[Syrian refugee dives off an overcrowded dinghy whille approaching a beach on the Greek island of Lesbos, after crossing part of the Aegean Sea from Turkey]ANKARA (Reuters) - The number of migrants and refugees crossing the Aegean Sea from Turkey into Europe is falling significantly, as collective efforts are making a difference in the migrant crisis, NATO General Secretary Jens Stoltenberg said on Thursday. At a joint news conference with Turkey's foreign minister in the capital Ankara, Stoltenberg also said that authorities must remain flexible as human smugglers can change their routes. (Reporting by Dasha Afanasieva and Tulay Karadeniz; Writing by David Dolan; Editing Humeyra Pamuk)