DOI: 10.5061/dryad.f4qrfj755
title: Escalated begging does not compromise nestling health

description: A widely accepted explanation for the reliability of offspring begging
 signals assumes a differential benefits model balanced by direct viability
 costs independent of offspring nutritional condition. However, supporting
 evidence for this idea is inconclusive and often hampered by
 methodological limitations, including differential stimulation protocols
 and reliance on single, potentially biased markers of nestling health.
 This study tested the existence of direct, intrinsic, and
 condition-independent trade-offs between begging and body mass, immunity
 and oxidative stress by manipulating the begging effort of spotless
 starling (Sturnus unicolor) nestlings while maintaining constant food
 intake. We addressed potential problems of previous experimental
 protocols, ensuring uniform stimulation levels and evaluating multiple
 immune and oxidative markers. We observed no significant effects of
 experimentally increased begging effort in any of the 14 physiological
 markers analysed, with 95% confidence intervals of effect sizes
 consistently including zero or one (for the lysis capacity of plasma),
 indicating no biologically relevant effects. Overall, our findings suggest
 no physiological trade-offs associated with intense begging.
description: <strong>Experimental design</strong>
 The study was conducted during the spring of 2022 in a nest-box
 breeding population of spotless starlings (<em>Sturnus
 unicolor</em>) in central Spain (Soto del Real, Madrid). Spotless
 starlings are medium-sized colonial passerines that typically lay two
 asynchronous clutches per season, with a modal brood size of four
 nestlings (Veiga and Polo 2016). Hatching dates were determined through
 regular inspections. All procedures were reviewed by the Animal
 Experimentation Ethics Committee of the University of Castilla-La Mancha
 and approved by the competent authority of the Junta de Comunidades de
 Castilla-La Mancha (approval reference: PR-2020-03-08), thus complying
 with current European, Spanish and Institutional guidelines for the care
 and use of animals. The experiment involved 58
 nestlings from 29 nests at the end of the linear growth phase (9-10 days
 after hatching, (Muriel et al. 2021). In the afternoon preceding the
 experiment (at 8 days of age), we selected two chicks of intermediate mass
 rank from each brood, ensuring at least two nestlings remained to prevent
 parental desertion. Initial blood samples (350 µl) were taken from the
 jugular vein of the focal chicks to measure basal levels of immune and
 oxidative markers. We also weighed the nestlings (accuracy = 0.1 g) and
 randomly assigned them to either a high-begging (HB) or low-begging (LB)
 treatment. Nestlings were then transported in a warm container to the
 laboratory, where they were placed in individual nest cups inside an
 incubator (RCOM 50 PRO, Autoelex, Korea) with controlled temperature
 (27-33 °C) and humidity (55-60%), ensuring identical environmental
 conditions and potential stressors. That afternoon, nestlings were
 conditioned to a standard begging stimulus (a playback of a parental
 nest-feeding call recorded from the same population) while being fed
 crickets (<em>Acheta domestica</em>) ad libitum.
 Early the next morning (day 9), nestlings were weighed after the
 first meal of the day. We estimated the daily food intake based on their
 mass, following the allometric relationship by Weathers (Weathers 1996):
 daily food intake = 0.98 × M^0.814, where M is nestling body mass in
 grams. The daily food was divided into 12 equal portions, corresponding to
 12 begging sessions conducted every hour from 8:00 to 20:00. Feeding
 intervals were based on mean intervals of parental feeding rates per
 nestling obtained from continuous recordings of 48 nests aged 6-8 days in
 our study population (mean interval ± SE = 59.05 ± 4.27 min). Any
 deviations from expected food intake were compensated for in subsequent
 sessions. The food consisted of alternating crickets and tiny omelette
 chunks (boiled egg), each weighed individually (Redondo et al. 2016).
