Yellowstone Handbook 2019

Nearly 300 bird species have been sighted in Yellowstone National Park, including raptors, songbirds, shorebirds, and waterfowl. About 150 species build their nests and fledge their young in the park. WILDLIFE Birds Records of bird sightings have been kept in Yellowstone since its establishment in 1872. These records document nearly 300 species of birds to date, including raptors, songbirds, shorebirds, and waterfowl. Approximately 150 species nest in the park. The variation in elevation and broad array of habitat types found within Yellowstone contribute to the relatively high diversity. Many of the birds are migratory species. There are currently no federally listed bird species known to breed in Yellowstone National Park. The Yellowstone National Park bird program monitors a small portion of its breeding bird species to gather information on reproduction, abundance, and habitat use. Data is collected on multiple species from a wide variety of taxonomic groups, and Quick Facts Number in Yellowstone 285 documented species; approximately 150 species nest in the park. Species of Concern • Trumpeter swan • Golden eagle • Common loon Current Management The Yellowstone National Park bird program monitors the park’s bird species, including species of concern. The program’s core activities are monitoring raptors (bald eagles, ospreys, peregrine falcons, golden eagles), wetland birds, and passerine/near passerine birds (songbirds and woodpeckers). 248 Yellowstone Resources and Issues Handbook, 2019 has been maintained for 25 or more years for several species. Long-term monitoring efforts help inform park staff of potential shifts in ecosystem function, e.g., climate change effects, for Yellowstone’s bird community and may guide future conservation of the park’s birds and their habitats. Climate Change The timing of the availability of food sources for birds may change with rising temperatures and changing weather patterns. Birds are sensitive to shifts in seasonal weather patterns and show a relatively rapid response to these fluctuations. For example, climate change has been shown to influence migration patterns, population size and distribution, the timing of reproduction, and nesting success for birds. Through monitoring, birds can be used as environmental health indicators to help managers detect changes in ecosystem function and, if necessary, take appropriate management action. The Yellowstone bird program monitors the spring arrival of species to the park, as well as the timing of nest initiation and fledging for several raptor species, which may be useful in observing the effects of climate change in Yellowstone. More Information Annual Bird Program Reports. National Park Service, Yellowstone National Park. http://www.nps.gov/yell/ naturescience/birdreports.htm Crick, H.Q.P. 2004. The impact of climate change on birds. Ibis 146:48–56. Follett, D. 1986. Birds of Yellowstone and Grand Teton national parks. Boulder, CO: Roberts Rinehart. FREQUENTLY ASKED QUESTION: Where are good birding locations? which makes identification easier. That depends on what kind of birds you want to see, the time of day you are looking, and your location in the park. In general, riparian areas and wetlands, especially those with shrubby willows, aspen, and cottonwoods attract the greatest diversity and abundance of songbirds. Watch for birds on early morning walks from mid-May through early July. At all times, but especially during the nesting season, birds should be viewed from a distance. Getting too close can stress a bird (as it can any animal) and sometimes cause the bird to abandon its nest. As with all park wildlife, visitors should keep at least 25 yards away from birds and their nests. Hayden Valley is one of the best places to view water birds and birds of prey. Shorebirds feed in the mud flats at Alum Creek. Sandhill cranes often nest in the valley. Ducks, geese, and American white pelicans cruise the river. Bald eagles and osprey hunt for fish along the river; northern harriers fly low looking for rodents in the grasses. Great gray owls are sometimes seen searching the meadows for food (these birds are sensitive to human disturbance). Blacktail Ponds and Floating Island Lake, between Mammoth and Tower Junction, and the Madison River west of Madison Junction are also good places to look for birds. Many birds, such as American robins and common ravens, are found throughout the park. Other species live in specific habitats. For example, belted kingfishers