En tråd her på "Netfugl" for nyligt omhandlede bestemmelse af Korsnæb. Her redegjorde Kim Frost på forespørgsel på glimrende vis for karakterer Stor og Lille korsnæb imellem.
I flugten kan man se yderligere karakterer, hvis fuglene set tilstrækkeligt godt. Denne fugl viser Stor korsnæbs store hoved, der medvirker til et jizz lidt ala Dværgpapegøje. Det store hoved går fra alle vinkler direkte over i kroppen, hvorved helhedsindtrykket bliver ovalt. Set nedefra virker hovedet så bredt som kroppen, samt noget afrundet, idet det brede næb næsten flyder sammen med hovedet.
Lille korsnlb er i flugten en mere "konventionel" finke, i formen tættere på Grønirisk med smallere hoved end krop. Næbbet, der er smallere, opfattes tydeligere som et vedhænd på hovedet.
Set fra siden går Stor Korsnæbs overnæb næsten direkte over i panden, Hos Lille Korsnæb er næbbet bedre afsat fra panden. Man opfatter tit Stor korsnæbs næs som ovalt - som et halvt æg stukket ind i kraniet på fuglen.
Et kendetegn, der blev anvendt i firserne var at Stor korsnæb generelt har mere lyst langs næbbets flige end Lille korsnæb. Kendetegnet anvendes vist ikke så voldsomt mere, men på denne fugl ser man en ret tydelig tendens.
Kommentar på engelsk på foresprøgsel fra Holland:
Note the large, parrot-like head with head and body appearing as an ellipse. The head apperas as broad as the body, creating a jizz as in a small parrot (lovebirds from East Africa).
In Common Crossbill, the head appears narrower than the body and the jizz thus is similar to Greenfinch. In Common, the bill appears narrower than and well seperated from the head.
Side view shows that the upper mandible and the forehead of Parrot creates a flattish outline, whereas in Common, the upper mandible is more well seperated from the rounder forehead. The bill is elliptic with deep. rounded lower mandible; side view shows that bill of Parrot appears squarish - in Common the lower mandible is flatter and the bill typically appears longer than broad.
Formerly, the larger amount of pale along the cutting edges in Parrot then in Common was regarded as a reliable character. There seems nowadays to be less focus on this character.
Som nævnt under tidligere foto: dette ikke for at spille smart, men en reaktion på forespørgsel fra Holland om en engelsk, ganske hjemmegjort og spontan reaktion.
Huh? The features of identification mentioned above does not (in my norwegian eyes) apply at all on this bird. Note the apparent long bill (in relation to height) and the weak bending of both the upper and lower mandible. Bright cutting edges can appear like this on CC's as well. There are large structural differences (geographical variation) in CC's. Some may superficially look like PC's.
This bird represent an individual with a rather small bill - compare it to photo from same day of a male, and ypu will see representatives of individual variation - the "weak-billed" bird, which appeared in the same flock as the large-billed matching bill shape, e.g. given by Svensson (1992) in the "ringing guide".
Falkenberg drwns notoce to "large geographical variation". It will be extremely interesting to see details here!
HBW gives slight geographical variation, with birds from southern range (Mediterranean inlands) having an in average very slightly larger billl than Northern European breeders. Neither Svensson (1992) mentions other than very slight geographical variation. So please clarify, if any details are known - this could prove of much use for field birders in the forthcoming winter.
Intraspecific differences in bill shape reflect food preferences of the various CC's. In North-America they state: "In general, small-billed Red Crossbills (N-American version of Common Crossbill) favour spruces and large-billed Red Crossbills favour pines." (Cornell - web). This is also valid in Europe and Asia (Newton 1972, Glutz und Bauer 1997, Dementiev 1970 and more…). At Turøy Bird Observatory (western Norway) we ringed and caught CC's some autumns. They were of course measured carefully. Despite only catching CC's, they showed what I'd like to call a huge variation in bill proportions. When collecting some birds out of the mist-nets we were pretty confident that they were Parrot Crossbills. ONLY the measurements gave us the specific answer; CC's.
KMO is correct when saying the Svensson's ID guide to European passerines states that there is only a slight variation in CC bill proportions. However, he has only included a few (three) ssp. from the Mediterranean in addition to the nominate curvirostra. Nothing is said about eastern birds. CC's are distributed from western Europe to eastern Asia, and in North-America. In Cramp and Perrins (BWP) some of the eastern birds included have measurements with larger bills than western. It is said in the same volume that Asian and American CC's vary more than European birds in bill size. No wonder, the geographical area covered is significantly smaller in Europe.