 Whole egg is considered a high-quality diet (Moreno-Rueda and Redondo
 2012), while insects are the bulk of the natural diet for nestlings (Veiga
 and Polo 2016). During each feeding session, both
 nestlings in each dyad were carried together, covered by a cloth, to an
 adjacent room and stimulated to beg using the same playback of a feeding
 call. Each session included 1-4 trials in a random sequence determined
 beforehand as in Rodríguez-Gironés et al. (2001). Transporting both
 nestlings together ensured they experienced the same stressors and
 acoustic stimulation, which can influence glucocorticoid levels. To induce
 differences in begging effort, LB nestlings were fed immediately after
 gaping, while HB nestlings were stimulated to beg repeatedly by playing
 the playback and placing forceps over their mouths for 30 seconds longer
 than LB nestlings, resulting in a maximum cumulative duration of 2 minutes
 more per session in the 4-trial sessions. This duration was chosen to
 ensure differences in hourly begging rates between experimental groups
 comparable to previous studies assessing the physiological impact of
 begging. Our protocol resulted in differential begging rates higher than
 45.5% of previous studies (Leonard et al. 2003; Moreno-Rueda and Redondo
 2011, 2012; Moreno-Rueda et al. 2012; Redondo et al. 2016), exceeded by
 six studies (Soler et al. 1999; Kilner 2001; Rodríguez-Gironés et al.
 2001; Moreno-Rueda 2010; Soler et al. 2014; Nettle et al. 2017).
 Two 4-trial begging sessions (at 11:00h and 17:00h) were recorded
 with a digital video camera (Panasonic HC-V180) to validate the effects of
 the experimental manipulation on begging effort. A trained observer, blind
 to the experiment's purpose and chick treatments, analysed the videos
 at a reduced speed (0.125x) using Solomon Coder software (Version: beta
 19.08.02, (Péter 2013). Postural begging intensity was assessed on a
 five-level ordinal scale: 0 (no begging), 1 (gaping, neck flexed, body
 horizontal), 2 (gaping, neck extended, body horizontal), 3 (gaping, neck
 extended, body off the nest floor, back reclining), and 4 (fully
 stretched, vertical back, sometimes wing flapping) (adapted from (Redondo
 and Castro 1992). For each trial, we recorded the time spent by the
 nestling at each postural intensity level and calculated the total
 duration of the begging bout by summing these durations. A summed begging
 score was computed by multiplying the duration of each begging level by
 its rank and summing them (Leech and Leonard 1996; Kilner 2001). The mean
 postural intensity was obtained by dividing the summed begging score by
 the total duration. Nestlings were weighed again at the end of the
 day. The same procedure was repeated on day 10, except
 that after the last begging session, a 350 µl blood sample was collected
 from the jugular vein to analyse post-treatment immune and oxidative
 stress markers. All samples from both days 8 and 10 were collected while
 recording the time elapsed between opening the nest box or the incubator
 and sample collection (always &lt; 3 min) to minimize disturbance
 effects on corticosterone (CORT) values (Jimeno et al. 2017). Samples were
 stored at 4°C until centrifugation (5 min at 4°C and 9,000g) within 2
 hours after collection. Plasma and pellet were separated, the pellet was
 washed with cold saline solution, and both fractions were frozen at -80°C
 until analysis. Nestlings were returned to their original nests the
 following morning (day 11). At this moment, one randomly selected
 non-experimental nestmate was also blood-sampled within 3 minutes after
 opening the nest box to analyse potential differences in CORT levels due
 to laboratory procedures. To verify that our
 experimental manipulation induced elevated begging in HB nestlings within
 the range of natural begging durations, wWe used data frommeasured
 individual durations of begging bouts in 164 feeding events of from 41
 broods with 9-10 days-old chicks, recorded using an infrared video camera
 (BOBLOV PD50-32GB)., to calculate the duration of begging bouts under
 natural conditions. This allowed us to verify that our experimental
 manipulation induced elevated begging in HB nestlings, but still within
 the range of natural begging durations in wild broods. 
