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

Bolsa Chica Lowlands Restoration Monitoring
2008 Annual Report
The reduced number of territories documented in 2008 could be related the to extensive inundation of
some cells by rainfall and tidal influence, though males were observed actively defending territories
that were inundated throughout and did not have higher, dry areas that other territories near zone edges
did. A clear trend between marsh inundation and usage by breeding birds was not observed.
Considerable movement by the birds between zones was noted, particularly with birds leaving to
forage for extended periods of time on the riprap, mudflat, and eelgrass of the FTB, likely resulting in
missed documentation of territories. To compensate for this to some extent, the surveys during Year 2
were conducted twice within the season. Although many individuals were mapped on the same
territories between surveys, a large number of territories were only observed on one survey or the
other, and there were 18% more territories on one date than the other. Examination of Figure 1-19
shows that although the total number of territories was relatively similar, the physical distribution of
territories between surveys was considerable in many locations. The most variable zones were located
in the FTB and MTB, which had 50% and 60% more territories on one date than another, respectively.
Zone 11 also had high variability and appeared to have a large number of territories in a small area. It
is expected that this variability will continue in future counts; however, continuation of the two-survey
approach may help provide a better picture of the range of usage of the site. It is also recommended
that the surveys be conducted in late February and March to reduce further complications related the
presence of dispersing juveniles. The Belding’s Savannah sparrow will normally return to their
breeding grounds in January and start breeding by March.
The density of territories of Belding’s Savannah sparrow at Bolsa Chica was low in comparison to
assessments of territory size at other sites. In their study of 54 territories at Sweetwater Marsh in San
Diego County, Powell and Collier (1998) found that territories ranged from 84.5m 2 to 999.5m 2 with an
average of approximately 475m 2 . Massey (1979) measured territories at Anaheim Bay in Orange
County that ranged between 250m 2 and 375m 2 at 14 territories. The estimation of territory size at
Bolsa Chica is much larger (1,836m 2 ), however this calculation takes into account all available
pickleweed habitat, including that which may not be occupied, and is therefore likely an overestimate.
The birds were sometimes observed defending territories in very close proximity to each other.
Several years of subsequent survey will need to be completed in order to better consider whether there
is a general decline in usage of the site by Belding’s Savannah sparrows, or if 2008 was just a year of
reduced nesting for other reasons. When the MTBs are fully operational with muted tidal connections
to the FTB, much of these zones will be inundated daily, with the higher edges of the zones remaining
dry. Future surveys will reveal the degree of usage these zone receive once they are tidal.
The quality of habitat in the FTB is expected to improve over time, as pickleweed becomes better
established at Rabbit Island and on the upper edge of the mudflats of the bench on the eastern shore.
California Least Tern and Western Snowy Plover Monitoring
Methodology
California least tern nest monitoring occurred on North Tern Island (NTI), South Tern Island (STI),
Nest Site 1 (NS1), Nest Site 2 (NS2), and Nest Site 3 (NS3) (Figure 0-1). NTI and STI are located in
Inner Bolsa Bay, outside of the project survey area, but are included in this report in order to give a
more complete understanding of tern reproductive success at the Bolsa Chica complex. NS1, NS2, and
NS3 were created by the restoration project. NS1 is in the FTB bordering the FTB and Inner Bolsa
Merkel & Associates, Inc. 91