Description
The adaptiveness of adoption for donors, recipients, and offspring remains
unsettled despite long-standing interest. Using decade-long data on
individually marked female and duckling common eiders (Somateria
mollissima), displaying frequent alloparenting, we examined factors
influencing the likelihood of females donating young and ducklings being
adopted. We explored how donor traits, including maternal body condition,
relative head size (a proxy of relative brain size), and relative hatching
date, and offspring characteristics such as body condition relative to
siblings, affect these processes. At least one offspring was permanently
adopted in 34.7% of brood observations. Females in better body condition
and larger relative head size were less likely to donate offspring, while
the likelihood of offspring transfer was higher in larger natal broods.
The odds of offspring donation peaked just before the population’s
hatching peak, suggesting that recipient availability influences adoption.
Ducklings in poorer body condition than their natal broodmates and those
whose mothers were in lower body condition were, respectively,
significantly and marginally significantly more likely to be adopted.
Offspring transfers may thus result from physiological and cognitive
constraints, rather than reflecting a fitness-maximizing strategy.
Donating young and becoming adopted ultimately align with a salvage
strategy for poor-condition donors and poor-condition offspring, but are
likely driven by constraints rather than active tactics. Multiple tenders
in broods prevented unique recipient identification, yet prior research
suggests that recipients may accrue fitness benefits. Future research
quantifying the fitness consequences for all parties in different
environmental contexts is required for a more comprehensive understanding
of alloparental behavior. Keywords: alternative reproductive tactics, body
condition, cognitive constraints, common eider, conspecific brood
parasitism, salvage strategy
# Breaking bonds: maternal and offspring state shape constraint-based
brood adoption in a seaduck **Article title:** Breaking bonds: maternal
and offspring states relate to constraint-based brood donation in a
seaduck\ **Journal:** Behavioral Ecology\ **Manuscript ID:**
BEHECO-2025-0052.R2\ **Authors:** Markus Öst; Benjamin Steele; Kim
Jaatinen\ **Corresponding author:** Markus Öst
([[email protected]](mailto:[email protected])) ## Dataset overview This
repository contains the raw data underlying two logistic regression
analyses reported in the manuscript: 1. **Female-level analysis** —
factors associated with whether a female was a *donor* (lost at least one
duckling to another brood) vs. a *reference* (no permanent loss).\
**File:** `Data1_BEHECO-2025-0052_clean.csv` (cleaned, standardized
variable names) 2. **Duckling-level analysis** — factors associated with
whether an individual duckling was *adopted* into another brood vs.
*stayed* in the natal brood.\ **File:** `Data2_BEHECO-2025-0052_clean.csv`
(cleaned, standardized variable names) ## File formats and encodings * All
tabular data are UTF-8 encoded comma-separated values (CSV) files with one
header row and no BOM. * Missing values are represented by empty
cells/`NA`. * Decimal separator is a period. * No thousands separators are
used. ## Variable dictionary ### 1) `Data1_BEHECO-2025-0052.csv`
(female-level) | Variable | Type | Units / Coding | Description | |
----------------------------------------------- | ------- |
------------------- |
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `year` | integer | year | Study year (2008–2017). | | `female_id` | integer | id | Unique identifier of the focal female (steel band number), referring to the potential donor. | | `female_age_years` | integer | years | Minimum age since banding in breeding population (0 = banding year/first recorded breeding; 1 = the following year, etc.). | | `female_breeding_experience_firsttimer0_prior1` | integer | 0/1 | 0 = first recorded breeder; 1 = previously banded breeder. | | `viable_brood_size_at_hatching` | integer | number of ducklings | Number of live, viable ducklings at hatch. | | `female_body_condition_index` | float | index (unitless) | Size-corrected body condition: standardized residuals from a linear regression predicting female projected weight at hatching from structural size (radius–ulna length). Positive values indicate better condition (see Methods). | | `donor_status_1donor_0reference` | integer | 0/1 | 1 = female donated/lost ≥1 duckling to another brood (permanent); 0 = no permanent loss (reference). | | `female_relative_head_size_index` | float | index (unitless) | Size-corrected head volume residuals (proxy for relative brain