DOI: 10.5061/dryad.9kd51c5jv
title: Individual optimization of reproductive investment and the cost of incubation in a wild songbird

description: Despite avid interest in life-history trade-offs and the costs of
 reproduction, evidence that increased parental allocation reduces
 subsequent breeding productivity is mixed. This uncertainty may be
 attributable to environmental heterogeneity in space and time,
 necessitating experiments across a range of ecological contexts. Over
 three breeding seasons, we cross-fostered clutches between nests to
 manipulate incubation duration in a wild population of Carolina wrens, a
 species in which only females incubate, to test for a cost of incubation
 on current and future reproduction. Prolonged incubation affected maternal
 productivity in a manner dependent upon the current environment and
 initial investment in eggs, suggesting incubation is optimized according
 to other components of reproduction and individual quality. Effects of
 incubation duration on foster-nestling condition varied between years,
 being costly in one, beneficial in another, and neutral in the third. The
 proportion of young fledged, females’ probability of breeding again within
 seasons, and subsequent clutch sizes all declined with increasing
 incubation effort, effects which became more pronounced as seasons
 progressed. Therefore, costs of incubation were almost entirely dependent
 upon maternal quality and environmental variation, illustrating the
 importance of conducting experiments across a range of environmental
 settings for understanding the costs of reproduction and evolution of
 life-histories.
description: Data were collected from wild Carolina wrens
 (<em>Thryothorus ludovicianus</em>) breeding at the Edward J.
 Meeman Biological field station in southwest TN, USA.
 Data were standardized using z-scores and analyzed using SAS v.
 9.4 (more info can be found in the attached Statistical Code and README
 files). 
description: Individual optimization of reproductive investment and the cost of
 incubation in a wild songbird. (2023). The American Naturalist. Authors:
 Kelly D. Miller*, Ashley J. Atkins Coleman, Kelly L. O'Neil,
 Alexander J. Mueller, Rin D. Pell, and E. Keith Bowers *corresponding
 author (kdmller3@memphis.edu) ***Dataset published to Dryad updated Dec.
 2023 after an error was discovered - one nest was included in the
 originally-published dataset which had been excluded from analyses due to
 partial-brood depredation (only 1 nestling remained, which invariably
 affected measures of parental investment). All authors assisted with data
 collection. K.D. Miller and E.K. Bowers wrote the statistical code. This
 study examined the life-history costs of incubation over three years via a
 manipulation of its duration. The costliness of incubation varied within
 and between years, being entirely dependent on environmental conditions
 and maternal quality. The data collected for this experiment at the Meeman
 Biological Station is contained in a .csv file entitled
 "AmNatDATA." Weather data from the National Oceanic and
 Atmospheric Association station USW00013893 is contained in a .csv file
 entitled "WeatherData" These data were collected from 2018-2020.
 Column headings (variable names) for the AmNatDATA.csv file are described
 below. Most data were standardized prior to analysis by converting to
 z-scores. In the data file, standardized variables are indicated by
 "STD_" before the variable name. Missing data are indicated by a
 period. YEAR: the year in which the nest was created. NEST: nestbox and
 clutch/brood number - A__4z1 represents box A 4, clutch/brood 1 of that
 year. NEST_YEAR: a combination of the NEST and YEAR variables - the last
 two digits of the year follow the nestbox and clutch/brood number. NE:
 number of eggs - the number of eggs present in the nestbox prior to
 hatching. CS: clutch size - the total number of eggs produced in a nesting
 attempt. E1D: egg-1 date - the day of the year (ordinal calendar) on which
 the first egg of the clutch was laid. INCUB_EFFECT: the expected change in
 incubation duration (days) for females after swapping clutches of eggs
 between nests - based on the E1D for the nests involved in the clutch swap
 - positive numbers indicate a longer expected incubation duration and
 negative numbers indicate a shorter expected incubation duration.
 CAT_EFFECT: a categorical grouping of our experimental manipulation; all
 females experiencing a lengthened incubation period (+1-3d) are considered
 "Lengthened," females experiencing a shortened incubation period
 (-1-3d) are considered "Shortened," while those that did not
 experience a change in incubation duration are considered
 "Control." SWAP_DATE: the day of the year (ordinal calendar) on
 which we performed the entire clutch cross-fostering manipulation. BD0:
 brood-day zero - the day of year (ordinal calendar) on which hatching
 begins. INCUB: incubation duration - the number of days a female spent
 incubating eggs. NY4: the number of young present on brood-day four.
 NY_FLEDGED: number of young fledged. FBAND: female band number. FBAND2:
 the last 5 digits of a female's band number. FEM_MASS: female mass
 (g). BRED_SUBSEQUENTLY: a binary variable denoting whether a female did
 (1) or did not (0) breed again within the current year. SUBSEQ_FEM_MASS:
 female mass at her subsequent nest within the same year. SUBSEQ_CS:
 subsequent clutch size - if a female did breed again within the current
 year, the clutch size of her next clutch. FEM_BREED_NEXT_YEAR: a binary
 variable denoting whether a female did (1) or did not (0) breed the
 following year. FEM_ORIGINAL_EGG_SIZE: average egg volume (mL) of a
 female's original clutch, calculated using Hoyt's (1979)
 formula. FOSTER_EGG_SIZE: average egg volume (mL) of the foster clutch a
 female received, calculated using Hoyt's (1979) formula.
 NESTLING_MASS: average nestling mass (g). SUCCESS: a binary variable
 denoting whether a nest was successful (fledging at least 1 young - 1) or
 unsuccessful (0). Column headings (variable names) for the WeatherData.csv
 file are described below. DATE: the day of the year since 01 Jan. YEAR:
 the year in which the data were collected. MONTH: the numerical month of
 the year. PRCP_CM: total amount of precipitation in centimeters. TAVG_C:
 average temperature in Celsius.