Random Measurement Error and Specimen Shrinkage in Short-tailed Shearwaters Puffinus Tenuirostris

• Published in: Marine ornithology Vol. 44; no. 1; pp. 11 - 20
• Main Author: Totterman, Stephen L.
• Format: Journal Article
• Language: English
• Published: 01.04.2016
• Subjects: Marine; Procellariidae; Puffinus tenuirostris
• ISSN: 1018-3337; 2074-1235
• DOI: 10.5038/2074-1235.44.1.1149

External biometrics have many applications in ornithology, and study skins are a major source of these measurements. However, measurements can be imprecise, and skins tend to shrink when they dry - two problems rarely investigated for petrels (family: Procellariidae). This study examined measurement error and shrinkage for 15 biometrics, using Short-tailed Shearwater Puffinus tenuirostris as the subject species. Random measurement error, defined as the variability of repeated measurements of a particular character taken on the same individual relative to its variability among individuals in a particular group, ranged from 0.3% for head plus bill length in dry specimens to 36% for tarsus width in freshly dead birds. Shrinkage of skin specimens stabilised within 2-5 months after preparation. Average fresh-dry shrinkage ranged from 0.2% for head plus bill to 12% for tarsus height. A new method was used to estimate shrinkage variability among individuals. "Shrinkage variation," defined as the proportion of unexplained variance (1 - r super(2)) in the correlation between paired fresh and dry measurements of a particular character after correcting for measurement error, ranged from 0% for wing chord to 33% for bill base width. More robust biometrics from this study were measurements of large, inflexible characters with well-defined measurement "landmarks."