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Population and trophic relationships among diving ducks in Chesapeake Bay are diverse and complex as they include five species of bay ducks (Aythya spp.), nine species of seaducks (Tribe Mergini), and the Ruddy Duck (Oxyura jamaicensis). Here we considered the relationships between population changes and diet over the past half century to assess the importance of prey changes to wintering waterfowl in the Bay. Food habits of 643 diving ducks collected from Chesapeake Bay during 1999-2006 were determined by analyses of their gullet (esophagus and proventriculus) and gizzard contents and compared to historical data (1885-1979) of 1,541 diving ducks. Aerial waterfowl surveys, in general, suggest that six species of seaducks were more commonly located in the meso- to polyhaline areas of the Bay, whereas five species of bay ducks and Ruddy Ducks were in the oligo- to mesohaline areas. Seaducks fed on a molluscan diet of Hooked Mussel (Ischadium recurvum), Amethyst Gemclam (Gemma gemma), and Dwarf Surfclam (Mulinia lateralis). Bay ducks and Ruddy Ducks fed more on Baltic Macoma (Macoma balthica), the adventive Atlantic Rangia (Rangia cuneata), and submerged aquatic vegetation (SAV). Mergansers were found over the widest salinity range in the Bay, probably because of their piscivorous diet. Each diving duck species appears to fill a unique foraging niche, although there is much overlap of selected prey. When current food habits are compared to historic data, only the Canvasback (Aythya valisineria) has had major diet changes, although SAV now accounts for less food volume for all diving duck species, except the Redhead (Aythya americana). Understanding the trophic-habitat relationships of diving ducks in coastal wintering areas will give managers a better understanding of the ecological effects of future environmental changes. Intensive restoration efforts on SAV and oyster beds should greatly benefit diving duck populations.
This paper presents information on the most common species of waterfowl that breed in the Chesapeake Bay including Mallard (Anas platyrhynchos), Wood Duck (Aix sponsa), American Black Duck (Anas rubripes), Canada Goose (Branta canadensis), and Mute Swan (Cygnus olor). Long-term (40 years) and short-term (13 years) trends in breeding populations were evaluated using the North American Breeding Bird Survey and the Atlantic Flyway Breeding Waterfowl Survey. Species that have adapted to landscape-level and local habitat changes in the past 40 years have expanded, especially Mute Swans, Canada Geese, and Mallards, while species that are less tolerant of these changes such as American Black Ducks have declined. Wood Ducks may be showing some recent declines in the Bay region, even though the Atlantic Flyway population is increasing. Losses of forested wetland habitats around the Bay may account for some of this decline.
The Chesapeake Bay plays a significant role in the life cycle of Bald Eagles (Haliaeetus leucocephalus) along the entire Atlantic coast of the U.S. In addition to supporting a resident breeding population, the Chesapeake Bay is an area of convergence for post-nesting and subadult Bald Eagles from breeding populations in the southeastern and northeastern U.S. The convergence of three geographically distinct populations (northeast, southeast, and Chesapeake Bay) suggests that the Bay plays a particularly important role in the recovery of Bald Eagles in eastern North America. Since the ban on DDT and formal listing under the Endangered Species Act, the Chesapeake Bay breeding population has increased dramatically. Between the early 1970s and 2001 the population within the Bay and vicinity has grown exponentially from 60 to 646 pairs with an average doubling time of just over eight years. Reproductive rates have increased over this time period and are now similar to those documented prior to the DDT era. With the current rate of increase, the population is expected to reach saturation within the next decade. Bald Eagles continue to be vulnerable to the potential introduction of new biocides into the estuary, human disturbance within nesting and foraging areas, and the loss of habitat to urban and industrial development. The tidal fresh reaches of the estuary appear to support core breeding areas, as well as, concentration areas for migrant populations and should be priorities for long-term conservation efforts.
The Chesapeake Bay supports the largest Osprey (Pandion haliaetus) breeding population in the world. The population experienced a dramatic reduction due to biocide-induced reproductive suppression in the post World War II era and reached an estimated low of 1,450 pairs by the early 1970s. By the mid 1990s, the population recovered to an estimated 3,500 pairs and breeding was documented on 427 of 878 named tributaries of the tidal Bay. Recovery has been exponential but spatially variable with average doubling times for defined geographic areas varying by more than an order of magnitude. Rates of population growth have been negatively related to salinity with the highest rates occurring within tidal fresh reaches suggesting that recovery has progressed from the main stem of the Bay toward the fall line. Virtually nothing is known about the breeding ecology of Ospreys in the lower saline waters of the Bay. The increase and diversification of man-made structures used for nesting has made a fundamental contribution to recovery and current distribution. A synthesis of information from several field sites throughout the Bay shows a collective increase in reproductive rate (young/active pair) from less than 0.8 in the 1960s to more than 1.2 by the mid-1980s followed by a reduction to below 1.0 in the late 1980s. Threats to the population continue to be the release of new classes of contaminants into the estuary and anthropogenic activities that have the potential to suppress reproductive rates and juvenile/adult survivorship.
