:: I do not understand from what did the problem. Some russian ethnographer could collect the russian song on territory of the Ukraine, Koshits collected ukrainian song on Kuban region. The phrase "Cossacks song" not quite exact. On Kuban veins not only Cossacks but also Inogorodnie (Иногородние), which Сossacks were not. Besides Cossack song were and on Ukrainian and in Russian. We do not know collected Koshits song in Russian. No no sources about this. The phrase "collecting Ukrainian songs in Kuban region" to my mind - more exact.