Audio recordings
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The recordings on this guide were made over a fifteen year period from different locations primarily in eastern North America. Unless otherwise indicated, all audio recordings on each species' home page were made during the day from birds that were visually identified. Each recording (or spectrogram) includes the date and the state or province where the recording was made. The initials (if recorded by one of the authors) or name of the recordist are included in parentheses, and a short behavioral description is included. We tried to include the best audio examples possible for inclusion in this guide, but flight calls are challenging to record for many species. In some cases, after considerable effort, we felt lucky to have any recording at all for certain species. The point here is that some of the recordings on this guide have distracting background noise and are not as clear as one might be accustomed to on typical audio guides. In addition, the nocturnal flight call recordings typically have a hissier background sound than the diurnal recordings because of the greater amplification used in making the recordings. Overall we feel the quality of the recordings on this guide is sufficient to serve their educational purpose.
Nocturnal flight calls: For many species, we believe we have identified nocturnal flight calls and, if so, we typically present a link from the species' home page to a nocturnal flight call page. Identifying nocturnal flight calls is a challenging endeavor because the birds cannot be seen to verify species identity. Our identifications are based primarily on comparison with diurnal flight call recordings of visually identified birds. These identifications are supported by comparison between the date and location where the night flight call was recorded and known migration timing and routes of passage for each species. In addition to circumstantial evidence, confidence is added by gaining knowledge on the flight calls of other species. One truly does not know the nocturnal flight call of any species until one knows the flight calls of all other possible contenders. Identification of one species aids in the identification of others, much as a jigsaw puzzle gets easier as one progresses. So, our nocturnal flight call identity evidence is buoyed by the fact that we tackle the whole and provide evidence for all species - the process of elimination. That said, our confidence level in the identification of these nocturnal flight calls varies from one species to another. In cases where our confidence level is high, we present examples of these calls along with the modifier "presumed". In cases where our confidence level is somewhat lower, we present them as "hypothetical". For many species we have not presented any nocturnal flight calls. In some of these cases, we simply have not documented their call at night (or whether they even give any flight call at all). In other cases, we have identified their call type down to a group of species (such as some of the zeep warblers) but have not been able to distinguish one from another with a high level of confidence. With more study, we expect continued progress in distinguishing species by their nocturnal flight calls.
Audio recording equipment: Most recordings in this guide were made using Sennheiser shotgun microphones, either the 816T, MKH70, ME88, or ME66. Sound was recorded on a Sony TCD-D10 digital audio recorder or Marantz PMD430, PMD221, or PMD222 audio cassette recorders. Some nocturnal flight call recordings were made using a homemade flowerpot microphone (see www.oldbird.org) and various commercial hi-fi video cassette recorders. Though we have used a variety of equipment with potentially variable acoustic rendering, the inclusion of audio recordings on this guide was based on how the recordings sounded. All recordings on this guide sound true to our field experience with the species when played back through good speakers or headphones.
Audio manipulation: Many audio recordings were filtered to remove low or high frequencies in order to help make the flight call stand out more clearly from distracting background noise. Also, some recordings had distracting noisy sections edited out. This may have slightly altered the natural cadence of a calling sequence in some cases, but these edits have not resulted in any calling cadence that sounds unnatural to our ears.
Audio specifications: All audio recordings with flight call frequencies under 10 kHz were digitized at a 22050 sampling rate. Recordings with frequencies above 10 kHz were digitized at 44100 kHz sampling rate. All recordings were digitized with a 16-bit soundcard. Most recordings in the guide are monaural (single track); however, a few stereo cuts are indicated.
Audio playback: This guide is intended to be used on personal computers, and many computer systems have relatively poor-quality speakers. The quality of the recordings will be affected by the quality of the playback system. If one has poor-quality speakers on his or her computer, a solution is to buy a set of headphones. Cheap headphones will reproduce sound much better than cheap computer speakers, and high-quality headphones will reproduce sound the best. Another option would be to invest in better quality computer speakers or even to hook up your home stereo system to your computer.
Audio Recordists: The majority of the recordings on this guide were made by the authors. Additional recordings were donated or made available by the following recordists and institutions. All rights, including copyright, to these recordings are reserved for the authors or institutions who made them available. Contact information for the institutional sound archives is listed below. For copyright info for one of the additional recordists cuts, contact admin@oldbird.org.
Recordists A. Lang Elliott Michael Green Stephanie Jones Daniel F. Lane Ted Mack John O'Brien Christopher L. Wood
Institutional natural sound archives Borror Laboratory of Bioacoustics Department of Evolution, Ecology, and Organismal Biology Ohio State University, Columbus, Ohio. http://blb.biosci.ohio-state.edu/
Macaulay Library of Natural Sounds Cornell Laboratory of Ornithology 159 Sapsucker Woods Road Ithaca, New York. 14850 |