Bear River Migratory Bird Refuge Research Articles

Impact of environmental factors on the variability of the avian dawn chorus

The avian dawn chorus is especially prominent during the spring and summer when birds are breeding. The short-term and seasonal variation (timing, level, duration, and spectrum) of the avian dawn chorus is not well understood, and this study represents an initial effort to correlate changes in different chorus characteristics with different environmental variables. Acoustical data were gathered with a Larson Davis Sound Level Meter at the U.S. Fish and Wildlife Service Bear River Migratory Bird Refuge from March through August 2021 and 2022 and were analyzed for variation in start time and acoustical characteristics. Although it has been shown that the chorus start time is roughly correlated with civil twilight, we found that they ranged from 3 h before nautical twilight to half an hour after. Additionally, daily maximum SPL during a dawn chorus can vary during the peak breeding season by more than 40 dB. We analyzed the effect of several environmental variables on the dawn chorus, including nearby water levels, cloud coverage, wind, etc., as well as overall seasonal variation. Our findings highlight the importance of water and demonstrate the need for continued research and analysis of daily variation. Results will be discussed.

Evolution of the dawn chorus throughout the breeding season at an inland migratory bird refuge

The dawn chorus is a defining acoustic event for many environments with vocal bird populations. To study short and long-term changes in spectral characteristics of the dawn chorus at an inland migratory bird refuge, Larson Davis 831C sound level meters (SLM) were deployed at Utah’s Bear River Migratory Bird Refuge from March to August in 2021 and 2022, overlapping with the breeding seasons of many resident and migratory species of birds. The SLMs collected one-second temporal resolution data in one third octave (OTO) frequency resolution both years, as well as audio recordings during 2022. The relative contributions of the bird-relevant OTO bands (∼500 Hz–12.5 kHz) to the total energy are analyzed for each chorus. One result shows that the chorus’s spectral composition varies markedly for different locations within the refuge throughout the breeding season. The results show the value of the relatively low-resolution data in studying overall chorus characteristics. Additionally, the audio recordings have been analyzed using BirdNET species identification software to correlate changes in chorus characteristics with changes in species and behavior over the breeding season.

Egg morphometrics and egg shape coefficients for White-faced Ibis (Plegadis chihi)

Egg size is a useful metric for maternal investment, offspring quality, and contaminant studies. Yet these values and the egg shape coefficients required to estimate egg size are not available for many species, including White-faced-Ibis (Plegadis chihi). We provide egg morphometrics derived from 319 White-faced Ibis eggs sampled at Bear River Migratory Bird Refuge, Great Salt Lake, Utah, from 2010 to 2012. Measured egg length (mean ± SD) was 51.20 ± 1.99 mm, egg width was 36.08 ± 1.15 mm, and whole egg mass was 34.1 ± 3.3 g. Estimated whole egg volume was 34.63 ± 3.73 cm3 and estimated egg shape coefficients were 0.507 for Kv (whole egg and egg contents), 0.547 for Kw (whole egg), and 0.524 for Kw (egg contents only). In addition, we documented expected declines in egg mass over time due to incubation (–0.22 g/d) and desiccation during storage (–0.03 g/d), that should be accounted for prior to analyses that use egg mass of freshly laid eggs.

Acoustical characteristics of avian choruses in a western migratory bird refuge

Migratory bird refuge soundscapes are seasonally dynamic due to changes in wildlife populations. Some of the most prominent acoustical events in a bird refuge are the morning and evening avian choruses, particularly during spring and early summer when breeding activity of birds is high. For this study, near-continuous spectral data were collected at the U.S. Federal Fish and Wildlife Services Bear River Migratory Bird Refuge. Although data fidelity can be compromised by wind and rain, changes in the avian chorus characteristics over time are observed. Likely correlations with avian migration and refuge land management are discussed.