are found near rivers and streams while Steller’s jays are found in moist coniferous forests. Birds that can be viewed in Yellowstone year-round include the common raven, Canada goose, trumpeter swan, dusky grouse (formerly blue grouse), gray jay, black-billed magpie, red-breasted nuthatch, American dipper, and mountain chickadee. A few species, such as common goldeneyes, bohemian waxwings, and rough-legged hawks migrate here for the winter. Visitors may report sightings with a bird observation form, available at www.nps.gov/yell/learn/nature/wildlife-sightings. htm and at visitor centers. Please note: The use of audio bird calls is illegal in the park. McEneaney, T. 1988. Birds of Yellowstone: A practical habitat guide to the birds of Yellowstone National Park— and where to find them. Boulder, CO: Roberts Rinehart Publishers. Yellowstone National Park 2014. Field Checklist of the Birds of Yellowstone National Park. Staff Reviewers Doug Smith, Senior Wildlife Biologist Lauren Walker, Wildlife Biologist Wildlife 249 WILDLIFE Spring is a good time to look for birds. Migration brings many birds back to the park from their winter journeys south; other birds are passing through to more northern nesting areas. Songbirds are singing to establish and defend their territories; and many ducks are in their colorful breeding plumages, Most birds migrate to lower elevations and more southern latitudes beginning in August. At the same time, other birds pass through Yellowstone. Hawk-watching can be especially rewarding in Hayden Valley late August through early October. In early November, look for tundra swans on the water. Great horned owls are one of more than a dozen raptor (birds of prey) species in Yellowstone. WILDLIFE Raptors The park supports 19 breeding raptor species. Additional species use the Yellowstone landscape during migrations and seasonal movements. The bird program monitors bald eagles, ospreys, and peregrine falcons. Bald eagles and peregrine falcons were previously listed as endangered and threatened species and the park has continued monitoring since their delisting. The osprey is monitored because of the decline of one of their primary food sources—the cutthroat trout in Yellowstone Lake. Other species that occur in the park such as golden eagles and Swainson’s hawks are of growing conservation concern throughout their ranges in the United States. Yellowstone Raptor Initiative The Yellowstone Raptor Initiative was a five-year (2011–2015) program designed to provide baseline information for golden eagles (Aquila chrysaetos), red-tailed hawks (Buteo jamaicensis), Swainson’s hawks (Buteo swainsoni), American kestrels (Falco sparverius), prairie falcons (Falco mexicanus), and owls as focal species. In addition to surveys conducted by park biologists, the initiative relied on citizen science to acquire valuable data on raptors in the park. Surveys located 28 pairs of golden eagles, and more likely breed within the park. Observed breeding success was low on average and should be the subject of research in the future. Researchers were surprised at the high density of red-tailed hawks in the northern range compared to other regions of similar habitat. Red-tailed hawks also exhibited variable breeding success and efforts to monitor this species using citizen science are ongoing Swainson’s hawks proved a difficult species to survey in Yellowstone. Most studies have focused 250 Yellowstone Resources and Issues Handbook, 2019 on their association with agricultural land, and the park represents a somewhat unorthodox habitat for Swainson’s hawks. Surveys demonstrated that at least 17 species of raptor use Hayden Valley as a migration corridor, comparable to that observed at other migration sites in the Intermountain Flyway. The Initiative provided the first look at owl distribution and occurrence in the park. Continued surveys, especially in the park interior, will improve our knowledge and understanding of this under-studied group of raptors. Finally, while not monitored during this study, accipiters are of growing conservation concern, particularly northern goshawks, and should be considered in future raptor studies. Owls Owl surveys continued after the completion of the Raptor Initiative in 2015, enabled by volunteers. Surveys provide an index of sites that attract advertising males of several northern forest owl species. Over the eight years of study, the greatest owl species diversity was observed in 2018, following a low in 2017. in 2018, observers detected