DOI: 10.5061/dryad.g79cnp5w9
title: Are urbanization and brood parasitism associated with differences in telomere lengths in song sparrows?

description: Urbanization reflects a major form of environmental change impacting wild
 birds globally. Whereas urban habitats may provide increased availability
 of water, some food items, and reduced predation levels compared to rural,
 they can also present novel stressors including increased light at night,
 ambient noise, and reduced nutrient availability. Urbanization can also
 alter levels of brood parasitism, with some host species experiencing
 elevated levels of brood parasitism in urban areas compared to rural
 areas. Though the demographic and behavioral consequences of urbanization
 and brood parasitism have received considerable attention, their
 consequences for cellular-level processes are less understood. Telomeres
 provide an opportunity to understand the cellular consequences of
 different environments as they are a well-established metric of biological
 state that can be associated with residual lifespan, disease risk, and
 behaviour, and are known to be sensitive to environmental conditions. Here
 we examine the relationships between urbanization, brood parasitism, and
 blood telomere lengths in adult and nestling song sparrows (Melospiza
 melodia). Song sparrows are a North American songbird found in both urban
 and rural habitats that experience high rates of brood parasitism by
 brown-headed cowbirds (Molothrus ater) in the urban, but not the rural,
 sites in our study system. Among adults and nestlings from non-parasitized
 nests, we found no differences in relative telomere lengths between urban
 and rural habitats. However, among urban nestlings, the presence of a
 brood parasite in the nest was associated with significantly shorter
 relative telomere lengths compared to when a brood parasite was absent.
 Our results suggest a novel, indirect, impact of urbanization on nestling
 songbirds through the physiological impacts of brood parasitism.
description: # Are urbanization and brood parasitism associated with differences in
 telomere lengths in song sparrows? **rTLDryad.masterfile.csv** The data
 presented here is relative telomere length, and life history data
 collected from adult and nestling wild song sparrows (Melospiza melodia),
 and how they relate to urbanization, and brood parasitism by brown-headed
 cowbirds (Molothrus ater). ## Description of the data and file structure
 Code and data for Journal of Avian Biology Submission JAV-03220 
 **Variables:** * plate - qPCR plate number * Age.day  - Age of nestlings
 in days since hatch, which is indicated by day zero * Habitat - the
 habitat type that the individual was sample, either urban or rural *
 SOSP.brood.size – number of song sparrow nestlings in a nest. *
 Total.brood.size- Total number of nestlings in a nest, derived from adding
 number of song sparrows and number of brown headed cowbird nestlings in a
 given nest. * rTL - Relative telomere length * date -  Calendar date the
 sample was collected. * sex – sex of individual determined either through
 visual examination of physical characteristics or genotyping. * Site - The
 individual research site the bird was sampled from. * Age..year. - The age
 in years of the sampled bird. Within this, “HY” stands for “Hatch year”
 and means the bird was a nestling at time of sampling and been born that
 year and “ASY” stands for “After Second year” meaning the individual was
 an adult at time of sampling * year = calendar year bird was sampled * NID
 = Unique nest id given to every nest in the study. * Para.comp = nests
 that are used for the brood parasitism comparison. Only included urban
 nests that were either parasitized, or not parasitized by brown headed
 cowbirds. * Bhco.hab – categorizing nests within the brood brood
 parasitism comparison as either parasitized (urban.yes) or not parasitized
 (urban.no) * nest.para -  category defining if a nest was parasitized or
 was not parasitized by brown headed cowbirds. * Nest.para.fig -  used to
 filter nests for creating the nest parasitism figure. ### Code/Software
 Annotations are provided throughout the script, libraries need are
 included in the script and below. CODE: Data Analysis for Dryad 09.11.23.R
 Software: R Statistical Software v. 4.2.2. Packages used library(Rmisc)
 library(tidyverse) library(car) library(lme4) library(lmerTest)
 library(lubridate) library(glmm) library(predictmeans) library(lsmeans)
 library(gridExtra) library(effects) library(emmeans) library(broom)
 library(modelr) library(performance) library(ggpubr)