DOI: 10.5061/dryad.3j9kd51tf
title: Data from: Environmental constraints can explain clutch size differences between urban and forest blue tits: Insights from an egg removal experiment

description: Urban environments present novel ecological challenges to wild species. In
 birds, urban populations generally exhibit reduced clutch sizes compared
 to forest populations. However, whether smaller urban clutches are
 adaptive or a result of environmental constraints is unclear. To
 investigate these two hypotheses, we quantified the ability of urban and
 non-urban blue tits (Cyanistes caeruleus) to lay new eggs after an
 experimental manipulation aimed to increase egg production. We removed the
 first four eggs laid by urban and forest birds to test their ability to
 produce new eggs. If the urban environment imposes constraints on egg
 production, we predicted that urban birds would not lay new eggs. If the
 small clutches of urban birds are an adaptive response, we predicted they
 would lay new eggs to reach the optimal clutch size for the
 environment. Consistent with the environmental constraint
 hypothesis, our results suggest that urban females do not lay new eggs to
 the same extent as forest birds following egg removal. Forest birds laid
 approximately two new eggs after our experimental manipulation, while
 urban birds laid approximately 0.36 new eggs following egg
 removal. Our manipulation resulted in a brood reduction in the
 urban habitat, and nestlings from urban experimental nests had higher
 survival than those from urban control nests. This suggests that females
 might be misjudging urban habitat quality and produce a clutch with more
 eggs than nestlings they can rear. Overall, our results suggest
 that environmental constraints could limit the number of eggs that urban
 females lay, generating urban versus non-urban differences in this trait.
description: --- # **Data from:** Environmental constraints can explain clutch size
 differences between urban and forest blue tits: Insights from an egg
 removal experiment This dataset contains all the data that was collected
 and analysed for a project investigating whether urban and forest blue tit
 populations respond differently to an egg removal experiment. --- Mark D.
 Pitt, Norah S.S. Alhowiti, Claire J. Branston, Eugenio Carlon, Jelle J.
 Boonekamp, Davide M. Dominoni, Pablo Capilla-Lasheras. **Environmental
 constraints can explain clutch size differences between urban and forest
 blue tits: insights from an egg removal experiment**. --- For any further
 information, please contact: Mark Pitt, email:
 [markdavidpitt@gmail.com](mailto:markdavidpitt@gmail.com) ## Description
 of code: The statistical software used to analyse our data was
 R v.4.3.2. Scripts are numbered in order of where they appear in the
 manuscript. Each script contains a small description to the section of the
 manuscript to which it is relevant. ## Description of data: The data from
 this project is contained in a single excel document consisting of four
 sheets. Data is not available for any cells which contain missing values
 or N/A. Additionally, data contained in the file
 "individual_egg_data.RDS" contains information on the volumes
 for each egg, and is generated from the R script 
 "03a_egg_volume_data_prep.R". This RDS file contains all the
 information contained in Sheet 2 from the
 "Pitt_et_all_database.xlsx", plus an additional column titled
 "eggID", which is a unique identifier given to each egg included
 in the study (with no eggs sharing their unique identifier with another). 
 --- ### Sheet 1: ALL BROODS This sheet contains information on the clutch
 ID's, which analyses the clutch was included in, the clutch sizes,
 brood sizes, number of fledglings, egg laying dates, and hatching dates
 for all the nests included in the project. #### Key: * Column A:
 **analysis_total_number_eggs**- Dictates whether a clutch was included in
 the analysis investigating the number of eggs laid in both treatment
 groups in urban and forest habitats. * Column B:
 **analysis_total_number_eggs_reason** - For clutches excluded from the
 analysis investigating the number of eggs laid, the explanation behind
 this removal is given in this column. * Column C: **analysis_egg_volume**-
 Dictates whether a clutch was included in the analysis investigating egg
 volume in both treatment groups in urban and forest habitats. * Column D:
 **analysis_egg_volume_reason** - For clutches excluded from the analysis
 investigating egg volume, the explanation behind this removal is given in
 this column. * Column E: **analysis_nestling_survival** - Dictates whether
 a brood was included in the nestling survival analysis for both treatment
 groups in urban and forest habitats. * Column F:
 **analysis_nestling_survival_reason** - For broods excluded from the
 analysis investigating nestling survival, the explanation behind this
 removal is given in this column. * Column G: **EXPERIMENTAL_GROUP** - The
 treatment group nests were assigned. Either *EXPERIMENTAL* or *CONTROL*.
