A few different species in the trap last night.
I found this Southern Hawker dragonfly basking in my garden yesterday. It is a common species in Devon and on Dartmoor.
I found a Chinese Character moth in the trap last night. It is a small animal with a wing length of around 12mm and is a member of the Hook-tip family.
There is much debate around why this moth Cilix glaucata has its English name. There is an interesting thread here from a language website. The main theory suggests that if you look carefully at the large brown / grey spot in the middle of the wing you can see some very faint white lines / dots which make the shape |_|_| which is a Chinese character which according to Wikipedia means ‘mountain’. Another theory suggests the wing markings resemble a Chinese silk painting.
Take your pick on the English name derivation, the more amazing thing about this moth is why in evolutionary terms it is shaped and coloured as it is – it is mimicking a bird dropping – any predator that saw it would think twice about eating it!
The British Trust for Ornithology (BTO) has just published a paper in Nature Communications entitled “Population decline is linked to migration route in the Common Cuckoo”. Scientists at the BTO led by Chris Hewson have been using tiny satellite trackers attached to cuckoos so that they can plot their progress and routes. This is what part of the abstract of the paper stated
” ….by tracking 42 male Common Cuckoos from the rapidly declining UK population during 56 autumn migrations in 2011–14. Uniquely, the birds use two distinct routes to reach the same wintering grounds, allowing assessment of survival during migration independently of origin and destination. Mortality up to completion of the Sahara crossing (the major ecological barrier encountered in both routes) is higher for birds using the shorter route. The proportion of birds using this route strongly correlates with population decline across nine local breeding populations.”
This is a graphic from the recent BTO News magazine which summaries the findings regarding route choices. In essence UK cuckoos either use the eastern route through Italy / The Balkans or the western route through France / Spain when migrating south. Interestingly all birds use the western route to return to Britain. The research statistically proved that mortality of birds travelling south via the western route was significantly higher than for birds using the eastern route even though the western route is shorter.
The paper includes this graphic with the following caption ‘Cuckoo migration route use and breeding population change for each tagging location’.
From this we can see that 6 Dartmoor birds were tagged four used the eastern route and two used the western one (yellow/red pie charts). The undying pink / grey dots on the UK map show the change in abundance of cuckoo populations across the UK as measured by the BTO Atlas Projects in 1988–91 and 2007–11. Dark pink indicates a good increase and dark grey a big decrease (see the colour scale on the right side of the map above +0.75 = 75% increase in abundance and -0.75 = 75% decrease in abundance between the two survey periods. It is currently not clear why the western route is more hazardous – it might be land use change and drought in southern Spain – more research on this required.
The BTO team then correlated the route data with the abundance change data – this is shown in Supplementary Table 2 – I have turned that data into a little graph so it is easier to understand.
The axis which runs along the bottom of the graph shows the proportion of cuckoos using each route, 1 = all birds using the eastern route and 0 = all birds using the western route. The Dartmoor birds score 0.58 = 58% of Dartmoor cuckoos use the eastern route and 42% use the western route. The scale which runs up the graph shows the change in abundance of cuckoos between the two BTO Atlas survey projects. The Syke / Kintail population score 0.433 = a 43.3% increase. The Sherwood Forest population score – 0.465 = a decrease in abundance of 46.5%. The Dartmoor population is -0.242 = a decrease in abundance of 24.2%. The BTO work proves that there is a statistically significant correction between these two factors i.e. the proportion of birds using the western route strongly correlates with population decline across nine local breeding populations.
With the publication of the Devon Bird Atlas late last year we already knew that cuckoos in Devon were in big trouble.
The Devon Atlas does show a strong population still on Dartmoor but as I have argued before this population is also declining (see here). I produced a graphic which showed the changes on Dartmoor between the two survey periods.
Four 10 x 10km squares had increased numbers of tetrads (2x2km squares) where cuckoo bred, three showed no change but nine showed declines. Overall cuckoo bred in sixteen fewer tetrads in 2007-13 compared to 1977 to 85.
The data in the BTO paper ascribes the decline to 24.2% on Dartmoor using the BTO Atlas data (comparing 1968-72 with 2008-11). The paper also clearly shows that the 42% of Dartmoor cuckoos which migrate via the western route suffer a higher mortality rate than the 58% which use the eastern route which goes some way to explaining the decline.
However mortality rate on migration cannot be the whole story – it cannot explain the 75% decline in Devon. Away from Dartmoor and Exmoor the cuckoo is now virtually extinct in the county when 30 years ago it was common. The change in land use in lowland Devon is almost certainly the culprit here. I have written about this before – see here and have discussed the decline in the population of large hairy caterpillars which cuckoos are so fond of.
Fortunately further research is being conducted at Exeter University by Professor Charles Tyler and his team which includes Sara Zonneveld and Lowell Mills who are both conducting PhD research on this very topic. I am very much looking forward to hearing about what they have discovered. Their work along with the BTO’s migration work (and other relevant research from the RSPB) will I hope help us piece together what has happened to our cuckoos so that we might have a chance in the future to do something about it.
I was also pleased to see Devon Birds credited in the acknowledgements section of the BTO paper. I understand that Devon Birds provided funding to help acquire some of the satellite trackers.
There are a group of moths known as the Footman moths and last night I had four different species in my trap. All footman species have caterpillars which feed on lichens.
This is a Four-spotted Footman – this is the male (the female has two spots on each forewing). It is a large moth being around twice the size of other footman species – as a result it is unmistakable. Nationally this is a rare moth but there are strong colonies in Devon, Cornwall and the Isles of Scilly. It has the designation of National Scarce A which means it occurs as a breeding species in between 16-30 10 km squares. However it is also a known immigrant species so numbers can be bolstered by animals from the continent. Impossible to say whether this is a breeding species in my garden or an immigrant.
This is a Scarce Footman – a much more compact species which has the habit (which is the ID clincher) of appearing very thin as it rolls its wings around its abdomen. It is a local species but is more common than its name suggests.
Spent much of yesterday at Seaton Wetlands by the River Axe at a Devon Birds meeting. We did manage to get out and have a look around in the morning. I’ve never been there before but was impressed. A lot of money has been spent in recent years creating new habitats and putting in infrastructure (boardwalks and hides) for visitors. It is managed by East Devon District Council.
We also saw a Peregrine and heard a Whimbrel along with a Kingfisher. Well worth a visit.
I found a Mocha in my moth trap this morning. According to Waring, Townsend and Lexington in their Field Guide to Moths of Great Britain and Ireland it is a Nationally Scarce B moth – which means it is found in less than 100 10km squares in the UK.
Here is the distribution of the species via the National Biodiversity Network