With the news of two male Two-barred Crossbills being seen on Whalsay yesterday Brydon hatched the plan of us spending the day scouring Unst for more. The result was our complete failure to find any at all despite searching the regular haunts of the recent trio. The only Crossbills that we encountered were two male Common Crossbills and the comparison of resultant sonograms of their flight calls with Magnus Robb's Dutch Birding paper here reveal them to be of the vocal type 'Glip' Common Crossbills.
Male 'Glip' Common Crossbill at Ungirsta
Sonogram of flight call of 'Glip' Common Crossbill (type C)