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27 January 2026

16 Pages

Mineral Element Profile in African Penguin (Spheniscus demersus) Feathers and Its Possible Relationship with Molting

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1
Department of Drug Science and Technology, University of Torino, Via Pietro Giuria 9, 10125 Turin, Italy
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Fondazione Zoom, 10060 Cumiana, Italy
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Department of Chemistry, University of Torino, Via Pietro Giuria 7, 10125 Turin, Italy
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Zoom Torino, 10060 Cumiana, Italy
Analytica2026, 7(1), 11;https://doi.org/10.3390/analytica7010011
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Abstract

Molting is an important biological and physiological stage in penguins, influenced by environmental and nutritional factors. Feather composition analysis before and after molting can consequently place boundaries on element bioaccumulation and excretion. We quantified and compared elemental concentrations in African penguin (Spheniscus demersus) feathers collected pre- and post-molt across three zoos to evaluate how molt stage and zoo-specific conditions influence feather elemental composition. Feathers were retrieved from individual penguins at Zoom Torino (Italy), Overloon ZooParc (Netherlands), and Zoo Magdeburg (Germany). Quantification of elemental concentrations were performed by analytical methods, with both ICP-OES and HR-ICP-MS techniques. A statistical approach involving MANOVA and factorial analysis helped identify important trends. Pre-molt features had more variability than post-molt, with both showing significant differences in elemental concentrations. Factorial analysis showed geogenic trends in Mg, Sr, and Ni trends as well as anthropogenic trends in Pb. While Na and K differed among all treatment groups, this likely points to physiological adaptations in response to increased demand during feather regrowth. Additionally, inter-zoo comparisons highlighted distinct elemental profiles linked to local environmental and dietary conditions, particularly in Zoo Magdeburg, where Na levels were markedly elevated. This study highlights the influence of environmental and dietary conditions on feather composition during molt, offering insights for improving captive penguin welfare and broader ecological implications related to climate change and pollution.

1. Introduction

Molting is a fundamental biological step in birds, during which they renew their plumage to ensure optimal functionality, thermal insulation, and flight capability. The process is essential for maintaining the health and survival of avian species, particularly in extreme environments where feather integrity directly impacts survival [1,2]. For penguins, whose dense, waterproof feathers are essential for thriving in cold marine habitats, molting is an indispensable and crucial life event. African penguins (Spheniscus demersus), in particular, undergo a “catastrophic molt”, a brief period in which they replace their entire plumage [3,4,5]. The complete loss of plumage has a substantial impact on the behavior of these animals, compromising both their swimming ability and their protection against weather conditions [4]. During the molt, penguins are forced to remain on land, with no possibility of feeding at sea; they therefore undergo a considerable loss of body mass, which can reach up to 47% of their initial weight [3]. The molting period thus represents a critical phase not only from a physiological perspective, but also from behavioral and ecological viewpoints. Because molt integrates energetic constraints, land confinement, and rapid feather synthesis, it is a useful window for studying how physiology and environmental exposure interact during feather growth [6,7]. In recent years, disruptions in molting patterns have raised concerns about penguin populations, both in the wild and in captivity. Emerging evidence suggests that environmental changes, dietary shifts, and increased pollution exposure may affect penguins’ health. Overfishing and climate change, for example, have altered the availability of key nutrients in natural habitats, potentially delaying molt or feather regeneration [8,9,10]. Research conducted in controlled environments is fundamental, as it allows for systematic and accurate monitoring of both behavioral and environmental variables, ensuring a level of precision and control that is difficult to achieve under natural conditions. Understanding the factors influencing molting is therefore critical for the conservation and welfare of captive penguins and for gaining insight into the influence of climate change and pollution on the survival of wild populations [11]. The molting period involves substantial physiological changes, including the mobilization and accumulation of mineral elements into feathers [12]. For example, Mg and Ca are vital for structural integrity and feather formation [13], while Fe plays a key role in pigmentation and oxygen transport [14]. Na and K are critical for maintaining metabolic and physiological processes, and trace elements, such as Ni and Pb, can further reflect environmental exposure or anthropogenic impact [15,16,17,18,19]. As chemical archives, feathers can offer a window into the interplay between an animal’s biology and its environment during molt. However, direct comparisons of pre- and post-molt multielement feather composition in penguins remain limited, particularly under controlled zoo conditions where diet, management, and enclosure characteristics can be documented. This is a critical gap because distinguishing physiological molt-stage signatures from site-specific exposure patterns is necessary for both biomonitoring interpretation and evidence-based husbandry. These site-specific differences can highlight the importance of adapting management practices to local conditions to optimize mineral intake and support penguins’ health. Penguin feathers have been increasingly used in recent years as bioindicators of environmental contamination and physiological state [20]. Different studies have demonstrated the utility of feathers as bioindicators for assessing the accumulation of trace elements and metals in seabirds, reflecting both geogenic sources and anthropogenic impacts [21,22]. For instance, Mikoni et al. highlighted the role of heavy metals, such as lead (Pb) and cadmium (Cd), as markers of industrial pollution, while elevated levels of magnesium (Mg) and strontium (Sr) often correlate with natural geological features [23]. Moreover, feathers have been used to compare metal exposure in wild and captive birds, offering insights into how habitat, diet, and management practices influence metal accumulation [24,25]. The research by Jerez emphasized the geographic variability in feather element profiles, linking local soil and water compositions to metal concentrations in bird tissues [22]. Furthermore, studies on penguin species, including those in Antarctica, have illustrated the importance of integrating biomonitoring approaches to inform conservation strategies [21]. Despite this progress, fewer studies have examined how feather element composition differs across molt phases within the same managed population, and how such differences interact with controlled environmental conditions.

