DOI: 10.5061/dryad.msbcc2g7d
title: Data from: Reduced fitness of females in a facultatively polygynous species: A 32-yr study of Savannah sparrows

description: The evolution of mating systems reflects a balance of the
 often-conflicting interests of males and females. Polygyny, a mating
 system in which males have multiple mates, presents a fitness benefit to
 males, but the consequences for females are less clear. Females with
 polygynous social mates may suffer reduced fitness, especially secondary
 females who typically receive less male support. We use 32 years of
 detailed reproductive data on a population of Savannah sparrows
 (Passerculus sandwichensis) breeding on Kent Island, NB, Canada, to
 investigate the effects of females’ social mating status on six indices of
 female fitness: survival, clutch size, fledging success, number of
 fledglings produced per nest and annually, and recruitment of offspring.
 Secondary females produced fewer fledglings per nest and annually than did
 monogamous or primary females, and their young were less likely to recruit
 into the breeding population. Yearling secondary females also had lower
 survival rates than older secondary females. Combined with higher rates of
 partial brood loss among secondary females, our results suggest that
 secondary females are unable to provide enough care to consistently fledge
 all nestlings in their broods, likely due to reduced male provisioning.
 Given that the sex ratio of breeders in the population is female-biased,
 we suggest that polygyny persists despite its fitness costs because some
 females must mate polygynously to “make the best of a bad situation.” Our
 study demonstrates the value of detailed, long-term population monitoring
 data for understanding mating systems and using multiple indices of
 fitness to analyze the costs of polygyny.
description: # Reduced fitness of females in a facultatively polygynous species: a
 32-yr study of Savannah sparrows
 [https://doi.org/10.5061/dryad.msbcc2g7d](https://doi.org/10.5061/dryad.msbcc2g7d) ## Description of the data and file structure We used 32 years of detailed reproductive data on a population of Savannah sparrows (*Passerculus sandwichensis*) breeding on Kent Island, NB, Canada, to investigate the effects of females’ social mating status on six indices of female fitness: survival, clutch size, fledging success, number of fledglings produced per nest and annually, and recruitment of offspring. We mark all individuals breeding within the study area and find and monitor all nest attempts to produce reproductive data including hatching date; number of eggs, nestlings, and fledglings; and fledging or failure date of the nest. All nestlings and unbanded adults are banded and measured. Assignment of territories and mating status (monogamous or polygynous) are based on field observations of marked individuals. ### Files and variables Note that all dates are in yyyy-mm-dd format. Missing values are NAs. #### File: nests\_mp.csv **Description:** This file contains records of every nest used in this study, identified by a unique nest key. ##### Variables * nest_key: A unique identifier for each nest. * year: Year of breeding attempt. * nest_id: Location and attempt code of nest (not uniquely identifiable). * eggs_laid: Number of eggs laid in the nest. * female_id: Band number of the female parent of the nest (uniquely identifies individual females) * male_id: Band number of the male parent of the nest (uniquely identifies individual males) * found_date: Date the nest was found. * hatch_date: Date the first egg in the nest hatched. * eggs_hatched: Number of eggs in the nest that hatched. * fledglings: Number of fledglings that fledged from the nest. * fledge_date: Date nestlings fledged from the nest. * study_site: Code that identifies different areas of the study site * fate: Fate of the nest. AB = abandoned during building, AE = abandoned with eggs, AN = abandoned with nestlings, DN = dead nestlings, FL = fledged, KN = killed nestlings, PE = predated with eggs, PN = predated with nestlings, U = unknown, XE = nest stepped on, R = experimental removal * mating_status: Whether the nest belonged to a monogamous (MO) or polygynous (PG) pair * female_number: Whether the female parent of the nest was monogamously mated or the primary female of a polygynous male (female number = 1) or the secondary female of a polygynous male (2) * female_color: Female's color band combination (may not be unique between individuals). Abbreviations represent the plastic color bands given to each individual, with letters on the left hand side of the period representing color bands on the left leg and letters on the right side representing colors on the right leg. A = aluminum, B = black, G = green, L = light blue, N = navy, O = orange, R = red, S = striped, V = violet, W = white, Y = yellow. Description applies to all fields involving color band codes. * male_color: Male's color band combination (may not be unique between individuals) * clutch_number: Whether the nest was a first brood, second brood, or replacement clutch (indicated with an R). Uncertainty in assignment is indicated with an E (for "estimated"). * x_coord: Longitudinal coordinate of the nest. * y_coord: Latitudinal coordinate of the nest. * fail_date: Date the nest failed (abandoned or predated). * experiment: Codes for experimental treatments * excl = predator exclosure