The Ecology of Tijuana Estuary, California: An Estuarine Profile

More documents

Recommendations

Info

Table 10. The shorebird species sampled by Boland (1981 1 and abbreviations of their common names. Nomenclature from AOU (1 983). -- Species SANDPIPERS Least sandpiper, Calidris minutilla Western Sandpiper, C. mauri Sanderling, C. alba Dunlin, C. alpine Red knot. C. canutus Ruddy turnstone. Arenaria inferpres Short-billed dowitcher, Limnodromus griseus' Long-billed dowitcher, L. scolopaceus* Willet, Catopfrophorus semipalmatus Whimbrel. Numenius phaeopus Marbled godwit, Limosa fedoa Long-billed curlew, N. americanus WADERS Wilson's phalarope, Phalaropus tricolor Northern phalarope, P lobatus Greater yellowlegs. Tringa melanoleuca Black-necked stilt, Himantopus mexicanus American avocet, Recurvirostra americana PLOVERS Snowy plover, Charadrius alexandrinus Semipalmated plover, C. semipalmatus Killdeer, C. vociferus Black-bellied plover, Pluvialus squatarola Code LS WS S DUN RK RT DOW DOW WIL WH MG LBC WP N P GYL BNS A A SP SPP K BBP 'The short-billed dowitcher and long-billed dowitcher are difficult to d~stinguish in the field and were combirled by Soland. Figure 44. Field sites used in Boland's (1981) study of shorebirds. (1981) focused on habitat utilization and feeding strategies. He recorded 21 species (scientific names provided in Table 10) and observed feeding behavior in five tidal habitats (Figure 44): steep wave-swept beach, sandflat, mudflat, mudbanks, and salt marsh. Data on abundance for all five habitats are included here for comparison, while feeding strategies on the beach are discussed in Section 3.8. The estuarine channels were by far the most heavily used foraging habitat in 1979-80 (Table 1 1). The shorebird community is highly seasonal in its occurrence, with highest densities found in winter. The times of arrival and departure of different species did not coincide during Boland's study. Differences were great enough that he was able to separate early from late fall-arrivi~g species and species that wintered at Tijuana Estuary from those that migrated further south (Table 12). Only three shorebirds (snowy plover, killdeer, and black-necked stilt) used Tijuana Estuary for breeding. Boland found that many more species and individuals fed on sandflats and mudflats than mudbanks, beach, or salt marsh areas (Table 13). Willets and western sandpipers dominated the data set, and both were found primarily on the sandflat. Dowitchers, which were the most abundant species in December-January, were common on both sandflats and mudflats. The species that fed in the same habitats appeared to partition their activities among different sediment depths and water depths (Figure 45). Waders, such as the greater yellowlegs, fed on items in the water column and on the sediment surface. Long-billed sandpipers (e.g., marbled godwit) probed deep into the sediment, often wading deeply into the water. Short-billed sandprpers like the western sandpiper probed less deep and remained near the edge of the water; while plovers (e.g., semipalmated plover) fed on the surface of moist-to-dry sediments. Boland concluded that the length of leg and bill determined the feeding strategy of each species,
-" and that the community was composed of species that differed in leg and bill lengths (Figure 46). Such different morphologies should reduce competitive interactions by reducing overlap in where the birds feed. However, as Boland pointed out, tides constantly change the depth of water so that longer and shorter legged birds that take foods from the same spots do so at different times. Thus, they cannot avoid competition where food supplies are limiting. Boland (Universiy of California, Los Angeles, pers. comm.) has begun to test these ideas through gut analyses of eight shorebird species and quantltatlve analyses of ~nvertebrate food availability at Morro Bay, Californ~a (central California). While there were no studies that quantified the effect of estuary mouth closure on shorebirds, Jorgensen (pers. comm.) estimates that shorebird abundance was reduced 70% during this period, an effect attributed to the absence of tidal submergence and exposure of bottom sediments. Since the sandy shore habitat was not affected by the obstruction of the estuary mouth, some species may have shifted to this habitat for feeding or may have migrated to other