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Individual optimization of reproductive investment and the cost of incubation in a wild songbird

Cite this dataset

Miller, Kelly et al. (2023). Individual optimization of reproductive investment and the cost of incubation in a wild songbird [Dataset]. Dryad.


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.


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 (

***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.


Data were collected from wild Carolina wrens (Thryothorus ludovicianus) 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). 


University of Memphis