around nest in 2022-2024 * E1, E2, and E3 = estimated clutch number * C = control nest (in clutch enlargement experiments) * CE, CEGN, CN, EXCL, GE, GECN, GEGN, GN refer to exclosures for gulls and other minor treatments that should not have affected sparrow reproductive success in relation to gull model experiments (Wheelwright et al. 1997, *Animal Behavior*) * SOSP = nest swaps with song sparrows * temp = temperature probes placed in tests * CORT = corticosterone fed to nestlings in first week of life * Notes: Various notes about the observation. When the identity of a parent was uncertain, the individual's color combo is included in the notes field with a question mark (e.g., "ns.n??", "nl.r?") * found_day: Ordinal found date. * hatch_day: Ordinal hatch date. * diff: Difference between found and hatch days. * avg_diff: Average difference in a given year between found and hatch dates. * first_egg_day: Date first egg was laid in the nest. * n_fledglings_m: Number of total fledglings produced by the male parent in that year. * n_fledglings_f: Number of total fledglings produced by the female parent in that year. * n_attempts_f: Number of total nest attempts made by the female parent in that year. * fledged: Whether young fledged from the nest or not (logical, true or false). * n_nests_fledged: The total number of successful nest attempts (produced fledglings) by a female in that year. * female_status: Female's mating status, the combination of mating status and female number. MO = monogamously mated, PG 1 = primary female of a polygynous male, PG 2 = secondary female of a polygynous male * known_age.female: Whether female parent is known-age (banded as a nestling at the study site; logical, true or false). * banding_age.female: Age at which female parent was banded. AHY = after hatch-year, ASY = after second-year, J = juvenile, N = nestling, SY = second-year. * banding_date.female: Date female parent was first banded. * banding_year.female: Year female parent was first banded. * birth_year.female: Year female parent was born. * known_age.male: Whether male parent is known-age (banded as a nestling at the study site; logical, true or false). * banding_age.male: Age at which male parent was banded. AHY = after hatch-year, ASY = after second-year, J = juvenile, N = nestling, SY = second-year. * banding_date.male: Date male parent was first banded. * banding_year.male: Year male parent was first banded. * birth_year.male: Year male parent was born. * female_age: Age of female parent in years during the observed nest attempt. * female_age_code: Age code of female parent for the observed nest attempt. SY = a yearling female breeding for the first time (1 year old). ASY = older than yearling (&gt; 1 year old). * male_age: Age of male parent in years during the observed nest attempt. * male_age_code: Age code of male parent for the observed nest attempt. SY = a yearling female breeding for the first time (1 year old). ASY = older than yearling (&gt; 1 year old). * n_males: Number of breeding males in the study area in the current year. * n_females: Number of breeding females in the study area in the current year. * sex_ratio: Sex ratio in the current year (number of females/number of males). * popn_size: Number of breeding adults in the study area in the current year. * annual_density: Density of breeding adults in the study area in the current year (number of breeding adults divided by 10.7, the area of the study site in hectares). Unit: birds/ha. #### File: clutch\_size.csv **Description:** Dataset used for the analysis of factors influencing clutch size. Each record is one nest attempt. All variables are the same as in nests_mp unless otherwise noted. ##### Variables * fledged.f: Binary, whether or not young fledged from nest (0 = no young fledged, 1 = at least one young fledged). * clutch_num.f: Whether the nest is a first brood (1) or second brood (2). * max_clutch: The maximum clutch size Savannah sparrows will lay, always equal to 5 eggs. Used as an offset in the clutch size model. * prop: Proportion of eggs that hatched in the nest. * first_egg_day_ctr: Grand mean-centered first egg day (see definition above). * annual_density_ctr: Grand mean-centered annual population density (see definition above). * rel_first_egg_day: First egg day group mean centered by clutch number and female mating status. #### File: nest\_sub.csv **Description:** Dataset used for the analysis of factors influencing fledging success. Each record is one nest attempt. All variables are the same as in nests_mp.csv and clutch_size.csv. #### File: females\_by\_year.csv **Description:** Dataset used for the analysis of factors influencing whether a female survived from the current year to the subsequent year. Each record is one female in the current year (females may have multiple records for multiple years). All variables are the same as in nests_mp or clutch_size unless otherwise noted. ##### Variables * female_id: Band number of the female. Uniquely identifies individuals but may be repeated in multiple years. * mating_status: Female's mating status in the current year (monogamous, MO; or polygynous, PG). * female_number: Female's number in the current year (1 if monogamous or primary polygynous, 2 if secondary polygynous). * female_status: Female's mating status and number in the current year (MO if monogamous, PG 1 if primary polygynous, PG 2 if secondary