individuals of six owl species: boreal owl (6), great horned owl (8), northern saw-whet owl (6), northern pygmy-owl (2), long-eared owl, and great gray owl (1). For the second year in a row, a nesting pair of long-eared owls was observed in Indian Creek Campground. While long-eared owls have long been assumed to breed within the park, these are the first recorded nests by this species. Bald Eagles The bald eagle (Haliaeetus leucocephalus) was named the national symbol of the United States by Congress in 1782. Found near open water from Mexico to Alaska, bald eagles may range over great distances but typically return to nest in the vicinity where they fledged. In Greater Yellowstone they feed primarily on fish, but also on waterfowl and carrion. Numbers declined dramatically during most of the 1900s due to habitat loss, shooting, and pesticide contamination. In 1967, the US Fish and Wildlife Service listed the bald eagle as an endangered species in 43 states, including Idaho, Montana, and Wyoming. Habitat protection, restrictions on killing, and restrictions on pesticide use led to population growth and delisting of the species in 2007. Bald eagles nesting in northwestern Wyoming are part of the Rocky Mountain breeding population that extends into Idaho and Montana. Bald eagles, which may reuse the same nest year after year, occupy territories near the park’s major rivers and lakes. The number of eaglets that fledge each year depends partly on weather and can fluctuate widely. Juveniles may migrate west in the fall but adults often stay in the park year-round. Historically, about half of the park’s known bald eagle nests have been in the Yellowstone Lake area, where the productivity and success rates are generally much lower than in the rest of the park. However, in 2018, only seven of seventeen active nests in the park were on Yellowstone Lake. Of those seven, three were successful and fledged four young in total. A recent study found little evidence to support the claim that cutthroat trout declines have resulted in lower nesting success for bald eagles on Yellowstone Lake. Outlook Research has shown that human presence can disturb eagle nesting and foraging, therefore nest areas in national parks may be closed to visitors. Yellowstone manages nest sites on a case by case basis. Bald Eagle Quick Facts Number in Yellowstone • In 2018, park staff monitored 32 bald eagle territories. Of 16 active nests 9 (56%) successfully fledged young. Habitat • Bald eagles are usually found near water where they feed on fish and waterfowl. They also generally nest in large trees close to water. • Identification • Large, dark bird; adult (four or five years old) has completely white head and tail. Behavior • In severe winters, eagles may move to lower elevations such as Paradise Valley, north of the park, where food is more available. On these wintering areas, resident eagles may be joined by migrant bald eagles and golden eagles. • Females larger than males, as is true with most predatory birds. • • Immature bald eagles show varying amounts of white; they can be mistaken for golden eagles. 11 young were produced. Productivity for active nests in 2018 (0.7 young per nesting female), was just below average (0.73). Feed primarily on fish and waterfowl, except in winter when fish stay deeper in water and lakes and rivers may be frozen. Then they eat more waterfowl. Eagles will also eat carrion in winter if it is available. • Form long-term pair bonds. • Some adults stay in the park yearround, while others return to their nesting sites by late winter. • Lays one to three eggs (usually two) from February to mid-April. • Both adults incubate the eggs, which hatch in 34 to 36 days. • At birth, young (eaglets) are immobile, downy, have their eyes open, and are completely dependent upon their parents for food. • Can fly from the nest at 10–14 weeks old. • Some young migrate in fall to western Oregon, California, and Washington. Wildlife 251 WILDLIFE Population Bald eagles are a recovered endangered species. WILDLIFE Golden Eagles Golden eagles (Aquila chrysaetos) are large, longlived raptors that feed on grouse, small mammals (e.g., rabbits, marmots, and ground squirrels), and carrion. Across the western USA, and in Wyoming in particular, there are growing concerns about the status of golden eagle populations due to broadscale energy development (wind, gas) and increasing human activity. To better understand the current population status and the drivers of population trends across the