The uropygial gland of the European hoopoe as a symbiotic organ.

This study is the first to describe the presence, localization, and temporal distribution of epithelial (E)-, neural (N)-, and placental (P)-cadherins within the chicken uropygial gland (UG) during the post-hatching growth period, using immunohistochemistry and Western blot techniques. In the luminal epithelium and secretory tubules of the UGs of 1-day-old chicks, the germinative layer sebocytes (GLS) exhibited cytoplasmic immunostaining for P-cadherin, while they were negative for E-cadherin. However, the secretory layer sebocytes (SLS) showed a membranous staining for both cadherins. N-cadherin was only localized in the lateral membrane of the end-bulb cells. From the 7th to the 150th day of post-hatching, all cadherins were detected in the membrane of SLS of the luminal epithelium and peripheral and central zones. E- and N-cadherin immunostainings were weak in the cytoplasm of GLS, but P-cadherin was strong. In addition, N-cadherin was strongly localized in the membrane of some GLS of peripheral tubules adjacent to the capsule. These results indicate that the localization patterns of cadherins differ based on the type of cadherin, age, and zones and cell layers of the UG. This suggests that cadherins play unique roles in maintaining tissue architecture and regulating holocrine secretion during the post-hatching growth of chicken UG.

High frequency of plastic-derived contaminants (phthalate acid esters) in the preen gland of dead procellariiform seabirds from the Patagonian Sea.

The ongoing worldwide outbreak of high pathogenicity avian influenza (HPAI) H5 of the Goose/Guangdong (Gs/GD) lineage has caused unprecedented mortality amongst an ever-expanding number of avian and mammalian species. This includes black-headed gulls, which suffered high mortality from this virus in 2022 and 2023. We performed pathological and virological analyses on black-headed gulls and a common tern found dead in a breeding site in The Netherlands in spring 2023 in order to characterise the pathogenesis of HPAI Gs/GD virus infection in these species. We found a strong tropism of HPAI H5 Gs/GD virus for the central nervous system, pancreas, lungs, and the preen gland, with acute necrosis as the main associated lesion. Affected organs revealed high virus RNA loads and intralesional expression of virus antigen, confirming HPAI H5 Gs/GD virus infection as the cause of disease and mortality. Genetic sequencing showed that this HPAI H5 Gs/GD clade 2.3.4.4b virus belonged to the gull-adapted BB genotype. Comprehensive pathogenesis studies in a cohort of wild animals naturally infected with HPAI H5 Gs/GD virus are scarce, yet the knowledge gained may fill knowledge gaps to help mitigate future HPAI outbreaks.

A 24-year-old female saker falcon (Falco cherrug) was presented for a hyperkeratotic lesion associated with the uropygial gland. Owing to perceived anesthetic risks, a conservative medical approach was initially chosen over surgical excision. The treatment involved local debridement and supportive care, which provided temporary improvement. However, the lesion recurred multiple times, leading to the decision to perform complete surgical excision of the uropygial gland. The falcon underwent cardiopulmonary arrest during the procedure and was unresponsive to resuscitation. Histological analysis identified a compact cystic mass characterized by atypical proliferation of the keratin and squamous cell layers, consistent with an infiltrating keratoacanthoma of the uropygial gland. Additional findings included necrotizing hepatitis, focal splenic necrotic lesions and white pulp depletion, pyogranulomatous nephritis, pulmonary edema, and infiltrative chronic-active enteritis. Amphophilic intranuclear inclusion bodies were observed in the basal layer of the uropygial mass and in hepatocytes. Immunohistochemistry confirmed the presence of avian alpha-herpesvirus antigen in liver, kidney, and uropygial gland. To the authors' knowledge, this is the first documented case of uropygial keratoacanthoma in a bird of prey.