size). Higher values = relatively larger head. | | `hatch_date_offset_from_annual_median_days` | integer | days | Hatch date minus the population’s annual median hatch date (negative = before peak; positive = after). | ### 2) `Data2_BEHECO-2025-0052_clean.csv` (duckling-level) | Variable | Type | Units / Coding | Description | | ----------------------------------------------- | ------- | ------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `year` | integer | year | Study year (2008–2017). | | `female_id` | integer | id | ID of the natal (donor) female associated with the duckling. | | `duckling_weight_g` | integer | g | Weight of individual duckling at hatch. | | `duckling_tarsus_mm` | float | mm | Tarsus length of individual duckling at hatch. | | `adopted_status_1adopted_0stayed` | integer | 0/1 | 1 = duckling permanently adopted into another brood; 0 = remained in natal brood. | | `female_body_condition_index` | float | index (unitless) | Natal female’s body condition index: standardized residuals from a linear regression predicting female projected weight at hatching from structural size (radius–ulna length). Positive values indicate better condition (see Methods). | | `duckling_tarsus_mm_centered_within_brood` | float | mm | Within-brood deviation of the focal duckling’s tarsus length from the mean tarsus length of all ducklings in its natal brood. | | `duckling_weight_g_centered_within_brood` | float | g | Within-brood deviation of the focal duckling’s weight from the mean weight of all ducklings in its natal brood. | | `duckling_body_condition_centered_within_brood` | float | index | Within-brood deviation of the focal duckling’s body condition from the mean body condition of all ducklings in its natal brood. Duckling body condition was calculated as standardized residuals from a linear regression of hatch weight on structural size (tarsus length); higher values indicate better condition. | | `female_age_years` | integer | years | Minimum age since banding in breeding population (0 = banding year/first recorded breeding; 1 = the following year, etc.). | | `female_breeding_experience_firsttimer0_prior1` | integer | 0/1 | 0 = first recorded breeder; 1 = previously banded breeder. | | `viable_brood_size_at_hatching` | integer | number of ducklings | Number of live, viable ducklings at hatch for natal female. | | `hatch_date_offset_from_annual_median_days` | integer | days | Hatch date minus the population’s annual median hatch date (negative = before peak; positive = after). | ## Study site, data collection, and derived variables (summary) Fieldwork took place in the Tvärminne archipelago (59°50′N, 23°15′E), Western Gulf of Finland, from 2008 to 2017. Data were collected at two time points: (i) capture of incubating females in late incubation and (ii) nest revisits at the estimated hatching of each brood. Refer to the variable dictionary above for variable definitions and calculations, and to the manuscript for full details. ## Code & analyses Statistical analyses were performed in R 4.0.4 using binomial GLMs with model selection and model averaging. Non-base packages: * **MuMIn 1.43.17** (model selection and averaging) * **varTestnlme 1.3.5** (variance component tests) * **rptR 0.9.23** (repeatability estimates) ## Ethical approvals Fieldwork complied with Finnish regulations; permits: ESLH-2009-02969/Ym-23; ESAVI/1697/04.10.03/2012; ESAVI/2831/04.10.07/2015. ## File naming conventions Filenames and column names use ASCII, lowercase_with_underscores; indicator variables are coded 0/1 as documented in the variable dictionary. ## How to cite this dataset Öst M, Steele B, Jaatinen K (2025). Breaking bonds: maternal and offspring states relate to constraint-based brood donation in a seaduck. Dryad Digital Repository. [https://doi.org/10.5061/dryad.d51c5b0hb](https://doi.org/10.5061/dryad.d51c5b0hb). ## Contact Corresponding author: Markus Öst ([[email protected]](mailto:[email protected])).
unsettled despite long-standing interest. Using decade-long data on
individually marked female and duckling common eiders (Somateria
mollissima), displaying frequent alloparenting, we examined factors
influencing the likelihood of females donating young and ducklings being
adopted. We explored how donor traits, including maternal body condition,
relative head size (a proxy of relative brain size), and relative hatching
date, and offspring characteristics such as body condition relative to
siblings, affect these processes. At least one offspring was permanently
adopted in 34.7% of brood observations. Females in better body condition
and larger relative head size were less likely to donate offspring, while
the likelihood of offspring transfer was higher in larger natal broods.
