Divergent primary moult-A rare moult sequence among Western Palaearctic passerines.

Gregorio Moreno-Rueda,Yosef Kiat

doi:10.1371/journal.pone.0187282

Abstract

Wing morphology strongly affects flight performance which may consequently decline during feather moult due to the creation of feather gaps in the wing. Hence, the size and shape of moult-related wing gap may directly affect flight capacity. Here I examined the rare divergent primary moult sequence compared to the more common descendant moult sequence. In the divergent moult, the focus of primary moult is shifted from P1 (primary feather numbered descendantly) to another primary between P2 and P5, and then primaries are moulted in two concurrent waves, one descendant and the other ascendant. The result of this rare moult sequence is the splitting of the wing gap to two smaller gaps. Using a large moult database including 6,763 individuals of 32 Western Palaearctic passerine species, I found evidence of divergent moult only among 27 individuals of 12 species. I examined the speed of wing-feather moult for each individual that moulted divergently compared to a control group of individuals at the same moult stage which moulted following the common descending sequence. The results indicate that the sequence of primary moult and moult speed are correlated. Individuals which moulted divergently moulted their primaries with higher moult speed than descendant moulters. The applicability of this study is weakened by the dearth of moult data, thus making it difficult to draw conclusions for a large range of species. Ornithologists and bird ringers are therefore encouraged to collect more basic moult data during their field study.

Highlights

Data Availability Statement: The data are available from the Open Science Framework database
The moult database included a total of 6,763 individuals from 32 Western Palaearctic passerine species: 2,218 individuals from 32 species were sampled during the post-breeding moult and 4,545 individuals from 25 species were sampled during the post-juvenile moult
The sample size of species included in the database used in this study and the evidence for the divergent primary moult sequence

Summary

Introduction

Data Availability Statement: The data are available from the Open Science Framework database (https://osf.io/g9ecv/). Unlike other keratin structures, such as hair and claws, feathers cannot be renewed continuously from their base and are replaced only following the shedding of old feathers This shedding occurs before new replacement feathers are fully developed, and this time lag between feather shedding and the full growth of the new feather creates a feather gap. I hypothesized that in cases of divergent sequence moult, the aerodynamic cost of wing moult is lower as a result of splitting the moult-related feather gap (two small gaps instead of one larger gap). For this reason, I predicted that the divergent sequence is correlated with higher wing-feather moult speed than the commonly used descendant sequence. The splitting of the moult-related feather gap allows birds to moult their primaries at a high speed with a reduction in the aerodynamic costs associated with moult

Methods

Results

Discussion