Literature Insights on Feathers Elements Content

This study addresses these gaps by investigating the element composition of penguins’ feathers associated with the molting process, focusing on pre- and post-molt differences. Molting, a key biological process influencing elemental accumulation, is analyzed to reveal temporal changes in trace element exposure and the physiological demands associated with feather growth and replacement. Eighteen elements (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Sr, and Zn) were quantified in pre- and post-molt feathers of penguins housed in three institutions: Zoom Torino in Turin, Italy, ZooParc Overloon, Holland, and Zoo Magdeburg, Germany. All samples were washed, mineralized with acid digestion, and analyzed with Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) and High-Resolution Inductively Coupled Plasma Mass Spectrometer (HR-ICP-MS). Advanced chemometric techniques (MANOVA and Factor Analysis) were applied to identify key elements influencing the molting process. The findings of this research have the potential to deepen our understanding of penguins’ ecology and physiology, offer practical implications for zoo management, and provide information to optimize care practices for captive penguins to support their health and welfare. Furthermore, these insights contribute to broader ecological studies highlighting the interaction between physiological and environmental exposure during molt, providing information about the influence of climate change and pollution on the survival of wild populations.

2. Materials and Methods

2.1. Zoological Institutions

The study was promoted by Fondazione Zoom, the research body of the Biopark Zoom Torino, an Italian biopark. Fondazione Zoom is a research organization dedicated to the conservation of biodiversity, ecosystem regeneration and the promotion of environmental education, research, and sustainable development initiatives. Samples were collected in three zoological institutions affiliated with the European Association of Zoos and Aquaria (EAZA), that promotes high standards of animal welfare, conservation, research, and education across European zoological gardens; the three institutions are Zoom Torino, Italy, Overloon ZooParc, The Netherlands, and Magdeburg Zoo, Germany. All these zoos are deeply involved in coordinated breeding programs under the EAZA Ex-situ Programme (EEP), the official management program for animal populations held in EAZA institutions. It includes coordinated breeding plans, genetic management, demographic monitoring, transfers between institutions, and long-term conservation goals for threatened species. Each EEP is overseen by a coordinator (species expert) and a studbook keeper (responsible for the population’s genealogical records).
At Zoom Torino, the first immersive bioparc in Italy, the penguin exhibit is meticulously designed to simulate the Bolder Beach near Cape Town, in South Africa, where there is one of the largest African penguin (Spheniscus demersus) colonies. The habitat consists of an outdoor and an indoor area. The outdoor area, which spans 1500 m2, contains a sloping swimming pool of 120 m2; the design of the pool helps diving and surfacing. The water provided to animals in this enclosure is no pretreated fresh water, with a temperature between 15 °C and 21 °C and a pH = 7.5. The exhibit substrate is made up of gravel and sand, with some areas rich in pebbles and stones.
To ensure animal welfare, several shaded areas have been created and three types of nests have been provided: underground, external and inside the large boulders that dot the sandy area. The indoor area is a secluded and heated space of 30 m2 within the habitat, with a temperature-regulated pool of 5 m2. This space provides a quarantine area for sick animals or a living space in case of extreme weather, which animals can access freely during wintertime. It also works as a storage room for food, medicines and other amenities necessary to maintain a functioning enclosure.
The exhibit of Overloon ZooParc covers approximately 900–1000 m2 and features a predominantly natural substrate. The native soil is overlaid with coastal-type sand and scattered rocks, creating heterogeneous microhabitats that support thermoregulation and behavioral enrichment. The main pool has a surface of 300 m2, reaching a maximum depth of 1.60 m. Its bottom consists of sand and rocks, promoting natural underwater exploration and smoother locomotion. Water temperature is not artificially regulated, fluctuating with local climate and seasonal changes, thus exposing the animals to a more environmentally realistic thermal profile.
The penguin exhibit at Magdeburg Zoo measures 203 m2, making it a compact but efficiently designed space optimized for animal use. The pool occupies only 61 m2, but it includes varying depth gradients that allow swimming, diving and rapid surfacing, thereby supporting a range of natural aquatic behaviors. Rocky areas are integrated throughout the exhibit to offer shelter, vantage points, and visual barriers—key elements for managing social interactions and reducing potential stress. The enclosure also includes shaded areas and artificial shelters designed to replicate nesting conditions and offer protection from weather fluctuations. Although smaller than exhibits in other zoological institutions, the spatial arrangement of terrestrial and aquatic components maximizes behavioral opportunities and facilitates smooth transitions between land and water. Together, these institutions are important for the conservation of aquatic birds, and participating in international breeding programs and contributing to research efforts enhanced their understanding of penguins’ health and ecological needs, provide a valuable framework for investigating the effects of environmental conditions, management practices on penguin welfare, with a specific focus on the critical molting process and exposure to environmental pollutants.

