Reproductive success of Field Sparrows (Spizella Pusilla) in response to invasive Morrow’s Honeysuckle: does Morrow’s Honeysuckle promote population sinks?
2015
The bush honeysuckle genus (Lonicera) comprises a suite of invasive shrubs that are naturalized in early successional landscapes throughout many parts of central and eastern United States. Although several studies have connected the use of bush honeysuckle as a nesting substrate to decreased nesting success, few have examined its potential effects on the growth or decline of songbird populations. From 2007–2009, we examined the nesting success of Field Sparrows (Spizella pusilla) in southwestern Pennsylvania old-fields to assess reproductive success based on nesting substrate and the density of Morrow’s honeysuckle (Lonicera morrowii) surrounding the nest site. We used the information-theoretic approach to model nesting success as a response to nest substrate, cover of Morrow’s honeysuckle, midpoint of nesting attempt, and clutch size. Our model indicated that Morrow’s honeysuckle, as a substrate and when found in dense patches surrounding the nests of Field Sparrows, had a negative impact on nesting success. We developed a population model to determine if the measured reproductive success (17% ± 5) could maintain a stable population. Results of the population model yielded 1.21 female offspring/adult female. This was not sufficient to maintain a stable population and resulted in a population sink. A sensitivity analysis indicated that adult survivorship was the most influential parameter in the population model, indicating that although breeding success was important, it was not the primary driver of population stability.
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