2007 Annual Monitoring Report (pdf 16MB) - Bolsa Chica Lowlands ...
2007 Annual Monitoring Report (pdf 16MB) - Bolsa Chica Lowlands ... 2007 Annual Monitoring Report (pdf 16MB) - Bolsa Chica Lowlands ...
Western Snowy Plover Nesting at Bolsa Chica, 2007 December 2007STI was surveyed by vehicle from the West Levee Road and on foot as part of the least tern surveys.NTI is used primarily by nesting elegant terns (Thalasseus elegans) and black skimmers (Rynchopsniger).NS1, NS2, and NS3 are sectioned by markers which form the basis for data recording. NS1 issectioned south to north from A though CC. NS1 was surveyed by vehicle, in the same manner asthe Seasonal Ponds, either from the West Levee Road or the eastern slope of NS1. Due to nestingpatterns of least terns, black skimmers, and other terns, vehicle surveys were suspended mid-seasonother than from the West Levee Road north to Section M. NS1 was also partially surveyed on foot aspart of least tern surveys from CC south to M. Each nest located on NS1 was marked with a numberedtongue depressor and mapped for ease of relocation on subsequent visits. NS2 was surveyed by vehiclefrom the East Levee Road weekly using a spotting scope and once a month on foot. There was nonesting activity on NS2 this season. NS3 was surveyed by vehicle from the north end of the site.It was usually possible to follow the movements and determine the fate of chicks of each brood sincethere was dispersion over space and time sufficient to differentiate between broods. In a few casesbanded adults identified specific broods, although banding of chicks has not been done at BolsaChica since 2000. Broods were observed 3 - 5 days per week. These regular brood observationswere conducted to determine chick survival or fledgling production, as well as to detect movementbetween cells and use of specific cells for brood rearing.A range-wide, breeding season window survey was conducted at Bolsa Chica in May 2007. Thesurvey was conducted in the same manner as in previous years and in accordance to the guidelinesset out in the Recovery Plan for the Pacific Coast Population of the Western Snowy Plover (USFWS2007).PROTECTION FROM PREDATORSOnce a nest was discovered, a welded wire mini-exclosure (ME) was anchored in place over the topof the nest and left in place until the eggs in the nest hatched. The MEs used in previous years (2-inch x 4-inch welded wire mesh, forming a cube 20 inches on a side), when centered over the nest,provided a distance of about 10 inches that a coyote (Canis latrans) must extend its forelimb throughthe ME opening to reach the eggs. Since some coyotes have been able to reach the eggs with thisdimension, wider MEs (28-inch width on all four sides and 16-inch height) were deployed in 2006that require a 14-inch reach to rake eggs out of the center of the ME-protected area. All MEs in useduring 2007 were of the wider variety.Observations were made of potential predators during the surveys. Predator management actionswere then enacted commensurate with the threat to snowy plover breeding activity by that specificpredator. Predator management has been a necessary recovery action for the least tern for decades.In places, such as Bolsa Chica, where snowy plover nests in proximity to the least tern, predatormanagement activities on behalf of one species will also benefit the other species. In 2007, predatormanagement was undertaken by Wally Ross under contract to U. S. Fish and Wildlife Service(USFWS).Since June 2002, anchored MEs were usually deployed on every nest from the time the nest wasdiscovered until hatching. The American crow (Corvus brachyrhynchos) has been a serious,omnipresent predator of snowy plover eggs in previous years at Bolsa Chica. However, loss ofsnowy plover eggs to crows has been virtually eliminated due to the ME protection. When diggingMerkel & Associates, Inc. 6
Western Snowy Plover Nesting at Bolsa Chica, 2007 December 2007marks or egg loss evidence indicated visitation by a mammalian predator, drop-door traps weredeployed by predator control staff. When ground squirrels were implicated, commercial poison baitstations were also deployed.In 2007, simulated nest scrapes were constructed using quail eggs injected with bitter tasting, nonlethalcontents. This aversion technique has been successfully used in previous years in an attempt todeter coyote depredation of snowy plover eggs. (Several “digging” attempts, some successful atstealing plover eggs, some not, in 2005 suggested that coyotes were possibly cueing in on the MEsand learning to reach through the wire mesh to rake eggs out.) The use of “aversion” nests wasintended to teach coyotes to leave ME-covered eggs alone, without harming or removing coyotes.From February 1 through April, these “aversion nests”, 3 baited eggs each, were constructed in