Species of conservation concern often receive intensive management to improve vital rates and facilitate recovery. Piping plovers (Charadrius melodus) are federally listed in the United States and concerns over nest depredation have prompted widespread use of plover-permeable predator exclosures placed around nests (0.5-2-m radius). While effectiveness of exclosures for improving nest survival has been demonstrated, concerns remain about decreased chick survival (through predator cueing or density-dependent processes) or increased vulnerability of adults to predation (ambush as adult leaves exclosure). Either one of these concerns could demographically outweigh the benefits of increased nest survival. During 2014-2016, we conducted an experiment designed to evaluate survival of uniquely identified nests (n = 418), chicks (n = 453), and adults (n = 367) at wetlands across the Northern Great Plains, USA. We assigned wetlands (n 2014 = 26,
in formulating the ideas and analyses presented here. The hard work and dedication of greater than 125 seasonal field technicians who collected and archived the data are especially noteworthy. We also want to thank the greater than 700 observers from other Federal and State agencies, nonprofits, and the public that reported banded piping plovers across their entire range. Max Post van der Burg and Brian Tangen provided detailed technical reviews of earlier drafts of this document which greatly improved this report. All capture and handling methods used in this study were in accordance with protocols approved by the Institutional Animal Care and Use Committee and within guidelines of an approved study plan by the USGS Northern Prairie Wildlife Research Center Animal Care and Use Committee.
Nest survival is a key demographic parameter, yet little effort has been made to improve the accuracy of fieldbased methods for assigning nest fates to shorebird nests. We used remote cameras to validate estimates of nest fate from field methods and to assess variation in accuracy of nest-fate assignment for Snowy Plover Charadrius nivosus in Utah, USA. We correctly identified the fates of 84% of nests in the field, and photos from camera monitoring revealed incorrect assignments for 22% of successful nests and 7% of depredated nests. Traditional field methods could be improved by checking nests more frequently when hatching date nears and spending additional time searching for eggshell evidence, especially when nests are in areas susceptible to weather disturbance.
The relationship between the rate of predation and prey abundance is an important component of predator–prey dynamics. However, functional responses are less straightforward when multiple predators compete for shared prey. Interactions among competing predators can reduce or enhance effects of predation on prey populations. Because many avian populations experience high rates of nest predation, understanding the role of specific predators on nest mortality will lead to more informed conservation and management strategies which attempt to increase productivity by removing certain predators or managing habitat to limit their impact. Our goal was to evaluate effects of specific predators and the influence of nest abundance on nest mortality. We monitored snowy plover Charadrius nivosus nests across 7 years at two study areas in Utah, USA, with remote cameras. We modelled predator‐specific hazard rates for nest mortality in a Bayesian framework to assess relationships between competing predators and the role of nest abundance on predator‐specific hazard rates. We found that hazard rates for nest mortality by gulls Larus spp. decreased with increasing nest abundance, whereas nest mortality by foxes Vulpes spp. and ravens Corvus corax initially increased, indicating that dietary switching may occur when nests become more abundant. Nest mortalities of specific predators were often not independent and ranged between compensatory (e.g. mammalian mesopredators) and superadditive (e.g. avian predators) across the breeding season. The non‐independence between nest mortalities suggests that reductions in some predators may not translate to additive increases in overall nest success. Analyses of cause‐specific mortality are rarely applied to avian nests, but examination of interacting impacts among competing predators on nest survival may provide insight into specific drivers of avian population dynamics. A free Plain Language Summary can be found within the Supporting Information of this article.
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