August usually means one or other set of weather conditions: prolonged dry, hot spells or warm spells with weather fronts and associated strong winds and rain showers. This year it seems to be the latter, so welcome autumn 2017!
The last few days have seen wind directions move round with the weather fronts: now, we have slack winds and a southerly or south easterly wind system: mist and some fog, poor enough visibility. This has brought the Swallows down closer to the ground and even more are calling in the mist, just out sight. I certainly get the impression that the move south is on, or coming soon. Traditionally I think of the third week of September as a period of very large passage, with steady streams of birds coasting it in low, direct flight, with no deviation from this, no doubt to protect energy levels. Right now, birds are gathering on wires, twittering information amongst their kind, and taking short ‘test’ journeys and searching out safe communal roosts, away from the nest sites of summer, where home was a mud nest on an eave or a beam, concealed in and around farm buildings.
Swallows migrate by day and can break their journey, to drink or feed as they need; they often congregate in favoured coastal lakes and headlands before taking flight over open seas, using the shortest possible route away from safe coasts and timing their departure to coincide with a tail wind or ahead of a weather front. Regardless of how skilled they are as migrants; harsh weather can disorientate them and by contrast more desert like conditions will be endured at the African end of the long journey. Small wonder then that Swallows rear up to three broods of five young in a decent Irish summer: they need the numbers to cover all eventualities. The long journey south can take place over the period September to December, with the welcome in Southern Africa just as important in that hemisphere, Swallows, a harbinger of summer- twice in one year.