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The effects of time of day and observer vantage points on recorded waterbird species diversity and numbers of individuals of each species (especially New Zealand scaup (Aythya novaeseelandiae), the most common species) from a New Zealand wetland were analysed statistically and compared using rank abundance plots. There were significant differences between counts of total numbers of species, total numbers of individuals, and numbers of New Zealand scaup made from three observer positions and this effect was attributed to differences in observer elevation. Time of day had no significant effect on total numbers of species, total numbers of individuals of all species, and numbers of New Zealand scaup counted. However, rank abundance plots indicated a time of day effect on counts made at the least elevated of the observer positions. Overall, these effects were sufficient to introduce bias into waterbird counts and to require they be assessed during long-term monitoring programmes.