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ofthe risk ofincorporating an unknownnumber ofhybrids into the - PPT Presentation

Gibbins British Birds103 ID: 99016

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ofthe risk ofincorporating an unknownnumber ofhybrids into the ÔcachinnansÕsample.Moreover,as we may be picking uponly the most striking birds in Europe,thereis a danger ofdeveloping criteria based on anunrepresentative sample.Studies ofwintering in the Middle East suffersimilar problems,owing to the presence ofextremely similar taxa whose identificationhas yet to be fully resolved (notablybarabensis).Access to the heart ofthebreeding range ofwhere bothHerring and Yellow-legged Gulls are absent,is difficult and few western ornithologistshave studied the species there.Consequently,we are largely constrained to studying in wintering areas and must be aware ofthe problem ofcircular reasoning.Circularity is most problematic with lesstypical individuals.In part 2 we therefore useringed individuals ofknown provenance tohelp to develop criteria for the separation ofhybrid from pure individuals.Circularity isless ofan issue with the ÔclassicÕbirds that arethe focus ofpart 1.Nonetheless,to studywe have travelled to parts ofthebreeding range (e.g.several trips to theDanube Delta,Romania) and areas ofthesouthern Baltic where occurs inlarge numbers in the immediate post-breeding period and can be the most abun-dant large gull at some localities (e.g.on theCuronian Spit in Lithuania).The majority ofplates show birds from these areas.Since thepaper is aimed at British birders,it may seemthat examples ofphotographed inBritain are under-represented in the plates;this is a product ofthe need to limit theproblems ofcircularity.ÔHerring GullÕis used here to refer collec-tively to both races;ÔargentatusÕis used whenreferring specifically to the Scandinavian/Baltic race and ÔargenteusÕwhen referring tothe British/west European race.Yellow-leggedGull is referred to as ÔÕand relatesonly to Mediterranean birds.The AtlanticIsland populations ofYellow-legged Gull rep-resent a taxon whose status is still debatableand which,in any case,have rather darkimmature plumages and structural traits thatmake them unlikely to be confused with.We treat typic,as the extent and nature ofgeographicplumage variation has yet to be firmly estab-lished.Nonetheless,future work may revealconsistent differences between eastern andwestern birds (see section on adults).Fig.1illustrates key terms used in the text.Patterns of occurrence in BritainIt is difficult to assess the number ofcurrently occurring in Britain each year.This relates chieflyto the fact that thespecies is now soareas that observersdo not necessarilyreport all sightings.Nonetheless,it isis recordedmore frequentlynow than in the pastand that there arestrong seasonal andgeographic patternsto its occurrence.Caspian Gulls aremost frequent insouthern England,particularly thesoutheast.The firstbirds arrive in late Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 A lone Caspian Gull rests with a group of Herring Gulls on a landfill sitein Poland (17 Jan 2004).Can you see it? It is white-headed,dark-eyed and isholding its bill distinctly downwards.Some fine ÔpencilÕ streaks are visible onthe lower rear neck.It is below-right of centre. Ruud Altenburg BB March 2010 editorial 18/2/10 15:09 Page 144 summer and early autumn,when themajority ofrecords come from the coastlinebetween Kent and Suffolk.Juvenile now occur regularly in early August,when many young British Herring Gulls arenot even fully independent.These are not necessarily from the nearest breedingareas,since juveniles may disperse far fromtheir natal colony soon after reaching inde-pendence.For example,a bird at Espoo,Finland,on 26th July 2004 had been ringedas a pullus on 27th May on the River Dnperin southern Ukraine (49¡46ÕN 31¡28ÕE).Con-sequently,observers should be looking outfor first-calendar-year (1CY) from late July onwards.Post-breeding adultstend not to be seen in Britain until later inthe autumn;this delayed arrival may belinked to the progression ofprimary moult.Following their arrival,many birds moveinland and disperse northwards as theautumn and winter progress.They are sup-plemented by new arrivals,perhaps linked tocold weather on the Continent.For example,hundreds ofare present atlagoons along the coast ofLithuania inautumn but these disappear in midwinter,once the water freezes (Vytautas Pareigispers.comm.).The largest numbers ofin Britain are recorded in winter,withbirds seen regularly on favoured landfill sitesand in reservoir roosts in southern andcentral England.However,they remain dis-tinctly scarce in north and northwest Britain;there are few records north ofthe River Teesand the species remains extremely rare inScotland (fewer than five records) andIreland.Very few are recorded in the summermonths.This probably reflects the movementofbirds back to the Continent,but perhapsalso the relative difficulty ofidentifyingmoulting immatures in summer and the factthat gull-watching in Britain tends to be awinter pursuit.Size and structureCaspian Gulls can be strikingly large,tallbirds,but most individuals are similar inlength and weight to Herring Gull and so donot stand out on size alone.However,is structurally distinctive at all ages,British Birds103 ¥ March 2010 ¥ 142Ð183 Fig.1.Key terms,feather groups and plumage features referred to in the text.All images showcachinnans:upper two are from an adult (Latvia,April 2009),lower left is a 1CY (Romania,September2006),lower right is an adult (Romania,September 2008).All images Chris Gibbinsventralinner greater covertsscapularsscapularslower row ofmedian coverts BB March 2010 editorial 18/2/10 15:09 Page 145 often described as ÔlankyÕor ÔganglyÕ.It hasrelatively long,thin-looking legs (the extralength is particularly noticeable in the tibia)and often seems to stand taller than HerringGull.Next to ,its legs tend to looklonger and less robust.However,someare long-legged compared withHerring Gulls,so observers should