The odds of offspring donation peaked just before the population’s
hatching peak, suggesting that recipient availability influences adoption.
Ducklings in poorer body condition than their natal broodmates and those
whose mothers were in lower body condition were, respectively,
significantly and marginally significantly more likely to be adopted.
Offspring transfers may thus result from physiological and cognitive
constraints, rather than reflecting a fitness-maximizing strategy.
Donating young and becoming adopted ultimately align with a salvage
strategy for poor-condition donors and poor-condition offspring, but are
likely driven by constraints rather than active tactics. Multiple tenders
in broods prevented unique recipient identification, yet prior research
suggests that recipients may accrue fitness benefits. Future research
quantifying the fitness consequences for all parties in different
environmental contexts is required for a more comprehensive understanding
of alloparental behavior. Keywords: alternative reproductive tactics, body
condition, cognitive constraints, common eider, conspecific brood
parasitism, salvage strategy
# Breaking bonds: maternal and offspring state shape constraint-based
brood adoption in a seaduck **Article title:** Breaking bonds: maternal
and offspring states relate to constraint-based brood donation in a
seaduck\ **Journal:** Behavioral Ecology\ **Manuscript ID:**
BEHECO-2025-0052.R2\ **Authors:** Markus Öst; Benjamin Steele; Kim
Jaatinen\ **Corresponding author:** Markus Öst
([[email protected]](mailto:[email protected])) ## Dataset overview This
repository contains the raw data underlying two logistic regression
analyses reported in the manuscript: 1. **Female-level analysis** —
factors associated with whether a female was a *donor* (lost at least one
duckling to another brood) vs. a *reference* (no permanent loss).\
**File:** `Data1_BEHECO-2025-0052_clean.csv` (cleaned, standardized
variable names) 2. **Duckling-level analysis** — factors associated with
whether an individual duckling was *adopted* into another brood vs.
*stayed* in the natal brood.\ **File:** `Data2_BEHECO-2025-0052_clean.csv`
(cleaned, standardized variable names) ## File formats and encodings * All
tabular data are UTF-8 encoded comma-separated values (CSV) files with one
header row and no BOM. * Missing values are represented by empty
cells/`NA`. * Decimal separator is a period. * No thousands separators are
used. ## Variable dictionary ### 1) `Data1_BEHECO-2025-0052.csv`
(female-level) | Variable | Type | Units / Coding | Description | |
----------------------------------------------- | ------- |
------------------- |
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `year` | integer | year | Study year (2008–2017). | | `female_id` | integer | id | Unique identifier of the focal female (steel band number), referring to the potential donor. | | `female_age_years` | integer | years | Minimum age since banding in breeding population (0 = banding year/first recorded breeding; 1 = the following year, etc.). | | `female_breeding_experience_firsttimer0_prior1` | integer | 0/1 | 0 = first recorded breeder; 1 = previously banded breeder. | | `viable_brood_size_at_hatching` | integer | number of ducklings | Number of live, viable ducklings at hatch. | | `female_body_condition_index` | float | index (unitless) | Size-corrected body condition: standardized residuals from a linear regression predicting female projected weight at hatching from structural size (radius–ulna length). Positive values indicate better condition (see Methods). | | `donor_status_1donor_0reference` | integer | 0/1 | 1 = female donated/lost ≥1 duckling to another brood (permanent); 0 = no permanent loss (reference). | | `female_relative_head_size_index` | float | index (unitless) | Size-corrected head volume residuals (proxy for relative brain size). Higher values = relatively larger head. | | `hatch_date_offset_from_annual_median_days` | integer | days | Hatch date minus the population’s annual median hatch date (negative = before peak; positive = after). | ### 2) `Data2_BEHECO-2025-0052_clean.csv` (duckling-level) | Variable | Type | Units / Coding | Description | | ----------------------------------------------- | ------- | ------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `year` | integer | year | Study year (2008–2017). | | `female_id` | integer | id | ID of the natal (donor) female associated with the duckling. | | `duckling_weight_g` | integer | g | Weight of individual duckling at hatch. | | `duckling_tarsus_mm` | float | mm | Tarsus length of individual duckling at hatch. | | `adopted_status_1adopted_0stayed` | integer | 0/1 | 1 = duckling permanently adopted into another brood; 0 = remained in natal brood. | | `female_body_condition_index` | float | index (unitless) | Natal female’s body condition index: standardized residuals from a linear regression predicting female projected weight at hatching from structural size (radius–ulna length). Positive values indicate better condition (see Methods). | | `duckling_tarsus_mm_centered_within_brood` | float | mm | Within-brood deviation of the focal duckling’s tarsus length from the mean tarsus length of all ducklings in its natal brood. | | `duckling_weight_g_centered_within_brood` | float | g | Within-brood deviation of the focal duckling’s weight from the mean weight of all ducklings in its natal brood. | | `duckling_body_condition_centered_within_brood` | float | index | Within-brood deviation of the focal duckling’s body condition from the mean body condition of all ducklings in its natal brood. Duckling body condition was calculated as standardized residuals from a linear regression of hatch weight on structural size (tarsus length); higher values indicate better condition. | | `female_age_years` | integer | years | Minimum age since banding in breeding population (0 = banding year/first recorded breeding; 1 = the following year, etc.). | | `female_breeding_experience_firsttimer0_prior1` | integer | 0/1 | 0 = first recorded breeder; 1 = previously banded breeder. | | `viable_brood_size_at_hatching` | integer | number of ducklings | Number of live, viable ducklings at hatch for natal female. | | `hatch_date_offset_from_annual_median_days` | integer | days | Hatch date minus the population’s annual median hatch date (negative = before peak; positive = after). | ## Study site, data collection, and derived variables (summary) Fieldwork took place in the Tvärminne archipelago (59°50′N, 23°15′E), Western Gulf of Finland, from 2008 to 2017. Data were collected at two time points: (i) capture of incubating females in late incubation and (ii) nest revisits at the estimated hatching of each brood. Refer to the variable dictionary above for variable definitions and calculations, and to the manuscript for full details. ## Code & analyses Statistical analyses were performed in R 4.0.4 using binomial GLMs with model selection and model averaging. Non-base packages: * **MuMIn 1.43.17** (model selection and averaging) * **varTestnlme 1.3.5** (variance component tests) * **rptR 0.9.23** (repeatability estimates) ## Ethical approvals Fieldwork complied with Finnish regulations; permits: ESLH-2009-02969/Ym-23; ESAVI/1697/04.10.03/2012; ESAVI/2831/04.10.07/2015. ## File naming conventions Filenames and column names use ASCII, lowercase_with_underscores; indicator variables are coded 0/1 as documented in the variable dictionary. ## How to cite this dataset Öst M, Steele B, Jaatinen K (2025). Breaking bonds: maternal and offspring states relate to constraint-based brood donation in a seaduck. Dryad Digital Repository. [https://doi.org/10.5061/dryad.d51c5b0hb](https://doi.org/10.5061/dryad.d51c5b0hb). ## Contact Corresponding author: Markus Öst ([[email protected]](mailto:[email protected])).
| Date made available | 3 Nov 2025 |
|---|---|
| Publisher | DRYAD |
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