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Bloodsucking leeches of the genus Theromyzon sp. are the only leeches in North America known to feed directly in the nasal passages, trachea, and beneath the nictitating membrane of the eyes of migratory birds. Three species of nasal leeches have been reported from North America, T. rude, T. tessulatum, and T. biannulatum. Other genera of leeches feed on the exposed surfaces of waterfowl.
Mycotoxins are toxins produced by molds (fungi) that, when they are ingested, can cause diseases called mycotoxicosis. These diseases are are not infectious. The effects on the animal are caused by fungal toxins in foods ingested, usually grains, and are not caused by infection with the fungus. Many different molds produce mycotoxins and many corresponding disease syndromes have been described for domestic animals. However, only two types of mycotoxin poisoning, aflatoxicosis and fusariotoxicosis, have been documented in free-ranging migratory birds. Until recently, sickness or death caused by mycotoxins were rarely reported in migratory birds. Identification of mycotoxins as the cause of a mortality event can be difficult for a number of reasons. The effects may be subtle and difficult to detect or identify, or the effects may be delayed and the bird may have moved away from the contaminated food source before becoming sick or dying. Also, grain containing toxin-producing molds can be difficult or impossible to recognize because it may not appear overtly moldy. Techniques to detect and quantify a variety of mycotoxins important to domestic animal and human health are available through many diagnostic laboratories that serve health needs for those species. These same techniques are applicable for wildlife. Further study and improved diagnostic technology is likely to result in identification of additional types of mycotoxins as causes of disease and death in waterfowl and other wildlife.
S eagrass ecosystems are widely recognized as some of the most productive benthic habitats in estuarine and nearshore waters of the gulf coast. Seagrass meadows provide food for wintering waterfowl and important spawning and foraging habitat for several species of commercially important finfish and shellfish. Physical structure provided by seagrasses affords juveniles refuge from predation and allows for attachment of epiphytes and benthic organisms. Seagrass communities also support several endangered and threatened species, including some sea turtles and manatees. Changes in seagrass distribution can reflect the health of a water body, and losses of seagrasses may signal water-quality problems in coastal waters. Losses of seagrasses in the northern Gulf of Mexico over the last five decades have been extensive--from 20% to 100% for most estuaries, with only a few areas experiencing increases in seagrasses.
Field and wetland conditions in the rice prairies of Louisiana and Texas are highly dynamic habitats. Rice prairies are important habitat for many species of migratory birds, including shorebirds, wading birds, and waterfowl. Ground sampling a variety of fields to assess habitat availability is very labor intensive, and accessibility to private lands makes statistical habitat sampling almost impossible. Aerial video is a tool we can use for assessing availability of these highly ephemeral habitats because of the short-duration repeatability of the surveys. The strong statistical basis of line transect theory allows quantitative estimation of habitat availability. We used ground surveys of field conditions and shorebird ground counts to correlate spectral signatures with shorebird habitat availability. This video system can also be used to identify and map distribution of invasive plant species known to affect suitability of stopover habitat for shorebirds and landbirds.
Rice and/or crawfish are cultivated in over 225,000 ha of shallow earthen impoundments within 160 km of the Gulf of Mexico along the coast of Louisiana. The region includes both the Gulf Coastal Plain and Prairie and the Lower Mississippi River Valley. Annual loss of 4,475 ha of coastal wetlands in Louisiana due to subsidence, erosion, and rising sea level has significantly reduced desirable freshwater habitat in the region. The suite of resident, migrant, breeding, and wintering waterbirds depending on this region includes grebes, pelicans, cormorants, anhingas, wading birds, waterfowl, coots, rails, gallinules, shorebirds, gulls, terns, and kingfishers. These taxa utilize the artificial freshwater wetland habitat provided by the agricultural wetlands. Numerous other birds utilize riparian areas associated with these artificial wetlands. Crawfish ponds are especially valuable cool season habitat for predaceous waterbirds because they provide shallow water systems rich in invertebrate and small vertebrate prey during the period from mid-autumn through mid-spring when most rice fields are drained. Because most crawfish ponds are not drained until late spring or early summer, predictable, food-rich, shallow water waterbird habitat is available throughout the region when rice fields are being cultivated for rice production. Incorporation of crawfish management into government-sponsored land conservation programs should encourage land owners to sustain standing water habitat outside of program mandated fill/drain requirements. Farmers could adjust the times when their impoundments are filled or drained to maximize benefits to many species, especially migrating shorebirds.