bemindful ofthis when confronted with anapparently lanky bird.There are marked dif-ferences in size and structure between male(see Malling Olsen &Larsson 2003) and these differences may bemore marked than for other large gulls(Gibbins 2003).Some,presumably males,canlook incredibly long-legged,yet others,pre-sumably females,can actually look rathershort-legged.Consequently,birders and com-mittees should not automatically dismiss abird that lacks the textbook long-legged look.body,generally looks pear-shaped,and nor-mally lacks the bulky feel ofthe head ofHerring Gull and (especially) The headoften looks ÔanorexicÕ,as thoughthere is little flesh covering the skull;thismeans that head shape equates more closelyto skull shape than for other large gulls.Theoften-quoted,but perhaps over-emphasised,ÔsnoutyÕlook is due to a combination ofthelong sloping forehead and the relatively long,slim bill,which gives the front ofthe head atapering,Ôpulled-outÕappearance.Thissnouty look can be a striking and definingfeature,but it is important to note that notall show it.For a significant pro-portion of(presumed) females,the billlength is unremarkable,and,because oftheirhigher,more rounded heads,they may recallCommon Gull L.canus.Conversely,somelarger males can have a robust bill and asolid,more angular head that overlaps inappearance with both Herring and Yellow-legged Gulls.Yellow-legged Gulls typicallyhave a deeper,blunter bill and a larger,moreangular head,yet,as with other gulls,malesand females can be rather different,and theslighter individuals overlap with Herring andeven Lesser Black-backed Gulls L.fuscus.Fur-thermore,from the Atlantic coastofthe Iberian Peninsula tend to be smaller,less robust and less rangy than Mediter-ranean birds.Most Caspian Gulls appear longer-billedthan Herring Gull and They havea more gentle,even curve to the culmen anda less obvious gonydeal angle;unlike HerringGull and there is little or nobulging at the gonys and the general impres-sion is ofa gently tapering bill.Data inMalling Olsen & Larsson (2003) indicate thatthere is actually much overlap in the billand Herring Gull(males:Herring 46.4Ð64.9 mm,mean 54.6,50.7Ð63.5 mm,mean 56.3;females:Herring 44.9Ð59.0 mm,mean 49.7,48.0Ð59.5 mm,mean 51.9).Thus,the longer-billed impression given by results from the interaction ofits shape,depth and length,accentuated in some birdsby the pear-shaped head and long neck.Gibbins (2003) assessed the ratio betweenbill length and gonys depth (measured fromphotographs;length and depth as indicatedin fig.1) in a sample ofHerring and CaspianGulls (n = 68).Most Herring Gulls werescored as having a ratio of1.75Ð2.00 whereaswere scored as 2.25Ð2.50.Thus for the bill is most oftenmore than twice as long as its maximumdepth,while for Herring it is most frequentlya little less than twice its maximum depth.can be extremely long- andslim-billed,with ratios up to 3.25,comparedwith a maximum of2.5 in Herring.Note thatbill deformity is not uncommon among gulls(especially first-years),so a long,slim bill isnot,in itself,sufficient for identification orrecord acceptance.The body shape ofdistinctive.One ofthe most noticeable fea-tures is the attenuated rear end;this is a con-sequence ofa flat back,limited or absenttertial step and relatively long wings.The tipofthe tail falls one-third to halfway along theexposed primaries,while on Herring Gull itusually reaches halfway or slightly further(this comparison holds good only for birdsthat are not moulting their outer primaries).Herring Gulls and are generallyless attenuated and have a more prominenttertial step although,especially in hotweather,can appear to have a verylong rear end.The belly profile ofoften continues behind the legs as a ventralbulge that sags below the wings,making the Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 BB March 2010 editorial 18/2/10 15:09 Page 146 British Birds103 ¥ March 2010 ¥ 142Ð183 1W) Caspian Gull,Latvia,15Aug 2008.A typical,elegant individual.Apartfrom three or four newupper scapulars,this bird isin full juvenile plumage.Romania,17 Sep 2008.Note the simple narrowfeathers,lacking strongnotches;compare thegreater-covert and tertialHerring Gull in plate 53.The jizz is distinctive:it is alarge but elegant bird,witha small,pear-shaped head,long tibia and a relativelystrong contours.Note theventral bulge,also apparenton the birds in plates 50 &1W) Caspian Gull,Latvia,12 Sep 2009.This bird hasmore second-generationscapulars than the previousindividuals.The diffuse paledistal portion of the inner6Ð7 greater covertsbases and forms a wing-bar.On this individual there isacross the lower mediancoverts.Chris GibbinsChris GibbinsChris Gibbins BB March 2010 editorial 18/2/10 15:09 Page 149 150 Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 1CY (juv) Herring Gull,14 Aug 2008.Typical juvHerring Gulls such as thisidentification problems.Note the stocky,compactshape and heavily notchedoverall appearance,with thenotches especially obviouson the greater coverts.Thetertials and scapulars havepale fringes that have clear1CY (juv) Yellow-leggedGull,Spain,13 Aug 2009.A typical,strongly markedmichahellis.The tertials havesimple,sharply definednarrow fringes that extendonly around the distal partof the feather,and thegreater coverts haveextremely obvious notches.There is a dark maskaround the eye.Romania,2 Sep 2006.Astriking bird,with a well-marked tail patternand an extensively whiteunderwing.The ÔwindowÕ inand more distinct than onmichahellisthan on most HerringGulls.Note the palewebs of P2 and P3:theseare less frequently presentmichahellisand,when theyare,are typically smallerand less prominent than cachinnansChris GibbinsChris GibbinsChris Gibbins BB March 2010 editorial 18/2/10 15:09 Page 150 British Birds103 ¥ March 2010 ¥ 142Ð183 Romania,14 Sept 2008.Thisis an example of a bird withdarker inner primaries(overlapping withmichahellis);note also that ithas fine but extensive palebrown barring on theunderwing-coverts.This shown in plate 51.1CY (juv) Herring Gull,North-east Scotland,2 Nov2008.A typical