Nathan E. Thomas

Associate Professor



Shippensburg University

Department of Biology
 232 Franklin Science Center
Shippensburg, PA 17257
email: nethomas@ship.edu
phone: (717) 477-1748

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.


Future Research

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.