With the DDT ban enacted in the early 1970s, piscivorous bird populations have grown exponentially throughout the tidal reach of the Chesapeake Bay. However, avian population growth is not uniform throughout the Chesapeake Bay watershed; several species including Bald Eagles (Haliaeetus leucocephalus) and Ospreys (Pandion haliaetus) experienced significantly greater population growth rates in riverine tidal freshwater and oligohaline regions than in higher salinity portions of the bay. Shifting fish prey resources may provide an explanation for the observed influence of salinity on distribution of piscivorous bird populations. Changes in the fish resources available to avian predators over the past 40 years include changing temporal and spatial distribution of fish prey, as well as shifts in taxonomic and trophic structure of resident and migratory fish assemblages. Historical ecological changes, including long- and short-term changes in the abundance of anadromous clupeid fishes, Atlantic Menhaden (Brevoortia tyrannus), and the relatively recent introduction and establishment of non-indigenous fishes, within tidal freshwater rivers may be influencing piscivorous bird distributions and abundance, particularly for Bald Eagles and Ospreys, in the Chesapeake Bay. Predator-prey interactions among piscivorous birds and fish prey have received little attention from wildlife managers. Collaborative efforts between fishery scientists and avian ecologists will ultimately lead to better ecosystem management of the Bay’s living resources.
A search of the Contaminant Exposure and Effects-Terrestrial Vertebrates (CEE-TV) database revealed that 70% of the 839 Chesapeake Bay records deal with avian species. Studies conducted on waterbirds in the past 15 years indicate that organochlorine contaminants have declined in eggs and tissues, although p,p’-DDE, total polychlorinated biphenyls (PCBs) and coplanar PCB congeners may still exert sublethal and reproductive effects in some locations. There have been numerous reports of avian die-off events related to organophosphorus and carbamate pesticides. More contemporary contaminants (e.g., alkylphenols, ethoxylates, perfluorinated compounds, polybrominated diphenyl ethers) are detectable in bird eggs in the most industrialized portions of the Bay, but interpretation of these data is difficult because adverse effect levels are incompletely known for birds. Two moderate-sized oil spills resulted in the death of several hundred birds, and about 500 smaller spill events occur annually in the watershed. With the exception of lead, concentrations of cadmium, mercury, and selenium in eggs and tissues appear to be below toxic thresholds for waterbirds. Fishing tackle and discarded plastics, that can entangle and kill young and adults, are prevalent in nests in some Bay tributaries. It is apparent that exposure and potential effects of several classes of contaminants (e.g., dioxins, dibenzofurans, rodenticides, pharmaceuticals, personal care products, lead shot, and some metals) have not been systematically examined in the past 15 years, highlighting the need for toxicological evaluation of birds found dead, and perhaps an avian ecotoxicological monitoring program. Although oil spills, spent lead shot, some pesticides, and industrial pollutants occasionally harm Chesapeake avifauna, contaminants no longer evoke the population level effects that were observed in Ospreys (Pandion haliaetus) and Bald Eagles (Haliaeetus leucocephalus) through the 1970s.
Colonially nesting wading birds (herons, egrets, and ibis) are a highly visible, biologically significant component of the mid-Atlantic coastal avifauna. Populations of these species were decimated by extensive market hunting in the late nineteenth century, recovered, and additional species colonized the region. Herein, we summarize changes in species, numbers of breeding pairs, and colony sites for ten species of wading birds surveyed four times over a 26-year period (1977 to 2003) within the Chesapeake Bay and Atlantic coastal barrier island region. Over the period of surveys, wading bird breeding colonies increased 246% (to 537) and numbers of breeding pairs increased 67% (to 26,589). Expansion among Great Blue Herons (Ardea herodias), Great Egrets (Ardea alba), Yellow-Crowned Night-Herons (Nyctanassa violacea) and Glossy Ibis (Plegadis falcinellus), primarily accounted for the dramatic increase, while declines were recorded for Snowy Egrets (Egretta thula), Cattle Egrets (Bubulcus ibis) and Black-crowned Night-Herons (Nycticorax nycticorax). Rapid loss of breeding wading birds along the Atlantic coastal lagoon system during the last decade is of particular conservation concern.
