Tuesday, 29 September 2015

In for the count

Chris Durdin, NWT Thorpe Marshes

Three of us who visit NWT Thorpe Marshes regularly have been making a point of counting orange-tip butterflies and Norfolk hawker dragonflies.

The idea is to do simple, repeatable ‘transects’, with a view to finding out how these species are doing from year to year. Orange-tips and Norfolk hawkers were chosen as they are key marshland species while also being fairly easy to see, identify and count. We noted what was seen on various sections of the regular circuit around the marshes, alongside simple weather data.

Orange-tip butterfly, photo by Chris Durdin
Orange-tips, though they also come into gardens, link strongly with the grazed marshes at Thorpe as that’s where a favourite larval food plant grows, namely lady’s smock – also known as cuckoo flower or milk maid. The time for orange-tip surveys was April and May, with the highest count on five survey visits being 17 on 11 May. Of course weather and when, as volunteers, we are free to visit both play a part in results. From past experience we can expect to see many more orange-tips if a visit is made on a warm day in late April.

Norfolk hawker dragonfly, photo by Chris Durdin
Norfolk hawker dragonflies are a good indicator of the quality of the wetland’s ditch system, and June and July are the key months. Derek Longe saw 39 Norfolk hawkers on 24 June, but that was topped by Susan Weeks who recorded no less than 46 on 30 June, the peak count from 12 survey visits. That’s a reminder of what a fine place Thorpe Marshes is to see dragonfly that is the emblem of the Broads Society, all the more surprising on the edge of suburban Norwich.

These survey results on their own are little more than snapshots of the nature reserve, we know, but we hope that patterns will begin to show if we can build a data set over a few years.

Chris Durdin leads monthly wildlife walks at NWT Thorpe Marshes. Details of monthly walks on http://www.honeyguide.co.uk/thorpemarshes.htm

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