N. R. Mathew

Conservation considerations for the River Tywi with special regard to its Little Ringed Plover Charadrius dubius and Sand Martin Riparia riparia populations

Introduction

Due to the recent SSSI designation of the River Tywi because of its value to the fish species Allis Shad Alosa alosa and Twaite Shad Alosa fallax and its shingle inhabiting invertebrates. now is perhaps an opportune time to re-emphasise its ornithological importance. The river (and its tributaries) are known to harbour significant populations of Little Ringed Plover and Sand Martin - as well as Kingfisher Alcedo atthis and Common Sandpiper Actitis hypoleucos. All 4 species depend on an actively eroding river to provide them with their required breeding habitat.

Little Ringed Plover Charadrius dubius.

This Plover nested on the Tywi for the first time in 1986 (Mathew. 1986). It is dependent on the ability of the river to deposit extensive shingle banks of pebble-sized material, as a suitable substrate for its eggs. A clutch of 4 is usual.

History

The Little Ringed Plover bred for the first time in Britain in 1938. There was a steady increase from this first pair to 12 pairs in 1947. From then until 1964 the annual rate of increase was 15% (Vaughan), dropping to 8% from 1967. By 1984 there were 608 pairs while in 1991 the population was estimated at between 825 and 1070 pairs (Parrinder, 1993).

Breeding did not take place in Wales until 1970, at an industrial site, and in 1974, a pair nested on shingle along the River Severn. Numbers had risen to 6 pairs in 1984. They soon after rose steeply (concurrent with the colonisation of the Tywi) until a Welsh population 61 pairs was calculated in 1991, all but 3 on rivers (Tyler, 1991).

Fig. 1(a) The Increase in Numbers of the Little Ringed Plover breeding on the River Tywi and its Tributaries.

Fig 1(a) (incorporating data from Friese, 1992) shows that the rate of increase on the Tywi was greater than either that for Wales, or for Britain as a whole. The minority of suitable shoals on the Tywi had been adopted by 1991 (Fig. 1 (b) ) but in that year Friese (1992) thought that having found two examples of pairs nesting within 30 metres of each other, the population could potentially double. However it does appear that an asymptote is being reached with only an average annual rate of increase of 4% after 1991, compared to 60% before that year.

Fig. 1.(b) Distribution of Little Ringed Plover pain in 1991 on the Tywi, Cothi, Bran Rivers (from Tyler, 1991)

With an average density of I pair per 1.2 kilometre in 1997 (and on some lengths 5 pairs per kilometre), the Tywi is the most important river in the U.K. for this species and holds approximately 4-5% of its total population. Some birds still nest along continental rivers and in prime habitat 31 breeding pairs have been recorded on 60 km of the River Warta in Poland (Hagemeijer, et al, 1997). This, therefore, reflects the importance of the river as a natural breeding habitat in European context.

The Welsh population is considered to be of particular interest (Tyler, 1991) in that the vast majority of birds are nesting on natural sites (alongside rivers), whereas the reverse is true in England, and latterly on the continent, where most birds have changed to using man-made habitats This seems to have implications for survival rates.

The Tywi had high initial success but then rapidly succumbed to factors like flooding, wet or chilly weather, disturbance and predation (as indeed had happened to some extent earlier in England) Hatching success (at 54% of clutches in 1991) is comparable to that found elsewhere, but chick survival seems to be far lower. Fledging details are only available for recent years as in earlier years it was the hatchlings that were counted (Friese, 1993. 1994). 1993 was a poor year when much damage was caused by heavy rain, flooding and then a thunderstorm - and only 9 or 10 young birds flew This could have resulted in the smaller number of birds nesting the following year; which between them produced only 8 fledglings, even though the weather was fine Similarly, in 1995 there was a fine summer and a record number nested, but the result was only 12 'flyers' This gives productivity per pair for the] years as 0.24, 0, 22 and 027. Boyd in 1902 (cited in Vaughan) calculated that, with a death rate of 35% which he had estimated. 2 13 fledged young were required per pair to maintain a stable population. High breeding success rates are given for Germany and Holland, namely 36% (number of fledged young from number of eggs).

It seems that the Tywi must be relying on fresh immigration to maintain its population of Little Ringed Plovers. The results of ringing by Barry Stewart between 1988 and 1992 seems to bear this out. Very few birds ringed on the Tywi were "controlled" on the river in subsequent years.

It could well be that greater success is experienced at man-made sites owing to natural predators being deterred by the presence of humans.

