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Animal Behavior & CognitionBehavioral Ecology
Peer-reviewed journal article

Long-term evaluation of the association between dominance, bib size, sex and age

N. SilvaiD, Liliana R. SilvaiD, Pietro Bruno D'AmelioiD, André C. FerreiraiD, Annick Lucas, Rita CovasiD, Claire DoutrelantiD

Abstract

The association between dominance and phenotypic traits ( badges of status) has been recently questioned, since it has been found to show more variation across populations and time than expected. Using an eleven-year dataset, encompassing more than 1,800 individuals, we studied the association between the size of a melanin-based plumage trait (a black patch under the beak or bib), individual attributes (age and sex) and dominance. Our study model, the sociable weaver (Philetairus socius), is a small passerine, which lives year-round in colonies of varying size. Bib sizes were obtained from pictures and automatically pre-processed with an object segmentation deep learning network. We recorded 36,346 dominance-related interactions to estimate dominance hierarchies. We then investigated the effect of sex and age on bib size, and the overall and between-year association of bib size and age with dominance for each sex. We found that bib size increased with age within individuals of both sexes. Age was a strong and consistent predictor of dominance in males, but not in females. Nevertheless, dominance was not correlated with bib size in males and in females. Finally, these relationships did not strongly vary between years. Our results suggest that males and females may use different factors to regulate dominance interactions. Furthermore, our longitudinal dataset allowed us to show that bib size is not a badge of status in our population even though its growth encodes information on age. These results highlight the importance of considering multiple traits over time when studying morphological signalling of dominance hierarchy.

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In-depth summary

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Claude Opus 5.5 · xhigh effort · 8 Nov 2026 · from the full text of version 2 (21 Nov 2025) · CC BY 4.0

Across eleven years and more than 1,800 sociable weavers, black bib size grew with age but did not predict dominance; age predicted dominance in males only.

Badges of status, notably house sparrow bibs, have been undermined by meta-analyses revealing publication bias and high heterogeneity, and earlier short-term sociable weaver studies gave conflicting bib-dominance results. Long-term, sex-specific data paired with automated bib measurement let this work test whether the badge relationship holds across individuals and years.

Key results

  1. ShownWithin-colony normalized bib size did not predict dominance score in both-sexes or male-only hierarchies; a weak positive female-only association depended on two low-sample years and disappeared when they were excluded.

    Both-sexes: 0±0.01, T=0.19, P=0.852; between-males: -0.02±0.01, T=-1.69, P=0.092; between-females: 0.04±0.02, T=2.34, P=0.020, falling to 0.02±0.02, T=1.06, P=0.290 after removing 2013 and 2016 (N=19 and N=12 females). · Dominance in relation to bib size and sex; Dominance in relation to bib size, sex and year; 4.1. Association between dominance, bib size and…

  2. ShownMales outranked females, and age strongly predicted dominance in males but not in females; dominance rank was moderately repeatable within individuals across years.

    Sex effect 0.30±0.02, T=18.61, P<0.001; age×sex 0.11±0.02, T=7.2, P<0.001, with dominance 9.39% (males) vs 1.36% (females) higher per year of age; male-only hierarchies 0.16±0.01, T=11.77, P<0.001 vs female-only -0.01±0.02, T=-0.35, P=0.725; dominance repeatability 0.38 [0.28; 0.49]. · 3.2. Overall association between dominance, bib…; Dominance in relation to age and sex; Dominance in relation to age, sex and year

  3. ShownLinks between dominance and bib size or age were largely stable across 2013 to 2019, with only scattered single-year exceptions and a male age effect that held every year.

    Significant year-specific bib slopes only for males in 2016 (both-sexes, -0.06±0.03, P=0.030), between-males in 2014 (-0.06±0.03, P=0.042) and females in 2013 and 2016 (0.14±0.06 and 0.17±0.08); female age slope negative only in 2017 (-0.07±0.03, P=0.033). · Dominance in relation to bib size, sex and year; Dominance in relation to age, sex and year

  4. ShownBib size grew with age in nearly every individual at a similar rate, while birds differed mainly in baseline bib size; birds with longer tarsi and males carried slightly larger bibs.

    Age effect 0.02±0.01, T=2.58, P=0.010; positive within-bird slopes in 99.8% of individuals, +1.37%/year in females vs +1.21%/year in males; conditional R² 0.67 (full), 0.64 (no random slopes), 0.26 (no random intercepts or slopes); tarsus 0.02±0.00, P<0.001; males 1.29% larger (1.57 vs 1.55 cm²); repeatability 0.41 [0.37; 0.44]. · 3.1. Factors associated with bib size; 4.3. Association between bib size, age and sex

  5. SuggestedA YOLO-based object segmentation model automated bib measurement from field photographs. It matched earlier manual image-editor measurements and ran much faster than a human.

