Thursday 29 August 2019 – Breeding Water Rail?

An indifferent morning’s ringing, not entirely unexpected with fresh NW winds the night before, saw 33 birds of 17 species trapped with 30 new, 2 re-traps and 1 UK control Reed Warbler. New birds: 2 Blackbird, 7 Blackcap, 1 Blue Tit, 1 Bullfinch, 3 Chiffchaff, 1 Dunnock, 1 Great spotted Woodpecker, 1 Pied Flycatcher, 1 Reed Warbler, 1 Robin, 2 Sedge Warbler, 1 Song Thrush, 1 Tree Pipit, 1 Whitethroat, 4 Willow Warbler and 2 Wren.

Things tailed off quickly towards noon and I was taking the net down at the southern end of Marsh Ride when a juvenile water rail scuttled across in front of me. Fully grown, but with a brown bill, white throat and buffish belly it was the first time I have seen this plumage. I am assuming that this is indicative of breeding on the reserve for the second year in a row.

The area around the southern end of Marsh Ride is the wettest part of the reserve in the summer, which makes me wonder what else would breed if the reedbed were wetter. Those of you who know me will be well aware that I have a bee in my bonnet about the way historical drainage works at SML have adversely impacted on the reserve by lowering the water table, introducing gradients from north to south and from east to west, which have accelerated the natural succession from reedbed to wet woodland. In 1991, an independent environmental survey at the Ley concluded:

In 1945 South Milton Stream took a more central course down the upper section of the valley to disappear into the reedbed less than one third of the way down. By 1989 the drainage pattern had been altered with the new course of the main channel taking a more northerly route and extending another 500 metres down the length of the ley before the flow disperses into the reeds. The construction of this ditch has contributed to the drying out of the adjacent marsh . . .

. . . The health of the reedbed is dependent on a high water table, particularly in the growing season from April to August, the very season when water availability may be reduced. It should be remembered that any measures to speed up the water flow through the the Ley by ditching,  the deepening and widening of ditches, or their clearance will tend to depress the level of the adjacent water table. The north ditch has been cleared in the past to enhance the removal of effluent and to separate the flow from the main body of the reedbed. In the absence of excessive nutrient loading, a better strategy might be to divert the stream water into the reedbed at a point higher up the valley and allow the natural reedbed to treat any excess nutrients in the water. Mass flow of water through the reedbed is preferable to unimpeded water movement through a ditch system.”

Despite this professional advice, in 1994, just three years later, major ditching work took place and South Milton Stream, which used to be about 0.5m deep, meandering along the northern edge of the reedbed, was straightened, widened and deepened to about 2m.

South Milton Stream – From this in 1991
To this in 1994

At the same time in 1994 works were completed on “improvements” to the public footpath across the reedbed, which was frequently impassable during the winter months. In essence, a 1m high, earth dam was constructed across the width of the reedbed using spoil excavated from the ditch. It was recognised at the time that this would impede the natural flow of water down the Ley and lateral drains were installed. Unfortunately, in the absence of a hydrologist, no allowance was made for impact of the ditching works on the water table and these drains are high and dry apart from periods when the marsh is already at its wettest.

The public footpath – From this in 1991
To this in 1994

Although suspected by many, adverse impacts have been hard to prove but measurements of hydrostatic pressure made in 1996 show the wettest area at the bottom end of South Milton Stream, where the ditch discharges into the reedbed, instead of the expected gradients down and across the Ley. The wetter area at the end of transect 2 is caused by underground seepage and is now the major source of freshwater into the central reedbed. It is also the area where Water Rails have bred and last year’s Spotted Crake was heard.

Average piezometer readings of hydrostatic pressure in 1996 (blue = wetter areas)

The impact of all these alterations on the reeds themselves has also been measured and the results from a series of transects across the reserve to measure reed growth clearly illustrate an adverse effect on the biomass of reeds with a north-south gradient across transect 1 and significantly reduced growth across the whole width of transect 2 caused by the deepening of South Milton Stream and construction of the footpath respectively.

Location of transects used to determine biomass of Common Reed (Phragmites australis) in 1996

Biomass of Common Reed (Phragmites australis) g-1m-2 across three transects at South Milton Ley in 1996

Too much advice!

