{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,20]],"date-time":"2026-07-20T11:02:52Z","timestamp":1784545372090,"version":"3.55.0"},"reference-count":49,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2026,7,17]],"date-time":"2026-07-17T00:00:00Z","timestamp":1784246400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Veterinary Sciences"],"abstract":"<jats:p>Woodpeckers (Picidae) are exposed to repeated mechanical loading and particulate material during climbing, drilling, pecking, and foraging on tree trunks, but the microscopic organization of their eyelids and nictitating membrane remains poorly known. This study asked whether European woodpeckers share a common histological pattern of ocular adnexa and whether selected structural features may be interpreted in the context of ocular surface protection. The upper eyelid, lower eyelid, and nictitating membrane were examined in 40 birds representing six European woodpecker species using routine histological and histochemical methods. In all of these species, the eyelids showed a layered organization with a keratinized anterior palpebral surface, non-keratinized conjunctival surface with goblet cells, marginal zone, musculofibrous stroma, and no tarsal glands. Species-related differences were observed in the examined material in epithelial thickness, skin fold development, melanin pigment distribution, and marginal zone organization. The lower eyelid contained a compact fibrous tarsal plate and CALT represented by lymphoid nodules and diffuse lymphocytes, with morphologically identified HEV-like venules located within or close to lymphoid tissue. The nictitating membrane showed regional variation in the marginal plait, leading edge, epithelial surfaces, stromal pigmentation, and fold organization. These findings provide the first comparative histological baseline for the eyelids and the nictitating membrane of European Picidae and support the cautious interpretation that these structures may contribute to mechanical, mucosal, and immune protection of the ocular surface in woodpeckers. Because sample sizes were unequal, these interspecific observations should be treated as descriptive, sample-level findings rather than definitive species-level traits.<\/jats:p>","DOI":"10.3390\/vetsci13070702","type":"journal-article","created":{"date-parts":[[2026,7,20]],"date-time":"2026-07-20T09:32:54Z","timestamp":1784539974000},"page":"702","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Histological Diversity of Eyelids and the Nictitating Membrane in Six Woodpecker Species (Picidae)"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-1154-8736","authenticated-orcid":false,"given":"Joanna","family":"Kle\u0107kowska-Nawrot","sequence":"first","affiliation":[{"name":"Department of Biostructure and Animal Physiology, Division of Animal Anatomy, Faculty of Veterinary Medicine, Wroc\u0142aw University of Environmental and Life Sciences, Ko\u017cuchowska 1, 51-631 Wroc\u0142aw, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Aleksandra","family":"Kroczak-Zda\u0144kowska","sequence":"additional","affiliation":[{"name":"Department of Genetics, Faculty of Biology and Animal Science, Wroc\u0142aw University of Environmental and Life Sciences, Ko\u017cuchowska 7, 51-631 Wroc\u0142aw, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Adam","family":"Urant\u00f3wka","sequence":"additional","affiliation":[{"name":"Department of Genetics, Faculty of Biology and Animal Science, Wroc\u0142aw University of Environmental and Life Sciences, Ko\u017cuchowska 7, 51-631 Wroc\u0142aw, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Grzegorz","family":"Zaniewicz","sequence":"additional","affiliation":[{"name":"Ecophysiology and Behavioral Ecology Research Unit, Department of Vertebrate Ecology and Zoology, Faculty of Biology, University of Gda\u0144sk, Wita Stwosza 59, 80-308 Gda\u0144sk, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9079-549X","authenticated-orcid":false,"given":"Aleksander","family":"Chr\u00f3szcz","sequence":"additional","affiliation":[{"name":"Department of Biostructure and Animal Physiology, Division of Animal Anatomy, Faculty of Veterinary Medicine, Wroc\u0142aw University of Environmental and Life Sciences, Ko\u017cuchowska 1, 51-631 Wroc\u0142aw, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4296-3174","authenticated-orcid":false,"given":"Dominik","family":"Poradowski","sequence":"additional","affiliation":[{"name":"Department of Biostructure and Animal Physiology, Division of Animal Anatomy, Faculty of Veterinary Medicine, Wroc\u0142aw University of Environmental and Life Sciences, Ko\u017cuchowska 1, 51-631 Wroc\u0142aw, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,17]]},"reference":[{"key":"ref_1","unstructured":"Baumel, J.J., King, A.S., Breazile, J.E., Evans, H.E., and Vanden Berge, J.C. (1993). Handbook of Avian Anatomy: Nomina Anatomica Avium, Nuttall Ornithological Club. [2nd ed.]