Treecreepers!

Walking to the IFW for some afternoon studying, and moreover to check on a running experiment, I passed a patch of thin deciduous trees when a thin, high-pitched, ethereal trill sounded; it was 2 Eurasian Treecreepers. Actually I didn't have my bins on me (naughty as usual), not expecting to come across much interesting I guess, and there would not have been any chance to distinguish by naked eye which specie of treecreeper it was, if it hadn't called. I am learning the songs slowly through xeno-canto, an excellent, fastly growing birder-shared database of uploaded bird vocalizations (it would be nice though to have a "Stokes Guide to European Bird Songs!").
By the way, Short-toed Treecreeper must take the award for the "Bird named for the Most Discrete Field Marking"! According to Birds of Europe (2nd ed. Svensson, Mullarney, Zetterstroem), the Short-toed is more likely at lower elevations (range map does show extensive coverage over most of continental Europe, except the tallest areas such as the Alps and Transylvania.) and often is found in parks and gardens in towns...but I am quite sure it sounded more like the plain (eurasian) Treecreeper. Well, it also is winter so they are all over searching for food! I will however have my bins on me tomorrow on the way to work, in case I have another chance to observe them, at which time I will check plumage details (pattern of wing-bar edges on folded wing, the presence of spots on the primary tips, relative bill length, etc...but toe length will be last for sure!) for a confirmation of my hypothesis. Good birding all! And let this be a lesson: don't ever leave home without some decent optics on your person :)