Nesting ecology of White-faced Ibis (Plegadis chihi) in Great Salt Lake, Utah

We studied the nesting ecology of White-faced Ibis (Plegadis chihi) at 3 sites within the Bear River Migratory Bird Refuge, Great Salt Lake, Utah, USA. Ibises built nests in small mounds (mean height = 14.4 ± 4.3 cm) above shallow water (mean depth = 12.0 ± 6.6 cm) located within patchy vegetation (mean percent vegetative cover = 17.2 ± 17.8% vegetative cover) with mean vegetation height of 31.7 ± 9.8 cm. White-faced Ibis typically laid a clutch of 3 or 4 eggs (mean clutch size = 3.08 ± 0.76) and initiated nests over a 50 d period between 24 April 2012 and 12 June 2012. Mean nest success was 38% (95% CI: 31–45%) and hatching success of eggs from successful nests was 76 ± 26%. Although most of the breeding parameters estimated for White-faced Ibis nesting in Utah were comparable to other populations in Oregon and Idaho (USA), nest success may now be lower than has been historically documented.

Life in the Tar Seeps

Life in the Tar Seeps Gretchen E. Henderson (bio) Click for larger view View full resolution [End Page 158] ________ In the rearview mirror, the Wasatch Mountains of Utah rise from the Great Basin. Low hills shoulder limestone caves, tucked into parched slopes of tall grass that roll toward Great Salt Lake like ancient waves. Long-gone shorelines band the hills like rings in a bathtub. A two-lane paved road cuts between dips in the knolls, edged by marshlands that spread through the Bear River Migratory Bird Refuge. On this February day, the chill has fogged into crystalline snow, blurring the marshlands, hills, and mountains until we lose sight of all distances, just the road around us. Almost imperceptibly, the air smells like rotten eggs. “You always hear that the lake is dead, but it’s so alive that it smells,” says Jaimi Butler. Jaimi is the coordinator of the ten-year-old Great Salt Lake Institute (GSLI), an interdisciplinary environmental research center dedicated to this understudied ecosystem. She is driving a blue minivan with a fiery flame decal on its door. Her five-year-old daughter, Cora, sits in a car seat behind me watching The Angry Birds Movie on an iPad, beside Greg McDonald, the regional paleontologist for the Bureau of Land Management. We are heading to Rozel Point, on the remote north arm of Great Salt Lake. We left Salt Lake City after dawn and drove north, skirting the east edge of the lake. Greg and Jaimi are meeting for the first time, hoping to partner on a project to set up camera traps on the lake’s tar seeps—also known as oil or petroleum seeps, and nicknamed death traps—which lie near the monumental 1970 land artwork by Robert Smithson, Spiral Jetty. Jaimi has lived in Utah her entire life; Greg has lived here for two years. As a visiting professor in environmental humanities at the University of Utah, I am a newcomer to this place. A colleague knew of my interest in Spiral Jetty and connected me with Jaimi, which is how I’ve found myself on Jaimi and Greg’s quest: tracking what animals get stuck in the tar seeps, glimpsing fossils in the making. I know little about Great Salt Lake, and nothing of tar seeps. As a kid in San Francisco, I wasn’t interested in dinosaurs or fossilized bones. My family’s summer road trips drove right past Great Salt Lake, without stopping, en route to national parks. I have taken this drive only once, back in October with my husband, coming cross-country from Washington, DC. Our destination was Spiral Jetty. I had dreamed of following its spiral, fifteen hundred feet of earth and salt-crusted black basalt unfurling three times counterclockwise. I am interested in how natural spaces— national parks, wildlife refuges, land art—require collaborative stewardship by land managers, scientists, artists, curators, Indigenous groups, and other partners who care for living environments as they evolve over time. As different groups share their stories of a single place, they can merge approaches and resources to support each other’s coexisting narratives. “We would be underwater here,” Jaimi says, steering the minivan along the highway. She nods toward parallel ridges in the hills, called benches, that mark the ancient lake levels. She has spent her adult life working at Great [End Page 159] Salt Lake and now, for the GSLI, coordinates partnerships around its shores. The GSLI, based at Westminster College in Salt Lake City, is the local steward of Spiral Jetty, and is joined in its efforts by the Utah Museum of Fine Arts, the Utah Department of Natural Resources, and the New York– based Dia Art Foundation. Jaimi travels monthly to the artwork—almost three hours each way, over remote dirt roads—to take water and salt samples, look for tagged pelicans, host local science teachers, and monitor the number of visitors to the artwork by checking a road counter. “Spiral Jetty was underwater for many years,” she says. “Soon after Smithson built it, the lake covered it up. It didn’t reemerge until 2002.” As we wind past low hills, Jaimi and Greg name...

