In 2018, the Corps identified 1.2 acres on the western-most portion of East Sand Island where DCCO could nest undisturbed by human hazers during the breeding season. Based on nest densities from previous years, the Corps estimated that approximately 5,400 breeding pairs of DCCO could nest in the 1.2 acre colony, consistent with the goals of the management plan. Corps contractors constructed a privacy fence to delineate the colony area from the remainder of the island and they installed cameras to detect and monitor the breeding colony remotely.
Corps contractors completed site preparations on the colony area on April 9 and initiated monitoring surveys on April 25. DCCO began loafing on beaches at East Sand Island in mid-April, but did not begin roosting overnight breeding behaviors mid-May.
Several adult and juvenile bald eagles (Haliaeetus leucocephalus) were present on the island in late April. Eagle presence and predatory behavior influenced the stability of the DCCO breeding colony, flushing adults and predating nests with increasing frequency in May and June before tapering in early July, following a decrease in river levels. Following the departure of eagles from the island in early July, the DCCO stabilized and grew to its peak colony size of 3,672 active nests (95% CI = 3,662 – 3,682) on July 25. As described in the 2015 management plan, the peak breeding season colony size was enumerated by counting the number of active nests observed in late incubation during the nesting cycle (FEIS Chapter 5, Page 22). Due to the disturbances by bald eagles and gulls, the timing and status of nest activity throughout the colony varied widely. Staff observed the first DCCO egg May 20, and DCCO were still laying and incubating eggs in early August when the first chicks fledged from nests. Colony monitoring effects concluded in late September as DCCO juveniles fledged from nests and foraged in the estuary.
We limited our management effects in 2018 to hazing adults and collecting a limited number of eggs to ensure the colony size did not exceed management goals (5,380-5,939 breeding pairs), per the management plan. In addition, the Corps used passive dissuasion measures effectively in some areas, including the use of reflective tape, balloons, and eagle and coyote effigies; however, we needed repeated human presence in other areas to prevent the successful establishment of nests. In total, the team collected three eggs from East Sand Island over the course of the breeding season and hazing was successful at eliminating nest attempts on portions of the island outside of the designated colony. These efforts supported the Corps’ efforts to maintain the colony size goals outlined in the 2015 management plan while simultaneously supporting a DCCO breeding colony on ESI.
In 2018, the USFWS coordinated efforts to estimate the size of the Western Population of DCCO in conjunction with the Pacific Flyway Council’s monitoring strategy. The Corps supported these efforts by funding surveys at sites where data would not otherwise be collected by other entities. This allowed monitoring of 43 sites and allowed surveying of an additional 80 sites, for a total of 123 colony sites or colony complexes monitored and analyzed. Results are pending as the data is preliminary and not yet finalized; when USFWS finalizes the data, we will update the results.