Thursday, 25 December 2008

The Danger Of Sonograms ?

Cracking day up here in NE Scotland today. Prime site visit today so hopes were high.

Arrived at around 11.30am a bit later than hoped but just as the remaining fog had been burned off by the sun. The woods (native pine) were pretty quiet save for a few coalies and the odd Siskin and a parties of Redpoll sp. over.

I picked up (by ear) a small group of crossbills flying down the valley from me, distance around 200 to 250m hence faint sonograms:



These reminded me of sonograms of a suspected Parrot at Potarch posted on Bird Forum (arggh) last year, or earlier this year, I forget which. Are these Parrot Fc2's and if so why ? Discuss. Come, on the blog is getting more interactive and lets get it onto Crossbills ! The black 'noise' BTW is not because my DAT mic has packed in but is in fact white noise from a stream that was behind where the birds were flying. Like all parabolas this high frequency stuff is really pronounced.

Here is another one from the same recording at around 17 secs:

Same birds ? Different type ? Tune in later for my synopsis and thoughts, which might just hopefully make you all stop trusting sonograms at face value. It's all in the evidence I supplied above.

And that was it for the day. I got excited later when I saw pine seeds floating down from a Scots Pine ( ladden with perfect cones for crossbills BTW) but no falling cones made me suspcious - these should be affling every 1 to 2 minutes per bird. And there he was, a Red Squirrel munching away of Pinus sylvestris.

4 comments:

Stephen Menzie said...

Fc1?

Paul said...

Given the title of your post, I guess they are not the Fc2s that they may superficially look like. So perhaps they are Fc1s as Stephen suggests. If you can bring yourself to look at my 'Crossbills on Deeside' thread on your favourite website, there are some similar confusing Fc2/Fc1 calls in post#39.

As it was me that posted the potential parrot calls at Potarch that you refer to, I would say that I am still not certain what they were. It was clearly possible that there may have been some sonogram structure missing, but the frequency was low and using your advice of listening to the calls rather than looking at sonograms I compared the recording with known recordings that I could find and I did think they sounded more like the parrot Fc2 than any published Fc1s.

I guess the main problem I have with sonograms is that it is still not clear what the relative importance is of fine structural detail vs. frequency and coarse structure.

Merry Christmas!

Loxia Fan said...

Hi Paul,

I actually still have your 'parroty' call on file. On listening to the ones I recorded yesterday with your one from earlier in the year, to my ears they sound the same - certainly last night they did !

Several things come out of this I think. As I put up the parabola and monitored the birds as I was recording them I thought they were Common types - the calls sounded chippy rather than choopy. However, an in spate river in the background does not help as well as the fact that they are over 200 m away and were not seen (despite trying).

Are the calls in the first sonogram the same birds as those in the second ( they were all from the same recording and were in the same party)? Well, I don't know ! However, on listening to the calls in sonogram one and two, again they sound the same. They do not look the same on the sonogram, however !

Then there is the doppler effect. This effects the frequency (or pitch) of the call on the sonogram - the further away the bird the lower the relative frequency, or pitch, of the call. This may have been the case with your call Paul as it was quite distant as I recall ? It thus looked within the frequency for Parrot Crossbill. I have also seen this with caught crossbills on their release - the call they give fluctuates in pitch slightly as it flies away. Now, in my sonogram the 'lower' Fc2 type ones are quite dark so higher in amplitude -however I have enhanced the contrast to highlight the call! The ones in sonogram two are higher pitched though are fainter in amplitude, so that does not seem to make sense.

My cautious assessment of these is that they are common types, most likely Fc1 types as Stephen suggests ( well done lad !). This is primarily on aural assessment of call timbre and the fact that the calls in the second sonogram sound the same as those in the first. However, bear in mind that distant calls are a minefield even with a Telinga if the ambient conditions are not favourable. There are limitations and in some cases the bird will have to go unidentified.

I should add as a short footnote that I was sent some calls from some Dutch Parrot crossbills from last year and these, whilst clearly being Fc2 type, were quite high pitched ! I had recorded one identical to this in Upper Deeside the previous year.

Next question: what are all these Common Crossbills doing in a native pinewood ?

Merry Christmas !

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