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Dr Vince Lea

Oak before Ash – summer’s a splash!

Well, it has certainly been very dry, after a very dry winter and a drought last summer, we really need a bit of rain. Leaf break of the two main trees of the countryside is actually linked to temperature, with oak being more influenced by warmth whereas ash is more influenced by the day length which doesn’t change much. It’s been a pretty early and very dry spring so far, which has moved some things ahead of schedule; while the weather was kind to migrating birds early in April and insects had a lovely time up to Easter, the second half of the month was cooler with some northerly winds which slowed things down and in particular the later arriving migrant birds were held up.


Butterflies started appearing well before April, but we formally start counting them on the 1st April, with counts every week till the end of September. This regular monitoring means we can see how different one year is from the next, or from the average. Last year we had the Beast from the East, which meant that the first 2 weeks of April were a write-off for butterflies, and we had only reached 5 species recorded by week 4. This year, we had 8 species on the wing by week 2 and orange tips and speckled woods seem to be having a good month.

Speckled wood

Birds on the farms

While the early arriving birds such as blackcap, chiffchaff and willow warbler were on course in early April, some of the more flexible resident species were nesting very early, with hatched blackbirds and long-tailed tits by mid-month. This means the resident birds are able to take advantage of the early insects, while by the time the migrants have got here, partnered up, built nests, laid eggs and then eventually hatched them, much of the first flush of caterpillars is over and they struggle to feed their chicks. Late April (after a scorching Easter) saw a slowdown of migration with northerly winds, and some second clutches of blackbird eggs were laid before the majority of migrant birds arrived. The early swallows were not joined by en masse arrivals, and later species like swift and turtle dove are still a few days behind schedule. The dry conditions probably dissuaded any lapwings from staying to nest, and we are already seeing problems with the Bourn Brook which is flowing very slowly and turning green as the warmth and slow flow allows the algae to grow. The lack of floods has helped our early nesting moorhens, however, which are now regularly nesting in the brook using reed cover to hide their nests from crows etc. and, thanks to the lack of mink, they are pretty safe unless we get a sudden downpour and flood!

Highlight of the Month

My highlight of the April monitoring was to find a large number of water vole signs on the last 500m of the Bourn Brook at Lark Rise; we had more signs here than the whole of the brook had in 2011 when we started mink control.

The disappointment of the month was spending a day looking for willow tits at Margaret Wood in Yorkshire. We had a record of this declining species there a few years ago, and 2019 is an official survey year for willow tits, so I searched the whole wood and all the surrounding woods, playing a sound recording of willow tit song to tempt any to come and say hello – but not a one was to be seen. It was nice to see the tree sparrows still doing well at Margaret Wood and I took some red millet to keep them happy, but willow tits are disappearing from the countryside without anyone really noticing them go. It is a difficult species to see and identify and most people have not heard about them, but they are an important species because the British ones are a unique race and they are one of only 2 species of tit which can dig out their own nesting hole in a rotten tree – the other being crested tit which only occurs in the north of Scotland. These ‘excavators’ help other species by providing used holes for future nests.

Dr Vince Lea
(Head of Wildlife Monitoring)