20 Peacocks, 9 Small Tortoiseshells and the first Small White of the year were seen in warm sunshine on the 6th and in warm, sultry conditions on the 7th a male Brimstone was fluttering around the Observatory. At least 30 Peacocks, 2 Commas and a Red Admiral were on the Estate on the 8th and another Brimstone and the first Speckled Wood of the spring were seen on the 9th. A Brimstone was seen again near the Elms on the 15th and again on the 17th, along with the first Large White of the year, the first Green-veined White was seen on New Downs on the 19th, a  Holly Blue was in the Elms on the 20th and 2 Orange Tips were fluttering along the Green Wall on the 22nd, with another on the Estate. Warm weather in the last week of the month encouraged the appearance of the first Small Copper on the 27th and the month ended with a significant emergence of 20-30 Speckled Woods and an influx of 6 Red Admirals.

The first five transect walks of the season produced some interesting results. Although total numbers were similar (66 this year, compared to 67 in 2009) numbers of individuals of species that winter as adults were significantly higher this year (56, compared to 29 last year), but it was clear that the cold April weather had made spring emergence significantly late. Only 10 individuals of butterfly species that winter as pupae had been recorded by the end of the month, compared to 38 individuals at the same time in 2009.