Warblers on Holt Island 2025
Holt Island is not a static environment. It is continually changing. It looks like the floods of the 2023/24 winter have had a significant effect on some of the plants, and indirectly on some of the birds – including warblers. By the winter 2024/25, it was clear that ivy and elder were suffering badly. By the spring of 2025 most of the Ivy and Elder trees were dying back all over the Island. Some clumps of Ivy did survive, along with one or two Elders on the higher ground, but no or few flowers were produced on either in 2025 and therefore no fruits. The remaining Ivy was unable to sustain large insect populations, or to provide pollen and fruits in the late autumn and winter. It was greatly missed by the Wrens, Goldcrests and several warblers. Read more
The European Cauliflower Gall – October 2025
Holt Island has a number of Ash trees on it; the trees have large bunches of Ash keys. But if one looks closely there are a number of brown lumps in with the Ash keys. These are European Cauliflower Ash Galls. They are formed by the gall mites Aceria fraxinivora. The galls are formed in the flower clusters; the eggs of the mites being laid soon after they open. As the mites are mainly female, the eggs do not need fertilizing.
The mites are very small, around 0.5mm long cylinders. Scanning electron microscopy images can be seen here. They can pierce individual plant cells, on which they feed. The surrounding cells enlarge and multiply and this forms the gall, which can be 2 cm long, they will turn brown and black and will stay on the tree for up to two years.
Recent additions to the Botanical List for Holt Island Nature Reserve – January 2025
While the seemingly perpetual floods of 2024 caused much concern to the reserve management, they did allow some previously unseen plants to be identified. The slow emergence of the nettles closest to The Waits meant that the early leaves of the rather straggly buttercup seen during the late summer were in full view and it could be identified as the Celery-leaved buttercup (Ranunculus sceleratus). It is generally a plant of wet habitats such as riverbanks.
Rather more complicated to identify fully was the Bur-marigold. It is thought to be the Nodding Bur-marigold (Bidens cernua): one of several species of Bur-marigold. A more accurate identification requires dissection of the seed-bearing achenes. Again, it is a plant that frequents damp riverbank areas.
Red-Tipped Clearwings – August 2024
At the end of July I was asked to go moth trapping on Holt Island, but not the conventional moth trapping in the evening but in the middle of a very hot day.
Clearwings are a form of day flying moth. They are from the Sesiidae family, related to the Burnet and Forester moths. There are about fifteen species in the British Isles, they have clear panels in their wings, from which their name derives, so the wings resemble stained glass. They are wasp mimics, due to the shape and transparent wings. They are very under recorded.
Warblers Caught on Holt Island 2020 – 2023
The numbers of birds caught at any site can vary between years for a number of reasons, including weather effects; variations in effort that is put into catching the birds; long term climate change; vegetation changes and more recently the pandemic. Between 2020 and 2023 we have tried to keep the level of effort as constant as possible, but there were minor issues affecting this due to flooding and bad weather. The pandemic also had an effect on when we could or could not go out.
In 2023 wide strips were cut in the large reed bed at the western end of the Island linked by a path. This allowed us to put nets up in the middle of the reed bed for the first time. This resulted in an increase of the numbers of Reed and Sedge Warblers caught in the early part of the season. Later on, when the reeds grew back, it became too difficult to get in to this area.