Effects of Waterfowl Hunting on Raccoon Movements

Nontarget wildlife may react to hunters with avoidance, ambivalence, or attraction, depending upon the frequency of contact and the consequences of past contacts. We studied raccoons (Procyon lotor) located within the Bear River Migratory Bird Refuge, Utah, before and during waterfowl hunting seasons to assess changes in the size of their distributions, locations, and travel distances. Raccoon distribution size did not change with the onset of hunting. Once hunting began, raccoons were located more frequently in areas with lower densities of hunters and less frequently in areas with higher densities of hunters. Raccoons also responded to the presence of waterfowl hunters by traveling shorter distances at dawn, when hunters were active, and longer distances at dusk. This shift in movement to dusk may have allowed raccoons to exploit food resources provided by hunters, such as litter and wounded ducks, when few waterfowl hunters were in the marsh.

Systems modeling to improve the hydro‐ecological performance of diked wetlands

AbstractWater scarcity and invasive vegetation threaten arid‐region wetlands and wetland managers seek ways to enhance wetland ecosystem services with limited water, labor, and financial resources. While prior systems modeling efforts have focused on water management to improve flow‐based ecosystem and habitat objectives, here we consider water allocation and invasive vegetation management that jointly target the concurrent hydrologic and vegetation habitat needs of priority wetland bird species. We formulate a composite weighted usable area for wetlands (WU) objective function that represents the wetland surface area that provides suitable water level and vegetation cover conditions for priority bird species. Maximizing the WU is subject to constraints such as water balance, hydraulic infrastructure capacity, invasive vegetation growth and control, and a limited financial budget to control vegetation. We apply the model at the Bear River Migratory Bird Refuge on the Great Salt Lake, Utah, compare model‐recommended management actions to past Refuge water and vegetation control activities, and find that managers can almost double the area of suitable habitat by more dynamically managing water levels and managing invasive vegetation in August at the beginning of the window for control operations. Scenario and sensitivity analyses show the importance to jointly consider hydrology and vegetation system components rather than only the hydrological component.

Use of Remote Sensing to Assess Changes in Wetland Plant Communities Over An 18-Year Period: A Case Study from the Bear River Migratory Bird Refuge, Great Salt Lake, Utah

Successfully managing wetlands requires monitoring changes in plant community composition. We used remote sensing techniques to document the replacement of desirable native wetland vegetation with invasive species in response to catastrophic flood disturbance in the 1980s and to evaluate wetland vegetation management between 1998 and 2010. We conducted our study at the Bear River Migrator Bird Refuge wetlands, which are located on the northeastern arm of the Great Salt Lake in northern Utah. We acquired high-resolution airborne multi spectral imagery of the refuge in 1992 and 2010 to quantify changes in vegetation cover over time. We produced classified vegetation maps for the years 1992 and 2010 to calculate vegetation and water cover in management units. Classification results indicate that invasive vegetation is fast replacing native species in areas adjacent to the water deliver canals. We also compared vegetation changes to historical data provided by refuge managers, and these data contained information about the management activities undertaken in the wetland units over the study period. We found that the managers’ efforts to control the expansion of invasive species—such as keeping the units full of water throughout the year, adjusting water depth to manage salinity levels and aquatic vegetation, and undertaking burning or mechanical disturbance when needed—were successful in most of the units, although some units were still invaded by undesirable plants. Here we demonstrate how wetland managers can use remote sensing and historical data of vegetation cover to understand which native plant species are most susceptible to replacement by invasive species, how vegetation responds to management actions, and ultimately how managers can promote diverse plant communities with high wildlife value.