A 24-year-old female saker falcon (Falco cherrug) was presented for a hyperkeratotic lesion associated with the uropygial gland. Owing to perceived anesthetic risks, a conservative medical approach was initially chosen over surgical excision. The treatment involved local debridement and supportive care, which provided temporary improvement. However, the lesion recurred multiple times, leading to the decision to perform complete surgical excision of the uropygial gland. The falcon underwent cardiopulmonary arrest during the procedure and was unresponsive to resuscitation. Histological analysis identified a compact cystic mass characterized by atypical proliferation of the keratin and squamous cell layers, consistent with an infiltrating keratoacanthoma of the uropygial gland. Additional findings included necrotizing hepatitis, focal splenic necrotic lesions and white pulp depletion, pyogranulomatous nephritis, pulmonary edema, and infiltrative chronic-active enteritis. Amphophilic intranuclear inclusion bodies were observed in the basal layer of the uropygial mass and in hepatocytes. Immunohistochemistry confirmed the presence of avian alpha-herpesvirus antigen in liver, kidney, and uropygial gland. To the authors' knowledge, this is the first documented case of uropygial keratoacanthoma in a bird of prey.

Uropygial secretions are thought to play an antimicrobial role in birds, but few studies have compared their effectiveness across multiple species and microorganisms using standardized methods. We evaluated the antimicrobial activity of uropygial secretions from 212 individuals of 11 passerine species in southwestern Spain, testing their inhibitory effects against Bacillus licheniformis , B. subtilis , Candida albicans , Escherichia coli , and Salmonella typhimurium by flow cytometry. Antimicrobial activity varied significantly among species and microorganisms: house sparrows Passer domesticus consistently exhibited stronger and broader responses, whereas activity against S. typhimurium was generally low. Phylogeny, migratory status, and social behavior did not explain variation, but uropygial gland size was positively associated with antimicrobial activity both globally and in some bird species. Body condition exhibited species‐specific associations with antimicrobial activity, showing positive correlations in some bird species and negative correlations in others. Overall, our findings highlight the uneven distribution of antimicrobial defenses among passerines and underscore the importance of comparative, chemically informed, and methodologically standardized approaches to clarify the ecological and evolutionary significance of uropygial secretions.

The uropygial gland is a gland peculiar to birds, and it is widely recognized that its secretion confers water-repellent properties on the feather coat and maintains the suppleness of the feathers. The aim of this study was to reveal differences in the developmental patterns and the regulatory mechanisms of the uropygial glands among different goose breeds (Sichuan White goose, SW; Landes goose, LD; and Gang goose, GE) through comparative analysis of their uropygial gland histomorphological parameters and transcriptomic data during the period from week 0 to week 30 post-hatching. Morphologically, our results showed that the uropygial gland weight of LD was significantly lower than that of SW (P < 0.01) and GE (P < 0.05) at week 10 but was significantly higher than that of SW and GE at week 30 (P < 0.01). Histologically, the tubular area of zone I, the interlobular septum, luminal area, and epithelial thickness of zone II, and the luminal area of zone III increased with age in the uropygial glands among almost all three goose breeds. Moreover, these histological parameters differed most significantly at week 30, when the luminal area and epithelial thickness of zone II were significantly greater in SW than in LD (P < 0.05) but the luminal area of zone III was significantly greater in LD than in SW (P < 0.05). Comparative analysis of the uropygial gland transcriptomes of LD and SW at week 10 and 30 further identified several key genes, signaling pathways, and interactions networks that are involved in regulating the breed- and age-related goose uropygial gland development. The uropygial glands of LD might have a stronger capacity of lipid synthesis and secretion when approaching the age of sexual maturity. GPAT3, LPIN2, EP300, and MGMT involves breed-related uropygial gland development. LCAT, PLPP3, TIMP2, and MFAP5A involves age-related uropygial gland development. Besides, the glycerophospholipid metabolism pathway may be the main regulatory pathway for lipid metabolism in the uropygial gland of LD.

