Identifier

etd-07062015-155406

Degree

Master of Science (MS)

Department

Renewable Natural Resources

Document Type

Thesis

Abstract

The Rusty Blackbird (Euphagus carolinus) has gained notoriety in recent years as one of the fastest declining North American bird species, with a global population loss of as much as 95%. Causes of the decline are not completely understood, but the high rate of forested wetland change in the southeastern United States suggests that wintering habitat degradation may be a primary driver. To better inform management on critical wintering grounds, I surveyed 68 sites in Louisiana where Rusty Blackbirds had been known to occur to address how occupancy changes with habitat type and colonization and extinction rates vary with ground cover, rainfall, and invertebrate biomass. Rusty Blackbirds use a large area while foraging on the wintering ground, therefore management may need to be targeted to even larger spatial scales. I assessed the relationship between statewide Rusty Blackbird abundance data from the Louisiana Winter Bird Atlas and landscape scale habitat within 512 unique USGS 7.5-minute quadrangles using datasets on land cover, cropland cover, and soil type. Results indicate that forested wetlands are important habitats associated with Rusty Blackbird presence, but only under certain conditions. Rusty Blackbirds prefer shallow water for foraging. At my sites, deep water cover increased with the cover of forested wetlands and may have deterred Rusty Blackbirds from using primarily forested wetland sites. The most important variables associated with transience were wet leaf litter and invertebrate biomass, which were both positively associated with colonization and negatively associated with extinction probability. For the Louisiana Winter Bird Atlas data, the top model included all explanatory variables for Rusty Blackbird abundance. Abundance increased with cover of soil hydrologic groups C, C/D, and D, which are capable of retaining surface water, suggesting that at larger scales water cover is more important than any particular habitat type. Pecans are an important food source for wintering Rusty Blackbirds and pecan orchards had the strongest positive relationship with abundance. In addition to maintaining pecan groves on the landscape, Rusty Blackbirds may benefit from management for shallowly flooded forested wetlands that can support high amounts of wet leaf litter on the ground’s surface and abundant invertebrates.

Date

2015

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Stouffer, Philip C

DOI

10.31390/gradschool_theses.1841

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