Western Snowy Plover Nesting at Bolsa Chica 2019
By Peter Knapp and Rachel Woodfield
Editors note: the following is the Executive Summary of the highly detailed Western "Snowy Plover Nesting at Bolsa Chica, Orange County, California 2019" by Peter Knapp and Rachel Woodfield that can be found on the Amigos de Bolsa Chica website at https://amigosdebolsachica.org/bolsa_chica_restoration/2019_Bolsa_Chica_WSP_Report.pdf
In 2019, California Department of Fish & Wildlife (CDFW) staff and volunteers continued the annual monitoring and management of western snowy plovers at Bolsa Chica Ecological Reserve (Reserve). Surveys were conducted daily from mid-February to mid-September. Observers documented the location of any new nests, installed welded-wire mini-exclosures (ME) over each nest to protect it from predators, monitored the nests each day, and later followed each brood until fledging. In addition, a range-wide Winter Window Survey and a range-wide Breeding Season Window Survey were conducted. Calculations were also made to estimate the minimum number of adults present at Bolsa Chica during the breeding season for the US Fish and Wildlife Service.
In 2019, the first snowy plover nest was established on March 30 and the last brood fledged on September 5. There was a total of 119 nests, producing 321 eggs, of which 283 hatched chicks, with 112 fledglings produced. There was an overall fledge rate (fledglings/male) of 1.70 for 2019. This continues the high fledge rates of recent years, indicating an increase in the plover population at Bolsa Chica. The continued use of MEs resulted in low rates of egg predation.
The most utilized regions of Bolsa Chica for snowy plover nesting were the Seasonal Ponds and the Muted Tidal Basin, with 41% and 27%, respectively, of all nests. The most successful individual cell was Cell 10 in the Seasonal Ponds, producing 16% of all fledglings. Cell 46 in the Muted Tidal Basin produced 7 nests, with 20 eggs, 20 chicks, and 12 fledglings.
The range-wide Winter Window Survey conducted in January to estimate the winter population size found 26 adults within the Reserve. The range-wide, Breeding Season Window Survey conducted on May 20 resulted in a count of 94 adult snowy plovers in the Reserve. The highest Estimated Minimum Number of Adults was determined to be 109.
Each year, the date of initiation of the tenth nest is recorded. The tenth nest in 2019 was initiated on April 9. This is approximately one week earlier than 2018, which itself was two weeks later than the prior 5-year average of April 1. In addition, the time period that there were 70 or more breeding adults present was 80 days. This was an increase from 2018 (65 days).
There was a high rate of chick loss in 2019 (171 chicks), continuing the high rate of chick loss observed from 2017 through 2019. By comparison, the average chick loss from 2014 through 2016 was 100 chicks. More loss would be expected with the increase in the number of nests in 2017-2019, however the 2014-2016 time period had a higher fledge rate, with over 50% of chicks fledging. This was the sixth consecutive year that the management goal of 70 adults in the breeding season was surpassed at the Reserve, as specified in the U.S. Fish and Wildlife Recovery Plan for the Pacific Coast Population of the Western Snowy Plover.
A key recommendation for 2020 is to provide predator management. In 2019 there was no predator management because the CDFW employee charged with this task retired. Fledgling success can only be improved through reduction of predators, such as American kestrels, which are believed to be the primary predator of plover chicks. This is essential to improving reproductive success at Bolsa Chica, which provides the best nesting option for snowy plovers within a 60-mile radius. A second recommendation is to recognize that the Muted Tidal Basins now account for over 25% of plover nesting. Impacts to plovers should be carefully considered while developing remedies to the poor functionality of the Muted Tidal Basin.