Problems/Threats

Weather -/ rain and cold

Flooding - natural

Flooding - artificial, releases from Llyn Brianne to increase spring flows and coinciding with main egg laying period (Fig. 1(c)).

Gravel extraction.

Trampling by livestock.

Predation of eggs. young-mammalian/avian.

Conservation Measures

Due to the work in particular of Friese and Stewart, (as reported in Tyler, 1991) the interests of the Little Ringed Plover were enshrined in the old National Rivers Authority's "The River Tywi Catchment Plan. Action Plan 995" (the responsibilities of the aforementioned body are now carried out by the Environment Agency). There is a commitment not to release any large volumes of water from Llyn Brianne in the breeding season. There is a possible conflict here with the angling interest who see releases of water as encouraging a spring run of salmonid: however the spring run is wildly seen to be of declining importance.

Gravel extraction by farmers when eggs are in the nest is a fairly common cause of failure For this reason the Environment Agency will not consent to extraction at known nesting sites, except for the period August 15th to September 30th. However, many extractions take place illegally and the EA find it difficult to take action, especially with the presence of a large legal (under an Interim Development Order) commercial extraction company south of Llandovery. But obligations to protect a Schedule I (WCA 1981) species remain.

Keeping livestock away from the shoals is up to the riparian land owner, though it was a stated objective of the old National Rivers Authority to secure riverbanks generally against livestock. Farmers are reluctant to undertake large permanent fencing schemes because of a) problems with flood debris and b) the loss of productive land. However, much could be achieved with temporary electric fencing.

It is not thought that disturbance (e.g. from anglers) is a significant problem for the

Plover, which shows great determination in returning to its eggs at the earliest opportunity Indeed human presence may deter natural predators.

Perhaps the greatest factor operating in favour of the bird's success is it's own persistence; when losses (of eggs or very young chicks) occur it is willing to repeat it's endeavours, sometimes up to three times before succeeding (or giving up). Fig I (c) shows the egg-laying period: clutches are rarely laid as late as July as time is by then running out -the river is usually bereft of Plovers by mid-August.

Fig. 1.(c) Laying Dates of Little Ringed Plovers (34 pairs on the River Tywi in 1991) (from Tyler)

Recommendations

Farmland conservation schemes Like Tyr Cymen (now superseded by Tir Gofal) can advise riparian landowners against gravel extraction at the wrong time of the year and encourage the use of electric fencing to keep livestock off nesting sites.

Sand Martin (Riparia ripana)

The Sand Martin is a species, like the Little Ringed Plover, that is a summer visitor and is also dependent on the active processes of the river, but in this case on its powers to erode vertical bank suitable for the excavation of nesting burrows Nesting sites are usually chosen on sections of vertical bank that are receiving active erosion (mainly in the winter; Birds are usually faithful to nesting sites, excavating fresh burrows where the winter floods have washed out the previous years. Very often holes are excavated in lines, taking advantage of strata of differing hardness and stability, but on other occasions a colony will be found in a bank of homogenous material with holes scattered at random. Some sites seem very ill chosen with holes frequently less than a metre above the surface of the river. On the Tywi colonies vary In size, from ID or so up to 250 nesting holes with the majority being over 80.

History

The Sand Martin is known for its fluctuations in numbers largely due to conditions experienced in its winter quarters. i.e. droughts in Sahel. The last crash in numbers occurred in 1984, since when there has been a slow but steady increase reflected in the counts made along the Tywi and its tributaries (Friese. 1988).

517 nestholes were counted in 9 colonies between Llanegwad and Llandovery - on the rivers Tywi, Cothi, Dulas and Bran - in 1987. In 1988, 1.092 were found in 17 colonies, at least 3 of which had not been present the previous year.

In 1989, 1400 were counted between Carmarthen and Cilsan (west of Llandeilo) Total counts continued in 1992 when there were 1370 on the Tywi between Carmarthen and Llandovery

In 1994 there was a total of 2, 089 burrows on the Tywi and its tributaries (1, 692 on the Tywi alone) and in 1995 at least 2, 195 on these same rivers (except for the Bran); a 40% increase over the previous year.(Friese, J, 1992, 1993, 1994 and pers. comm.)

Birds nesting along the Tywi have been ringed (Stewart, 1991). Over the two summers of 1989 and 1900, 958 Sand Martins were ringed and there were 15 recoveries, or "controls" from other sites, including 6 from a reedbed at Icklesham in Sussex, and a young bird recovered in France 20 days after ringing.

Problems/Threats

Flooding - natural. Summer floods can wash out nests and drown young.

Flooding - artificial. Releases from Llyn Brianne endanger some low level colonies.

Bank works. Nesting sites actual or potential, could be lost when eroding banks are "protected" by stonework-boulders or gabions.

Predation. An unknown mammalian predator is in the habit of scratching out accessible holes.

Conservation Measures

There are no positive measures being taken to conserve the Sand Martin although it profits from LA policies regarding the Little Ringed Plover in that it is protected from artificial floods at nesting time.

Although considered a fairly common and widespread species, it is very much dependent on local geology for suitable nesting sites. Such sites in Wales are virtually confined to riverbanks and in some places coastal cliffs of similar material (Lovegrove, et al., 1994), whereas in England, like the Little Ringed Plover, much more use is made of man-made sites such as sand or gravel pits. Rivers are crucial to this species in Wales, particularly the one offering the most suitable habitat-the Tywi. The importance of this river in a Welsh context can be seen clearly in the "New Atlas". Using estimates from this the Tywi catchment appears to hold between 1% and 2% of the British breeding population.

As with the Little Ringed Plover, the biggest factor in its favour is probably its persistent attempts at nesting, though unlike the former species which usually will try to raise one brood (not counting replacements), the sand martin will attempt two or three broods in a season.

Recommendations

There should be a presumption against the use of 'hard' bank protection schemes except where absolutely necessary.

The EA would probably refuse consent for bank protection works to be carried out at known nesting sites, but it is also important to ensure a future supply of nesting sites Sand martins are quick to take advantage of suitable sites as they appear; a good example exists just upstream of Llandeilo where a section of gabion has collapsed. This site indicates how adult hoc, piecemeal bank protection schemes are not only ugly and expensive, but also don't work, Some boulders had been placed to protect a gas pipe crossing the river, but this had the effect of producing a scour immediately before the boulders and then the deflection of the river currents to the opposite north bank where the aforementioned gabions were eroded out. To remedy this, in the summer of 1995 the boulders were repositioned about 100 m further up, at a point experiencing vigorous erosion, and the south bank below this position was reprofiled, covered with geotextiles and sown with grass. By January 1996 this work was in the process of being undone with sections of matting billowing in the water and the bank again adopting a vertical profile - with also a new island or eyot forming in mid-channel.

References

Friese, J (1988) Sand Martin. Colonies in the River Tywi and its Tributaries 1987-1988. Carmarthenshire Bird Report 1988.

Friese. J. (1992) Breeding Wader in Carmarthenshire. Carmarthenshire Birds.

Friese, J. (1993) Carmarthenshire Birds 2.

Friese, J. (1994) Carmarthenshire Birds 3.

Gibbons. D West. Reed. J. B. and Chapman. R. 1993. The New Atlas of Breeding Birds in Britain and Ireland 1988-1991. T & AD Poyser London.

Hagemeijer, E.J.M. and Blair, MI. (Editors) (1997). The EBBC Atlas of European Breeding Birds: Their Distribution and Abundance. Poyser.

Lovegrove, R., Williams, G. and Williams, !. 1994. Birds in Wales. T & AD Poyser. London

Mathew. NorthR (1986) Little Ringed Plovers breeding on the Tywi near Llandeilo. Carmarthenshire Bird Report 1986.

National Rivers Authority (1994) "The River Tywi Catchment Management Plan: Consultation Report." 1994.

National Rivers Authority (1995) "The River Tywi Catchment Management Plan: Action Plan." 1995.

N.R.A (1995) Understanding River Bank Erosion from a Conservation Perspective

Parrinder, F in Gibbons et al (1993) The Little Ringed Plover, in the "New Atlas".

Stewart. B (1990) Bird Ringing in Carmarthenshire 1988-1990. Carmarthenshire Bird Report 1990.

Stewart. B (1991) Bird Ringing in Carmarthenshire 1989-1990. LIanelli Naturalists Newsletter. Winter 1990-91.

Tyler, S.J. (1991) Little Ringed Plovers in Wales in 1991. Report to NRA. R.S.P.B Vaughan, R. (1980) Plovers. Terence Doltan Ltd

Ward, D., Holmes, North Jose. P (1994). The New Rivers and Wildlife Handbook. R.S.P.B., NRA.. Wildlife Trusts.