August 2022

Authors: Akresh, M. E., D. I. King, S. L. McInvale, J. L. Larkin and A. W. D’Amato.

This study investigated species turnover along gradients of silvicultural (forest harvest) intensity. Silvicultural treatments are generally discreet, as a “forest stage” is identified and often maintained through selective logging and habitat management. The study conducted a meta-analysis in which the degree of canopy cover and the amount of cross-sectional stem area (known as Basal Area) were analyzed for forest stands that were less than 15 years post-treatment. The findings of the study suggested that those bird species often associated with shrub/scrub habitats (referred to as early successional habitat) peaked in clear cut areas while species found in mature forest patches tended to drop in abundance rapidly with tree loss. While these results may not seem surprising, a number of species had a quadratic relationship with the two measured forest variables. For shrub/scrub habitats, Gray Catbirds (Dumetella carolinensis) and Indigo Buntings (Passerina cyanea) both preferred intermediate levels of canopy cover and basal area, suggesting that their presence tends to peak and then decline as early successional habitats are newly forming and then mature past a certain stage. A “Goldilocks” scenario, if you will. The same relationship was evident when looking at mature forest stands for species such as Blue-gray Gnatcatcher (Polioptila caerulea), Eastern Wood-Pewee (Contopus virens) and Blue-headed Vireo (Vireo solitarius), suggesting that some tree harvest promotes these species, while too much or too little tends to create a habitat that does not provide for their habitat needs.

Why It Matters: As more habitat is converted to suit human expansion, it is important to know how our conserved forest tracts might be managed if we seek to promote certain species. Studies such as this empower us to make effective conservation strategies for habitat specialists, such as the Blue-headed Vireo, or species with declining trends, such as the Eastern Wood-Pewee.

Authors: Augustine, S. H., M. P. Strager and C. T. Rota

This study examined connectivity of migratory routes taken by Canada Warblers (Cardellina canadensis) breeding in WV, which is the only US state with a positive population trend. To determine this, researchers attached 32 geolocator tags to male warblers in 2020 and determined that individuals breeding in WV overwintered in north-central Colombia. Further, the routes taken by birds during the spring and fall migration were offset from one another by an average of 232km (144mi). This suggests a form of loop migration has been adopted by the birds breeding in this region and sheds light on where conservation efforts should be concentrated along migratory corridors.

Why It Matters: The Canada Warbler has declined dramatically throughout most of its range. In Rhode Island, the species has experienced a 59% decline in distribution between 1987 – 2019 and in the states of CT, RI and MA, the species has declined in abundance at a rate of 4.4% per year over a 50-year period. Understanding the full annual cycle of the species, which includes migratory routes taken and connectivity between breeding populations is critical to our ability to reverse this declining trend. Studies such as this, although conducted in a different state, elucidate behavioral and evolutionary trends which can assist with conservation across the entire geographic range of the species.

Authors: Anderson, M. A. Valdiviezo, M. Conway, C. Farrell, R. K. Andringa, A. Janik, I. Rusyn and S. Hamer

The authors of this study hypothesized that the degree of exposure birds face from neonicotinoid pesticides (neonics) will vary based on genetic similarity, foraging habits, location and season. Within three areas of Texas, 266 blood samples were collected and analyzed for neonics. Almost half of all samples (n = 101) had detectable levels of neonics, with Imidacloprid (the most commonly used neonic) being the most common form detected. Across all seasons, 14 out of 17 avian families had detectable levels of neonics, spanning insect, grain and fruit-eating birds.  

Why It Matters: Neonics are pervasive chemicals that can be transported across the landscape due to their properties of poor soil binding and high water-solubility. The potential long-term, chronic exposure risk to birds is great and studies such as this continue to elucidate the threat that these chemicals pose to the health of bird populations in and adjacent to areas of neonic application. This study is particularly pertinent to our work at Audubon because sampled birds came from refuge land, illustrating the capacity of these chemicals to infiltrate protected habitats.

Authors: Dossman, B. C., A. D. Rodewald, C. E. Studds and P. P. Marra

The authors of this study utilized the MOTUS Wildlife Tracking System to track the migratory movements of American Redstarts (Setophaga ruticilla) as they migrated from nonbreeding grounds in Jamaica. Individual birds that initiated migration later (only by 10 days), increased migration speeds by 42% to make-up for lost time, but were significantly less likely to survive the migration. This suggests that speed is used to compensate for delays in migration. This compensatory mechanism unfortunately appears to lessen the overall survival of individual birds.