individualshowing an extensive paleinner-primary window andheavily marked rump,uppertail-coverts and tailbase.Despite the late date,this bird appears not yet tohave any second-generationfeathers (hence,juvenileplumage).The innerprimaries have a complexpattern of dark arrowheadsand crossbars on a paleground colour.1W) Yellow-legged Gull,Romania,14 Sep 2008.Theunderwing is much darkercachinnans,with adark and pale bands.Theinner webs to the innerare at the paler end of thescale,but note that it lackswebs of the innerChris GibbinsChris GibbinsChris Gibbins BB March 2010 editorial 18/2/10 15:09 Page 151 152 Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183coverts,much less obvious than those ofHerring Gull and .Normally,thepattern on the inner greater coverts appearsto be more vermiculation than notching.Abird with strongly notched greater covertsshould be checked carefully for other anom-alous features.Caution is needed with ,as some lack notches on their greatercoverts (instead,some simply have sharp palefringes).An oft-quoted feature ofduring their first winter (1CY/2CY birds) isthe presence ofa second pale wing-bar,onthe lowest row ofmedian coverts.This,however,is rarely evident on fresh juvenilesin July and August.The first-generation tertials oftypically have a muddy-brown base and adiffuse pale fringe around the distal portionofthe feather.The pale fringe sometimescoalesces with pale oval patches in the centralpart ofthe feather to form an extensive paletip,reminiscent ofthe pattern on a juvenileCommon Gull (e.g.plate 50).The exactpattern varies subtly but the key point is thatthe pale fringe lacks the notches ofHerringGull (plate 53) and is generally broader andless sharply defined than shown by typical(plate 54).Most juvenile are as striking inflight as they are on the ground (plates 55 &56).From above and below,the generalimpression is clearly different from HerringGull (plate 57),and while they look similar tofrom above,their underside isquite different.The relatively white under-wing is perhaps the most obvious in-flightfeature of.This is created by theoff-white ground colour to the underwing-coverts;the secondaries and primaries arealso paler (silvery to off-white) than those ofHerring and Most have a degree ofsoft,grey-brown barring onthe axillaries and underwing-coverts,so theunderwing is not wholly white (e.g.plate 56).The underwing-coverts ofHerring Gull aremuch more extensively and strongly markedwith brown and the general impression istherefore ofa much darker and ratheruniform underwing.In (plate 58)the underwing-coverts are heavily markedwith dark,chocolate brown over a pale basecolour,often creating a contrasting pattern oflight and dark bands.However,some lack such extensive dark marks so froma distance their underwings can look surpris-ingly pale.The incidence ofpale underwingsmay be more prevalent in eastern popula-The underwing ofsome strikingly white,and photographs suggestthat some birds drop some underwing-coverts and axillaries during their firstwinter;this exposes the paler bases toremaining feathers and heightens the appear-ance ofa white underwing.Conversely,observations on breeding lakes in Romania(i.e.birds with known provenance) indicatecan have quitewell-marked underwings,with dark brownbarring and spotting across many feathers,especially the lesser underwing-coverts andaxillaries.Such dark birds tend to have morecontrasting underwings than Herring Gulls,as the brown barring sits on an otherwiserather pale ground colour.This creates adegree ofoverlap with The contrasting black-and-white patternofthe rump and tail ofis strikingin flight and often likened to that ofa Rough-legged Buzzard .The generalpattern is more like that ofHerring Gull.Juvenile Herring Gulls show avariable but usually extensive scatter ofdarkbars and spots on the rump,uppertail-coverts and tail base.This reduces the con-trast between these areas and the broader,more diffuse tail band,which averages a littlebrowner than that of.Both have avery dark (black-looking) tail band that con-trasts strongly with the white rump and tailbase.Malling Olsen & Larsson (2003) statedis Ôfuller andmore eventainly,the tail band ofmany uneven,being noticeably deeper on thecentral tail feathers.In general,the tail bandcachinnansismore even in width but onsome it is clearly deepest in the middle,andhence uneven.While many tail band is deep across its whole width,onsome it is no fuller than for .Inshort,the depth and evenness ofthe dark tailband are thus ofno real value for the separa-tion ofThere is agreater tendency for the dark tail band of BB March 2010 editorial 18/2/10 15:09 Page 152 154 Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 Gull,Finland,20 Oct 2008.cachinnansNote that,for example,scapulars have a silverytone and only a narrowshaft streak.This bird hasnot (at least by this date)included any coverts ortertials in its post-juvenileGull,Latvia,9 Apr 2009.Thisbird has the typical pale andsilvery overall appearancecachinnans.Itsscapulars lack stronganchors.It has gained manynew wing-coverts duringpost-juv moult and by earlyspring these are faded andblend in with remainingThe lower tertials are first-generation,but the upperones are greyer,second-generation ones,probablymoult.This combination ofbut not of Herring Gull.2CY (1W) Yellow-legged Gull,Spain,16 Apr2006.The post-juv moult ofmichahelliscachinnans,but typicallyfeathers (visible here in thescapulars,tertials andcoverts) are stronglymarked with bars andanchors.Yellow-legged Gullcoverts in the post-juvmoult;this bird has had amore extensive moult thanmany and only a few first-generation feathers arevisible in the wing.HerringGulls do not look like thisuntil mid July of theirsecond calendar-year.Chris GibbinsChris GibbinsHannu Koskinen BB March 2010 editorial 18/2/10 15:09 Page 154 British Birds103 ¥ March 2010 ¥ 142Ð183 2CY (1W) HerringGull,Latvia,13 Apr 2009.Note the strongly markedscapulars and heavilynotched greater coverts,as well as the compact jizz.Gull,UAE,7 Feb 2009.Some Caspian Gulls,likethis one,have rather