Wader populations at Musselburgh
by R. W. Furness

From Scottish Birds (1973) 7: 275-281.

Between 1969 and 1973 observations were made to determine the numbers of waders frequenting the shore between Leith Docks and Cockenzie Power Station in the Firth of Forth and to discover where the birds fed and roosted. It was hoped that a comparison with unpublished counts made between 1959 and 1961 by J. Ballantyne would reveal the effects of man-made alterations of the coastal habitat. Information relating to past wader roosts in the area was provided by J. Ballantyne, D.I.M. Wallace and Loretto School Bird Club reports. For the period 1959-61 some 30 counts were available and there were 70 for the period 1969-73, and so the changes in numbers are considered to be accurately recorded.

Land reclamation during 1959-71 removed less than one fifth of the area of mussel beds and a smaller proportion of the sand and rock areas previously available to the waders. In 1971, reclamation began at Seafield. It is assumed that the amount of food available to the waders remained unchanged during 1959-72, but in 1973 the reclamation at Seafield reached such a stage that waders were no longer able to feed there to any great extent.

Several changes have also taken place that have affected the roosting habits of the waders. A shingle spit formed at the mouth of the Esk and grew irregularly throughout the 1950s. Morrison's Haven, which held part of the wader roost before 1959, was filled in, forcing the birds to roost elsewhere. In 1964, at the mouth of the Esk, the construction of lagoons was begun for the dumping of waste ash from Cockenzie Power Station (plate 21, plate 22). These were built on a roost site previously used by some of the waders. Construction was completed by 1966 and produced three lagoons filled with water and one, at the west end, only partially flooded. The east lagoon was first to be used for ash-dumping, which by 1969 had produced a semi-solid ash surface. By 1971 the east lagoon was full, and the ash had dried to a firm surface. Dumping began in the adjacent east-central lagoon, where a soft ash surface immediately formed.

Feeding areas

The study area was divided into sections according to substrate type. Where possible, physical barriers (e.g. sewage pipes) were used to demarcate the feeding sections, as this reduced the chance of missing or double-counting birds feeding near the boundary of a section (fig. 1).

The numbers of each species feeding in each section were counted at low tide twice in January and twice in March. The four counts gave very similar results (table 1), except for Redshank, whose distribution in spring differed from that in mid winter, probably because large numbers were present during the spring counts. About 85% of the waders fed in two of the eight sections, half of them in section G. Some species had much more restricted feeding distributions than the population as a whole (table 2). In particular, Bar-tailed Godwits were found almost exclusively at Seafield. When this area was reclaimed the winter flock (about 700 in previous winters) fell to 200 in 1972/73, and these birds fed in sections C, D and F, where they had previously not been found. A similar decrease occurred in the numbers of Dunlin, some of which also found feeding sites in sections where they had previously been less numerous.

Table 1. Percentage of each species found in each feeding section, January 1971

	A	B	C	D	E	F	G	H	Total population
Oystercatcher	1	6	4	10	5	0	73	0	1000
Ringed Plover	0	38	25	0	0	0	38	0	40
Golden Plover	47	0	0	0	6	0	47	0	900
Turnstone	10	0	5	29	10	0	48	0	110
Curlew	4	8	6	4	4	0	75	0	140
Bar-tailed Godwit	0	98	2	0	0	0	0	0	420
Redshank	7	26	7	7	7	0	45	0	300
Knot	6	1	0	0	0	0	93	0	1650
Dunlin	6	67	0	0	0	0	28	0	2050
All species	10	31	1	2	2	0	54	0	6600

Table 2. Species with restricted feeding habitat

	Percentage of total population in one section
Bar-tailed Godwit	97 in B
Knot	93 in G
Dunlin	70 in B
Oystercatcher	70 in G
Curlew	70 in G

Results averaged from four counts made in 1971.

Roosting areas

Since the 1940s the whole Musselburgh wader population has never roosted together. In the 1940s there were four sub-roosts. Redshanks roosted on Loretto Newfield, where they obtained worms at high tide. This roost has remained ever since. The shingle spit was used by several species, but it was not a reliable roost site, for it varied in size and position and so held only about 100 birds. Morrison's Haven was a regular roost (on rocks), used by a total of about 300 birds, Oystercatchers, Redshanks and Turnstones. Dunlins and Ringed Plovers also roosted in small numbers along the shore, but most of the Dunlins, Knots, Bar-tailed Godwits and Curlews went to Aberlady Bay to join the birds that fed there.

When the shingle spit grew in the 1950s, larger numbers roosted there, but the situation remained fairly static until the construction of the lagoons and the filling in of Morrison's Haven. This deprived the Oystercatchers and Turnstones of their former roost, and the Oystercatchers moved onto the partially built lagoon walls, whereas the Redshanks dispersed along the sea-wall. When the lagoons were completed the waders took to roosting in the west lagoon; all except the Redshanks on Newfield, and even they came onto the lagoon if they were disturbed from their preferred site. On rare occasions the roosting birds were forced to leave the lagoon roost, and when this occurred they would go to the sites they had used before the construction of the lagoons.

After 1966 there was a gradual increase in the number of people visiting the lagoons for recreation. This increased the disturbance, and the Oystercatchers and Redshanks that roosted in the west lagoon used the newly formed ash surface in the east lagoon with increasing frequency. By the end of 1971 the east lagoon had been filled and had overspilled into the east-central lagoon. The Oystercatchers immediately moved into this lagoon to roost on the newly formed surface. Thus the major roost changes have been

1959 Oystercatchers, Redshanks and Turnstones moved from Morrison's Haven to the shore.
1964 Oystercatchers moved from the shore to the lagoon walls.
1966 All species except Redshank moved into the west lagoon.
1968 Oystercatchers and Redshanks moved from the west to the east lagoon.
1972 Oystercatchers and Redshanks moved from the east to the east-central lagoon.

