干旱区生态环境知识资源中心

Populations of North American grassland birds have suffered drastic declines. The causes of these declines are only partially understood and may vary among regions. During the 2004 and 2005 breeding seasons we recorded survival information from 220 nests of four bird species in nine study sites representing three habitat types of the desert grasslands of central Mexico, where grassland birds had not yet been studied. We predicted that land-use change from shortgrass steppe to heavily grazed savannah-type grasslands and agriculture would negatively affect nesting success, number of fledglings and nest abundance. We also examined temporal effects on reproductive success. We found some evidence that nest survival of savannah sparrows Passerculus sandwichensis, loggerhead shrikes Lanius ludovicianus and white-winged doves Zenaida asiatica varied with date, and that nest survival of the dove was lowest in agricultural sites. However, confidence intervals were large, suggesting that other variables were also important. Whereas white-winged dove nests were notably more abundant in agricultural areas compared to the other habitat types, western meadowlark Sturnella neglecta nests were not found in agricultural areas. Ploughing caused the largest proportion of nest failures in agricultural areas and, on average, all species fledged fewer young per nest in agricultural areas. Therefore, minimizing agriculture and adjusting harvest times could enhance conservation of grassland-nesting birds in central Mexico. Our study also suggests that inter-annual variation in rainfall can change the onset of nesting by at least 2 months.