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Message: <blockquote data-quote="RoyW" data-source="post: 1939380" data-attributes="member: 71737">There are some interesting views raised in this thread, and in the links that have been posted. It is certainly an area that warrants further study in all species mentioned, but particularly in Crossbills where there may be sympatric speciation taking place. As to whether or not there are currently more species of Crossbill that should be recognised (or perhaps less species), it is obviously possible to argue the point from both sides. IMO a lot more needs to be known before we can really come to any conclusions about whether Crossbills of different call types & bill sizes really recognise each other as different species. If call types are the only way we can really tell them apart (because of overlap in measurements etc - regardless of whether the measurements are statistically different), and call types can be changed (eg. breeding pairs matching calls), then how can we know that there is not much mixing?If bill size affects the food that each bird can most easily feed on, it is not surprising that birds with similar bill sizes are found feeding, and breeding, in the same areas/times of year. Birds with different bill sizes may choose to breed at other times simply because they breed when food availability is at it's best (dependent on the type of trees present). Of course, those who support the idea that there are several 'cryptic' species that we can't readily tell apart may well be correct - they just haven't proved their case yet!Personally I don't feel that birders have to be able to tell two birds apart for them to be valid species (as has been said, it's whether the birds themselves consider themselves sufficiently different that matters - but if the birds can 'switch', or choose different partners in different circumstances, then they are not different species).</blockquote>

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