Monitoring demographic response over time is valuable for understanding population dynamics of endangered species. We quantified the variation in survival patterns for three small isolated island populations of endangered waterfowl in the Hawaiian Archipelago. Laysan Teal Anas laysanensis were individually marked and the fate of 1,150 individuals were followed from different cohorts among the two reintroduced (Kure and Midway Atolls) and the single relict (Laysan Island) populations for time series of 4, 10 and 15 years respectively. We applied a non-parametric Kaplan-Meier estimator to describe variation between the populations in survival for different cohorts. For Laysan Island and Midway Atoll, we used log-rank tests to determine the effects of cohort, island and sex on survival. Birds in the Laysan Island population had significantly higher survival than those in the Midway population, and males had higher survival than females in both populations. The proportion of females surviving at Midway Atoll was 40% lower than for females on Laysan Island at year 5. The oldest bird observed from Laysan Island was at least 15.5 years old and had been ringed as an adult. The Kure Atoll founder cohort ( n = 28) had 100% survival 18 months post-release, but this dropped by 39% during the first avian botulism type C outbreak. Ten of twenty-eight founders and a population of 60–70 birds persisted on Kure Atoll in 2020. We summarised mortality records to generate hypotheses to explain the cause-specific mechanisms driving the observed survival differences. Mortality data showed that the survival differences between islands in Laysan Teal survival was driven by chronic epizootics of avian botulism type C at Midway and Kure Atoll.
Wetlands of the Prairie Pothole Region (PPR) in the Great Plains of central North America are numerous, densely distributed, and have highly productive plant and animal communities (Photo 49). When in a natural, unaltered condition, these wetlands store relatively large amounts of organic carbon in their soils (Photo 50). Human alterations, such as extensive drainage and land-use conversion for agriculture (Figure 7), have been linked with the loss of soil organic carbon (SOC) and associated emission of carbon dioxide (CO 2 ), as well as impacts to other ecosystem services provided by these wetlands, such as wildlife and waterfowl habitat, plant biodiversity, flood mitigation, groundwater recharge, nutrient removal and retention, and recreation (Gleason et al., 2011). It has been estimated that more than half of the wetlands of the PPR have been lost due to drainage and other disturbances, with losses approaching 90 percent in some areas (Dahl, 2014; Serran et al., 2018). The goal of this case study was to identify land-management strategies that are consistent with maintaining and increasing SOC stocks of PPR wetlands. Two overarching strategies generally are promoted to preserve and enhance SOC stocks of PPR wetlands: avoided drainage and rewetting or restoration. Avoided drainage involves protecting natural, unaltered wetlands from impacts of human actives with the purpose of retaining wetland functions and services such as carbon storage. Rewetting or restoration involves reestablishing natural hydrology and land use with the purpose of enhancing wetland functions and services that were previously lost due to human activities. Avoided drainage provides immediate and long-lasting benefits, while replenishing SOC through rewetting and restoration requires many decades. Both strategies are associated with higher methane (CH 4 ) emissions but lower CO 2 and nitrous oxide (N 2 O) emissions.
An important measure of success for wildlife managers is hunter satisfaction, and it often has been assumed that harvest success is related to satisfaction and may even be a surrogate measure for hunter satisfaction. However, introduction of the multiple satisfactions concept, showing that hunters seek and receive a number of benefits from hunting in addition to harvest success, has directed research into the factors associated with hunter satisfaction and the relevant role of harvest success. In 1998, the South Dakota Game, Fish and Parks Department (SDGFP) established the Lower Oahe Waterfowl Hunting Access Area (LOWHAA) located approximately 15 miles north of Pierre, South Dakota. It was managed to provide a variety of quality goose hunting opportunities along the Missouri River. Part of the package included field decoy-only areas with limited access, via registration, to ensure an uncrowded goose hunting experience. The registration process for gaining access included collecting harvest information and a question measuring hunters’ satisfaction. A review of data collected by the SDGFP (1998 – 2011) measuring hunting participation, harvest, and satisfaction with the day’s hunting experience at the decoy-only unit of the LOWHAA revealed a strong relationship between goose harvest and satisfaction of the hunting party, but also identified a segment of hunters for whom harvest success was not related to satisfaction. A better understanding of this segment of hunters may identify factors that managers can influence to maintain or increase hunter satisfaction.
