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Tuesday, 15 November 2016

Murmuration by moonlight

Monday 14 November 2016

Wheeling flocks of hundreds of starlings over the Exe reed beds as the supermoon rose gleaming over the horizon ... is what we should have seen. Instead we were victims of meteorology. Over 30 of us stood in the dank gloom between the sewage works and the roar of the motorway, under a duvet of smothering cloud, looking at nothing.

We knew wildlife frequently fails to read the text books, or event programmes, but, we thought, at least there would be the incidental astronomy of the biggest supermoon of the century, the largest for 70 years, to view. No chance; not even the bright pinpoint of Venus could pierce the ambient fug.

So, no murmuration, and no moon either. Starlings have declined significantly, by some 80% over recent years*, but that wasn’t necessarily the reason for their absence from the Exe reed beds this evening. Flocks regularly re-locate their roosts from place to place, perhaps pursuing good feeding grounds or communal warmth, or to reduce individual risk from predators, three of the explanations postulated for flocks to converge, and the resulting murmuration displays**.  

Before the start time, a small group of 20-30 starlings was seen heading over Riverside Valley Park towards the city centre. Murmurations needn’t be a coastal or rural phenomena, and a University of Gloucestershire and Royal Society of Biology survey study over 2014-15*** received murmuration records from urban Manchester, Belfast, Edinburgh, Glasgow, Belfast and Port Talbot, not just Brighton pier. They have certainly been seen over the Exe reed beds from the Old Sludge Beds nature reserve and from Topsham. Just not on 14 November 2016.

Although missing during the organised event, the starling murmuration season continues all through winter, with flocks progressively increasing in size as birds arrive from the Continent, so there should be other chances for an independent trip to the site to view the spectacle near Exeter. Autumn dusk can be an interesting atmospheric time in any case: snipe and redwing were calling, and we saw and heard common and green sandpiper, plus a bolt of blue kingfisher; ranks of cormorants warmed their feet on the high tension power lines; gulls and corvids rotated above, perhaps tracking an insect swarm, or a thermal generated by the motorway, or both. A late pipistrelle bat flitted briefly overhead.

And, despite being denied the opportunity to witness the supermoon in full refulgent glory, there will be a nearly complete moon for the next couple of evenings, for a ‘slightly not quite so super’ moon. Supermoons are not so uncommon: each full moon at perigee on its elliptical orbit around, and when closest to, the Earth, gives the supermoon effect. The 14 November event was special because the moon was exceptionally close: at 221,524 km distance, compared to more typical 356,400 km****, and with the moon rising within hours of becoming full at 1.52pm, this was a kind of extra enhanced supermoon, not recurring for 18 years.     

Many thanks to all those who joined us and persevered through the event. Because the wildlife didn't share the same level of commitment, I couldn't bring myself to take a photo, but here's the poster, as a memento of what could have been, with Dawn Monrose's great picture of the elusive avifauna. Maybe we'll try again for the next extra-supermoon on 25 November 2034. 

References and sources
*      RSPB website
**    Andrew J King & David JT Sumpter 2012 Quick Guides Murmurations Current Biology 22 (4): pR112–R114 open access
***   University of Gloucestershire and Royal Society of Biology study, led by Dr Anne Goodenough 
**** Peter Grego 2010 Philip’s Moon Observer’s Guide revised ed. Octopus Publishing / Philip’s, London; SNAPPA science website

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