DOI: 10.5061/dryad.cnp5hqcdx
title: Data from: Dissecting factors behind temporal trends in the timing of breeding in two songbird species – evolutionary change or phenotypic plasticity?

description: Warming climate has led to significant phenological advances in many plant
 and animal populations. Whether these advances represent evolutionary
 responses or phenotypic plasticity remain typically unknown. Using 53
 years long time-series of individually marked Great (Parus major) and
 Willow Tits (Poecile montanus), we investigated whether the significant
 breeding time advances in these species could be explained to result from
 evolutionary responses, phenotypic plasticity, or both. In the case of
 both species, we did not find any evidence for changes in breeding values
 for timing of breeding, suggesting that the observed changes do not have a
 genetic, and hence, evolutionary basis. In contrast, we found that
 annually fluctuating environmental effects explained most of the variation
 in first egg lay dates, suggesting that advances in breeding time were
 attributable to phenotypic plasticity. We further inferred that phenotypic
 plasticity in response to spring temperatures can fully explain the
 observed advancement of Great Tit phenology over time, whereas Willow Tits
 have advanced their phenology much beyond what would be expected from
 phenotypic plasticity in response to spring temperatures. The latter
 observation suggests that some other yet unidentified environmental
 factor, uncorrelated with spring temperatures, likely explains about half
 of the advancement in their breeding time.
description: # Dissecting factors behind temporal trends in the timing of breeding in
 two songbird species – evolutionary change or phenotypic plasticity?
 GENERAL INFORMATION This README file was updated on 3.4.2025 A. Paper
 associated with this archive Citation: Vatka, Emma; Orell, Markku; Merilä,
 Juha (2025) Dissecting factors behind temporal trends in the timing of
 breeding in two songbird species – evolutionary change or phenotypic
 plasticity? B. Originators * Emma Vatka, Ecology and Genetics Research
 Unit, Faculty of Science, University of Oulu, & Research Programme in
 Organismal and Evolutionary Biology, Faculty of Biological and
 Environmental Sciences, University of Helsinki * Markku Orell, Ecology and
 Genetics Research Unit, Faculty of Science, University of Oulu * Juha
 Merilä, Research Programme in Organismal and Evolutionary Biology, Faculty
 of Biological and Environmental Sciences, University of Helsinki, &
 Area of Ecology & Biodiversity, School of Biological Sciences, The
 University of Hong Kong C. Contact information Emma Vatka Ecology and
 Genetics Research Unit, Faculty of Science, University of Oulu, P.O. Box
 8000, FI-90014 Oulu University, Finland
 [emma.vatka@oulu.fi](mailto:emma.vatka@oulu.fi) D. Dates of data
 collection Years 1969-2021 and 1971-2023 for Great Tits and Willow Tits,
 respectively E. Geographic Location(s) of data collection Oulu, Finland (N
 65°05’, E 25°33’) F. Funding Sources Kone Foundation (grant number
 202008514), Research Council of Finland and the University of Oulu. ACCESS
 INFORMATION 1. Licenses/restrictions placed on the data or code: N/A 2.
 Data derived from other sources: N/A 3. Recommended citation for this
 data/code archive Vatka, E., Orell, M. & Merilä, J. (2025) Data from:
 Dissecting factors behind temporal trends in the timing of breeding in two
 songbird species – evolutionary change or phenotypic plasticity?
 [https://doi.org/10.5061/dryad.cnp5hqcdx](https://doi.org/10.5061/dryad.cnp5hqcdx) DATA & CODE FILE OVERVIEW ## Description of the data and file structure Data of first egg laying dates from first clutches of individually marked Great Tits (*Parus major*) and Willow Tits (*Poecile montanus*) were collected near Oulu, Finland in years 1969 - 2021 and 1971 - 2023, respectively. Pedigree files are constructed for animal model analyses with package MCMCglmm in R. To be able to run the analyses of phenotypic plasticity, please download climate data on daily mean temperatures from Oulu airport observation station for a period of 01/01/1970 - 17/08/2023 from the Finnish Meteorological Institute open data web-service: ([https://en.ilmatieteenlaitos.fi/download-observations](https://en.ilmatieteenlaitos.fi/download-observations)). Create a file named "temperatures_climwin1.csv" and include two columns with the following names: "temperature" (this column has the daily mean ambient temperature, °C) and "Date" (in format dd/mm/yyyy). ### Files and variables #### File: Animal models.RData **Description:** R data file including animal model objects built with the script 'script_Dissecting3.R' #### File: LD\_data\_GT\_WT.csv **Description:** First egg laying dates of Great Tits and Willow Tits in Oulu, Finland ##### Variables * animal;IND;Year;LD;dam;f.age;species;Date: * animal: identity of the breeding female. Variable is used in animal models to link the data with the pedigree information. * IND: identity of the breeding female. Variable is used to model permanent environmental effects experienced by a breeding female * Year: breeding year * LD: laying date of the first egg in a genuine first clutch as Maydays (1 = 1st of May) * dam: identity of the breeding female. Used in analysis for temporal trends in the timing of breeding to control for pseudoreplication. * f.age: age of the breeding female (as one year old (1), older (older) or unknown age (not.known)) * species: study species: GT = Great Tit *Parus major*, WT = Willow Tit *Poecile montanus* * Date: date of the first egg laying date (dd/mm/yyyy), used in an analysis with 'slidingwin' in package 'climwin' #### File: WT\_pedigree\_2023.csv **Description:** Pedigree of individually marked Willow Tits in Oulu study area (data until 2023) ##### Variables * animal;dam;sire: * 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: GT\_pedigree\_2021.csv **Description:**  Pedigree of individually marked Great Tits in Oulu study area (data until 2021) ##### Variables * animal;dam;sire: * 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. ## Code/software Data is in .csv files, can be viewed in, e.g., Notepad or Excel.  Code scripts and workflow: The script attached was used to produce the results in manuscript titled "Dissecting factors behind temporal trends in the timing of breeding in two songbird species – evolutionary change or phenotypic plasticity?" using program R. SOFTWARE VERSIONS R, version 4.0.4 R libraries: lme4, version 1.1-26 MCMCglmm, version 2.30 coda, version 0.19-4 climwin, version 1.2.3 arules, version 1.6-6