DOI: 10.5061/dryad.xpnvx0kvh
title: Changing food availability and its effect on the heritability of offspring size in woodland passerine birds

description: Climate warming has been associated with widespread body size declines in
 many vertebrate taxa, but relatively little is known about possible
 climate warming induced shifts in trait heritabilities. The main goal of
 the study was to investigate how changing food availability affects
 evolutionary potential of four traits related to nestlings’ body size. We
 used long-term, pedigree structured data of two woodland passerines living
 in the boreal zone, the Willow Tit (Poecile montanus) and the Great Tit
 (Parus major), to study how food availability for their nestlings has
 changed in time, how this has influenced their morphological traits (viz.
 wing, tail & tarsus length & body mass) and their
 heritabilities and evolvabilities. This was done by assessing
 heritabilities under varying food availabilities using random regression
 animal models. We found that caterpillar food availability had increased
 over the 25 years long study period and that this was accompanied by
 increases of nestlings’ body mass, but not other morphological traits. All
 traits were heritable in both species, but additive genetic variance,
 heritability and evolvability were affected by food availability only in
 the case of the wing length, being higher under low food availability (the
 Great Tit) or higher under low and high food availability (the Willow
 Tit). We conclude that changes in food availability seem to have limited
 influence on evolutionary potential of body size traits in these two
 passerine birds.
description: # Changing food availability and its effect on the heritability of
 offspring size in woodland passerine birds Dataset DOI:
 [10.5061/dryad.xpnvx0kvh](https://doi.org/10.5061/dryad.xpnvx0kvh) ##
 Description of the data and file structure Paper associated with this
 archive Citation: Vatka, Emma; Orell, Markku; Rytkönen, Seppo; Merilä,
 Juha (2025) Changing food availability and its effect on the heritability
 of offspring size in woodland passerine birds. Journal of Animal Ecology.
 Dates of data collection: Years 1996-2020 Geographic location of data
 collection: Oulu, Finland (N 65°05’, E 25°33’) ## Data and code file
 overview Data on morphological measures of Willow Tit (*Poecile montanus*)
 and Great Tit (*Parus major*) nestlings were collected with standard
 methods during years 1996–2020 for which also food availability data was
 available. Nestlings were measured at the age of two weeks (13 days or 14
 days old for the Willow Tit and the Great Tit, respectively; 0 = hatching
 date of the oldest young). Wing length and tail length were measured using
 a ruler to nearest mm. Tarsus length was measured using a vernier calliper
 to nearest 0.01 mm, and body mass with either a Pesola spring balance or
 digital scales to nearest 0.1 g. Data on caterpillar food availability
 during nestling periods was collected with the frass-fall method for years
 1996–2020. Biomasses of caterpillars (g/m2) living in canopies of birch
 (*Betula* spp.) were estimated in weekly periods. We assumed that the
 weekly caterpillar biomass estimate reflects daily caterpillar abundances
 during the frass-fall collection period. We then calculated brood-specific
 average caterpillar food availabilities per day during nestling periods
 (from the hatching date until the date of nestlings’ measurement). The
 unit for food availability is g/m2/day. Pedigree files are constructed for
 animal model analyses with package MCMCglmm in R. ### Files and variables
 #### File: GT_pedigree_20.csv **Description:** Pedigree of individually
 marked Great Tits in Oulu study area (data until 2020) ##### Variables *
 animal: identity of the bird individual * dam: identity of the mother of
 the individual. 'NA' for missing information. * sire: identity
 of the father of the individual. 'NA' for missing information.
 #### File: WT_Data_Morfo.csv **Description:** Morphological measures and
 food availabilities for individual nestlings of Willow Tits in Oulu,
 Finland ##### Variables * animal: identity of the nestling bird. Variable
 is used in animal models to link the data with the pedigree information. *
 BroodID: identity of the brood of the nestling. Variable is used to model
 shared environmental conditions experienced by nestlings of same broods. *
 Vuosi: year * Mittaaja: identity of the measurer (encrypted). * Pa: body
 mass (g) * Si: wing length (mm) * Py: tail length (mm) * Ni: tarsus length
 (mm) * Ruoka: average caterpillar food availability during the nestling
 period (g/m2/day) * F.ID: female identity * M.ID: male identity #### File:
 WT_pedigree_20.csv **Description:** Pedigree of individually marked Willow
 Tits in Oulu study area (data until 2020) ##### Variables *
 animal: identity of the bird individual * dam: identity of the mother of
 the individual. 'NA' for missing information. * sire: identity
 of the father of the individual. 'NA' for missing information.
 #### File: scrip_WT.R **Description:** The script attached was used to
 produce the results regarding the Willow Tit in manuscript titled
 "Changing food availability and its effect on the heritability of
 offspring size in woodland passerine birds" using program R (it is
 ready to use in the R-script for the statistical analyses). The script
 includes the following analyses: * Testing for a temporal trend in food
 availability * Effects of food availability on nestlings body size traits
 * Effect of food availability on brood size * Temporal trends in
 nestlings' body size traits * Random regression animal model analyses
 * Evolvability and CVe calculations #### File: script_GT.R
 **Description:** The script attached was used to produce the results
 regarding the Great Tit in manuscript titled "Changing food
 availability and its effect on the heritability of offspring size in
 woodland passerine birds" using program R (it is ready to use in the
 R-script for the statistical analyses). The script includes the following
 analyses: * Testing for a temporal trend in food availability * Effects of
 food availability on nestlings body size traits * Effect of food
 availability on brood size * Temporal trends in nestlings' body size
 traits * Random regression animal model analyses * Evolvability and CVe
 calculations #### File: GT_Data_Morfo.csv **Description:** Morphological
 measures and food availabilities for individual nestlings of Great Tits in
 Oulu, Finland ##### Variables * animal: identity of the nestling bird.
 Variable is used in animal models to link the data with the pedigree
 information. * BroodID: identity of the brood of the nestling. Variable is
 used to model shared environmental conditions experienced by nestlings of
 same broods. * Vuosi: year * Ruoka: average caterpillar food availability
 during the nestling period (g/m2/day) * Mittaaja: identity of the measurer
 (encrypted). * Si: wing length (mm) * Py: tail length (mm) * Ni: tarsus
 length (mm) * Pa: body mass (g) * F.ID: female identity * M.ID: male
 identity ## Code/software Code scripts and workflow: The scripts attached
 were used to produce the results in manuscript titled "Changing food
 availability and its effect on the heritability of offspring size in
 woodland passerine birds" using program R. Software version: R,
 version 4.3.1 R libraries: lme4, version 1.1-35.1 MCMCglmm, version 2.35
 arules, version 1.7-8 pedigree, version 1.4.2 coda, version 0.19-4