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Marsworth Reservoir CES

Marsworth CES is located near Tring, the old BTO HQ and has been running as a CES for 35 years. Our main species are reed warbler, sedge warbler, chiffchaff, blackcap with the usual residents plus a few Kingfishers, reed buntings, lesser whitethroats and the occasional spotted flycatcher.
The land is owned by CaRT and managed by Herts & Middlesex Wildlife Trust (HMWT).
We have 540' (168m) of standard nets, with four rides going out into the reed bed and three 40'nets in the woodland.
Our average annual total over the last 25 years is 682 captures.

Changes over time
Thirty-five years of constant effort ringing has revealed some interesting changes in species composition: willow warbler was a common breeder when ringing started at Marsworth but now only breeds in very favourable years, while chiffchaff have increased three-fold. Sedge warbler numbers have fallen compared with reed warbler, garden warbler has declined while blackcap numbers have nearly doubled.
Willow tit used to be a regular breeder at the site but has not been caught since 1997 and marsh tit is now also disappearing from the site.

Habitat Management
We aim to keep the habitat constant. The willow is cut back rotationally over winter, we take out the tallest growth and anything that is growing out towards the reeds.



One of the woodland net rides


Cetti's Warbler arrived in 2003 and now breed most years. Susceptible to cold weather they disappeared after the cold winters of 2012/3 but are now back and we estimate that there are 2 or 3 breeding females at Marsworth this year (2017).