heavilymarked second-generationscapulars and overlap withHerring Gulls in thisrespect.However,note theand median coverts dottedones,and the characteristicGull,UAE,March 2007.By early spring,some 1WCaspian Gulls areextremely pale andabraded,especially thosethat have wintered inhotter climates.The onceblackish areas are fadedbrown and the sun-bleached wing-coverts lackany clear pattern.Thewhite.Chris GibbinsChris GibbinsChris Gibbins BB March 2010 editorial 18/2/10 15:09 Page 155 be highly distinctive,typically showing asilvery-grey ground colour (paler grey thanthose ofadults) with a simple dark shaftstreak and either a rather diffuse subterminalanchor pattern or a dark basal diamond;most lack strong crossbarring.The silveryground colour fades rapidly as the winterprogresses and the dark markings becomemore subdued,leading to an increasinglypale and uniform-looking bird.On many,the lowest row ofsecond-genera-tion scapulars appear paler and more lightlymarked than the rest,and hence form a paleband separating the upper scapulars from thebrown wing-coverts.Younger feathers in amoult sequence may differ in pattern fromolder ones (Howell 2001),which may explainthe presence ofthis pale band.Typically,are quite different(plate 61):their second-generation scapularsare strongly marked with heavy crossbars anda broad,dark anchor near the tip.The samerelative differences occur on any new wing-coverts or tertials moulted in during theusually have simple andsubtle patterns,strong and boldones.The pattern on the second-generationscapulars ofHerring Gull is extremely vari-able (plate 62) but in broad terms is interme-diate between that of.The ground colour ofeachfeather ranges from pale,sandy brown to midbrown,and most have darker crossbars andan anchor pattern towards the tip.It isextremely rare (perhaps unknown) for genet-ically pure Herring Gulls to have the silvertone and simple dark shaft streak ofclassicImportantly,however,a signifi-cant proportion ofhave ratherheavily marked second-generation scapulars(e.g.plate 63).The striking appearance ofmany during their first winter stems from acombination ofthe patterns on new second-generation feathers and wear on remainingfirst-generation ones.Wear is especiallyevident on birds reared earlier in moresoutherly and easterly areas,where sunbleaching and sand blasting (on dry beaches)take their toll on feather condition.Even inSeptember,1CY around the BlackSea can be rather worn and shabby.LightÔpencilÕstreaking on the head and body pro-gressively wears away,and can give rise to astartlingly white appearance,compared withHerring Gull.By midwinter,any remainingstreaks are confined to a neat necklacearound the lower rear neck.The white headisolates and emphasises the dark eye.Weartends to simplify and thus emphasise thepattern on remaining first-generation greatercoverts (dark base,pale distal bar) and,onsome,the second pale bar (on the lowest rowofmedian coverts) becomes prominent.Thefact that this second bar is less frequentlyapparent on the same feathers in late summersuggests that its prominence is related towear and fading.By spring,most paler than in autumn,with a more subduedcontrast between the whites,greys,brownsand blacks.The first-generation feathers canlook rather washed-out,with the feather pat-terning less clear.For those individuals thatincluded some coverts or tertials in the post-juvenile moult,these (now somewhat worn)feathers show up as discontinuities on anotherwise juvenile wing (plate 60).On some,pure grey feathers are distributed randomlyacross the scapulars (these may be third-gen-eration feathers grown during the winter),giving an overall impression quite unlikeHerring Gull;in fact,such advanced (and especially those which also havesome second-generation coverts and tertials)are more likely to be mistaken for a second-winter Herring Gull than a first-winter.Thealso fades over thewinter and those that have retained theirfirst-generation coverts and tertials can be atrap for the unwary.Despite their originalnotched patterns,the worn coverts ofcan become surprisingly uniform byspring.Similarly,tertial wear makes thefeather pattern more difficult to discern andso it is effectively inseparable from that of.The rangy appearance ofsomemeans that observers faced with aworn,putative in the latewinter/early spring period should be wary.Careful assessments ofbill shape,head pro-portions,call and details ofthe underwingare critical at this time.During their first autumn and winter,asmall proportion oftail feathers (certainly less than 20%,and Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 BB March 2010 editorial 18/2/10 15:09 Page 156 158 Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 2CY (1S) Caspian Gull,Latvia,17 Aug 2008.This is an example of the more distinctive plumagetype seen in late summer,with some silvery-grey (probably third-generation) mantle feathers andlower scapulars on the right side.The greater coverts are a rather uniform mid brown.The new(dark) second-generation primaries have much more rounded tips than the remaining first-generation ones.This large,elegant bird should not pose any identification problems.Chris Gibbins 2CY (1S) Caspian Gull,Lithuania,10 Sep 2009.Chris Gibbins BB March 2010 editorial 18/2/10 15:09 Page 158 British Birds103 ¥ March 2010 ¥ 142Ð183 Gull,UAE,7 Feb 2009.The plumage tones areessentially pure white,silverand black,much sharperHerring Gulls.The dark eyecontrasts markedly withand the typical grey-fleshtones are evident on thelegs,especially the tibia.the greater covertsmatches that of 1W birds Ðuniform dark bases and aGull,Latvia,10 Apr 2009.3CY (2W) HerringGull,North-east Scotland,8 Mar 2009.As shown bythis and plate 73,theplumage of 2W HerringGulls is extremely variable.Nonetheless,typically theylook much less mature thancachinnans:they lack sharpappearing to be a mix ofoff-white and light browntones.Note particularly thepale eyes of these birds.Chris GibbinsChris GibbinsChris Gibbins BB March 2010 editorial 18/2/10 15:09 Page 161 162 Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 