NLRG was formed in 1957 to help in the study of birds in the Lancaster and District Birdwatching Society area. There are currently 12 active ringers. Species currently being studied include: Pied Flycatcher, Bearded Tit, Sand Martin, Twite, Goosander, Oystercatcher and Grey Wagtail. Migration has been studied for 28 years at Heysham. We welcome anyone who wants to observe, help or perhaps wish to become a ringer. Photo: A Heysham-ringed Twite on the Mull of Kintyre (thanks to Eddie Maguire)

Saturday, 8 December 2012

A few preliminary observations on this autumn's Coal Tit irruption

1985 saw the first major Coal Tit irruption along the Lancashire coast, recorded at Heysham and Fylde sites.  These were in typically irruptive mode, mainly on 'vis mig' in high-flying noisy southbound flocks but with the occasional temporary landfall on the top of a bush before setting off again.  No tapes were used in 1985, therefore very few were caught and ringed

The intervening years saw a few smaller irruptive movements and then this last autumn has seen the largest numbers since 1985

As was also the case in 1985, southbound movements were recorded at Lancashire coastal sites, notably Heysham and Rossall but there was little evidence, perhaps surprisingly, of anything comparable happening at Walney, usually a major funnel for landbirds on 'vis mig'.  Reports from the remainder of the British Isles, however suggested at huge movement in Ireland with one Kerry site reporting "500 birds" and suspected Irish birds reaching the Scillies and perhaps mainland Cornwall.  Elsewhere there were reports of continental birds along the east and south coasts

Were these movements connected?  Noting 'preliminary' in the title, I have no idea why Coal Tits were moving in such numbers along the Lancashire coast this autumn and indeed in a relatively restricted time period, peaking on 8th-10th October.  This time we taped lured a decent sample and they were ALL juveniles.  Indeed, a high proportion of them retained significantly yellow cheeks, more akin to late July/August captures, perhaps suggesting a delayed breeding season/fledging courtesy of the June weather and known delays to Blue Tit broods in our own nestboxes.  Another part of the "no idea why" relates to where they came from!  An 'easy' theory is that the planting of upland conifers has created a population of Coal Tits where a proportion (of exclusively juveniles?) in some years may be forced to move due to altitude/excellent breeding season producing too many birds for the woodland to support and/or serious cone failure.  There are some previous recoveries to back this up e.g. a bird caught in our area in winter which had been ringed in Hamsterley Forest, Durham

We need to find out if extensive areas of likely-source conifers such as Kielder have indeed a) had a decent breeding season, despite the weather and b) "lost" a fair proportion of their birds since the end of September.  Any upland conifer surveyors/feeding station operators able to help here? 

Stats: the first noticeable irruptive birds at Heysham Obs were 19 on 27/9 and early/mid October saw 426 with a maximum of 164 passing through on 9th.  However, the Rossall peak was on the previous day and there is indeed some evidence that the vis mig coverage at Heysham on 8th was not as conscientious as it could have been!  Rossall had 92 heading south on 8th and 'just' 49 on 9th.  The 'tap' was very much turned off after the 19th October, despite reasonable weather inducing some noticeable Long-tailed Tit movements - these, however, tend to continue to move later in the autumn than Coal Tit

The annual ringing total at Heysham was c175 (previous highest annual total of 61 in 1994) with most of these being taped-lured autumnal vis mig birds.  In contrast, there were no flocks of Blue Tit in the whole of the autumn at Heysham - they were in unbelievably low numbers, with just a dribble of ones and twos, despite a well-stocked feeding station in operation.  Two protocols needed to be observed here.  First of all, not to blunder over to the mist nets until the flock had all found its way in.  'Watch them and delay the visit as long as is possible within mist netting protocol' was the order of the day. 

This is so you have maximum chance of being able to release them as the same entity and therefore hopefully retaining the same irruptive mode as prior to capture.  Releasing them individually could radically alter their behaviour pattern, as was indeed suspected with one or two birds which were subsequently regularly retrapped.  However, this could have happened anyway - in this respect, I cannot find any references showing what happens when irruptive behaviour of this species ceases.  Does the whole flock settle down together, or do individual birds gradually lose the urge and are left behind?  There must surely be something on this somewhere - any help? 

Evidence from feeding stations such as Teddy Heights near Arnside from mid-October suggested that much larger numbers (of obviously "relatively settled" birds which may indeed never have been in irruptive mode) were being ringed than in previous years with some evidence to suspect multiple arrival, rather than a slow accumulation of individuals (retrap data).  Defining birds attending a feeder as "relatively settled" can be inferred from the Heysham situation where the tape-luring location was no more than 20m from the feeding station, but the irruptive birds were not in the least bit interested in nyger and sunflower hearts

Finally, I was pressed into publishing this on the blogsite before I really had any time to research properly, so please hit the comment button if you can help answer some questions posed here

Pete Marsh


RB said...

'Yellow cheeks' in October might be more suggestive of Irish Coal Tit (of any age) rather than juveniles. They should have finished moulting before that point, and so have lost virtually all juvenile head feathers. But Irish race has yellowish cheeks in all ages. Ageing by looking for OGC and tail tip shape would be most reliable.

Pete Marsh said...

Please contact me off site for fuller discussion here - I prefer to respond to people I can identify and would not post anonymously myself. Thanks

Three quick points here:
GCs and tail used on all birds for ageing

Highly synchronised flocks contained both birds with no yellow on cheeks as well as a few with yellow bits still remaining, hence the comment re-possible delayed clutches in poor weather. A few blue tit of the very few caught were also rather yellow cheeked rather later than usual (one of my nest box blue tits took c5 weeks between 1st egg and full clutch with 10/11 fledging!)

Finally, I did 4.5 years ringing in Northern Ireland and there was nothing very 'irish' about the coal tits that far north (some recent stuff by Garner on this I think), therefore for these to be irish birds, bearing in mind the southern heading of the irruptive flocks through Heysham, it would have to be a very contrived and highly unlikely form of reorientated reverse migration