Browsing by Author "Wolfson, David"

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    Migratory Ecology and Movement Patterns of Mid-Continent and Eastern Sandhill Cranes
    (2018-07) Wolfson, David
    Sandhill cranes (Antigone canadensis) are long-lived birds with relatively low recruitment rates, making accurate knowledge of abundance and distribution critical for well-informed harvest management. Minnesota is one of few states containing portions of 2 different breeding populations of greater sandhill cranes (A. c. tabida)—the Mid-continent Population (MCP), which has a harvest season in northwestern Minnesota in the fall, and Eastern Population (EP), which is not currently harvested in the state. Although the historical range boundaries of these populations have not been in close proximity during the 20th century, EP cranes are currently experiencing a significant increase in population size and a concurrent expansion of breeding range. A better understanding of range boundaries and information regarding fine-scale space use of cranes (both adults and juveniles) at different times of the year, is necessary to inform harvest management (e.g., determination of appropriate hunting zone boundaries and timing of harvest season). Our objectives were to 1) evaluate the current range boundaries of the 2 populations in Minnesota and whether the populations overlap on their breeding areas and autumn staging grounds; and 2) characterize the fine-scale movements and behavior of cranes after their arrival on breeding grounds in the spring until fall staging. We captured and attached Global Positioning System–Global System for Mobile Communications transmitters to 50 cranes in the zone between the historical breeding-range boundaries of the 2 populations. We were able to document, for the first time, overlap between the breeding ranges of EP and MCP sandhill cranes. EP and MCP cranes also both used some of the same staging areas in northwestern Minnesota, where recreational harvest targeted at MCP cranes began in 2010. Moreover, we observed multiple cranes using both Mississippi and Central flyways when migrating between breeding and wintering grounds; choice of flyway has historically been used to assign population affiliation (Mississippi Flyway = EP, Central Flyway = MCP). Juvenile and adult cranes exhibited different movement strategies during the spring and summer. Juveniles traversed larger areas and were more likely to display long-distance roaming behavior, whereas adults were more likely to revisit the same areas. We hypothesize that these differences may reflect constraints adults experience when nesting and brood rearing, and differential knowledge of the landscape between adult and juvenile birds.
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    A multi-faceted evaluation of a reintroduced waterfowl species: Migration ecology, ecotoxicology, and population genetics of trumpeter swans in the Midwest
    (2024-06) Wolfson, David
    Trumpeter swans (Cygnus buccinator), the largest waterfowl species in North America, were widespread throughout much of the continent prior to European colonization. Due to unregulated market hunting, trumpeter swans were nearly extirpated, and reached an estimated low of ~70 individuals in the lower 48 U.S. states during the 1930s. The creation of new protected areas coupled with management efforts allowed trumpeter swan abundance to recover, and they were successfully reintroduced to the western Great Lakes region in the late 20th century to re-establish the Interior Population (IP). However, a general lack of information about IP trumpeter swan ecology has hindered conservation decision-making. I partnered with agency biologists from seven U.S states and one Canadian province to gather information on IP trumpeter swan annual movements and migration patterns, the prevalence of lead (Pb) in free roaming swans, and the genetic makeup of trumpeter swan populations in North America. Before addressing the previously mentioned aspects of trumpeter swan ecology, in Chapter 1, I provide a review of piecewise regression, a flexible type of breakpoint analysis. I provide an overview of piecewise regression and then describe six case-studies, using piecewise regression on a variety of datasets that include a range of species, data types, ecological responses, statistical signals, and timeframes. In Chapter 2, I use the methodology described in Chapter 1 (i.e., piecewise regression) to quantify annual movements and migration patterns in IP trumpeter swans. We (multiple state agency biologists and other collaborators) deployed 133 GPS-GSM transmitters on trumpeter swans across the current IP breeding range (i.e., the greater Midwest) during 2019–2022. Individual tracking data revealed that IP trumpeter swans are partial migrants, with a continuum of strategies each year, from local movements to long-distance migration. Much of the variability in movement patterns was related to factors tied to natural history demands (e.g., breeding status) and response to environmental conditions (e.g., through associations with breeding latitude). In Chapter 3, I present a baseline assessment of the prevalence of lead in all trumpeter swans associated with the dissertation and an additional flock in Nebraska. I estimated blood lead concentration for 119 IP trumpeter swans and detected lead in all individuals. However, 91% of swans had blood lead levels in the ‘background’ range (not considered to produce negative physiological effects), 7.5% of swans had blood lead levels in the ‘sub-clinical’ range, and only 1.5% of swans had blood lead levels in the ‘clinical’ or ‘severe’ range of lead toxicity. Finally, in Chapter 4 I present a comparative assessment of the genetics of trumpeter swans in North America. I collected 150 genetic samples from IP trumpeter swans captured during 2019–2022 and also obtained 79 reference samples from the other two North American trumpeter swan populations. These samples provide evidence that all three populations are genetically distinct and that the High Plains flock of the IP has lower genetic diversity compared to the other groups, likely a result of smaller population size, relative geographic isolation, and potential founder effects.
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    R Code and Output Supporting: Modeling individual variability in habitat selection and movement using integrated step-selection analyses
    (2024-03-11) Chatterjee, Nilanjan; Wolfson, David; Kim, Dongmin; Velez, Juliana; Freeman, Smith; Bacheler, Nathan; Shertzer, Kyle; Taylor, Chris; Fieberg, John; nchatter@umn.edu; Chatterjee, Nilanjan; Fieberg Lab
    This repository contains data and R code (along with associated output from running the code) supporting all results reported in: Chatterjee, Nilanjan; Wolfson, David; Kim, Dongmin; Vélez, Juliana; Freeman, Smith; Bacheler, Nathan; Shertzer, Kyle; Taylor, J.; Fieberg, John 2024. Modelling individual variability in habitat selection and movement using integrated step-selection analysis. Methods in Ecology and Evolution. The code demonstrates how to model the individual variation in habitat selection and movement parameters using integrated step-selection analysis.