 <strong>Immunological and oxidative stress
 assays</strong> We quantified several
 immunological markers involving cell-mediated, humoral, and integrated
 immunity of both innate and acquired components. Specifically, we assessed
 the inflammatory T-cell mediated immune response elicited by an antigen
 using the phytohemagglutinin (PHA) skin test (Salvante 2006); the cellular
 capacity to fight infections and other diseases by quantifying the number
 of white blood cells (WBC) relative to 10,000 erythrocytes and the ratio
 of heterophils to lymphocytes (H:L ratio) in blood smears (Salvante 2006);
 complement activity and natural antibody levels using the
 lysis/agglutination assay (Matson et al. 2005); the acute-phase response
 to infection, inflammation, or trauma by measuring plasma haptoglobin
 levels (Millet et al. 2007); and plasma capacity to defeat micro-organisms
 by quantifying bacterial (<em>E. coli</em>) killing capacity
 (Matson et al. 2006). We assessed oxidative stress by
 targeting different components of the system with several biomarkers of
 oxidative damage and antioxidant mechanisms (Halliwell and Gutteridge
 2007; Monaghan et al. 2009; Pérez-Rodríguez 2009). Specifically, we
 measured a marker of oxidative damage by quantifying a by-product of lipid
 peroxidation in plasma (malondialdehyde acid, MDA) (Mateos and Bravo
 2007); two markers of the combined action of nonenzymatic antioxidants in
 plasma, the Trolox Equivalent Antioxidant Capacity (TEAC) (Miller et al.
 1993) and the OXY-adsorbent Assay (Costantini 2011); the absolute levels
 of a key intracellular endogenous antioxidant (total glutathione, tGSH) in
 erythrocytes; and an oxidative status index based on the functional levels
 of that antioxidant, the reduced to oxidized glutathione ratio (GSH:GSSG
 ratio) (Halliwell and Gutteridge 2007). We quantified
 plasma CORT levels to ensure our stimulation protocol caused similar
 stress levels between both nestling groups and to control for potential
 effects of the levels of this hormone on begging and physiological
 variables. Detailed protocols for these techniques are available in the
 Supplementary material. In our study, we rigorously
 followed a blind methodology for the PHA skin test, as measurements were
 made by a single person (S.C.) entirely unaware of nestling identity and
 previous laboratory procedures. Additionally, biochemical analyses were
 conducted blind to the experimental treatments, with samples from each
 dyad run in the same session in random order.
 <strong>Statistical analyses</strong>
 We performed statistical analyses using R 4.3.1. To enhance model
 stability, convergence likelihood, and accuracy of parameter estimates, we
 Z-transformed all continuous independent variables (mean-centered with an
 SD of 1) (Harrison et al. 2018). To verify that our
 experimental manipulation (HB and LB treatment) created the expected
 differences among groups, we conducted separate
 linear mixed models with for
 time begging, begging score, mean postural intensity, and time
 spent at high postural intensity levels (4 and 5) as response variables,
 with the experimental treatment as the main predictor. We included the
 order of the begging trial (up to 4), the begging session (11:00 h or
 17:00 h), and the day (day 9 or 10) as covariates, with the nest of origin
 nested within the date of arrival at the laboratory as random effects. We
 also assessed food consumption by nestlings using the total weight of food
 consumed (boiled egg and crickets) during the two-day experiment as the
 response variable. This model included the experimental treatment as the
 main predictor, initial body mass as a covariate, and the nest of origin
 nested within the date as random effects. To assess the
 effect of the begging manipulation on body mass, corticosterone levels,
 immune function (PHA skin test, total WBC count, H:L ratio, lysis and
 agglutination capacity, haptoglobin levels, bacterial killing capacity),
 and oxidative stress markers (MDA, TEAC, OXY, tGSH, GSH:GSSG ratio), we
 used linear mixed models for each response variable. Lysis capacity was
 analysed using a generalized mixed model with a binomial error
 distribution due to low variability (76 samples had titres of 0, 28 of 1,
 and only 2 samples had titres of 2). To control for
 initial levels of each physiological marker, we included the experimental
 treatment (HB or LB) in interaction with the time of the measurement (pre-
 or post-treatment) as the main predictor to analyse the change due to the
 treatment (Repeated measurements model). Initial mass (day 8) was included
 in all models as a covariate (except when mass was the response variable).