polygynous). * female_survived: Whether the female survived from the current year to a subsequent year (logical, true or false). * female_survived.f: Whether the female survived from the current year to a subsequent year (binary, 1 if survived, 0 if not). #### File: fledglings\_sub.csv **Description:** Dataset used for the analysis of factors influencing the total number of fledglings produced by a female in a year. Each record is one female in the current year (females may have multiple records for multiple years). All variables are the same as in nests_mp or clutch_size unless otherwise noted. ##### Variables * start_day: The date at which a female commenced breeding in the current year, defined as the first egg date of her first nest attempt that year. * f_yr: The combination of a female's band number and year (uniquely identifying). * start_day_ctr: Grand mean-centered start day. * rel_start_day: Start day group mean-centered by clutch number and female mating status. #### File: fl\_data.csv **Description:** Dataset used for the analysis of factors influencing the number of fledglings produced per nest by a female. Each record is one nest. All variables are the same as in nests_mp or clutch_size unless otherwise noted. ##### Variables * prop: The proportion of nestlings in the nest that fledged. #### File: recruit\_data.csv **Description:** Dataset used for the analysis of factors influencing whether a fledgling recruited into the breeding population. Each record is one individual fledgling. All variables are the same as in nests_mp or clutch_size unless otherwise noted. All nest-level variables (e.g. nest_key, eggs_laid, female_id, found_date, etc.) refer to the individual's natal nest. ##### Variables * year: The year in which the individual fledged. * band_id: The individual's band number (uniquely identifying). * adult_color: The individual's color band combination as an adult. * hy_color: The individual's color band combination as a nestling. * sex: The individual's sex, male or female or unknown. * birth_year: The individual's birth year. * known_age: Whether the individual was known-age, i.e. banded as a nestling. * banding_age: The age at which the individual was banded (see banding age variables above). * mother_id: Mother's band number. * father_id: Father's band number. * banding_date: Date on which the individual was first banded. * mother_color: Mother's color band combination. * father_color: Father's color band combination. * location: Location on the study grid where individual was banded. * weight: Mass of the individual in grams. * tarsus: Tarsus length of the individual in mm. * wing_l: Wing length of the individual in mm. * tail_l: Tail length of the individual in mm. * bill_l: Bill length of the individual in mm. * bill_d: Bill depth of the individual in mm. * date_measured: Date on which the individual was measured. * time_measured: Time at which the individual was measured. * sex.morph: Sex of the individual. * age_in_yrs: Age of the individual in years when banded. * age_in_d: Age of the individual in days when banded. * color: Color band combination when banded. * year.morph: Year when banded. * fat_score: Fat score, range 0-7. * bander_id: Initials of the bander. * was_mother: Whether the individual was ever recorded as a breeding female in the study area (used to determine whether individual recruited; logical, true or false). * was_father: Whether the individual was ever recorded as a breeding male in the study area (used to determine whether individual recruited; logical, true or false). * was_captured: Whether the individual was ever recaptured in the study area (used to determine whether individual recruited; logical, true or false). * recruited: Whether the individual ever bred or was recaptured in the study area (logical, true or false). * fledge_date_noNA: Fledge date with missing dates estimated (see the related article, Mueller et al. *Behavioral Ecology*, for details). * weight_ctr: Grand mean-centered weight. * fledge_day: Ordinal date of fledging. * fledge_day_ctr: Grand mean-centered date of fledging. * recruited.f: Whether the individual ever bred or was recaptured in the study area (binary, 1 if recruited, 0 if not). * rel_fledge_day: Fledge date group mean-centered by clutch number and female mating status. * age_combo_full.f: Combined sexes and ages of parents * age_combo.f: Combined ages of parents (ASY, ASY if both parents older; ASY, SY if one parent older and one yearling; SY, SY if both yearlings). #### File: Three\_islands.kml **Description:** A GIS layer containing polygyons with boundaries of the Three Islands Archipelago (Kent Island, Hay Island, Sheep Island), NB, CA, and boundaries of the study area. #### File: KI.kml **Description:** A GIS layer containing polygyons delineating forests, buildings, shorelines, and the outline of Kent Island, NB, CA. #### File: us\_states.zip **Description:** A GIS layer containing a polygyon outline of Maine, USA, used for a reference map. #### File: canada\_provinces.zip **Description:** A GIS layer containing a polygyon outlines of Canadian provinces, used for a reference map. ## Code/software All analyses were run in R (v. 4.2.3, R Core Team 2023). Models were fit using the package glmmTMB (v. 1.1.7; Brooks et al. 2017), model diagnostics checked using DHARMa (v. 0.4.6; Hartig 2022), and estimated marginal means generated using emmeans (v. 1.8.5; Lenth 2023).