Abstract Predation is a key ecological factor influencing prey populations, and for ground-nesting birds, nest predation is a critical determinant of reproductive success. Investigating nest predation in cryptic species poses unique challenges because their nests are difficult to locate, and monitoring efforts can cause disturbances or even increase predation risk. Artificial nests are commonly used to study nest predation. However, this method often fails to accurately replicate real nest predation dynamics, particularly for cryptic species. In this study, we compared the predation rates of real nests of the Tetrao urogallus (Western Capercaillie) with artificial nests monitored using camera traps, both with and without the application of bird scent derived from capercaillie uropygial gland secretions. The results showed that artificial nests treated with bird scent exhibited a predation rate of 52.2%, closely matching the rate observed in real nests (51.4%). In contrast, artificial nests without scent significantly underestimated predation, with a rate of only 6.3%. Martens (Martes martes and M. foina) and red foxes (Vulpes vulpes) were identified as the primary nest predators, with 38–56% of predated nests by these species across treatments, preying similarly toward both real and scented artificial nests. These findings highlight that incorporating bird scent into artificial nest studies significantly improves the accuracy of predation rate estimates. We recommend the widespread adoption of this method in nest predation research to better replicate natural conditions, minimize biases related to scent-dependent predators, and enhance the reliability of nest predation assessments.

Accumulation of persistent organic pollutants and benzotriazole UV stabilizers in the preen gland oil of Tristram's storm-petrel (Hydrobates tristrami).

The present investigation aimed to analyze the microbial communities inhabiting the feathers of the domestic pigeons at different age stages through both isolation of bacteria and fungi (culture-dependent) and 16S rRNA and ITS amplicon sequencing for bacteria and fungi, respectively (culture-independent), then evaluate the antimicrobial properties of the preen gland secretions of these isolates. Feather samples were collected from pigeons at three different ages: juvenile, adult, and senescent. One hundred fifty microbial species were identified; 108 were bacterial, and 42 were fungal species. The dominant microbial populations were Bacillus pumilus, Pseudomonas aeruginosa, and Aspergillus flavus. The antimicrobial activities of the preen gland secretions were assessed for their respective MIC, MBC, and MFC assays, confirmed by DNA cleavage assay. The obtained results demonstrated that the preen secretions of juvenile individuals were more effective against microbial colonization than senescent birds, indicating a possible age-related decline in the efficiency of secretions with aging. The study emphasizes the ecological relevance of the gland secretions in maintaining plumage health status and preventing microbial colonization, which indicates a pivotal role in defensive mechanisms in combating bacterial and fungal invasion.

The avian uropygial gland secretes preen oil, a complex blend of lipids that birds spread on their feathers during preening. Although preen oil is known to help birds maintain feather condition, there has been increasing evidence suggesting preen oil also affects other organisms that reside on bird feathers, such as bacteria, mites, and lice. In a series of experiments, we investigated the effects of Rock Dove (Columba livia) preen oil on the behavior and survival of feather-feeding wing lice (Columbicola columbae). These lice spend the majority of their lives hidden between flight feather barbs to avoid bird preening. However, because lice cannot feed on flight feathers, they regularly migrate to bird body regions to consume thinner insulative feather barbs. We found that lice strongly preferred to spend time on body feather regions treated with preen oil compared with untreated feather regions, but this preference disappeared when lice encountered preen oil on either flight feathers or on filter paper arenas. As lice are only known to feed on body feathers, our data suggest that preen oil may be consumed by lice or that lice prefer to feed in preen oil-rich regions to increase the chances of encountering and perhaps consuming bacteria or mites that feed on preen oil. Contact with preen oil also influenced louse locomotion, with lice reducing the turn rate (though not velocity) while walking on arenas treated with preen oil, which is also consistent with a preference for preen oil. However, in vitro survival analyses showed that lice kept on preen oil-treated body feathers experienced a moderate but significant reduction in survival compared with lice on untreated body feathers. In contrast, lice on treated and untreated flight feathers showed similar rates of survival. Overall, our behavioral data and survival analyses suggest that louse interactions with preen oil are more complex than previously thought. Further research is needed to determine how these in vitro impacts of preen oil on louse behavior and survival influence bird-louse interactions in more natural settings.