ecosystem, park biologists began focused study of golden eagles in Yellowstone in 2011. Surveys located 28 golden eagles territories inside the park, 20 within the northern range alone. The resulting density in northern Yellowstone (one territory per 49.7 km2) is relatively high. Likewise, territory occupancy rates from 2011 to 2018 have been consistently high (100%). In contrast, low average productivity at these nests (0.36 young/occupied territory) is driven by both infrequent nesting attempts and low nest success. For example, in 2018, researchers monitored 22 occupied territories; 9 pairs nested and 6 nests were successful in fledging 7 young. With such low productivity, the Yellowstone golden eagle population may be dependent on outside immigration, although much about the status of the park’s golden eagle population remains unknown. In other studies, reproductive failure of eagles and other raptors has been correlated with weather (e.g., high failure in high precipitation years), often interacting with food availability. Ongoing research is investigating golden eagle habitat use in Yellowstone’s northern range to better understand local population dynamics. Outlook In response to broad concerns about golden eagle populations, Wyoming has initiated a golden eagle working group and the US Fish and Wildlife Service has instituted a western US study modeling eagle habitat suitability, human development risks, lead exposure, and large-scale movements. Better understanding of the ecology of YNP eagles requires study of their food habits, toxicology, survival, and movement both within and outside the park. In recent years, extensive data relating to these key topics have been collected in two study areas flanking the park to the north and east and complimentary research within the park is ongoing. 252 Yellowstone Resources and Issues Handbook, 2019 Golden eagles are named for the yellow feathers at the base of the neck. More Information 1940. Bald Eagle Protection Act of 1940 In 16 US Code 668668d, 54 Stat. 250. Baril, L.M., D.W. Smith, T. Drummer, and T.M. Koel. 2013. Implications of cutthroat trout declines for breeding ospreys and bald eagles at Yellowstone Lake. Journal of Raptor Research 47(3): 234–245. Buehler, D.A. Bald Eagle. The Birds of North America Online. http://bna.birds.cornell.edu/bna/ Crandall, R.H. 2013. Identifying environmental factors influencing golden eagle presence and reproductive success. Thesis. University of Montana, Missoula, Montana, USA. Harmata, A. 1994. Yellowstone’s bald eagles: Is the park a “black hole” for the national symbol? Yellowstone Science 2. Harmata, A.R. and B. Oakleaf. 1992. Bald eagles in the greater Yellowstone ecosystem: an ecological study with emphasis on the Snake River, Wyoming, Edited by Wyoming Game and Fish Department. Cheyenne, WY. Harmata, A.R., G.J. Montopoli, B. Oakleaf, P.J. Harmata, and M. Restani. 1999. Movements and survival of bald eagles banded in the Greater Yellowstone Ecosystem. Journal of Wildlife Management 63(3):781–793. Preston, C.R., R.E. Jones, N.S. Horton. 2017. Golden Eagle Diet Breadth and Reproduction in Relation to Fluctuations in Primary Prey Abundance in Wyoming’s Bighorn Basin. Journal of Raptor Research 51(3): 334-346 Swenson, J.E. 1975. Ecology of the bald eagle and osprey in Yellowstone National Park. M.S. Bozeman, MT: Montana State University. Steenhof, K., M.N. Kochert, T.L. McDonald. 1997. Interactive Effects of Prey and Weather on Golden Eagle Reproduction. Journal of Animal Ecology 66:350-362 Staff Reviewers Doug Smith, Senior Wildlife Biologist Lauren Walker, Wildlife Biologist Research A recently completed study conducted by park biologists found a significant relationship between the declines in cutthroat trout and osprey reproduction at Yellowstone Lake. Recent increases in the number of young cutthroat trout caught by the Yellowstone fisheries program during the fall netting assessment are encouraging. An increase in cutthroat trout production may lead to an increase in nesting pairs of ospreys and improved nesting success at Yellowstone Lake. Ospreys are monitored by park staff. In 2017, 27 active nests were monitored in Yellowstone. More Information Baril, L.M., D.W. Smith, T. Drummer, and T.M. Koel. 2013. Implications of cutthroat trout declines for breeding opsreys and bald eagles at Yellowstone Lake. Journal of Raptor Research 47(3): 234–245. Poole, A.F., R.O. Bierregaard, and M.S. Martell. Osprey. The Birds of North America Online. http://bna.birds.cornell. edu/bna/ Staff