. Publications of the Nuttall Ornithological Club No. 23."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Jochems, B., and Phillips, T.E. (2015). Histological and ultrastructural studies on the conjunctiva of the Barred Owl (Strix varia). PLoS ONE, 10.","DOI":"10.1371\/journal.pone.0142783"},{"key":"ref_3","unstructured":"Maggs, D.J., Miller, P.E., and Ofri, R. (2013). Third eyelid. Slatter\u2019s Fundamentals of Veterinary Ophthalmology, Elsevier Saunders. [5th ed.]."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"29","DOI":"10.1002\/ajmg.a.32597","article-title":"Elements of morphology: Standard terminology for the periorbital region","volume":"149A","author":"Hall","year":"2009","journal-title":"Am. J. Med. Genet. A"},{"key":"ref_5","unstructured":"K\u00f6nig, H.E., Korbel, R., and Liebich, H.-G. (2016). Avian Anatomy: Textbook and Colour Atlas, 5M Publishing. [2nd ed.]."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Nickel, R., Schummer, A., and Seiferle, E. (2004). Lehrbuch der Anatomie der Haustiere. Band V: Anatomie der V\u00f6gel, Verlag Paul Parey.","DOI":"10.1024\/0036-7281.147.6.275b"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"367","DOI":"10.1111\/azo.12223","article-title":"The differences in the eyelids microstructure and the conjunctiva-associated lymphoid tissue between selected ornamental and wild birds as a result of adaptation to their habitat","volume":"99","author":"Marycz","year":"2018","journal-title":"Acta Zool."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Montiani-Ferreira, F., Moore, B.A., and Ben-Shlomo, G. (2022). Wild and Exotic Animal Ophthalmology. Volume 1: Invertebrates, Fishes, Amphibians, Reptiles, and Birds, Springer.","DOI":"10.1007\/978-3-030-71302-7"},{"key":"ref_9","first-page":"6019","article-title":"The avian membrana nictitans: Anatomy and function","volume":"54","author":"Schobert","year":"2013","journal-title":"Investig. Ophthalmol. Vis. Sci."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Kle\u0107kowska-Nawrot, J.E., Kroczak-Zda\u0144kowska, A., Urant\u00f3wka, A.D., Barszcz, K., and Go\u017adziewska-Har\u0142ajczuk, K. (2025). Descriptive histological analysis of the upper, lower, and third eyelids and the conjunctiva-associated lymphoid tissue in birds of prey. BMC Vet. Res., 21.","DOI":"10.1186\/s12917-025-04677-0"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"74","DOI":"10.1007\/s12565-015-0274-1","article-title":"Light and electron microscopic study of the eyelids, conjunctiva-associated lymphoid tissue and lacrimal gland in Bilgorajska Goose (Anser anser)","volume":"91","author":"Nowaczyk","year":"2016","journal-title":"Anat. Sci. Int."},{"key":"ref_12","first-page":"371","article-title":"Specific antibody production against a soluble antigen in the Harderian gland of the domestic fowl","volume":"26","author":"Burns","year":"1976","journal-title":"Clin. Exp. Immunol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"289","DOI":"10.1016\/j.dci.2011.04.012","article-title":"Conjunctiva-associated lymphoid tissue in avian mucosal immunity","volume":"36","author":"Gulley","year":"2012","journal-title":"Dev. Comp. Immunol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"1852","DOI":"10.2460\/ajvr.1991.52.11.1852","article-title":"Morphologic characterization of conjunctiva-associated lymphoid tissue in chickens","volume":"52","author":"Fix","year":"1991","journal-title":"Am. J. Vet. Res."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"222","DOI":"10.1177\/030098588902600306","article-title":"Conjunctiva-associated lymphoid tissue (CALT) in normal and Bordetella avium-infected turkeys","volume":"26","author":"Fix","year":"1989","journal-title":"Vet. Pathol."