Saturday 13th April

South Milton Ley sites in a shallow valley running northwest from Bigbury Bay in South Devon. Consequently, it receives far fewer spring migrants than the headlands to either side. Yesterday was no exception. The first decent dry day for four weeks, it was chilly and overcast when I arrived and windier than I would have liked. Marsh Ride was accessible with caution, although extremely glutinous underfoot in places. Nevertheless, it was the perfect time of year to get the Hemlock Water Dropwort under control before the stems become too woody to cut easily. Thirty minutes with a slasher and both sides of the 48m ride were cleared. I can relax into maintenance mode now!

On the downside, someone had trashed the 12m Blaca Ride, cutting the guy ropes, hiding one of the mist net poles in the undergrowth and stealing most of the carabine hooks I use to quickly attach the net loops. Luckily, I had enough spares to reinstate things. I expect some damage in the autumn, when there is a budget camp site on a neighbouring farm, but spring vandalism is unusual. School holidays, I guess!

Bird wise things were quiet with just sixteen trapped only half of which were migrants: 2 Blackbird, 3 Blackcap, 3 Blue Tit, 1 Cetti’s Warbler, 5 Chiffchaff, 1 Dunnock and 1 Robin.

A new age for sewage!

Following on from my recent posts about spills and contamination arising from South West Water’s South Milton Waste Water Treatment Works, the Environment Agency has released 2023 storm overflow data today. The figures are shocking. 2023 was named by the Met Office as the 6th wettest year since its records began in 1836. The national data for 2023 shows a 54% increase in the number of sewage spills compared to 2022, and a 13% increase compared to 2020.

At SML the CSO operated for a total of 1512 hours or 63 days. The number of spills increased by 300% compared to 2022 and by 274% compared to 2021. With 93 spills in 2023, the CSO was operating every four days throughout the year!

A Chiffchaff encounter in Portugal

I have just received news from the BTO of a Chiffchaff ringing control or encounter as we are supposed to call them these days. This is SML’s 50th Chiff control since 1993. Ringed as a first year on 30/09/23 the bird was trapped on 19/11/23 at Quinta da Atalaia, Setúbal, Portugal, 50 days and 1342 km later. Details of all controls at SML since 1970 can be accessed via the following link SML Ringing Controls1970-present.pdf  

South West Water, spills, excuses and scum!

In my post of 27^th February, I reported on the continuous spill of waste flowing from the South Milton Waste Water Treatment Works directly into South Milton SSSI. This now seems to have stopped and work to increase the capacity of the Settled Storm Overflow Tank has been completed. This, of course, is progress, although long overdue. However, whilst the surface spill has stopped, my colleague Nick Townsend has photographed a floating, brown scum collecting upstream of both the Marsh Ride and Boardwalk bridges.

Naturally, South West Water denies any responsibility, claiming that the source is environmental. In the fourteen years I have been ringing at SML I have never seen anything like it. It is strange that this event should coincide with work at the WWTW and even stranger that there is no sign of scum collecting on bridge supports upstream of the works!

SWW’s record at South Milton is not one to be proud of. I have been trying to get detailed storm overflow data from them for a number of years. On 15^th March I finally received data for 2020 and 2021. They refused to supply information for 2022 as, according to them, this could jeopardise the entire Ofwat investigation into their performance, which is ongoing.

Comparing the data supplied with Met Office rainfall data does not fill me with confidence. For example, in Feb/Mar 2020 the storm overflow operated continuously for over 30 days (exceptional circumstances apparently)! No explanation from SWW but I am assuming there was a pump failure at the works, which took over a month to rectify. Does no one monitor these sensors?

It is equally unreasonable to expect action if a problem arises during the Christmas/New Year period with eight continuous days of discharge. Apparently, it is much easier and cheaper to allow waste to spill into an SSSI than attempt to sort out a problem during a holiday period.

The data from 2021 are no better with another continuous spill lasting over 14 days during late January into February. Rainfall during this period could hardly be described as exceptional for the region or time of year.

