Brimstone Butterfly Sunday’s warm sunshine was perfect for the first butterfly surveys of the year – we do them every week from the start of April through to the end of September. We saw four different species: peacock, comma, small tortoiseshell and brimstone. These species are widespread and possible to see in gardens, especially in rural areas. They are all species that spend the winter hibernating as adults, so they start to appear as soon as it warms up. Sometimes this happens in January if it’s very warm. They go back into hibernation if it turns cold again.

The next wave of butterflies to appear are the ones that spend their winter as pupae, and warmth brings about their final metamorphosis. We’ve started to see the first few of these in warm spots, but it takes a bit longer for most to emerge in the wider countryside. Examples that are on the wing now include the orange tip, green-veined white and speckled wood. It is a great time to start learning about butterflies as fewer than 10 species are likely to occur during April, and those that spend the winter as caterpillars go through their two phases of metamorphosis during the spring and make their appearance in May. The big rush comes in July when 20 species are likely to be flitting around in profusion, making identification more of a challenge.

Today, I did the second bird survey at Westfield. The cast list was almost identical to last week, with the addition of blackcaps, a Water Vole summer migrant, and a pair of starlings which may be thinking of breeding – a species we scarcely get as breeding birds these days.

I was also really pleased to see a water vole in the Bourn Brook. This was the last bit of the Bourn Brook to be colonised by water voles; they came downstream from the remnant populations in Bourn, and up from the River Cam where the TFC gamekeeper had been mink controlling for many years, so these populations have now probably merged at Westfield and their genetics will be much helped by this.

Spring Blackthorn.It is a great time to look at our two commonest hedge shrubs, especially for those not sure about the difference between the hawthorn and blackthorn. Blackthorn is in flower now, but has no leaves, whereas hawthorn is in leaf right now, but has no flowers. Well, I did see a couple of hawthorns just starting to flower, but this is remarkably early for them. It is also known as May blossom; its old name is now irrelevant thanks to climate change. It is one of the key species recorded as part of Nature’s Calendar, a recording scheme anyone can get involved in; see https://naturescalendar.woodlandtrust.org.uk/

Dr Vince Lea
Head of Wildlife Monitoring 

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