RESEARCH SCIENTIST
NUTRIENT ALLOCATION
IN WATERFOWL
Samantha E. Richman (Livingston Ripley Waterfowl Conservancy), Keith A. Hobson (Environment Canada),
and Shiway W. Wang (Sedna Ecological, Inc.)
The application of stable isotopes to
describe animal diets and trace origins has revolutionized the way we study the
ecology of individuals and communities. This is particularly true for birds,
which have a variety of tissues that are easy to collect without destructive
techniques. However, despite tremendous advances in this field, key parameters
in isotopic models still require controlled laboratory investigation or
ground-truthing for many species on isotopically distinct diets. By
incorporating valid species-specific baseline values of isotopic discrimination
factors, we can determine how nutrients are allocated from resources to tissues
(blood, feather, claw, eggs). For example, a recent major development in the
way we understand endogenous (e.g., nutrients from the body, termed ‘capital’)
and exogenous (e.g., nutrients from the diet, termed ‘income’) contributions to
eggs by laying female birds involves diets that differ in source nutrients.
This approach has been largely successful in quantifying nutrient allocations,
but relies on an untested assumption that the isotopic link between endogenous
body tissues to eggs laid under a strictly capital strategy resembles that of a
carnivorous bird under a purely income strategy The true capital discrimination
factor remains elusive because it is generally difficult to get birds to lay in
captivity without food. To study nutrient allocation to body tissues and eggs,
we are using captive waterfowl (large
carnivorous common eiders, omnivorous lesser scaup, and herbivorous black
ducks) to determine isotopic discrimination factors for birds on single-source,
homogenous diet that differ in source nutrients (fish meal of marine origin or
corn-based terrestrial source). These results will provide the baseline data
and foundation for future work to improve models incorporating stable isotopes
to understand the ecology of waterfowl.
Postdoctoral Research Fellow
Program in Wildlife & Conservation Biology
Natural Resources Science, University of Rhode Island
GROWING FAST AND DYING YOUNG: INFLUENCE OF FORAGE QUALITY ON GROWTH AND SURVIVAL OF AVIAN HERBIVORES
Samantha E. Richman and Scott R. McWilliams (University of Rhode
Island), in collaboration with James O. Leafloor (Environment Canada)
and William H. Karasov (University of Wisconson-Madison)
Avian herbivores such as geese in Arctic ecosystems are
highly sensitive to reduced quantity and quality of available forage like that
caused by overgrazing. To determine the effects of diet quality on growth and
survival of sympatric goose populations, we raised 100 Canada and 100 Snow
goose goslings on grass-based diets that included a factorial combination of
three levels of protein (10, 14 and 20%) and two levels of neutral detergent
fiber (30 and 45%), but similar energy content (~18 kJ/g). Survival of Snow but
not Canada goslings was significantly affected by both dietary protein and
fiber content. Goslings fed the low protein diets had ~40-65% lighter body mass
and reduced structural growth compared to goslings raised on the higher protein
diets. The effects of dietary fiber were more extreme for Snow compared to
Canada gosling in part because Canadas increased food intake (corrected for
body size) by ~100% while Snows increased food intake by only 15% when fed the
high-fiber diets. Apparent Metabolizable Energy was similar between species,
but lower for diets with high fiber content. Canada goslings had larger gizzard
mass and small intestine length than Snow goslings in response to increased
fiber content. These results indicate that Snow gosling had higher protein
requirements than Canadas, and that there were interspecific differences in compensatory
growth that were explained by their digestive physiology. Although phenotypic
flexibility in gosling growth and digestive system allows geese to respond
successfully to habitat change, there appears to be a lower limit to the
quality of forage eaten (<10% protein and high fiber) that is to a degree species-specific.
