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multiple inornate warblers in Cornwall

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  • multiple inornate warblers in Cornwall

    Yellow-browed Warbler, Cornwall, Carnon Downs, four today at sewage works; also 3 Siberian Chiffchaffs and 4 Firecrests

    wow. If that isn't a typo, then isn't this a European winter record? The cold seems to be concentrating/displacing wintering sibes (+45 Chiffchaffs at the same site on the 2nd)....
    Last edited by Alex Lees; February 9th, 2012, 01:21 PM.
    Dept. of Zoology, University of Cambridge, UK

    My website - Neotropical Bird Club -Tropical Forest Research - Punkbirder - Wikiaves

    In natural science the principles of truth ought to be confirmed by observation. Carolus Linnaeus

  • #2
    If I'm right, 4 Yellow-broweds + 3 Siberian Chiffs + 45 normal Chiffs = 52 inornate warblers. I'm assuming that (a) Firecrests count as ornate, and (b) the 3 Siberians are not included in the 45 Chiffs?

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    • #3
      Originally posted by MichaelF View Post
      If I'm right, 4 Yellow-broweds + 3 Siberian Chiffs + 45 normal Chiffs = 52 inornate warblers. I'm assuming that (a) Firecrests count as ornate, and (b) the 3 Siberians are not included in the 45 Chiffs?
      Sure, sensu lato, but I was using it in the DIMW (species name)tradition..... Maybe Alan (or someone else) could comment on the number of Chiffs at this site - exceptional or representative of other sewage works in the SW too?
      Dept. of Zoology, University of Cambridge, UK

      My website - Neotropical Bird Club -Tropical Forest Research - Punkbirder - Wikiaves

      In natural science the principles of truth ought to be confirmed by observation. Carolus Linnaeus

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      • #4
        Originally posted by Alex Lees View Post
        ..... Maybe Alan (or someone else) could comment on the number of Chiffs at this site - exceptional or representative of other sewage works in the SW too?
        I can't comment with any precision but no doubt there is someone 'out there' from Cornwall who can! A potentially relevant stat, however, is that during his targetted study of Chiffchaffs wintering in SW England, Greg Conway trapped 694 individuals in the 6 winters between 1999/2000 and the publication of his BB note in August 2005 (BB 98: 427-429), so that implies a healthy wintering population. Coincidentally, I have just speculated with members of the ex 'tristis panel' on what effect this series of cold winters (or at least very cold spells within winters) might have on the tendency of Chiffchaffs to winter in the UK - same applies to YbW etc too. The theory is that individuals are increasing in winter as they have found 'successful' new wintering areas and have passed on their migration strategy to their offspring, and so on. Most tristis already appear to target the SW preferentially but collybita are more widespread. Will a series of winters with severe weather end up with increased fatalities and lead to fewer birds wintering in NW Europe? More locally, maybe more will end up in SW England, with birds vacating regions further north and east which are more affected by severe winter weather and 'discovering' the relatively benign climate of the SW of England?

        Alan
        Last edited by ARD; February 9th, 2012, 05:26 PM.

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        • #5
          some in-hand shots of the Yellow-broweds
          http://pendeenbirding.blogspot.com/2...ch-carnon.html

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          • #6
            More re wintering Chiffchaffs.

            No doubt a recent copy of Cornwall bird report will provide data for Cornwall?
            For some other southern regions, Flood, Hudson and Thomas (2007) give the following figures inter alia for Chiffchaffs wintering in Scilly:

            ‘ … an all-island tally of 20 – 30 is typical (e.g. 14 in 1976/77, 20 in 1979/80, 38+ 1998/99, 50 – 60 2003/04), sometimes seemingly more (e.g. 47 on Dec 9th 1984 on St Mary’s with 17 still present on Jan 5th 1985), other times seemingly less. Cold weather can slash winter numbers, with wintering birds wiped or forced out in the cold spell of January 1979.’

            Brown and Grice (2005) ‘Birds in England’ quote the 1986 BTO ‘Winter Atlas’ that between 300 and 600 Chiffchaffs wintered in the UK in the early 1980s and also note that over 100 wintered in Hampshire in the early to mid 1980s (from Clark and Eyre 1993) and 60 – 100 in the London area in early 1990s (from Dennis 1992).

            There are some more BTO stats here and of course the recently completed Atlas project will clarify the current picture.

            Alan
            Last edited by ARD; February 9th, 2012, 04:44 PM.