 All models included nestling ID nested within the nest of origin and the
 date of arrival at the laboratory as random effects. For the PHA skin test
 model, treatment was the only predictor since only one measure was taken
 per nestling (day 10), and nestling ID was therefore removed as a random
 effect. Additional covariates included handling time (time from opening
 the nesting box or incubator until blood collection) for the CORT model
 and levels of uric acid for the TEAC model (Cohen et al. 2007).
 Differences in MDA levels according to treatment and time were also
 checked, considering triglyceride levels as covariate (Pérez-Rodríguez et
 al. 2015). To investigate potential time-dependent
 effects on mass gain (Soler et al. 2014; Redondo et al. 2016), we
 conducted separate models testing differences in body mass on the first
 (day 9) and last day of the experiment (day 10). In these models, the
 variable "time of measurement" was a categorical factor with two
 levels (beginning or end of the day). Failures to obtain sufficient blood
 volume in some individuals led to varying sample sizes between markers. We
 removed the entire dyad from the analysis of that marker if any
 measurement was missing (either initial or final values).
 We confirmed the robustness of our results by means of two other
 additional analytical approaches. First, we replaced the categorical
 factor "Treatment" with a continuous variable accounting for the
 average time each nestling spent begging. Second, we used nestling dyads
 as our experimental unit and modelled how final HB-LB differences in
 physiological variables were explained by differences in begging as the
 main predictor (Within-Dyad differences model) (Kilner 2001; Leonard et
 al. 2003). Both approaches account for individual variability in begging
 effort within each "Treatment" level and inconsistencies in
 creating uniform differences in begging effort between HB and LB across
 all dyads (see Supplementary material for details). To
 address multiple testing when analysing how experimental treatment
 affected multiple physiological variables, we applied a
 <em>P</em>-value correction using the Benjamini-Hochberg
 method to control for false discovery rate in begging, growth,
 immunological, and oxidative stress analyses (Benjamini and Hochberg 1995;
 Storey and Tibshirani 2003). To measure the magnitude
 of the effects found in our study, we calculated effect sizes (adjusted
 standardized mean differences for dependent samples (Hedges' g), and
 odds ratio (OR) for the probability of lysis capacity) with their 95%
 confidence intervals (CIs), following recommendations by Nakagawa and
 Cluthill (2007) and Lakens (2013), using the <em>esc</em> R
 package (Lüdecke 2019). Additionally, we report standardized beta
 coefficients (β) with 95% CIs from our models to consider the influence of
 other factors (initial values, covariates, random effects) on the effect
 of the treatment on the physiological variables. These coefficients
 estimate standardized effect sizes for fixed effects in multiple
 regressions (Schielzeth 2010). We considered effect sizes whose CIs
 included zero (for Hedges' g or β) or one (for the odds ratio) as
 ‘no-effect’ (Nakagawa and Cuthill 2007; Tenny and Hoffman 2017).
