16 April 2011

All quiet

Almost a complete lack of passage at Uskmouth today, just a few Grasshopper Warblers, one Lesser Whitethroat, one Wheatear and 15 Sand Martins overhead. The winter appears to have decimated (actually, worse than decimated) the Cetti's population, we appear to be down to 20-25% of recent peak numbers, just six recorded today.

A brief example of the levels of disturbance caused by the adjacent Uskmouth Power Station along the western boundary of this National Nature Reserve.

Cetti's Warbler and vehicle noise by darrylspittle

Of course, the Cetti's Warbler song and the noise from the vehicle occupy different frequency bands. Nothing of the Cetti's Warbler song dips below 1886 Hz and nothing of the vehicle noise reaches above 1448 Hz; if Cetti's Warblers have an effective built in high pass filter they may not give a toss, somehow though, I doubt this is the case. Just to prove the lack of overlap in 'acoustic space', the soundfile is split into three sections: 1. 'as heard', recording with no filtering beyond normalization to -1.0 dB; 2. 'Cetti's Warbler song', recording after application of a high pass filter with a cutoff frequency of 1800 Hz and a rolloff of 36 dB per octave; and 3. 'vehicle noise', recording after application of a low pass filter with a cutoff frequency of 1450 Hz and a rolloff of 36 dB per octave.

PS. Details of the machine making all the racket can be found here. Nice isn't it.
PPS. Hopefully, more on the warbler report tomorrow,... watch this cyberspace.

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