Elizabeth Craig
University of New Hampshire, Shoals Marine Laboratory, Department Member
Foraging habitat use by colonial waterbirds breeding in New York Harbor was examined to identify resources that were particularly important for the provisioning of young. Stable isotope values of carbon, nitrogen, and sulfur were measured... more
Foraging habitat use by colonial waterbirds breeding in New York Harbor was examined to identify resources that were particularly important for the provisioning of young. Stable isotope values of carbon, nitrogen, and sulfur were measured in nestling waterbird feathers to determine the habitat type (ranging from marine to freshwater and anthropogenic) in which adults primarily foraged. Six species were investigated: Black-crowned Night-Herons (Nycticorax nycticorax), Great Egrets (Ardea alba), Glossy Ibises (Plegadis falcinellus), Double-crested Cormorants (Phalacrocorax auritus), Great Black-backed Gulls (Larus marinus), and Herring Gulls (L. argentatus). Waterbird populations exhibited both inter- and intra-specific variation in stable isotope values (P < 0.001), indicating variation in foraging habitat use among focal species across the estuary. Therefore, depending on the species-and region-specific conservation goal, management strategies would potentially need to target very different foraging habitats for protection and remediation. For instance, habitat use by Double-crested Cormorants closely reflected available habitat near nesting colonies, while Glossy Ibises used primarily freshwater resources at one colony and marine resources at another, despite the fact that both colonies were located in marine environments. Great Egrets and Double-crested Cormorants both showed significant regional variation in isotopic niche size, and both species of gulls (considered to be generalist scavengers) were found to have isotopic niche sizes reflecting a specialist diet. Stable isotope analysis of nestling feathers provided novel information about the foraging resources that were most important to waterbirds in regions across the harbor.
Research Interests:
The diet-tissue discrimination factor is the amount by which a consumer’s tissue varies isotopically from its diet, and is therefore a key element in models that use stable isotopes to estimate diet composition. In this study we measured... more
The diet-tissue discrimination factor is the amount by which a consumer’s tissue varies isotopically from its diet, and is therefore a key element in models that use stable isotopes to estimate diet composition. In this study we measured discrimination factors in blood (whole blood, red blood cells and plasma), liver, muscle and feathers of Double-crested Cormorants (Phalacrocorax auritus) for stable isotope ratios of carbon, nitrogen and sulfur. Cormorants exhibited discrimination factors that differed significantly among tissue types (for carbon and nitrogen), and differed substantially (in the context of the isotopic variation among relevant prey species) from those observed in congeneric species. The Double-crested Cormorant has undergone rapid population expansion throughout much of its historic range over the past three decades, leading to both real and perceived conflicts with fisheries throughout North America, and this study provides an essential link for the use of stable isotope analysis in researching foraging ecology, diet, and resource use of this widespread and controversial species.
Research Interests:
The double-crested cormorant (Phalacrocorax auritus) has undergone population expansion throughout much of its historical range since the 1970s, resulting in increased pressure on foraging habitats including real and perceived competition... more
The double-crested cormorant (Phalacrocorax auritus) has undergone population expansion throughout much of its historical range since the 1970s, resulting in increased pressure on foraging habitats including real and perceived competition with commercial and sport fisheries and impacts on the aquaculture industry. The specific objectives of this study were to determine the stable isotope ratios of birds wintering at aquaculture facilities and natural freshwater and marine habitats, and to determine what percent of birds at distinct breeding colonies wintered in each of these habitats. We exploited natural variation in isotopic ratios of carbon, nitrogen, and sulfur (from feathers) to determine the winter habitat use (i.e., aquaculture, natural freshwater, or marine) of birds collected on their summer breeding grounds in the eastern United States (from Minnesota to Vermont). The distribution of winter habitat use varied significantly across breeding colonies and between male and female cormorants. More specifically, use of aquaculture winter habitat was most
prevalent in birds breeding in Lake Huron and Lake Erie. Overall, aquaculture habitats were used more by males, and marine habitats were used more by females. The stable isotope approach used in this study provided dietary confirmation of previously observed migratory patterns in the double-crested cormorant.
Because aquaculture was primarily used by males, and these males migrated to a broad range of breeding colonies, we suggest that targeting breeding birds to reduce aquaculture depredation is a less efficient strategy than managing birds at depredation sites on the wintering grounds. Published 2015. This article is a U.S.