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            • #7
              Originally posted by Alex Lees View Post
              The cold seems to be concentrating/displacing wintering sibes (+45 Chiffchaffs at the same site on the 2nd)....
              If I remember correctly, there have been at least another 5 or so YBW discovered since Xmas in Devon and Somerset.

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              • #8
                Originally posted by ARD View Post
                Will a series of winters with severe weather end up with increased fatalities and lead to fewer birds wintering in NW Europe? More locally, maybe more will end up in SW England, with birds vacating regions further north and east which are more affected by severe winter weather and 'discovering' the relatively benign climate of the SW of England?

                Alan
                One wonders about density dependent processes then, how many insectivores can one sewage farm support if all the peripheral winterers have to empty into the choice habitats whenever it gets cold? Is there anything special about this sewage farm - other than geographical location (size, habitat) that makes it attractive or is it just the fact that someone is watching it? It would be interesting to see if any more Richard's Pipits come out if the woodwork too...
                Dept. of Zoology, University of Cambridge, UK

                My website - Neotropical Bird Club -Tropical Forest Research - Punkbirder - Wikiaves

                In natural science the principles of truth ought to be confirmed by observation. Carolus Linnaeus

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                • #9
                  Haven't made any thorough analysis but my impression is that here in the midlands, at least, there are two rather different types of niche.
                  The first is the small, old-fashioned type of STW, with small filter-beds, a few legacy, small, sludge beds and, for their size, a good density of peripheral trees and hedgerows. An exampe of this type is Kempsey in Worcs, where several tristis have wintered in the past (though not more recently?). This type of STW is fast disappearing, as they are 'upgraded', and presumably newer STW technology will prove less attractive (lower insect abundance). Off-setting this, perhaps, is the new tendency to plant areas of reeds and reed-mace at STWs.
                  The second niche, is water outflow channels, where water from larger STWs exits via culverts to a nearby river. Such outflows rarely (never?) freeze and again are usually quite well-flanked by vegetation. An example here in the West Midlands is the outflow from the STW near Hams Hall, Warks, which is a regular wintering haunt for Chiffchaffs, though usually not more than 4 or 5 individuals. Presumably this 'feature' of larger STWs has a longer-term future.
                  I don't know whether Greg Conway's studies in SW England extended to habitat characteristics and associated Chiffchaff abundance.


                  Alan

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                  • #10
                    Alan, Alex and co

                    I visited this site (Carnon Downs Sewage Works) on Friday 20 January and found it to be full of insects and insect-eating birds - in other words a fabulous wintering site. At that time, I recorded 48 chiffchaffs, including several Scandinavian and 3 'good' Siberians. There were also a good number of Blackcap, Firecrest and Goldcrest at the site, the birds all favouring the bushes at the east end of the workings

                    I also easily found Siberian Chiffchaffs at nearby Helston Sewage Works, as well as a juvenile Barn Swallow - my first-ever January bird in Britain

                    Yellow-browed Warblers were around in good numbers, although I only connected with one out of 7 that I went for. Three at this one wintering site is a UK first though, as Alex has intimated above

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                    • #11
                      From here: http://btoringing.blogspot.com/2012/...ut-sewage.html


                      04 February 2012
                      It's all about the sewage

                      It’s well known that wintering Chiffchaffs have a great affinity with the southwest, with Devon and Cornwall home to an unknown, but undoubtedly large, proportion of the UK wintering population. Looking back at just the last five winters (December to February in each of 2006-07 to 2010-11), we hold electronic ringing records of 918 Chiffchaffs, with no fewer than 244 ringed in Devon and 187 in Cornwall. Over these years, the highest winter total was 86 birds ringed in Devon in 2008-09.

                      Despite this winter being relatively mild, we’ve been having great success in catching wintering Chiffchaffs at several sites in Cornwall, thanks largely to the support of South West Water in allowing us access to works areas. Since the start of the year, we’ve ringed 105 Chiffchaffs at just three sewage works in Cornwall, including 41 on one day alone. This compares well to previous years, with the highest winter total nationally being 265 in 2009-10.

                      The racial identity of these birds is also interesting, with a small proportion being of northern races: either abietinus or tristis (Siberian Chiffchaff, above). Interestingly though, yesterday morning saw us catch a French-ringed bird, perhaps indicating an alternative origin of these wintering birds. There are just 13 previous records of French-ringed Chiffchaffs in the UK, of which three have been in Cornwall and two in Devon.

