Saturday, 25 February 2017

the weak hweet part two

In this post I described how a bird that ticked most of the plumage boxes for a siberian chiffchaff threw us a curve ball by making some rather untristis noises - and I finished by suggesting that it would be great to get some more recordings. It's far from being the first time that tristis looking birds have made unusual calls - there is plenty to read about it here and here, for example

Well, fortunately for me, an excellent opportunity came along.

There have been several chiffchaffs on my local patch this winter (perhaps 7 all together - a remarkable number of wintering birds for a scottish site) and a local ringer expressed an interest in doing a study to see how long they lingered on their wintering grounds and ultimately, whether any remained to hold territory. I knew that some of these birds looked like tristis and some of them sounded like tristis, so this presented me with an opportunity to have a look at some of these birds in the hand, record any noises they made, and ultimately to be able to link calls with plumage types.

After an excellent first session during which 5 different birds were caught, we were delighted to get an unringed bird in the nets almost immediately on our second session.

Plumage wise it was a bit of a puzzler, appearing quite dark and olive but with nice whitish underparts, dark bare parts, decent super and reduced impact eye-ring. I suspect that in better light it would have looked paler - this picture was taken pretty much at first light, and I reckon that a certain coldness can still be detected in the mantle - still, it's a confusingly green looking bird! While we admired it and puzzled over it's origins it began to call...

While it could basically be described as sounding like 'hweet', there are obvious differences between it and the standard collybita call. The differences can be seen on the sonogram in the prior post linked at the top of this one, but there are audible differences too. You can hear the call here:

To me this sounds subtly, but clearly higher pitched, thinner, and weaker. It's also damn near identical to the calls recorded on that first encounter - quite probably near enough to say that it's the same bird - and definitely near enough to say it's the same call type.

This call was the only one given while the bird was in the hand, and I was cautious that it might not be doing its 'normal' call under the duress of being handled. We had the initial (awful) recordings of course, but it was nice to get more confirmation that this was a call that was regularly being used. Below is a recording made in the field of a chiffchaff that despite being seen briefly, looked pretty good for a tristis. Unfortunately I didn't get to see whether it was ringed or not.

Below, some of the calls above can be seen in comparison with the in-hand calls and those from the initial encounter, and the field recording can be heard here:

Unfortunately on this occasion the bird did not shed any feathers. Luckily though it did on a later date so hopefully we will be able to get a genetic confirmation of what this bird is. Personally I have no idea but I guess I'd be a little surprised if it didn't come back from the lab as a tristis. Whatever it comes back as, it'll hopefully go some way towards answering the general confusion over what these variant calling birds are.

I'd welcome any feedback on this birds appearance or any other encounters with chiffs that call like this.

Monday, 20 February 2017

Refining your sonograms with Window size and type

Tucked away in the Audacity menu, hiding in the preferences tab, are two ways of refining the appearance of your sonograms. These involve changing the size of the window (it doesn't actually change the size of the window as it appears on the screen) or changing the window type. This changes the way in which the sonogram is generated and can therefore have some effect on its appearance. 

Changing the window size effects how much frequency detail is revealed. The general rule is the larger the number, the more frequency detail one gets at lower frequencies. The payoff is that there is less temporal resolution, but I find that this is less critical when viewing sonograms of birdcalls. How the window size effects the appearance of the sonogram can be illustrated nicely with this rather poor recording of a distant tawny owl (that has been ‘cleaned’ with a bit of noise reduction). To alter the size, open the 'Audacity' dropdown and select 'Preferences'. Select the 'Spectograms' tab, then, experiment with the window size options in the relevant dropdown.

The first sonogram shows a sonogram with a window size of 512, and the second with a window size of 2048 - see how the frequency detail is so much easier on the eye at 2048.

Changing the window type usually has a less radical effect on how your sonogram appears, but it can be worthwhile experimenting with different options if you have a sonogram that could look better. Again, choose the 'Prefefences' from the 'Audacity' menu, and experiment with the different window types in the 'Spectograms tab. Here, this firecrest call is displayed with the default window type, which is called ‘Rectangular’. 

Not very helpful! Changing it to the second option, called Bartlett, helps thins a little, but still, doesn’t really produce anything that you can really work with. 

Choosing the option called Gaussian(a=4.5) however, produces something much more useful. I don’t know of any hard and fast rules regarding how choosing different window types might improve your sonograms, so it’s always worth just experimenting with a few options in order to get the best results.

Friday, 17 February 2017

The weak 'hweet'

On 3rd January 2017, Ryan Irvine and I found a couple of chiffchaffs in Nigg Bay, Aberdeen. This has become a regular wintering site for chiffs over the last few years (possibly the only one in NE Scotland) and has hosted the odd Siberian chiffchaff too.

When we got the first few glimpses of the first bird, we assumed that we had stumbled into another 'tristis' bird, based on plumage features. Rather confusingly though, while we watched it, this bird called several times and consistently gave calls that to our ears sounded like a weak version of the standard collybita 'hweet'. At this point a proper Siberian chiffchaff call started up and we abandoned the original chiff to get views and recordings of the bona fide Sibe. The original bird is shown in the photos below.

