13/06 Thatcham Marsh LNR CES Visit 2026.05

Location: Thatcham Marsh LNR CES Visit 2026.05

Session: 07/06/2026 07:30 to 11:00hrs

Present: JHW, IW, JL, CMD, PRY, IQ.

Weather: Breezy, sunny periods, warm.

Nets: 192M reed bed ride + 2x12M separate rides set in scrub (site B) up from 06:30 to 10:30hrs.

Lures (none):

Chiffchaff an adul male - the last bird of the session and there should be more of these about - Reed Warbler 

Notes: The tree that fell on the ride last winter at the north end of the reed bed has made it increasingly difficult to squeeze the 2A portion of nets in and it has also pushed the ride southward such that there was about a 5metre overlap with the 1A portion. It was decided to reduce the 2A portion by 6metres by replacing one of the 18metre nets with a 12metre net -  the overal coverage is about the same just less overlap between the two portions of the ride. It was breezy for most of the session and the 2A length of reed bed ride was particulalrly affected, it being more exposed to the westerly that was blowing. As mentioned before it seems there are fewer Reed Warbler in the vacinity of the rides. I counted four singing males along the ride when most previous years at least double this number would have been present. Some of the Reed Warbler we did encounter showed little or no sign of breeding activity – BPs in early stage of development and CP difficult to see, some had no sign of either suggesting they were recent arrivals and that a portion of those that arrived earlier this season may have moved on. As can be seen in the table below the overal capture was about 50% better than last years matching visit. However about 30% of this visits total came from the two scrub nets - not erected for last years matching visit. Most of the scrub net birds were juveniles.

Recaptures: (17 )
Cettis Warbler ringed: 12/07/2025, 29/09/2025, 12/10/2025, 26/04/2026x2,
Chiffchaff ringed: 07/06/2026
Sedge Warbler ringed: 26/04/2026, 31/05/2026, 10/05/2026,
Reed Warbler ringed: 03/06/2023, 03/05/2025,18/05/2025, 02/08/2025, 23/05/2026, 31/05/2026x2.          

Robin ringed: 07/06/2026

Sightings: No geese sightings is unusual; most adults will be approaching their flightless moult period though. Pochard with chicks on adjacent pit. A few Swifts over and a lone male Pheasant flew over north towards “the hill”. Cuckoo still about calling occasionally. Common Tern over a couple of times. A Sparrowhawk high up also the usual Red Kites and a Buzzard and the Kestrel visited the hill less frequently than in recent weeks. A Raven called briefly towards the end of the session. The Garden Warbler near the gate is still singing, a Nuthatch called from the scrub briefly mid-session. A family party of Bullfinch was calling at nets up and just the single pair of Reed Bunting on the reed bed. The Common Hawker had flown into a net while we were taking it down and was carefully extracted and flew off ok – fortunately it had not had time to begin “eating” the net. Marbled Whites on the wing, the first I’ve seen this year.

10/06 Nest Box Report for 2026

 Nest Box Monitoring: 2026

Summary: Four Nest Monitors visited 161 nest boxes on 34 dates between  25th Mar and 8th June 2026. Nest Box occupation has improved over the last six years for Blue Tit and Nuthatch less so for Great Tit. Successful Outcome in Brackets (Bagnor Estate pre-2026 nest records not included in the following table)

                       Species        2021           2022           2023           2024           2025           2026

                       Blue Tit       45(23)         56(39)        56(49)         79(66)        85(72)         77(72)

                      Great Tit       29(21)         33(28)        36(28)         52(49)        34(32)         47(44)

                     Nuthatch         7(5)             4(2)            5(3)           12(11)          6(6)           11(10)

     Spotted Flycatcher           -                  -                  -                  -               1(1)                -

           Pied Flycatcher           -               1(0)               -                  -                  -                  - 

  Failed Pre Egg Stage           9                12               20                8                19               10

                Unoccupied          29                16               16                6                15               16

2026 Summary  161 boxes monitored – 97 Greenham Common, 64 Snelsmore Common.

Species                    Occupied                Succesful                    Failed

Blue Tit                          77                         72                                 5

Great Tit                         47                         44                                3             

Nuthatch                        11                         10                                 1 

Unknow Sp.                   10                           -                                  -

Unoccupied                   16                           -                                  - 

Bagnor Estate 39 Boxes

The Bagnor Feeder CES operation ceased winter 2025/26 so JL did not monitor the Nest Boxes in 2026.

