Multimodal imaging and molecular analysis of a 350-year-old purple heron mummy

The discovery of glacially preserved remains offers a rare and invaluable opportunity to explore long-term tissue preservation, diagenetic alterations, and microbial colonisation. In this study, we examined a 350-year-old glacier mummy of a purple heron (Ardea purpurea) recovered from the Austrian Alps, specifically from the Gurgler Ferner glacier in Tyrol, Austria, at an altitude of 3.004 m in the area of the Hochwildehaus towards Hochwilde and the Annakegele, marking the first documented instance of an avian glacier mummy in this region. A comprehensive multimodal analytical approach was employed, integrating micro-computed tomography (micro-CT), histology with conventional and specialised stains, fluorescence microscopy, Raman spectroscopy, attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, and molecular analysis of bacterial and fungal DNA. Micro-CT and histological analyses revealed exceptional preservation of cortical and trabecular bone, intact osteocyte lacunae, and structurally well-preserved epiphyseal growth plates. Additionally, remnants of soft tissues, including muscle, skin, feather quills, and lung tissue, were identified. Raman and ATR-FTIR spectroscopy supported preservation of the bone mineral phase, characterised by carbonate apatite signatures, while indicating a reduced relative detectable organic contribution in the glacier mummy bone. Fluorescence microscopy further identified post-mortem colonisation by environmental fungi (Orbilia, Davidiella, Itersonilia) and bacteria (Sphingomonas, Paenibacillus, Alkalibacillus). These findings underscore the extraordinary preservation conditions provided by glacial environments and highlight the value of integrative, multimodal methodologies for studying ancient remains. This study not only expands our understanding of avian tissue preservation under frozen conditions but also provides critical insights into the interplay between biological and environmental factors in long-term preservation.