Another Trend Test

Since the first article was recieved with interest, I thought I'd quickly try a slightly different tack on a different species. Dusky Thorn was the one hailed in the State of Britain's Larger Moths as showing the greatest decline of all species, so I thought I'd see if my rudimentary stats would show something up. So below we have two graphs. The first is in line with what I'd done for the Heart and Dart & Large Yellow Underwing, in that it is the number of individuals weighted against 'Trap Nights'.

It is now know that this is a species with large peaks and troughs in it's abundance, and it certainly had a few good years as soon as the report was published. It did occur to me that my method would come unstuck if a lot of recording additional effort was put in at times of year when the given species was not on the wing - so more people taking part in the Winter Garden Moth Scheme would cause a drop in the averages of summer species, so I tried this:

And this shows the average catch across the various years - so recording effort is taken into account, but only when the moth is trapped.Interesting that the huge peak of 2009 in the previous chart has been levelled out. Essentially it was well recorded in 2009 compared to total recording effort, but the average catches were, well, average I suppose! 2011 looks like it was a poor year for this common garden species, but I've not yet got all the 2012 data in so can't say whether that is a trend or a blip.

Cwmbach, Last Night

With a mild night forecast, I decided to run my 22w actinic garden trap overnight. It was damp and drizzly, with a minimum temperature of 10.40 C, but there was also a fresh Southerly breeze blowing, so I didn't know what to expect this morning, though a few moths on the top of the trap were a good sign.
In all I had twenty three moths of twelve species, including a December Moth. which I'm always pleased to get.

December Moth

The full list is:

Epiphyas Postvittana x 2
December Moth x 1
Red-green Carpet x 2
Common Marbled Carpet x 1
Spruce Carpet x 6
Epirrita agg x 2
Feathered Thorn x 3
Blair's Shoulder-knot x 1
Red-line Quaker x 1
Yellow-line Quaker x 1
Flounced Chestnut x 1
Silver Y x 2

Cwmbach Winter GMS: Week 1

It rained for most of the night and then became cool and foggy, so I wasn't surprised to get only four moths of three species, one of which- Red-green Carpet- doesn't for some reason count for the WGMS.

Red-green Carpet x 1
Turnip Moth x 1 (Same individual as I had yesterday)
Angle Shades x 2

It's so easy to take the common species for granted and certainly in the summer, I rarely get the chance to really LOOK at the moths, so it was nice, today to have the time to really appreciate just what a stunning moth the Angle Shades is!

Unseasonal Hofmannophila - Llandaff North

Just potted a Brown House Moth from a lighted window. This appears to be the latest Glamorgan record and the first November record on the GMRG database.

Species Trends

Whilst waiting for a database to update this afternoon I wondered how easy it would be to get a quick assessment of how a common species had faired over the past few years given the GMRG dataset. This first chart simply shows the number of records per year for Heart & Dart and Large Yellow Underwing over the past 22 years.

But of course that doesn't take into account recording effort - there was a lot more trapping done in the mid naughties, so this one takes into account the number of 'trap nights' in each year.

I'm no statistician, but it looks to me as thought the pre 1995 data should be excluded from any further analysis (which makes some sense in terms of GMRG's formation etc), but also that Large Yellow Underwing is being recorded as frequently now as ever. Perhaps more useful are the next two, which show the number of individual moths, weighted against trapping effort.

Garden trap 8th Nov

Only 3 moths in the garden last night, in spite of being mild.

Acleris schalleriana

1 Red-green Carpet and 2 Acleris schalleriana I believe, judging mainly by the elongated costal blotch. Anybody agree?

Wednesday night in woodland for a few hours was better; still 10.5 degrees at 11pm
Epirrita sp.               20
Chestnut                   2
Merveille du Jour     2
December Moth       1
Feathered Thorn       6
Acleris sparsana       2
Common Marbled Carpet   2
Mottled Umber         1

Cwmbach, Last Night

I ran my garden trap through the mild (7.00C), damp night and recorded seven moths of four species. As the minimum temperature was over a degree warmer than the 6th, I'd expected more, but it only goes to illustrate the unpredictable nature of things, particularly at this time of year.

The list is as follows:

Epiphyas postvittana x 1
Red-green Carpet x 3
Spruce Carpet x 2
Turnip Moth x 1

Turnip Moth