summaryTropical forests are disappearing very rapidly, so there is often not time for thorough quantitative studies. It therefore becomes increasingly important to use rapid, reliable and informative methods which are also adjusted to tropical logistic constraints. In this paper we use data from seven dry and semi-humid temperate forest patches in Bolivia and three humid, temperate forests in Ecuador to estimate the efficiency, potential biases and the amount of information obtained by the 20-species list method, which we applied in a rapid assessment of avian species richness. Even when used without any standardizations, 20-species lists produce more data than simple species lists, particularly on the amount of survey effort, the order of species richness, the relative abundances of species and the α-diversity index. This approach precludes comparisons with lists from other sites. However, when applied with standardization of area, altitude and effort, the method is neither easier to use nor superior to point counts (based upon vocalizations) in combination with dawn chorus tape-recordings. In species-poor habitats, it is more appropriate to use lists of fewer species. The method is recommended due to its simplicity and the increased quantity of information produced, but it requires a reasonable amount of observer competence and is therefore unfit for use by people ignorant of local avifaunas.

Hpeg, J . T., Karnick, E. S. & Frdander, A . 1994. Scanning electron microscopy of mouth appendages in six species of barnacles (Crustacea Cirripedia Thoracica).-Acta Zoologica (Stockholm) 75: 337-357.The morphology and setation of mouth appendages (trophi) are investigated with scanning electron microscopy in the balanomorph barnacles Semibalanus balanoides, Bafanus balanus and B. nubilus and in the pedunculate barnacles Pollicipes polymerus, P. cornucopia and Lepas anatifera. It is difficult to uphold a clearcut distinction between denticles and setae and several types of setae also intergrade with each other. The trophi of Pollicipes polymerus and P. cornucopia have the most 'generalized' morphology. The palps of Pollicipes and L. anatifera are simpler than those in balanomorphs and carry a single type of sera. In L. anatifera the mandibles and maxillules are adapted to a semi-predatory feeding habit by carrying large, pointed teeth, but this species lacks the foliate-serrate setae which populate the pa@ in the other species studied. Compared with Pollicipes and Lepas, the three balanomorphs have palps with a complex setation. The trophi in S. balanoides differ from the two species of Balanus in numerous features of setation and denticulation, notably in having the palps populated by plumodenticulate setae homologous to purely denticulated types in Balanus. It is suggested that SEM studies of barnacle trophi will provide characters of use in estimating phylogeny.

Since our paper on the efficiency and biases of 20-species lists (Poulsen et al. 1997) went to press we have recognized a further two biases in the method, after discussions with C. Rahbek. We remarked in our paper that the abundance curves were behaving rather strangely and that “the importance of these phenomena needs to be investigated in more detail”. The behaviour may be due to the method setting constraints on the highest possible frequency, namely the number of times a species occurs in 20-species lists. This could affect the calculation of the expected abundances and hence the a-index. Another bias must be the indirect way of determining the relative abundances, ignoring the true number of individuals. A species with many individuals will be given the same relative abundance as a species with very few individuals if both species occur in the same number of 20-species lists. We do not know the importance of these constraints but recommend that the method is not used until the results of a current computer modelling study examining its efficiency (S. Herzog and M. Kessler pers. comm.) are known.