11 July 2010

The full text

Now that Birding World have published a rather space restricted version of the Lundy Shearwater gubbins, and Birdwatch are unlikely to print any of the more technical bits, here is my full text of the sound recording and analysis of the Barolo (who knew it lacked a patronymic apostrophe?) Shearwater,...

Robb et al., (2008) and Sangster, G. & Robb, M.S. (in prep.) describe differences in the vocalizations between the three forms of north Atlantic ‘little’ shearwaters and between the sexes within each taxa. Aerial call data and methodological information, kindly supplied by Magnus Robb, have enabled a preliminary comparison of the Lundy bird’s vocalizations with those of baroli, boydi and lherminieri.

Vocalizations of the Lundy bird were recorded on the night of 8th-9th June 2010. Recordings were made with a Telinga StereoDAT mic and Sound Devices 702 recorder (bit depth 24, sampling rate 48 kHz). Sonagrams were produced using Raven Pro version 1.3 Build 32 with settings: window type Hann, window size 512 samples (3dB filter bandwidth 135Hz); time grid 50% overlap, hop size 256 samples; frequency grid DFT size 512 samples, grid spacing 93.8 Hz; brightness varied as required and contrast 50.
The table below shows measurements taken from the sonograms, sample sizes differ as each measurement could not be taken from every sonogram.

Conclusions regarding the identification of the bird to a particular form, in comparison to Sangster, G. & Robb, M.S. (in prep.), should be made in the light of the fact that the Lundy recordings included both aerial and terrestrial calls. That said, measurements of the duration of the longest exhaled note and the proportion of the exhaled section of the call made up of the longest exhaled note, both fell outside the range of data available for boydi and all but outside the range for lherminieri. In addition, the measures of duration of exhaled notes, the duration of a phrase and the maximum pitch of the fundamental frequency of the inhaled note all broadly point towards baroli.

Differences between the sexes in baroli include males having: exhaled notes containing clearer harmonics; higher pitched inhaled notes; and the entire phrase being longer but including fewer exhaled notes. The Lundy recordings strongly support the sexing of this individual as a male, in particular, the clear harmonics in the exhaled notes.

A recording of this bird can be heard here.

Robb, M. & The Sound Approach (2008). Petrels night and day: a Sound Approach guide. The Sound Approach, Poole, UK.
Sangster, G. & Robb, M.S. (in prep.). Vocalizations and species-limits in the north Atlantic clade of small shearwaters (Procellariiformes: Puffinus).

Thanks to Magnus Robb for information provided and valuable comment.

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