Penguins depend on tightly packed feathers for waterproofing, insulation, buoyancy, and efficient swimming. Because worn feathers must be replaced simultaneously, penguins undergo a rapid, energy-intensive molt on land, often after gaining weight and accumulating reserves. Previous studies have associated molting with changes in thyroid hormones, stress hormones, fasting, and lipid metabolism. However, hormone patterns vary among penguin species and environmental conditions, and few studies have tracked hormones and metabolites together throughout the complete molting cycle. The metabolic pathways connecting endocrine signals to feather synthesis therefore remain poorly understood, creating a need for longitudinal research that follows individual penguins before, during, and after molting.
A study (DOI: 10.48130/animadv-0026-0005) published in Animal Advances on 16 April 2026 by Kentaro Nagaoka's team, Tokyo University of Agriculture and Technology, reports that elevated T4 was associated with coordinated changes in amino acid metabolism, particularly the trans-sulfuration pathway that may supply sulfur-containing compounds required for feather keratin formation.
The researchers followed five healthy adult male Humboldt penguins housed at Enoshima Aquarium in Japan. Residual blood samples collected during routine veterinary examinations were analyzed at five stages: before molting, on the first day of feather shedding, when feather loss was completed, and at 14 and 28 days after completion. Molting occurred naturally over approximately 10–14 days. Unlike wild penguins that typically fast during this period, the captive birds could continue eating voluntarily, although their food intake declined. The researchers recorded body weight and measured blood biochemical indicators, T4, triiodothyronine (T3), and corticosterone. They also used untargeted gas chromatography–mass spectrometry to profile serum metabolites. Principal component analysis, analysis of variance, heatmap clustering, and correlation analysis were applied to identify time-dependent metabolic changes and their relationships with body weight and hormones. Body weight increased substantially before molting, peaked when feather shedding began, and then declined toward the end of the molt. T4 also peaked at molt onset but remained elevated until molting was complete, supporting its proposed role in initiating and sustaining feather regeneration. By contrast, T3 and corticosterone did not change significantly. The stable indoor temperature and continued access to food may have reduced the need for T3-mediated heat production and prevented a marked stress response. Metabolomic analysis distinguished molting samples from nonmolting samples and identified 14 metabolites that changed significantly over time. The strongest variations involved L-cystathionine, 4-hydroxyproline, and D-maltose. L-lysine, calcium, cholesterol, L-cystathionine, and 4-hydroxyproline were strongly associated with body-weight changes, while L-cystathionine, triglycerides, methionine, aminoadipic acid, and ornithine correlated with T4. Changes in trans-sulfuration metabolites appeared sequential: upstream methionine increased around molt onset, followed by L-cystathionine during molting and L-cystine afterward. This pattern suggests that sulfur-containing amino acid metabolism is progressively activated to provide cysteine-related materials for keratin synthesis and feather construction.
Overall, the study presents an integrated account of how endocrine signals and metabolic pathways change across the Humboldt penguin molting cycle. It identifies T4 as a central hormonal signal and suggests that amino acid pathways are mobilized in stages to support new plumage formation. Because the study included only five captive males, the authors caution that the findings may not apply directly to females or wild populations. Future research involving additional animals, species, environments, and molecular measurements could clarify causal mechanisms and guide evidence-based nutritional and veterinary support for penguins experiencing normal or abnormal molts.
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References
DOI
10.48130/animadv-0026-0005
Original Source URL
https://doi.org/10.48130/animadv-0026-0005
About Animal Advances
Animal Advances (e-ISSN 3065-7660) is an open-access journal which published by Maximum Academic Press in partnership with Nanjing Agricultural University. The journal is dedicated to delivering cutting-edge discoveries and progress in animal sciences to a diverse audience, encompassing scholars, academicians, and practitioners in the industry.