Primary moult of adult Laughing Doves Spilopelia senegalensis: introduction of the relative duration index and a comparison of moult indices

Abstract

A new moult index, the relative duration index (RDI), was developed to quantify progress through moult using the Underhill–Zucchini model of primary avian moult, with the Laughing Dove Spilopelia senegalensis as a case study. The RDI weights individual primaries in accordance with their estimated relative moult durations in the same way that proportion feather mass grown (PFMG) weights primaries in accordance with their relative masses. A sample of 1 893 moult records of adult Laughing Doves was used to study their primary moult. Moult parameters were estimated for three moult indices: the traditional moult score (TMS), PFMG and the RDI, and for each of the 10 primaries. Comparing the moult parameter estimates of each of the three indices to their respective cumulative growth curves obtained from the progression of moult of individual primaries, PFMG had the closest fit. However, any of the three moult indices would give satisfactory results for the Laughing Dove. Laughing Doves had an estimated primary moult duration of 215 days, with mean start and end dates of 3 November and 6 June, respectively. The standard deviation parameter was 66 days, which implies a lack of synchronisation of moult in adult doves. It was hypothesised that the RDI might be an appropriate moult index for species that moult one feather at a time and for which the individual moult durations are not proportional to their mass, as seen in Laughing Doves. However, this was not the case as PFMG provided the best fit. The RDI might also prove to be an appropriate moult index for species that moult multiple feathers simultaneously during part of the moult period and these feathers grow more slowly than when fewer feathers are moulting simultaneously.