Tuesday, 22 November 2016

Lakenheath Fen - Crane powerhouse

The fact that Lakenheath Fen RSPB reserve was a carrot field some 20 or so years ago is often repeated.  The detail that has gone into the design of the site and the management for key species is less often appreciated.  This is no airy-fairy, lets see how it develops type of reserve, beloved of some sections of the conservation community.  This is a targeted and planned development that now delivers for Bitterns, Cranes, Bearded Tits, Marsh Harriers, Water Voles, Otters and a range of specialised wetland and Breck plants and invertebrates.

This week, I attended the ecological review for the year and undertook the annual audit.  There were a minimum of 5 booming Bitterns, with at least 3 successful nests. We reviewed the results of the fish survey throughout the reserve and discussed the habitat management. The detailed management undertaken for Bitterns that has led to a remarkable recovery in the UK is well known, but perhaps the work for Cranes less so.  Cranes have also had a good year at Lakenheath Fen with three chicks fledged from the 2 nesting pairs.  But this is no chance event, rather the result of considerable effort by site staff.

The case of Cranes is an interesting one.  Recently released figures show a total of 48 pairs in the UK this year:  a combination of 27 pairs of (mainly) wild birds in 4 population centres and 21 pairs of the ongoing re-introduction scheme in Somerset. At least 16 young were reared this year. The population in the Fens is doing well, contributing 7 of these fledged youngsters, whilst the Broads contributed 4 and Somerset just one.

There have been several re-introduction schemes of various species of cranes around the world.  None have been totally successful.  They have suffered from various problems such as imprinting on humans, lack of migratory instinct, poor productivity and the cranes generally failing to think and act like wild cranes, particularly when it comes to predators! The well publicised nesting attempts of some of the released birds where they clearly fail to recognize good nesting habitat or exhibit typical crane behaviour is a good example.  Lets hope these issues can be resolved.

So how has Lakenheath become the UK crane powerhouse? The birds first appeared in 2007.  DNA analysis of feathers suggested a Finnish/Russian origin.  Over 10 years, 23 clutches of eggs have been laid, with 11 chicks fledging: an average of 0.55 young per pair.  The fledging rate was poor at first but is increasing in recent years; the last 5 years average 0.8 and a remarkable 1.5 for the last 2 years.  Detailed study of the Cranes by site staff since they first appeared at Lakenheath, notably by Norman Sills, has led to a good understanding of their requirements.   Habitat management seeks to create ideal conditions for both nesting and chick rearing.  However, it is predation, mainly by Foxes that poses the major threat to the youngsters.  Habitat manipulation can help with this but ultimately some control of Foxes is required.  To ensure success, the latest technology of trail cameras and thermal imagers is used in conjunction with a skilled marksman.

The reedbed management aims to create structural diversity for the benefit of the key species.  Cutting and grazing are the key management tools and also aim to enhance viewing opportunities for visitors.  No airy-fairy stuff this – rather it is determined and targeted conservation effort that brings results.

Photo below - Dartmoor ponies eating reed and typha rhizomes


No comments: