COMPLETED PROJECTS
Evaluation of Ecological Factors Affecting Avian Diseases
Investigator: Murray Clayton, University of Wisconsin-Madison
Funding: U.S. Geological Survey
Expected Completion: July 31, 2006
Avian botulism occurs frequently at the Salton Sea, often killing hundreds to thousands of birds during a single outbreak. Knowledge of the environmental factors that contribute to the proliferation of Clostridium botulinum type C, the bacterium that causes avian botulism, could aid in developing possible preventative actions. Using data gathered by NWHC investigators at Salton Sea in previous studies, this project evaluated associations between the occurrence of avian botulism, the agents that cause the disease and a variety of environmental factors. The seasonal pattern in pH was closely associated with the prevalence of the type C toxin gene in 1999. C. botulinum type C was more likely to be actively growing at higher pH. This project found the BoNT/E gene in the sediments in 1999 and 2002. This opens up a new set of questions regarding the Salton Sea ecosystem and Clostridium botulinum type E. This suggests that some botulism cases assumed to be type C may actually have been type E. More intensive sampling needs to be done to more accurately determine the distribution of the type E toxin gene at the Salton Sea.
Investigator: Christine A. Ribic, USGS, University of Wisconsin-Madison
Funding: USFWS Partnership for Wildlife, Wisconsin Department of Natural Resources, USDA-Hatch Program
Expected Completion: September 30, 2006
Grassland birds have been experiencing dramatic declines in population over the past 30 years. These declines are attributed in part to breeding habitat loss, fragmentation, predation, and wintering ground habitat loss. Our research took place in southwestern Wisconsin, where less than 1% of native grassland present during pre-settlement times remains. Current grassland primarily consists of non-native cool season species and lies in a state of high fragmentation, intermixed with small blocks of woodland, agriculture, and residential development. Our goals were to determine what species depredate grassland bird nests and to understand how these predators use various grassland types (Conservation Reserve Program (CRP) fields, pastures, and prairie remnants) and edge types (wooded, non-wooded, or field interiors) across the landscape. Sand track stations were placed on wooded and non-wooded edges in CRP (n=7), pastures (n=5), and prairies (n=5) from May-July 2002 through 2004 to monitor wildlife activity. We also included track stations on CRP interiors. Raccoon had the highest activity rate (hits/station/day) of all species on pasture sites every year (0.102, 0.105, and 0.046 in 2003, 2003, and 2004, respectively). White-tailed deer had the highest activity on CRP and prairies in 2002 (0.195 and 0.232, respectively). In 2003 and 2004, eastern cottontail had the highest activity on CRP (0.094 and 0.075, respectively) and prairie (0.058 and 0.057, respectively). Raccoon and white-tailed deer tended to be more active along wooded edges, and raccoon are rarely detected on CRP interior stations. Thirteen-lined ground squirrels were most active on non-wooded edges and CRP interiors. Predator activity varied across the landscape on track station sites. We deployed video cameras on 44 grassland bird nests from 2002 to 2004 that included eastern meadowlark, bobolink, Henslow’s sparrow, grasshopper sparrow, western meadowlark, and upland sandpiper. We detected numerous predators depredating nests, the majority being mammals. Thirteen-lined ground squirrel had the most depredation events (6), while raccoon was documented 3 times. Management aimed at removing or controlling wooded vegetation in larger grassland habitats may reduce predation effects; but in small, fragmented habitats, this might not hold true. Species that prefer wooded edges, such as raccoon, may decrease in number when wooded vegetation is removed; but other non-edge species, such as thirteen-lined ground squirrel, could benefit from such management and predation rates would remain unchanged. Instead, management should focus on creating and maintaining large, contiguous blocks of grassland to improve grassland bird nesting success.
The Role of a Newly Isolated Virus as a Source of Mortality in Long-tailed Ducks
Investigator: Joanne Paul-Murphy, University of Wisconsin-Madison
Funding: U.S. Geological Survey
Expected Completion: February 28, 2006
A novel adenovirus was isolated from dead long-tailed ducks (Clangula hyemalis), a species of sea duck (Tribe Mergini), in association with a mortality event near Prudhoe Bay, Alaska, in 2000. The prevalence of the virus was determined in live-trapped long-tailed ducks at the mortality site and at a reference site 100 km away where no mortality was observed. Prevalence of adenovirus antibodies in serum samples at the mortality site was 86% compared to 10% at the reference site. Furthermore, 50% of cloacal swabs collected at the mortality site and only 7% of swabs from the reference site were positive for adenoviruses. In 2001, no mortality was observed at either of the study areas, and virus prevalence in both serum and cloacal samples was low, providing further evidence that the adenovirus was linked to the mortality event in 2000. This newly described virus is most closely related to group 1 avian adenoviruses based on sequence homology with sequences obtained from GenBank, DataBank of Japan, the European Molecular Biology Laboratory and Protein Data Bank sequence databases using the program BLAST and phylogenetic analysis using maximum likelihood methods and the program PHYLIP. Experimental infections of 5-week-old mallards (Anas platyrhynchos), with either a relatively high dose of virus (1.6 x 106 IU, n = 9) or a lower dose (3.5 x 105 IU, n = 9) caused mild lymphoid infiltration of the intestine within 7 days after exposure compared with controls (n = 8). Petechial hemorrhage of the mucosa and dilation of the intestine, especially the duodenum, occurred within 14 days after exposure. These lesions are similar to those seen in long-tailed ducks experimentally exposed to similar amounts of virus. However, lesions were much less severe in mallards and lymphoid necrosis and inclusion body hepatitis did not occur. This adenovirus appears to cause mild disease in ducks in captivity under experimental conditions. However, it is possible that it causes severe disease in free-living ducks under adverse circumstances. Because 10 of the 15 species of sea ducks that occur in North America have declined dramatically over the past 30 years, this virus along with other pathogens of sea ducks, should be investigated as possibly contributing to the declines or preventing the recovery of populations.
Demographic Analysis on the Causes of Mortality and Related Factors Affecting the California Sea Otter Population
Investigator: Christine A. Ribic, USGS, University of Wisconsin-Madison
Funding: U.S. Geological Survey
Expected Completion: December 31, 2005
The sea otter (Enhydra lutris nereis) has undergone a tremendous decline and recovery as a species over the last three centuries, declining from an estimated 150,000-300,000 individuals in the early 18th century to a low of 1,000-2,000, and recovering to number approximately 50,000 individuals in the late 20th century (Riedman and Estes 1990). In 1914, the southern (Californian) sea otter population was estimated to number 50 individuals (Riedman and Estes 1990). Since that time, this population has grown to > 2000 animals (Estes 1990). However, population growth rate appears to have declined in recent years: over the interval 1982-1995 population growth rate was 5.5% (95% confidence interval 4.9 to 6.2%), while it has declined to -0.6% (95% confidence interval -2% to 1%) during 1996-2002. Concern about the viability of the southern sea otter population has led to a number of concurrent studies on the population ecology of the southern sea otter and its habitat. This project examined demographic and spatial patterns of diseases and other sources of mortality in the southern sea otter.
Mortality associated with infectious diseases increased substantially for adult males, at its peak an almost 17-fold increase. The cause of the increase and subsequent decrease in infectious disease in adult males is unknown. The most common cause of death within the infectious disease category for males was protozoal encephalitis caused by Toxoplasma gondii and/or Sarcocystis sp. (12 of 29 carcasses). The peak in infectious disease mortality rates for adult males is coincident with an increase in annual precipitation in California, which may account for increased exposure if increased precipitation leads to increased runoff and consequently more exposure to parasite oocysts. However, increased runoff alone is insufficient to account for the increased mortality rates, as other age/sex classes do not follow the same pattern of increase and decrease in mortality rates. Perhaps when increased runoff leads to increased parasite abundance of infectious stages of these parasites, adult males are at greater risk because of increased movement rates and home range sizes of adult males relative to other age classes and increased feeding rates due to larger energetic requirements.