3CY (2W) HerringGull,Latvia,13 Apr 2009.This bird has a rather morecachinnans-like plumagethan many (i.e.it has a greysaddle and upper tertials),but the greater coverts areheavily speckled and it hasextensive diffuse streaks onits head and body;also,itsstocky,compact jizz shouldpreclude any confusion.2CY (2W) Yellow-legged Gull,Spain,20 Dec2006.Compared withcachinnansof this age,notethe solid structure,darkstreaking around the eyeand foreneck,and especiallythe heavily marked greatercoverts.As with cachinnansmichahellisand body,pure grey saddleand many wing-coverts)makes them look olderthan Herring Gulls of thesame age.3CY (2W) Yellow-legged Gull,Spain,8 May2009.By early spring,3CYYellow-legged Gullsbecome extremely cleanand bright;compared withcachinnans&71,note the bright yellowbill/yellow-toned legs andthe strongly notchedcoverts.The eye is clearly rather pale.Chris GibbinsChris GibbinsChris Gibbins BB March 2010 editorial 18/2/10 15:10 Page 162 British Birds103 ¥ March 2010 ¥ 142Ð183 Gull,Lithuania,10 Sep 2009.Note thewhite underwing,with justa few isolated light brownspots and crescents,andthe small mirror on P10.This bird is just completingits moult into 2W plumage,fully grown.Gull,Lithuania,10 Sep 2009.and-white tail,Venetian-blind pattern on the middleprimaries (clearer on thefar wing),grey saddle and3CY (2W) HerringGull,North-east Scotland,8 Mar 2009.The overallimpression is of a ratheruniform brown bird,without strong plumagecontrasts.The tail isextensively dark and therump and uppertail-covertsare well marked.Chris GibbinsChris GibbinsChris Gibbins BB March 2010 editorial 18/2/10 15:10 Page 163 colour.The axillaries tend to be unmarked,pure white.Second-winter frequently have contrasting light and darkbrown bands on their underwing-coverts,sothe underwing looks much darker overall;darker birdsresemblegraellsii Lesser Black-backed Gull.In flight,the general impression oftheupperwing is very similar to thatoffirst-winters,with blackish-brown outerprimaries,secondaries and primary coverts.The pattern on the second-generation innerprimaries is extremely variable,but at leastsome have a strong Venetian-blind pattern Ðpale,greyish inner webs on the inner pri-maries that contrast markedly with blackishouter webs.This contrast is much lessmarked on most Herring Gulls.On some,the inner-primary pattern is lessdistinctive,with light brown rather than greyinner webs;such birds are similar to HerringGulls.Some have a diffuse palelozenge on the outer web ofthe inner 4Ð5primaries (as for first-generation feathers),but on others the distal part ofthese feathersis a rather uniform brown.The rump and tail pattern ofrather variable at this age (plate 77) but typi-cally the pattern is distinctly different fromHerring GullÕs.In the most striking ,the rump,uppertail-coverts and tailbase are unmarked,pure white and contrastmarkedly with a narrow black tail band.Mostfrequently,the tail band has fine black ver-miculation along its basal edge.In others,therump and uppertail-coverts have some iso-lated spots and bars and the tail band is morecoarsely and extensively vermiculated.InHerring (plate 78),the rump and tail baseare,on average,more spotted and barred andthe tail band is browner,deeper and lesssharply defined,so the general appearance ismuch less clean and striking than in .A bird whose tail/rump pattern doesnot differ markedly from Herring GullÕshould be checked for other anomalous fea-tures (see part 2).Most second-winter have asmall but distinct mirror on the outerprimary (P10).On some it is small andsandy-grey,on others it is large and whitish,but is generally clearly visible.This feature isextremely useful for separating Herring andCaspian Gulls,although not wholly diag-nostic:a small proportion (c.1Ð5%) ofsecond-winter Herring Gulls,particularlyargentatus,have a P10 mirror,while a smallproportion oflack a P10 mirror.It is extremely rare for second-winter to have a mirror on P10 (the authorshave seen only one such individual);whenpresent it is very small and usually apparentonly in good quality photographs.Bare partsThe bare parts ofsecond-winter begin to take on some distinctive hues.Thelegs are invariably a rather sickly grey (ÔdeadfleshÕ),compared with the distinctly pink legsofHerring Gulls.The legs ofsecond-winterare extremely variable:yellowish,greeny-yellow,flesh or grey-flesh.The basal two-thirds ofthe bill usuallybecomes much paler than on first-summers,ranging from greyish-pink on some to dull greeny-yellow on others.Typi-cally,there is a dark smudge near the tip thatextends back along the cutting edge towardsthe base.The pale bill tip is usually muchmore prominent than on first-winters.However,while typically have thisbill pattern,the colours and patterns ofalltaxa vary markedly:there is much overlapand it is not hard to find Herring Gulls andthat match The eye is almost invariably dark-lookingin second-winter ,contrastingsharply with the white head.Most HerringGulls and begin to develop palerirides at this age (greyish or brown) and so abird with distinctly pale eyes is unlikely to beOlder immature plumages(3CYÐ5CY birds)Moult and plumage developmentThe second complete moult takes placeduring the summer and autumn ofthe thirdcalendar-year and brings in new,pure greyfeathers to the mantle,wing-coverts and ter-tials.The third-generation primaries havesmall white tips (unlike first- and second-generation ones),as well as large mirrors onP10 and,most frequently,also on P9.Theouter primaries are otherwise blackish andthe inner ones have adult grey tones.Once Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 BB March 2010 editorial 18/2/10 15:10 Page 164 166 Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 Gull,Lithuania,10 Sep 2009.This bird isouter primaries are notquite fully grown).Anumber of subtle features,used collectively,make 3Wdistinctive,but as all arefound from time to time inHerring Gulls,none arediagnostic.This bird andshow Ôlead shotÕ eyes,white head,greeny-yellowbill and grey-flesh legs.Gull,Latvia,10 Apr 2009.The