Portsdown Hill

Site feature providing a more detailed description, photos and other information for the observer.

Photo 1 - View East Along Central Section Showing Chalkhill Blue Breeding Area


  • Imposing chalk downland escarpment overlooking Portsmouth and the Solent.

  • A central part of the escarpment designated SSSI for its variety of flora and fauna.

  • Wildlife haven on the doorstep of a major city.

  • Chalk downland butterflies include Chalkhill Blue and Small Blue.

  • Green Hairstreak and Brown Argus also present.

  • Fascinating military history including series of defensive forts built during the nineteenth century and second world war tunnels.


Portsdown Hill is a chalk downland escarpment stretching for several miles and overlooking Portsmouth, the Solent and the Isle of Wight. Its strategic position has resulted in the hill playing a significant role in Britain's military history over several centuries - a series of military forts (the Palmerston Forts) built during Napoleonic times being very obvious evidence of that. Despite its proximity to a large city, conservation management and scrub clearance efforts on Portsdown Hill in recent years have substantially improved the quality of its chalk downland, to the benefit of the wildlife, including butterflies. Even the flower-rich ramparts of several of the military forts now provide good butterfly habitat.


The area of the hill (Photo 1) (map) located between the disused Paulsgrove and Wymering chalk quarries is probably the richest area for butterflies and is the main breeding site for Chalkhill Blue. Access to the area is through a gate (map) close to Lime Grove and just to the east of the largest of the disused quarries (Paulsgrove), which leads to a network of paths on the hillside. In May, spring species include Orange Tip, Brimstone, Red Admiral and Peacock.  Green Hairstreak can also be found in small numbers around the margins of bushy areas on the lower slopes. Late July/August is the best time for Chalkhills, but Common Blue, Marbled White, Meadow Brown and Gatekeeper should also be seen in this area. Other species to keep watch for include Brown Argus, Small Copper, Small Blue and Clouded Yellow.


Small Blue (especially the main spring brood) can usually be found amongst the scrub on the south side of the imposing chalk face of the Paulsgrove quarry. In particular, follow the chalky path here at the bottom of the slope heading west, below the western end of the quarry (Photo 2 below looking from it to the quarry face). Look out for Green Hairstreak amongst the gorse in this area too. Visits here can sometimes be accompanied by the raucous screeches of a pair of Peregrine Falcons which have been nesting high on the quarry face for several years.

Photo 2 - Scrub Area To The South-West Of The Disused Quarry At Paulsgrove


The area is home to a colony of Small Blue

Since the hill provides such a good vantage point, it is not difficult to maintain one's bearings. You can gradually make your way east along the hill towards the other quarry at Wymering. The return can be made by retracing steps or introducing a variation using the network of paths.