Effects of different rearing systems on the development of uropygial gland in three goose breeds.

The present investigation aimed to analyze the uropygial gland's (UG) histological architecture and histochemical variation in the domestic pigeon at four posthatching age stages. The small and relatively undeveloped UG was observed at 1-day-old, and then the gland started to increase in size and complexity with age to reach its full functional size in the adult. The stroma became more organized with increased collagen fiber deposition, supporting the growing gland with age. The secretory tubules were more developed in the mature and adult pigeons than in other ages. The epithelial layer had four layers: basal layer, intermediate layer, secretory layer, and degenerative layer. The histochemical analysis using Mallory's trichrome stain revealed a positive reaction with all ages. The capsule, interlobular septum, papilla areas, and CT appeared blue, and the cellular components appeared red. The staining intensity increases with age till it becomes intensely blue with well-developed collagen in adults. Herbst corpuscles were encapsulated by a connective tissue sheath and comprised nerve cells arranged along the central axon, enveloped by collagen fibers. The findings from the current study may have a potential implication in poultry science and developmental biology.

During the breeding season, lymphocytes assemble into ellipse-shaped clusters in the uropygial gland of the jungle crow Corvus macrorhynchos

Symbiotic microbiota are important drivers of host behaviour, health, and fitness. While most studies focus on humans, model organisms, and domestic or economically important species, research investigating the role of host microbiota in wild populations is rapidly accumulating. Most studies focus on the gut microbiota; however, skin and other glandular microbiota also play an important role in shaping traits that may impact host fitness. The uropygial gland is an important source of chemical cues and harbours diverse microbes that could mediate chemical communication in birds, so determining the factors most important in shaping host microbiota should improve our understanding of microbially-mediated chemical communication. Hypothesizing that temporal, geographic, and taxonomic effects influence host microbiota, we evaluated the effects of season, migration distance, and taxonomy on the uropygial gland microbiota of 18 passerine species from 11 families. By sampling 473 birds at a single stopover location during spring and fall migration and using 16S rRNA sequencing, we demonstrate that season, followed by migration distance, had the strongest influence on uropygial gland microbial community composition. While statistically significant, taxonomic family and species had only weak effects on gland microbiota. Given that temporal effects on gland microbiota were nearly ubiquitous among the species we tested, determining the consequences of and mechanisms driving this seasonal variation are important next steps.

The antipsychotic medication haloperidol has been used for many years in avian medicine as a pharmacologic therapy for refractory feather destructive behavior in pet parrots. However, despite its common use, there are no published studies evaluating its efficacy and adverse effects in psittacine birds. The goal of this study was to report the signalment, clinical presentation, dosing regimen, response to therapy, and adverse effects of companion psittacine birds prescribed oral haloperidol therapy at a single veterinary referral hospital. Included cases were pet psittacine birds that were prescribed haloperidol between 2012 and 2022 and had sufficient follow-up information available to assess efficacy and adverse effects. Nineteen parrots met the case criteria for inclusion. Haloperidol was prescribed for 17 birds with feather destructive behavior, 1 bird for excessive sexual behavior, and 1 bird prophylactically after surgery of the uropygial gland. The most common species prescribed haloperidol were grey parrots (n = 5) (Psittacus erithacus), umbrella cockatoos (n = 4) (Cacatua alba), and Pionus spp. (n = 2). Most (12/18 [67%]) birds were classified as having a positive response to haloperidol administration. The initial median (interquartile range) total daily dose for all birds in the study was 0.24 mg/kg (0.18-0.4 mg/kg). Adverse effects were reported in 9/19 (47%) birds with grey parrots being the most common species displaying adverse effects. The most common adverse effect reported was lethargy in 5/19 (26%) birds. Some adverse effects were mitigated by adjusting dosing, and more severe adverse effects resolved after discontinuing haloperidol. This study provides descriptive data for a commonly used antipsychotic medication to assist veterinarians treating avian patients.