• Cropland expansion from 2008 to 2016 was mostly from losses of grassland (88%), with 3% losses from wetlands (a total of nearly 275,000 acres of wetlands, concentrated in the Prairie Pothole Region). Given the lack of national or regional datasets to track changes in RFS acreage, the extent of wetland losses directly attributable to the RFS cannot be more accurately estimated in the RtC3. • Wetlands gains and losses are not distributed evenly across wetland types or sizes. Since 2007, the nation has lost 120.3 thousand acres of palustrine (marsh-like) wetlands and gained 205.9 thousand acres of lacustrine (lake-like) habitats in the conterminous United States. The diverse wetlands within these classes support different species and perform different ecosystem functions, including loss of functions that impact watershed hydrology, water quality, and water quantity. • Small, seasonal wetlands are being lost at the fastest rate. The loss and consolidation of small wetlands to promote crop production has negatively impacted amphibians, invertebrates, and other aquatic species that depend on shallow water depths for reproduction. Shifts to longer hydroperiods in large or consolidated wetlands have more uniform (less diverse) invertebrate communities and can support fish that prey on insects and amphibians. • Small wetlands and ponds are primary sources of water for aquifer recharge in the Northern Prairies. Recent studies in the Canadian portion of the Prairie Pothole Region found that while permanent ponds and wetlands are sources for recharge to aquifers, wetlands with surface water ponds that dry out every year play the dominant role in groundwater replenishment. • While some Endangered Species Act-listed and other waterbirds have declined, waterfowl (ducks, geese, swans) as a group have not experienced declines over the past decade, possibly due to availability of food (grains), increased precipitation, and the interspersion of ponded waters and agricultural fields along migration routes. • Shifts to corn and soybean production have resulted in more frequent application of chemicals, including pesticides and fertilizers. Increased usage of neonicotinoid insecticides is of particular concern because of their high toxicity to invertebrates, which are important food sources for wetland-dependent taxa. • Evidence from the Prairie Pothole Region suggests that trends in larger wetland size, shifts to lakes and ponds (vs. vegetated wetlands), and prolonged and more frequent flooding are due to the combined effects of climate change and increased wetland ditching and consolidation. These trends are highly correlated with increased annual precipitation, which is projected to continue.
Traveling through Yellowstone National Park (YNP), visitors frequently stop to enjoy the park’s birds: small songbirds flitting about the willows, sandhill cranes engaged in their ritual mating dances, or myriad species of waterfowl loafing in one of the park's many wetlands. Typically while driving the roads of YNP, a majority of visitors consider a stopped car and raised binoculars a sure sign of some large mammal sighting. Bird watchers in YNP are familiar with this expectation and steel themselves to deliver the tough news. Certainly the park boasts its share of large charismatic birds, including trumpeter swans and bald and golden eagles; however, next to the bison, wolves, bears, and elk that bring so many visitors to Yellowstone, the park’s birds often seem overlooked.
Unusual wildlife mortality events provide a unique opportunity to collect information on demographics, disease, and body condition in affected wildlife, which may be useful for informing oil spill damage assessments and future spill responses. In November 2007, the Cosco Busan Oil Spill occurred in San Francisco Bay, California, a globally important wintering area for waterfowl. The spill resulted in the mortality of scoters Melanitta spp. and scaups Aythya spp., species that have declined significantly over recent decades. We examined the demography (sex and age ratios) and prevalence of grossly apparent disease (acanthocephalan parasite infection and mycotic disease) in 288 Surf Scoters M. perspicillata , White-winged Scoters M. deglandi , Greater Scaup A. marila , and Lesser Scaup A. affinis killed in the oil spill. The proportions of females and juveniles in examined Surf Scoters was unexpectedly high (0.98:1, females:males, 0.73:1 juveniles:adults) for this species with normally strong male- and adult-biased populations. This disproportionate mortality of female Surf Scoters could result in a greater population impact on this female-limited species, suggesting a mechanism for steep declines in San Francisco Bay scoter numbers in the years after the Cosco Busan oil spill. Significantly greater rates of acanthocephalan infection in juvenile vs. adult Surf Scoters indicated a possible interaction between acanthocephalan parasitism and juvenile-biased mortality in our sample. Birds that died during rehabilitation had significantly greater rates of mycotic disease (10% infected) than birds found dead in the field (3%), indicating that infections began or worsened during rehabilitation. Greater Scaup had proportionally greater rates of infection with mycotic disease (26% of individuals) than other species, indicating that they may be particularly susceptible to the disease. We encourage the documentation of demographics and disease as a regular part of future responses to oil spills, or other mortality events, to gain insight into population impacts and improve rehabilitation efforts of affected populations.