                      The sewage works sites are also important for various other wintering species, and yesterday’s catch also included two Firecrests and two Yellow-browed Warblers (below) in amongst the more expected 35 Chiffchaffs. The Yellow-broweds are of particular note, as of the 902 electronic ringing records we hold, just six have been in winter (five in December and one in January).
                      ************************************************** *******************

                      Imagine saying that 10 years ago: catching 2 Yellow-broweds and 35 Chiffchaffs on one day in February in England. And it doesn't even make the birding news.

                      I suppose it suggests that these birds are successfully wintering, possibly getting back to breed, and therefore setting up a new and successful migration route that explains the increasing numbers we've seen over 20 years.
                      Last edited by mafting; February 9th, 2012, 11:28 PM.

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                      • #12
                        Originally posted by LeeEvans View Post
                        Alan, Alex and co

                        I visited this site (Carnon Downs Sewage Works) on Friday 20 January and found it to be full of insects and insect-eating birds - in other words a fabulous wintering site. At that time, I recorded 48 chiffchaffs
                        How do you count 48 Chiffchaffs? Seems incredibly precise for such a mobile little bird.

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                        • #13
                          As a Cornwall based birder, who happens to live in Carnon Downs, I’ve been visiting this and the other five suitable sewerage works (Ponsanooth, Gwennap, Helston, Culdrose and Coverack) regularly and indeed, have found a high proportion of the Yellow-browed Warblers reported in the last month or so.

                          My own impression is that the combination of a relatively mild winter, punctuated by occasional colder periods that have been responsible for the high numbers. The mild winter has allowed the birds to survive, but during the colder periods they concentrate at the sewerage works. It’s also highly likely that there’s a longer term trend towards increased numbers of over-wintering phylloscs. I also suspect that birds move between Gwennap, Ponsanooth and Carnon Downs, which are all relatively close together. Thus, two of the Carnon Downs birds, could have been the two I previously found at Gwennap. I should also add that both Mark Grantham and I have been giving them exceptional coverage and reporting this year, which has also no doubt encouraged others to visit the sites. That said, I think overwintering phylloscs are fairly common. Although I haven’t been keeping a tally, and the following is rather back of envelope, here’s a few thoughts on likely numbers backed up by some very unscientific calculations:

                          Between the 9th and 13th of January I visited all six sewerage works. My total estimated haul was:

                          P. inornatus: 4
                          P. c. tristis: 8
                          sub-tristis: 10+
                          P. c. abietinus: 30+
                          P. c. collybita: 160+ (c. 65 at Carnon Downs alone – c.50 of which were caught and ringed)
                          P. c. collybita x trochilus: 1

                          I suspect that is a pretty accurate total for the sewerage works. The harder bit is to estimate is how many winter away from sewerage works. Over a slightly longer period, I also saw c. 40-60 nominate chiffchaffs in various sheltered or south-facing hedgerows and valleys, the difference being I’ve probably covered less than 1% of the suitable habitat in the Falmouth Bay and Lizard area. I’ve also seen both inornatus and the other Chiffchaff races away from sewerage works recently, suggesting the other taxa also over-winter away from sewerage works. Assuming conservatively that I actually visited 2% of the available habitat and saw 40 Chiffchaffs, and assuming the proportion of tristis and inornatus to collybita is similar outside sewerage works as inside, this would give totals away from sewerage works of:

                          P. c. collybita: 2,000
                          P.c. tristis: 100
                          P. inornatus: 50

                          Just in the Falmouth Bay and Lizard area alone!! Those numbers seem high and are almost certainly inaccurate, not least because it's difficult to estimate the area of suitable habitat or the area surrounding sewerage works from which the birds are drawn during cold spells. They do, however, suggest a sizeable population of tristis and inornatus over-wintering in SW Britain.
                          Last edited by Ilya Maclean; February 10th, 2012, 10:24 PM.

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                          • #14
                            Cool, thanks Alan, Lee, Richard and Ilya... Now some of these YBWs have rings on them then maybe we can see if they pinball between different sewage works during the same winter. Ilya's figures do seem high but a useful starting point, I guess the proof will be in the discovery of new YBWs in 'suboptimal' habitats, something to keep one going in the quest for the prize overwintering Setophaga. Still four at one site keeps one thinking about viable population sizes and wondering what is happening further south on the Celtic Fringe. Does NW Spain/Brittany have any similar sites? Maybe we're getting inexorably closer to closure on some of the mysteries of the whole sibe Phyllosc phenomenon - cf speculation below.

