DOI: 10.5061/dryad.612jm64kb
title: Stable immune function during moult regardless of age-specific moulting strategy in a European passerine

description: This file contains data on moulting status, moult progression and baseline
 innate immune function (bacterial-killing ability, lysis, agglutination,
 haptoglobin concentration) in adult and juvenile blackbirds captured in
 Lund, southern Sweden, in 2019–2020 (Aug–Oct). Moult, the regular
 replacement of feathers, is a resource-intensive avian annual cycle stage.
 Resource allocation to support feather regrowth may require downregulation
 of other physiological processes, such as immune function, which is
 critical for preventing disease-related mortality. At the same time, the
 emergence of new feathers may increase the risk of skin injury and
 infection, potentially requiring sustained or enhanced immunocompetence
 during this period. While previous studies have compared immune function
 between moulting and non-moulting individuals, it remains unclear how
 immune function changes throughout moult. Moreover, little is known about
 how these dynamics manifest in age-specific moulting strategies, such as
 the partial juvenile or complete adult moult typical of most passerines.
 Here, we investigated how immune function relates to moult progression in
 Eurasian Blackbirds (Turdus merula), focusing on post-juvenile body moult
 in first-year birds and on primary wing feather moult in adults. We also
 assessed immune function prior to moult to determine whether immunity is
 down- or upregulated during moult. Four functionally distinct parameters
 of baseline innate immune function were quantified: bacterial-killing
 ability, complement activity, natural antibody titres, and haptoglobin
 concentration. We did not detect differences in any immune parameter
 between moulting and not-yet-moulting adults, and immune function remained
 stable throughout moult progression in both age groups (i.e. for both age-
 specific moulting strategies). Our results, therefore, do not provide
 evidence for a trade-off between immunity and feather regrowth. Instead,
 maintaining immune function may be needed to offset increased infection
 risk during moult, but further research – ideally incorporating measures
 of individual condition or experimental approaches – is warranted. Our
 study provides new insights into immune regulation during a critical, yet
 understudied, annual-cycle stage, and indicates directions for future
 research.
description: # Stable immune function during moult regardless of age-specific moulting
 strategy in a European passerine Dataset DOI:
 [10.5061/dryad.612jm64kb](https://doi.org/10.5061/dryad.612jm64kb) ##
 Description of the data and file structure We recorded moult status
 (not-yet moulting, moulting, completed moult) and the progression of
 primary wing feather moult in adult blackbirds. We also assessed the
 extent of body feather replacement in juvenile blackbirds. In addition, we
 took a small blood sample from each bird to measure four parameters of
 baseline innate immune function (bacterial-killing ability, lysis,
 agglutination, haptoglobin concentration).  ### Files and variables ####
 File: Moult_immune_function_data.csv **Description:**  ##### Variables *
 ID: individual metal ring number * age: age class (juv = juvenile
 (first-year); ad = adult (second-year or older) * sex: sex (determined in
 the field (for adults) or in the lab (for juveniles, using molecular
 sexing techniques)) * year: year of capture * date: capture date *
 julian_date: capture date (as Julian date) * moult_status: moult status
 (categorical: yes = moulting; no = not-yet moulting; completed = moult
 completed) * percent_moult: post-juvenile body moult progression (% body
 feathers replaced) * moult_score: adult primary wing feather moult
 progression (score: 0-20) * BKA_prop: bacterial-killing ability
 (proportion of *E. coli* killed) * lysis_score: lysis (titre), measure of
 complement activity * agglut_score: agglutination (titre), a measure of
 natural antibodies * hp_conc: haptoglobin concentration (mg/ml) * X450.nm:
 sample redness (absorbance at 450nm prior to haptoglobin measurement) ##
 Code/software Our dataset is in the CSV (Comma-separated Values (.csv))
 format. We used Excel Version 16.102.3 (25110228) to generate the file. ##
 Access information The R code used for data analysis and visualisation for
 the corresponding article can be accessed via GitHub
 ([https://github.com/mvklumpp/Blackbirds](https://github.com/mvklumpp/Blackbirds)).