Richman, SE, Leafloor, JO, Karasov, WH, and SR McWilliams (2014 Early view) Ecological implications of reduced forage quality on growth and survival of sympatric geese. Journal of Animal Ecology doi: 10.1111/1365-2656.12270 PDF
Richman, SE, Leafloor, JO, Karasov, WH and SR McWilliams (2012) Influence of forage quality of growth and survival of Canada and Snow goose goslings. North American Duck Symposium, Memphis, TN, Abstract PDF
Richman, SE,
SR McWilliams, JO Leafloor and WH Karasov (2012) Growing Fast and Dying
Young: Effects of foraging quality on growth and survival of Arctic
herbivores. North American Ornithological Congress,
Vancouver, British Columbia, Poster PDF
SEA DUCK PREDATION ON MUSSEL AQUACULTURE:
A GROWING CONFLICT
Samantha E. Richman (Université du Québec à Rimouski UQAR, Fisheries and Oceans Canada), Elisabeth Varennes (UQAR), Magella Guillemette (UQAR), Sveinn Are Hanssen (Norwegian Institute for Nature Research), and John Bonardelli (Shellfish Solutions)
The cultivation of blue mussels (Mytilus edulis) is a growing industry worldwide; however predation
by migrating sea ducks has become an enormous challenge to mussel growers
causing extensive financial losses.
Mussels are a principle prey item for sea ducks, which take advantage of
mussel farms that provide a highly abundant and easily accessible food
source. Because cultivated mussels tend
to have higher growth rates, thinner shells, and higher flesh content than
intertidal mussels, farmed mussels are especially appetizing to migrating sea
ducks, and a small flock can decimate a farm in a short period of time. To protect their farms, growers have adopted several
techniques to deter ducks (including loud recordings, cannons, shooting,
chasing, etc.) but all have had limited success and often lead to habituation. In
Atlantic Canada, protective socking material has been tested, however results
have indicated that the socking material may impact mussel growth rates and has
limitations during production and harvest. Raft culture structures have used
predator control nets which are highly effective. However, in areas prone to
winter sea ice or long-line culture, use of predator control nets have limited
application and may interfere with international wildlife laws. As a result,
there is a pressing need for a practical, cost-effective, and
conservation-friendly means to protect mussel farms without impacting species
of conservation concern.
Richman, SE (2013) Sea duck predation on mussel aquaculture: a growing conflict - PDF
RESTING METBOLISM IN AIR AND ON WATER FOR AUKLETS AND OTHER DIVING BIRDS
Samantha E. Richman (University of Wyoming) and James R. Lovvorn (Southern Illinois University)
For small aquatic endotherms, heat loss while floating on water can be a dominant energy cost, and requires accurate estimation in energetics models for different species. We measured resting metabolic rate (RMR) in air and on water for a small diving bird, the Cassin’s auklet (Ptychoramphus aleuticus), and compared these results to published data for other diving birds of diverse taxa and sizes. RMR was higher on water than in air for alcids, cormorants, and small penguins but not for diving ducks, which appear exceptionally resistant to heat loss in water. Changes in RMR (W) with body mass either in air or on water were mostly linear over the 5- to 20-fold body mass ranges of alcids, diving ducks, and penguins, while cormorants showed no relationship of RMR with mass. The often large energetic effects of time spent floating on water can differ substantially among major taxa of diving birds, so that relevant estimates are critical to understanding their patterns of daily energy use.
Richman, S. E. and J. R. Lovvorn. 2011. Effects of air and water temperature on resting metabolism of auklets and other diving birds. Physiological and Biochemical Zoology 84:316-332. PDF
PREDATOR SIZE, PREY SIZE AND THRESHOLD FOOD DENSITIES: DOES A COMMON PREY BASE SUPPORT FEWER LARGE ANIMALS?
Samantha E. Richman (University of Wyoming) and James R. Lovvorn (UWyo, now at Southern Illinois University), in collaboration with John Y. Takekawa and Susan Wainwright de la Cruz (USGS San Francisco Bay)
Allometry predicts that a given habitat area or common prey biomass supports fewer numbers of larger than smaller predators; however, birds from related taxa or the same feeding guild often deviate from this pattern. In particular, foraging costs of birds may differ among locomotor modes, while intake rates vary with accessibility, handling times, and energy content of different-sized prey. Such mechanisms might affect threshold prey densities needed for energy balance, and thus relative numbers of different-sized predators in habitats with varying prey patches. Our results show that threshold densities of total prey numbers for different-sized ducks depend on prey size structure and depth in the sediments. Thus, heterogeneity in disturbance regimes and prey population dynamics can create a mosaic of patches favoring large or small predators. Whether a given area or total prey biomass will support greater numbers of larger or smaller predators will vary with these effects.