Influenza A viruses (IAVs)maintained among wild waterfowl, gulls, shorebirds, and some seabirds, and typically do not cause disease. Some avian-origin IAVs that have previously spilled over into domestic poultry have developed a highly pathogenic phenotype and have become important pathogens affecting both wild birds and poultry. These avian-origin IAVs have important implications to the production and trade of domestic birds, conservation and management of wild birds, and the risk of spillover of zoonotic influenza to humans handling infected birds.
We found that the absence of existing conservation measures would reduce wintering mallard population size by ~70-80%, underlining the importance of current wetland easements for waterfowl foraging. Under standard conditions, the partial active flooding of easements later in the season and the upgrading of unmanaged wetlands to managed status resulted in greatest mallard populations, indicating that active flooding (stored water release) was able to considerably increase carrying capacity under strong drought conditions.
Since the early 1970's, the numbers of some waterfowl species such as mallard ( Anas platyrhynchos ), blue-winged teal ( A. discors ), and northern pintail ( A. acuta ) have reached or nearly reached the lowest ever recorded. Low nest success (the proportion of nests in which one or more eggs hatch) in key breeding areas, including the U.S. Prairie Pothole region, is partly responsible for declines in duck numbers (Klett et al. 1988; Johnson et al. 1992).
Foods consumed by canvasback ducks (Aythya valisineria), food availability, and energetic relationships were studied on Navigation Pool 7 of the upper Mississippi River in 1978, 1979, and 1980. Canvasbacks fed primarily upon winter buds of American wildcelery (Vallisneria americana) and tubers of stiff arrowhead (Sagittaria rigida). In 1980, waterfowl consumed 40% of 380,160 kg of wildcelery winter buds on a portion of Pool 7 referred to as Lake Onalaska. Daily energy expenditure based on estimates from the literature suggests that individual canvasbacks require a minimum of 125 g (dry wt) of wildcelery winter buds each day. Extrapolation of use-days and the daily energy requirement suggests that 3,470 ha of wildcelery are required to support a canvasback population represented by 5 million use-days.
The value of natural wetlands to bird populations is well-recognized, and declines in waterfowl numbers are often attributed to losses in wetland area. if the destruction of wetland reduces bird populations, then adding wetland habitats might improve the situation. This idea was tested in Tijuana Estuary in the late 1980s.
Underwater plants are a valuable part of the Great Lakes ecosystem, providing food and shelter for aquatic animals. Aquatic plants also help stabilize sediments, thereby reducing shoreline erosion. Annual fall die-offs of underwater plants provide food and shelter for overwintering small aquatic animals such as insects, snails, and freshwater shrimp. In some areas, underwater plants may be the dominant primary producer in the food chain supporting animal populations. Fish, for example, are usually more abundant where underwater plants are found. Plants and associated animals are a source of food for fish and waterfowl in the Great Lakes (Table 1). Despite the importance of underwater plants in the Great Lakes, very little is known about them, partly because of the difficulty of observing the plants in their natural habitat. The purpose of this field guide is to aid in the identification of common underwater plants in the Great Lakes. These plants are found mostly in shallow, nearshore waters along sheltered bays, peninsulas, and the four connecting rivers of the Great Lakes, including the St. Lawrence River (Figure 1). Connecting rivers are especially favorable for aquatic plants because they are shallow, have a consistent flow of water, and are protected from heavy wave action typical of other Great Lakes shorelines.
Changes in disease patterns and trends reflect changing relationships between the affected species (host) and the causes of disease (agent). Host-agent interactions are closely linked to environmental factors that either enhance or reduce the potential for disease to occur. As a result, wildlife disease patterns and trends are, to a substantial extent, indicators of environmental quality and changing host-agent interactions within the environment being evaluated. The types, distribution, and frequency of diseases causing major avian die-offs have changed greatly during the 20th century. Too little is known to assess the changes of most avian diseases that result in chronic attrition rather than major die-offs, or about those that affect reproductive success, reduce body condition, or affect survival in other indirect ways. Nevertheless, the changing patterns and trends in highly visible avian diseases provide notice of problems needing attention. Information on the status of disease in wild birds was obtained from National Wildlife Health Center (NWHC) evaluations of the cause of death for more than 30,000 carcasses from across the United States during the past two decades, reports of avian mortality received from collaborators, the scientific literature, and NWHC field investigations of bird mortality. Comprehensive assessments of causes of wild bird mortality, magnitude of losses, and geographic distribution of specific diseases are not possible from these data, although we can identify general relationships for waterfowl and some other species.