description: # Escalated begging does not compromise nestling health
 [https://doi.org/10.5061/dryad.f4qrfj755](https://doi.org/10.5061/dryad.f4qrfj755) ## Description of the data and file structure Further research should explore alternative explanations for honest begging signals, such as differential cost models or cost-free equilibria, moving beyond the scope of differential benefits models. Datasets are saved as .csv files witth comma separation. Missing data are indicated as empty cells. Codes were run using R software version 4.4.1 ## File list ### DATASETS -Begging_data (.csv): data on nestling begging behavior during the four recorded begging sessions. -Nestling_physiology (.csv): data on nestling food intake, body mass, immune and oxidative stress markers. ## CODES -Begging_models (.R): code for running models related to the analysis of how the experimental treatment affected begging (time begging, begging score, mean postural intensity and time begging at postural levels 4 and 5. -Main_results (.R): Code for running models testing the effect of experimental treatment on food intake, body mass, CORT, immunological and oxidative stress markers -Time_begging_models (.R): Code for running models testing the effect of time begging instead of factor "Treatment" on body mass, CORT, immunological and oxidative stress markers -Within-dyad_differences_models (.R): code for running models testing the effect of within-dyad differences (HB-LB) in time begging on within-dyad differences in body mass, CORT, immunological and oxidative stress markers. -Effect_sizes (.R): Code for computing effect sizes of the differences in mean values of final physiological measures between HB and LB nestlings. -Figures (.R): code for elaborating Figures 1 and 2 of the manuscript. ## Description of the dataset files ### -Begging_data.txt This file contains the data used to analyse how the experimental treatment affected begging. Columns: -“ID”: nestling ID, which combines the nest of origin (e.g. 332) and the treatment (e.g. HB). -“Date”: experiment date, whereby “0” corresponds to the day of the first experimental broods. -“Nest”: nest of origin ID. -“Treatment”: experimental begging treatment (coded as: "HB" = "High-begging"; "LB" = "Low-begging"). -"Day": experiment day of each nestling dyad, whereby “1” corresponds to the first of the two days in the laboratory. -"Session": recorded begging session per day, whereby “1” corresponds to the 11:00h session and "2" to the 17:00h session. -"Trial": order of begging trial per session where nestlings were stimulated to beg (up to 4). -"Time_begging": duration (s) of total begging bout per trial. -"Begging_score": total begging effort score measured as the duration of each begging level multiplied by its rank and then summed all of them. -"Mean_postural_intensity": mean level of postural begging intensity obtained as the begging score divided by the total duration. -"BEG45": duration (s) of the time begging at postural intensity levels 4 and 5 per trial. -“Mass_initial”: initial chick body mass (g) at day 8 post-hatching (before the start of the experiment). ### -Nestling_physiology.txt This file contains the data used to analyse the effect of experimental treatment (High- or Low-begging) on food intake, body mass, immune and oxidative stress markers. Columns: -"Group": a code specifying whether nestlings belonged to experimental groups at the laboratory (coded as "Exp") or came from natural broods used to analyse control levels of CORT (coded as "Natural"). -“Date”: experiment date, whereby “0” corresponds to the day of the first experimental broods. -“Nest”: nest of origin ID. -“ID”: nestling ID, which combines the nest of origin (e.g. 332) and the treatment (e.g. HB). -“Treatment”: experimental begging treatment (coded as: "HB" = "High-begging"; "LB" = "Low-begging") and natural broods used to analyse control levels of CORT (coded as "Natural"). -"Time": time of measurement, coded as "inital" (before the begging treatment) and "final" (after the begging treatment). -“Mass”: chick body mass (g). -“Mass_initial”: initial chick body mass (g) at day 8 post-hatching (before the start of the experiment). -"Dif_mass_initial": difference between HB and LB initial body mass (g) within nestling dyads. -“Mass_final”: final chick body mass (g) at the end of the day 10 post-hatching (at the end of the experiment). -"Dif_mass_final": difference between HB and