Preen gland bacteria are thought to be the key producers of preen oil components such as chemosignalling molecules including volatile organic compounds (VOCs) and antimicrobial compounds including peptides and antimicrobial VOCs. However, data on the preen oil bacteriome and chemical composition are limited to a small subset of bird species, and the presence of antimicrobial peptides is largely unexplored. Here, we performed an exploratory study to characterize, for the first time, the preen oil chemical and proteomic profiles and to explore the possible contribution of the bacteriome to the production of preen oil VOCs and antimicrobial peptides (bacteriocins) in eight passerine species, each represented by a single individual. Preen oil bacteriome, chemical and proteomic profiles varied among birds. The bacterial profiles were dominated by the genera Streptococcus, Lactococcus, Corynebacterium and Cutibacterium. The chemical profiles mainly consisted of alcohols, ketones and carboxylic acids. The biological functions primarily associated with the proteomic profiles were proteolysis and response to oxidative stress. Although we were unable to explore a direct association between the bacteriome and chemical profiles, the preen oil contained bacteriocin- and VOC-producing bacterial genera capable of producing detected microbially-derived VOCs (mVOCs), the relative abundance of which varied between birds. Riparian species showed the highest chemical diversity and high abundances of putative preen oil mVOC-producing bacteria, which could suggest habitat-specific adaptations. This exploratory study may significantly contribute to the formulation of hypotheses on the potential role of host ecological factors in the variation of preen oil bacterial, chemical and proteomic profiles in passerines.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10482-025-02182-w.

The microbiome of the uropygial gland and integuments where birds spread the uropygial secretion may play crucial roles for their hosts, but it has been poorly studied, especially in wild species. Exploring bacterial communities associated with the uropygial secretion of birds is particularly interesting in species under strong selection pressures due to pathogenic infection. Here, by high‐throughput 16S rRNA amplicon sequencing, we characterized and compared the bacterial communities of the uropygial gland surface of three African hornbill species (Family Bucerotidae), as well as the bill and feathers of females from two of these species and the nestlings of the other one. In accordance with previous knowledge of avian microbiomes, we expected to find differences associated with species identity, age and the sampled integument. Overall, we found that: 1) the microbiome was similar among species, 2) but there were slight differences associated with the sampled body regions. Moreover, 3) we observed no consistent variation in the microbiota with age, and 4) females and nestlings sharing a nest harboured more similar gland surface microbiota compared to females and nestlings that did not share a nest. These species often reuse nest cavities, sealing them with a plug made from diverse material. Once sealed, they remain enclosed in the nest for a long period. This behaviour opens the possibility that the nest environment is key shaping the microbiota of these species and might serve as a reservoir of the sampled bacterial communities. Moreover, behavioural mechanisms such as preening may contribute to the transmission of bacteria from the uropygial gland to other body regions, enhancing bacterial similarities. This study contributes to our understanding of the role of the nest environment in structuring bacterial communities in wild birds and provides the first thorough characterization of the microbiome inhabiting different body integuments of southern African hornbills.

The European hoopoe (Upupa epops) conforms a paradigmatic example of animals cultivating bacteria in their uropygial gland that protect them against pathogenic infections. We here explore the hypothesis that enterococci are the responsible bacteria of such beneficial effect. We did so by comparing the antimicrobial activity against three indicator bacteria of colonies isolated from cultures of enterococci and mesophilic bacteria from the uropygial skin or secretion of nestlings, brooding or non-brooding females, and males of the subspecies longirostris in Hainan (China). In accordance with the hypothesis, enterococci isolated from nesting birds are more active than those from non-nesting birds. Moreover, enterococci from the uropygial secretion were more active than those isolated from the skin or than mesophilic bacteria isolates. These results therefore support the hypothesis that, during the nesting phase, hoopoe females and nestlings cultivate enterococci in their uropygial gland with relatively high antimicrobial activity.