Progress 10/01/06 to 09/30/11
Outputs
OUTPUTS: During the course of this project we used a systematic random sample to collect soil from 31 grid cells within long-term study forest (Ecology Woods). Soil samples were analyzed at the University of Delaware Soil Science Laboratory, Newark, DE for P, K, Ca, Mg, Mn, Zn, Cu, Fe, Be, S and Al. We sampled for Ca rich prey using a standardized protocol from the same 31 locations. We collected and analyzed Hg from seven forest bird species: American Robin (n = 11), Gray Catbird (n = 12), Carolina Wren (n = 5), Northern Cardinal (n = 4) and Wood Thrush (n = 23), Song Sparrow (n = 2) and Scarlet Tanager (n = 2). We also located and monitored wood thrush nests to estimate nest survival and productivity. Soil samples had average (SE) calcium contents of 241.0 (+- 40.53) mg/kg. Soil pH averaged (SE) 4.0 +- 0.05 with the highest pH being 4.6. Calcium-rich prey abundance was very low at UDW. Surveying 62 traps at 31 sites yielded an average of less than one prey item per taxon per trap. The number of prey items per trap varied among the 62 traps with capture ranging from 0 to a maximum of 34 at one trap. Among the traps, 61% attracted no prey items, 34% attracted 1 to 10 items, and 5% attracted more than 10 prey items. The mean (SE) number of items per trap was 2.1 +- 0.19. There was no correlation between either soil calcium and prey availability (r = -0.004, P = 0.983) or pH and prey availability (r = -0.056, P = 0.764). The mean concentration of Hg differed among species (F6,50 = 8.552, P < 0.001). The Carolina Wren had higher mean Hg concentrations, 0.23 +- 0.053 (mean SE), than Gray Catbird, American Robin, Northern Cardinal and Song Sparrow (Tukey HSD: P = 0.001 for GRCA, P < 0.001 for AMRO, P = 0.001 for NOCA and P = 0.003 for SOSP). The Wood Thrush had higher Hg levels, (0.14 + - 0.016) than the American Robin and Northern Cardinal (P = 0.001 for AMRO, and P = 0.035 for NOCA, Figure 2). The individual with the highest Hg level was a Carolina Wren with 0.414 ppm, followed by a Wood Thrush with 0.337 ppm. Of the ten individuals with the highest concentration, seven were Wood Thrush. Among Wood Thrush, Hg blood burden did not vary by sex (F1,19 = 0.880, P = 0.36). Successful nesting attempts and young fledged were chosen as indicators of both male and female reproductive success, since both sexes play a critical roll at these stages. Mercury blood concentration did not affect either the number of successful nests (F1,19 = 0.206 P = 0.655) or young fledged (F1,19 = 1.512, P = 0.234). This project supported five undergraduate research projects where students were mentored and trained in forest ecology, avian ecology, and field biology. Students also worked directly with faculty to manage and analyze data and present their work at UD undergraduate research conferences. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
This project provided the foundation for our change in knowledge regarding the interactions among soil chemistry, non-native plant invasion, and higher trophic interactions. We did not detect major Hg burdens in our target species and therefore shifted the investigation to focus on the soil chemistry interactions. We found very low pH and Ca rich prey at our long-term study site which lead to further sampling of soil and prey. Primary soil nutrients, such as Ca, determine the competitive ability of non-native invasive plants as well as the composition of the arthropod community. Changes in soil Ca availability thus can affect the abundance of bird prey directly when invertebrates are Ca limited (e.g., Gastropoda, Crustacea) and indirectly through host plants (e.g. herbivorous Insecta). The impact of calcium availability on urban avoiders like wood thrush or urban adapters like the gray catbird in urban environments is not yet known. Data from this research suggests that patterns observed in more intact systems are not maintained in urban fragments. In 2009 and 2010, we established urban fragment study sites in Newark, Delaware and Amherst, Massachusetts to study the effects of soil chemistry on plant invasion and the response of the invertebrate and bird communities to these novel plant communities. We found that invertebrate abundance differed in relation to soil Ca availability. Gastropods and crustaceans were positively associated with soil Ca while insects, mostly herbivorous, may be negatively affected by increases in non-native plant cover associated with high soil Ca levels. Sites differed in the extent of invasion by R. multiflora which affected the avian community. Wood thrush had greater nest density in un-invaded sites while gray catbird had greater nest density in invaded sites. At one site, invasion by R. multiflora increased since 1966 and concurrently, wood thrush densities declined while catbird densities increased. We also found an interaction between R. multiflora cover, Ca:Al, and snail abundance.
Publications
- Brown, William P., and Roland R. Roth. 2009. Age-specific Reproduction and Survival of Individually Marked Wood Thrushes, Hylocichla Mustelina. Ecology 90: 218-229.