intertidal flats in the region. The return of shorebirds to Tijuana Estuary has been much more rapid than that of the former dominant bivalves, and a diverse community utilized the mudflat and sandflat habitats during the fall 1985 migration. The potential for recovery Tabfe 11. Principal foraging habitats for the shorebirds at Tijuana Estuary, as identified by Boland (1 981 1. Shore. Shore & Marsh & Marsh. & Shore Chanriels Channels Charjnels Channels Sanderling Ruddy turnstone Least sandpiper Long-btlled Willet Wtiinrbrel Marbled godwtt Western sandpiper curlew Snowy plover Dunlin Black bellled Red knot plover Dow~tcher Wilson s phalarope Northern phalarope Greater yellowlegs Black-necked stg~lt American avocet Semtpalmated plover Ktlldeer - - Table 12. Seasonal occurrences of shoreb~rds at Tijuana Estuary, as deterrntned by Boland (1 981 1. Early drrlvirig Early arrsvlng Late arriving Breeding & Breedtng inigrants & wintering 8 wintcrcng w~ntertng rn~grant - * - -a- - Ruddy turnstone Least sandpiper Dunlin Snowy plover Black-necked Whimbrel Western sandpiper Arner~can Killdeer stilt Wilson s phalarope Sanderl~ng avocet Northern phalarope Red knot Sernlpdirrtaied Dciwitther plover Willet Marbled godw~t Long-billed curlew Greater yellowlegs Black-bellfed plover -- -- -- - - - - --- - - - - - .
Page 1 and 2:
June 1986 I THE ECOLOGY OF TIJUANA
Page 3 and 4:
The findings in this report are not
Page 5 and 6:
CONVERSION TABLE Metric to U.S. Cus
Page 7 and 8:
Page 4.5 Energy Flow ..............
Page 9 and 10:
Number Page The channel fish cornrn
Page 11 and 12: ACKNOWLEDGMENTS The California Sea
Page 13 and 14: Figure 1. Lacatlcrn of 71juana Estu
Page 15 and 16: Figure 3. Map6 of Tijuana Estuary s
Page 17 and 18: FI(I(uPc$ 4. Wei&rahOt@ patt@rns of
Page 19 and 20: also limitrng Hot, dry desert winds
Page 21 and 22: 2.3 LAND USE HlSPQWV Through exami!
Page 23 and 24: The nearby bridge remained, and ext
Page 25 and 26: flushing until mid-December 1984. E
Page 27 and 28: with seawater. Even in years with s
Page 29 and 30: flats ~n winter but not in midsumme
Page 31 and 32: Each "island" of higher topography
Page 33 and 34: The vegetation and soils of the upp
Page 35 and 36: populations (Massey 1979) The brrds
Page 37 and 38: c~n~entrations of insects, especial
Page 39 and 40: Frgufe 29. The Ifght-footed clapper
Page 41 and 42: Figure 30. During winter (above) th
Page 43 and 44: anlmal footprints, In the hardpan f
Page 45 and 46: Tijuana Estuary salt marsh Such exp
Page 47 and 48: Frgura 36 The etraracrel an& tidal
Page 49 and 50: ^_ _I __"___I _-a_. -- fable 7. Inv
Page 51 and 52: Pre- 1980 (excluding Hosrner Rehse
Page 53 and 54: Table 8. Average density (number/m2
Page 55 and 56: changes in envlronment has not been
Page 57 and 58: was dominated by goby species, Cali
Page 59 and 60: compared the ,chthyoplankton commun
Page 61: Figure 43, Birds of the intertidal
Page 65 and 66: Willet (1 73) i - Water Depth (cm)
Page 67 and 68: Table 14. Early information on dune
Page 69 and 70: Figure 48. Birds that nest on the s
Page 71 and 72: CHAPTER 4 ECOSYSTEM FldNCTlONlNG St
Page 73 and 74: were no? irght-saturated untri expo
Page 75 and 76: Table 17. Conceptual model of chann
Page 77 and 78: Table 19. Net aboveground productiv
Page 79 and 80: _I___ I__-~--- 4.4.1 Nitragen Fluxe
Page 81 and 82: i i t 1 1 I Table 22. Standing crop
Page 83 and 84: calculated from chlorophyll a measu
Page 85 and 86: Dissolved Organic Biomass Carbon De
Page 87 and 88: CHAPTER 5 THE ROLE OF DISTURBANCES
Page 89 and 90: Table 25. Changes in elevation in t
Page 91 and 92: Table 26. Change in pickleweed cano
Page 93 and 94: Table 27. Occurrence (in circular 0
Page 95 and 96: perennials can survive long periods
Page 97 and 98: An experiment was designed to deter
Page 99 and 100: CHAPTER 6 MANAGEMENT CONSIDERATIONS
Page 101 and 102: Closely associated with the researc
Page 103 and 104: c. Dredging at Tijuana Estuary will
Page 105 and 106: Table 30. Predicted impacts of redu
Page 107 and 108: footed clapper rails; the picklewee
Page 109 and 110: overwashas, and slabiiizatran rs rl
Page 112 and 113:
REFERENCES Allen, L.G. 1980. Struct
Page 114 and 115:
Minsky, D. 1984. California least t
Page 116:
30272 -101 REPORT WUMENTATION 1. RE
show all

The Ecology of Tijuana Estuary, California: An Estuarine Profile

Create successful ePaper yourself

Delete template?

Save as template?