LB final body mass (g) within nestling dyads. -"Mass_gain": difference between final and initial body mass (g). -"Dif_mass_gain": difference between HB and LB body mass gain (g) within nestling dyads. -“Massd1”: chick body mass (g) at day 9 post-hatching (the first day of experiment) at the start (8.00h) and the end of the day (21:00h). -“Massd1_8h”: initial chick body mass (g) at day 9 post-hatching (at the start of the day). -"Dif_massd1_initial": difference between HB and LB initial body mass (g) at day 9 post-hatching within nestling dyads. -“Massd1_21h”: final chick body mass (g) at day 9 post-hatching (at the end of the day). -"Dif_massd1_final": difference between HB and LB final body mass (g) at day 9 post-hatching within nestling dyads. -“Massd2”: chick body mass (g) at day 10 post-hatching (the second day of experiment) at the start (8.00h) and the end of the day (21:00h). -“Massd2_8h”: initial chick body mass (g) at day 10 post-hatching (at the start of the day). -"Dif_massd2_initial": difference between HB and LB initial body mass (g) at day 10 post-hatching within nestling dyads. -“Massd2_21h”: final chick body mass (g) at day 10 post-hatching (at the end of the day). -"Dif_massd2_final": difference between HB and LB final body mass (g) at day 10 post-hatching within nestling dyads. -“Food_total”: weight (g) of total food consumed during the two-day experiment. -"Filter_natural_broods": a filtering code to exclude those experimental dyads lacking control siblings from natural broods ("0") in order to analyse differences in corticosterone between experimental (lab) and nestlings from natural broods. -"CORT": Coticosterone values (ng/ml) -"CORT_initial": initial values of corticosterone (ng/ml) -"CORT_final": final values of corticosterone (ng/ml) -"Dif_CORT_initial": difference between HB and LB initial values of corticosterone (ng/ml) within nestling dyads. -"Dif_CORT_final": difference between HB and LB final values of corticosterone (ng/ml) within nestling dyads. -"Change_CORT": difference between final and initial values of corticosterone (ng/ml). -"Handling_time": time (s) from opening the nesting box or incubator until blood collection. -"Handling_time_final": time (s) from opening the incubator until the last blood collection of experimental nestlings. -"Dif_handling_time_final": difference between HB and LB final values of handling time (s) within nestling dyads. -"PHA": PHA skin test. T cell–mediated immune response, measured as the difference between initial (9:00h of the second day of the experimet) and final (12h later) swelling of the patagium skin (mm). -"Dif_PHA": difference between HB and LB PHA within nestling dyads. -"Total_WBC": total white blood cells count measured as the number of white blood cells per 10,000 erythrocytes. -"Total_WBC_initial": initial values of white blood cells per 10,000 erythrocytes. -"Total_WBC_final": final values of white blood cells per 10,000 erythrocytes. -"Dif_total_WBC_initial": difference between HB and LB initial values of white blood cells per 10,000 erythrocytes within nestling dyads. -"Dif_total_WBC_final": difference between HB and LB final values of white blood cells per 10,000 erythrocytes within nestling dyads. -"Change_total_WBC": difference between final and initial values of white blood cells per 10,000 erythrocytes. -"HL": heterophil:lymphocyte ratio. -"HL_initial": initial values of heterophil:lymphocyte ratio. -"HL_final": final values of heterophil:lymphocyte ratio. -"Dif_HL_initial": difference between HB and LB initial values of heterophil:lymphocyte ratio within nestling dyads. -"Dif_HL_final": difference between HB and LB final values of heterophil:lymphocyte ratio within nestling dyads. -"Change_HL": difference between final and initial values of heterophil:lymphocyte ratio. -"Lysis_prob": probability of plasma complement activity being positive (coded as "1" if they presented or "0" if not). -"Lysis_prob_initial": initial values of the probability of plasma complement activity being positive. -"Lysis_prob_final": final values of the probability of plasma complement activity being positive. -"Dif_lysis_prob_initial": difference between HB and LB initial values of the probability of plasma complement activity being positive within nestling dyads. -"Dif_lysis_prob_final": difference between HB and LB final values of the probability of plasma complement activity being positive within nestling