From March 1999 to August 2000, we used mist-netting, point counts, and radio-tracking to study habitat use, area requirements, and breeding of the Ivory-billed Woodcreeper Xiphorhynchus flavigaster in the tropical deciduous and semi-deciduous forest (arroyo forest) of the Chamela-Cuixmala Biosphere Reserve, western Mexico. The Ivory-billed Woodcreeper was a common, year-round resident. Breeding commenced at the end of the dry season (May) and continued during the rainy season through August. Our observations suggested that only the female builds the nest, incubates, and feeds nestlings. Ivory-billed Woodcreepers commonly foraged alone, but sometimes joined mixed-species flocks that passed through their territories, occasionally following army ant swarms. Home-range size varied from 6–36 ha, although most birds' home range was 15 ha or less. We did not find differences in home range size or mobility between the dry and rainy seasons, and we did not find a correlation between the size of the home range and the extent of semi-deciduous forest it included. We did not find evidence that suggested a greater use of semi-deciduous forest than of dry deciduous forest. We hypothesize that foraging habits and low competition could explain the lack of selection for semi-deciduous forest and the strong site fidelity exhibited by members of this species.