Seasonal changes in resource use and reproduction within a guild of nectar-feeding phyllostomid bats were studied between 2002 and 2004 in a west Mexican dry forest using mist-net captures and diet analysis over 82 nights during both dry and wet seasons. The local guild consisted of three resident species, Glossophaga soricina, Leptonycteris yerbabuenae, Musonycteris harrisoni, and of Anoura geoffroyi, which was mostly captured during the wet season. The proportion of L. yerbabuenae females more than doubled during the dry season. Diet was accessed by identifying the pollen collected from the bats' bodies and by analysis of faecal material. Bats used at least 28 different nectar plants over the year. In the dry season, 91.9% of all bats carried pollen while only 54.6% did so in the wet season. Bat individuals used the highest number of plant species during the dry season, mainly the cactus Pachycereus pecten-aboriginum, various Bombacaceae and the Capparaceae Cleome spinosa. Niche overlap was higher in the dry season than in the wet season. Musonycteris harrisoni and Leptonycteris yerbabuenae showed the largest overlap and both relied heavily on cactus flowers, whereas G. soricina supplemented its nectar diet with fruits. While reproductive females of most species were found only in the flower-rich dry season, G. soricina showed a bimodal reproductive pattern.