Environment

Common Tern breeding at Hedgecourt Lake 2026

Background

The rafts have been in place for a number of years but not formally monitored to my knowledge. Occupancy has been good, with several pairs seen in most years. Breeding success is largely unknown.

The rafts were, I understand, introduced to provide an alternative to the Maid of Kent as a nesting location. This has been largely successful as the Maid of Kent has been unused by the birds in recent years. A fourth raft was added in 2024/25 in an attempt to increase the size of the colony by providing more nest sites.

Common Terns were badly affected by Avian Influenza but numbers appear to be back to where they were.

American Mink are known to be resident in and around Hedgecourt Lake. Gauging the impact of these alien predators on the terns is another motive for conducting formal monitoring of the birds breeding performance. See Mink Control later.

Methods and recording

Common Terns arrive in the UK from early/mid-May and usually begin breeding soon after.

They lay a clutch of 3 eggs on shingle and incubate their eggs for around 21 days. Fledging takes place around 25 days after hatching.

Visits to the rafts, by boat, were made periodically from mid-May. Observations were recorded and uploaded to the BTO Nest Record Scheme.

Results

Old raft – the one nearest the modern house – early occupancy by moorhens provided unwelcome competition for the terns. Although the moorhens were evicted (by the terns) and the terns laid eggs, the nest failed at the egg stage. A dead adult bird – possibly a tern – was present in late May.

Green plastic sided raft – a clutch of three eggs was complete in early June. Two juveniles made it to fledging stage by early July. A dead adult bird – possibly a tern – was noted on the final visit in mid-July.

Newest raft – the smallest of the pair of rafts – a clutch of 3 eggs was complete by the end of May and 2 hatched young were noted in early June. Both made it to fledging stage by early July.

Fourth raft – the larger of to close together – not used for nesting.

Discussion

Four fledged young from three attempts is a positive outcome but not indicative of a “bumper” year. Food appeared to be plentiful as the birds were often seen diving successfully for small fish quite close to the rafts suggesting that provisioning was not taking a lot of time or energy on the part of the adults.

That only three nesting attempts appear to have been made does not fully reflect the size of adult Common Tern population at Hedgecourt as 9 adults birds were seen in early June.

The old raft has been known to successfully host two nests in a single year, so, with the fourth raft empty, it appears that other factors are at play.

A key feature is early occupancy of the rafts by resident species, especially moorhens. This has been witnessed in other years and is an obvious deterrent to tern occupancy. The rafts could be temporarily covered in late winter and only uncovered as soon as the terns arrive at the site.

The presence of dead adult birds – either terns or gulls – is extremely worrying. The presence of American Mink is one cause of these mortalities especially as the birds were left in situ. Mink often kill indiscriminately and do not consume everything they kill. Disease and natural causes cannot be ruled out but two fatalities on the rafts points towards mammalian predation.

Conclusion

The rafts did their job. No birds used the Maid of Kent and two pairs bred successfully on the rafts well away from lake users.

Predation at egg stage cannot be ruled out and while gulls are usually the main culprit, almost no gulls were present at the lake in late May early June. Two losses at the hatched young stage were sustained but no clear cause is known however, the presence of two dead adult birds indicates a need to research the possible impact of American Mink on the rafts.

Suggested actions

Annual maintenance of the rafts to be conducted when higher water levels make it easier to get a power boat alongside. Work to include checking the mesh sides to deter mink.

Place cheap tarpaulins/old boat covers, over the rafts in late winter to deter the moorhens.

Liaise with Waterlife Recovery Trust, which has American Mink eradication programmes running on some river systems in Surrey, with a view to finding out how to monitor and discourage them, before the next tern breeding season.

Matt Kirk

BTO Volunteer/CMYC member

July 2026

Mink Control (Pending Committee Approval 27 July 26)

Matt K., made contact with the Waterlife Recovery Trust regarding mink control. They are very keen for us to be involved.

The way it works is:

They loan us a "Smart" trap that is prepped with scent.  If anything goes in the trap is sends an alert to nominated volunteers by text message.  By law, the trap must then be checked within 12 hours.  If there's a mink in the trap, it must - by law -  be destroyed humanely (air rifle of specified calibre).  The carcass is sent to Waterlife for DNA analysis to map its origins in the river system.

The trap can be deployed all year round but late summer/early autumn offers a good window as this is when the young leave the den and are on the move.  Mating season (February and March) is also a good time to trap as the adults are looking to pair up.

The Waterlife project is supported by Natural England so there is no requirement to notify them.

In terms of input from CMYC, we will need a couple of volunteers to act as trap checkers.  I am happy to be one.  We need to have someone prepared and competent in destroying any animals that are trapped. 

I'm not sure this is the kind of volunteer role that you would want to advertise!  I'm not overly squeamish about this and would do it but would need a Club rifle!  (£100 plus ammo).

There are other options.  Waterlife are checking to see if there is anyone in the area working on a similar project who might do this for us.  Unfortunately, the project officer is too far away to be able to do the shooting for us.  Another possibility might be someone in EGAS.

I have arranged to meet the project officer at the Club on Tuesday 11th August to discuss how we can join the project and see if we have anywhere suitable where a trap might be sited.  We don't want it in an obvious location but it has to be on CMYC owned land - possibly on the edge of the reedbed around Clubhouse Bay.

I assume the Committee needs to approve us joining the project so will feedback further details after the meeting with the Trust on the 11th.

There's more information at  Waterlife Recovery Trust .