Research

Dr. McWilliams’ research focuses on the behavior, physiology, and ecology of individuals and how these characteristics determine population-level patterns of resource use, social organization, and interspecific interactions. He is particularly interested in the energetics, nutrition, and digestive physiology of threatened wild vertebrates, in the physiological and ecological implications of body size in herbivorous geese, and in how natural or anthropogenic environmental change impacts the ecology and physiology of wild vertebrates. Recent projects have addressed the life history and ecology of threatened salamanders, habitat selection of ruffed grouse in relation to forest management, physiological ecology of gosling growth in arctic ecosystems, and physiological and behavioral ecology of neotropical migrant songbirds.

Research and Employment Opportunities

We regularly offer excellent opportunities for scientists at all levels to join our research team at University of Rhode Island. Postdoctoral and graduate research opportunities are advertised wisely and this page lists current openings. We encourage interested applicants to contact us about future opportunities that have not yet been advertised.

Postdoctoral Positions:

Contact Dr. McWilliams directly about these opportunities.

Graduate Research Assistantships:

Full-time research/teaching assistantships are usually available each Fall semester. These opportunities are usually advertised on the TWS listserv, the ESA listserv, the on-line Ornithological Newsletter, and other places. There are also links at the NRS homepage that provide further information about the Graduate Program at URI. All graduate students in our research team are trained as part of one of two graduate programs: Ecology & Ecosystem Sciences, or Integrative & Evolutionary Biology.

Block Island Songbird Stopover Research
Avian Ecology at URI
Forestry and Wildlife Habitat at URI

Current projects

My research primarily focuses on the nutritional and physiological ecology of wild vertebrates, with an emphasis on species of conservation interest. Using a combination of field and laboratory approaches, I have studied a diversity of vertebrates including carnivorous salamanders, herbivorous waterfowl and grouse, as well as insectivorous, frugivorous, and granivorous passerine birds. Three common themes are evident in my research: (1) I regularly use comparisons between species to reveal broadscale patterns in nutritional and physiological ecology, (2) the research questions that I investigate focus on aspects of the physiology and nutrition of wild vertebrates that are relevant to the animal’s ecology, and (3) I conduct integrative studies of a given organism. For example, I combine work on metabolic physiology, membrane transport of nutrients, digestive physiology, nutritional requirements, feeding behavior, ecological energetics, and constraints (e.g. morphological, developmental, physiological) on prey and predator form and function. To accomplish such an integrative research program requires successful collaboration. Below I provide examples of some current research projects that demonstrate these common themes.

Use of Stable Isotopes in Studies of the Nutritional and Physiological Ecology of Migratory Birds
Plant physiological ecologists have used natural variation in stable isotope ratios to study photosynthesis, water balance, and nitrogen metabolism in plants. In contrast, animal physiological ecologists have made much less use of naturally occurring stable isotopes in their research despite its great potential. Recently, animal ecologists interested in migratory birds have used stable isotope ratios to reconstruct diets and to trace movements between breeding and wintering areas. However, most of the significant advances in the near future will come only after we have a better understanding of the physiological processes that influence stable isotope signatures in free-living animals.

A primary focus of my NSF CAREER grant is to use stable isotopes to study metabolic routing of dietary nutrients in birds. For example, we have used stable isotopes of carbon and nitrogen to detect protein deficiency in growing goslings. Theoretically, animals deficient in dietary protein must recycle endogenous nitrogen thereby enriching the N isotope ratio. Using controlled laboratory studies, we compared isotope ratios of Canada and Snow goose goslings raised on diets with either deficient or adequate protein levels, and found they indicated protein deficiency in growing goslings. In addition, David Podlesak (PhD 2004) and I have recently used stable isotopes to quantify how certain dietary nutrients are metabolically routed to certain tissues during fasting and flying in migratory warblers. The advantage of using naturally occurring stable isotopes for this work is that the results can be easily applied to free-living birds. For example, we have conducted field studies of diet switching in free-living songbirds at migration stopover sites by comparing patterns of stable isotopes in selected wild fruits and insects, and in the breath, blood, feces, and feathers of the birds. Current projects in which we use stable isotopes include further studies of metabolic routing of dietary nutrients in passerine birds, habitat use of goslings in Hudson Bay (Canada), energetics of passerine birds during long-distance flight, and estimating body composition of live songbirds at stopover sites during their migration.