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"111","DOI":"10.2478\/orhu-2023-0007","article-title":"Diversity of cranial shape in European woodpecker species (Picidae)","volume":"31","author":"Pecsics","year":"2023","journal-title":"Ornis Hung."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Schuppe, E.R., Rutter, A.R., Roberts, T.J., and Fuxjager, M.J. (2021). Evolutionary and biomechanical basis of drumming behavior in woodpeckers. Front. Ecol. Evol., 9.","DOI":"10.3389\/fevo.2021.649146"},{"key":"ref_18","unstructured":"Winkler, H., Christie, D.A., and Nurney, D. (1995). Woodpeckers: A Guide to the Woodpeckers, Piculets and Wrynecks of the World, Pica Press."},{"key":"ref_19","unstructured":"del Hoyo, J., Elliott, A., and Sargatal, J. (2002). Family Picidae (Woodpeckers). Handbook of the Birds of the World. Volume 7: Jacamars to Woodpeckers, Lynx Edicions."},{"key":"ref_20","unstructured":"Baker, J.K. (2016). Identification of European Non-Passerines, British Trust for Ornithology. [2nd ed.]."},{"key":"ref_21","unstructured":"Blasco-Zumeta, J., and Heinze, G.-M. (2023). Identification Atlas of the Continental Birds of Southwestern Europe, Tundra Ediciones."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1080\/03078698.2025.2573475","article-title":"Moult, ageing and sexing of European Hoopoe, Bee-eater, Kingfisher and woodpeckers","volume":"41","author":"Jenni","year":"2026","journal-title":"Ringing Migr."},{"key":"ref_23","unstructured":"Kle\u0107kowska-Nawrot, J., Kroczak-Zda\u0144kowska, A., Urant\u00f3wka, A., Zaniewicz, G., Badenhorst, S., Chr\u00f3szcz, A., Stegmann, K., Barszcz, K., and Poradowski, D. (Vet. Res. Commun., 2026). Anatomy, Histology and Histochemistry of the Harderian and Lacrimal Glands in the Great Spotted Woodpecker (Dendrocopos major), Vet. Res. Commun., revised manuscript under review."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Kroczak, A., Wo\u0142oszy\u0144ska, M., Wierzbicki, H., Kurkowski, M., Grabowski, K.A., Piasecki, T., Galosi, L., and Urant\u00f3wka, A.D. (2021). New Bird Sexing Strategy Developed in the Order Psittaciformes Involves Multiple Markers to Avoid Sex Misidentification: Debunked Myth of the Universal DNA Marker. Genes, 12.","DOI":"10.3390\/genes12060878"},{"key":"ref_25","unstructured":"AviList Core Team (2026, July 05). AviList: The Global Avian Checklist, v2025. Available online: https:\/\/www.avilist.org\/checklist\/v2025\/."},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Billerman, S.M., Keeney, B.K., Rodewald, P.G., and Schulenberg, T.S. (2020). Gray-headed Woodpecker (Picus canus), version 1.0. Birds of the World, Cornell Lab of Ornithology.","DOI":"10.2173\/bow"},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A., and de Juana, E. (2020). Eurasian Green Woodpecker (Picus viridis), version 1.0. Birds of the World, Cornell Lab of Ornithology.","DOI":"10.2173\/bow.grnwoo3.01"},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A., and de Juana, E. (2020). Great Spotted Woodpecker (Dendrocopos major), version 1.0. Birds of the World, Cornell Lab of Ornithology.","DOI":"10.2173\/bow.frbwoo1.01"},{"key":"ref_29","unstructured":"del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A., and de Juana, E. (2020). Middle Spotted Woodpecker (Dendrocoptes medius), version 1.0. Birds of the World, Cornell Lab of Ornithology."},{"key":"ref_30","unstructured":"del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A., and de Juana, E. (2020). Lesser Spotted Woodpecker (Dryobates minor), version 1.0. Birds of the World, Cornell Lab of Ornithology."},{"key":"ref_31","unstructured":"del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A., and de Juana, E. (2020). Black Woodpecker (Dryocopus martius), version 1.0. Birds of the World, Cornell Lab of Ornithology."},{"key":"ref_32","unstructured":"International Committee on Veterinary Histological Nomenclature (ICVHN) (2017). Nomina Histologica Veterinaria, World Association of Veterinary Anatomists. [1st ed.]."},{"key":"ref_33","unstructured":"Burck, H.-C. (1975). Technika Histologiczna, Pa\u0144stwowy Zak\u0142ad Wydawnictw Lekarskich."},{"key":"ref_34","first-page":"289","article-title":"Demonstration of all connective tissue elements in a single section; pentachrome stains","volume":"60","author":"Movat","year":"1955","journal-title":"AMA Arch. Pathol."