dyads. -"Change_lysis_prob": difference between final and initial values of the probability of plasma complement activity being positive. -"Agglut": natural antibody titers (agglutination titer). -"Agglt_initial": initial values of natural antibody titers (agglutination titer). -"Agglut_final": final values of natural antibody titers (agglutination titer). -"Dif_agglut_initial": difference between HB and LB initial values of natural antibody titers (agglutination titer) within nestling dyads. -"Dif_agglut_final": difference between HB and LB final values of natural antibody titers (agglutination titer) within nestling dyads. -"Change_agglut": difference between final and initial values of natural antibody titers (agglutination titer). -"Hp": haptoglobin levels (mg/ml). -"Hp_initial": initial values of haptoglobin levels (mg/ml). -"Hp_final": final values of haptoglobin levels (mg/ml). -"Dif_Hp_initial": difference between HB and LB initial values of haptoglobin levels (mg/ml) within nestling dyads. -"Dif_agglut_final": difference between HB and LB final values of haptoglobin levels (mg/ml) within nestling dyads. -"Change_Hp": difference between final and initial values of haptoglobin levels (mg/ml). -"A450pre": pre-scan absorbance at 450 nm. -"A450pre_final": final values of pre-scan absorbance at 450 nm. -"Dif_A450pre_final": difference between HB and LB initial values of pre-scan absorbance at 450 nm within nestling dyads. -"Dead_cells": percentage of E. coli cells lysed by plasma relative to the initial concentration. -"Dead_cells_initial": initial values of % E. coli cells lysed by plasma relative to the initial concentration. -"Dead_cells_final": final values of % E. coli cells lysed by plasma relative to the initial concentration. -"Dif_dead_cells_initial": difference between HB and LB initial values of % E. coli cells lysed by plasma relative to the initial concentration within nestling dyads. -"Dif_dead_cells_final": difference between HB and LB final values of % E. coli cells lysed by plasma relative to the initial concentration within nestling dyads. -"Change_dead_cells": difference between final and initial values of % E. coli cells lysed by plasma relative to the initial concentration. -"MDA": plasma levels of malondialdehyde (µmol/L). -"MDA_initial": initial values of plasma levels of malondialdehyde (µmol/L). -"MDA_final": final values of plasma levels of malondialdehyde (µmol/L). -"Dif_MDA_initial": difference between HB and LB initial values of plasma levels of malondialdehyde (µmol/L) within nestling dyads. -"Dif_MDA_final": difference between HB and LB final values of plasma levels of malondialdehyde (µmol/L) within nestling dyads. -"Change_MDA": difference between final and initial values of plasma levels of malondialdehyde (µmol/L). -"Filter_MDAtri": a filtering code (usable "1" and non-usable "0") data to analyse the effect of begging treatment on MDA adding triglyceride levels as covariate. -"MDA_res": residuals of plasma levels of malondialdehyde after correcting for triglyceride levels. -"MDA_res_initial": initial values of residuals of plasma levels of malondialdehyde after correcting for triglyceride levels. -"MDA_res_final": final values of residuals of plasma levels of malondialdehyde after correcting for triglyceride levels. -"Dif_MDA_res_initial": difference between HB and LB initial values of residuals of plasma levels of malondialdehyde after correcting for triglyceride levels within nestling dyads. -"Dif_MDA_res_final": difference between HB and LB final values of residuals of plasma levels of malondialdehyde after correcting for triglyceride levels within nestling dyads. -"Triglyceride": plasma triglycerides (mg/dL). -"Triglyceride_final": final values of plasma triglycerides (mg/dL). -"Dif_triglyceride_final": difference between HB and LB final values of plasma triglycerides (mg/dL) within nestling dyads. -"TEAC": nonenzymatic antioxidants in plasma using the Trolox Equivalent Antioxidant Capacity assay (mmol Trolox Eq/L). -"TEAC_initial": initial values of nonenzymatic antioxidants in plasma using the Trolox Equivalent Antioxidant Capacity assay (mmol Trolox Eq/L). -"TEAC_final": final values of plasma levels of nonenzymatic antioxidants in plasma using the Trolox Equivalent Antioxidant Capacity assay (mmol Trolox Eq/L). -"Dif_TEAC_initial": difference between HB and LB initial values of nonenzymatic antioxidants in plasma using the Trolox