 Experimental nests had four eggs removed from the nest, control clutches
 had no eggs removed. * Column H: **CROSS_FOSTER_GROUP** - Dictates to
 which habitats nestlings were cross-fostered. Either *BETWEEN* or *WITHIN*
 or *NOT CROSS-FOSTERED*. Nestlings that were cross-fostered between
 habitats were urban-forest, while within habitat cross-fosters could be
 urban-urban or forest-forest. * Column I: **NESTBOX** - The unique number
 identifier assigned to each nestbox. Each nestbox number represents a
 unique clutch ID. * Column J: **LOCATION** - The location that the clutch
 was located. Either *KELVINGROVE* (the urban habitat) or *SCENE* (the
 forest habitat). * Column K: **HABITAT**- The habitat that the clutch was
 located. Either *urban* (Kelvingrove Park) or *forest* (SCENE). * Column
 L: **PAIRED_NESTBOX** - The nestbox ID of the nest to where chicks from
 the brood were to be cross-fostered. * Column M: **julian_1st_egg** - The
 date when the first egg was recorded in a clutch. In Julian days
 (represented as the number of days since 01/01/2022), which is needed for
 the analysis. * Column N: **1st_EGG_LAYING_DATE** - The date (dd/mm/yy)
 when the first egg was recorded in a clutch (dd/mm/yy). Converted to
 Julian days (see above). * Column O: **EGGS_FIRST_VISIT** - The number of
 eggs recorded in the nest on the first egg laying check. * Column P:
 **julian_hatch_date** - The date when hatching was first detected in a
 clutch. In Julian days (represented as the number of days since
 01/01/2022), which is needed for the analysis. * Column Q: **HATCH_DATE**
 - The date (dd/mm/yy) when hatching was first detected in a clutch.
 Converted to Julian days (see above). * Column R: **IN_NEST_CLUTCH_SIZE**
 - The final number of eggs that the female incubated IN the nest. For
 control treatment nests, this is equal to the number of eggs they laid.
 For experimental birds, this is equal to the number of eggs they laid - 4,
 as four eggs were removed from the clutch to manipulate laying effort. *
 Column S: **NUMBER_EGGS_LAID** - The total number of eggs laid by a
 female. * Column T: **EGGS_IN_NEST_DAY3_PRE_CF_MANIPULATION** - The number
 of eggs in the nest three days after the first chick hatched (day 2). *
 Column U: **NUMBER_HATCHED_EGGS** - The number of eggs that hatched in the
 nest. * Column V: **BROODSIZE_DAY3_PREMANIPULATION** - The number of
 chicks in the nest before cross-fostering took place. * Column W:
 **DATE_CROSSFOSTERING_MANIPULATION -** The date (dd/mm/yy) cross-fostering
 occurred. * Column X: **TIME_CF_MANIPULATION** - The time at which
 cross-fostering occurred (hh:mm). * Column Y:
 **BROODSIZE_DAY3_POSTMANIPULATION** - The number of chicks present in the
 nest after the cross-fostering occurred. * Column Z: **BROODSIZE_DAY7** -
 The number of chicks in the nest on day seven (six days after the first
 chick had hatched). * Column AA: **BROODSIZE_DAY13** - The number of
 chicks in the nest on day thirteen (twelve days after the first chick had
 hatched). * Column AB: **NUMBER_FLEDGLINGS** - The number of chicks that
 successfully fledged from the nest. --- ### Sheet 2: Egg Volumes This
 sheet provides further details on each egg that was recorded in the
 clutch, including when it was laid and all the egg volume measurements
 (egg volume was measured three times using three separate images of each
 egg). #### Key: * Column A: **EXPERIMENTAL_GROUP** - The treatment group
 nests were assigned. Either *EXPERIMENTAL* or *CONTROL*. Experimental
 nests had four eggs removed from the nest, control clutches had no eggs
 removed. * Column B: **NESTBOX** - The unique number identifier assigned
 to each nestbox. Each nestbox number represents a unique clutch ID. *
 Column C: **LOCATION** - The location that the clutch was located. Either
 *Kelvingrove_park* (the urban habitat) or *SCENE* (the forest habitat). *
 Column D: **HABITAT**- The habitat that the clutch was located. Either
 *urban* (Kelvingrove Park) or *forest* (SCENE). * Column E:
 **Number_of_eggs_present** - The number of eggs already present in the
 nest when a new egg was recorded in the nestbox. * Column F
 **EARLIEST_LAYING_ORDER** - The earliest possible position in laying order
 for each egg. * Column G: **LATEST_LAYING_ORDER** - The latest possible
 position in laying order for each egg. * Column H: **EGG_LABEL** - The
 label given to each egg. Reflects the eggs position in the laying
 sequence. When two eggs were recorded on the same day, given either an A
 or B (e.g., egg 3A and 3B would represent eggs 3 and 4 in the laying
 sequence, but as they were found on the same day the laying order cannot
 be discerned). * Column I: **julian_earliest_lay_date** - The earliest
 possible laying date for each egg in the clutch. In Julian days
 (represented as the number of days since 01/01/2022), which is needed for
 the analysis. * Column J: **EARLIEST_LAY_DATE** - The earliest possible
 laying date (dd/mm/yyyy) for each egg in the clutch. Converted to Julian
 date (see above). * Column K: **julian_latest_lay_date** - The latest
 possible laying date for each egg in the clutch. In Julian days
 (represented as the number of days since 01/01/2022), which is needed for
 the analysis. * Column L: **LATEST_LAY_DATE** - The latest possible laying
 date (dd/mm/yyyy) for each egg in the clutch. Converted to Julian date
 (see above). * Column M: **accurate** - Whether we obtained accurate
 information on the laying order positions and laying dates for each egg.
 Either *1* (where information on laying dates were accurate), or *2*
 (where there was uncertainty regarding the lay date). Only eggs assigned a
 value of *1* were included in the analysis. * Column N: **volume -** The
 volume (mm^3^) measurement of the egg obtained from each photograph. *
 Column O: **photo_id** - The unique identifier given to each photograph. *
 Column P: **no_eggs_photo** - The number of eggs included in each
 photograph. * Column Q: **EGG_REMOVED?** - Whether the egg was
 experimentally removed from the nest. Either *Y* (yes) or *N* (no). *
 Column R: **weight_g** - The mass (g) of the experimentally removed egg. *
 Column T: **rep** - Reflects the measurement number for each egg. Egg
 measurements were taken from three separate images, so this column
 reflects measurements from images *1*,*2* and *3* of each egg. Used in the
 repeatability analysis to determine how repeatable our measurements were
 for each egg. * Column U: **Group** - The egg laying group eggs were
 assigned to. Either *1* (eggs one to three in the laying sequence), or *2*
 (eggs four and beyond in the laying sequence). --- ### Sheet 3: ALL
 NESTLINGS This sheet provides further details on each individual nestling,
 including the unique BTO ring numbers they were assigned, as well as
 information on individual mortality. #### Key: * Column A: **RING_NUMBER**
 - The unique BTO ring number assigned to each individual nestling. *
 Column B: **julian_hatch** - The date when hatching was first detected in
 a clutch. In Julian days (represented as the number of days since
 01/01/2022), which is needed for the analysis. * Column C: **hatch_date**
 - The date (dd/mm/yy) when hatching was first detected in a clutch.
 Converted to Julian days (see above). * Column D: **site_hatch** - The
 location that the nestling hatched in. Either *SCENE* (the forest habitat)
 or *Kelvingrove_Park* (the urban habitat). * Column E: **habitat_hatch** -
 The habitat that the nestling hatched in. Either *urban* (Kelvingrove
 Park) or *forest* (SCENE). * Column F: **nestbox_hatch** - The unique
 number identifier assigned to the nestbox the chick hatched in. Each
 nestbox number represents a unique clutch ID. * Column G: **site_rearing**
 - The location that the nestling was reared in (after cross-fostering).
 Either *SCENE* (the forest habitat) or *Kelvingrove_Park* (the urban
 habitat). * Column H: **habitat_rearing** - The habitat that the nestling
 was reared in (after cross-fostering). Either *urban* (Kelvingrove Park)
 or *forest* (SCENE). * Column I: **nestbox_rearing** - The unique number
 identifier assigned to the nestbox the chick was reared in (after
 cross-fostering occurred). Each nestbox number represents a unique clutch
 ID. * Column J: **julian_fate** - The date when the nestlings fate
 (fledged or dead) was known. In Julian days (represented as the number of
 days since 01/01/2022), which is needed for the analysis. * Column K:
 **date_fate** - The date (dd/mm/yyyy) when the nestlings fate (fledged or
 dead) was known. Converted to Julian days (see above). * Column L:
 **fate** - The fate of the nestling. Either *FLEDGED* or *DEAD*. --- ###
 Sheet 4: ALL NESTLING WEIGHTS This sheet provides further details on each
 individual nestlings mass throughout the experimental period. #### Key: *
 Column A: **NESTBOX** - The unique number identifier assigned to each
 nestbox. Each nestbox number represents a unique clutch ID. * Column B:
 **LOCATION** - The habitat that the clutch was located. Either
 *Kelvingrove_park* (the urban habitat) or *SCENE* (the forest habitat).
 Note that some nestlings from GCU (another urban site) were included as
 part of the cross-fosterings, but these were excluded from all of the
 analyses presented in the current project. * Column C: **HABITAT**- The
 habitat that the clutch was located. Either *urban* (Kelvingrove Park) or
 *forest* (SCENE). * Column D: **RING_NUMBER** - The unique BTO ring number
 assigned to each individual nestling. * Column E: **exp_period** - The
 period of the experiment where individual biometrics were taken. Either
 *pre-manipulation* (before cross-fostering occurred) or
 *post-manipulation* (after cross-fostering occurred). * Column F:
 **julian_date** - The date that mass, wing, and tarsus measurements were
 obtained from each nestling. In Julian days (represented as the number of
 days since 01/01/2022), which is needed for the analysis. * Column G:
 **DATE** - The date (dd/mm/yyyy) that mass, wing, and tarsus measurements
 were obtained from each nestling. Converted to Julian days (see above). *
 Column H: **TIME** - The time when measurements were taken from each
 nestling (hh:mm). * Column I: **AGE** - The nestlings age when
 measurements were taken. Nestlings were measured on days two, six, and
 twelve after hatching. * Column J: **WEIGHT** - The body mass (g) of the
 nestling. * Column K: **time_category** - The time that nestlings were
 measured, but as a categorical variable. Either *morning* (before 12:00
 hrs), or *afternoon* (after 12:00 hrs).