Finally, some good news. For 90 consecutive days from 3^rd October 2021 to the end of the year there were no reported storm overflow discharges. Progress apparently, until examination of the data reveals that the sensor had failed. There were 1,102 storm overflows with sensors in the South West Water region in 2021. Does the company not stock spare sensors? Why did it take 3 months to organise a replacement?

Chiffchaffs 2023/24 winter summary

It has been two weeks since the first male Chiffchaffs breeding in the Reserve started to return from their winter quarters and most of the locally wintering birds departed northwards. I have been updating the figures in my January 15^th post, which now stand at 175 individuals trapped beside the sewage works this winter and an estimated population of 422 birds (based on ratios of ringed/unringed birds caught). The number of birds has been creeping upwards annually with an average population over the last 8 winters of 286 birds. As far as I can ascertain this is the highest number recorded anywhere in the UK, although I suspect that there are similar totals at sewage works in Cornwall.

It’s always exciting when I catch a bird returning from previous winters. This year 19 returning Chiffchaffs have been trapped with 12 from 2022/23, 6 from 2021/22 and one elderly bird first ringed in the 2020/21 winter. These birds seem to be incredibly site faithful. 255 were trapped in the winter of 2022/23. Allowing for annual mortality rates of 80% and 66% for 1^st years and adults respectively would raise these figures to an estimate of 81 birds. Further manipulating this total to allowing for the fact that the capture/recapture model suggests that only 41% of the birds present were trapped this winter gives a corrected total  (81/41)*100 = 197 returning birds out of 255 processed last winter, a return rate of 77%.

27th February 2024, Good Water and Bad Water!

South Milton Stream and the bridge to Marsh Ride, February 2024

I’ll start with the good. As I reported way back in December, the reedbed is as wet as I can remember. A decision was made a few years ago to stop dredging South Milton Stream, the principal source of water into the reserve. The intention being to allow the stream to establish its own depth and width naturally and for water to spill into the reedbed during periods of high flow. There is no doubt that this has been a success with water now flowing across the width of the reedbed and the middle and lower valley acting as a natural floodplain for the first time in thirty years. However, I don’t think I’ll be accessing Marsh Ride any time soon as you can see from the photos above and below!

View Across the bridge and along Marsh Ride, February 24

A pool of effluent at the bottom of the South Milton Sewage Works site.

Now for the bad. Effluent was pouring into the SSSI from South West Water’s adjacent sewage works today, ironically whilst company officers were meeting with South Milton Parish Council. The lower part of the Waste Water Treatment Works is flooded with a large pool of dirty brown water.

The stream of effluent flowing into the SSSI

This, in turn, is overflowing continuously straight into the reserve. Over 50m of permissive footpath are now saturated with who knows what! Having contracted Giardiasis, a particularly unpleasant intestinal parasite, following a previous spill from the works, I was not impressed!

The condition of the footpath

I suppose I ought to mention the birds! 34 were caught in four drier nets today. The best being 4 Firecrests. Others: 1 Blue Tit, 17 Chiffs, 1 Dunnock, 3 Goldcrest, 2 Great Tit, 2 Long-tailed Tit, 1 Robin, 2 Song Thrush & 1 Wren.

12th February 2024

The ongoing works at South Milton STW have driven off most of the wintering Chiffchaffs and a northwesterly wind pushed the remainder away from the nets. Just 11 birds were trapped in a long 5 hours. Consolation prize, the last bird caught was a re-trap Chiffchaff NNA604, ringed on 10^th October 2023 in Monk’s Cross, York. Total: 1 Blue Tit, 1 Chiffchaff, 2 Dunnock, 1 Goldcrest, 3 Long-tailed Tit and 2 Robin.

27th January and 1st February 2024

Visits to South Milton Ley in the middle of winter are never an attractive proposition. With the site exposed to the prevailing south-westerly wind and muddy paths underfoot, the going can only be described as heavy. This year the water table in the reedbed is as high as I can remember, rendering the main net rides out of bounds. This is not a massive loss as, apart from a few Cetti’s Warblers, the other target species, Reed Buntings, have decreased from around 100 a winter down to single figures in recent years.