Marbled Godwit migration characterized with satellite telemetry

ABSTRACT Marbled Godwits (Limosa fedoa) breed in 3 disparate areas: The majority breed in the prairies of midcontinental North America, but there are also 2 small and widely separated tundra-breeding populations, 1 in eastern Canada and 1 on the Alaska Peninsula, USA. The major winter ranges include the Atlantic, Pacific, and Gulf coasts of the USA and Mexico. Bear River Migratory Bird Refuge at Great Salt Lake, Utah, USA, is a major stopover site, hosting large godwit populations in the spring and fall. Although the distributions of Marbled Godwit populations and their habitats across the landscape are generally known, the linkages between them are not. We tracked 23 Marbled Godwits equipped with satellite transmitters from sites in Utah, Mexico, Canada, and coastal Georgia during 2006–2010. Our goals were to characterize the migration strategy of Marbled Godwit populations and to determine migratory connectivity of major breeding, staging, and wintering areas. We found that: 1) godwits breeding in the w...

Adaptive wetland management in an uncertain and changing arid environment

Wetlands in the arid western United States provide rare and critical migratory bird habitat and constitute a critical nexus within larger social-ecological systems (SES) where multiple changing land-use and water-use patterns meet. The Bear River Migratory Bird Refuge in Utah, USA, presents a case study of the ways that wetland managers have created adaptive management strategies that are responsive to the social and hydrological conditions of the agriculture-dominated SES within which they are located. Managers have acquired water rights and constructed infrastructure while cultivating collaborative relationships with other water users to increase the adaptive capacity of the region and decrease conflict. Historically, water management involved diversion and impoundment of water within wetland units timed around patterns of agricultural water needs. In the last 20 years, managers have learned from flood and drought events and developed a long-term adaptive management plan that specifies alternative management actions managers can choose each year based on habitat needs and projected water supply. Each alternative includes habitat goals and target wetland water depth. However, wetland management adapted to agricultural return-flow availability may prove insufficient as population growth and climate change alter patterns of land and water use. Future management will likely depend more on negotiation, collaboration, and learning from social developments within the SES than strictly focusing on water management within refuge boundaries. To face this problem, managers have worked to be included in negotiations with regional water users, a strategy that may prove instructive for other wetland managers in agriculture-dominated watersheds.