Lovvorn, J.R., de la Cruz, S.E.W., Takekawa,
J.Y., Shaskey, L.E., Poulton, V.K., and S.E.
Richman (2013) Niche
partitioning, threshold food densities, and species abundance in diminishing
habitats for diving ducks. Marine Ecology
Progress Series, 476:251-268 PDF
Richman, SE and JR Lovvorn (2009) Predator size, prey size, and threshold food densities of diving ducks: does a common prey base support fewer large animals? Journal of Animal Ecology 78:1033:1042 PDF
Photos of Spectacled eider under the metabolic dome and diving using wings as well as feet; similar to the white-winged scoter.
Most birds swim underwater by either feet alone or wings alone, but some sea ducks often use both. For white-winged scoters (Melanitta fusca), we measured costs (feet only vs. wings + feet simultaneously. Dive costs repaid during the recovery period after a dive bout were an important fraction (27–44%) of total dive costs, and removing costs of extraneous surface behaviors increased resolution of differences between dive types. Scoters using wings + feet had 13% shorter descent duration, 18% faster descent speed, 31% fewer strokes/m, and 59% longer bottom duration than with feet only. The cost of time underwater for dives using wings + feet was 32 to 37% lower than with feet only (P = 0.09 to 0.15). When indirect methods were used to partition descent costs from costs of ascent and bottom phases, using wings + feet lowered descent cost by an estimated 34%. Thus, using wings + feet increases descent speed and lowers descent cost, leaving more time and energy for bottom foraging. For birds in cold water, the large savings may result from both biomechanical and thermoregulatory factors.
Richman, SE and JR Lovvorn (2008) Cost of diving by wing and foot propulsion in a sea duck, the white-winged scoter. Journal of Comparative Physiology B 178:321-332 PDF
Check out a video from Joel Heath's study on common eiders diving under the Arctic sea ice. Sea ducks, like scoters and eiders, diving using their wings and feet in a coordinated stroke cycle that allows them to get to the bottom faster, stay down there longer, and use less energy to get there - enjoy!
ON THIN ICE: FORAGING ENERGETICS OF THE SPECTACLED EIDER WINTERING IN THE PACK ICE OF THE BERING SEA
Samantha E. Richman (University of Wyoming) and James R. Lovvorn (UWyo, now at Southern Illinois University) in collaboration with Jackie Grebmeier and Lee Cooper (University of Maryland)
The spectacled eider (Somateria fischeri), a Threatened species, winters in pack ice of the Bering Sea. In dives 40-70 m for benthic invertebrates, the high energy costs of foraging are offset by high benthic biomass. However, there is evidence that the dominant clam prey has changed from Macoma calcarea to Nuculana radiata, perhaps adversely affecting the foraging energetics of the eiders. We studied effects of differences in nutrient and energy content, crushing resistance of shells, digestibility, gut retention time, areal density, shell length, and depth in the sediments on the relative foraging value of M. calcarea vs Nuculana radiata. Considering energy content, digestibility, and intake rates at these burial depths for 1,200 clams m-2, energy assimilated was 14-19% higher for Nuculana radiata than M. calcarea of the same length classes. However, larger M. calcarea yielded 58% higher intake of assimilable energy than smaller Nuculana radiata; this pattern emphasizes that relative foraging value depends strongly on size (age) structures of different prey populations, which vary with recruitment, growth, and mortality in different seasons and years. Our results show that impacts of long-term benthic change on eiders depend not only on shifts in total clam abundance, but also on species differences in digestibility, size structure, and size-dependent nutrient content and burial depth.