Over the past one hundred years, dramatic changes have taken place in populations of colonial-nesting seabirds that breed within Chesapeake Bay and the Maryland-Virginia coastal region. Populations of species that were decimated by extensive market hunting in the late nineteenth century recovered, additional species colonized the region and in the past ten years many species have declined. During 2003, over 72,000 pairs of seabirds of thirteen species bred within the region. Breeding population sizes are presented and population trends evaluated based on benchmark census information from 1977 and regional censuses compiled during 1993 and 2003 by the states of Maryland and Virginia. Since the 1970s, Brown Pelicans (Pelicanus occidentalis) and Double-crested Cormorants (Phalacrocorax auritus) expanded into the region and now represent six percent of the seabird guild. Gull populations have exhibited important changes and have affected other seabird species. Significant population declines have occurred in Black Skimmers (Rynchops niger), Gull-billed Terns (Sterna nilotica), Royal Terns (Sterna maxima), and Common Terns (Sterna hirundo). Since 1993, populations of ten of thirteen seabird species have declined, many significantly. Conservation challenges for seabird species in the region include: 1) habitat change and loss as a result of sea-level rise, 2) increasing mammalian predator populations, 3) competition for colony sites, 4) human infrastructure conflicts, and 5) changing fisheries populations and harvest. Conserving and managing colonial-nesting seabirds in the coming decades as the human population continues to increase in the mid-Atlantic region will present significant challenges to future generations.
From 1993 to 1999, we conducted banding and telemetry studies of fall migrant Soras (Porzana carolina) in the historic rail hunting and exceptional stopover habitat of the Wild Rice (Zizania aquatica) marshes of the tidal Patuxent River. Drift traps equipped with audio lures produced 3,897 Sora and 417 Virginia Rail (Rallus limicola) captures during the seven-year study. Sora captures were characterized by a high proportion (70% to 90%) of young-of-the year and a paucity of between-year recaptures (N = 12). Radio-telemetry studies depicted Soras as long-distance migrants with high stopover survival and a critical dependence on tidal freshwater marshes for migratory fattening. Here, the high productivity of Wild Rice, Smartweeds (Polygonum spp.) and other seed-bearing annual plants seem intrinsically linked to Sora migratory fitness. A stopover period of >40 days and mean mass gain of 0.6g/d suggests Soras are accumulating large fat reserves for long-distance flight. Radio tracking confirmed Soras as strong flyers with a demonstrated overnight (ten h) flight range of 700-900 km. Given the potential size of fat reserves and the ability to use tail winds, it is conceivable for Soras to make nonstop flights from the Patuxent River to Florida, the Bahamas, or even the Caribbean. Once a widely hunted species, a single sport-hunting recovery from our 3,900 bandings attests to the decline in popularity of the Sora as a game bird in the Atlantic Flyway. We suggest the few between-year recaptures observed in our bandings results from three possible factors: 1) the strong influence of wind drift on migration, 2) different migration chronology or flight path of AHY versus HY birds, and/or 3) high mortality of especially HY birds during Atlantic coastal and Gulf crossings. The critical dependence of Soras and other seed-dependent, fall-migrant waterbirds on highly productive yet limited tidal freshwater marsh habitats make conservation of such areas a priority mission within the Chesapeake Bay.
Emergent tidal marshes are a dominant feature of the Chesapeake Bay’s estuarine environment and account for an approximate 123,100 ha of the 185,870 ha (66%) of classified wetlands. Tidal marshes vary in salinity, structure, and plant composition according to their geographic position in the Bay. Chesapeake Bay marshes support breeding bird populations that are of regional or national conservation significance. Marsh bird communities vary with marsh type, geographic position, salinity, patch size, and landscape context. Marsh loss has been significant over the past two hundred years primarily as a result of urban, industrial, and agricultural development. Protective legislation enacted in the 1970s has slowed the rate of loss but marshes continue to be degraded and population of marsh birds continue to decline from the invasion of exotic species, ground predators, poor management practices, encroachment by development, and sea-level rise. Despite these concerns, there is still relatively little information on the population trends of most marsh birds or on the distribution of some of the Bay’s highest species of concern such as Black Rails (Laterallus jamaicensis), King Rails (Rallus elegans), Saltmarsh Sharp-tailed Sparrows (Ammospiza caudacuta), and Henslow’s Sparrows (Ammodramus henslowii). Marshes along the bay’s fringe, tributaries, and islands that currently support species at risk of extinction in the Bay are in immediate need of identification and protection. High marshes on the Delmarva peninsula, support greatest concentrations of species at risk and are marshes among the most at risk of loss and degradation. Management to reduce or abate threats to marsh birds is critical to their long term survival.
