Data from: Nestling growth and brood reduction in the southern yellow-billed hornbill (Tockus leucomelas)
Data files
Nov 17, 2025 version files 784.72 KB
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Hornbill_Analyses_Ecology-Evolution_09.18.25.Rmd
35.99 KB
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Rainfall-FINAL.csv
1.19 KB
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README.md
5.09 KB
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YBH-Date-FINAL.csv
380.26 KB
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YBH-Growth-FINAL.csv
362.19 KB
Abstract
Hatching asynchrony is common among altricial bird species and has long been hypothesized to facilitate brood reduction, which in turn may maximize reproductive outputs in environments with variable resource availability. Despite its prevalence, the drivers and mechanisms of brood reduction are not well understood for many species. The southern yellow-billed hornbill, Tockus leucomelas, is a useful model for understanding brood reduction because it exhibits extreme hatching asynchrony and a unique nesting strategy where the female and the brood are sealed within a cavity, sheltered from predators. Here, we documented aspects of breeding biology in artificial nest boxes and assessed the influence of various factors on nestling growth and mortality. Earlier-hatched nestlings had higher growth rates throughout development and were more likely to survive to fledge than their younger siblings. Maternal presence in the nest had positive impacts on growth rates of later-hatched nestlings, likely reflecting the female’s role in mitigating sibling competition. Despite differences in growth and survival during the nesting period, weight at fledging did not differ according to hatch order, suggesting that later-hatched nestlings may fare similarly to older siblings if they survive to fledge. Using a path analysis, we found support for the hypothesis that rainfall (a proxy for resource availability) indirectly influences the likelihood of brood reduction via its effects on the growth rate of the youngest nestling. Brood size, per se, was also a significant predictor of the youngest nestling growth rate and brood reduction. These relationships between hatch order, brood size, nestling growth and mortality, and environmental variables provide support for some predictions of the brood reduction hypothesis for the function of hatching asynchrony and advance our understanding of brood reduction dynamics in this species.
Dataset DOI: 10.5061/dryad.jsxksn0pj
Description of the data and file structure
Our data includes 3 .CSV files: 1) data with rainfall (Rainfall-FINAL.csv), 2) data with nestling growth rate (YBH-Growth-FINAL.csv), and 3) data with nestling brood reduction (YBH-Date-FINAL.csv). YBH-Growth-FINAL.csv and YBH-Date-FINAL.csv contain the same nestlings and nest boxes (the IDs are the same), however the former also includes information about change in growth and the latter includes information about brood reduction.
All analyses were performed in R: Hornbill_Analyses_Ecology-Evolution_09.18.25.Rmd .
Files and variables
File: Rainfall-FINAL.csv
Description: Data includes rainfall measurements from CHIRPS: Rainfall Estimates from Rain Gauge and Satellite Observations for our study system.
Variables
- Year: Year of rainfall
- Spring_Rain_mm_CHIRPS: Spring rainfall from CHIRPS (mm). Missing data represented with NA. Not used in analyses.
- Total_Rain_mm_CHIRPS: Total rainfall for that year from CHIRPS (mm). Used in analyses.
- Year_Range: Corresponding breeding/field season for data entry
File: YBH-Growth-FINAL.csv
Description: Data includes the measurements and observations from nestlings, including change in growth, made when nest box was visited. All IDs for nestlings and boxes correspond to YBH-Date-FINAL.csv
Variables
- Year: Year of observation
- Box: Box ID used in the field
- Box_Clean: Box ID used in data analysis (often Box IDs were repeated between years)
- Month: Month of observation
- Date: Date of observation
- Species: Species of hornbill (always southern yellow-billed hornbill or YBH)
- CurntBrdSze: Number of hatched nestlings present at time of observation
- FemPresnt.: If the mother was present in the nest
- FemPresent_Clean: If the mother was present in the nest: Y (yes), N (no), and NA
- ChickID: Identity of nestling (band number or other descriptive characteristic)
- ChickID_Clean: Identity of the nestling used for data analysis. The ID is formatted to be Box_Clean-Rank. For example, the first hatched nestling in Box_Clean 3 would have a ChickID_Clean of 3-1.
- Rank: The order at which the nestling hatched (i.e. oldest chick was rank 1)
- Survival_Clean: If the nestling survived to fledge: Y (yes), N (no), and NA
- Fate: Comments on what happened to the nestling
- Band: Band number of nestling
- HatchDate: Estimated date the nestling hatched
- Age: Estimated age at measurement
- MassTot: Total mass of the nestling and the bag (grams)
- Bag: Mass of the bag (grams)
- BirdMass: Mass of the nesting (grams)
- MassChange: Change in mass from the last measurement (grams)
- Comments: Additional comments on nest and nestlings
File: YBH-Date-FINAL.csv
Description: Data includes the measurements and observations from nestlings, specifically related to nestling mortality, during nest box visits. All IDs for nestlings and boxes correspond to YBH-Growth-FINAL.csv .
Variables
- Year: Year of observation
- Box: Box ID used in the field
- Box_Clean: Box ID used in data analysis (often Box IDs were repeated between years)
- Month: Month of observation
- Date: Date of observation
- Species: Species of hornbill (always southern yellow-billed hornbill, or YBH)
- CurntBrdSze: How many hatched nestlings were present in the nest
- Brood_Reduction: Whether or not brood reduction occurred if: 1) the brood size decreased from the last observation and the nestlings were too young to fledge or 2) if there were specific comments about observed nestling mortality
- EverBroodRed: If the nest ever experience brood reduction during the entire observation period
- FemPresnt: If the mother was present in the nest
- FemPresent_Clean: If the mother was present in the nest: Y (yes), N (no), and NA
- ChickID: Identity of nestling (band number or other descriptive characteristic)
- ChickID_Clean: Identity of the nestling used for data analysis. The ID is formatted to be Box_Clean-Rank. For example, the first hatched nestling in Box_Clean 3 would have a ChickID_Clean of 3-1.
- Rank: The order at which the nestling hatched (i.e. oldest chick was rank 1)
- Survival_Clean: If the nestling survived to fledge Y (yes), N (no), and NA
- EverBroodDead: If the nestling eventually died due to brood reduction
- Fate: Comments on what happened to the nestling
- HatchDate: Estimated hatch date of nestling
- Age: Estimated Age of nestling
- MassTot: Total mass of the nestling and the bag (grams)
- Bag: Mass of the bag (grams)
- BirdMass: Mass of the nesting (grams)
Code/software
All statistical analyses were performed in R with the attached R Markdown file: Hornbill_Analyses_Ecology-Evolution_09.18.25.Rmd. It produces growth plots and statistical models showing how hatch rank affects mass and development.
Access information
Data was derived from the following sources:
- CHIRPS Rainfall Data