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 2007The State and Federal Endangered California least tern also nests at Bolsa Chica, usually on STI. In2006, they nested on STI and on the new NS1. Snowy plover egg-laying typically begins severalweeks before the least tern begins its egg-laying. This has been the case at Bolsa Chica. The twospecies tolerate the co-location of their nests, although inter-specific antagonism between adults andbetween adults and chicks was occasionally evident.Black skimmers and elegant terns alsonested on NS1 in 2007. Both speciestypically nest on NTI but the blackskimmers and some of the elegantterns abandoned that nesting site inJune and moved to NS1. It isunknown if this is a trend or whetherthe skimmers will return to NTI insubsequent years. The tight colonialstyle of nesting of the elegant ternsand the black skimmers did notexclude the snowy plover from anyportion of the nesting area. However,it is unknown whether their presenceon NS1 had an effect on the overallreproductive success of the snowyplover once the nests hatched and thechicks left the protection of the ME.Elegant terns surrounding an active snowy plover nest protected by an ME.Photo: P. KnappIn 2007, the first plover nest was initiated April 9, later than in the preceding 10 years of the study(Figure 3). Even with this late start, 10 (20%) nests had been initiated by May 1, which is a greaternumber of nests in all previous years with the exception of 2004 (18, 27.7%) and 2005 (12, 23.5%).Half of the nests had been initiated by May 28. The active nest chronology in Figure 4 shows a fairlysteady nest count from early May until mid-July which is a normal trend at Bolsa Chica with theexception of 2004 when breeding had 2 peaks of nesting. Although the trend was steady, there werefewer nests during the prime nesting period than in the past 2 years, but a greater number than in the97-03 average. The last nest hatched on August 12, which is comparable or later than in previousyears (Figure 3).EGG, CHICK, AND FLEDGLING PRODUCTIONAll 50 nests in 2007 were judged to be completed clutches. Seven completed clutches were 2-eggclutches, while 43 were 3-egg clutches (Appendix 1). None of the 50 total nest attempts were lost topredators, however, 2 complete clutches, one with 3 eggs and one with 2 eggs, failed to hatch. The 2nests that were abandoned appear to be unrelated to each other. One was located on NS1 and wasfound on June 8. The second abandoned nest was located on Cell 32 and was found on June 28.At least 143 snowy plover eggs were produced at Bolsa Chica in 2007, with 13 eggs abandoned orfailing to hatch. From the 143 total eggs produced, 130 chicks were produced. Of these 130 totalchicks produced in 2007, only a maximum of 25 chicks (19.2%) were estimated to have survived tofledge (Table 2). This high degree of chick loss must be considered severe.Merkel & Associates, Inc. 8
Western Snowy Plover Nesting at Bolsa Chica, 2007 December 2007Figure 3. 1997-2007 Bolsa Chica Active Nest ChronologyForty-eight nests survived to hatch (hatching success rate of 96% or nest failure rate of 4%). This isthe highest hatching success rate since surveys began in 1997 and the lowest fledgling rate since1999 (Figure 6). These figures represent continued high nest numbers at Bolsa Chica, but a decliningfledgling rate (Figure 5).In 2007, 8 dead eggs were observed, excluding eggs in abandoned nests. With 143 total eggs laid in2007, 5.6% of total eggs were dead eggs. No analysis was made of these 8 dead eggs to determinewhether they were sterile or had exhibited some degree of development before expiration. Includingthe 2007 breeding season, the ten-year average percent of dead eggs is 4.2% (60/437).The total fledgling count was more difficult to determine in 2007 than in past years due toinsufficient geographic and temporal separation of broods, hampering efforts to maintain broodidentity all the way to fledging during the middle part of the season. Most broods were hard tofollow due to rarity of banded parents and continual reconfiguration of brood territories orboundaries. Through field observation, we did conclude that a maximum total of 25 chicks wereproduced in the 2007 breeding season.Merkel & Associates, Inc. 9
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Western Snowy Plover Nesting at <strong>Bolsa</strong> <strong>Chica</strong>, <strong>2007</strong> December <strong>2007</strong>Figure 3. 1997-<strong>2007</strong> <strong>Bolsa</strong> <strong>Chica</strong> Active Nest ChronologyForty-eight nests survived to hatch (hatching success rate of 96% or nest failure rate of 4%). This isthe highest hatching success rate since surveys began in 1997 and the lowest fledgling rate since1999 (Figure 6). These figures represent continued high nest numbers at <strong>Bolsa</strong> <strong>Chica</strong>, but a decliningfledgling rate (Figure 5).In <strong>2007</strong>, 8 dead eggs were observed, excluding eggs in abandoned nests. With 143 total eggs laid in<strong>2007</strong>, 5.6% of total eggs were dead eggs. No analysis was made of these 8 dead eggs to determinewhether they were sterile or had exhibited some degree of development before expiration. Includingthe <strong>2007</strong> breeding season, the ten-year average percent of dead eggs is 4.2% (60/437).The total fledgling count was more difficult to determine in <strong>2007</strong> than in past years due toinsufficient geographic and temporal separation of broods, hampering efforts to maintain broodidentity all the way to fledging during the middle part of the season. Most broods were hard tofollow due to rarity of banded parents and continual reconfiguration of brood territories orboundaries. Through field observation, we did conclude that a maximum total of 25 chicks wereproduced in the <strong>2007</strong> breeding season.Merkel & Associates, Inc. 9
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