Bioacoustics collections contain recordings of sounds produced by animals. The technology that made possible the capture of ephemeral sound events appeared more than 100 years ago (Koch 1955). However, for biologists who sought to record animal sounds in the field, technological innovations in truly portable sound equipment and reliable media emerged only after World War II. Nevertheless, before the introduction of the portable magnetic tape recorder, pioneers at Cornell University experimented with recording sound on motion picture film (Brand 1935). A recording field-trip required a truckload of equipment, and it took weeks to get the film developed. But there were successes with this cumbersome technology, including the only known recording of the Ivory-billed Woodpecker (Campephilus principalis), made in 1935 by the Cornell expedition to Louisiana (Kellogg 1962). Biologists who rediscovered the Ivory-billed Woodpecker in Arkansas in 2004 were trained to listen for the bird with this recording, and it is crucial to researchers in the Bioacoustics Research Program at Cornell in evaluating more than 17,000 hours of automated recordings made to detect calling individuals since December 2004.

A specimen in a bioacoustics collection is a recording of one target animal or group of animals and the associated metadata. The sounds produced by the animal(s) are usually recorded in one session for a variable length of time (seconds, more often minutes, or even days, as technological advances improved storage capacity). Specimens are obtained on master field recordings that may contain multiple specimens and multiple species from multiple locations. A “label” for an acoustic specimen, separating it from other specimens on a master tape (or other media), is the narration by the recordist (Kroodsma et al. 1996). In the era of reel-to-reel tape, specimens were cut out of the master tape. Thus, specimens in bioacoustics collections are termed “recordings” or “cuts.” More recently, especially with the advent of analog cassettes, cuts were duplicated from the master field recordings, preserving the integrity of the master field tape.

A white leader tape was added to each specimen obtained from the master field tape. This leader served as a visible label onto which was written information about species, location, and date. The specimen was then spliced onto a tape reel containing cuts from the same species. This species reel organization simplified retrieval of specimens and until very recently was the way all major sound collections maintained their sound specimens. The three major collections, listed in alphabetical order, are (1) Borror Laboratory of Bioacoustics (BLB), The Ohio State University (blb.biosci.ohio-state.edu); (2) Macaulay Library (ML), Laboratory of Ornithology, Cornell University (birds.cornell.edu/lns); and (3) National Sound Archive (NSA), Wildlife Division, The British Library ( www.bl.uk/nsa). Other important collections include (and see Kettle 1989): Bioacoustics Laboratory and Archive (BLA), Florida State Museum; Center for Sound Communication, Odense University, Denmark; Sound Library, The Australian National Wildlife Collection; and Library of Wildlife Sounds, Museum of Vertebrate Zoology, University of California.

Analog magnetic tape, depending on the formulation, has a life expectancy of 10–40 years and degrades with each use through magnetic particle loss. Thus, analog tape collections started in the late 1940s were recently faced with loss if not duplicated. Duplication to new analog tape stock has the same limitations, is labor-intensive, and is becoming costly as digital media erodes the market for analog media. Digital duplication to files on a computer hard drive or transfer to other digital storage media such as optical disk is also labor-intensive. However, digital storage possesses many advantages—including lack of degradation, rapid streaming to new media, and random access—that make it a superior archival solution.

Digital technology has initiated a new era in animal sound recording, rivaling in importance the introduction of magnetic tape recording and affecting everything from how sound is obtained to how it is stored, documented, and examined. Though digital sound recording has been available for more than two decades, the archive community moved cautiously until standards for digitizing were established.

Critical to the accurate digitizing of animal sounds was the availability of computer hardware capable of sample rate and amplitude resolution (bits) sufficient to accommodate the full spectral and dynamic ranges of most animal sounds. Archives also require reliable, affordable media that maintain integrity over time. Optical disk media that tested to archival requirements did not become available until the mid-1990s (technical reports addressing these and other issues can be found in Grotke [2004] and on the BLB website [see Acknowledgments]). Storage on optical disk reduces housing space and storage requirements, and life expectancy is on the order of 100+ years (judging from accelerated aging tests). Redundant backups are made (a working and an archival disk, at minimum), and the original analog tapes are compactly stored under optimal conditions offsite. The current digital revolution in sound archives should bring about (1) creation of a digital archive, (2) development of internet accessibility, and (3) improvement in acoustic analysis tools for research and conservation efforts.

