A storm and a study save piping plovers
By Holly Kays, College of Natural Resources and Environment
In December 1992, a massive storm rocked the island community of West Hampton Dunes, N.Y. Dark waves reared high, and frothy ocean water pounded the sandy soil.
In the 1960s, the U.S. Army Corps of Engineers had installed a line of groins — low rock walls intended to control erosion — along the length of the island, but the groins were not built along the entire perimeter and the unprotected area became progressively narrower as its sand eroded. The December storm was the last straw for this thin strip of land. Like giant fists, the waves punched straight through the island. The ocean rushed through the breach, displacing massive amounts of sand and toppling the houses built on it. The island was transformed.
The transformation was disastrous for the human residents of West Hampton Dunes; their homes and portions of the beach were gone. Since the corps’ method of groin installation had precipitated the disaster, the courts directed the agency to renourish the beach so the homes could be rebuilt. The slow process of restoration soon began.
In the meantime, piping plovers, shorebirds that have been listed as threatened since 1986, deemed the post-storm island a perfect habitat. Within eight years, the island’s plover population grew from zero to 39 pairs, adding another layer of complexity to the corps’ plans to restore the seaside community.
Jim Fraser, professor of fisheries and wildlife sciences at Virginia Tech, had been studying the reasons for the piping plovers’ decline since its designation as an endangered species, so when the U.S. Fish and Wildlife Service required the corps of engineers to monitor post-storm plover populations on the island, Fraser applied for the grant. He wanted to move beyond simple monitoring, however, to accomplish his own research goals. “We told them that our mission at the university is not to do monitoring,” explains Fraser. “We had to make this a research project. They were willing to fund that, so they got their monitoring and we got our research.”
During the 12-year study, Fraser focused on investigating the plover population’s response to changes in the quality and amount of habitat available, as well as the impact of predators. When the ocean rushed through the island, it eliminated the houses and roads that had created disturbances, decreased habitat suitability, and acted as physical barriers to wildlife movement. Just as importantly, it created intertidal flats — shallow areas on the leeward side of barrier islands that are prime feeding habitat for the plovers, which eat the insects and invertebrates found there. However, as the village recovered from the storm’s effects, plover numbers declined once more. Fraser’s study sought to quantify the mechanisms of these population changes.
His team used two main methods to investigate the effect of predation by such animals as raccoons and foxes on the piping plover population. The first compared the number of predators trapped in a given year with the proportion of that year’s plover chicks surviving to maturity. Although the village implemented the trapping inconsistently, the results showed conclusively that fledgling survival rates increased significantly during years when more predators were trapped.
In the second predation-related investigation, Fraser’s team recorded the success of nests that were circled by cages that allowed plovers to enter and exit freely but kept predators out. Although the results showed that egg success increased significantly with the use of these exclosures, overall chick survival did not. Since piping plovers are able to walk but unable to fly for the first 25 days after hatching, hatchling plovers were easy prey as soon as they left their nests.
The remaining research determined piping plover density and habitat quality. Researchers had been calculating nest densities — first using hand-drawn maps, later using GPS and geographic information systems — since the study’s genesis. To relate these densities to habitat suitability, they took cores from intertidal mud flats and trapped terrestrial prey in various areas of the island throughout the breeding season. They found that the intertidal mud flats contained abundant food when the plovers arrived in mid-March, but little to none existed in areas containing herbaceous vegetation, indicating why nest densities are highest near the intertidal flats.
In 2001, doctoral student Jonathan Cohen, now graduated and a fisheries and wildlife research scientist at Virginia Tech, began running the project’s field operations, lending his own unique approach to the study. Cohen started banding birds in order to more closely monitor their annual survival, home range size, and the rate of return to the same site during consecutive breeding seasons (site fidelity). The U.S. Fish and Wildlife Service had previously prohibited traditional bird banding when it discovered that the bands injured the birds’ feet, but Cohen proposed a new banding technique, which the service approved. Using this method, Cohen found that site fidelity decreased significantly when habitat shrank, and that home range size was smaller when the birds lived closer to intertidal flats. The decreasing home range size close to intertidal flats was a key finding of the study; coupled with data showing that food is more abundant in those areas, it implied that intertidal mud flats are highly suitable habitat for piping plovers. “These results are something you would expect,” says Cohen, “but for threatened and endangered species, it’s important to document them because managers need to be able to replicate the process.”
Cohen was instrumental to Fraser’s study even apart from his innovative banding technique and home range analysis. The study ended in 2004, leaving Fraser with a dataset spanning a 12-year period, the result of multiple experiments run by many different students. Fraser and Larry Houghton, a 2005 Ph.D. graduate who ran field operations from 1996 to 1999, were coauthors with Cohen on the resulting data analyses. Cohen’s work in compiling data resulted in five published papers, including a Journal of Wildlife Management monograph. “We wouldn’t have that monograph if it wasn’t for him,” says Fraser of Cohen. “He was huge in terms of bringing the project to a close in a good way.”
Cohen’s analysis has greatly impacted piping plover management and conservation. Possibly the study’s most significant outcome was the reliable data it generated, which managers can offer as evidence in management cases that go to court. “Sometimes you feel like you’re proving the obvious,” Cohen admits, “but in legal arguments, suddenly ‘everybody knows’ isn’t good enough.” Trustworthy data is necessary to legally justify controversial management actions, and in the case of piping plovers, such conflict happens frequently. Both humans and plovers prize the same beachfront habitats. Fortunately for piping plover managers, the study’s 12 years of carefully analyzed research has gone a long way toward quantifying important elements of the plovers’ habitat needs. The data proves the significance of intertidal flat preservation and predator trapping to preserving the species, and it will enable managers to defend such actions in court.
According to Cohen, the research has also helped to “get the importance of intertidal flats into the general consciousness of managers.” Prior to Fraser’s study, managers commonly focused on protecting sand areas for plovers without considering the sand’s proximity to foraging areas. The data help managers to consider a more complete picture of the plovers’ needs.
In addition, the study has illuminated the issue of predation. “Historically, these islands were relatively predator-free for the plovers,” Fraser explains, “but we’ve built bridges to them, and now the predators can go back and forth as they choose.”
The plover study clearly demonstrated that chick predation was a limiting factor to population size. Between the two methods of predation control that the study investigated — trapping predators and exclosing nests — only predator trapping reduced overall predation rates. Managers have heeded these results. “Predator trapping is becoming more and more prevalent,” says Cohen.
The study has quantified many critical elements of plover population dynamics, but Cohen and Fraser want to learn more. In particular, Cohen is interested in studying the distribution, abundance, and survival of adults during the non-breeding season, and Fraser would like to research methods of managing predators and creating artificial plover habitats on the coast, a technique the Army Corps of Engineers already implements to aid Missouri River plover populations.
There are still many areas for the researchers to explore, but Fraser’s team has provided managers with the tools to create more favorable conditions for piping plovers and the U.S. Fish and Wildlife Service with the hard data it needs to defend its conservation practices in court. For people and piping plovers, it is better than another storm.