EARLY SPRING WEEKS
Sadly, in 2017 the charter companies stopped offering flights/package holidays to the island for the main birding weeks in April and first week of May. Many hotels are still open during this period and you can reach the island by flying via Athens (reached from many UK and western European airports). I strongly recommend you come out during the top weeks (last week of April and first week of May). Leaving it until later in May when the charter companies start flying means you are missing the best birding weeks Lesvos offers.
PLEASE NOTE that I am not a travel agent, or an agent for any of the charter companies, so I cannot answer queries specifically about their package holidays or flights. Please contact them directly.