DOI: 10.5061/dryad.8sf7m0cw3
title: Offspring sex ratio is affected by pre-breeding rainfall and hatching order in a cooperative breeding bird

description: Selection may favour sex ratio adjustment when the fitness benefits of
 producing male or female offspring vary. In birds, sex ratio bias at
 hatching has been particularly well-studied in cooperative breeding
 species, primarily in helper-at-the-nest systems wherein young remain with
 their parents and help raise subsequent broods. In these systems, breeding
 females are expected to skew offspring sex ratio in favour of the helping
 sex if sufficient resources exist. In communal laying systems multiple
 group members breed and raise the young and offspring dispersal varies,
 making it difficult to predict whether and how breeders should skew
 offspring sex ratio. We tested for sex ratio bias in smooth-billed anis
 (Crotophaga ani), a communal laying cuckoo with low within-group
 relatedness, high offspring dispersal, and high annual turnover in group
 membership. One male performs nocturnal incubation and sires more
 offspring, suggesting these males may have higher reproductive variance
 and thus that it may be beneficial for his mate to produce more male
 offspring. We hypothesized that pre-breeding rainfall influences food
 availability and thus offspring sex ratio, predicting that breeding
 females skew production towards the more beneficial sex (i.e., males) in
 high food years, consistent with the Trivers-Willard hypothesis. Females
 may also adjust sex ratio across the hatching order, so we predicted a
 male-bias in first hatched chicks in larger broods that should experience
 greater competition. Contrary to our first prediction, more male chicks
 hatched when pre-breeding rainfall was lower. In partial support of our
 second prediction, marginally more first hatched chicks were male in
 larger broods. Based on these results, we propose the nestling competition
 hypothesis and predict that when nestling competition is high (i.e., in
 poor years and in large joint broods), mothers should produce more of the
 more competitive sex.
description: Data were collected from wild breeding smooth-billed anis at a
 single study site (Cabo Rojo National Wildlife Refuge) over 5 breeding
 seasons (2005, 2011-2014). Nests were located and monitored regularly
 throughout each breeding season to
 determine the beginning of egg laying, onset of incubation, beginning of
 hatching, and end of hatching. We used molecular techniques to determine
 the sex of each chick.We used rainfall data collected from a U.S. Fish and
 Wildlife Service weather station on the Cabo Rojo NWR (17°58’23" N,
 67°09’46" W; data available at
 https://wrcc.dri.edu/cgi-bin/rawMAIN.pl?txPCAB). Rainfall data from this
 station during the breeding season were not available for 35 study days,
 largely due to the U.S. government shutdown in 2013. To determine rainfall
 for these days, we used data from the USGS-NRCS/SCAN weather station near
 the main entrance to the refuge (17°59’00’’N, 67°10’00’’; data available
 at https://wcc.sc.egov.usda.gov/nwcc/site?sitenum=2066). Data organization
 and analyses were conducted in R version 4.0.3 (R Development Core Team,
 2021), using base R and the packages dplyr (Wickham et al., 2023) and lme4
 (Bates et al., 2015). Data visualization was done using the package
 ggplot2 (Wickham, 2016). We followed
 all applicable international, national, and institutional guidelines for
 the care and use of animals in
 research.
description: Reference Information === Provenance for this README --- * File name:
 README\_SexRatio.md * Author: Leanne A Grieves * Other contributors:
 J.K.R. Tabh, J.S. Hing, J.S. Quinn * Date created: 2023-10-04 * Date
 modified: Dataset Version and Release History --- * Current Version: *
 Number: 1.0.0 * Date: 2023-10-04 * Persistent identifier: DOI: PENDING *
 Summary of changes: n/a * Embargo Provenance: n/a * Scope of embargo: n/a
 * Embargo period: n/a Dataset Attribution and Usage --- * Dataset Title:
 Data for the article "Offspring sex ratio is affected by pre-breeding
 rainfall and hatching order in a cooperative breeding bird" *
 Persistent Identifier: PENDING * Dataset Contributors: * Creators: Leanne
 A Grieves, Joshua K.R. Tabh, J. Sheng Hing, James S. Quinn * Date of
 Issue: 2023 * Publisher: McMaster University * License: Use of these data
 is covered by the following license: * Title: CC0 1.0 Universal (CC0 1.0)
 * Specification: https://creativecommons.org/publicdomain/zero/1.0/; the
 authors respectfully request to be contacted by researchers interested in
 the re-use of these data so that the possibility of collaboration can be
 discussed. * Suggested Citations: * Dataset citation: &gt; Grieves,
 L.A., J.K.R. Tabh, J.S. Hing, J.S. Quinn. 2023. Data for the article
 "Offspring sex ratio is affected by pre-breeding rainfall and
 hatching order in a cooperative breeding bird", Dryad, Dataset,
 PENDING * Corresponding publication: &gt; Grieves, L.A., J.K.R. Tabh,
 J.S. Hing, J.S. Quinn. 2023. Offspring sex ratio is affected by
 pre-breeding rainfall and hatching order in a cooperative breeding bird.