It’s surprising how many of the occasional (and exclusively elderly) birders I meet at SML claim to have been ringers previously and how keen they are to advise me on how they used to do things, presumably around the middle of the last century! In reality, many of them probably held a trainee permit for a few years or possibly even a C permit in the days when they gave them away in packets of Cornflakes! I’ve certainly been unable to find any of them mentioned in the Devon Birds ringing reports and suspect that the 3,500 birds I ringed before getting my C permit in 2014 is more than they processed in their lifetime. Nevertheless, I’ve had to endure frequent lectures on how many nets to put up, where to place them and how often to do net rounds etc. Many of these well-meaning commentators have been oblivious to the fact that listening to their monologues actually prevents me from getting on with net rounds and ringing.

Once qualified, ringers in the UK can pretty well ring where and what they like, (within the limitations of their permits), and activities range from those who only participate in scientific studies through to what I call “hobby ringers” who randomly ring at different sites or in their back garden when the mood takes them. South Milton Ley has had a spectrum of ringers over the years, ranging from those obsessed with migrants and rarer species who wouldn’t consider ringing resident birds, through those who cherry pick, turning up only during peak migration periods, to others whose goal was to trap as many birds of as many species as possible. I suspect that I fall closer to the latter category but my scientific background keeps this in check as I recognise the value of systematic and reproduceable sampling.

After all, as an example, what is the value of targeting Aquatic Warblers? We know where they breed and where they winter and, as far as I am aware, there have never been any recoveries of a British ringed bird. There is far more to be gained from the systematic ringing of the commoner breeding and wintering species both in terms of population monitoring and effective habitat management. For the first time, systematic ringing throughout the year is now revealing quantitative information about populations, distribution, survival and productivity of the birds at SML, something which is sadly lacking from almost all of Devon Birds’ other reserves.

To that end, I am currently working on the second draft of a paper about Chiffchaffs wintering at SML. The first draft was sent to five referees by the journal and returned covered in electronic red ink. Almost all of these comments were constructive but they need to be addressed and the statistical analysis has to be beefed up before I can re-submit. I’ll keep you posted on progress!

Sunday 25th August 2019 – Access Issues

In 2018, following an initiative by the former Devon Birds Chairman Kevin Cox, access restrictions at South Milton Ley were lifted allowing the public to use the paths around the perimeter of the reserve. However his plans to allow dogs in were blocked, following a concerted campaign by Devon Birds’ members.

In practice, the changes have made little difference to the numbers of visitors. Outside of the early breeding season, when males are singing throughout the reserve, birds can be extremely difficult to see in the dense cover of the reed bed and there is little to grab the attention of people making their way through to Thurlestone Sands. Concerns about litter, barbeques, theft and vandalism have proved to be largely unfounded. Late summer is the one period of concern.

A field adjacent to the sewage works operates as a low cost, no frills camp site from late July to the end of August each year. Their website asks guests to respect the environment and the surrounding countryside, which the majority do but it is clear that a few of the campers are not “country savvy”. Earlier this month I wondered what the farmer’s reaction would have been to a family playing football in the middle of his ripening wheat field!

Net loop attached to the pole with a carabiner and elastic cord

As a lone ringer, I have done everything I can to reduce the time it takes to set up and take down the nets at SML. In many of the net rides I attach the net loops to the poles using small carabiners or snap hooks, tied to the poles with elastic cord, rather than by slipping the loops over the poles themselves.  This means I can leave the poles tethered in place between sessions which halves the setting up time. Unfortunately, these carabiners seem to be attractive to campers and there have been several thefts, always at this time of year. It has now reached the stage where I take a bag of replacements with me and remove those carabiners closest to the path at the end of a session, which rather defeats the object of using them in the first place!

Dog owners are the other issue. A minority seem to think that they and their animals have a right to access other people’s land without restriction. Thus, when I intercepted a family today, with two dogs off the lead and running around a net ride, I was not best pleased. A medium sized dog blundering into a mist net can reduce it to shreds in seconds and at c.£100 a net this is best avoided. I know another ringer who would have hurled abuse at them and adopted a confrontational approach and I had to resist the urge myself. I did point out that they had entered the reserve via a gate with a large “No Dogs” sign on it and then explained that dogs were a significant threat both to my nets and any trapped birds but also to the ground nesting and feeding birds, reptiles and small mammals at the Ley and that, even when on a lead, there is overwhelming evidence in the literature that their presence reduces the numbers and diversity present.

To be fair to the family, the animals were immediately restrained, and they offered to retrace their steps to the entrance. It was their assumption that they had a right to enter the reserve with their animals and could ignore the signs on the gate that rankled. Putting that aside, I explained what I was doing and how ringing data contributes to conservation efforts and showed them the ringing process with a Robin, Dunnock and Pied Flycatcher. They were a little surprised at the use of a film canister to weigh the birds and I had to reassure them that it was quicker and eliminated the risk of injury when compared to previous methods! PR exercise over, they continued on their way to the beach.