Mortality rates associated with infectious diseases increased almost three-fold for females (>1 year). It is unknown why this mortality source would increase in the early part of the decade and then remain high. The most common cause of death in this category for females was bacterial infection (22 of 46 cases). Increasing mortality due to bacterial infections, as well as other infectious diseases, may be indicative of a general increase in disease susceptibility in sea otters, perhaps related to increased exposure to environmental toxins or malnutrition. The latter might be expected to increase if otters were approaching ecological carrying capacity.
Trauma mortality rates increased substantially for both adult males and females. For both sexes, the most common cause of death in the trauma category was bite by great white sharks (Carcharodon carcharias) (males: 24/42; females 13/20). It is not known if the increase in shark mortality is related to a potential increase in shark numbers, or a change in spatial distribution of sharks and/or otters. One possible explanation could be a change in the distribution of other shark prey species (e.g., pinniped species) has led to an increased contact rate between otters and sharks. Further research on shark-related mortality is necessary; if current trends continue it may inhibit population growth and may result in otter population declines.
Simulated sea otter population growth rate was most sensitive to variation in infectious disease mortality. This finding lends credence to the hypothesis that population growth in the first half of the 1990s was the result of a coincident increase in infectious disease mortality. However, removing all mortality associated with infectious diseases (assuming no compensation) results in a maximum level significantly below that observed for northern populations, suggesting that although significant, infectious disease mortality is unlikely the sole cause of suppressed population growth relative to northern otter populations.
We found that the proportion of otters dying due to emaciation declined with decreasing latitude in the southern portion of the range, but found no spatial trend in the northern portion. The proportion of otters dying from emaciation in the southern portion of the range did not correlate with average population counts nor with instantaneous population growth so density dependence is unlikely the cause of this pattern. Interestingly, the abundance of emaciated otters and those that died from bacterial infections correlates in the southern portion of the range. The origin of the bacterial infection in most of these otters was not apparent; however, in a few there was evidence of perforating trauma that may have allowed the bacteria to colonize tissue and grow. Perhaps malnourished otters are immunosuppressed, and consequently unable to contain the bacterial growth. We found a significant increase in the number of shark-killed otters north of Monterey Bay, consistent with other studies.
We found a significant relationship between the proportion of sandy habitat and proportion of otters dying from protozoal encephalitis. Otters foraging in soft-bottom, sandy habitats prey heavily on bivalves and so would likely be more often exposed to protozoal spores than otters foraging in rocky habitats. We also found a significant increase in the proportion of otters dying from acanthocephalan peritonitis near Monterey, similar to the results of others.
Our analysis illustrates the difficulties of using passive carcass recovery to assess patterns of cause-specific mortality in wildlife. For example, there was a clear under-representation in the number of otters recovered and/or receiving full necropsies in the center portion of the range. While over 30% of all observations of live otters were in the central portion of the otter's range, only about 5% of all recovered otter carcasses and only 1% of necropsied otters came from these regions. Consequently, we have limited information on mortality sources for much of the core of the sea otter range. Given that the numbers of otters counted in these areas have been relatively stable since systematic counts began, it may be that excess mortality is not threatening otter population stability there, and so a detailed understanding of mortality sources there is not necessary for otter conservation. However, this lack of information from the core of the range means that our present understanding of causes-of-death in otters comes primarily from the northern and to some extent southern periphery of the otter's range. Consequently, caution should be applied in extrapolating conclusions about the consequences of various mortality sources across the range, given that the ecological conditions in the peripheral areas are not likely representative of the entire range.