},{"key":"ref_35","unstructured":"Bacha, W.J., and Bacha, L.M. (2012). Color Atlas of Veterinary Histology, Wiley-Blackwell. [3rd ed.]."},{"key":"ref_36","first-page":"1001","article-title":"Tarsal plate: Protective structure peculiar to buzzard\u2019s (Buteo buteo) palpebra inferioris","volume":"16","author":"Onuk","year":"2010","journal-title":"Kafkas Univ. Vet. Fak. Derg."},{"key":"ref_37","first-page":"253","article-title":"Avian ophthalmology","volume":"17","author":"Almela","year":"2007","journal-title":"Eur. J. Companion Anim. Pract."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"592","DOI":"10.1007\/s11427-019-1664-1","article-title":"Biomechanism of resistance to retinal injury in woodpecker\u2019s eyes","volume":"63","author":"Lu","year":"2020","journal-title":"Sci. China Life Sci."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"83","DOI":"10.1038\/sj.eye.6702163","article-title":"Protective ocular mechanisms in woodpeckers","volume":"21","author":"Murphy","year":"2007","journal-title":"Eye"},{"key":"ref_40","first-page":"1270","article-title":"Conjunctiva-associated lymphoid tissue in the human eye","volume":"41","author":"Knop","year":"2000","journal-title":"Investig. Ophthalmol. Vis. Sci."},{"key":"ref_41","first-page":"566","article-title":"Lacrimal drainage-associated lymphoid tissue (LDALT): A part of the human mucosal immune system","volume":"42","author":"Knop","year":"2001","journal-title":"Investig. Ophthalmol. Vis. Sci."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"835","DOI":"10.1007\/978-1-4615-0717-8_118","article-title":"A functional unit for ocular surface immune defense formed by the lacrimal gland, conjunctiva and lacrimal drainage system","volume":"506","author":"Knop","year":"2002","journal-title":"Adv. Exp. Med. Biol."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"929","DOI":"10.1007\/s00347-003-0936-6","article-title":"Eye-associated lymphoid tissue (EALT) is continuously spread throughout the ocular surface from the lacrimal gland to the lacrimal drainage system","volume":"100","author":"Knop","year":"2003","journal-title":"Ophthalmologe"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"271","DOI":"10.1111\/j.1469-7580.2005.00394.x","article-title":"The role of eye-associated lymphoid tissue in corneal immune protection","volume":"206","author":"Knop","year":"2005","journal-title":"J. Anat."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"873","DOI":"10.1007\/978-1-4615-0717-8_123","article-title":"Organized mucosa-associated lymphoid tissue in human nasolacrimal ducts","volume":"506","author":"Paulsen","year":"2002","journal-title":"Adv. Exp. Med. Biol."},{"key":"ref_46","doi-asserted-by":"crossref","unstructured":"Siebelmann, S., Gehlsen, U., H\u00fcttmann, G., Koop, N., B\u00f6lke, T., Gebert, A., Stern, M.E., Niederkorn, J.Y., and Steven, P. (2013). Development, alteration and real-time dynamics of conjunctiva-associated lymphoid tissue. PLoS ONE, 8.","DOI":"10.1371\/journal.pone.0082355"},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"963","DOI":"10.1139\/z86-146","article-title":"Anatomy of the avian membrana nictitans","volume":"64","author":"Sivak","year":"1986","journal-title":"Can. J. Zool."},{"key":"ref_48","first-page":"159","article-title":"A comparative study of the nictitating membrane of birds and mammals","volume":"62","author":"Stibbe","year":"1928","journal-title":"J. Anat."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"11","DOI":"10.1111\/azo.12450","article-title":"Analysis of the kinetics of the eyelids of Little Owl Athene noctua","volume":"105","author":"Mahmoud","year":"2024","journal-title":"Acta Zool."}],"container-title":["Veterinary Sciences"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2306-7381\/13\/7\/702\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,7,20]],"date-time":"2026-07-20T10:08:12Z","timestamp":1784542092000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2306-7381\/13\/7\/702"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,7,17]]},"references-count":49,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2026,7]]}},"alternative-id":["vetsci13070702"],"URL":"https:\/\/doi.org\/10.3390\/vetsci13070702","relation":{},"ISSN":["2306-7381"],"issn-type":[{"value":"2306-7381","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,7,17]]}}}