Volume 44, No. 1

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Random measurement error and specimen shrinkage in Short-tailed Shearwaters Puffinus tenuirostris




TOTTERMAN, S.L. 2016. Random measurement error and specimen shrinkage in Short-tailed Shearwaters Puffinus tenuirostris. Marine Ornithology 44: 11 - 20

Received 21 July 2015, accepted 27 October 2015

Date Published: 2016/04/15
Date Online: 2017/02/28
Key words: biometrics, morphometrics, petrel, shearwater, measurement error, precision, shrinkage


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 - r2) 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."


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