Equivalent Antioxidant Capacity assay (mmol Trolox Eq/L) within nestling dyads. -"Dif_TEAC_final": difference between HB and LB final values of nonenzymatic antioxidants in plasma using the Trolox Equivalent Antioxidant Capacity assay (mmol Trolox Eq/L) within nestling dyads. -"TEAC_res": residuals of nonenzymatic antioxidants in plasma using the Trolox Equivalent Antioxidant Capacity assay after correcting for uric acid levels. -"TEAC_res_initial": initial values of residuals of nonenzymatic antioxidants in plasma using the Trolox Equivalent Antioxidant Capacity assay after correcting for uric acid levels. -"TEAC_res_final": final values of residuals of nonenzymatic antioxidants in plasma using the Trolox Equivalent Antioxidant Capacity assay after correcting for uric acid levels. -"Dif_TEAC_res_initial": difference between HB and LB initial values of residuals of nonenzymatic antioxidants in plasma using the Trolox Equivalent Antioxidant Capacity assay after correcting for uric acid levels within nestling dyads. -"Dif_TEAC_res_final": difference between HB and LB final values of residuals of nonenzymatic antioxidants in plasma using the Trolox Equivalent Antioxidant Capacity assay after correcting for uric acid levels within nestling dyads. -"Change_TEAC_res": difference between final and initial values of residuals of nonenzymatic antioxidants in plasma using the Trolox Equivalent Antioxidant Capacity assay after correcting for uric acid levels -"Uric": plasma uric acid levels (mg/dL). -"Uric_final": final values of plasma uric acid levels (mg/dL). -"Dif_uric_final": difference between HB and LB final values of plasma uric acid levels (mg/dL) within nestling dyads. -"OXY": antioxidant capacity of plasma using the OXY-adsorbent Assay (µmol HClO neutralized). -"OXY_initial": initial values of antioxidant capacity of plasma (µmol HClO neutralized). -"OXY_final": final values of antioxidant capacity of plasma (µmol HClO neutralized). -"Dif_OXY_initial": difference between HB and LB initial values of antioxidant capacity of plasma (µmol HClO neutralized) within nestling dyads. -"Dif_OXY_final": difference between HB and LB final values of antioxidant capacity of plasma (µmol HClO neutralized) within nestling dyads. -"Change_OXY": difference between final and initial values of antioxidant capacity of plasma (µmol HClO neutralized). -"tGSH": total levels of glutathione (mmol/g). -"tGSH_initial": initial values of total levels of glutathione (mmol/g). -"tGSH_final": final values of total levels of glutathione (mmol/g). -"Dif_tGSH_initial": difference between HB and LB initial values of total levels of glutathione (mmol/g) within nestling dyads. -"Dif_tGSH_final": difference between HB and LB final values of total levels of glutathione (mmol/g) within nestling dyads. -"Change_tGSH": difference between final and initial values of total levels of glutathione (mmol/g). -"GSHGSSG": ratio of reduced to oxidized glutathione. -"GSHGSSG_initial": initial values of the ratio of reduced to oxidized glutathione. -"GSHGSSG_final": final values of the ratio of reduced to oxidized glutathione. -"Dif_GSHGSSG_initial": difference between HB and LB initial values of the ratio of reduced to oxidized glutathione within nestling dyads. -"Dif_GSHGSSG_final": difference between HB and LB final values of the ratio of reduced to oxidized glutathione within nestling dyads. -"Change_GSHGSSG": difference between final and initial values of the ratio of reduced to oxidized glutathione. -"Time_begging": duration (s) of total begging bout per trial. -"Begging_score": begging effort score measured as the duration of each begging level multiplied by its rank and then summed all of them. -"Mean_postural_intensity": mean level of postural begging intensity obtained as the begging score divided by the total duration. -"BEG45": duration (s) of the time begging at postural intensity levels 4 and 5 per trial. -"Dif_time_begging": difference between HB and LB values of time begging within nestling dyads. -"Dif_begging_score": difference between HB and LB values of begging score within nestling dyads. -"Dif_mean_postural_intensity": difference between HB and LB values of mean level of postural begging intensity within nestling dyads. obtained as the begging score divided by the total duration. -"Dif_BEG45": difference between HB and LB values of time begging at postural intensity levels 4 and 5 within nestling dyads.