2.2. Feather Collection

Feather samples were methodically collected in two distinct phases for each penguin: pre-molt and post-molt. Initially, samples were gathered approximately two weeks before the onset of the molt in spring 2023, aimed at assessing the condition of feathers in their fully grown state. Subsequent collection occurred post-molt, approximately 4–6 weeks later, to observe a new feathers state. The collection protocol was standardized to ensure comparable sample collection in different zoos as much as possible. Primarily, feathers were taken, retrieving naturally shed feathers found in the penguin enclosure. In cases where shedding was insufficient, non-invasive sampling was conducted by collecting feathers from specific regions of the penguin’s body, such as the back and wings, using sterile scissors. The veterinary teams of each zoo carried out all the procedures with extreme care to avoid causing stress or discomfort to the animals. Samples were stored in labeled plastic containers, with careful classification according to the individual penguin, the date of collection, and the zoological institution of origin. Due to logistical constraints, the Magdeburg Zoo was not accessible for feather collection pre- and post-molt; therefore, a mixture of feathers from the two periods, collected in the penguins’ nest, was provided for each individual. While this limits a direct quantitative comparison with the other institutions, the mixed sample still offers valuable insights. Accordingly, Magdeburg samples were used only for inter-zoo (site) comparisons and were not considered in true pre-/post-molt statistical comparisons. The composite samples were analyzed to assess environmental differences in pollutant exposure between the three areas of study. This approach allows us to identify potential disparities in environmental contamination between the institutions, providing an important context for understanding how local environmental conditions may influence feather composition. Table 1 summarizes the number and kind of samples collected in each facility. A total of 26 penguins were included in the study, 9 of them providing a mixed sample from Magdeburg Zoo, 11 individuals from Zoom Torino, and 6 penguins from Overloon Zooparc. Samples were collected pre- and post-molt for the individuals from Zoom Torino and Overloon Zooparc (Table S1). In addition, to ensure the welfare of the penguins and to avoid excessive stress, some samples could not be obtained in sufficient amounts to support multiple analytical replicates. Consequently, only standard deviations and an average relative standard deviation percentage (RSD%) are reported.
Table 1. Samples campaign in the three areas of study.

2.3. Instruments and Reagents

The feathers were washed with a mixture of a 0.01% Trixon-X-100 solution, methanol (CH3OH), and High Purity Water (HPW) produced with Millipore Milli-Q Plus system (18.2 MΩ cm). Sample acid digestion was performed in tetrafluoromethoxyl (TFM) vessels, using a Milestone MLS-1200 Mega (Milestone, Sorisole, Italy) microwave oven. All solutions were prepared in HPW and with reagents of analytical grade. Standard solutions were prepared from 1000 mg L−1 Sigma-Aldrich solutions. Nitric acid (HNO3, 65%, Sigma Aldrich, St. Louis, MO, USA), and hydrogen peroxide (H2O2, 30%, Sigma Aldrich St. Louis, MO, USA) were also used. Based on the expected concentration levels of target elements, analytes of interest were determined with a Perkin Elmer Optima 7000 (Perkin Elmer, Norwalk, CT, USA) Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) or with an Element 2 (Thermo Fisher Scientific, Waltham, MA, USA), High-Resolution Inductively Coupled Plasma Mass Spectrometer (HR-ICP-MS).

2.4. Analytical Method

The sample wash pre-treatment procedure was based on Squadrone et al. work [25]. It involves different steps aimed at removing external contaminants. Firstly, the feathers were immersed in 20 mL of a 0.01% Trixon-X-100 solution for four hours. After this step, the feathers undergo two rinses with deionized or HPW, each with a final volume of 20 mL, to eliminate the previous residual solvent. The third step involved two washes using 20 mL CH3OH. Finally, feathers were rinsed with 20 mL of HPW to ensure the removal of residual solvents and were dried under a laminar flow hood until they reached a constant mass.
Washed samples were then mineralized by wet digestion with acid and oxidant, following our previous similar works [26,27]. In this case, between 0.05 and 0.1 g of feathers, depending on availability, were subjected to microwave digestion with 7 mL of HNO3 (70% v/v) and 1.5 mL of H2O2 (30% v/v). All samples solution was then filtered with Whatman 0.45 µm filters and diluted to 30 mL with HPW and analyze. Mineralization efficiency and accuracy of the analytical method were verified by processing the Certified Reference Materials (CRM) ERM®-DB001, namely human hair, Bovine Liver CRM 185 and Tomato Leaves Standard Reference Material (SRM) 1573a similarly to our previous work [28]. Recovery percentages (R% = (mg kg−1 detected/mg kg−1 certified) × 100) ranged from 81% to 114% and are reported in Table 2. Initially, only the certified reference material ERM®-DB001 was analyzed because, in the absence of a feather-specific CRM, it was considered the closest available material in terms of keratinous composition. However, given the limited number of certified elements in ERM®-DB001, we subsequently decided to extend the method accuracy assessment by including additional certified reference materials.
Table 2. Results obtained from the analysis of reference materials.
Elemental quantification was performed by an external calibration method (five point), by preparing a series of home-made standard solutions by diluting 1000 mg L−1 Sigma-Aldrich monoelemental solutions by HPW and the acid mixture used for the samples’ mineralization to match the matrices between samples and standard solutions. To evaluate the stability of plasma performance during the analysis, one of the home-made standard solutions prepared for the calibration curve with an intermediate concentration (Table S5) was periodically read as quality control. The variation in its intensity was then used to correct the samples’ intensity with respect to the calibration curve by a standard-sample bracketing correction method, as reported in the Supplementary Material. Figure S1 shows the variation in the intensity of the quality control standard during sample analysis performed by ICP-MS and ICP-OES. The signal intensities gradually changed during the analysis, remaining within ±30% of the intensity of the first signal recorded at the beginning of the analysis. The observed smooth drifts in signal intensities were efficiently corrected using the standard–sample bracketing method. This method was employed as an alternative to internal standard correction to assess the temporal variation in instrumental drift in the analyte signal intensities. In Table S6 the wavelengths or the isotopes used for the quantification of the elements are reported with the limit of detection (LOD).

2.5. Statistical Treatment

A chemometric treatment was performed to explore the correlation between all the variables and the similarity or difference between samples. Data were pretreated and processed using XLSTAT 4.4 software (Addinsoft, Paris, France). For elements with concentration below the limit of detection (LOD) in more than 40% of the measurements, the variables were not considered for the statistical treatment. In the case of a few missing data (concentration lower than the LOD), a random value was set between zero and the detection limit. Multivariate analysis of variance (MANOVA) was used to test whether the overall elemental profile differed among groups, considering element concentrations as dependent variables and (i) molt phase (pre- vs. post-molt) or (ii) zoological institution as grouping factors. For the pre-/post-molt MANOVA, only Torino and Overloon samples were included; Magdeburg composite samples were excluded because they could not be assigned to a specific molt phase. Significance was assessed at α = 0.05. Results are reported primarily using Wilks’ Lambda, and consistency across alternative multivariate criteria (Pillai’s trace, Hotelling–Lawley trace, and Roy’s largest root) is also provided.
To support interpretation of multivariate patterns, factor analysis was performed on the same datasets to reduce dimensionality and identify groups of correlated elements. Factor extraction was based on principal components, and Varimax rotation was applied to obtain a simpler and more interpretable factor structure.