The extent to which species use roosts other than the lagoons was examined by summing the low-tide counts for each section and comparing this feeding population with the high-tide count made in the west and east lagoons on the same day (table 3). On the four count dates Golden Plovers roosted exclusively inland (although they do sometimes roost in the lagoons). An almost constant number of Redshanks roosted on Loretto Newfield (when undisturbed), but the proportion of the March total was very small, since about 1000 passage birds had moved into the area, and all of these roosted in the lagoons. Some Turnstones and Ringed Plovers remained on the shore or sea-wall at high tide, and here again the proportion doing so was smaller when large numbers were present in March. Other differences are probably the result of errors in counting. Where the roost count exceeded the feeding total, the difference was taken to be zero, for no birds from the lagoon roost are thought to feed outside the eight sections.

Table 3. Percentage of feeding populations
that roosted away from the lagoons

	January	March
Golden Plover	100	100
Redshank	56	5
Turnstone	33	10
Ringed Plover	12	8
All other species	0	0

Averaged from four counts

Table 4. Effect of the distance of the former roost site from
the feeding area on the numbers of each species

	Bird-months per year 1959-61	Bird-months per year 1969-72	increase (x times)	former roost sites
Golden Plover	15	770	60	Inland
Bar-tailed Godwit	70	2160	30	Aberlady
Knot	480	7340	15	Aberlady
Curlew	140	1350	10	Aberlady
Dunlin	1190	10990	9	Aberlady
Oystercatcher	1340	11790	9	Local
Ringed Plover	130	610	5	Local
Redshank	1010	3890	4	Local
Grey Plover	5	15	3	Local
Turnstone	380	1160	3	Local

Note: The unit used is bird-months per year. This measures the amount monthly
averages for each species uses the roost by summing the 12 each species.

The most dramatic change in the roosting behaviour of the wader population occurred when the lagoons were built. The roost moved from shifting shingle and rocks to a large flat expanse of mud, sheltered on all sides by steep embankments. The Musselburgh population then increased from a pre-1966 constant winter level of about 800 birds to a post-1966 winter average of more than 7000, though the transition was gradual rather than immediate. Table 4 shows the increase observed in the numbers of each species by comparing the sum of the average number of each species present in each month of the year for the years 1959-61 and 1969-72. Data for 1972/73 are excluded, because they are influenced by the reclamation at Seafield. The table shows that the species that used to roost at a greater distance from the feeding areas increased more than those that roosted nearby, The latter also increased considerably, presumably because they gained a more secure roost site. The species that had previously flown to Aberlady to roost now saved themselves a 20-mile return flight between feeding periods, and this is reflected by the large increase in numbers that occurred. Before 1966, Golden Plovers were rarely found on the shore at high tide, because they are very sensitive to human disturbance and so were forced to roost inland. Large numbers took to roosting in the lagoons when these were constructed, but as human disturbance there increased each winter so the number of Golden Plover declined. In 1972/73, however, the lagoons were frequently undisturbed, and large numbers of Golden Plovers were again at the roost.

Two other changes in roost site took place, involving Oystercatchers and Redshanks. With the increasing pressure of human disturbance these species took to roosting in the east lagoon and later in the east-central lagoon when a solid surface formed there. There, only 409 yards from their original lagoon roost, they avoided most of the disturbance to which they had been subjected previously. This was followed by an increase in the average winter numbers from around 1000 in 1969/70 to around 3000 in 1971/72. No such increase was recorded elsewhere in the Forth (BTO Estuaries Enquiry unpublished counts).

Because over 90% of the Musselburgh population of Bar-tailed Godwits fed at Seafield, this species was greatly affected by the reclamation that took place from 1971 and which has now completely obliterated their former feeding area (section B). The shore at Seafield was used as a dump for demolition refuse in 1971 and, although it did not then encroach on the intertidal feeding area of the Godwits it stopped people from using the shore for recreation, allowing the birds to feed undisturbed. As a result their numbers were about 50% higher in 1971/72 than in previous winters (800 birds compared to 500 in previous winters). However by 1972/73 the area had been walled in and the Godwits were unable to feed there.

It seems therefore that, at least for the past 14 years, the numbers of waders wintering in the Musselburgh area has been considerably influenced by the amount of disturbance to which the birds have been subjected, and by the quality of the roost site, i.e. its proximity to the feeding area and the extent to which it protects the birds from disturbance.

I am most grateful to J. Ballantyne for allowing me to use his notes and for considerable help in this study. I would also like to thank Dr L.L.J. Vick and D.I.M. Wallace for allowing me to use their notes, and Dr P.R. Evans for constructive criticism of the first draft of this paper.

Comparison of counts made of waders in the Musselburgh area in 1969-73 with others made in 1959-61 shows a considerable increase in the winter population of all species. Examination of the past and present roost sites suggests that it is mainly the quality of these that has determined the numbers of waders inhabiting the area. Cases of change of roost site are examined, and their effect on numbers is shown. The feeding distribution of the waders is examined in relation to coastal development.

HAMILTON, D. 1929. Bird life by the Esk at Musselburgh. Scot. Nat. 179: 157-162.
HAMILTON, D. 1934. Bird life by the Esk at Musselburgh. Scot. Nat. 206: 51-54.
HAMILTON, D. 1939. Bird life by the Esk at Musselburgh. Scot. Nat. 238: 96-98.
LORETTO SOHOOL. 1955. Bird Club Report.

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