The last week or so has seen the arrival of quite a few Comma butterflies at the reserve. These are the autumn generation and are looking very fresh, (see featured image, taken October 1st 2016 ) leading you to believe they have not been around long.
The life cycle of these butterflies is quite interesting: they emerge from hibernation in March giving rise to a summer generation, which can breed rapidly, leading to an autumn generation usually around September. At the Gravel Pits, however, the autumn generation has only been noticeable the last few weeks which may be typical for more northerly regions. Looking at butterfly records for previous years, the autumn generation also seems to be the more abundant of the two, with considerably more sighted than in the summer months. If you take a trip down the reserve, in the next few weeks, keep your eyes peeled when passing many of our bramble bushes.
It has been a disappointing year for butterflies so far, but there have been a few encouraging signs. Despite their low numbers, a male and female Large skipper were seen on the South Lawn on 18th June and a Common blue (see featured image) was found by Phil Reed on 19th June. There used to be a healthy colony of Common blues at the Gravel Pits, so this was particularly pleasing, after one was spotted last year.
Both the Gravel Pits and Sun Lane had established colonies but both seemed to die out quite suddenly. Birdsfoot trefoil (often known as ‘eggs and bacon’) is their foodplant and their absence was made doubly disappointing since Sun Lane has had this in abundance in recent years. The Gravel Pits can’t boast the same quantities, but there are now several good patches.
After a bit of exploring a small colony of Common blue was discovered just over the road from the Gravel Pits and, last year, one individual was spotted on the South lawn on several occasions – a small nick in its wings making it identifiable as the same butterfly. So if you visit either of the reserves any sightings will be gratefully received since the hope is they will re-establish themselves again.
Thank you to all those that came to the walk tonight. The weather was kind to us and there was even a bit of sun at one stage. We hope everyone enjoyed the orchids. It was good to have some extra eyes to spot things we often miss. One example was a Snout moth (see featured image) – a nice find by one of our party. It looks like we have Common Spotted orchids as well.
2016 has to be one of the best years for orchids at the Gravel Pits for a very long time. Quite what the count is is hard to determine since there are that many (see the featured image for just one example). They are largely on the South Lawn but there are also a few on the North Lawn which is encouraging. Most look to be Southern Marsh Orchids although some are likely to be hybrids.
The Gravel Pits is a good place to spot some of the less common ducks. The featured image shows a male Goosander preening itself ,next to an Oyster catcher, the far side of the river. Some of the lagoons attract other species such as this pair of Tufted ducks, seen this afternoon. They are slightly smaller than than a mallard and their distinctive yellows eyes can be seen in the photo on the right. The male is all black apart from white flanks and the female is brown with paler flanks. They are thought to feed on a mixture of plant matter, molluscs and insects.
Whilst not technically on the Nature Reserve, an estimated 40+ Broad-leaved Helleborine orchids have sprung up at the Gravel Pits. The featured image shows just how well they blend in with the greenery. See below for a close-up.
This is an interesting question. On recent visits to the reserve, the same Common Blue butterfly has been sighted on numerous occasions, usually in the same spot. We are pretty sure it is the same butterfly as it has a nick in it’s wings at a specific place and it seems to have been there for the best part of a month. One of the methods of determining the longevity of butterflies is the ‘Mark-Release-Recapture’ technique; butterflies captured in a net and given a unique number by a series of dots that are added to their underwings using paint or a special type of marker pen (see the featured image: 1-2-4-7 marking system; Ehrlich and Davidson, 1960). Like the nick in the wings of our Common Blue, it gives you a way of identifying an individual and if enough are marked it is possible to build up sufficient information to create an estimate of longevity. If the same individual is recaptured at a later date the days that have elapsed between it’s marking date and the last capture date can be recorded. This technique can also be used for studying dispersal of butterflies (their flight characteristics).
On studying a colony of Silver Studded Blue butterflies in North Wales the longest period between first and last captures I found was 26 days, for a female. The average period between first and last captures was just over 3 days. Maybe one day we will be able to fit tiny tracking devices to butterflies but for the moment this is still a commonly used technique. How longevity varies between species is another question, but our Common Blue is still there after a month and it is looking in surprisingly good condition!
After our work party, on the 11th July, we were wondering whether the White Letter Hairtreaks had emerged yet, but the following day confirmed they are back in good numbers. They still seem to like to sit on the Creeping Thistles, down near the drainage ditch (near the bench), but have also been sighted near the other end of the site, quite close to the entrance at times. As well as Creeping Thistle, they have been spotted sitting on Ragwort and nettles. An elm tree, by the metal gate, seems to be the food plant of the larvae, on the first lawn.
We have noticed what we thought was Common Birdsfoot Trefoil (Lotus corniculatus) at the site and were hoping this could spark a resurgence of Common Blue butterflies. On a recent visit by the Bradford botany group, the Common Blue in this picture was actually found on Meadow Vetchling (Lathyrus pratensis), also known as Meadow Pea. Other plants, used by the Common Blue include: Greater Bird’s-foot-trefoil (L. pedunculatus), Black Medick (Medicago lupulina), Common Restharrow (Ononis repens), White Clover (Trifolium repens) and Lesser Trefoil (T. dubium). We are hoping to receive a species list from the botanist’s visit so hopefully this will give us some more information.