 Animal Behaviour. Submitted. DOI: PENDING Contact Information --- * Name:
 Leanne A Grieves * Affiliations: Department of Biology, School of Earth,
 Environment and Society, McMaster University; Macaulay Library, Cornell
 Lab of Ornithology, Cornell University, Ithaca, NY, 14850 * ORCID ID:
 0000-0002-6836-2177 * Email: lag296@cornell.edu * Alternate Email:
 lagrieves@gmail.com * Address: e-mail preferred * Alternative Contact:
 postdoctoral co-PI * Name: James S Quinn * Affiliations: Department of
 Biology, McMaster University * Email: quinn@mcmaster.ca * Address: Life
 Sciences Building 435, McMaster University, Hamilton, ON L8S 4L8 ***
 Additional Dataset Metadata === Acknowledgements --- * Funding sources:
 Natural Sciences and Engineering Research Council of Canada (NSERC)
 postdoctoral fellowship awarded to LAG and discovery grant to JSQ. Wilson
 Ornithological Society grant to J.S.Q. and J.K.R.T., Queen Elizabeth II
 Graduate Scholarships to J.K.R.T. and J.S.H. Dates and Locations --- *
 Dates of data collection: Field data collected between September and
 December 2005, 2011-2014 * Geographic locations of data collection:
 Fieldwork conducted in Cabo Rojo National Wildlife Refuge, Puerto Rico
 (see publication for details) * Other locations pertaining to dataset
 contents: Wet lab work performed by LAG, JKRT, and JSH at McMaster
 University. *** Methodological Information === * Methods of data
 collection/generation: see manuscript for details Links to other publicly
 accessible locations of the data === * DOI: PENDING *** Data and File
 Overview === Summary Metrics --- * File count: 14 * Total file size: 13.4
 MB * Range of individual file sizes: 2.1 KB - 799 KB * File formats: .csv,
 .txt, .pdf Table of Contents --- * SexRatio-4Oct23.csv *
 SexRatioMS-SI-27Sept23.pdf * SexRatioRCode.txt Setup --- * Unpacking
 instructions: n/a * Relationships between files/folders: Detailed in file
 useage * Recommended software/tools: RStudio 2023.03.0; R version 4.0.3
 File Usage --- * Main analyses: SexRatioRCode.txt * Require files *
 SexRatio-4Oct23.csv File/Folder Details === Details for:
 SexRatio-4Oct23.csv --- * Description: a file containing nest ID,
 offspring sex, brood size, and precipitation data for use in this study. *
 Format(s): .csv * Size(s): 23.7 KB * Dimensions: 323 rows x 13 columns *
 Variables: * CANID: bird ID (unique identifier) * Year: study year
 (breeding season) * Territory: breeding group * Nest: Nest ID * Sex:
 offspring (chick) sex * Obs.Prop.Male: proportion of males in brood *
 Exp.Prop.Male: expected proportion of males in brood * Obs.Over.Exp:
 observed divided by expected * Hatch.Category: position in hatching order
 (first hatched, last hatched, or middle hatched chicks) * Brood.Size:
 brood size (total chicks hatched from brood) * First.Egg: date first egg
 was laid * First.Chick: date first chick hatched * Breed.Precip: total
 precipitation 30 days prior to date first egg was laid Details for:
 SexRatioMS-SI-27Sept23.pdf *** * Description: a .pdf file containing
 supplementary materials (Figures and Tables) referred to in main article
 text. See main article for more details * Format(s): .pdf * Size(s): 166
 KB * Dimensions: na * Read file for details <br> Details for:
 SexRatioRCode.txt *** * Description: a text file containing the R code
 used for all analyses presented in this paper. The file is currently
 formatted for use with R Studio * Format(s): .txt * Size(s): 207 KB *
 Dimensions: na * See file annotations for details. Briefly, in this
 observational study across 5 breeding seasons, we evaluated the influence
 of pre-breeding season rainfall, hatching order, and brood size on the
 proportion of male offspring in a brood (model 1) and the likelihood of
 first hatched offspring being male (model 2) *** END OF README