Factors Affecting Nest Success and Predator Assemblage of Breeding Birds in Semiarid Grasslands

Author(s): Helen T. Davis, Ashley M. Long, Jeremy A. Baumgardt, Tyler A. Campbell, Michael L. Morrison

Published: February 2019

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Woody encroachment has influenced wildlife distributions and, thus, predator-prey dynamics, for many taxa in North American grasslands. In 2015 and 2016,we examined howvegetative characteristics influenced avian nest predator assemblages and nest predation rates in semiarid grasslands of south Texas, where encroachment of woody plant species is common. We monitored 253 nests of 17 bird species and deployed infrared cameras at 107 nest sites within four vegetation types at our study sites.We also used data from a concurrent,multispecies monitoring project within our study area to assess predator activity within these same vegetation types. We divided bird species into four nest types based on nest shape and size (i.e., small, medium, and large cup-shaped nests and exposed nests with little structure).Wethen used logistic regression to examine relationships between shrub cover, concealment, and distance to edge and the probability of nest success and predation by snakes.We observed a significant decrease in nest success of our medium-sized, cup-shaped nest typewhen shrub cover increased at the nest site, indicating small increases in shrub cover (≈10%) could have substantial impacts on birds using this nest type. Snakes were our primary predator at camera-monitored nests (59%), and snake activity increased by 6.7% with every 10% increase in shrub cover at the nest site. Results of our study will help inform management of bird species using semiarid grasslands affected by woody encroachment and offer recommendations for improved nest success.