Tuesday, 19 October 2010

Scottish and Parrot Crossbill Catch and Variant Calls, Tuesday 12th October

After all the wet and windy weather in September (frustratingly coinciding with my days off) finally some moderate sucess ! With light winds and an overnight frost, ringing conditions were favourable and at 12.30pm this cracking female was caught at one of my drinking pools in upper Deeside:

This bird, an adult female had nearly finished its primary wing moult up to P9, though interestingly no secondaries had started moulting yet, and was aged as a 4F ( female hatched before current calendar year). I am beginning to think that some Parrot and Scottish Crossbills don't moult all (or possibly in rare occasions any?) of their secondaries depending on when they finish breeding ? The only other possibility is that it could have been a second year bird that has had an extensive post-juvenile moult where it has replaced it's primaries, but not the secondaries. However, the lack of any old (juvenile) greater coverts, adult type alula and and adult primary coverts discounted this possibility.The minimum bill depth was bang on for Parrot type. It was also 'big-headed' in the hand and was over 50g in weight (typical for Parrot Crossbill). However, though this bird gave a classic Parrot flight call on release (Fc2) it's excitement call (which it gave when it landed) sounded more like Scottish Crossbill ! Indeed, on the sonagram the excitement call (or toop) was somewhere between Parrot and Scottish Crossbill.

So, should we all be concerned by this anomaly and earnestly start burning our copies of "Sound Approach" and "Summers et al (2002)" ? Well no, hold off on the matches and lighter fuel, at least until I offer this explanation. To start with, a fact - Crossbills are social finches, and social finches, have been known to 'learn' calls (see Mundinger). Variant calls, or more specifically a call that appears to contain features of two crossbill types, do not necessarily infer that the individual giving it is of that mixed parental lineage eg. a hybrid. I think it is way too simplistic or convenient to say that because a call appears "half Parrot and half Scottish" on a sonagram that this explains the provance of the bird. The 'white-coats' (crossbill speciation sceptics who constantly cite the lack of gentic divergence between the forms ) as well as cynical crossbill call sceptics will love this bird that I caught - it gave two calls, or a mixture of two, so which call gets precedence, Scottish or Parrot ? How can I call it Parrot when it gave a Scottish type call ? Well, as I said the excitement call had features of both Parrot and Scottish - to me it sounded Scottish-ish, especially the short duration harmonics, but the fundamental note (the lowest note) could easily be interpreted as Parrot in shape. The flight call was a stone-waller Parrot - a big resounding "Ch-oop". If we are going to discuss which calls are more useful diagnostically, flight calls or excitement calls, then I would say flight calls, for two reasons, though this hasn't always been my position:

1) In my studies of the new "Scottish" type calls that appears to have emerged since the last big studies in the 1990's, but picked up by me when I started recording in 2004, I have noticed that the coresponding excitement calls (Ec's) are quite variable - some look like normal Scottish EcC (excitement call C) with typically only one harmonic and the main note either being inflected or not, whilst others give a cross between EcA and EcD, both Common and Parrot type calls respectively. Biometrics collected through catching and ringing individuals have proven the intermediate bill depths of this 'new' call type are consistent with Scottish Crossbill. More on this exciting stuff soon !

2) In the USA, flight calls are apparently considered more diagnostic than excitement calls. In a recent exchange of emails with Matt Young at Cornell late last year, Matt re-iterated this situation to me and asked me what "we" used in preference diagnostically on this side of the pond. "Excitement Calls" was my answer, though this answer was mostly 'conditioned' by the European crossbill literature, and in particular the work previously conducted in Scotland. I then thought about the situation with these new Scottish calls where I was struggling to reconcile matching Fcs to Ec's (in known individuals) and viola, the excitement calls are variable, but the flight calls are (relatively) consistent !

The reason that excitement calls appear to be variable may well be down to the context that they are given - these calls are given in various states of aggrevation and threat, from other crossbills, competitors (such as Siskins) or potential predators, as well as at the nest for various reasons. Excitement calls can also sound quite similar between the species - compare EcA (common) with EcD (parrot) and also EcC (scottish) with EcE (common), they are very similar and are easily confusable by ear. I don't think we fully understand the mechanisms of this yet, which may well affect our interpretation. However, an excitement call, or toop, functions universally amongst crossbills to say " I am not chuffed", "watch out" or "get off" and may vary accordingly, but will presumably be understood across 'species'. The flight calls, on the other hand, are given as contact calls within a flock and would presumably need to be recognizabe to other members of that flock to communicate where to feed and when to leave to feed (or drink) and also for lone birds to locate where flock members are feeding or are safe (eg. on release after being trapped !). These too may be contextual, which may explain subtle variation, for example harmonics are produced with increased amplitude eg. when the bird is in an an excited state and these harmonics can effect the appearance of the call on a sonagram, and may even result in a wrong diagnosis. This said, it does seem that flight calls are perhaps more consistent based on retrap crossbills and ones in situ that have been repeat sound recorded.

So, the bird above I can happily call a Parrot rather than Scottish on:

a) Size, bill depth and bill structure. The Scottish types are over a milimetre less in bill depth, which is overall usually more rectangular, and are up to around 10 grams lighter.

b) Flight call. The Scottish type birds, particularly the "new" ones, give a completely different call. This one gave a Parrot call.

The next bird caught was a re-trap male colour-ringed Parrot Crossbill (initially ringed in 2006, but retrapped by me in 2009):

Thankfully, my bios matched (though 0.1mm bigger in bill depth this time - pine resin ? !) and even more thankfully it gave the same flight call it gave in 2006, 2009 and now 2010 !  Although it is frustrating not to get some new rings on a caught bird, these retraps do give extremely important call and moult data can be compared to with previous years, for example I can compare the stage of moult of this bird with exactly a year previously.

The last two birds were caught at 4.15 pm just as was about to take the net down (having already taken down one net due to an increasing breeze). One was an unringed Scottish female and the other a retrap colour-ringed Scottish male (caught by me in October 2009).

I metal ringed and colour-ringed the female first:

This is a 'classic' Scottish bill profile, intermediate in bill depth and rectangular in shape. Doesn't it look more like a common Crossbill than a Parrot ? ! This female, an adult, was more than half way through her post breeding primary moult but with the secondaries all old. Most exciting for me is that the flight call it gave was one of the 'new' types, different from the published ones. So, a very valuable bird.

An example of the "new" Scottish flight call from a trapped and released colour-ringed bird in 2009:

Unlike the flight calls previously described for Scottish Crossbill these flight calls have a trailing component that is as strong, or stronger, than the intial one ( the opposite of previous Scottish). They also sound very different, more like a "ti-reep", the second syllable being more pronounced. I have recorded these in Deeside since 2004 and elsewhere since. A more detailed preview and summary on these new calls will follow on here soon and I hope to publish the results - I now have my own biometrics and as far as I know this is the only complete data set that has calls to match bios for this 'type' as well as breeding and feeding data.

The male had a slightly smaller bill depth than the female, but still Scottish in characteristic:

Don't worry I wasn't catching crossbills in the dark - it was only 16:30 but the sun, though still high, had gone behind the tall mountains and I had to shoot on flash to get any contrast or colour detail ! This bird didn't call on release ( some don't) but in 2009 it gave the 'new' Scottish type flight call.

New articles and preview of publications coming up soon including Parrot Crossbills feeding on Larch, New Scottish Calls (!!) and field identification of Parrot and Scottish Crossbill for birders........keep tuned and tell your friends.

© Lindsay Cargill 2010

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