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

Friday 8 October 2010

Parrot Crossbill Predation

Eurasian Pygmy Owl and Parrot Crossbill (from http://niaolei.org.cn/posts/10555)

I thought that photo might get your attention ! No not from my Deeside site but rather somwhere colder and much further East ! Apologies to the anonymous photographer (as no name was attached to it) but I have linked to the original website.

Crossbills are strange birds; they are very wary when coming down to the ground to drink, get grit or bones (for calcium) yet when they are feeding in trees you can stand only a few feet from them and they are oblivious to your presence (helpful for reading rings !).

Even with my 1000's of hours field time I have never witnessed Crossbill predation per se eg. an actual kill, though I have observed unsucessful attempts by Sparrowhawks on several occasions, and Merlins (twice), both aimed at Parrot Crossbill flocks. Clearly Pygmy Owls have some adaptation for catching Parrot Crossbills ! Predation by avian predators it would seem is a rare occurence.

In Scotland there are several species that can predate Crossbill nests (eggs and nestling predation): Red Squirrel (Greys don't tend to occur in Pine Crossbill habitats), Corvids, Pine Marten, Great Spotted Woodpecker (and Green Woodpecker at one of my sites) and Sparrowhawk ( I have witnessed the latter though the chicks successfully 'exploded' and evaded predation). However, this said, the severity of the weather, particularly wet, snow and wind combined with the availability of cones (and how 'open' the cones are) will have far more impact on productivity than all the predators combined.

Friday 1 October 2010

"Last Catch", 30th August 2010

This is my last catch of crossbills, from August 30th in upper Deeside. I caught two Common Crossbills (and a Meadow Pipit !), that were lured in to the vicinity of the drinking pool with a taped call - they were trapped in an area of natural/semi-natural Scots Pine. Common Crossbills have been present, feeding on the pines (which are closed) and nearby Larch and Spruce for the last two months:

Female Common Crossbill

Common Crossbills are usually fairly recognizable in the hand being much smaller bodied than Parrots and a bit smaller than Scottish. The key measrement however is bill depth. This one was quite big with a minimum bill depth of 10.6 mm but still well within range for Common Crossbill.

Common Crossbills can sometimes be difficult to age precisely due to an extensive breeding season that can last most of a calendar year (depending on cone/seed availability) and also due to the fact that some suspend their moult (if irrupting and/or breeding in their 2cy) whilst other juvenile 1/2 cy's can have extensive or erratic post juvenile moult - though the former will still often show 3 generations (or ages) of feather and can be aged quite easily. Another factor is that crossbill 'years' don't necessarily conform to our calender years eg. January to December, and as such the age codes ringers use may not conform like they do for other bird species. The dead crossbills that Dougie Preston sent me from the 2009 invasion had examples of arrested or suspended post juvenile moult - these will feature in a later post.

The female had adult type wing feathers that were quite worn, no old (or juvenile) greater coverts so was aged as a Euring Age 4 or a 4F. She had also replaced two primary coverts (indicated below, and much darker than the older feathers):

Moulting Primaries and Primary Coverts

One of the associated primaries P1, slightly darker than the older feathers, was nearly fully grown and the other was just coming in so this bird appeared to be active wing moult. Another useful ageing criteria was provided by Jenni and Winkler's fantastic Moult book which states that Common Crossbills never replace PC1 and PC2 (primary coverts 1 and 2) or even PC3 as part of their post juvenile moult so the age of a Euring 4 ( born before the present calendar year is safe). This female also had a brood patch score of 4 meaning she must have bred some time over the Summer and would explain the commencement of wing moult with the first two inner primaries.

The male's bill depth was 0.1mm bigger - positive assortative mating ? ! This bird was also in wing moult with two new primaries and associated primary coverts. Quite a big billed curvirostra, though overall bill is 'rectangular', culmen is not steeply downcurved and the tip of the lower mandible is at a shallow upward incline:

Male Common Crossbill

Notice how the bill appears big relative to the size of the head (which was small) ? After releasing the two birds one after the other, and recording their flight calls (both Common type Fc's) I noticed a colour ringed crossbill feeding in a Scots Pine tree right by the ringing station. I got the scope out and it took some time to get the positions of all 3 colours and the metal but I eventually confirmed it as Parrot Crossbill that was ringed 15/10/06 at the same site. This bird was on its own and I took the opportunity to collect and measure some of the cones it was foraging on. The first one it dropped was this cone:

Parrot Foraged Cone

The above cone resembles the shredded appearance of a Scots Pine cone that has been worked by a Scottish or Common Crossbill , yet the bird that foraged it was defintely a Parrot on bill depth and also flight call. So what gives ? Well, clearly like all things crossbill there is no definitive, and inconsitency and variation prevails ! I guess it depends on the structure of the individual cone as the bird then dropped a cone that was more typical of a Parrot foraged closed Scots Pine Cone:

Typical Split Parrot Foraged Cone

I have observed Parrot Crossbills only partly prising open certain cones many times so my conclusion is that crossbills cannot be identified with 100% certainty by examining the condition of the cones that they depredate, though for most birds this may be a safe assumption and is generally useful. Parrot Crossbills 'split' the cones by making an entrance to the scale with the culmen tip then 'working' that hole, by inserting the mandible then manipulating it through up to 90 degrees which then splits the scales - which is why Parrots are 'bull-necked' and have extremely well developed neck and cheek muscles. They will also sometimes literally 'peel' the scales. It is a bit of a 'domino effect' - once they have got one scale open the others are much easier. They will work a cone like this one for anything up to one and half two minutes at this time of year.

Hopefully when the wet and windy weather finally subsides I can get out and catch some more ! A more thorough review of Parrot feeding will appear in the future as I have scads of pictures of birds feeding, including some colour ringed Parrots feeding on Larch ( which apparently they don't feed on according to some authors !).

© Lindsay Cargill 2010