Vanessa at night - migrations

Eddie John eddie at grayling.dircon.co.uk
Sun Feb 3 13:20:58 EST 2002


Hello all

I have recently joined this group and have followed the 'night-flying' discussion since Nick Greatorex-Davies reported my comments to the group on 23 Jan.  

Patrick Foley's question is timely, as I had prepared the following just before his posting, so I feel even more justified in sending it!

I apologise in advance if I have missed the point of the current discussion, but may I ask if there are those who question the possibility of night-time migratory flights?  For example, do they accept the ability of V. cardui to cross large stretches of open water i.e. distances that require at least part of the migration to be undertaken at night?  Or is the current discussion only concerned with 'resident' species with a predilection to fall from roosts, or otherwise be disturbed at night?!

My paper, referred to by Nick G-D, published in the Entomologist's Record (Vol 113 Pages 269:282, Nov/Dec 2001) describes a migration of many millions of cardui across Cyprus last year.  Numbers were crudely estimated at 48 million over a front of about 200km and the peak of the migration lasted for about four days/nights.   To help paint a clearer picture, Cyprus is the most easterly of the Mediterranean islands, about 70km from Turkey to the north, 105k from Syria to the east and 340km from Israel to the south-east.  Regular migrations of V. cardui occur across Cyprus but last year's was spectacular for the numbers involved.  My paper details over 50 one-minute counts of migrating cardui, by several recorders, at different points on the island. Yes, all these were during the day, but most were early morning, starting at 07.40hours.  

Given the direction of flight (north-westwards), the climatological factors required to produce the flush of larval host plant necessary to produce a mass migration, and the fact that a north-westerly migration of cardui was noted in Israel between 12 -20 March, the likely source of the Cyprus migration was this same migration which originated in the Negev region of Israel (Ref: D. Benyamini, 'The process of migration build-up of V. cardui in Spring 2001 in Israel', News of the Israeli Lepid. Soc. 18(1): 20-21.).  (The extent of the front was also, independently, estimated by D. Benyamini at 200km). 

Now, to the question of night flight.  Large numbers of incoming cardui were seen, in full migratory flight, heading northwards from the south coast of Cyprus from early in the morning, on several successive mornings.  There had been NO build up of numbers on any of the previous evenings, so they had not already arrived in daylight hours the previous evening - the bulk of the migration for that day having already passed through. The bearing, as I have mentioned, indicates Israel as the source - some 340km away.  Dawn, in Cyprus towards the end of March, would have occurred about an hour or two (I'm checking exact sunrise times) before the first of the timed migrant sightings, so, for there NOT to have been any flight during the hours of darkness would have required the migrants to cover 340km in an impossibly short time!!

Another, non-anecdotal, reference: 'European migrations of the Painted Lady vary enormously in their size and flight-paths.  In many years, vast numbers are seen streaming north across the Mediterranean, flying by day or night, flitting with their wings powerfully and then gliding, so they can rest on the wing.' (Jeremy Thomas and Richard Lewington, The Butterflies of Britain and Ireland, London, 1991).

Eddie John
Eddie at grayling.dircon.co.uk
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