Greenham Common Bowdown NR Ian Quelch Monitored 22 Boxes

Blue Tit          12-Successful     1-Young Deserted       

Great Tit          3-Successful

Nuthatch          1-Succesful       1-Eggs Deserted

Unknown Species                     1-Eggs Deserted

Unoccupied     2

Greenham Common Peaked Hill Jan Legg Monitored 32 Boxes

Blue Tit          14-Successful                                          

Great Tit          7-Successful     1-Young Deserted

Nuthatch          3-Successful      

Unknown Sp   2-Ceased Before Laying.

Unoccupied     4 plus 1 box fell off tree after the last maintenance visit and before the 1st check visit

Greenham Common Peckmore Copse Ian Quelch Monitored 20 Boxes

Blue Tit            6-Successful     1-Young Deserted      

Great Tit          8-Successful      

Nuthatch          2-Successful

Unoccupied     2 plus 1-Occupied By Non-Avian Species

Greenham Common Sandleford Copse Jone Ayres & Derek Bingham monitored 23 boxes

Blue Tit          11-Successful     1-Ceased Before Laying

Great Tit          8-Successful

Nuthatch          1-Successful

Unoccupied     2

Snelsmore Common JanLegg monitored 64 boxes

Blue Tit          28- Successful    1-Young Deserted      1-Eggs or Predated

Great Tit        25-Successful     1-Young Deserted

Nuthatch          3-Successful

Unknown Sp   3-Ceased Before Laying

Unoccupied     8                         

Pulli Ringed JL Decided Not To Ring Nest Boxes pulli  in 2026.

A brood of 6 Nuthatch Ringed at Snelsmore Common – to keep my hand in.

07/06 Thatcham Marsh LNR

Location: Thatcham Marsh LNR

Session: 07/06/2026 07:30 to 11:00hrs

Present: JHW, IW, CMD, JL.

Weather: Mostly overcast, light breeze, cool.

Nets: 3 x12M separate rides set in scrub (site B) up from 08:00 to 10:45hrs.

Lures (none): 

Notes: A non-CES visit so we concentrated on mowing the reed bed ride. We put three nets up in the scrub which CMD looked after while we cleaned up the reed bed ride. All bar the Robins and the Cetti’s Warbler were 3J birds (recently out of the nest) still in juvenile plumage. We took the nets down a bit early as it looked and felt like it was about to rain – it didn’t though!

Recaptures: (01)

Robin ringed: 12/10/2025

Sightings: Not much time to do any watching/listening while mowing/strimming the net ride so probably missed a few but a good species total though. Cuckoo still active. Heard the Mute Swan take-off from the pits south of the railway.

31/05 Thatcham Marsh LNR

Location: Thatcham Marsh LNR CES 2026.04

Session:   31/05/2026 06:00 to 11:00hrs

Present:   JHW, IW, RAD, JL, JA.

Weather: bright sunny, calm, hot.

Nets: 198M Reed Ride (site A) + 1 x12M separate rides set in scrub (site B) up from 06:30 to 10:30hrs.

Lures (none): 

Notes: The first cooler day after a very hot period. As can be seen below the total for visit CES 2026.04 is a little better than the 2025.04 visit, particularly for Reed Warbler. However, for the time of year the reed bed still seems quieter than usual - fewer Reed and Sedge Warblers singing and very few other species seem to be venturing onto the reed bed than in the recent past. To test these perceptions below are a couple of charts that plot the totals for most years the group has been in existence.

Provisors are:

·       In the early days until the 1980s ringing on the marsh was less structured, the number of nets erected or there locations not recorded.

·    Site names were general for much of the marsh until the 1980s when specific areas ringed were recorded including the number and location of nets erected.

·     Ringing was less regular and was alternated with other sites such as Hambridge Lake and at Thatcham south of the railway. On occasions this meant that ringing was at best sporadic and some years few visits were made due to poor weather and the alternation.

·      The number of active ringers (effort) has also been a factor; numbers peaked in the early 1970s at 18 members then dropping to four in the early 1980s before peaking at again in 2010 at 14 active members – currently there are usually between four and six ringers in attendance.

·    All records still in existence for Thatcham Marsh have been added to the data system back to 1973 prior to this there are gaps due to data not yet being entered or no longer in existence and which may account for the lower numbers for this period.