areaswhere snowy plovers had nested in the past. Some nests were covered with an ME and some werenot. The use of aversion nests in 2007 contributed to no egg predation in 2007. Chick predation bycoyote in 2007 will be discussed in a following section.RESULTS AND DISCUSSIONNEST DISTRIBUTION AND CHRONOLOGIESRainfall in 2007 was below average and both flats and prepared nest sites were available andunflooded throughout the nesting season. The distribution of nests indicates that NS1, the SeasonalPonds, and NS3 were the preferred nesting sites in 2007, with approximately 54% of all 2007 snowyplover nests located on the newly created NS1 and NS3 (Figure 2, Table 1). There was no nestingactivity on NS2 this season. STI attracted 4 nests.NS1 had 38% (19) of all nests. The Seasonal Ponds also had 38% of the nests but these were wellspaced in 7 different cells. The most utilized cells were Cell 11 (12%), Cell 32 (8%), Cell 13 (6%),and Cell 22 (6%). Distribution of nests on the Seasonal Ponds appears to fluctuate annually. Forexample, Cell 22 had 3 nests in 2007, 12 nests in 2006, and no nests in 2005. NS3 had 8 (16%)nests. Figure 2 shows the location of all nests located in the Bolsa Chica study area.Table 1. 2007 Nest, Nest Fate, and Reproductive Success Distribution by CellLocation Total Nests Nests Failed*Nests Hatched(# chicks)FledglingsNest Site 1 19 1 18 (50) 17Nest Site 3 8 0 8 (21) 3Cell 11 6 0 6 (17) 4Cell 32 4 1 3 (7) 0South Tern Island 4 0 4 (11) 0Cell 13 3 0 3 (8) 0Cell 22 3 0 3 (9) 13 other areas 3 0 3 (7) 0Total 50 2 48 (130) 25*Both nest failures in 2007 were due to nest abandonment.Appendix 1 provides the cell location, start and end dates, nest fates, eggs and chicks produced foreach nest.Merkel & Associates, Inc. 7
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Western Snowy Plover Nesting at <strong>Bolsa</strong> <strong>Chica</strong>, <strong>2007</strong> December <strong>2007</strong>marks or egg loss evidence indicated visitation by a mammalian predator, drop-door traps weredeployed by predator control staff. When ground squirrels were implicated, commercial poison baitstations were also deployed.In <strong>2007</strong>, simulated nest scrapes were constructed using quail eggs injected with bitter tasting, nonlethalcontents. This aversion technique has been successfully used in previous years in an attempt todeter coyote depredation of snowy plover eggs. (Several “digging” attempts, some successful atstealing plover eggs, some not, in 2005 suggested that coyotes were possibly cueing in on the MEsand learning to reach through the wire mesh to rake eggs out.) The use of “aversion” nests wasintended to teach coyotes to leave ME-covered eggs alone, without harming or removing coyotes.From February 1 through April, these “aversion nests”, 3 baited eggs each, were constructed in areaswhere snowy plovers had nested in the past. Some nests were covered with an ME and some werenot. The use of aversion nests in <strong>2007</strong> contributed to no egg predation in <strong>2007</strong>. Chick predation bycoyote in <strong>2007</strong> will be discussed in a following section.RESULTS AND DISCUSSIONNEST DISTRIBUTION AND CHRONOLOGIESRainfall in <strong>2007</strong> was below average and both flats and prepared nest sites were available andunflooded throughout the nesting season. The distribution of nests indicates that NS1, the SeasonalPonds, and NS3 were the preferred nesting sites in <strong>2007</strong>, with approximately 54% of all <strong>2007</strong> snowyplover nests located on the newly created NS1 and NS3 (Figure 2, Table 1). There was no nestingactivity on NS2 this season. STI attracted 4 nests.NS1 had 38% (19) of all nests. The Seasonal Ponds also had 38% of the nests but these were wellspaced in 7 different cells. The most utilized cells were Cell 11 (12%), Cell 32 (8%), Cell 13 (6%),and Cell 22 (6%). Distribution of nests on the Seasonal Ponds appears to fluctuate annually. Forexample, Cell 22 had 3 nests in <strong>2007</strong>, 12 nests in 2006, and no nests in 2005. NS3 had 8 (16%)nests. Figure 2 shows the location of all nests located in the <strong>Bolsa</strong> <strong>Chica</strong> study area.Table 1. <strong>2007</strong> Nest, Nest Fate, and Reproductive Success Distribution by CellLocation Total Nests Nests Failed*Nests Hatched(# chicks)FledglingsNest Site 1 19 1 18 (50) 17Nest Site 3 8 0 8 (21) 3Cell 11 6 0 6 (17) 4Cell 32 4 1 3 (7) 0South Tern Island 4 0 4 (11) 0Cell 13 3 0 3 (8) 0Cell 22 3 0 3 (9) 13 other areas 3 0 3 (7) 0Total 50 2 48 (130) 25*Both nest failures in <strong>2007</strong> were due to nest abandonment.Appendix 1 provides the cell location, start and end dates, nest fates, eggs and chicks produced foreach nest.Merkel & Associates, Inc. 7
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