected from many individuals at the
same site over consecutive days and regressed against energetic
condition can demonstrate the effectiveness of a site for
stopover. When several metabolites are measured from the same
sample this can illustrate the energetic condition of the individual
upon capture, as many metabolites have documented patterns of increase
and decrease over the course of a single stopover. The plasma
corticosterone data was collected to further understand the quality of
stopover sites. These data were measured and analyzed
following
the Migration Modulation hypothesis which states that higher levels of
baseline corticosterone may be maintained during migration but the
stress response will be muted to prevent a further increase from acute
stress, thus protecting from skeletal muscle breakdown. These
studies demonstrated no apparent significant difference between habitat
types for plasma metabolites, nor for creatine kinase.
However,
plasma corticosterone was higher in managed sites at baseline levels
and showed a greater increase at natural sites. This suggests
that natural sites may be more effective than managed sites as stopover
habitat.
Exercise
physiology
By studying changes in metabolic rate during different seasons, or
within the same season from different locales, we can begin to
understand the differential migration or wintering strategies used by a
variety of species. My research has included measures of
resting,
active and thermogenic metabolic rates in migratory shorebirds and
wintering passerines. Due to expected correlation of basal
metabolic rate (BMR) and maximum aerobic capacity we expected to see
higher levels of both during spring migration than fall due to the
faster pace at which birds migrate in the spring. This was
studied by measuring oxygen consumption by birds in a metabolic chamber
for BMR and birds in a metabolic hop-flutter chamber for maximum
aerobic capacity. In addition, birds were expected to have an
increased maximum aerobic capacity correlated with increased exercise
capacity thus leading to elevated maximum thermogenic capacity during
spring relative to fall migration. This was investigated
using a
cold circulating water bath and metabolic hop-flutter
chamber.
Data defining metabolic rates are important to understand changes in
physiology over the annual cycle and may become important in the future
to serve as background data for studies on species which are either
known or expected to be declining.
Physiology
Do changes in migration speed between spring and fall impact metabolite
and corticosterone profiles? How do these changes impact
requirements during stopover? Most previous studies have
focused
on passerines when studying metabolite profiles and only limited work
has been completed on migrants during both spring and fall.
Due
to the faster rate of migration during spring, it is expected that
birds are able to put on fat more quickly which would show a steeper
correlation with energetic condition. Conducting studies that
compare metabolite profiles during both migratory seasons, and on
shorebirds, would provide important information about the changes that
occur physiologically between seasons. Additionally, it would
be
expected that corticosterone levels would be maintained at higher
baseline levels if spring migration is more stressful than fall
migration. If birds maintain these higher levels then they
may be
less prone to acute stressors, such as cold or reduced prey
availability, which are more likely to occur during spring migration.
Habitat
connectivity
What role does the connectivity of habitat play in avian
migration? Do birds require the same connectivity in spring
and
fall? Previous investigators have suggested that shorebirds
may
use several wetlands that are in close proximity to each other to
functionally form a single large wetland. Other birds may
follow
this model which would impact studies of overall habitat quality and
availability, especially in highly fragmented landscapes.
Furthermore, if birds require connectivity of habitats to form a single
connective complex this increases the difficulty of habitat reserve
planning as tracts of habitat are generally preserved and managed
individually rather than as one functional unit.
Climate
change influence
on habitat
Will migrants be able to meet their physiological demands 10 years from
now? 100? What changes need to be made now to
ensure their
future survival? I am particularly interested in the climate
induced changes of habitats and the effect on the stopover biology of
migrants. Several models currently exist that predict overall
expected climate change and the regional impacts on current climates,
furthermore some models have been modified to predict habitat changes
that will occur in the coming decades based on this climate
data.
Pairing these models with physiological data permits the investigator
to determine whether the physiological demands of migrants can be met
in the face of environmental change. This investigation could
also lead to the prediction of population declines or migratory shifts,
temporally or geographically, that may occur due to climate
change. If species will not be able to meet the physiological
demands under the current management strategies, this information will
lead to a shift in management practices to provide the requisite
habitat requirements for the use of future planning efforts such as
refuges, natural areas, and general conservation of species and
habitats.
Do these topics interest you? Are you interested in graduate
school? Contact me if you are interested in pursuing a
graduate
degree through the M.S.
program in Biology at Shippensburg
University.
If you are an undergraduate at Shippensburg and would like to
get
involved in this type of research or have your own ideas please contact
me.
Education
Ph.D.,
University of South
Dakota
B.S., Indiana
University of
Pennsylvania
Selected
Presentations
2011.
Association of Field
Ornithologists, Cooper Ornithological
Society and Wilson Ornithological
Society Joint Meeting. March 9-12.
Kearney, Nebraska. Intraspecific
correlations between minimum and maximum metabolic output in birds: Do
intraspecific data support the aerobic capacity model for the evolution
of endothermy?
2009. Association of Field
Ornithologists and Wilson Ornithological Society Joint Meeting.
April 9-12. Pittsburgh, Pennsylvania. Mid-continental habitat availability and
shorebird use of natural and anthopogenic wetlands.
2007.
Cooper Ornithological Society Annual Meeting. June 19-23.
Moscow, Idaho. Do
natural and managed wetlands provide equally effective stopover habitat
for shorebirds? Lessons from the mid-continent.
2006. North American Ornithologists' Conference.
October 3-7. Veracruz, Mexico. Macro- and microhabitat
selection
of shorebirds during stopover in the mid-continent of the United
States.
2006.
Shorebird Science in the Western Hemisphere.
February 27-March 2. Boulder, Colorado. Fall stopover duration at
natural
and managed sites in the Prairie Pothole Region.
2005. Cooper
Ornithological Society Annual
Meeting. June 12-15. Arcata, California. Plasma metabolites of
three
shorebird migrants during fall stopover in the mid-continent.
2005. South Dakota Academy of Science. April 8.
Sioux Falls, South Dakota. Shorebird
Stopover
Energetics.
2004. Cooper
Ornithological Society Annual
Meeting. May 6-9. La Crosse, Wisconsin. Fall stopover duration and
energetic condition of three shorebird species in the northern prairie
pothole region.
2004. South Dakota
Academy of Science.
April 2-3. Chamberlain, South Dakota. Fall stopover biology of
shorebirds at natural and managed wetlands.
2002. United States Fish and Wildlife Service Prairie Pothole
Eco-team Meeting. August 26-28. Prairie City, Iowa.
Length
of stay
of Least and Pectoral sandpipers at Big Stone National Wildlife Refuge.
