Collections of animal sound recordings serve many uses in education, entertainment, science and nature conservation. The first animal sound recording dates from as early as 1889, although systematic collecting did not begin until the 1950s. The largest collections between them now hold around 0.5 million recordings with their associated data. They preserve the sounds of all kinds or animals with multiple examples of their seasonal, geographical and individual variations. For example, the British Library National Sound Archive (NSA) has 140,000 recordings of more than 10,000 species of birds, mammals, insects and amphibians, donated by numerous individual scientists and amateur recordists worldwide. Preserving such large collections for the long term is a primary concern in the digital age. While digitisation and digital preservation have many advantages over analogue methods, the rate of technology change and lack of standardisation is a serious problem for the world's major audio archives. Techniques to reduce the risk of obsolescence include technology preservation, migration or emulation. Another challenge is to make collections more easily and widely accessible via electronic networks. On-line catalogues are already available for some collections (NSA collection: www.cadensa.bl.uk ; Borror collection: blb.biosci.ohio-state.edu/). Providing internet access to the actual audio is the next goal although because currently the data rate of most internet connections is slow compared to CD quality audio rates of 706 kbps, on-line recordings are short, low-quality clips of the archival versions.