De reactie van Ivan die Andrew Dixon gevraagd heeft te reageren:
There is no precise definition of a calidus. It is a concept based on the frequency of a specific combination of plumage characters in the breeding birds of a particular geographical area. The difference in appearance between peregrinus and calidus is very slight. calidus birds are characterised by light cheeks, narrow moustachial stripes, paler blue grey backs, lighter breasts, pale forehead patch and large size. Birds that possess most/all of these characters are found at higher frequency in breeding populations in Arctic Eurasia from the White Sea to Kolyma (though data on proportions of different plumage types in each region of this huge region are not actually available – so this is a necessarily vague definition). Birds breeding in Yamal/Taimyr can be indistinguishable in appearance from nominate peregrinus. The converse is also true – birds breeding in UK, France and Netherlands can have characteristics that best fit those described for the calidussubspecies.
Subspecific definition of the population and individuals breeding on Kolguev is pretty meaningless. Birds breeding on Kolguev are likely to show characteristics that match both nominate peregrinus and calidus – the island is west of the core area where calidus plumage types predominate and east of the core area whereperegrinus plumage types predominate.
There is no such thing as a genetic test for calidus. As calidus is not defined as a distinct genetic entity. It is just a plumage type that is more frequently found in a specific geographical area.
We can identify population structuring in Arctic Eurasian Peregrines, indicating limits to longitudinal gene flow and regional adaptation. But these genetic differences do not necessarily map on to the classical subspecies geographical distributions. Peregrines from Kola and Yamal are genetically distinct. In this case, Peregrines breeding in Kola are mainly peregrinus type and in Yamal they are mainly calidus type.
Vanochtend om 8:50h is in Nederland net ten noorden van Groenlo een tweede op Kolgoejev gezenderde Slechtvalk gepeild: 52.04912333, 6.59728833 .
Misschien lijkt die meer op een Calidus -mocht dat een ondersoort zijn.