extent of any brownremaining in the wing ofthis age group is variable Ðthis bird has rather a lot ofdark in the coverts,butnone in the tertials.Gull,Latvia,8 Feb 2010.A bird with soft,grey-brown patterning in thecoverts and some brownremaining in the tertials.All the plumage featuresand bare-part coloursvisible in this bird can befound from time to time in Herring Gulls,so itillustrates nicely the factthat identification of birdsin this age group should besupported by structure and,ideally,voice.Chris GibbinsChris GibbinsChris Gibbins BB March 2010 editorial 18/2/10 15:10 Page 166 British Birds103 ¥ March 2010 ¥ 142Ð183 3CY (3W) Yellow-legged Gull,Spain,December 2006.Birds of this age are variable.This one hasa rather large mirror in P10 but on others it is much smaller or even lacking.It has a clean white tailbut many retain vestigial dark marks.The extensive blackish-brown primary coverts contrast with theotherwise grey upperwing.The black of the primaries forms a solid wedge on the outer wing.Notethe asymmetrical wing-tip pattern Ð there is a mirror on P9 on the left wing but not the right wing.Such asymmetry is not unusual in gulls;consequently,where a particular feature is critical foridentification,it is always worth making sure that both wings have the correct pattern. Chris Gibbins 3CY (3W) Caspian Gull,Lithuania,10 Sep 2009.The primary pattern of this bird is beginning to takeon some of the features of adults Ð note the greytongues eating into the black wing-tip.The outerprimary coverts and the alula retain extensive,blackish-brown marks.Chris Gibbins 3CY (3W) Herring Gull,North-east Scotland,2Nov 2008.This bird shows an extensive brown washto its wings,a well-streaked head,has only limitedblack on P5 and (already) a very pale eye.Individuallyand collectively,these features make confusion withcachinnansunlikely.3W argenteusHerring Gullsregularly show a complete,deep black band across P5,unlike this argentatus,which has isolated dark smudges.So,the presence of a black band on P5 is not a keyfeature at this age.Note that P10 is not yet fully grown. Chris Gibbins BB March 2010 editorial 18/2/10 15:10 Page 167 fourth-generation primaries ofare similar to those ofadults,with a longwhite tongue on the underside ofP10 andgrey tongues eating into the black wing-tipon the upperside ofP8ÐP10.Bare partsThe third-winter bill has a mix ofblackishbrown and paler areas.Black is usually con-fined to the gonys region as a diffuse Ôthumb-printÕ,with a paler tip and basal third to thebill.Some isolated darker smudges are oftenpresent closer to the base,and many have afrom the gonys.The pale parts ofthe bill aremost frequently a dull greeny yellow,typi-cally with a strong grey cast.Some haverather more yellow-toned bills.Red is notprominent in the gonys ofofthisage.The legs are invariably a rather colour-less,dead-flesh grey,compared with thepinker legs ofHerring Gulls.The legs ofthird-winterare usually greeny-yellow or grey-yellow,with some having clearyellow tones;they can,however,occasionallybe dull flesh-coloured as in eyes ofmost still look darkbrown,but slightly paler irides may developfrom this age onwards.Most but not alland Herrings ofthis age havepaler (greeny- or greyish-yellow) eyes.It israre for ofthis age to have verypale (cream or yellow) eyes,and such birdsshould be scrutinised closely.Eye-ring colourtones ofthird-winter birds also begin toreflect those ofadults (see below).Despite often looking distinctive,third-winter and third-summer birds have no trulydiagnostic plumage features.In essence,thedistinctive features ofyounger birds havebeen lost,while the adult wing-tip patternhas not developed sufficiently for it to beconsidered critically important.Identifica-tion should be based on a careful assessmentofstructure,in combination with indicativeplumage features listed above,and theabsence ofanomalies.ofthis age can be partic-ularly tricky to separate from Near-adult often have dark eyesand smaller individuals can have bill shapeand overall jizz reminiscent ofsome lack grey tongues intheir third-generation primaries and sooverlap with however,theyshould have larger mirrors than Long call and associated posture are the bestway to separate the more difficult individ-Experienced gull-watchers are unlikely tomistake third- and fourth-winter HerringGulls for ,but others should beaware ofthe problem posed by argentatus.Some late-winter argentatus areclean-headedand share some aspects ofthe wing-tip pattern Ð with a long white tip toP10 and grey tongues that invade the blackwing-tip.While the irides ofmost HerringGulls will be rather pale by their third winter,a significant proportion retain dark eyes:aclearly pale eye in a near-adult gull is notgood for but a dark eye does notautomatically rule out Herring Gull.Adult Caspian Gulls are best located in gullflocks by a combination oftheir peculiar jizz,and relatively dark,small-looking eyes thatcontrast with the white head (plate 86).Iden-tification can then be confirmed by detailedstudy ofbill proportions,primary pattern,bare-part colours and upperpart tone.Thefollowing sections deal with these features inturn;plates 87Ð96 show a selection ofadultcachinnans,michahellisand Herring Gulls.Fig.2 shows the range ofadult upperparttones for and similar taxa,at leastin a British context.The figure uses theKodak Grey Scale,a scale that has numberedincrements from 0 (white) to 20 (black).Thescale itselfis not reproduced here and mostgull-watchers will not go into the field armedwith a copy ofit;fig.2 simply compares theupperpart tones among the various taxa andshows the degree ofoverlap between them.For grey-tone comparisons to be reliable,other taxa should be directly alongside ornearby.Observers also need to be aware ofthe effects oflight and viewing angle on theperception oftone.Diffuse sunlight or over-cast conditions are best:strong direct sun-light tends to bleach out subtle differences. Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 BB March 2010 editorial 18/2/10 15:10 Page 168 170 Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 Gull,Latvia,13 Apr 2009.The extensive dark areason the primary coverts,dark grey wash on theouter webs of P5ÐP7 andthe black band across theis not a fully adult bird.(centre left) with HerringGulls,Latvia,14 Aug 2008.This photograph allowsdirect comparison of jizz,bare-part colours and greytones of the two species.Essex,7 Feb 2009.ThisbirdÕs eye is at the dark endof the range.Steve ArlowChris GibbinsChris Gibbins BB March 2010 editorial 18/2/10 15:10 Page 170 British Birds103 ¥ March 2010 ¥ 142Ð183 Adult Caspian Gull,Romania,August 2006.The bill is particularly weak and has a fleshy tone toits basal portion.The eye of Caspian Gull is normally described as being dark,but rather few havetruly dark eyes.Most have a speckled iris,which in the field varies in colour from pale amber tobrown,depending on the density of speckling.The eye of this bird is medium amber. Chris Gibbins Adult (or near-adult) Caspian Gull,Romania,August 2006.This bird may be a female:it looksrather compact,the bill is not noticeably long and the head is high and rather peaked.Because of thedark eye,many such presumed female cachinnansare surprisingly reminiscent of a Common Gull.Thebroad black band across P5 is visible below the tertials.Brown tones to some greater coverts andtail feathers suggest that this bird may not be fully mature. Chris Gibbins BB March 2010 editorial 18/2/10 15:10 Page 171 orbital ring colour Ð pale-eyed having pale orange orbital rings and dark-eyed birds having redder orbitals Ð and thisrelationship is clearly worth further study.The leg colour ofadult variesseasonally and individually.In winter,the legsare typically pale,greyish-flesh;some have aweak,greenish-yellow tint.In spring and earlysummer,the legs ofmany adults become dis-tinctly brighter and yellowish.The proportionshowing truly yellow legs during the breedingseason is uncertain and may vary among pop-ulations and even from year to year (perhapslinked to diet).The leg colour ofan indi-vidual bird can vary during the course ofthebreeding season,probably as a function ofphysiological condition (Neubauer et al.2009).There is complete overlap in leg colourbetween and the Herring Gulls ofthe eastern Baltic (from pure pink to lemonyellow) so this feature is oflimited value.However,rarely matches the richyellow ofthe legs ofThe most likely problem is confusion with aHerring Gull from the eastern Baltic.Theseare quite unlike the Norwegian argentatusthat we are familiar with in the UK and canhave upperpart tones,bare-part colours andwing-tip patterns that are virtually identicalto those of.The potential for con-fusion is increased by the fact that theseargentatusmay look slightly longer-winged,longer-legged and longer-billed than argen-teus(although less obviously so than ).The occasional dark-eyed bird cancreate real problems.Concluding remarksThe aim ofpart 1 ofthis paper has been todescribe the appearance oftypical CaspianGulls.The birds featured in the plates are allrather typical and should not pose any iden-tification problems.Variability is a feature oflarge gulls,however,and observers shouldnot expect all to look identical.Nonetheless,there is what might be regardedas normal or typical variation (that outlinedabove) and that which is extreme or atypical.In part 2 we shall deal with the extremes anddiscuss birds that sit in the overlap zonesbetween the species.We shall also considerhybrids;this is a very real problem given thathybridisation is occurring in Poland,forexample,and that hybrids originating therehave been recorded in Britain.Beforebecoming embroiled in debates about themore difficult individuals,it is importantthat birders are familiar with the identifica-tion oftypical birds.We hope that part 1 hasprovided this familiarisation.AcknowledgmentsThe authors would like to thank Nic Hallam,HannuKoskinen,Ian Lewington and four anonymousreviewers,whose insightful comments greatlyimproved this manuscript.We are also grateful to RuudAltenburg,Steve Arlow,Hannu Koskinen,MikeLangman and Pim Wolf for sharing and allowing us touse their photographs.A number of birders sharedtheir knowledge and experience of duringthe preparation of this paper;we especially thankRuud Altenburg,Hannu Koskinen,Mars and TheoMuusse and Visa Rauste in this regard.Dmitri Mauquoykindly produced fig.1.ReferencesBakker,T.,Offereins,R.,& Winter,R.2000.Caspian Gullidentification gallery.Birding World13:60Ð74.Collinson,J.M.,Parkin,D.T.,Knox,A.G.,Sangster,G.,&Svensson,L.2008.Species boundaries in the Herringand Lesser Black-backed Gull complex.Brit.Birds101:340Ð363.Garner,M.1997.Large white-headed gulls in theUnited Arab Emirates:a contribution to their fieldidentification.Emirates Bird Report19:94Ð103.Ñ & Quinn,D.1997.Identification of Yellow-leggedGulls in Britain.Brit.Birds90:25Ð62.Gibbins,C.N.2003.Phenotypic variability of Caspian6:59Ð72.Grant,P.J.1986.Gulls:a guide to identification.2nd edn.Poyser,London.Gruber,D.1995.Die Kennzeichen und das Vorkommende Wei§kopfmšwen Larus cachinnansin Europe.19:121Ð127.Howell,S.2001.A new look at moult in gulls.Jonsson,L.1998.Yellow-legged Gulls and yellow-leggedHerring Gulls in the Baltic.4:74Ð100.Klein,R.1994.Silbermšwen Larus argentatusWeiâkopfmšwen Larus cachinnansin Mecklenburg Ð erste Ergebnisse einerRingfundanalyse.Vogelwelt115:267Ð285.Leibers,D.,& Dierschke,V.1997.Variability of fieldcharacters in adult Pontic Yellow-legged Gulls.19:277Ð280.