Saturday 18 October 2014

Week 39: Eyes on the Sky & Caddisfly

View NW from Barnfield, over the SW end of Dellfield towards Ryders

"Good morning, Eeyore," said Pooh.
"Good morning, Pooh Bear," said Eeyore gloomily. "If it is a good morning, which I doubt," said he.
"Why, what's the matter?"
"Nothing, Pooh Bear, nothing. We can't all, and some of us don't. That's all there is to it."
"Can't all what?" said Pooh, rubbing his nose.
"Gaiety. Song-and-dance. Here we go round the mulberry bush."
Winnie the Pooh by A. A. Milne 

It has been a week of grey gloom to rival anything lovely Eeyore might mutter. I confess I’ve not been immune to the dampening of spirits as the rain and low cloud have arrived, lingered and made themselves at home. However, it is Autumn migration and that really can be exciting, no matter how grey a day it is. On Wednesday morning, I plodded up to Westbrook Hay. The previous evening, there had been a report of a spectacular nocturnal migration of Thrushes over Berkhamsted, involving hundreds, if not thousands of Redwing and Song Thrushes, all heading south for the winter. I wasn’t quite sure what to expect at 10 o’clock in the morning, 2.5 hours after dawn, but you never know.

On arriving at Dellfield, I spotted at least 7 Mistle Thrushes with a couple of Redwing and Green Woodpeckers amongst them. All making the most of the damp earth and the worms which had been forced closer to the surface to avoid drowning. There were also some 20 Magpies and a small group of 12 Woodpigeons feeding on the meadow. All but the Redwing are resident birds.

With my eyes and ears well and truly open to the possibility of migrants, I made my way up through Dellfield, through Barnfield and on to Bovingdon Reach. I think I was still on Dellfield when the first flock of c100 Thrushes came over, heading northwest. Unusually, they were silent. I was expecting to hear the seeping of Redwing or the chacking of Fieldfare but I heard neither.


Over the course of more than an hour at Westbrook Hay, I recorded the following flyovers:

Part of one of the flocks of Redwing over Dellfield. 59 birds counted.
Quite possibly the worst photograph to appear on my blog
400+ Redwing over in groups of 60-100+. Mostly heading west/northwest. I suspect this is a very conservative count and I underestimated the size of the flocks.
3+ Meadow Pipits (heard)
2+ Skylark (heard)
8+ Chaffinch
150+ Starlings
2 Pied Wagtail (heard)
1 Swallow over north. I do hope he turned around at some point!

Other resident species noted
21+ Goldfinch
45+ Woodpigeon
70+ Starlings
8 Green Woodpeckers (they were surprisingly visible due to the damp earth and the availability of food).

Although the weather was dank, dark and grey, it was an exciting morning, with swathe after swathe of birds moving through. It was lovely to hear the Skylarks and Meadow Pipits flying over too. These are species which are mostly absent from Box Moor Trust land, something which I think the Trust hope to address. However, Meadow Pipits have been moving through on migration over the last couple of weeks (I heard them regularly whilst I was filming the Stonechat) and I enjoyed their chirpy presence albeit temporary.

Thursday, I managed a short visit to the Brickworks. It was a morning of countless Hornets, a Red Admiral, a Comma and at least 6 singing Robins setting up winter territories all within a small area.

Finally, on Friday, I followed up on Dan’s sighting of 5 Siskins at the Gadespring Cress Beds. The site isn’t open to the public but it is Trust land and I just wondered if the birds had stayed in the area. Unfortunately, the answer was no but I did walk into a mass emergence of Caddisflies, specifically Limnephilus lunatus. Its name, “lunatus”, derives from the Latin for half-moon-shaped and refers to the crescent on the rear edge of the wing.

    Caddisfly (Limnephilus lunatus)
    Caddisfly (Limnephilus lunatus)

This is an order of insects, Trichoptera, I’d not really looked into before. They are closely related to moths and butterflies, Lepidoptera, but instead of scales (Lepido) on their wings they have hairs, hence Tricho = hair and Pteron = wing. There are approximately 7000 known species of caddisfly, nearly 200 of which occur in the UK.

Much like the Craneflies, they go through a yearly life-cycle, with the adults only lasting 1-2 weeks and, within that time, they live to breed and lay eggs (it’s another species which rarely eats as an adult). The eggs are laid in a water body, in this case, the cress beds at Gadespring and within a few days the young larvae hatch. These go on to form protective casings around themselves, in Limnephilus lunatus this is constructed from plant materials, with their head and thorax protruding from the end so that they can feed.

When the time comes to pupate, the larva attaches its casing to a solid object in the water and closes up both ends for further protection. Within a few weeks, having munched its way out of the cocoon, the adult emerges.

Although Caddisfly can exist in poor quality waterbodies their presence in abundance is generally a good indicator of clean, unpolluted water. I’d say the latter applies to Gadespring. They are also a great source of food for other animals. “Freshwater fish, particularly trout, and eels feed on larvae and swimming pupae. Trout, birds, lizards, frogs, spiders, dragonflies, and bats feed on adults.” (Britannica)

Last year, I visited Thetford in Norfolk to see the Black-bellied Dipper, a rare visitor from the continent which had overwintered on the river Thet. Its primary food source was caddisfly larvae. It would routinely fish out a beak full of leaves (aka a caddisfly casing) and proceed to bash it apart to reveal the larva within. It was fascinating to watch and it demonstrates wonderfully the importance of clean water streams and rivers, and the creatures they support.
    Phase 1: Fish out the leaf casings
    Phase 2: Bash leaves apart

    Phase 3: Larva peaking out of leaf casing ready to be extracted
    Phase 4: Eat larva within

It’s a shame we don’t get Dippers around Hemel!

I should round things off with arguably the most gloomy, Eeyore inspired Oak photograph this year.


Martin Parr said...

An excellent blog, as ever, made me laugh! This could be a regular column in a Newspaper, I'm sure it would be a big winner!

Lucy @ A Natural Interlude said...

I suspect it was A A Milne that made you chuckle but I'll take all the help I can get ;o). Thanks Martin.