Date of Award

January 2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Brett J. Goodwin

Abstract

Greater prairie-chickens, Tympanuchus cupido pinnatus, are in decline across the majority of their already receding range due to changing land use patterns and habitat fragmentation. The Agassiz Beach Ridge region of northwestern Minnesota harbors one of the only sustained to increasing populations of prairie-chickens in the country due to the conversion of marginal agricultural lands to grasslands and through conservation entities securing tracts of land allowing for habitat stability and dispersal.

Nesting and brood-rearing habitats are the most limiting factors for population sustainability. Hens were marked with radio transmitters on booming grounds and at nest sites discovered by nest-dragging. Their reproductive ecology is described using three methods; habitat use and selection by brood-rearing hens, local invertebrate and vegetative predictors of brood use, and nest site characterization and success.

By combining remotely-sensed imagery with estimated locations gathered by triangulation I was able to evaluate habitat use and selection of brood-rearing hens in 2008 and 2009. There are signals, though not statistically significant, indicating differential habitat uses between successful and failed brood hens. Treed habitats were used more often than random by successful hens and completely ignored by unsuccessful brood hens Successful brood hens used soybeans in a random manner while unsuccessful brood hens selected soybean fields suggesting a landscape with greater amounts of grassland habitats would be more beneficial than one dominated by row crop agriculture.

For a site-specific view of brood hen use locations, hens were flushed 14 days after the nest hatched and again every 10 days until the brood reached independence in 2008 and 2009. At each flush location invertebrates, vegetation cover, vegetation density and litter depth were measured. Logistic regression analyses showed five parameters that could predict brood presence: greater percent coverage of introduced grasses, greater percent coverage of native forbs, more invertebrates less than 10 mm in length, fewer Orthopterans less than 10 mm in length, and fewer individuals from "Other" invertebrate orders. Site characteristics were recorded at the time of discovery for 150 prairie-chicken nests during the 2007-2009 nesting seasons. Apparent nest success decreased from 47.73% in 2007 to 35% in 2008 to 28.26% in 2009. Nests were evaluated based on three immediate vegetation types; native, smooth brome, and other introduced species. Litter depth and percent overhead coverage were not significantly different among vegetation types. Mean Visual Obstruction Readings were greater at hatched nests than failed nests for all three habitat types. Nests dominated by native vegetation were almost significantly less screened than nests found in smooth brome and other introduced vegetation. Clutch sizes of nests dominated by smooth brome were significantly larger than the other vegetation types

These findings suggest that landscapes with grasslands comprised of introduced grasses and native forbs that produce an abundance of invertebrates less than 10 mm are most likely to improve prairie chicken brood rearing success. To increase nesting success habitats should provide horizontal and vertical cover similar to that of an idle smooth brome planting that provides residual cover during nest initiation and grows quickly to conceal the hen during incubation. Greater vertical concealment appears to increase the likelihood of a nest hatching.

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