Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level



Biological Sciences


Kimberly G. Smith

Committee Member

Steven J. Beaupre

Second Committee Member

Gary R. Huxel

Third Committee Member

Ian C. Nisbet


Biological sciences, Common terms, Competition, Life history, Stable isotopes, Thermoregulatory cost


Life history is the inheritable rules that determine energy and time allocation towards different competing functions in the energy budget of an organism. Reproductive effort varies as organisms make reproductive decisions based on available energy. Factors influencing life histories are those that change energy and time budgets such as diet, competition, and environmental conditions.

Common tern (Sterna hirundo) life history phenotypes vary between islands in the Gulf of Maine. Common terns on offshore islands (>10km from mainland) and nearshore islands (5 to 10km from mainland) lay smaller clutches, hatching chicks with slower growth rates than common terns on inshore islands (mainland). Previous research suggests differences are due to offshore colonies consuming lower quality prey than inshore terns. Common tern diets on different islands were determined by carbon and nitrogen stable isotopes in juvenile feathers and observations of prey deliveries to juveniles by adults. Common terns on offshore islands were feeding low quality euphasiids (Meganyctiphanes norvegica) and had a depleted nitrogen signature relative to inshore islands feeding on fish.

Common terns could be competing with other tern species. Offshore island colonies contain arctic (Sterna paradisaea) and common terns, inshore and nearshore colonies contain common and roseate (Sterna dougallii) terns. Competition was determined by overlap of carbon and nitrogen stable isotopes in juvenile feathers and Morisita's index of dietary overlap for observed prey deliveries by adults to juveniles. Competition could exist between arctic and common terns on Matinicus Rock, an offshore island, and common and roseate terns on Outer Green Island, an inshore colony and Eastern Egg Rock, a nearshore island.

Decreased temperatures between islands also forces chicks to expend more energy for thermoregulation instead of growth. Thermoregulatory costs between offshore and inshore islands were measured using copper models representing tern chicks. Thermoregulatory costs were higher on offshore islands relative to inshore islands.

Common tern phenotype plasticity in the Gulf of Maine was mainly due to diet. Consistent cooler temperature on offshore colonies also influences energy dedicated to growth in juveniles. Competition may limit energy budgets, but possible competition could be seen on all island types.