The Pied Flycatcher apart, which was my first in eight years ringing at SML, things were pretty quiet with 35 new birds ringed: 4 Blackcap, 1 Blue Tit, 10 Chiffchaff, 1 Dunnock, 1 Garden Warbler, 1 Goldfinch, 1 Pied Flycatcher, 2 Reed Warbler, 2 Robin, 8 Sedge Warbler, 1 Spotted Flycatcher and 3 Tree Pipit.

22nd August 2019

As a weak ridge of high pressure begins to establish itself over southern Britain and the jet stream moves north I was expecting great things today. In the event it was pretty quiet and the birds had completely dried up by mid morning. Still managed to catch 45 new birds but that was well short of what I was expecting: 7 Blackcap, 1 Blue Tit, 4 Chiffchaff, 1 Dunnock, 1 Goldfinch, 10 Reed Warbler, 1 Robin, 13 Sedge Warbler, 2 Whitethroat, 3 Willow Warbler and 2 Wren.

20th August 2019

The busiest morning so far this year kept me fully occupied for the first few hours today. In fact, I didn’t manage to grab a cup of coffee until about 11am when things began to quieten down. 102 new birds of 16 species were ringed: 1 Blackbird, 6 Blackcap, 2 Bullfinch, 7 Chiffchaff, 1 Dunnock, 1 Garden Warbler, 3 Grasshopper Warbler, 2 Great spotted Woodpecker, 11 Reed warbler, 2 Robin, 43 Sedge Warbler, 2 Tree Pipit, 1 Whitethroat 13 Willow Warbler and 3 Wren.

Woodpecker damage – after the blood had been washed off!

Ringing woodpeckers is not without its hazards. One of the birds today was caught by its carpal and had grabbed two feet full of net. These had to be freed first in order to relieve the tension on the carpal joint and get the wing free. Unfortunately this put me within range of its bill and my right hand was well drilled by the time the bird was extracted.

Ichneumon wasp – possibly Ichneumon lugens

Finally, are there any ichneumon experts out there? The beast above was flying around the willows at the southern end of Marsh Ride but, with approximately 2,500 species of ichneumonid in the UK and little id information on line the best guess I can come up with is Ichneumon lugens (formerly Chasmius lugens). Overall length was 25-28mm, which continues my habit of only spotting the largest insects. It would be nice to nail down an id though as it’s definitely a new species for the reserve.

12th August 2019

A faulty starter motor, followed by the storms of last weekend, put paid to planned visits to SML last week so, despite a forecast of thundery showers, I seized the opportunity presented by lower winds on Monday. In the event I only had to close the nets once for about thirty minutes to allow a downpour to pass. Luckily, I had just completed a net round when it started to rain so there were only two birds, which had to be extracted in a hurry. These were ringed in the comfort of my car.

Migrant numbers were low and the ringing was steady. A tape lure playing Tree Pipit song attracted the first birds of the autumn with at least eight present, two of which found their way into a net. 53 birds of 14 species were ringed: 2 Blackbird, 4 Blackcap, 1 Blue Tit, 3 Chaffinch, 2 Chiffchaff, 2 Dunnock, 2 Garden Warbler, 5 Reed Warbler, 2 Robin, 12 Sedge Warbler, 2 Tree Pipit, 1 Whitethroat, 11 Willow Warbler and 3 Wren.

1st and 3rd August 2019

1st year Common Whitethroat

The first two visits in August produced nothing unusual but included a reasonable selection of the commoner migrants, including the first Whitethroats, Garden Warblers and Grasshopper Warbler of the Autumn. The commoner species such as Reed, Sedge and Willow Warblers were trapped in moderate numbers but I get the impression that the bulk of migrants have yet to start moving with swallows and wagtails still to arrive in the reed bed in numbers.

1st year Grasshopper Warbler

At least maintenance of the net rides becomes easier as the season progresses. The hemlock water dropwort, which is so difficult to control when it’s growing, has died back now and the only vegetation that regularly requires clearing is reeds which have toppled into the net rides as a result of wind or heavy rain. A small Elm tree had fallen right across Blaca net ride but I had anticipated this and arrived suitably equipped to clear it. These Elms self-seed and usually reach a height of about 4m before Dutch Elm Disease kills them off. Whilst unfortunate for the trees and the wider landscape, it does keep them below the optimum height for encouraging birds into the mist nets. In the event, I found that the tree was completely dead and the trunk had snapped at the base so it was easily dealt with.

1st year Willow Warbler