Ñ,Helbig,A.J.,& de Knifff,P.2001.Geneticdifferentiation and phylogeography of gulls in theLarus cachinnans-fuscusgroup (Aves:Charadriiformes).10:477Ð2462.Malling Olsen,K.,& Larsson,H.2003.Gulls of Europe,Asia and North America.Helm,London.Neubauer,G.,Zagalska-Neubauer,M.M.,Pons,J-M.,Crochet,P-A.,Chylarecki,P.,Przystalski,A.,& Gay,L.2009.Assortative mating without completereproductive isolation in a zone of recent secondary Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 BB March 2010 editorial 18/2/10 15:10 Page 176 British Birds103 ¥ March 2010 ¥ 142Ð183 Appendix 1. Juv and Caspian Yellow-legged HerringComments1st-winters ((AugÐApr)Normally distinctlypale;appears silvery or creamy-white atdistance on the moststriking birdsDark and heavilybarred but (rarely) canoverlap with darkerDark,though moreuniform than UnderwingStriking white rumpand tail,with relatively narrow Very similar toBrowner,deeper andless clear-cut tail band.Less contrast betweentail band and the moredensely marked rump Tail andrumpPale grey groundcolour (silvery) inclassic birds,eachfeather with a simpledark shaft streak andnarrow subterminalanchor.Some aremore heavilypatterned Strongly marked,withheavy anchor patternand heavy blackish-brown bars acrossbasal part ofeachVariable;most havepattern similar to,but withcrossbarring andsubterminal anchorsweaker Second-generationfrom Herring but verysimilar to Uniform dark baseand pale terminal areaforming clear bar,like Nike ÔswooshÕ.Pale fringes simple,lacking strong notchesTypically heavilynotched,particularlyon inner feathers;butextremely variable andsome have simplefringes that resembleExtremely variable,but normally wellnotched across allcoverts;birdsmatching are extremely rare GreatercovertsTypically clean-looking (whitish) withminimal streaking.Often has neat halfcollar offine streakingaround rear neckOverlaps with,but morefrequently has obviousdark eye mask and lesspronounced collarNormally extensivelycovered with diffusestreaks and blotches Head andbody colourSoft,greyish-brownDark,chocolatebrown,withcontrasting pale areasMid brown,intermediate betweenthe other two Colour ofupperparts(juvs only)Less prominent thanHerring,slightly moreOften with Venetian-blind pattern.Palelozenge-shapedpatches frequentlypresent on outer websnear tips ofP2Ð4/5Inner webs ofinnerprimaries onlyfractionally paler thanouters,so virtually nowindow.Generallylack pale lozenges onProminent window,with complexpatterning on feathertips ofP1Ð4/5 InnerprimarywindowExtremely useful but BB March 2010 editorial 18/2/10 15:10 Page 179 British Birds103 ¥ March 2010 ¥ 142Ð183 Appendix 1. 2nd winters Caspian Yellow-legged HerringComments(OctÐApr)(Overall,the clean white head and body and the extensive grey in the mantle and wings make typical this age look older and more striking than typical second-winter Herring.However,this plumage pattern overlapswith .Despite the very arresting appearance ofsome birds,no single feature is diagnostic,soidentification should be based on multiple character traits.Strong contrastbetween pale greyinner webs andblackish outer webs,creating Venetian-blindeffect on some birdsLacks Venetian-blindpatternLacks Venetian-blindpattern Innerprimaries Venetian-blind patternnot present on all,but whenpresent it is a veryuseful featureNormally strikinglywhiteContrasting dark barsover whitish basecolourTypically rather dirty-looking,with muchbrown spotting UnderwingStriking white rumpand tail contrastingwith black tail bandAs Tail band thicker,browner and lessclean-cut;less contrastwith tail base and rump Rump andPattern ofdistinct from typicalHerring,but overlapswith In most,the scapularsare dominated byclean,grey feathers,with limited brown,but some retain morebrown/spottedVariable mixture ofgrey and brownfeathers,butpredominant tone isusually brownish.Often heavily markedwith brown bars.Small proportionshow extensive greysaddle Mantle andGenerally,the scapularpattern (coupled withcoverts and whitehead) makesthan Herrings ofthisDark brownNormally pale-lookingbut dark on someNormally pale butdark on sizeableproportion Eye colourA pale eye wouldsuggest that a bird is,but allthree species can showdark eyes at this age BB March 2010 editorial 18/2/10 15:10 Page 181 182 Gibbins British Birds103 ¥ March 2010 ¥ 142Ð183 Appendix 1. Older Caspian Yellow-legged HerringCommentsimmatures((3rd-/4th-winters)At this age several features need to be used in conjunction as individually they are ofonly limited value.No onefeature is appreciably more valuable than the others.Should show a thick(deeper than wide),unbroken,black bandon P5;many also haveAs May show a completebut rarely as deep as s.Black onP4 less frequent than Black band Birds ofthis agelacking a completeare unlikely to beMost have extensivesharp black streaks,contrasting withotherwise grey wingAs Streaks browner,diffuse and contrastmuch less with rest ofupperwing,which,argentatus,can retaina brownish tinge tothe grey PrimarycovertsUseful for separatingHerring from the other species,butoverlap betweenMany have patternthat mirrors adultÕs,with grey tongueseating into the blackwing-tip;others lackthis and so the wing-tip resembles that ofthe other two speciesLacks tongues and soappearance is ofanextensive and solidlyblack wing-tipLess extensive black,butargenteuslack tongues;argentatusshowtongues but these arenormally lesscontrasting than on PrimarytonguesThe presence oftongues eliminates,but otherfeatures needed to rule out argentatusA neutral,CommonGull L.canus grey,butoften looks moresilvery at this age andso can appear to havepaler upperparts thanAverages slightlydarker than:toneranging fromCommon Gull toKittiwake Rissatridactyla greyPaler in argenteus,buts sits withinthe range ofargentatus.Slight Upperpartgrey toneUseful for locatingargenteuscan be picked out inflocks bytheir subtly paler toneMost frequently haslarge mirror on P10and often a small oneNo mirror,or only aL.a.argentatusoverlaps withcachinnans; argenteustypically has smallermirrors PrimarymirrorsUseful only forseparating from Grey fleshNormally strongyellow tones,or atleast greeny-grey Leg colourLooks dark in the fieldNormally pale (greeny,yellow or greyish-white) but some retaindark eyesAs Eye colourOverlap means this isofno real value at thisage,but a very pale-eyed bird is unlikely to be Pale yellow,often witha weak greenish tinge;variable darkmark/smudge behindbill tipOften rather bright,especially in summer:yellowish with blackin gonys and somescarlet red.Othersduller and overlapwith other speciesPattern normallyintermediate,but canmatch either Billcolorationand patternOverlap complete,but typical has dull bill with darkgonys smudge BB March 2010 editorial 18/2/10 15:10 Page 182