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D.A. Olsen

Publications and source records attributed to D.A. Olsen.

5 recordsLinked to original sources
USGS2008

Assessing habitat use by breeding Great Blue Herons (Ardea herodias) on the Upper Mississippi River, USA

Approximately 7,610 to 3,175 pairs of Great Blue Herons ( Ardea herodias ) nested along 420 river km of the Upper Mississippi River (UMR) from 1993 to 2003. Numbers declined precipitously in the mid-1990s stabilizing somewhat in the early 2000s. The average number of nests in colonies was 349 (SD = 283). Annual colony turn over rate for the eleven year period was 0.15 and ranged from 0.06 to 0.29 each year. The number of years that a colony was active was positively correlated with the average number of nests present while the colony was active. Of the eight colonies active in 1993 that averaged more than 349 nests, four were abandoned by 2003. Only one colony grew to greater than 349 nests during the study period. Custer et al. (2004) suggested that herons on the UMR may be limited by forage resources or foraging habitat and social factors, as evidenced by the even spacing of colonies that reflects the maximum feeding range of herons on the river. To rule out nesting and foraging habitat limitation, landscape habitat features of terrestrial and aquatic areas were examined for colony areas and areas without colonies. Available fish monitoring data were used to examine potential interactions between herons and forage resources. Colony areas did not differ from areas without colonies in any habitat feature. Indices of potential heron forage fish increased from 1993 to 2002, although low indices of fish abundance in 1993 were likely influenced by flood conditions that year. Although fish availability to herons is related to flows and water levels, available data suggested that herons did not negatively impact their potential forage base. Numbers of herons were not correlated with indices of fish abundance from the preceding year on a pool-wide scale. Indices of fish abundance were higher within 5 km of colonies than farther than 5 km from colonies, and indices of fish abundance increased from June through August both near and far from colonies. Numbers of herons and locations and sizes of colonies varied annually, whereas landscape features typically vary little if at all from year to year. Indices of fish abundance also varied greatly by sample location and year. Disturbance, particularly by humans in this highly used river, should be examined in relation to limiting foraging opportunities and influencing behavior (colony and individual) and productivity in colonies.

Illinois, Iowa, Minnesota, Missouri, Wisconsin↗
USGS2001

Effects of landscape composition and wetland fragmentation on frog and toad abundance and species richness in Iowa and Wisconsin, USA

Management of amphibian populations to reverse recent declines will require defining high-quality habitat for individual species or groups of species, followed by efforts to retain or restore these habitats on the landscape. We examined landscape-level habitat relationships for frogs and toads by measuring associations between relative abundance and species richness based on survey data derived from anuran calls and features of land-cover maps for Iowa and Wisconsin. The most consistent result across all anuran guilds was a negative association with the presence of urban land. Upland and wetland forests and emergent wetlands tended to be positively associated with anurans. Landscape metrics that represent edges and patch diversity also had generally positive associations, indicating that anurans benefit from a complex of habitats that include wetlands. In Iowa the most significant associations with relative abundance were the length of the edge between wetland and forest ( positive) and the presence of urban land (negative). In Wisconsin the two most significant associations with relative abundance were forest area and agricultural area ( both positive). Anurans had positive associations with agriculture in Wisconsin but not in Iowa. Remnant forest patches in agricultural landscapes may be providing refuges for some anuran species. Differences in anuran associations with deep water and permanent wetlands between the two states suggest opportunities for management action. Large-scale maps can contribute to predictive models of amphibian habitat use, but water quality and vegetation information collected from individual wetlands will likely be needed to strengthen those predictions. Landscape habitat analyses provide a framework for future experimental and intensive research on specific factors affecting the health of anurans.

Iowa, Wisconsin↗
USGS2000

Landscape associations of frog and toad species in Iowa and Wisconsin, U.S.A

Landscape habitat associations of frogs and toads in Iowa and Wisconsin were tested to determine whether they support or refute previous general habitat classifications. We examined which Midwestern species shared similar habitats to see if these associations were consistent across large geographic areas (states). Rana sylvatica (wood frog), Hyla versicolor (eastern gray treefrog), Pseudacris crucifer (spring peeper), and Acris crepitans (cricket frog) were identified as forest species, P. triseriata (chorus frog), H. chrysoscelis (Cope's gray treefrog), R. pipiens (leopard frog), and Bufo americanus (American toad) as grassland species, and R. catesbeiana (bullfrog), R. clamitans (green frog), R. palustris (pickerel frog), and R. septentrionalis (mink frog) as lake or stream species. The best candidates to serve as bioindicators of habitat quality were the forest species R. sylvatica, H. versicolor, and P. crucifer, the grassland species R. pipiens and P. triseriata, and a cold water wetland species, R. palustris. Declines of P. crucifer, R. pipiens, and R. palustris populations in one or both states may reflect changes in habitat quality. Habitat and community associations of some species differed between states, indicating that these relationships may change across the range of a species. Acris crepitans may have shifted its habitat affinities from open habitats, recorded historically, to the more forested habitat associations we recorded. We suggest contaminants deserve more investigation regarding the abrupt and widespread declines of this species. Interspersion of different habitat types was positively associated with several species. A larger number of wetland patches may increase breeding opportunities and increase the probability of at least one site being suitable. We noted consistently negative associations between anuran species and urban development. Given the current trend of urban growth and increasing density of the human population, declines of amphibian populations are likely to continue.

Book chapter↗
USGS1998

Effects of landscape composition and wetland fragmentation on frog and toad abundance and species richness in Iowa and Wisconsin, USA [abstract]

We examined the relationships between anuran diversity and landscape features in the Upper Midwestern United States. Anuran relative abundance and species richness were measured using data collected by Wisconsin and Iowa state calling surveys conducted from 1990-1995. Landscape features surrounding survey points were determined using National Wetland Inventory and Wisconsin Wetland Inventory maps. We tested several hypotheses suggested by the literature. We hypothesized that the relative abundance and species richness of anurans that breed in ephemeral wetlands is positively correlated with the surrounding area of temporary wetlands and emergent wetlands. We hypothesized that the relative abundance and species richness of anurans is positively correlated with patch diversity and wetland edges, in the absence of local fragmentation effects. We hypothesized that the relative abundance and species richness of anurans is positively associated with forests but negatively associated with agriculture and urban areas. Our results show that the interspersion of different wetland types and the concomitant increase in wetland edge habitats were generally positive for frogs and toads and anuran abundance and diversity were generally higher in association with forests, especially forested wetlands. The presence of agriculture did not always depress frog and toad populations or diversity; some species were associated with agricultural landscapes. The two states differed in how anurans were associated with landscape features like lakes and permanent wetlands. We found that frog and toad relative abundance and diversity were lower when urban areas were present. Managers can use models like ours, generated from landscape analyses, along with range maps and population trend analyses to get a comprehensive picture of the health of individual species and groups of species. Our models could be applied to the landscape as a whole, and used to predict species relative abundance and richness at new locations. Our work provides a framework for future experimental and intensive research on specific factors affecting the health of amphibians in the Upper Midwest.

Book chapter↗