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Red-winged blackbirds (RWBL) are a polygynous species, and disruptions to either territorial behavior or reproductive fitness of the males has potential to lower annual productivity of several females. A reduction in the number of fledglings produced per territory could ultimately result in lower damage to grain crops, at least on a local scale. It is thus feasible that socially acceptable nonlethal methods, including reproductive inhibition through either physical or chemical means, may accomplish a reduction in crop damage.
Scientists at the USDA, Wildlife Services' National Wildlife Research Center have shown that reproductive inhibition is an effective method for reducing local populations of some bird species. None of the studies, however, have had to meaningfully incorporate loss of statistical power through predation events on nests or eggs. We expect a crippling reduction in sample size (i.e., nests, eggs, nestlings, and fledglings) to occur over the course of any field experiment intended to measure the effects of reproductive inhibition on RWBL. Thus, developing a methodology to reduce predation of nests is a preliminary yet necessary step in the process of conducting any subsequent field-level tests.
We assessed the efficacy of 2.54-cm x 2.54-cm woven wire cylinders (measuring 366- cm height x 183-cm diameter) for reducing mammalian predation on nests of RWBL. If effective at reducing nest predation, we will use these exclusion devices to enhance sample sizes in future experiments designed to assess effects of reproductive inhibition by chemical or physical methods on annual productivity of RWBL.