Reviewers Doug Smith, Senior Wildlife Biologist Lauren Walker, Wildlife Biologist Quick Facts Number in Yellowstone • In 2018, 25 active nests were monitored, ~59% were successful, above the 32-year average (52%). Identification • Slightly smaller than the bald eagle. • Mostly white belly, white head with dark streak through eye. • • Narrow wings, dark patch at bend. • Fledglings have light edges to each dark feather on their backs and upper wing surfaces, which gives them a speckled appearance. • Productivity for active nests in 2018 (1 young per nesting female) was also above the 32-year average (0.89). The single active osprey nest on Yellowstone Lake in 2018 was not successful. Habitat • Dependent on fish for food, osprey are usually found near lakes (such as Yellowstone Lake), river valleys (such as Hayden, Madison, Firehole, and Lamar valleys), and in river canyons (such as the Gardner Canyon and the Grand Canyon of the Yellowstone River). Behavior • Generally returns to Yellowstone in April and leaves in September. • Builds nest of sticks in large trees or on pinnacles close to water. • Lays 2–3 eggs in May to June. • Eggs hatch in 4–5 weeks Wildlife 253 WILDLIFE Osprey Like many other birds of prey, osprey (Pandion haliaeetus) populations declined due to pesticide use in the mid-1900s and rebounded in the latter part of the century, after the banning of pesticides such as DDT. The first study of osprey in Yellowstone National Park occurred in 1917 by M. P. Skinner, the park’s first naturalist. It was not until 1987 that the Yellowstone National Park bird program began monitoring breeding osprey annually, although an extensive survey on reproduction, diet, and habitat was conducted during the 1970s. Ospreys are surveyed via fixed-wing aircraft and by ground-based surveys from May through August. During the survey flights, the majority of nests are monitored for occupancy and breeding activity. In addition, all suitable lakes and rivers are surveyed for potential new territories and nest sites. Since monitoring began, Yellowstone’s population of osprey has declined, particularly on and around Yellowstone Lake. Nest success has remained relatively stable, with about 50% of nests producing one to two young per year. WILDLIFE History In 1962, Rachel Carson sounded an alarm about the irresponsible use of pesticides with her landmark book Silent Spring. Among the dangers she described were the adverse effects of chemicals—particularly DDT—on the reproductive capacity of some birds, especially predatory species such as the bald eagle and peregrine falcon. Her book raised public awareness of this issue, and was one of the catalysts leading to the United States banning some of the most damaging pesticides. The peregrine falcon was among the birds most affected by the toxins. It was listed as Endangered in 1970. Yellowstone National Park was a site for peregrine reintroductions in the 1980s, which were discontinued when the peregrine population began TOM STANTON Peregrine Falcons The peregrine falcon is among the fastest birds, flying at up to 55 mph and diving at more than 200 mph when striking avian prey in mid-air. Peregrine populations began to decline in the 1940s because of pesticide contamination. One of three North American subspecies, the peregrine in Greater Yellowstone (Falco peregrinus anatum) was considered extirpated by the 1970s. As part of a national reintroduction program, captive-bred peregrines were released in Yellowstone and Grand Teton national parks during the 1980s. They typically reside in Greater Yellowstone from March through October, when their favored prey—songbirds and waterfowl—are most abundant. During winter they migrate as far south as Mexico or Central America. Peregrine falcons are a recovered endangered species in Yellowstone. increasing following restrictions on organochlorine pesticides in Canada and the United States, habitat protection, and the reintroduction program. The falcon made a comeback in much of its former range, and was delisted in 1999. In Yellowstone, the most nesting pairs recorded was 32 in 2007, and they produced 47 fledglings. Although nesting pairs may reuse the same eyrie for many years, their remote locations on cliff ledges makes it impractical to locate and monitor activity at all eyries in a single year. Yellowstone National Park’s protected conditions and long-term monitoring of peregrines provide baseline information to compare against other populations in the United States. Continued monitoring is