Blow's Downs Nature Reserve is a remnant of the chalk grassland which once covered the slopes of the Chilterns. Yellow Rattle, Squinancywort, Wild Thyme and the rare Great Pignut grow among the grasses here, and this is also one of the best places in Britain to see Ring Ouzel and other birds as they migrate north in the spring. Much of the Northern hillside is a Site of Special Scientific Interest (SSSI), which was purchased by the Wildlife Trust in 1995. The remainder of Blow's Downs was purchased for the Wildlife Trust by Dunstable Town Council with the aid of a lottery grant in 1997. Cottage Bottom Fields Nature Reserve is owned by Bedfordshire County Council. There is public access to all areas
The wildlife interest of Blow's Downs is increased by the variety of habitats found here. The open grassland contains many different plants because the thin, poor soil prevents any one species from overwhelming the others. This diversity is maintained by grazing livestock, which also stop the patches of Hawthorn and Blackthorn scrub from spreading into the grasses. The scrub provides food and shelter for many local birds but Blow's Downs is most famous as a place to see passage migrants such as Ring Ouzel, Northern Wheatear and both Black and Common Redstarts.
Blow's Downs lies on the steep northern face of the Chalk, forming a ridge of high ground which the Icknield Way follows from the Dorset Coast north-east to Norfolk. This has been a major trade route for thousands of years. Trees once grew here, but the Neolithic travellers who settled here over 5000 years ago felled the forest to create fields and pastures. Their graves or barrows may be seen on nearby hillsides. Dunstable was a centre for wool production in the Middle Ages and wealthy landowners grazed sheep here until wheat and other crops became more profitable than wool. Chalk grassland survives today on Blow's Downs only because the slopes were too steep to plough.