In creating a digital archive, we must preserve the historical analog collection, strive to streamline the addition of new specimens, and improve access to specimens. In a digital archive, specimens are digitized from the analog species reels and new material from master field recordings of various analog or digital formats on various media. The time-consuming editing process cannot be avoided, but digital data stored to computer files are easily accessed for editing; unwanted segments are deleted and specimens are copied into their own files. The digital files are then written to optical media (CD-R at the BLB and NSL, DVD-R at the ML) in the order processed rather than parsing them to species reels, thus reducing labor.

A protocol of error-testing each optical disk when it is written and sampling the collection across its life must be established to measure media integrity. Because access on optical disk is random rather than sequential, specimen retrieval, once the optical disk is located, is far more rapid than with tape media. Processing of loan requests is thus simplified, but necessitates a system to track a specimen's location. Thus, a database—to which an optical disk number and other data are automatically added to each specimen's record and from which data retrieval is simple—is critical to the functioning of a digital archive (Nelson and Gaunt 1997, Nelson et al. 2001). A byproduct of this systematic transfer of all specimens from analog to digital format has been verification that all specimens exist, that they are playable, and that the metadata are correct and complete in the database.

The ability to make recordings accessible over the internet is a major benefit to storing sound recordings digitally. The first step—giving users access to the full catalogue data via searchable databases—has been or soon will be accomplished for the major collections.

The second phase of internet accessibility is online access to the sound specimens themselves. The BLB site currently has sample sounds wherever a sound spectrogram is displayed (click on the spectrogram), and all recordings of sparrows, tanagers, and New World warblers are available for audition (the full collection will follow shortly). Streaming sound capability allows users to place orders for auditioned recordings that meet their needs. Distribution of specimens through our websites for offline use is also available.

In the past, users had to depend on our staff to make these decisions. With auditioning and downloading of files available, whole new projects and user bases can be accommodated. Users come with diverse goals, from researchers wanting sounds for descriptive, mechanistic (learning, sound production and transmission), comparative, and evolutionary approaches, to educators looking for samples for lectures, demonstrations, and student projects. Increasingly, we supply material for exhibits by museums and government agencies. We continue to service the general public, as well as commercial producers of films and documentaries, CDs of animal sounds, devices to attract or repel animals, and so on. Easy access to the sounds will facilitate research, conservation, and educational efforts.

This era of major changes to our archives, supported by funding from the National Science Foundation and the Office of Naval Research (to ML), is clearly enhancing our ability to process accessions and access existing specimens. Sounds are but one component of animal behavior. The ML has developed a sister collection to the sound collection that includes video images of animal behavior (Dantzker 2004).

Too often, animal sound recording efforts, especially those from published research, fail to be deposited in public archives. The professional researcher should know that these recordings are as important as traditional specimens and treat them accordingly (Kroodsma et al. 1996). An archive's internet site may, in the future, facilitate the transfer of specimens from recordists to archives by allowing contributors to enter data for their sounds online, to be used as a database for their collection and to be transferred to the archive database as specimens are deposited, possibly also over the internet. Other benefits to research should follow. For example, ML and Totally Hip Technologies have developed a QUICKTIME browser component that will allow any internet client to preview waveforms and spectrograms of any digital sound called up by a search. They have also developed annotation software that will allow demarcation and retrieval of specific segments within archive recordings.

Public sound archives will continue to serve the public by producing synoptic series on animal sounds, an area in which the ML has excelled, as has the BLA with its ARA record series. These are invaluable as aids in training students, ecotourists, native people, and others in identification of animals by voice, especially in areas where visual contact is limited or impossible, as in conservation and biodiversity identification efforts in the tropics (Gaunt and McCallum 2004).