Tricky Zygodons! Or are they?

Last Sunday I was able to attend a field trip of the South-East branch of the British Bryological Society, to Duddleswell Valley nestled in the expanse of Ashdown Forest. The key site in this valley is a wooded ghyll, which has been a very popular location for bryologists since at least when the brilliant botanist Francis Rose visited in the mid-1950s.

Once we had waded our way through no less than eight different species of Sphagnum mosses we arrived at this famous ghyll and what greeted us was a steep and slippery slope down to the stream below us. Luckily we all made it down safely and we were able to begin!

We worked our way slowly down the ghyll, finding extreme rarities such as Campylostelium saxicola; admiring huge walls of fruiting Pellia epiphylla and finding ourselves knee-deep in shallow-looking mud. I even managed to put my foot in the middle of the largest colony of Nardia compressa in South-East England!

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A large part of the only colony of Nardia compressa in the South-East

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Nardia compressa

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Campylostelium saxicola

Near the end of our excellent and bryophyte-rich walk we came across a good stand of willow trees with many species that we hadn’t yet encountered that day. These species included a small, inconspicuous tuft of moss, a Zygodon species. There are four regularly occurring Zygodon species in the South-East and they are hard to separate in the field. To be certain of an identification to species level you really need to get out the microscope.

Therefore I took a small part of the moss back with me to work on. I was expecting it to be a tricky task that might take me a while to perfect. What surprised me was that it was quite the opposite!

The features to look at are the gemmae. The gemmae of Zygodons are single cells that detach from the moss in order to reproduce asexually, meaning that the fusion of male and female sex-cells (gametes) is not necessary. When mosses and other organisms reproduce asexually like this it is referred to as fragmentation.

Not knowing how to get the gemmae off the moss and onto the microscope slide to examine, I first tried taking a small stem of the moss and seeing if I could spot any gemmae around it. This was unsuccessful and so for my second attempt I simply tapped the clump of moss onto the slide, added a drop of water and a cover slip. I placed this slide under the microscope and I could immediately see several gemmae under 100x and 400x magnification. That was much easier than I had expected!

Next came the actual identification of the Zygodon. The very helpful Brad Scott had narrowed my moss down to two species, Z. conoideus and Z. viridissimus. He also supplied photos of the gemmae of both conoideus and viridissimus, so all I needed to do was compare the gemmae of my moss with Brad’s excellent photos. It was clear: my moss was definitely Zygodon conoideus!

This experience has certainly shown me that not everything that needs microscopic examination is difficult. Certainly some species require very fiddly work to separate but that is not always the case.

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My photo of a gemma of Zygodon conoideus

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Twit.

Yesterday I found myself lying down on an edge of a crater-sized hole by the side of the River Cuckmere, with my binoculars pointing down at a tiny, drab, little brown job scurrying about amongst dead grass and plant matter. Streaked brown all over, it resembled a small mouse creeping about feeding on minuscule seeds. The only bit of colour on the whole bird was its tiny yellow bill which would open occasionally to emit its single-noted ‘twit’ call from which the bird’s name ‘Twite’ derives.

Twite are usually gregarious birds in winter, feeding among plants along the coast before returning in Spring to their breeding grounds in the moorland. They are most commonly found between October-March on the east coast of England, where British breeding birds meet continental birds in saltmarshes and other coastal habitats. They are only rarely encountered South of Suffolk nowadays despite there  having been a regular wintering population on the Swale in North Kent in the past. They are therefore real rarities in south coast counties such as Sussex and they have appeared to be declining too.

Before the 1990s, double-figure counts were annual phenomena. However between 1990 and 2000 they were only rare occurrences. Now they have declined so much in Sussex that the last record on the Sussex Ornithological Society’s sightings page prior to 2017 was of a single bird with Linnets at Pagham in November 2013.

This particular Twite was first discovered in a patch of brambles along the River Cuckmere, East Sussex on the 5th of February. I was expecting it to be only a short-staying bird and that it would disappear soon. However it was seen regularly until the 15th February. For a period of 5 days after that it was looking like it had left with no news reported on the Sussex Ornithological Society’s sightings page.

Fine weather in Sussex allowed us to visit the Seven Sisters Country Park, and I took the opportunity of making a short walk to the coast through the marshlands of the Cuckmere river delta with no prior thought of seeing the Twite.

However the route we took happened to pass the site where the bird had been frequenting. Only about 30 seconds after arriving at the crater-like hole in the riverbank where the bird had been seen previously, I noticed a tiny bird fly up to perch on a large unidentified object which could have been a large piece of Styrofoam packaging. It proceeded to drink from a hole in the odd object while I managed to get good views of the bird through my binoculars. Small size; brown, streaky appearance; yellow bill… it had to be the Twite!

After allowing me to get some photos of it in the open it flew back down into the dead plant matter and continued to feed only 5-10 metres away from me. Despite its amazingly effective camouflage I was able to watch the bird well for quite a long time. It appeared to be oblivious to my presence and wasn’t wary at all, which surprised me for such a small and vulnerable finch. It felt like a great privilege to be able to get such close views of this Sussex rarity.

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Feeding amongst the dead grass and plants

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Drinking from the unidentified object

Here you can find a short video of the Twite: