Two events in nature that usually herald the beginning of summer have started already, say researchers looking into reports from the public.
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Sightings of swifts have been reported across south-east England and Gloucestershire over the last few days.

Swifts usually return from migration around 10 May when temperatures are slightly milder.
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The flowering of hawthorn, normally around the middle of next month, is considered to signify the start of summer.

This year, the earliest flowering hawthorn was recorded on 9 April.

http://news.bbc.co.uk/1/hi/uk/6566401.stm