Avian Herbivores and the Importance of Body Size
Geese provide an interesting model for studying how avian herbivores circumvent the problem of combining the high energy demands of flight with the physiological limitations associated with eating leaves which are low in energy and nutrients and high in fiber. Much theory focuses on the implications of body size for the physiological ecology of mammalian herbivores but it has yet to be adequately applied to avian herbivores. Geese are an excellent group in which to study such issues because species such as the Canada goose vary 7-fold in body size. My previous work on avian herbivores has shown that highly selective feeding is one way geese escape some of the constraints associated with being a small avian herbivore. However, geese also show remarkable abilities to modulate digestive features in response to changes in diet quality and, as a result, they are able to maintain relatively high digestive efficiency on a wide range of diets. My current studies of geese focus on the allometrics of metabolic rate, gut capacity, digestive physiology, and foraging strategy within and between species. I am also conducting work in subarctic Canada on the nutritional and physiological ecology of growth in geese in relation to projected climate change.
Another current project (ongoing since 1999) focuses on habitat use and population dynamics of Ruffed Grouse in southern New England. This is a cooperative project with Brian Tefft, the state wildlife biologist with Dept. Environmental Management in Rhode Island. The primary goal of the proposed research is to assess how habitat quality and forest management practices affect home range and survival of grouse in southern New England, and to establish the efficacy of relocating grouse to enhance grouse populations in RI. Starting in fall 2005, this project expanded so that we are now assessing how forest management that produces early successional forest affects the southern New England bird community, in general, and Ruffed Grouse, in particular.

Incubation patterns in relation to disturbance of Piping Plovers at Cape Cod National Seashore
During incubation, birds must balance the need to attend the nest so that proper embryological development occurs with the need to leave the nest to forage and satisfy their energetic requirements. However, each time a bird leaves its nest the eggs may change temperature and the location of the nest may be detected by a predator. Since 2002, Eric Schneider (MSc candidate) and I have been investigating nest attendance patterns of the endangered Piping Plover at Cape Cod National Seashore (MA). The primary goal of the project is to use inexpensive iButton ® data loggers and thermocouples in plover nests to determine how human disturbance or predators affect nest attendance patterns of the plovers.

Contemporary Studies of the Nutritional and Physiological Ecology of Migratory Songbirds
(1) Digestive Physiology, Digestive Constraints, and Its Ecological Implications
Birds may often experience short-term changes in food quantity and quality. For example, frugivorous birds during migration may one day encounter preferred fruits that are ubiquitous allowing relatively constant food intake, whereas the next day their preferred fruits may be patchily-distributed and require much travel time between patches. In such situations, a bird’s daily pattern of food intake may differ from day to day. Theoretical optimality models make explicit predictions about how an animal’s digestive features should respond to short-term changes in food quantity and quality although prior to my work there had been no such tests of the models for changes in food intake. To test the predictions of the theoretical optimality models, we manipulated foraging costs in insectivorous warblers and frugivorous waxwings and measured whole-animal features such as digestive efficiency and passage rates using radioactive isotopes while also measuring suborganismal features that determine whole-animal performance such as tissue-specific levels of digestive enzymes and active and passive transport of specific nutrients across the intestinal membrane. All the theoretical predictions were rejected. Warblers and waxwings did not increase retention time and digestive efficiency in situations with higher foraging costs as predicted by the model, suggesting that these digestive parameters may be regulated to minimize feeding time rather than maximize rate of net energy gain. We have recently summarized the ecological circumstances that lead to digestive constraints in both birds during migration (McWilliams and Karasov 2005) and birds and mammals, in general (Karasov and McWilliams 2005).

