Bonnie Peterson mist-netting
BELDING'S SAVANNAH SPARROWS
Abby N. Powell
Alaska Cooperative Fish and Wildlife Research Unit
Belding's Savannah Sparrows (Passerculus sandwichensis beldingi) are endemic only to southern California's and Baja California, Mexico's coastal salt marshes. In California, over 75% of the presettlement acreage of California's coastal wetlands have been lost to human development by means of dredging and filling, altering of tidal prisms, and damming of rivers. Belding's Savannah sparrows are nonmigratory and therefore dependent on salt marsh habitat during all months of the year. They are considered endangered by the State of California.
Populations of Belding's Savannah Sparrows in California are weakly correlated with habitat area, but there are few large wetland fragments remaining within their range. We conducted research in a fragmented wetland complex, and measured territory sizes and reproductive success of sparrows as well as habitat characteristics. We found no relationship between territory size and reproductive success, but all available habitat within the marshes was occupied, suggesting that even low quality habitat was being used. Although reproductive success was not strongly linked to vegetational characteristics, we found significant differences in reproductive success between birds nesting in large wetland complexes versus those nesting in small, isolated marshes. Sparrows nesting in a small, isolated salt marsh failed to produce fledglings over the course of the breeding season, but birds nesting in a small, connected wetland succeeded. Large wetland complexes are likely to be population sources, while small, isolated marshes act as population sinks. Because of the overall rarity of salt marsh habitats in this region, all sizes of remnant marshes are important, and therefore restoration planning should take place on a regional level.
For more details on this work, see:
Powell, A. N. and C. L. Collier. 1998. Reproductive success of Belding's Savannah sparrows in a highly fragmented landscape. Auk 115:508-513.
Abby Powell's home