Exclosures to Protect Piping Plover Nests in Alberta, 1998-2001
Lance Engley and Dave Prescott
Nest depredation has been identified as a significant limiting factor to the Great Plains piping plover (Charadrius melodus) population. Previous studies conducted in eastcentral Alberta have shown that the use of predator exclosures can significantly reduce piping plover nest depredation (e.g., Heckbert and Cantelon 1996, Richardson 1999, Larson 2002). As a result, a large-scale program applying predator exclosures to piping plover nests was initiated in Alberta in 1998.
Three styles of predator exclosures were used during the course of this program: i) small (60 cm diameter), ii)medium (1.2 m diameter), iii) and large (3.0 m diameter). Medium-sized exclosures were used in a small-scale study in Alberta in 1996 and 1997 with a high level of success and therefore this style of exclosure was used in 1998 and 1999 as part of this program. However, in 1999 we recorded 26 incidents of predation by raptors on adult piping plovers at medium-sized exclosures. In three previous years of using medium sized predator exclosures, a total of four adult predations were recorded (Richardson 1998, Richardson 1999). Similar problems were encountered with medium-sized exclosures used elsewhere in North America, where the application of large exclosures had reduced the problem of raptors preying upon adults at exclosures. As a result, large exclosures were used in 2000 in an attempt to reduce predation of adult piping plover. While there was a large decrease in adult piping plover predation using the large exclosures, further refinement was still needed. In 2001, small exclosures were used for the first time with encouraging results.
In our study, we used the Mayfield method to determine nest success. Mayfield nest success for exclosed nests during the four-year program was 34.4%, compared with 24.5% for unexclosed nests. The main cause of failure for unexclosed nests was nest predation (77.1%) and for exclosed nests it was adult predation (37.3%). Overall, the small exclosures had the highest Mayfield nest success (72.4%), large exclosures were second highest (52.4%) and medium had the lowest Mayfield nest success (24.7%).
Continued experimentation with the small exclosure design is needed. Research is also needed into predator deterrence methods that will increase chick survival rates once they have left the exclosures.