On Nature Writing in the Nuclear Age

On Nature Writing in the Nuclear Age Cassandra Kircher (bio) John Hersey,. Hiroshima. New York: Alfred A. Knopf, 1946. Kristen Iversen,. Full Body Burden: Growing Up in the Nuclear Shadow of Rocky Flats New York: Crown, 2012 Terry Tempest Williams, Refuge: An Unnatural History of Family and Place New York: Pantheon, 1992. When Oppenheimer and company developed nuclear weapons in the 1940s, they not only created new methods of destruction and explosive ethical questions, but they also birthed—quite unknowingly—a new literary subgenre written in response to the Atomic Age. Beginning with John Hersey’s 1946 Hiroshima, published a year after the dropping of the world’s first atomic bomb, this subgenre has focused on the price we pay for nuclear development. Oftentimes categorized as literary journalism, Hiroshima profiles six survivors dealing with the aftermath of nuclear destruction and puts a human face on the 140,000 Hiroshima victims. When it came out in its entirety in the August 31st issue of [End Page 197] The New Yorker, the 31,000-word article jolted readers to attention in a way that more statistical and less personalized accounts of the bombing had not. Although the ripple effects of Hiroshima were strong and far-reaching, few literary accounts of the anti-nuclear weapons movement followed. What did follow instead were primarily factual and objective reports explaining and describing the explosive power that arrived in our lives at the end of World War II. It wasn’t until 1991, after the long-term effects of atomic weapons had begun to surface, that Terry Tempest Williams’s Refuge: An Unnatural History of Family and Place presented readers with a version of the post-Hiroshima subgenre that moved away from Hersey’s journalistic style and towards what may be described as the nuclear memoir. Beginning with Williams’s childhood bird-watching excursions, Refuge concerns itself less with telling other people’s stories and more with conveying the author’s own experiences watching the flooding of Utah’s Bear River Migratory Bird Refuge as well as the devastating cancer experienced by her mother. If Hiroshima is about the fast and harsh short-term impact of atomic bombs, Refuge is about their slow and brutal long-term effects. This growing discovery of the accumulating and delayed repercussions of low-level radioactive exposure more than anything, perhaps, explains the lapse between Hersey and the literary nuclear works that came later. The structure of Refuge reflects this delay: it isn’t until the book’s last chapter that readers learn about the fallout Williams’s mother was exposed to from aboveground atomic testing in the 1950s. In the passage below, Williams grapples with a smoking gun, the connection between cancer and exposure to nuclear contamination: It was at this moment that I realized the deceit I had been living under. Children growing up in the American Southwest, drinking contaminated milk from contaminated cows, even from the contaminated breasts of their mothers, my mother—members, years later, of the Clan of the One-Breasted Women. Williams’s deliberate delay of the cause-and-effect relationship between nuclear contamination and cancer mirrors the naïveté of a society that understood the immediate horror of atomic bombs, but had yet to learn about their long-term effects and, even more so, the costs of producing any kind of nuclear power. [End Page 198] Beautiful in its subtlety and lyricism, Refuge is considered a classic nature-writing text often taught in environmental literature courses alongside Rachel Carson’s Silent Spring and Aldo Leopold’s Sand County Almanac. Yet as a personal memoir chronicling the link between cancer and the Atomic Age, it has had little company in the world of creative nonfiction. Until last June, that is, with the publication of Kristen Iversen’s Full Body Burden: Growing Up in the Shadow of Rocky Flats. A hybrid that is both nuclear memoir (à la Williams) and literary journalism (à la Hersey), Full Body Burden depicts Iversen’s childhood living adjacent to Rocky Flats, a factory 15 miles northwest of Denver that manufactured plutonium triggers used to detonate nuclear bombs. In a recent interview Iversen articulates her debt to Williams. “Terry Tempest Williams gave...

Developing Adaptive Capacity to Droughts: the Rationality of Locality

The Bear River is driven by a highly variable, snow-driven montane ecosystem and flows through a drought- prone arid region of the western United States. It traverses three states, is diverted to store water in an ecologically unique natural lake, Bear Lake, and empties into the Great Salt Lake at the Bear River Migratory Bird Refuge (BRMBR). People in the Bear River Basin have come to anticipate droughts, building a legal, institutional, and engineered infrastructure to adapt to the watershed's hydrologic realities and historical legacies. Their ways of understanding linked vulnerabilities has led to what might appear as paradoxical outcomes: farmers with the most legally secure water rights are the most vulnerable to severe drought; managers at the federal Bear River Migratory Bird Refuge engage in wetland farming and make unlikely political alliances; and, increased agricultural irrigation efficiency in the Bear River Basin actually threatens the water supply of some wetlands. The rationality of locality is the key to understanding how people in the Bear River Basin have increased their adaptive capacity to droughts by recognizing their interdependencies. As the effects of climate change unfold, understanding social-ecological system linkages will be important for guiding future adaptations and enhancing resilience in ways that appropriately integrate localized ecosystem capacity and human needs.