3. Results and Discussion

3.1. Element Concentrations in Feathers (Univariate Discussion)

The concentrations of elements in the feathers of sampled penguins are presented in Tables S2–S4 and generally decrease in the following order: Ca > Mg > K > Na > Zn > Ni > Fe > Al > Cu > Sr > Mn > Ba > Pb > As > Cd > Mo. Co and Cr were below the LOD for all the samples analyzed. This dataset includes several Potentially Toxic Elements (PTEs), namely Al, As, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, and Zn. Among these, many elements are essential to animals, whereas others (As, Cd, Pb) have high toxicity even at low concentrations and warrant attention due to their potential health impacts on penguins’ organisms and low toxicity thresholds. The As concentrations in the dataset range from 0.04 to 0.35 mg kg−1, significantly below the 3 mg kg−1, which in avian tissue is often considered indicative of elevated exposure, suggesting that the penguins examined in this study may not be exposed to elevated concentrations of As [29,30]. The Cd concentration in the samples is relatively low, ranging from 0.012 to 0.274 mg kg−1, which is comparable to data reported in studies examining various penguin species across different geographical areas [21,22,24,25,31]. These values are well below 50 mg kg−1, which is often cited as a threshold for kidney dysfunction in birds [32]. It is important to underline, however, that many studies report that the distribution of Cd is not uniform among the different tissues of the bird, with a concentration in the feathers that is at least one order of magnitude lower than the internal tissues [33,34]. Similarly, the concentrations of Pb vary between 0.009 and 1.05 mg kg−1 across different groups, remaining well below the established limits of concern for wildlife (Figure S2 Supplementary Material). Toxicity levels for lead in birds are typically reported as 200 mg kg−1, indicating that the observed values do not pose an immediate risk [15]. Even at these levels, chronic lead exposure can impair neurological function, growth, and reproduction in birds, making this an important element to monitor over time. In the present study, the observed concentration range aligns with values reported in the literature, suggesting that the areas under investigation do not exhibit significant contamination by this element.
Beyond these three highly toxic elements, the dataset also highlights significant variations in the concentrations of essential minerals, such as Fe and Ca, which play critical roles in physiological functions. Calcium, a key element for bone and feather development [13], was present in consistently high concentrations across all samples, indicating adequate availability for the penguins. The concentration range varies from 365 to 12,189 mg kg−1 consistent with the values reported in the literature for penguin feathers [21,23,24,25]. Iron concentrations vary widely between samples, with values ranging from 0.03 to 110 mg kg−1. While these levels are not considered toxic, the variability could reflect differences in dietary intake, molt stages, or zoo management practices. Elevated iron concentrations are crucial for oxygen transport and feather pigmentation, particularly during phases of rapid feather growth [14]. Additionally, Mg and Na show noteworthy differences across samples. Magnesium, vital for biochemical processes [35], fluctuates between 30.7 and 1385 mg kg−1, while sodium, crucial for maintaining electrolyte balance [36], ranges from 4.8 to 359 mg kg−1. These variations might indicate different dietary compositions, environmental conditions in each zoo, and the water sources provided to the penguins.
Particularly in Magdeburg Zoo, data analysis revealed distinct patterns that differ notably from other zoos. Magdeburg samples showed higher sodium levels, which could indicate unique local dietary inputs or differences in water mineral content. These insights point to the necessity of adapting zoo management practices to local conditions to optimize mineral intake and ensure the health of captive animals. These minerals are vital for bone health and overall physiological functions, and their deficiency could lead to health issues such as bone demineralization or other metabolic disorders in penguins [37]. Further investigations at Magdeburg might focus on isolating specific factors contributing to this variation, thereby refining our understanding of environmental and dietary impacts on the mineral accumulation in penguin feathers.

3.2. Pre-Molt and Post-Molt Comparison

The dataset on element concentrations in penguin feathers is summarized in Table S4 as maximum, minimum, and variance for pre-molt and post-molt groups. Table S5 reports the average standard deviations and RSDs for each element. This section evaluates the variation between these groups. Element concentrations in pre- and post-molt penguin feathers sampled from the zoos of Turin and Overloon show clear differences between molt phases and between locations. In particular, analyte concentrations in pre-molt samples are higher for many elements in both sample sets. Some examples are Ca and Mn. The range of Ca in Turin pre-molt varies from 2.17 to 12.2 g kg−1, while the post-molt range is from 0.35 to 2.94 g kg−1, whereas in Overloon, it is slightly lower: from 2.63 to 9.74 g kg−1 in the pre-molt set and 0.74 to 3.65 g kg−1 in post-molt one. Similarly, Mn concentrations are higher in the pre-molt sample set in both zoos (26.49–3.44 for Turin and 36.36–7.47 mg kg−1 for Overloon samples) than in post-molt ones (1.65–5.88 for Turin and 1.44–3.68 mg kg−1 for Overloon samples). These differences may be linked to the physiological preparation for molting, where the metabolic demand for keratin synthesis and Ca deposition in growing feathers is heightened. Mn’s involvement in antioxidant defense systems further underlines the significance of these elements during the molting cycle. Understanding these patterns provides insights into the nutritional and physiological status of penguins, with potential applications for zoo management practices and conservation strategies.
Furthermore, pre-molt feathers have been exposed to the environment for a longer time than post-molt feathers, and they may have assimilated a larger portion of elements from soil, water or particulate matter. It must be recalled that feathers are washed before analysis, to remove the contribution of dust possibly deposited on them. Indeed, in both zoos, the variance in element concentrations is consistently higher before molt compared to post-molt, indicating a broader range of element accumulation before feather shedding. For instance, in Turin, the data variability of the group for Ca is significantly larger pre-molt than post-molt (890,760.41 mg2/kg2), reflecting greater variability in calcium content before molt. A similar pattern is observed for other elements, such as Mg and Fe, where pre-molt variability is notably higher, as shown by the boxplots in Figure S2 of the Supplementary Material for the Turin samples.
Overall, the significantly higher concentration and greater variability in pre-molt feathers across most elements points to more variable environmental exposure or metabolic accumulation before the molt, while post-molt feathers exhibit more uniform concentrations, reflecting the elimination of excess metals during feathers shedding. These findings underline the importance of molt as a critical period for detoxification in penguins. The significant differences between pre- and post-molt groups were assessed through the MANOVA application, as explained in the next paragraphs.