Why It Matters: Birds that find themselves overwintering in degraded habitats are often unable to procure the amount of resources they need to maintain fitness during migration or the subsequent breeding season. This study adds to the knowledge we already possess regarding the carryover effects of the nonbreeding season. It is important to remember that there are birds that overwinter on Audubon refuges and return to breeding destinations north of Rhode Island. Doing what we can to ensure that birds have ample resources to overwinter in good health is one of the goals of the Avian Research Initiative.

An example of a grassland strip planted among agricultural fields (photo: Iowa State University)

Authors: Giese, J. C., L. A. Schulte and R. W. Klaver

This presentation highlighted a long-running project in the Midwest United States called STRIPS (Science-based Trials of Rowcrops Integrated with Prairie Strips). The idea is simple: incorporate small strips of native vegetation among rows of agricultural products to provide habitat for birds and pollinators while increasing soil health and water holding capabilities of the landscape. Surveys conducted along rows of native habitat strips documented three times as many grassland bird species using these areas as were found in conventional crop fields. These strips of native vegetation are proving to be significant in their capacity to provide long-term sustainable habitats that promote native biodiversity.

Why It Matters: The STRIPS program is very intriguing as it has established the significant gains to landscape health that can come from devoting merely 10% of total crop area to native vegetation (Figure 3). The idea is simple and the benefits to birds, pollinators, runoff mitigation and nutrient retention are evident. Even small strips of native grassland habitat intermixed with agricultural crops would potentially increase the number of birds associated with these habitats. In Rhode Island, that would translate to more Red-winged Blackbirds (Agelaius phoeniceus), Song Sparrows (Melospiza melodia), Common Yellowthroats (Geothlypis trichas) and others. In addition, trials in the Midwest show that these strips promote four times as many plant species, twice the number of bird species, three times the amount of bird abundance, 40% less runoff, 90% less phosphorus export and 84% less nitrogen export from agricultural zones. This practice, if adopted by RI farmers, could greatly enhance our grassland bird habitat.

Authors: Strimas-Mackey M., D. Fink, T. Auer, A. Johnston, O. Robinson, S. Ligocki, W. Hochachka, C. Wood, I. Davies, M. Iliff and L. Seitz

This presentation highlighted new data products that have recently been made available from eBird. Habitat and environmental data from remote sensing are now incorporated into status and trends maps, creating a more refined and accurate result. A complete suite of data products are now available that can be used to visualize bird populations and compare to local datasets to increase our resolution of site-specific nesting biology.

Why It Matters: eBird data has provided some of the best (high resolution) information we currently have at our disposal on bird movements, distributions and abundances. Further refinement of the data is now allowing for the creation of models that account for weather and habitat. These eBird products are capable of informing our work at Audubon because they allow for comparison with the information we gather as part of our baseline dataset, which will also incorporate local habitat variables. This will allow us to determine whether birds nesting in Rhode Island are utilizing habitats the same way that occurs at larger spatial scales. In the event that birds in Rhode Island prefer unique habitats, specific management plans can be catered to the meet these localized breeding criteria.

Authors: Morales-Perez, A. L. and O. Monzón-Carmona

The authors of this study placed Acoustic Recording Units (ARUs) in three distinct habitat types (coastal, flood plain and wetlands) and utilized them to determine changes in bird communities as these habitats matured during a period of restoration. ARUs measured change over three habitat restoration phases (1-3 years post restoration) and in three distance categories (50-300m to nearest forest fragment). The authors documented an increase in avian species richness in the oldest sites (2.5 – 3 years post restoration) and those farthest from forest fragments. There was no change in bird communities in those habitat patches close to forest fragments or in those habitats still in the early phases of maturation (<2 years old).

Why It Matters: Although this study occurred in a semi-tropical location, the experimental design and methodology lend themselves well to the work we are doing at Audubon with our ARUs. The ability to use ARUs to measure change in bird communities through space and time makes them extremely useful as conservation tools. Upon completion of baseline data collection across Audubon properties at the end of 2022, our ARUs will be deployed to assess whether the community of breeding and migratory birds changes relative to extent of available habitat or proximity to fragmented habitat patches. This study provided a great deal of insight into the workflow that we will need to adopt to successfully measure these parameters.