Consequently, I have been concentrating my efforts around the western margins of the adjacent sewage treatment works, with wintering Chiffchaffs being the target species. Even this has been relatively unproductive since the middle of January as South West Water have finally started to increase the capacity of the storm water tank at the works. This will be of benefit to the reserve  as it should reduce the number of times untreated sewage is discharged into the SSSI. However, the disturbance from the three JCB’s operating on the site has seriously reduced the number of Chiffchaffs feeding around the works. It was really obvious that, when operations stopped for lunch, they reappeared within minutes. Fortunately for me the contractors took a lunch which lasted well over an hour so all was not lost.

In the end I trapped 53 birds of 10 species were trapped on the two visits combined: 2 Blue Tit, 1 Chaffinch, 33 Chiffchaff, 1 Dunnock, 1 Firecrest, 7 Goldcrest, 1 Great Tit, 1 Long-tailed Tit, 1 Robin and 5 Wren.

Wintering Chiffchaffs at South Milton Ley

Wintering Chiffchaff at South Milton Ley – photo Richie Moore

I was awarded my C permit in July 2014 and assumed responsibility for the ringing at South Milton Ley shortly afterwards. At the time I was still working so ringing opportunities were limited. However, since my retirement in October 2015, I have processed 2756 Chiffchaffs at SML and have paid particular attention to the population wintering around the sewage works. The presence of non-biting midges (Chironomidae) around the filter beds attracts large numbers of Chiffchaffs when other food sources are limited.

Historical counts of Chiffchaffs at South Milton WWTW and the adjacent nature reserve suggested a wintering population of 25–30 birds, with a maximum count of 53 in January 2017. However, my ringing has shown the wintering population to be considerably higher. Multiple ringing sessions throughout the winter months have enabled year-specific population estimates to be made using the Schnabel modification of the Lincoln-Petersen capture/recapture model. This model (see below) was developed for situations with multiple capture occasions and uses the ratio of ringed and unringed birds trapped during each ringing session together with the cumulative number of ringed birds to estimate population size. Live recaptures are the basis of the standard model, which requires all birds to have the same survival and capture probabilities and a minimum of three sampling occasions.

Formula used in the Schnabel model.

N = Σ (Ct Mt)      Σ Rt

Mt = the total number of previously ringed birds at time t, Ct = the number caught at time t, Rt = the number of ringed birds caught at time t

The following table lists the number of individuals trapped and the population estimated using the capture/recapture model each winter since 2016/17. The 2022/23 winter produced what is almost certainly the highest winter count for a single site in the UK and with 124 birds processed so far this winter and two months still to go this winter’s total is not going to be far behind.

	Birds processed	Estimated population
2016/17	119	227
2017/18	121	188
2018/19	149	198
2019/20	131	149
2020/21	Covid ringing restrictions
2021/22	135	289
2022/23	255	392
2023/24	175*	422
Average	159	286

*Total processed up to 27th February 2024

13th January 2024

The first session of the new year saw me arrive at South Milton Ley at dawn. The temperature was just above freezing but there was no frost. It was the prospect of a gentle northeasterly breeze that had tempted me out but it remained stubbornly overcast and depressingly cold all day. Ringing insectivores in low temperatures requires constant net rounds and warm bird bags! I only had four nets up, all within thirty metres of the ringing table so I was able to keep them under close scrutiny. However, after sticking my hand into a couple of cold bird bags, I decided that, if it was unpleasant for me it must be even worse for the birds so I kept the bags inside my jacket from then on to keep them at a more civilised temperature.

In the end I trapped 51 birds beside the sewage works, almost exclusively insect eaters: 1 Blackbird, 3 Blue Tit, 36 Chiffchaff, 4 Firecrest, 4 Goldcrest, 1 Robin and 2 Wren.