DOI: 10.5061/dryad.z8w9ghxsv
title: Data from: Plan ahead, or wing it? How storm-petrel parents adjust food delivery to young chicks

description: Parents must decide how to allocate energy gained from foraging between
 self and offspring. Storm-petrels (Procellariiformes: Hydrobatidae) are
 pelagic seabirds that travel hundreds of kilometers across multiple days
 before returning to the nesting burrow to feed a dependent chick. Parents
 return to the nest with food stored in the proventriculus, a portion of
 which is regurgitated to their offspring. As the chick grows, provisioning
 demands increase. However, it is unknown whether parents meet this
 increasing demand by (1) altering their foraging strategies to acquire
 more food or (2) allocating a greater proportion of their intake to the
 chick. We designed, validated, and implemented a new technology—the Burrow
 Scale Monitor—to measure Leach’s storm-petrels (Hydrobates leucorhous) as
 they entered and exited the nesting burrow. We monitored breeding adults
 over the first 30 days of chick rearing to determine whether storm-petrel
 parents adjust their foraging intake to the age of the chick or simply
 adjust energy allocation at the nest. Food delivery increased with chick
 age, but this increase was driven to a much greater extent by parents
 delivering a greater proportion of their body mass as food (i.e., a shift
 in parental allocation) rather than by adults adjusting their foraging
 strategy to match chick age. Only by measuring adult body mass on arrival
 and exit at the nesting burrow could we understand how parents adapt their
 provisioning strategy to the increasing demands of the growing
 chick. 
description: # Data from: Plan ahead, or wing it? How storm-petrel parents adjust food
 delivery to young chicks Dataset DOI:
 [10.5061/dryad.z8w9ghxsv](https://doi.org/10.5061/dryad.z8w9ghxsv) ##
 Description of the data and file structure We developed the Burrow Scale
 Monitor to passively measure adult mass of Leach's storm-petrels as
 they entered and exited their nesting burrow. We used these data to detect
 food delivery by parents to a single chick in the nesting burrow and the
 proportion of arrival weight that was allocated to the chick to test the
 parental strategy behind food allocation to chick or self. Data were
 collected at the Bowdoin Scientific Station at Kent Island, NB, Canada
 from 8 July to 9 August 2024. ### Files and variables *
 BEHECO-2025-0162_Main_Paper  * This is the data file on which all of the
 analyses presented to test the hypothesis addressed in the paper are
 based. Missing values are designated by "NA" for importing into
 R. * The fields include: * Burrow: ID for each nesting burrow and used as
 a random effect in all analyses * Filename: original data file on which
 the weight calculations as described in Supplemental Materials were based.
 These are the original raw data files from the Burrow Scale Monitor's
 weights were derived. The filename format is includes the date the data
 were collected. These are not necessary for any analyses and are only here
 for reference. See "Raw Data Availability" below. * RFID: Unique
 ID from RFID chip for the adults in the current analysis, if known. Used
 as a random effect in some analyses. * Wt_Entry: entry weight of the adult
 into the burrow on a particular feeding event (g) * Wt_Exit: exit weight
 of the adult from the burrow on a particular feeding event (g) * Wt_Del:
 difference betwen Wt_Entry and Wt_Exit (g) * LoadSize: ABS(Wt_Del) - food
 delivery to chick (g) * PCT: LoadSize / Wt_Entry (proportion) * ChickAge:
 unit = days where 0 = first day chick found in burrow * DOY: Day of year -
 BEHECO-2025-0162_Suppl * The data used in the Validation Procedure
 described in Supplemental Materials * The fields include: * File: original
 data file on which the weight calculations as described in Supplemental
 Materials were based. These are the original raw data files from the
 Burrow Scale Monitor's weights were derived. The filename format is
 includes the date the data were collected. These are not necessary for any
 analyses and are only here for reference. See "Raw Data
 Availability" below. * Run: the iteration for the bird tested *
 Weight_BSM: calculate weight of adult (g) * Scale: Actual weight of the
 adult (g) * Err_New: Scale - Weight_BSM (g) * Less43: flag for printing (0
 or 1) that designates Weight_BSM that were recalculated using the Manual
 method as described in the Supplemental Materials. ## Raw Data
 Availability * The raw BSM data collected and raw data analysis are
 described in Supplemental Materials * Raw data were collected at ~60z for
 24 hours resulting in daily files for each burrow of &gt; 70MB * Raw data
 are available on request (mauckr@kenyon.edu) ## Code/software Statistical
 Software: \-- All analyses were conducted in R version 4.1.1 (R Core Team
 2021). We used linear mixed effects modeling (‘lmer’) with the package
 ‘lme4’ version 1.1-27.1 (Bates et al. 2015) to estimate the relationships
 between variables in the field data. \-- All models involved normally
 distributed response variables. We used linear mixed models (LMM) fit by
 restricted maximum likelihood (REML) with the default ‘identity’ link.
 Within the LMMs, we used Satterthwaite's method in
 'lmerModLmerTest' to calculate the t-value of the independent
 variables (lmerTest Package version 3.1-3; 2021). ## Contact for
 information about the datasets * Robert Mauck * Kenyon College * email:
 [mauckr@kenyon.edu](mailto:mauckr@kenyon.edu)