Waterbird communities in rice fields subjected to different post-harvest treatments

In California's Sacramento Valley, the potential value of rice fields as ha bitat for waterbirds may vary with harvest method, post harvest treatment o f rice straw (chopped, burned, plowed), and extent of flooding. Re cent cha nges in rice harvesting methods (i.e., use of stripper-headers) and a legis lative mandate to decrease burning of rice straw after harvest may alter ha bitat availability and use. Thus, we investigated species richness and comm unity composition of nonbreeding waterbirds during October-March 1993-94 an d 1994-95 in rice fields of the northern Sacramento Valley. Most (85-91% of land area) rice was conventionally harvested (i.e., cutter bar), and the r emainder was stripped. Rice straw was left untreated in more than half of f ields (52% in 1994 and 54% in 1995), especially in stripped fields (56-70%) . In fields where farmers treated straw. the most common management methods were plowing (15-21%),burning (19-24%),and chopping (3-5%). Fields became increasingly wet from October through March as seasonal precipitation accum ulated and farmers flooded fields to facilitate straw decomposition and pro vide habitat for ducks. Species richness of waterbirds was greater (P < 0.0 02) in conventionally-harvested fields than in stripped fields; within harv est methods, species richness was consistently greater (P < 0.01) in floode d than non-flooded fields. By contrast, species richness did trot differ am ong straw treatments (P > 0.23). Species rich ness in stripped fields proba bly was low because foraging opportunities were limited by tall dense straw , decreased grain density, and infrequent flooding. We recommend that land managers wishing to provide habitat for a diverse waterbird community harve st rice using conventional methods and flood fields shallowly.