Body-condition indices are repeatable across short, but not long, time periods in crimson finches Neochmia phaeton.

Abstract

Abstract It is common in evolutionary ecology to interpret body-condition indices as indicators of individual quality, but this hypothesized relationship has been questioned and remains poorly validated. Here, we test one of the fundamental predictions of this condition-quality hypothesis, that relative-condition indices are repeatable within individuals, that is, that the index score of an individual relative to others is consistent over time. We sampled crimson finches (Neochmia phaeton) for seven commonly used condition indices and tested whether individual condition relative to conspecifics in the same context (e.g., breeding stage) was repeatable. We calculated the relative indices' repeatability across several temporal scales, from short (within breeding season) to long (more than 2 yr) time periods, as well as without consideration of timescale. Most relative-condition indices were repeatable when sampled without consideration of timescale, all were repeatable within a short time period, and none were repeatable over the longest time period. This provides only partial support for the condition-quality hypothesis, because although relative-condition indices were generally repeatable, this was primarily attributed to short-term, instead of long-term, repeatability. Condition indices may be meaningful indicators of short-term survival or fitness potential, but our findings are inconsistent with the idea that condition indices are indicators of inherent individual quality.