essential, not only for comparisons with other populations, but also because peregrine falcons and other raptors are reliable indicators of contaminants such as polybrominated diphenyl ether (PBDE), and of climate change. For example, to assess the levels Quick Facts Number in Yellowstone • In 2018 park staff monitored 28 of the 36 known peregrine breeding territories. Twelve territories were occupied. • • 254 Seven of the 8 active pairs with known breeding outcomes fledged 15 young in 2018 (88% nest success). Above the 31-year average (71%) and the highest observed since 2003. In 2018 average productivity was 1.9 young per occupied territory. Above the 31-year average (1.54 young per breeding pair), and the highest observed since 2003. Identification • Slightly smaller than a crow. • Black “helmet” and a black wedge below the eye. • Uniformly gray under its wings. (The prairie falcon, which also summers in Yellowstone, has black “armpits.”) • • Behavior • Resident in the park March through October, when its prey—songbirds and waterfowl—are abundant. • Lays 3–4 eggs in late April to midMay. • Young fledge in July or early August. • Dives at high speeds (can exceed 200 mph/320 kph) to strike prey in mid-air. Long tail, pointed wings. Habitat • Near water, meadows, cliffs. Yellowstone Resources and Issues Handbook, 2019 Nests on large cliffs over rivers or valleys where prey is abundant. of PBDE and other contaminants, scientists collect eggshell remains after peregrines have left their nests for the season. Recovery in Yellowstone More Information Baril, L.M., D.B. Haines, D.W. Smith, and R. Oakleaf. 2015. Long-term reproduction (1984–2013), nestling diet and eggshell thickness of peregrine falcons (Falco peregrinus) in Yellowstone National Park. Journal of Raptor Research 49:347-358. Enderson, J.H.,R.J. Oakleaf, R.R. Rogers, J.S. Sumner. 2012. Nesting performance of peregrine falcons in Colorado, Montana, and Wyoming, 2005–2009. The Wilson Journal of Ornithology 124(1):127–132. White, C.M., N.J. Clum, T.J. Cade, and W. Grainger Hunt. Peregrine Falcon. The Birds of North America Online. http://bna.birds.cornell.edu/bna/. WILDLIFE While the organochlorines found in peregrine eggshell fragments and feather samples have declined significantly, several studies indicate that certain flame retardant chemicals developed in the 1970s for use in electronic equipment, textiles, paints, and many other products leach into the environment and have been found in birds of prey at levels that impair their reproductive biology. In 2010, 2011, 2013, and 2014 eggshell fragments, feathers, and prey remains were collected from nest sites in Yellowstone after fledging occurred. Comparative data on eggshell thickness, which is an indicator of environmental contaminants, is within the range considered normal for the Rocky Mountain Region. The major cause of peregrine endangerment is no longer a threat and YNP’s peregrine population appears stable. Furthermore, although both productivity and nesting success have remained below the 31-year average for the last 5 years, both measures have increased slightly since 2015. The relatively low nesting success and productivity in the last decade warrants continued close monitoring of this species and may require further study to determine the cause(s). Staff Reviewers Doug Smith, Senior Wildlife Biologist Lauren Walker, Wildlife Biologist Wildlife 255 American white pelicans, sometimes mistaken for trumpeter swans at a distance, and other colonial nesting birds nest primarily on the Molly Islands in the southeast arm of Yellowstone Lake. WILDLIFE Wetland Birds Approximately 30% of the bird species that breed in Yellowstone depend on wetlands. Scientists are concerned about these species because wetlands are expected to diminish as global and local temperatures increase. Yellowstone has years of data about the rate and success of nesting for some wetland species, but little information about changes in the timing of nesting activity—an indicator of climate change. Colony Nesting Birds Colonial nesting birds nest primarily on the Molly Islands in the southeast arm of Yellowstone Lake. These two small islands are cumulatively just 0.7–1.2 acres in size, depending on lake water levels, yet hundreds of birds have nested there in a single year. Prior to the late 1970s, the Molly Islands were surveyed only intermittently. Some data goes back to 1890 when nesting American white pelicans (Pelecanus erythrorhynchos) and California gulls (Larus californicus) were