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: We continued the long-term (1973 - 2010) Wood Thrush demographics study in the UD Ecology woods in field season 2010. We located and found all Wood Thrush nests (n = 16) in the Ecology Woods and monitored them daily to determine nest fates. Based on previous year's work that indicated there was limited Hg contamination in the UD Ecology woods, we have concluded the Hg sampling. In 2010, we increased the sampling effort to include 20 other forest fragment patches in the greater Newark, DE area. This effort is in partnership with the Newark City parks, New Castle County Parks, Delaware State Park, and the University of Delaware. For all of these sites we've added a soil sampling and arthropod component to estimate the soil calcium availability and relate these patterns to forest breeding bird richness and reproductive success. PARTICIPANTS: In 2010 this project initiated collaborations with Newark City Parks, New Castle County Parks, and the Delaware State Parks. We also developed a formal partnership with the US Forest Service Northern Research Station which was partially responsible for expanding the effort to 20 more forest fragments. During the 2010 field season we hired a graduate student (Christine Rega) to oversee the expanded project and also added a significant amount of additional sampling (soil, arthropod, vegetation, and avian). We oversaw and supervised 5 field technicians, 2 undergraduate researchers, and a student from the College of Agriculture Summer Scholars Program. This project provided valuable experiences for these young ecological scientists. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: In 2010 we did make significant changes to the overall project due to our initial findings in the UD Ecology Woods where Hg levels in Wood Thrush were very low and the number of active nests per season is less than 20. Therefore, we've added a soil Calcium and calcium rich prey component to the study that is linking the multitrophic effects of soil calcium, calcium rich prey (for breeding birds), and avian territory density. This change in design expanded the study by adding 20 more forest fragments (n = 21 forest fragments) and sampling the entire breeding bird community rather than just the wood thrush. We can still report on the initial objectives of the project but we have added a significant amount of new information being collected.
Impacts
The initial findings based on soil and arthropod sampling in the UD Ecology Woods indicated that the site was acidic, had limited soil calcium, and the Wood Thrush population has declined significantly (1.8 % annual decline since 1973). The additional 20 forest fragments provide a greater range of variation in soil chemistry (Ca:Al) and increase the avian community sampling. Also, by partnering with the city, county, and state parks we have presented some preliminary findings and highlighted the importance of urban forest patches to both biological diversity and human well being to employees and to local youth camps.
Publications
- No publications reported this period
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: We completed the 37th year of this long-term Wood Thrush demographic study. We located and monitoring 22 Wood Thrush nests during the breeding season of 2009 in the UD Ecology Woods. We sampled soils, soils arthropods, and gastropods to estimate the prey availability along a gradient of soil pH and Ca availability. We also expanded the sampling area for the project to include 58 sites in Delaware where we counted forest breeding birds and conducted the soil sampling. We sampled Wood Thrush blood Hg and did not find high levels of Hg burden in the UD Ecology Woods. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Pilot sampling of soil chemistry and Ca rich prey in the UD Ecology Woods indicated that the soils were very acidic and there were low levels of Ca rich prey biomass. The sampling in the 58 sites in Delaware showed a clear pattern between soil pH, Ca rich prey, and bird abundance. These pilot data are providing the information for proposals to expand the Wood Thrush study and develop partnerships with Newark City Parks, Newcastle County Park, Delaware State Parks, and the US Forest Service. The focus will be to develop restoration procedures to increase the quality of urban forest fragments for maintianing forest breeding birds and biodiversity. We've also developed a partnership with EPA risk assessment program to use the long-term Wood Thrush demographic data to estimate quitting probabilities for breeding females that can be used to determine, given the timing of the breeding season, when a female is likely to stop attempting to breed. This information can then be used to estimate when the application of pesticides would have the least impact on breeding forest birds.
Publications
- Schaeffer, K. M., W. P. Brown, and W. G. Shriver. 2009. Misdirected parental care by a male eastern towhee at a wood thrush nest. Wilson Journal of Ornithology 121:427-429.
