Birds of the forest canopy are important components of tropical forest ecosystems, but difficulty of access or viewing into the canopy complicates their study. If ground methods are biased against canopy birds, as has been suggested, this bias could affect our understanding of forest ecology as well as biological monitoring and conservation practices. This study is the first to quantitatively compare results from ground- and canopy-based methods of censusing canopy birds. I used three methods to assess differences in ground-based and canopy-based methods for detecting forest birds in a 100-ha plot of lowland forest in northern Honduras: (1) point counts from the ground, (2) 22 repeat censuses from two canopy trees, and (3) single censuses from 22 canopy trees. I counted birds for a full annual cycle from April 2006 to April 2007 and recorded 157 species in over 4000 individual detections. Ground methods significantly underestimated species and familial richness as well as abundance of individuals in the canopy stratum. On the basis of these results, I predict that the use of ground methods alone misses 25 to 50% of the species richness for some migrant and resident families and underestimates the density of some species by as much as 25%. These findings highlight the risk of relying on ground-based methods for bird studies in structurally complex tropical forests; reliance on ground-based methods may negatively affect long-term biological monitoring and the setting of conservation priorities for tropical forests.