3.3. Pre- and Post-Molt Comparison (Chemometric Analysis)

In the chemometric processing of the dataset for comparing pre- and post-molt samples, the samples from Magdeburg Zoo were not included, as they represent a composite of pre- and post-molt conditions, which could not be distinctly categorized into either group. The MANOVA results indicate significant differences in element concentrations in penguin feathers when comparing pre-molt and post-molt samples from Torino and Overloon (Table 3). This confirms that feather samples collected in different molting phases exhibit varying concentrations of elements, demonstrating the capacity of feathers to accumulate mineral elements and remove them from the organism. Specifically, the rejection of the null hypothesis across multiple tests (Wilks, Hotelling-Lawley, Pillai, and Roy) demonstrates that the molting process significantly influences metal retention or elimination. The consistent p-value across tests (0.032) highlights the robustness of these findings and suggests that the molt period could be an important factor in element regulation. Furthermore, the results imply that the concentration of elements might impact the molt conduction itself, potentially affecting the efficiency or timing of this critical biological process. Further analysis is needed to explore the specific elements involved and their biological implications during molt and underscore the utility of feather analysis for monitoring both short-term and long-term environmental conditions, offering a valuable tool for assessing the impacts of pollution and climate change on penguin populations.
Table 3. Results obtained by MANOVA to assess the molting phase role in the concentration of the analytes considered.
In order to further assess this issue, a factorial analysis was performed on the same portion of the dataset, which confirmed pivotal insights into the environmental and dietary factors influencing bioaccumulation patterns. Factor 1, accounting for 41.19% of the variance, has strong correlations with Mg (0.799), Mn (0.667), Sr (0.853), Ca (0.877) and Ba (0.791) (Table 4). These elements point to an environmental influence, particularly reflecting geogenic origins. For instance, Mg and Sr are naturally abundant in soils, particularly in geologically active regions. Ca and Mn are crucial for biological processes [38], but their presence in high concentrations in the feathers also hints at environmental accumulation from the soil. Post-molt samples might exhibit higher concentrations of these elements due to the accumulation during feather regrowth. Furthermore, this highlights the interplay between environmental accumulation and internal biological processes during molt. As noted by Squadrone et al., the variability of these elements can also signal localized environmental conditions [25]. Feathers absorb minerals from the environment, and during the molting period, birds could experience changes in diet or environmental exposure that affect these levels. Factor 1 also shows a high correlation with Cd (0.765). Thus, natural and anthropogenic factors blend in this analysis, with the factorial loadings revealing these dual influences in elemental accumulation patterns, as discussed below.
Table 4. Correlations between variables and the factors derived from factorial analysis conducted on pre- and post-molt samples.
Factor 2, which accounts for 13.54% of the total variance, has notable inverse correlations with As (−0.807) and Mo (−0.668) and a high correlation with Ni (0.598), as shown in Table 4. As is typically associated with anthropogenic sources, such as industrial pollution [30], highlighting the importance of monitoring human activities in influencing elemental accumulation. In this study, As concentrations were similar to those reported by Squadrone et al. and lower than concentrations found in the work of Metcheva et al., suggesting effective industrial regulation in these regions [24,31]. Mo also has a high anticorrelation with Factor 2, similar to As, suggesting that these two elements could have a common origin or be influenced by the same environmental processes. Despite being an essential trace element involved in numerous enzymatic processes, Mo can be generated from both natural and anthropogenic sources, such as industrial or agricultural activity. Its presence in this area may indicate a contribution from human-induced contamination, although further investigation is needed to distinguish between different sources. Conversely, Ni shows a notable correlation with Factor 2, suggesting that its elevated concentration (mainly in Turin samples) is due to geologic factors more than anthropogenic ones. The elevated Ni levels in Torino reflect its natural geogenic origin from serpentinite-rich soils, as corroborated by D’Amico et al. [19]. Such findings provide critical insights into how geological features and local industrial practices interact to influence bioaccumulation patterns in penguin feathers [17]. Different works that analyze Ni in penguin feathers collected in the metropolitan area of Turin found similar concentrations. The opposite correlation of the three elements is indicative that, while Ni is mostly influenced by geogenic processes, As and Mo presence could be regulated by different factors, probably connected to anthropogenic activity and their consequential presence in biological systems. Factor 3 accounts for 12.55% of the variance and shows significant correlations with Na (0.606) and K (0.545) (Table 4). These elements are critical in metabolic and physiological processes, suggesting that Factor 3 captures variations related to physiological differences in the birds, potentially linked to diet or the birds’ electrolyte balance [18]. The high correlation with Na and K might indicate that the differences observed in this factor are more closely related to dietary intake or water source changes post-molt, rather than direct environmental contamination. The increase in Na and K levels post-molt may reflect physiological changes associated with feather regeneration, as birds might assimilate more minerals during this recovery phase. In the context of factorial analysis, Factor 3 reflects these internal physiological variations rather than external environmental accumulation. This complements Factors 1 and 2, which are more reflective of environmental accumulation and geogenic or anthropogenic influences. In conclusion, the factorial analysis suggested that variations in the concentrations of elements are not only due to contaminations or environmental factors but can be explained also with the natural biological processes of feather growth, metabolism and diet, especially during molt phases.