Glutz von Blotzheim (Handbuch der Vögel Mitteleuropas) mentions that the strength of the bill increases towards the south in Europe, related to the size of preferred cones. In addition the size of the bird decreases and the bending of the bill increases. The excellent Dementiev et. al. (Birds of the Soviet union 1970) list several CC ssp. with more powerful bills than the nominate, eg. mariae from the Crimean peninsula. This ssp. feeds on Cypress cones, which needs more powerful (bill-) tools to get entry to the seeds. From Cornell Lab of Ornithology: "The Red Crossbill shows a great deal of variation in bill shape and voice, and it may in fact be composed of several different species". I cannot see that there should be any different here in western Eurasia during migration when there obviously are birds from different populations present!
From the summary of Edelaar & Terpstra (2004) Ardea 92: 93-102: "The discovery of discrete vocal types of Common Crossbill in Western Europe opens the possibility that the nominate subspecies Loxia c. curvirostra in fact consists of a group of cryptic, vocally differentiated and reproductively isolated sibling species, reflecting a similar situation in North America. We compared measures of Common Crossbills collected at a single Dutch site by a single observer from 1983 to 2001. During 1983-84 – and to a lesser extent also in 1985-88 and 1992 – Common Crossbills had relatively long wings, low body masses, and deep but short bills compared to other years. Changes in methods or phenotypic flexibility of the measures do not explain these results. Biometric differences among years are likely linked to the proportional abundance of different populations of Common Crossbills at the catching site. A difference between years in the relationship between wing length and bill depth supports the idea that differences between populations are the result of selection, not neutral differentiation. These results are consistent with the variable presence of multiple, at times sympatrically occurring, cryptic species."
Thanks to Frode for his detailed comments. In theory, large-billed eastern populations of CC´s could occur here (as in the suspected eastern Common Bullfinches, during influxes, but I hope Frode agrees in, that the male in the photo taken from the same flock could hardly fall within the range of Common. I have another photo of the female, showing the bird from a slightly different angle - I shall immediately mail this photo to Netfugl.
Der er en (efterhånden ret gammel - 1996) hjemmeside, som mener at 6 "typer" (muligvis arter) kan skelnes indenfor de nordamerikanske små korsnæb:
Så vidt jeg husker, står der et eller andet sted på siden, at forskellene mellem nogle af af formerne er større end mellem store og små korsnæb.
Der mangler artsomtalen af Stor Korsnæb (nogen undersider er væk), så det citat findes ikke mere, tror jeg. Hans mening er dog formentlig stadig, som det ses af citatet nedenfor, at Lille Korsnæb bør opdeles i omkring 20 arter, hvoraf de 6 nordamerikanske kan ses og høres på hans side...
The "species" curvirostra is a grab bag of about 20 different forms, or subspecies. These forms vary more extensively in bill and body size than most other geographically variable "species" of birds. Some forms, such as ones on some Mediterranean islands, are almost as large as the parrot crossbill; others are far smaller, such as the North American Type 3 population and others in China, the Himalayas, and the Philippines. The underlying hypothesis used in this guide is that these forms are full species in their own right.
Tak til Jan for disse informationer!
De mange oplysninger om de forskellige former indenfor curvirostra-gruppen bør dog ikke forvirre den "menige" feltbisse, der herhjeme bør koncentrere energien om at kende Stor og Lille Korsnæb fra hinanden. Forskellene mellem de forskellige former er jo geografisk betinget over et meget stort område, og indenfor Europa kræver det gode observationsforhold overhovedet at kunne erkende forskellene.
Yderligere et billede af denne Store Korsnæb er lagt ud på Netfugl. Her ser man nok bedre undernæbbets meget buede form, der "fortykker" hovedet og skaber effekt af dobbelthage.
Tidligere ivrigt kommenteret fugl - billedet lige oven over (hvis du tager den fra artsoversigten) er i mine øjne meget mere klokkeklar - herværende fugl er af den noget langnæbbede type - som allerede bemærket.
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|Bemærk: at alle billeder har copyright og må ikke anvendes uden accept fra den respektive fotograf.|