(2) Diet Preferences for Specific Nutrients (e.g. Fatty Acids) and its Energetic Consequences
The nutrient requirements of an animal depend on its physiologically state. For example, during periods of fat storage (e.g. during migration or in the cold), birds store impressive amounts of fats comprised mostly of longchain unsaturated fatty acids. Theoretically, selectively feeding on long-chain unsaturated fatty acids may be advantageous because such fatty acids may be absorbed and/or metabolized more efficiently than saturated fats into a bird’s fat depots. We tested this hypothesis by offering warblers and vireos in different physiological states choices between diets that varied only in their fatty acid composition. We found that (1) birds prefered diets with mostly long-chain unsaturated fatty acids especially during energy-demanding periods of the annual cycle, and (2) both diet composition and selective metabolism were important in determining the fatty acid composition of depot fat in migratory birds. Barbara Pierce (PhD, 2003) and I recently conducted the first studies that demonstrate that birds with certain ratios of unsaturated to saturated fatty acids in their fat reserves have greater aerobic capacity while exercising. How migrating birds acquire preferred fatty acids in the wild is not well understood, but our recent work suggests that it has important implications for the energetics of migration. Current projects focus on how dietary fatty acids and antioxidants affect metabolism of fatty acids and exercise performance in birds during flight (in the windtunnel at the Max Planck Institute for Ornithology in Germany).

(3) Changes in Body Composition of Birds during their Migration
The dynamics of body composition influences nutrient requirements which then interacts with resource availability to determine length of stopover at sites along the migration route, the pace of migration, and ultimately the success and survival of individuals. Of the few studies reporting utilization of fat and protein reserves in migratory passerines, most use regressions of fat mass and body mass from birds sampled during migration to quantify protein reserves. Unfortunately, this method has a poor theoretical rationale and methodological shortcomings. Megan Whitman (MSc, 2002) and I completed the first cross-validation study that simultaneously uses two different nondestructive techniques (TOtal Body Electrical Conductivity (TOBEC) and isotope dilution) to independently estimate lean and fat mass of small songbirds during their migration. Using these techniques, we can estimate lean mass with precision of ca. 0.5 g and fat mass with precision of

(4) Phenotypic flexibility in physiological traits
The capacity of many physiological systems, including that of the digestive system, is matched to the prevailing demand but can be modulated in response to changes in demand. Such phenotypic flexibility in physiological traits may itself be a critical component of the adaptive repertoire of animals that may influence diet diversity, niche width, feeding rate, and thus the acquisition of energy and essential nutrients. However, the key organs of a physiological system are not exactly matched to the prevailing demand, but instead they provide some limited excess capacity. This so-called “spare capacity” is ecologically important because it defines the limits of shortterm response in animals. Because changes in feeding rate and diet are common in migratory birds, understanding the extent of spare capacity in their digestive system provides insights into when digestion may constrain diet choice and feeding rate. We have found that phenotypic flexibility in the digestive system of migratory birds is pervasive and has important ecological significance. Current projects focus on how the flexibility and capacity of the avian digestive system varies across taxa and how it is related to the phylogeny, ecology, and life history of birds.

Implications of the research for Wildlife Management and Ecology (a few examples)
My research on geese during spring has provided managers in California with information on the habitats and plant species selected by the Cackling and Ross geese, carrying capacity of specific habitat types, nutritional requirements of the geese, the effects of goose grazing on crop yield, and the sensitivity of geese to disturbance. This information is currently being used by state biologists who are purchasing and managing habitat particularly for Cackling geese because of their low population size. The goal of our gosling growth study is to identify the effects of protein limitation and dietary fiber on growth rates of sympatric arctic-nesting Canada and Snow geese. Information on growth rates and nitrogen requirements of Canada and Snow geese is particularly pertinent yet inadequate. Increased numbers of Snow geese have caused widespread destruction of their preferred salt-marsh plants. In response to this habitat destruction, snow geese are now nesting or raising broods in areas traditionally used primarily by Canada geese. We tested the hypothesis that interspecific differences in nutritional requirements of goslings allow Snow goose goslings to survive better than Canada goose goslings in arctic and sub-arctic habitats that are degraded. However, contrary to the predictions of the hypothesis, Canada goose goslings had lower protein requirements and tolerated higher fiber foods than Snow goose goslings. Thus, in the degraded, overgrazed habitats now common along Hudson and James Bay, Canada, interspecific differences in nutritional requirements of goslings can not explain why populations of Snow geese are increasing while populations of Canada geese are declining. Finally, my research on songbirds provides information about how much these migratory passerines eat and digest during migration, their dietary preferences at stopover sites during migration, and the importance of physiological constraints in limiting rate of fattening. As part of this research, we are using non-lethal methods such as deuterium and total electrical body conductivity (TOBEC) to determine how habitat quality influences body composition of small passerine birds during migration. These results and new techniques can be used, for example, in managing populations of threatened species of neotropical migrants.