We have been made aware that the estimate of individual repeatability that we used in our study (i.e. the intraclass correlation coefficient) overestimates repeatability, and that calculating repeatability using the analysis of variance-based method, as described by Lessells & Boag ), is a more appropriate estimate. Consequently, we have recalculated repeatability using this more appropriate approach and describe these changes below.
When pooling the behaviour of urban and rural birds, there was a non-significant trend towards low repeatability of territorial aggression score (r = 0.21, F52,105 = 1.54, p = 0.06). However, when considering each population alone there was a trend toward repeatability in rural, but not urban birds (urban: r = 0.02, F24,49 = 1.04, p = 0.46; rural: r = 0.28, F27,55 = 1.78, p = 0.07). Overall, when considering both populations simultaneously or each alone, territorial aggression score was not significantly repeatable within individuals.
In our study, we considered ‘repeatability’ to be the proportion of variation that is reproducible among repeated measurements. By contrast, we use the term ‘consistency’ to refer to the consistent difference in population means when measuring the same individuals at multiple times. Although the territorial aggression of individual male song sparrows was not individually repeatable, urban male song sparrows were more territorially aggressive than their rural counterparts at both time points, making the difference in behaviour across habitat types consistent. Thus, our corrected results show consistency in population differences without individual repeatability of behavioural scores. Further, our title should read ‘…elevated territorial aggression of urban song sparrows is consistent within a breeding period’ in reference to the consistent difference in population means, not the proportion of variation that is reproducible among repeated measurements.
Additional research is required to determine whether there is a habitat-related difference in the repeatability of territorial aggression in male song sparrows, which our re-analyses and prior work [2,3] suggest may be the case.
- © 2016 The Author(s)
Published by the Royal Society. All rights reserved.