3.4. Comparative Analysis of Samples from Different Zoos (Chemometric Analysis)

The same chemometric methods were applied comprehensively across the entire dataset to assess the differences and correlations among the various zoological locations. This analysis included the mixed samples from the Magdeburg Zoo to evaluate potential environmental or management influences on each sample set since no distinction has been made according to the molting period. The MANOVA results are shown in Table 5. The rejection of the null hypothesis across multiple statistical tests strongly suggests that the geographic location of the zoos significantly influences element accumulation in their feathers. The Wilks’ Lambda value of 0.004, alongside highly significant p-values (<0.0001) for all tests, demonstrates that the habitat of the penguins is a key factor in determining the variation in element concentrations. The observed F-values for Wilks (21.766), Hotelling-Lawley (21.822), Pillai (21.852), and Roy (29.770) tests exceed their corresponding critical values, further confirming the robustness of the findings. The consistently significant outcomes across all tests highlight that geographic location is a major determinant of element bioaccumulation in feathers. This could be due to differences in habitat, water quality, or food availability in the regions in which the penguins live. In particular, the next step will consist of the analysis of the feed eaten by the penguins. Further research is required to investigate which elements are most impacted by these environmental factors and to explore the potential biological implications of these findings for penguin health and conservation efforts.
Table 5. Results obtained by MANOVA to assess the sampling locations’ role in the concentration of the analytes considered.
As to the factorial analysis of the whole dataset, Factor 1 showed a high correlation with several elements (Table 6), including Ba (0.808), Ca (0.807), and Cd (0.840). These findings could indicate that Factor 1 potentially reflects physiological or environmental accumulation patterns common across the dataset. The implication of these correlations suggests that Factor 1 captures the general patterns of how these elements accumulate in the penguins, likely driven by consistent environmental exposure (e.g., dietary intake and/or habitat conditions).
Table 6. Correlations between variables and the factors derived from the factorial analysis conducted on the complete dataset.
Instead, Factor 2 majorly displayed strong inverse correlation with As (−0.718) and Pb (−0.405). As and Pb are known environmental pollutants often linked to industrial activities, waste, or other anthropogenic sources [39,40]. Therefore, Factor 2 could capture geographical or industrial differences between the penguin habitats or diets, especially in areas where contamination levels are higher.
On the other hand, Factor 3 showed high negative or positive correlation values with elements such as Ni (−0.715) and Mg (0.454), suggesting a reflection of either localized environmental contamination or exposure to these elements through their natural penguin diets or habitats. Ni variation could originate both from anthropogenic and natural sources. As reported in the previous paragraph, the natural geological characteristics of the Turin Area include a high presence of serpentinite rocks, which enrich the soil with Ni and Cr, contributing to higher baseline levels of these elements in the local environment, and affecting their concentrations in local flora and fauna [17,19]. The results provide insights for improving zoo management practices and conservation strategies. By identifying elemental differences linked to local environmental conditions, this study highlights the role of captive penguins as sentinels for monitoring pollution and ecological changes. Additionally, the pre-and post-molt comparisons provide a framework for assessing how environmental and dietary factors impact feather composition, that in tourn could has an impact on their development, with potential applications for wild populations. These findings could inform conservation strategies aimed at mitigating the impacts of pollution and climate change on seabirds globally. This framework has potential applications beyond captive settings. In wild colonies, repeated feather sampling across years (and across colonies) could help detect temporal shifts in pollutant exposure and resource availability, particularly for threatened seabirds where multiple stressors act simultaneously. While our study is based on managed populations, the identification of element patterns associated with local conditions and molt stage provides a basis for future monitoring designs that integrate feather chemistry with ecological indicators to better evaluate the combined pressures of pollution and climate variability on penguin conservation.
One limitation of this study is the inclusion of mixed feather samples from Magdeburg Zoos, which did not allow for a clear distinction between pre- and post-molt phases. While these samples still provide valuable insights into elemental concentrations and environmental conditions, they limit the ability to make direct temporal comparisons between molting stages. Future studies should prioritize the collection of distinct pre- and post-molt feather samples from all study sites to facilitate more robust temporal analyses. Additionally, logistical constraints in sample collection and the small sample size for some zoos may have influenced the statistical power of our findings. Expanding the sample size and increasing the number of replicates across all institutions will be critical for future investigations to validate and extend these results.

