Browsing by Subject "Hawk Ridge"

Now showing 1 - 3 of 3
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    Cloacal swabbing as a tool to study diet in migrating raptors using DNA metabarcoding
    (2021-05) Brouellette, Lisa
    While much research has gone into understanding the timing and patterns of migration, little has been done to understand the diet of raptors during migration. Most raptor dietary studies focus on the breeding season or winter, but migratory diet may be quite different due to differences in habitat type and prey availability along migration flyways. Here, we tested the efficacy of DNA metabarcoding to detect prey DNA on cloacal swabs. In 2019, we collected cloacal swabs from raptors during spring and fall migration in Duluth, MN. We analyzed 287 cloacal swabs from 11 species of raptors. We hypothesized that detection of dietary DNA on cloacal swabs would be influenced by the species of raptor swabbed, the size of the raptor, and migratory flight strategy (passive/soaring flight vs. active flight). Prey DNA was detected on 18.46% of cloacal swabs. Using a generalized linear model, we found that neither species, size, nor migratory flight strategy were better than the null model at explaining differences in detection of dietary DNA. To our knowledge, this is the first study to use cloacal swabbing and DNA metabarcoding to detect dietary DNA and our results indicate that this method has potential for further use.
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    Fall Raptor Migration Phenology and its Relationship with Weather
    (2018-12) Steiner, Ryan
    Changes in fall raptor migration phenology have been documented at hawk count sites across North America. Delays in fall migration phenology are the most common shift reported, however these changes vary from species to species. Changes in fall migration phenology are often attributed to climate change, but direct links to climate are rarely demonstrated. Those studies that do attempt to link the shifts to climate change often use global weather phenomena such as the North Atlantic Oscillation. Using updated methods, we examined fall migration phenology in 14 raptor species counted in 44 years at Hawk Ridge in Duluth, MN in relation to local and regional climate variables. Variables explored were related to temperature, favorable wind conditions, and cold fronts because these variables have been previously found to influence raptor migration. Weather variables were summarized using a principal components analysis. Raptor phenology was regressed against the top ten principal components using univariate models. Most raptors were found to be migrating later when temperatures were warmer. Favorable winds were also found to influence fall migration timing for most species, however some species responded to a greater percentage of the season having favorable winds, while others responded to greater wind strength of favorable winds. The weather variables used in this study provide a partial explanation for observed changes in migration phenology, but more study is needed to fully explore the mechanisms governing the timing of fall raptor migration.
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    Mercury accumulation in raptors
    (2016-01) Keyel, Edward
    Mercury (Hg) is a toxic heavy metal that when methylated to form methylmercury (MeHg), bioaccumulates in exposed organisms and biomagnifies through food webs. Most studies examining Hg concentrations in birds of prey have focused on species associated with aquatic systems such as Bald Eagle (Haliaeetus leucocephalus). My goal was to assess Hg concentrations in multiple species of migrating raptors in the upper Midwestern US. From 2009-2012, 966 raptors of 11 species were captured at Hawk Ridge, Duluth, MN, USA. Breast feathers were sampled and analyzed for total Hg concentrations, which is a good analog for methlymercury. Mean Hg concentrations ranged from 0.11 – 3.46 ppm. Carbon and nitrogen stable isotope values were analyzed for Sharp-shinned Hawk (Accipiter striatus) and Merlin (Falco columbarius) because they had the highest mean Hg concentrations with 3.46 and 2.15 ppm respectively. Stable isotope analysis suggested that both species consumed terrestrial prey and that total Hg concentration increased with trophic level. Further analysis of Sharp-shinned Hawk and Merlin feather samples show Hg increases with age. The Hg concentrations observed in Sharp-shinned Hawks, Merlins, and Northern Goshawks (Accipiter gentilis) represent a concern when compared with concentrations found in the American Kestrel (Falco sparverius); one of the few raptors with enough experimental data for comparison.