DOI: 10.5061/dryad.ttdz08mbd
title: Diet-manipulated body condition affects onset and speed of moult in Common Bulbuls in a tropical environment

description: Resource acquisition and allocation are central to life history theory,
 explaining the diversity of strategies among species as well as the
 distribution of events over the annual cycle. Moult is a major phase in
 the annual cycle of birds, but explanations for moult scheduling are
 heavily biased towards temperate systems with seasonal breeding patterns.
 Our research on a year-round breeding tropical bird, the Common Bulbul
 Pycnonotus barbatus (Bulbul), tests whether moult depends primarily on
 stored body reserves (capital) or on resources acquired throughout the
 moult period (income). Making this distinction elucidates trade-offs
 between moult and other annual cycle events, and responses to
 environmental change. We estimated moult start date and duration in
 captive Bulbuls whose body condition we experimentally manipulated by
 feeding them fruits or invertebrates 6–3 and 3-0 months before moult, and
 fruits or a mixed diet during moult. We studied free-living Bulbuls as the
 reference group. We found that moult onset is best predicted by the
 diet-manipulated condition just before moult, while moult duration is best
 predicted by the diet-manipulated condition during moult. Specifically,
 invertebrate-fed Bulbuls started moult 33 days later than fruit-fed
 Bulbuls. In addition, once invertebrate-fed bulbuls were switched to a
 mixed diet, they moulted 52 days quicker than fruit-fed Bulbuls, albeit
 still 36 days slower than free-living Bulbuls on average. Males started
 moult 15 days earlier and had a 20-day more variable start, but did not
 moult quicker than females on average. Our findings indicate that moult in
 Bulbuls is both income and capital-dependent, with moult initiation
 determined by individual body reserves and feather growth still occurring
 on a fruit-only diet, but significantly improved by dietary proteins from
 a mixed diet and in field Bulbuls. In this year-round breeding bird, moult
 seasonality is maintained in the absence of breeding but heavily
 influenced by foraging conditions.
description: # Diet-manipulated body condition affects the onset and speed of moult in
 Common Bulbuls in a tropical environment Dataset DOI:
 [10.5061/dryad.ttdz08mbd](https://doi.org/10.5061/dryad.ttdz08mbd) ##
 Description of the data and file structure ### Files and variables ####
 File: Diet_treatment_Groups.txt **Description of the variables** *
 Ring: Unique Ring number identifying individual birds * Switch: Diet
 treatment history of aviary birds 6-3 and 3-0 months before moult;
 fruit-fed throughout (FF), Invertebrate-fed throughout (II),
 Fruit-Invertebrate (FI), and Invertebrate-Fruit (IF) * Mid: Diet treatment
 3-0 months in aviary birds before moult; Fruits (F), and Invertebrates (I)
 * Long: Diet treatment 6-3 months in aviary birds before moult; Fruits
 (F), and Invertebrates (I) * During: Diet treatment during moult in aviary
 birds; Fruits (F), Mixed diet of fruits and invertebrates (I) #### File:
 Moult_scores_data.txt **Description of the variables** * Ring: Unique Ring
 number identifying individual birds * Sex: Two-level factor variable for
 males (M) and females (F) determined by molecular sexing in the
 laboratory. * Mass: Body mass measured in grams * Date: Capture date of
 bird * Scores: Scores of individual primary feathers; 5 for new, 0 for
 old, and 1-4 for different stages of growth. * Source: Two level factor
 variable for free living (Field) and aviary (Aviary) birds. * colfac: Four
 level factor combining sex and source of data; aviary males (MA), aviary
 females (FA), field males (MF) and field females (FF) ## Code/software All
 data analyses were carried out using R version 4.4.1