Government work and is in the public domain in the USA.
prevalent in birds breeding in Lake Huron and Lake Erie. Overall, aquaculture habitats were used more by males, and marine habitats were used more by females. The stable isotope approach used in this study provided dietary confirmation of previously observed migratory patterns in the double-crested cormorant.
Because aquaculture was primarily used by males, and these males migrated to a broad range of breeding colonies, we suggest that targeting breeding birds to reduce aquaculture depredation is a less efficient strategy than managing birds at depredation sites on the wintering grounds. Published 2015. This article is a U.S.
Government work and is in the public domain in the USA.
Research Interests:
Colonially nesting waterbirds transfer large quantities of aquatically derived nutrients into terrestrial systems, potentially altering community and ecosystem structure. Over the past three decades, the Double-crested Cormorant... more
Colonially nesting waterbirds transfer large quantities of aquatically derived nutrients into terrestrial
systems, potentially altering community and ecosystem structure. Over the past three decades, the Double-crested
Cormorant (Phalacrocorax auritus) has undergone rapid population expansion throughout much of its historic
range in North America, recolonizing habitats that had not supported colonial waterbirds for decades. Mounting
evidence suggests that these populations are degrading the habitats they colonize primarily through the destruction
of vegetation and the alteration of soil conditions. The study examined the effects of cormorants and cooccurring
long-legged wading bird species including Black-crowned Night-Herons (Nycticorax nycticorax), Great
Egrets (Ardea alba) and Snowy Egrets (Egretta thula) on their nesting habitats by observing plant and arthropod
community structure as well as soil and leaf litter characteristics at colonized and non-colonized sites on two islands
in New York Harbor. Understory plant species richness and total plant cover were reduced, and the arthropod
community shifted from primarily plant feeders to primarily carrion and dung feeders beneath cormorant nests in
comparison to adjacent non-colonized habitats. On the island where cormorants have been established longer, the
colony tended to be denser and larger and was associated with larger ecological impacts on plants, arthropods and
soils. Long-legged wading bird colonies and more recently established cormorant colonies were smaller, less dense,
and were generally associated with fewer ecological impacts.
systems, potentially altering community and ecosystem structure. Over the past three decades, the Double-crested
Cormorant (Phalacrocorax auritus) has undergone rapid population expansion throughout much of its historic
range in North America, recolonizing habitats that had not supported colonial waterbirds for decades. Mounting
evidence suggests that these populations are degrading the habitats they colonize primarily through the destruction
of vegetation and the alteration of soil conditions. The study examined the effects of cormorants and cooccurring
long-legged wading bird species including Black-crowned Night-Herons (Nycticorax nycticorax), Great
Egrets (Ardea alba) and Snowy Egrets (Egretta thula) on their nesting habitats by observing plant and arthropod
community structure as well as soil and leaf litter characteristics at colonized and non-colonized sites on two islands
in New York Harbor. Understory plant species richness and total plant cover were reduced, and the arthropod
community shifted from primarily plant feeders to primarily carrion and dung feeders beneath cormorant nests in
comparison to adjacent non-colonized habitats. On the island where cormorants have been established longer, the
colony tended to be denser and larger and was associated with larger ecological impacts on plants, arthropods and
soils. Long-legged wading bird colonies and more recently established cormorant colonies were smaller, less dense,
and were generally associated with fewer ecological impacts.
Research Interests:
Although post-combustion emissions from power plants are a major source of air pollution, they contain excess CO2 that could be used to fertilize commercial greenhouses and stimulate plant growth. We addressed the combined effects of... more
Although post-combustion emissions from power plants are a major source of air pollution, they contain excess CO2 that could be used to fertilize commercial greenhouses and stimulate plant growth. We addressed the combined effects of ultrahigh [CO2] and acidic pollutants in flue gas on the growth of Alternanthera philoxeroides. When acidic pollutants were excluded, the biomass yield of A. philoxeroides saturated near 2000 mmol mol1 [CO2] with doubled biomass accumulation relative to the ambient control. The growth enhancement was maintained at 5000 mmol mol1 [CO2], but declined when [CO2] rose above 1%, in association with a strong photosynthetic inhibition. Although acidic components (SO2 and NO2) significantly offset the CO2 enhancement, the aboveground yield increased considerably when the concentration of pollutants was moderate (200 times dilution). Our results indicate that using excess CO2 from the power plant emissions to optimize growth in commercial green house could be viable.