    Applied to approximately 13,300 pictures; agreement with the manual GIMP method and repeatability described as high for 20 individuals (300 pictures) across five years, with values given only in Table S1; processing 124 times faster than a human, based on 30 pictures. · 1. Introduction; 2.3. Bib size and YOLO: annotations, training…; 4.4. The growing importance of artificial…

Methods, data and reproducibility

Bib area was extracted from field photos with a fine-tuned YOLOv8l segmentation model, and dominance was scored as standardized David's scores from video-recorded feeder interactions. Linear mixed models related bib size to age, sex and tarsus length, and dominance to normalized bib size, age, sex, tarsus length and body condition, with year random or, in between-year tests, fixed.

  • Standardized bib photographs (three top-view images per capture) from 19 colonies at Benfontein Nature Reserve, South Africa, used in the bib size model (2014 to 2024) · sociable weaver (Philetairus socius) · n = 1,863 individuals; 3,831 observations
  • Video-recorded agonistic interactions at artificial feeders beneath seven colonies, 2013 to 2019 (550 hours of video) · sociable weaver (Philetairus socius) · n = 36,346 interactions; 409 individuals; 723 observations
  • Male-male interaction subset used to build between-males hierarchies · sociable weaver (Philetairus socius) · n = 16,261 interactions among 256 males
  • Female-female interaction subset used to build between-females hierarchies · sociable weaver (Philetairus socius) · n = 2,651 interactions among 267 females
  • Birds measured by both the manual GIMP method and YOLO, used to compare the two methods · sociable weaver (Philetairus socius) · n = 20 individuals (300 pictures)
  • Birds with bib size measured in at least two years, used for bib size repeatability · sociable weaver (Philetairus socius) · n = 959 individuals (2,927 observations)
  • Birds observed in at least two dominance seasons, used for dominance-rank repeatability · sociable weaver (Philetairus socius) · n = 184 individuals (498 observations)
  • Long-term capture-recapture records used to estimate mean minimum dispersal age for immigrant birds · sociable weaver (Philetairus socius) · n = 13 males; 184 females
Methods & tools
YOLOv8l (fine-tuned object segmentation), VGG annotations (reference labels, Table S1), GIMP / Photoshop CS5.1 (manual bib measurement), David's score (steepness R package), Scaled mass index (body condition), R 4.3.1, lme4 1.1-33, rptR 0.9.22, Dharma 0.4.6, emmeans 1.8.6, ggplot2 3.4.2, ggeffects 1.3.2
Reagents & environment
R 4.3.1 with lme4 1.1-33, rptR 0.9.22, Dharma 0.4.6, emmeans 1.8.6, ggplot2 3.4.2 and ggeffects 1.3.2; David's scores via the steepness R package; bib segmentation with a fine-tuned YOLOv8l model.
Reproducibility gaps
Data are cited only as Silva et al. (2025), with no URL or accession in the text; no code repository or YOLO model weights are linked.
Limitations (6)
  • Female-female interactions were scarce (32 out of 33 colonies fell short of the recommended ratio of 10 interactions per individual), so female hierarchies and their weak, year-dependent bib association remain uncertain. · stated by the authors
  • Dominance was scored only at feeders around the end of winter, in colonies of 7 to 82 birds; the authors note bib size might still act as a badge in other seasons, in colonies of several hundred, or for dispersing females. · stated by the authors
  • Only bib area was quantified; other plumage properties such as saturation or intensity, which might signal fighting ability, were not examined. · stated by the authors
  • Immigrant ages were imputed by adding a mean minimum dispersal age (estimated from N=13 males and N=184 females), and the authors note female ages are less accurate because females leave their natal colony. · stated by the authors
  • Bib size was min-max normalized within colony-year, so the tests concern relative rather than absolute bib size, and the scaling hinges on the extreme birds in small colonies (as few as 7 birds). · noted in this summary
  • The Results give an identical estimate for the sex effect and the age effect on bib size (0.02±0.01, T=2.58, P=0.010), which suggests a possible transcription error worth checking against Table 1. · noted in this summary

Who should read:Read this if you study status signalling, dominance hierarchies or melanin ornaments in wild birds, or want an example of deep-learning trait measurement applied to a long-term field dataset.

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