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Evaluating the validity of using unverified indices of body condition

Journal of Avian Biology

By:
, , and
DOI: 10.1111/j.1600-048X.2008.04462.x

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Abstract

Condition indices are commonly used in an attempt to link body condition of birds to ecological variables of interest, including demographic attributes such as survival and reproduction. Most indices are based on body mass adjusted for structural body size, calculated as simple ratios or residuals from regressions. However, condition indices are often applied without confirming their predictive value (i.e., without being validated against measured values of fat and protein), which we term 'unverified' use. We evaluated the ability of a number of unverified indices frequently found in the literature to predict absolute and proportional levels of fat and protein across five species of waterfowl. Among indices we considered, those accounting for body size never predicted absolute protein more precisely than body mass, however, some indices improved predictability of fat, although the form of the best index varied by species. Further, the gain in precision by using a condition index to predict either absolute or percent fat was minimal (rise in r2???0.13), and in many cases model fit was actually reduced. Our data agrees with previous assertions that the assumption that indices provide more precise indicators of body condition than body mass alone is often invalid. We strongly discourage the use of unverified indices, because subjectively selecting indices likely does little to improve precision and might in fact decrease predictability relative to using body mass alone. ?? 2009 The Authors.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Evaluating the validity of using unverified indices of body condition
Series title:
Journal of Avian Biology
DOI:
10.1111/j.1600-048X.2008.04462.x
Volume
40
Issue:
1
Year Published:
2009
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Avian Biology
First page:
49
Last page:
56
Number of Pages:
8