Influence of Population Reduction on Predator Home Range Size and Spatial Overlap

ABSTRACT The increasing populations of red foxes (Vulpes vulpes), raccoons (Procyon lotor), and striped skunks (Mephitis mephitis) in the Intermountain West have contributed to low waterfowl recruitment in recent decades. This effect prompted the need for predator removal at many waterfowl refuges, such as the Bear River Migratory Bird Refuge (BRMBR) in the Great Salt Lake ecosystem. Our study examined the effects of the removal of predatory mammals at the BRMBR on the home range size and spatial overlap of the remaining populations of red foxes, raccoons, and striped skunks. The removal of predators through traps, snares, and night‐shooting created a lower predator population during the predators' rearing and dispersal seasons. Predator removal did not result in a change of home range size for red foxes, raccoons, or striped skunks. In all species, home ranges were of similar size during the rearing and dispersal seasons and there were no differences among sexes. After predator removal, the proportion of a home range that overlapped with that of another conspecific decreased in foxes but increased in raccoons. However, predator removal did not change the proportion of inter‐specific home range overlap between foxes and raccoons. These findings indicate that home range sizes of these mammalian predators were not constrained by their population densities prior to predator management. In this situation, predator control may be only temporarily successful in reducing predator populations. Managers may achieve more permanent reduction in predator population by decreasing food and shelter resources, thereby reducing the carrying capacity of the landscape.

Habitat Use by Meso-Predators in a Corridor Environment

Red foxes (Vulpes vulpes), raccoons (Procyon lotor), and striped skunks (Mephitis mephitis) are found throughout the United States, wherever there is suitable denning habitat and food resources. Densities of these predators have increased throughout the Intermountain West as a consequence of human alterations in habitat. Within the Bear River Migratory Bird Refuge (hereafter, refuge), in northern Utah, USA, upland nesting habitat for ducks is limited to the levee banks and roadsides. Red foxes, raccoons, and striped skunks, which prey on upland nesting birds, are also abundant on the refuge. We studied red foxes, raccoons, and striped skunks' use of levees and the edges associated with them within a wetland environment. Red fox, raccoon, and striped skunk locations were negatively correlated with distance to the nearest dike (−0.78, −0.69, and −0.45, respectively). Animals incorporated more roads and/or levees into their home ranges than expected by chance (x = 2.6; Z < 0.001); incorporation of levees was greater during the dispersal season than the rearing season (P = 0.03). Skunk home ranges (average size, 3.0 km2) were oriented along roads and levees (P = 0.03), whereas raccoon (average size, 3.6 km2) and fox home ranges (average size, 3.5 km2) were not (P = 0.93, P = 0.13, respectively). Fox home ranges in the refuge were more oblong in shape than reported elsewhere (P = 0.03). However, home-range shapes of raccoons and striped skunks were similar to previous studies (P = 0.84, P = 0.97, respectively). The use of roads and levees within the refuge increases the possible travel distance and penetration of predators into wetland environments. This contributes to increased depredation of waterfowl nests and to decreased recruitment. Managers of similar areas might decrease depredation of waterfowl by disrupting the linear pattern of corridors, thereby decreasing the congestion of animal roads and levees. This would, then, decrease the encounter rates of predators and prey.

Effects of Livestock Grazing on Duck Nesting Habitat in Utah

Periodic vegetation disturbance is an important yet controversial tool for waterfowl managers. Some have reported livestock grazing removes residual vegetation and thus is detrimental to nesting ducks, and others argue that such disturbance is necessary to maintain grassland health. We evaluated the impact of winter livestock grazing on duck nesting at Bear River Migratory Bird Refuge, Utah. During winter 1999, 6 experimental plots were grazed by cattle and 6 were ungrazed; in winter 2000, 8 plots were grazed and 8 were ungrazed. All grazing treatments were conducted during 15 November–15 March and averaged a stocking rate of 9.5 animal unit months/ha. During the following spring nesting season, we measured visual obstruction readings (VOR) on grazed and ungrazed sites. Although VOR on ungrazed sites were greater than those on grazed sites, this difference became less important as the nesting season progressed. Winter grazing impacted the nesting habitat of early-nesting ducks such as mallards (Anas platyrhynchos), but not that of late-nesting species such as cinnamon teal (Anas cyanoptera) and gadwall (Anas strepera). When using livestock grazing to manage grasslands, waterfowl managers should consider their management goals, the species composition of breeding duck populations, and environmental conditions.

