2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...

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Bolsa Chica Lowlands Restoration Monitoring 2008 Annual Report was ceased due to disruption of the nesting birds and their chicks. Most nest data was collected prior to that time; however, fledglings for both the California least tern and the western snowy plover on NS1 had to be estimated. Results California Least Tern The data from the 2008 California least tern breeding season at Bolsa Chica Ecological Reserve were provided by CDFG and are summarized in Marschalek (2008). In 2008, the California least tern arrived at Bolsa Chica on April 14 and were last observed on the site August 19, which was very similar to past years. The terns nested primarily on STI and NS1, although one unsuccessful nest was located on the Seasonal Ponds in Zone 11 (Table 1-22). The least tern did not utilize NTI, NS2, or NS3. The first nest was initiated on May 19 on the STI nesting site. There were a total of 242 California least tern nests at Photo by Bonnie Peterson Bolsa Chica in 2008, only slightly higher than the 226 nests in 2007. The average California least tern on nest. clutch size was 1.8 eggs per nest. From an estimated 217 pairs, a total of 432 eggs were laid. Fledgling success for the 2008 season ranged from 100-150 fledglings with a rate of 0.41 to 0.62 fledglings per nest. This is compared to 15 fledglings in 2007 and a rate of 0.07 fledglings per nest. The first least tern fledgling was recorded on June 23. Table 1-22. 2008 California least tern reproductive success for each nesting location. Location Total Nests Nests Failed* Nests Hatched (# chicks) Fledglings Nest Site 1 184 25 159 (281) -- South Tern Island 57 2 55 (89) -- Seasonal Ponds 1 1 0 (0) 0 Total 242 28 214 (370) 100-150 California least tern nest predation was low at 19 nests (7.9% of all nests). Seven (2.9%) nests were abandoned prior to hatching, and one nest was lost to flooding. Black skimmer and the larger terns nested on NS1, an area where the California least tern had already established their nests. It is estimated that 19-26 least tern nests were subsequently lost through trampling by other terns and skimmers. In order to increase hatching success, where California least tern nests overlapped with the larger terns and black skimmer, nests were encircled with wire fences 20 cm high and 1m in diameter. The circular fences successfully protected the eggs from being trampled by larger birds. Three chicks were observed lost to depredation: one chick was lost to a red-tailed hawk and two chicks were depredated by ants. Merkel & Associates, Inc. 93
Bolsa Chica Lowlands Restoration Monitoring 2008 Annual Report Western Snowy Plover The complete 2008 results for the western snowy plover breeding season at Bolsa Chica can be read in the annual report (Knapp and Peterson 2008)(Appendix 1-G). The western snowy plover initiated its first nest on March 17, 2008 and the last nest hatched on August 9. The plovers nested on STI, NS1, NS3, and a number of zones within the Seasonal Ponds (Table 1- 23). A total of 67 nests were located at Bolsa Chica. Four completed clutches were 2-egg clutches, while 61 were 3-egg clutches. The remaining 2 nests were depredated prior to nest completion. From the 193 total eggs laid, 174 chicks were produced. Two of the 67 total nest attempts were lost to predators, one on Zone 22 early in the season and one on NS1. These nests were depredated prior to placement of the mini-exclosure over the nest. The probable predators for these nests were corvid and gull, respectively. Three nests, one with 3 eggs and two with 2 eggs, were abandoned. These nests were located on STI, NTI, and Zone 19, respectively. Of the 174 total chicks produced in 2008, a minimum of 57 and a maximum of 109 chicks (32.8 to 62.6%) were estimated to have survived to fledge. The minimum fledgling estimate per nest (0.85) is slightly below the average (0.95) of the study years. The maximum estimate of fledglings per nest (1.62) would exceed the previous high of 1.47 in 2005. Of the 67 nests, 24 nests did not fledge chicks. Of the 19 known nests producing chicks but not producing fledglings, one brood was depredated by gulls and one brood by coyote. The remaining 17 broods were most likely depredated by red-tailed hawk (STI) or American kestrel (Seasonal Ponds). There was potential for trampling of the chicks on NS1 due to overcrowding. Table 1-23. 2008 Western snowy plover reproductive success for each nesting location. Location Total Nests Nests Failed* Nests Hatched (# chicks) Fledglings Nest Site 1 37 1 36 (100) 33-83 Seasonal Ponds: 20 2 18 (51) 18 Cell 9 1 0 1 (3) 3 Cell 10 3 0 3 (8) 1 Cell 12 3 0 3 (8) 6 Cell 19 4 1 3 (9) 3 Cell 22 6 1 5 (15) 2 Road 3 0 3 (8) 3 Nest Site 3 5 0 5 (14) 3-5 North Tern Island 1 1 0 (0) 0 South Tern Island 4 1 3 (9) 3 Total 67 5 62 (174) 57-109 Merkel & Associates, Inc. 94
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