Investigator: Christine A. Ribic, USGS, University of Wisconsin-Madison
Funding: U.S. Geological Survey
Expected Completion: June 20, 2006
We field validated statistical models developed by Thogmartin et al. (2006) to predict abundances of grassland birds in the Prairie Hardwood Transition of the upper Midwestern United States. Roadside surveys were used to estimate relative abundances in 800-ha areas in the Iowa, Minnesota, and Wisconsin portions of the region in 2003-2005. We then compared observed abundances with predicted abundances using three measures of accuracy. The accuracy of the predictive models varied based on the accuracy measures used. Modeling efficiency values suggested that only the model for the Sedge Wren predicted abundance better than using the regional mean. Mean absolute errors also suggested that the relationship of observed and predicted abundances were different from a one-to-one correspondence. Spearman’s rho statistic for rank correlations, however, suggested that observed abundances were positively correlated to predicted abundances for all species except Henslow’s Sparrow. Our accuracy assessment suggested that the models could be useful in guiding future management and monitoring efforts, but should be used with caution. The models tended to be more accurate for more common species than rare species (e.g., Henslow’s Sparrow) and might not aid conservation efforts for the rarest species. Future modeling efforts of grassland bird abundances would be helped by more accurate information on the distribution of grasslands in the region, more detailed information on grassland structure, and a better understanding of the biological significance of environmental and climate variables on grassland bird populations.
Conservation plans for grassland birds in North America have included recommendations at landscape scales. The relationships of grassland bird populations to landscape structure, however, are variable and not well understood. Identification of management areas based on assumed landscape effects might exclude some species of conservation of concern. We examined the relationship between abundances of grassland birds and landscape structure in 800-ha landscapes in southwest Wisconsin, USA. First, we compared abundances among 6 landscape classifications with varying amounts of grassland and forest. Landscapes with more grassland and less forest were expected to support higher abundances than landscape with less grassland and more forest. Second, we identified landscape attributes important for explaining abundances and assessed the scales at which these variables were important using multiple regression. Breeding bird abundances were estimated using roadside surveys consisting of 3 stops per landscape. Landscape variables were measured for entire landscapes and along survey routes. Abundances of some species were higher in landscapes with more grassland and less forest, however, 4 species showed no relationship to landscape classification. Landscape variables at the 800-ha scale explained little variation in bird abundances for most species. Route level variables explained more variation in abundance than variables at the 800-ha scale for 5 species, but variation explained by route level variables also was low. Our results question the utility of landscape metrics for assessing management potential of areas. We believe conservation plans should focus both on landscape structure at large extents and local habitat variables
The Red-headed Woodpecker (Melanerpes erythrocephalus) has declined throughout its breeding range. The loss of natural Red-headed Woodpecker habitat in southwest Wisconsin because of fire suppression and conversion to agricultural has forced the species to use agricultural habitats. We quantified habitat associations of Red-headed Woodpeckers in an agricultural landscape in Wisconsin and compared habitat variables at points where woodpeckers were detected with random points. Logistic regression and Akaike’s Information Criteria were used to determine which variables were most important for differentiating between points of woodpecker detections and random points. We withheld 26% of the original data set to test the accuracy of the model using Receiver Operator Characteristic (ROC) analyses. Red-headed Woodpecker habitat associations were positively related to the number of snags and utility poles within 200-m of a point, the proportion of the area within 400-m of a point that was grazed forest, and the probability of adjacency between forest and open habitats within an 800-m radius. Mean forest patch size within an 800-m radius buffer was negatively associated with the presence of Red-headed Woodpeckers. The area under the ROC curve (0.71) suggested that the model was reasonable for discriminating between random points and woodpecker detections. Most (73%) of the locations of predicted Red-headed Woodpecker occurrence were accurate, however, woodpeckers also were detected (48%) at sites predicted to be random points by the model. Because management of forests for smaller patches with more edge is contradictory to forest management for other bird species of concern we recommend retention of snags in areas where small forest patches and interfaces between forest and open habitats already occur to promote habitat for Red-headed Woodpeckers.