                            Why do we get so many Yellow-browed Warblers?
                            The increase in the UK in the period 1960-1999 is spectacular; 1960-1969 (247); 1970- 1979 (759); 1980-1989 (3206); 1990-1999 (3266) (Figure 2). Furthermore in the five years following, there were two massive influxes: 825 birds in 2003 and a minimum of 1300 birds in 2005. So why the increase in records? It could be an observer artefact and be rising due to increasing observer coverage and competence, but examination of trends at sites with relatively constant effort (e.g. bird observatories) also reveals a steep increase and suggests that this effect may only be of relatively minor importance. Yellow-browed Warbler maintains a toe-hold as a European breeder with a population estimate of 45000-46000 pairs in the Polar Ural Komi Republic region (Hagemeijer & Blair 1997). This region is largely ornithologically unknown so there is no data on population trends, but populations of Siberian passerines across the Taiga are reported to be increasing; as is evident from long-term bird counts in the Pre-Ob (Golovatin 2001) and Pre-Baikal areas (Ananin 2001). These have shown a general increase in populations of taiga birds, possibly owing to climatic amelioration. The closest part of the known regular winter range for these European breeders would be in Sikkim, India which is at least 4900 km away, whereas the furthest point away that this species regularly winters is in Southern Thailand over 8000 km away.

                            One potential explanation for the observed increase in numbers of Yellow-browed Warblers year on year is the establishment of a viable wintering population in the Western Palearctic spread thinly across Southern Europe and the Middle East (e.g. Vinicombe & Cottridge 1994; Wernham et al 2002; Gilroy & Lees 2003). There has been an upsurge in recent winter records across the region and the first Sub-Saharan observation was made in December 2003 in Senegal (Cruse 2004) followed by a sight record from the Gambia. If Yellow-browed Warblers breeding in the Polar Urals migrate south west through Europe then suitable wintering areas in Iberia are just 3700 km away and coastal Senegal 7100 km. Evidence for their westward movement in Russia is largely anecdotal, but the species is described as a regular migrant through Pinega Zapovednik (in the Arkhangel’sk Region, east of the White Sea) (Rykova, 2001).

                            Although this hypothesis is attractive, it is not without problems, for instance where is the spring return passage of Yellow-browed Warblers through Europe and might the Sahara be too extensive a barrier to cross for a migrant without an evolutionary history of barrier crossing? Given the low numbers of Yellow-browed Warblers recorded on spring passage in the UK it is possible that they might take a more direct route back to the Urals, passing through central Europe with its much lower observer density, such loop migrations occur quite commonly in many migratory bird species (Newton 2010). That Richard’s Pipits have evidently established a viable wintering population in the Mediterranean basin but are also rarely recorded on spring passage is further evidence that such a largely unseen return migration might be possible (Grussu & Biondi 2005; A. Corso in litt.). An alternative explanation argued by de Juana (2008) to account for the paucity of spring records is to label these movements of Siberian Phylloscopus as exploratory movements (after Baker 1978). This assumes that such individuals appearing in Western Europe return back east in the same autumn and proceed to their normal winter quarters. Although this might account for the relative scarcity in Iberia there is no evidence for a second peak of records through central or south-east Europe of birds moving back east, which rather undermines the strength of the hypothesis. Conclusive answers as to the provenance and intended wintering grounds of ‘Lincolnshire’ Yellowbrowed Warblers will probably have to await the development of ultra-light satellite tags, although that is likely to be many years hence….


                            This from: Lees, A.C. 2011. Yellow-browed Warbler Phylloscopus inornatus: a scarce migrant no more? Lincolnshire Bird Report 2009: 164-168, Cupit Print, Horncastle
                            Dept. of Zoology, University of Cambridge, UK

                            My website - Neotropical Bird Club -Tropical Forest Research - Punkbirder - Wikiaves

                            In natural science the principles of truth ought to be confirmed by observation. Carolus Linnaeus

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                            • #15
                              Presence of adults in autumn would be a good indication that they were surviving to come back again, and it was deliberate and successful migration route. A quick look at 2010 ringing report shows 17 juvs, 42 unaged; similar numbers for the previous year.

                              Are any of those unaged likely to be adults?? And if they are, are any likely to be returning birds?

                              Are there any retraps of adults of other sibe migrants? Or any adults caught in autumn?

                              Are any of the larger number of 'northern/eastern' Chiffs adult? With so many Chiffs ringed at a few small hotpot sites, one might expect the birds to be inclined to come back to them in subsequent winters - is there any evidence of this through retraps?

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