IT is a place long associated with housing some of Scotland's most dangerous criminals. 

For decades, Carstairs has provided rehabilitative treatment for men who have committed horrifically violent crimes due to severe mental health conditions.

However, the country's high-security state hospital is also providing an unlikely but safe and peaceful sanctuary for a flock of nesting birds each year.

Scotland's coastline is home to thousands of Eurasian Oyster Catchers, which head inland at this time to build their nests.

They rely on instinct to locate the safest spots from the threat predators and disturbance and for hundreds of pairs this has meant migration ashore to what would seem like a highly unlikely location.

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The NHS facility in South Lanarkshire may be home to some of the country's most feared criminals but this is where the distinctive black and white wading birds know they are assured of peace and safety to hatch their young.

HeraldScotland:

There is no danger to the nesting birds - not even a fox can breach the sophisticated security systems that blend in effortlessly into the surrounding countryside perimeters.

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Staff and patients are said to take great 'delight' in the arrival of the cheerful Oyster Catchers on their annual pilgrimage before the return to the sandy estuaries of the coast when the chicks are able to fly.

The UK supports an internationally important number of wintering oystercatchers with up to 45 per cent of Europe’s population choosing to spend the winter here.

Overall, the breeding population in England has increased to around 110,000 pairs, but there has been a significant decline in Scotland, the reasons for which are unclear.

Due to these local declines, oystercatchers are Amber-listed in the UK and classed as Vulnerable in Europe as a whole.

HeraldScotland:

During the winter, oystercatchers are still very much a bird of tidal estuaries and rocky shores.

During the breeding season, however, they can be found much further inland thanks to populations moving along linear waterways. In Aberdeen and other Scottish towns, they have even been known to nest on rooftops.

The main diet of the oystercatcher seldom involves oysters in the UK but is predominantly bivalves, including cockles and mussels.

The longevity record for an oystercatcher stands at 40 years, one month and two days.

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Carstairs state hospital was constructed from 1936-39 but, owing to the Second World War, was initially used as an army hospital.

It opened as the State Institution for Mental Defectives in 1948, but it was not until 1957 that ninety 'criminally insane' prisoners were transferred there from HM Prison Perth.

A redevelopment of the hospital was approved by The Scottish Government in September 2007. Construction began in April 2008 and the new hospital facilities were officially opened on 26 June 2012.

Carstairs has an alarm system that is activated if any patient escapes to alert people in the vicinity, including those in the neighbouring town of Lanark, and local villages such as Ravenstruther.

The system is tested on the third Thursday of every month at 1pm when the all clear siren sounds.

The security staff who support the clinical teams are mostly made up of re-trained nurses which is said to be aimed at creating an environment focussed on patient care rather than imprisonment.