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Progress 01/01/07 to 12/31/07
Outputs
Current levels of environmental mercury (Hg), particularly in the form of methyl mercury (MeHg), pose an exposure risk to humans and to wildlife. Sources of environmental Hg include fossil fuel emissions, laboratory chemicals, fungicides, batteries, dental amalgams, pharmaceutical products, components of sewage effluent, and volcanoes (Boening 2000, Manahan 2000, Newman and Unger 2003). Environmental Hg is converted to MeHg in wetland systems through an anaerobic bacterial process (Atlas and Barta 1981); there is evidence that terrestrial systems also can produce MeHg (Ericksen et al. 2003). MeHg and other organic forms of Hg are also directly synthesized and variously used as biocides, especially as seed coatings (Newman and Unger 2003). MeHg is more easily dissolved, more volatile, and therefore more available in the environment than Hg and can produce harmful effects at concentrations ten times lower than un-methylated Hg (Boening 2000). The most common form of Hg
exposure is through diet, with fish as the dominant source for both humans and aquatic birds. As human health may be severely impacted by Hg exposure, fish consumption advisories and dietary guidelines are provided by federal agencies, such as the EPA's National Listing of Fish Advisories (http://map1.epa.gov/) and by state governments (e.g., State of Delaware, http://www.fw.delaware.gov/Fisheries/Advisories.htm) to minimize such exposure through fish. In aquatic birds, elevated Hg levels may cause a reduction in clutch size, greater embryo mortality, reduced hatchability, brain damage, impaired walking and flying, and death (Walker 2003). New evidence suggests that terrestrial systems, not just aquatic systems, may be experiencing greater availability of Hg in the environment. In particular, breeding songbird populations in acidified eastern forests may be at risk for elevated Hg levels (Hames et al. 2002, Rimmer et al. 2005). While the negative effects of Hg are well documented for
aquatic ecosystems through the biomagnification of biologically-active MeHg (Evers et al. 2003, Evers 2005), studies of Hg cycling in terrestrial ecosystems are more limited. In addition to direct deposition of Hg through precipitation and uptake through plant roots (Rea et al. 2002), gaseous MeHg may be absorbed stomatally in plant tissues (or perhaps methylated within the leaf), deposited as leaf litter, and magnified upward through the food web to songbird species that feed on invertebrates (Ericksen et al. 2003). As such, terrestrial songbird species are also susceptible to MeHg bioaccumulation and availability (Rimmer et al. 2005).
Impacts
Among Wood Thrush, Hg blood burden did not vary significantly by sex (ANOVA: F = 0.880, p > 0.05). Successful nesting attempts and young fledged were chosen as indicators of both male and female reproductive success, since both sexes play a critical roll at these stages. Mercury blood concentration did not significantly affect either the number of successful nests (ANOVA: F = 0.206 P > .05) or young fledged (ANOVA: F = 1.512 P > .05). Surveying 62 traps at 31 sites yielded an average of less than one prey item per taxon per trap. There was a wide disparity in the number of prey items per traps. Of the 62 traps, 61% attracted no prey items, 34% had 1 to 10 items, and 5% had more than 10 prey items. Of the 145 prey items surveyed, 132 were myriapods, 7 were slugs, 4 were snails and 2 were isopods. The low abundance of calcium-rich prey, less than one item per trap, could be linked to the recent decline in the breeding population of Wood Thrush in UDW (Roth unpublished
data) Hg levels did not significantly affect the number of successful nests or young fledged. UDW is likely a mercury accumulation site, and at these low levels, Hg blood burden does not affect Wood Thrush reproductive success. Other locations with greater exposure to Hg would show corresponding affects on reproductive success. To determine the extent of these effects, similar studies should be carried out in areas of varying mercury exposure. This study is still and progress and is one of the first to link Hg burden to reproductive success of Wood Thrush. A national Hg monitoring program is presently being proposed and this work will contribute to that effort.
Publications
- No publications reported this period
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Progress 01/01/06 to 12/31/06
Outputs
During the 2006 field season (May - August) we captured, banded, and collected blood for mercury analysis from 17 Wood Thrush. These samples were frozen, cataloged and submitted to the Northeast mercury monitoring network for analysis and comparison with 25+ other forested sites in the region. We found and monitored the fate of 15 nests and will be able to link the extent of Hg exposure to the reproductive success of each Wood Thrush. We analyzed 21 Wood Thrush feather samples from 3 time periods to aid in determining the efficacy of Wood Thrush as a bioindicator of Hg levels in eastern forests. In general, Wood Thrush Hg declined from 1990 to 2003. We also initiated a forest vegetation monitoring sampling design to track changes in forest condition over time and relate this to Wood Thrush demography.
Impacts
The atmospheric deposition of Mercury (Hg) has the potential to have negative impacts on humans, wildlife, and specifically, bird populations. Mercury, derived from electric utility emissions, manufacturing, agriculture and other sources, is deposited in precipitation (wet deposition), directly onto vegetation immersed in clouds and fog (occult deposition), and also by direct transfer of particles and gases (dry deposition). Mercury is a substantial component of atmospheric deposition and has long been known to have toxic effects on humans and wildlife. Because of increasing urbanization and other stressors impacting forested and coastal habitats and the well characterized elevated levels of Hg deposition and MeHg availability in northeastern North America, a better understanding of the ecological impacts of MeHg availability is a high national priority. An initial step in advancing our understanding of the effects of MeHg availability is to identify suitable
bioindicators. Birds are well established bioindicators of available MeHg, they are relatively easy to sample, and the effects of MeHg on behavior, physiology, and productivity are actively being investigated in the laboratory and in the wild. To that end, the objectives of this study are to determine variation in Wood Thrush Hg levels, to evaluate the effects of Hg on Wood Thrush reproductive success in the University of Delaware Woods, and examine the candidacy of the Wood Thrush as a suitable bioindicator of environmental Hg..
Publications
- No publications reported this period
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