first noted in the area. Caspian terns (Hydroprogne caspia) are suspected of nesting on the Molly Islands as early as 1917, although information on breeding status was not collected until 1933. Double-crested cormorant (Phalacrocorax auritus) nests were confirmed by 1928. Currently, pelicans, California gulls, and doublecrested cormorants nest with varying rates of success. Photographic interpretation from three aerial surveys conducted June through August 2018, showed approximately 197 pelican nests that fledged an estimated 51 young; 33 nesting double-crested cormorants fledged an estimated 21 young. Though California gulls were observed on the island, none attempted to nest. As in recent years, no Caspian terns were observed on the islands. 256 Yellowstone Resources and Issues Handbook, 2019 Habitat Birds nesting on the Molly Islands are subject to extreme environmental conditions ranging from flooding, frosts that can occur at any time of year, and high winds. As a result, birds nesting there experience large year-to-year fluctuations in the number of nests initiated and fledglings produced. Populations of American white pelicans, California gulls, and double-crested cormorants have declined over the last 20 years. Caspian terns have not nested on the islands since 2005. The reasons for the decline in colonial nesting birds are not well understood, but a previous study indicates that high levels of water in Yellowstone Lake are associated with low reproduction for nesting pelicans. Notably, quick spring melt-off events can cause a significant rise in the water level on Yellowstone Lake and flood the Molly Islands. The decline in cutthroat trout, a known food source for the Molly Island colonial nesting birds, may also influence nesting success. Furthermore, bald eagles on Yellowstone Lake that formerly depended on cutthroat trout may have switched prey to target the flightless and vulnerable young of these colonial nesting species. More Information Evans, R.M., and F.L. Knopf. American white pelican. The Birds of North America Online. http://bna.birds.cornell. edu/bna/ Varley, J. D., and P. Schullery. 1995. The Yellowstone Lake crisis: confronting a lake trout invasion. Yellowstone National Park, Wyo: Yellowstone Center for Resources, National Park Service. Staff Reviewers Doug Smith, Senior Wildlife Biologist Lauren Walker, Wildlife Biologist The common loon is a species of concern in Yellowstone. Population In 2018, biologists and park staff checked at least 28 known or historic loon territories. Seventeen of the territories were occupied by at least one loon. In total, the park housed 35 adult loons and 16 pairs. Eleven pairs attempted to nest, and two of those failed. The nine successful pairs produced nine loonlets during 2018. Quick Facts Number in Yellowstone • In 2018, 35 loons in total. 16 territorial pairs. Nine successful nests produced 9 young. Identification • Breeding adults (March–October) have black and white checkering on back, a black bill, red eyes, and iridescent green head and neck. The neck has a black and white chinstrap and distinctive collar. • Loon chicks hatch with a blackishbrown down and white belly and retain this plumage for two weeks. Body feathers emerge at 4½ weeks on the chick’s upper back. By six weeks, brown down only remains on the neck and flanks. • Gray juvenile plumage is present at seven weeks. • Juveniles and winter adults have dark upperparts and white underparts. Habitat • Summer on ponds or lakes: large lakes, such as Yellowstone, Lewis, and Heart Lakes; and smaller ones such as Grebe and Riddle Lakes. • Winter on open water. • • May be found foraging or resting on larger, slow moving rivers. Females generally lay two eggs, typically in June. • Males and females share incubation duties equally. Chicks hatch after 27–30 days. Both adults also care for their young. • Chicks are able to fend for themselves and attain flight at 11–12 weeks. • In late summer, adults form social groups, especially on larger lakes, before leaving in October. • Nest sites are usually on islands, hummocks in wetlands, or floating bog mats. • Pairs nesting on lakes smaller than 60 acres usually require more than one lake in their territory. Lakes smaller than 15 acres are rarely used. Behavior • Primarily eat fish (4–8 inches). • Unable to walk on land. • Migrate in loose groups or on own, not in organized flocks. Arrive at summer lakes and ponds at or soon after ice-off. • Four common calls: wail—for long distance communication, yodel—use