4. Conclusions

This study addresses the element compositions of African penguin feathers during pre- and post-molt phases in three different captive habitats. The results show higher concentrations and a higher variability in pre-molt samples for most elements; in particular, significant differences in Ca, Mg, Mn, and Na levels suggest an active process of mobilization and accumulation of mineral elements during the feather growth, resulting in a high variability of element content at the end of the molting cycle. Elevated Ca and Mn levels in pre-molt feathers indicate the mineral demands of feather keratinization, while changes in Mg and Na levels may reflect metabolic shifts and electrolyte balance regulation during feather regrowth. While MANOVA tests confirm the significant differences between pre-and post-molt samples, factorial analysis underlines distinct geogenic and anthropogenic influences on elements like Sr and Ni, respectively, with higher concentrations linked to local geological conditions, such as serpentinite-rich soils in Torino. Zoo-specific differences were also confirmed as significant by the MANOVA tests. These variances may reflect the dietary and environmental inputs, emphasizing the role of the local environment and management practices influencing feathers’ elemental contents. These findings underscore the need for tailored management strategies to assess the environmental and nutritional needs of captive penguins. In addition, the zoo-specific differences confirmed the potentiality of feathers as bioindicators of the mineral element contents of the habitat examined, offering, at the same time, valuable insights into how zoo management practices influence elemental accumulation during molting. These findings have implications for improving captive penguin welfare and understanding broader ecological and environmental dynamics. While this study provides a robust foundation, it is not without limitations. The use of mixed-feather samples from Zoo Magdeburg precludes a direct comparison of pre- and post-molt stages at that site. Future research should aim to address this limitation by standardizing sample collection protocols across all institutions. However, the composite sample was analyzed qualitatively to assess environmental differences in pollutant exposure. This approach allows us to investigate not only the accumulation of contaminants in the feathers before the molt, but also gives us data on the environmental status of the area and allows us to identify potential disparities in environmental contamination between the institutions and to provide an important context for understanding how local environmental conditions may influence feather composition. Analyzing animals’ feed, expanding the sample size and incorporating additional zoos, or, if possible, wild colonies, will also help validate these findings and provide a more comprehensive understanding of the interplay between environmental, dietary, and physiological factors during the molting process.
By identifying elemental differences linked to local environmental conditions, this study highlights the role of captive penguins as sentinels for monitoring pollution and ecological changes. Additionally, the pre- and post-molt comparisons provide a framework for assessing how environmental impact feather development, with potential applications for wild populations. These findings provide insights for improving zoo management practices, thus enhancing the welfare of captive penguins during critical periods, contributing to the ecological understanding and to the implementation of conservation strategies aimed at mitigating the impacts of pollution and climate change on this endangered species.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/analytica7010011/s1. Table S1 Details of samples included in the study; Table S2 Concentration of analytes (mg kg−1) in feather samples part 1; Table S3 Concentration of analytes (mg kg−1) in feather samples part 2; Table S4 Summary of data on elements in penguin feathers: maximum, minimum. The following groups are address: Turin and Overloon pre and post molt; all data; Table S5 Element concentrations in the quality control standard solution used for standard–sample bracketing correction during ICP-OES and ICP-MS analyses; Table S6 Average Standard deviation, RSD% and LOD for the element analyzed. Values are expressed in mg kg−1. The analytical technique and the isotope or analytical line used for the quantification are also reported; Figure S1 Relative intensity of the quality control standard solution during sample analysis by ICP-MS (top) and ICP-OES (bottom). The quantification of Na and K was performed using a different set of measurements compared to the other elements quantified by ICP-OES; therefore, the drift in signal intensity was different; Figure S2 Boxplot of all the variables taken into account.

Author Contributions

Conceptualization, L.F., E.T., O.A. and V.I.; methodology, A.G.; validation, L.F. and P.I.; formal analysis, L.F. and H.C.S.; investigation, P.I.; resources, O.A.; data curation, M.M. and S.B.; writing—original draft preparation, L.F.; writing—review and editing, V.I. and O.A. supervision, O.A.; project administration, O.A. and V.I.; funding acquisition, V.I. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Fondazione ZOOM.

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding author(s).

Conflicts of Interest

The authors declare no conflicts of interest.

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