DOI: 10.5061/dryad.jsxksn0pj
title: Data from: Nestling growth and brood reduction in the southern yellow-billed hornbill (<em>Tockus leucomelas</em>)

description: 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.
description: # Data from: Nestling growth and brood reduction in the southern
 yellow-billed hornbill (*Tockus leucomelas*) Dataset DOI:
 [10.5061/dryad.jsxksn0pj](https://doi.org/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