Effects of Livestock Grazing on Duck Nesting Habitat in Utah

Periodic vegetation disturbance is an important yet controversial tool for waterfowl managers. Some have reported livestock grazing removes residual vegetation and thus is detrimental to nesting ducks, and others argue that such disturbance is necessary to maintain grassland health. We evaluated the impact of winter livestock grazing on duck nesting at Bear River Migratory Bird Refuge, Utah. During winter 1999, 6 experimental plots were grazed by cattle and 6 were ungrazed; in winter 2000, 8 plots were grazed and 8 were ungrazed. All grazing treatments were conducted during 15 November-15 March and averaged a stocking rate of 9.5 animal unit months/ha. During the following spring nesting season, we measured visual obstruction readings (VOR) on grazed and ungrazed sites. Although VOR on ungrazed sites were greater than those on grazed sites, this difference became less important as the nesting season progressed. Winter grazing impacted the nesting habitat of early-nesting ducks such as mallards (Anas platyrhynchos), but not that of late-nesting species such as cinnamon teal (Anas cyanoptera) and gadwall (Anas strepera). When using livestock grazing to manage grasslands, waterfowl managers should consider their management goals, the species composition of breeding duck populations, and environmental conditions.

Optimal Trajectories for the Short-Distance Foraging Flights of Swans

Optimal flight theory relates body measurements (wing span, body cross-section, body mass) and aerodynamic variables (air density, drag, profile and induced power ratios) to the most energy-efficient velocity for long distance migration. For short-range (2–10 km) foraging flights the theory is expanded to include non-negligible costs for take-off and energy savings/losses for climbing to altitude (drag decreases with air density and therefore with altitude). The theory predicts clear differences between Tundra and Trumpeter swans. Generally speaking, for flights between 2 and 10 km Trumpeter swans can be expected to fly approximately 5–10 m lower in altitude and 1–2 ms−1more slowly than Tundra swans. Moreover, the total energy required for these foraging flights is approximately 150% larger for a Trumpeter than a Tundra swan (80 vs. 120 kJ of direct mechanical energy for a 5 km flight), suggesting that Trumpeter swans may be less inclined to take-off than Tundra swans. These factors indicate that even Trumpeters native to the area (as opposed to recently translocated) would be more vulnerable to hunting than native Tundra swans. The expanded theory is compared to observations made in Utah's Bear River Migratory Bird Refuge.

Nesting Ecology and Production of Western Grebes at Bear River Migratory Bird Refuge, Utah

-The nesting ecology of Western Grebes (Aechmophorus occidenti adult attentiveness and activities and nest predation were noted. Broods and adults were censused weekly throughout the summer by counting all birds seen from dike roads. In 1974 regular stops were made on the outside unit boundaries to scan the far sides of the refuge impoundments. Using this method, most of the water area of the refuge was covered. We classified grebes as: adults, class 1 young (on parent’s back), class 2 young (free-swimming downy young), or class 3 young (showing black on the head and neck). Because class 1 young were often concealed under a parent’s wings and back feathers, they were often difficult to count at a distance. Adult birds were often known to have young on their backs but estimating numbers was difficult. Class 3 birds, especially at later stages of development, resemble adults and thus were difficult to classify. Class 2 birds were the most conspicuous and thus presented the best estimate as to trends in breeding numbers and success of

Organochlorine pesticide and PCB residues in western grebes from Bear River Migratory Bird Refuge, Utah.

Organochlorine pesticide and PCB residues in western grebes from Bear River Migratory Bird Refuge, Utah.