·    In the mid-1980s ringing on the Thatcham LNR was prioritised from April until the last warblers left late Oct – Early Nov and on every visit each net ride was recorded including species encountered therein. In 1993 were joined the British Trust for Ornithology’s Constant Effort Site (CES) scheme that runs from late Apr to early Sep when 12 “official” visit limited to the reed bed ride of 198metres of net are made. Ringing in between and outside these visits also follows this structure including any peripheral nets rides erected.

The first chart shows the yearly totals for the primary species ringed Reed Warbler and Sedge Warbler. From 1989 numbers (with exceptions) become more consistent as we adopted CES type ringing methods. With some exceptional years it shows a steady decline in numbers of both species from 1990 and as perceived by us

The next chart indications species diversity, again the overall trend is downwards. Some account for this may be due to the number of nets erected at any one time and  their location also the loss of reed beds due to gravel extraction etc, and the steady encroachment of scrub into the reed habitat over the period. Prior to the mid-1960s passing stream trains would sometimes throw their fires. Setting fire to the nearby phragmites reed that would spread over the reed beds and curtail the encroachment of scrub growth. This probably accounts for the survival of the extensive reed habitat along the Kennet valley to the late1960s when steam power was replaced.

Session Capture details.

Recaptures: (13)

Blue Tit ringed: 23/05/2026

Cetti’s Warbler ringed:11/08/2024, 29/06/2025

Chiffchaff ringed 02/04/2023

Reed Warbler   ringed: 03/07/2022, 11/06/2023 03/05/2025, 10/05/2025x2, 02/08/2025, 18/05/2025, 26/04/2026, 02/05/2026

Sightings: Less activity this session, still some species singing but some have gone quiet – Garden Warbler? The juvenile Robins and Blue Tits  also a couple of tit families in the scrub towards the end of the session show that species are now fledging including some summer migrants – Blackcaps etc. The change in the weather to unsettled meant that fewer insects were out and about and for the first time this year more Banded Demoiselles than Beautiful Demoiselles seen.

23rd May CES visit 2026.03

Location: Thatcham Marsh LNR CES 2026.03

Session:   23/05/2026 06:00 to 11:00hrs

Present:   JHW, RAD, IW, JL, CMD.

Weather: bright sunny, calm, hot.

Nets: 198M Reed Ride (site A) + 2 x12M separate rides set in scrub (site B) up from 06:30 to 10:30hrs.

Lures (none):

Notes: It was quite hot this session even early morning. Some have the impression that we are not ringing as many Reed and Sedge Warblers as in the past, however looking at the last nine years 2017 to 2026 (we were not able to ring in 2020 due to covid restrictions) our total for CES visit 3 this year is about average over the period. 21 Reed Warblers in 2021 after a pause of a year is interesting but probably a coincidense! Sedge Warbler numbers have been dropping for some years now; it is a species moving its range north due to global warming - Willow Warbler similarly is moving north for the same reason. We have been regularly ringing this site since the 1960s although visits were not as structured as they are for CES ringing. However, both species numbers have reduced, also Reed Bunting were once found here in good numbers but are at just one pair in the vicinity of the reed bed net ride so far this year. Reed beds at Thatcham Marsh have much reduced since 1967 when the group formed. Many (most) former extensive reed beds are now angling pits following gravel extraction, and most others are overgrown with scrub with fragmented areas of reed. So a reduction in numbers is not unexpected.

Totals for CES visit 03 (2017 to 2026)    

For reference the average for May per decade since the CES started in 1993 is:

Recaptures: (21)

Blue Tit ringed: 10/05/2026

Cetti’s Warbler ringed: 26/04/2026

Chiffchaff ringed 17/04/2026, 02/05/2026

Dunnock ringed: 09/10/2024.

Reed Warbler   ringed: 03/06/2023, 11/05/2024, 10/05/2025x2, 18/05/2025, 21/06/2025, 23/08/2025, 26/07/2025, 26/04/2026x3, 05/05/2026,

Sedge Warbler ringed: 26/04/2026, 02/05/2026, 10/05/026, 26/06/2026

Sightings: Some gulls feeding high on (invisible to us) flying insect - probably small dragonflies or similar. The male Kestrel was again hunting over the former waste tip hill and flying over SSW towards the escarpment woodland below Greenham & Crookham Common sometimes carrying small prey. Goldcrest were singing again after being relatively quiet for the last two visits. Otherwise much as expected though few hirundine and no Chaffinch detected.