It wasn't until a week later that I decided to listen back through all of the recordings I made while trying to record the Sibe. I was surprised and quite pleased to find that I'd accidentally managed to record the original bird calling twice. Running it through Audacity, it quickly became clear that what sounded to our ears like a weak version of a standard 'hweet' bore very little resemblance to the sonogram of the standard call. Both call types are compared in the sonogram below.

The two calls on the right are the bird in the photos above - totally different to a collybita 'hweet', and reassuringly similar to one another. I can't find any similar looking calls in Xeno-Canto (although I can't say I've checked all of the chiffchaff calls as there are hundreds...) and there's nothing similar looking (or transcribed) on Alan Deans website, so I'm none the wiser as to where this bird and its unusual call might be from. One possible explanation is that this is not the whole call - sometimes birds give truncated versions of their usual call (I've heard yellow-browed warblers do this, for example) - and perhaps we're hearing the first part of a 'sweeoo'. It was a dull day, and when I've heard YBW truncating their calls it's generally been cold, dull or early.

It's worth noting that the photos over emphasize the coldness and paleness of the bird very slightly - in the field, there was a touch more olive/green in the mantle, too much yellow in the underparts, and even signs of streaking on the chest. Many people have suggested that it could still be tristis - with the calls being within known variations for this taxa. Particularly, it has been suggested that the calls of this bird look very similar to a variation in the Sound Approaches brilliant 'Catching the Bug'. 

While the shapes of this birds calls look very similar to those on page 164 of CtB, there are a few differences that are worth noting. The horrendous sonogram below compares the CtB variants with the bird above, and shows that these variant tristis calls cover a much wider frequency range, and are stronger at the top end of the frequency range rather than the bottom.

However, I guess if Siberian chiffchaffs can make one variant call then they're capable of making a few, and could easily do something similar to the calls above. The thing that could dissuade me from considering this to be a variant call was that we heard this bird doing this call upwards of ten times, and each call sounded like this (rather than throwing in variations here and there among more normal calls). In other visits to the site this winter I've only ever heard tristis calls (although the birds are largely silent, infuriatingly!) rather than a mixture of 'peeping' and 'hweeting' birds.

Whatever it is it's an interesting one, and I'd love to get a few more recordings of it!

Saturday, 11 February 2017

Comparison of some chiffchaff calls

Chiffchaffs. Where do you start?

Well, very often, you start with the call, as it's frequently the first hint you get that there is a chiffchaff nearby.

We're used to chiffchaffs saying 'huit' in the UK, and when we're lucky, we get to hear Siberian chiffchaffs making their 'peep' calls (other phonetic renderings are available - such as 'eehp'). To complicate things, we sometimes encounter chiffchaffs that say what can loosely be described as 'sweeoo', and it's a bit of a mystery where these birds or their calls are coming from. For a while, they were ascribed to the various subspecies, with collybita saying 'huit' and the now near-mythical abietinus responsible for 'sweeoo'. We now understand this not to be the case, so there are two positions to start from.

a) these birds are from a distinct population.

b) these birds are the offspring of late breeders, so we hear juvenile, or less crystalised calls at a time when we're not expecting it.

I don't know what the answer is - but what makes the whole thing more interesting is that the 'sweeoo' calls are highly variable, and that the birds that make them seem to be 'irruptive'. I don't necessarily want that to mean the same as it would mean with, for example, waxwings - it's just a way of describing that they can be very numerous in some years, and very uncommon indeed in others. 2016 was definitely a 'sweeoo' year.

Before we get too deep into the nitty gritty of sweeoos, huits, and peeps, lets just have a look at the structures of the different calls. Lining the recordings up on top of one another allows a rough comparison, but putting the calls side by side (and zooming in a bit more, as this will allow) gives a much better opportunity to look at the differences between all of the calls.

The composite is easy to make. I opened a new track in Audacity (tracks menu -> add new -> mono track), and then simply copied (highlight relevent section -> edit menu -> copy) and pasted (click in new track -> edit menu -> paste) into the new track. These ones have had some of the time between calls cut out (scissors tool) so they all fit nicely onto the same page. The real beauty of this is that it lines everything up at the same time/frequency ratio, which allows you to make a valid comparison of frequencies and shapes of motifs. The rapidly upward rising 'huit' is obviously different from the flat topped call of the tristis type bird. The two 'sweeoo' calls are different too. The presumed collybita juv has two parts to the call, the upward inflection at the beginning followed by the downsweep. The winter 2016 birds sounded very different, with some calls showing a clear third component to the call, ending on a smaller, shorter upsweep. This could be heard in the field on occasion, with some calls sounding clearly tri-syllabic.

Lining them up together also allows a comparison of the frequencies the birds call at, such as the sonogram below.

Here it's clear to see how the tristis type call utilises a much narrower range of frequencies than all of the others - which explains why the call is uncomplicated, and sounds flat. I always took this familiar tristis description to mean flat as in the musical sense - but now when I hear it, I 'hear' a flat motif on a sonogram - or at least a 'flattened' one. 

It's also clear that the 2016 'sweeoo' birds reach some really high frequencies. They sound high in the field, but here it can be seen that they reach over 5.5 khz, over 1 khz higher than their 'huit' calling cousins. 

None of this helps with the conundrum of where the variable 'sweeoo' calls come from of course. But the more we recognise them in the field, or even get good, useable recordings of them, the better equipped we will be to come up with a reasonable answer.