From 1986-2005, Virginia supported between 6% and 13% of the federally threatened Atlantic Coast Piping Plover (Charadrius melodus) breeding population with an annual average of 111 nesting pairs (SD ± 25.0, range = 84-192 pairs). The statewide population remained relatively static from 1986-2003 (x̄ = 104.4 pairs, SD ± 12.0, range = 84-127 pairs). In 2004, the population increased to 152 pairs and in the following year grew to 192 pairs. Over 95% of the state’s Piping Plover breeding activity occurred on the barrier islands. From 1986-1997, five pairs or less were observed at Craney Island, a dredge material deposition site in Portsmouth and at Grandview Nature Preserve, a high-use recreation area located in the City of Hampton. Predators and human disturbance likely account for the present-day absence of nesting pairs from both inland sites. From 1990-2002, annual productivity studies revealed an annual average of 1.14 fledged young per pair (SD ± 0.4, range = 0.59-1.65). The 2003 breeding season marked the first time Piping Plover productivity approached two fledged young per pair, which was followed by another increase in 2004 when productivity rose to over two fledged young per pair. The virtual doubling of Virginia’s breeding population observed in 2005 along with the recent increase in breeding success represents an important contribution to the overall security of the Atlantic Coast Piping Plover population. We attribute the vitality of Virginia’s Piping Plover population to the combined effects of predator management, public education and outreach, and the unique conservation status of the barrier islands that affords plovers a level of protection not found elsewhere within the Atlantic coast breeding range.
The conservation status of the American Oystercatcher (Haematopus palliatus palliatus) along the Chesapeake Bay, coastal bays, and barrier island shorelines of Maryland and Virginia has been investigated in detail in recent years. The region supports approximately 700 breeding pairs with more than 80% occurring on the east coast of the Delmarva Peninsula and less than 20% occurring along the shorelines of the Chesapeake Bay. The number of breeding pairs in Maryland appears to have been stable or to have increased slightly during the past 20 years. The overall trend of the breeding population in Virginia is less clear, but recent evidence suggests that numbers on the barrier islands are increasing after more than two decades of a declining trend. The coastal bays and barrier islands typically support between 1,500 and 2,000 wintering birds with most occurring on the east coast of the Virginia portion of the Delmarva Peninsula. The shorelines of both states together play an important role in supporting core breeding and wintering populations of the American Oystercatcher in the eastern United States. Throughout the region, oystercatchers are facing threats common to all coastal waterbird and shorebird species such as predation and overwash events. The threat of habitat loss to development, however, is not as alarming as in other areas of the species’s breeding range due to a significant amount of habitat being in protective conservation ownership or being unfit for development and recreation purposes. Habitat loss attributed to sea level rise, barrier island dynamics, and the indirect effects of development, such as pollution and contaminants, may play more important roles in the stability of breeding and wintering habitat for the American Oystercatcher in Maryland and Virginia.
In the past half century, many waterbird populations in Chesapeake Bay have declined or shifted ranges, indicating major ecological changes have occurred. While many studies have focused on the problems associated with environmental degradation such as the losses of coastal wetlands and submerged vegetation, a number of restoration efforts have been launched in the past few decades to reverse the “sea of despair.” Most pertinent to waterbirds, restoration of submerged aquatic vegetation (SAV) beds, tidal wetland restoration, oyster reef restoration, and island creation/restoration have benefited a number of species. State and federal agencies and non-government agencies have formed partnerships to spawn many projects ranging in size from less than 0.5 ha to ca. 1,000 ha. While most SAV, wetland, and oyster reef projects have struggled to different degrees over the past ten to twenty years with inconsistent methods, irregular monitoring, and unknown reasons for failures, recent improvements in techniques and application of adaptive management have been made. The large dredge-material island projects at Hart-Miller Island near Baltimore, Poplar Island west of Tilghman Island, Maryland, and Craney Island in Portsmouth, Virginia have provided large outdoor “laboratories” for wildlife, fishery, and wetland habitat creation. All three have proven to be important for nesting waterbirds and migrant shorebirds and waterfowl; however nesting populations at all three islands have been compromised to different degrees by predators. Restoration success for waterbirds and other natural resources depends on: (1) establishing realistic, quantifiable objectives and performance criteria, (2) continued monitoring and management (e.g., predator control), (3) targeted research to determine causality, and (4) careful evaluation under an adaptive management regime.
For decades, we have invested in research to document declining numbers of birds and the causes of those declines. But how much have we invested in trying to change the human behaviors that are affecting those declines, especially lately? Have we adequately used the knowledge of marketing specialists and economists? This paper looks at some of the root causes of bird population declines as they relate to human behaviors and attitudes and what the Virginia Coastal Zone Management Program is doing to try to reverse these trends. Human population growth, increasing separation of people from nature, sea-level rise, and the science-public information gap are four of the root causes identified; some proactive measures are suggested for improvements in each of these areas. Scientists need to become more proactive and engaged in the public discourse to try to get more environmental “buy-in” to reverse the environmental degradation we witness.