The Dipper population of Derbyshire, 1958-68
Philip Shooter
During the mid-1950's I spent a considerable amount of time walking
by the many rivers and streams in the Peak District of north-west
Derbyshire. As I descended from the rough moorland edges into the
greener valleys, or through the grey limestone dales, it seemed to me
that Dippers Cinclus cinclus were commoner in the area than had been
generally supposed. Their sedentary nature, and the existing public
access agreements covering almost all the streams in this National
Park, led me to undertake a population survey. It was soon clear that
only about 10% of the Dippers in Derbyshire bred outside the National
Park, mostly in the Matlock area which was easily accessible, so the
survey was extended to cover the whole county.
DISTRIBUTION
AND
TOPOGRAPHY
In 1955 the Derbyshire Ornithological Society listed all the parishes
in which Dippers were known to have bred; with their help I then
checked every possible river and stream again during 1958-60. The
occupied stretches were much as expected and (with the exception of
some small streams) these are shown in fig. 1. This also marks the
division of the Peak District into two parts—the 'Dark Peak', mosdy
moorland and rough upland pasture on Millstone Grit, and the 'White
Peak', pasture-land on Carboniferous Limestone with steep-sided
wooded dales. The rivers of the latter, some 300-400 feet below the
general altitude of about 1,000 feet, have very few tributaries compared
with those of the Dark Peak, and many are fed from underground;
for this reason they are warmer, the Wye being about 4°F more than
the Derwent at the same altitude. Almost all the Dipper records for
Derbyshire have been to the north-west of a line joining Sheffield,
Ambergate and Ashbourne, which are all about 300 feet above sealevel; south and east of this line the rivers appear to be too deep and
slow-moving.
POPULATION
During 195 8-62 the Dipper population was more or less static at about
107 breeding pairs: the Derwent and its headwaters, with the Amber,
held about 51, the Dove and streams around Ashbourne 22, the Wye
and its tributaries 20, the Goyt-Etherow system 13, and the Hipper
one. There were no hard winters during this period, but the prolonged
drought in the summer of 1959 made the limestone rivers (particularly
the Dove) almost dry by late summer, and up to six Dippers were then
seen feeding within a few feet of each other.
158
rivers occupied by Dippers
other rivers
county boundary
• ••
gritstone-limestone boundary
Fig. i. North-west Derbyshire, showing rivers and streams occupied by Dippers
Cinclus cinclus. The principal watershed (altitude 1,600-2,088 feet) extends N N E from
Buxton. The boundary between Millstone Grit (in the north and east) and Carboniferous Limestone is indicated
i6o
Dipper population of Derbyshire
The extremely severe winter of 1962/63 froze almost all the headwaters of the gritstone streams for many weeks, reducing the population
to 97 pairs in the summer of 1963. Numbers slowly recovered, but one
or two of the ten territories left unoccupied in 1963 remained so
until 1966. The winter of 1966/67 was much milder than usual, and
during the spring of 1967 five pairs were found in completely new
territories on gritstone in the south-east of the species* range, one on
the Hipper, one on the Amber and three near Matlock. Until then the
limestone population on the Dove and Wye had remained constant,
but in 1967 several surplus pairs were attempting to set up new breeding
sites between existing long-established territories, causing considerable
disruption. The lack of tributaries left little room for expansion
in the limestone area, whereas the many small tributaries of the
gritstone streams are used at times by additional pairs (although
many are hardly suitable for Dippers). In the event 112 pairs bred in
1967, but another cold winter reduced the population to its original
level of 107 or 108 pairs in the summer of 1968.
One nesting site was lost by the building of the new Errwood
Reservoir in the Goyt Valley, the only one destroyed during the survey
period. In the past, however, more than 15 miles of river have been
flooded by the construction of reservoirs in the gritstone area, probably
destroying between six and nine territories; these steep-sided reservoirs
are very deep and rarely visited by Dippers. Birds of prey are now very
scarce in the Peak District, apart from Kestrels Fako tinnunculus, and
overhanging rocks seem to afford plenty of roosting places which are
safe from ground predators; occasional clutches of eggs are also still
taken, mainly by children, but none of these factors is thought to have
any significant effect on the population. In the gritstone area the major
influence appears to be the severity of the previous winter, while
reduced breeding success resulting from excessive territorial competition probably plays a larger part on the warmer limestone rivers.
TERRITORIES
Dipper territories in the gritstone area range from five to more than
50 feet wide and vary a good deal in length, more or less compensating
for variation in width, whereas those on the Wye and Dove are fairly
uniform in both width (15-30 feet) and length. The only two stretches
of river where a fair comparison can be made between gritstone and
limestone are the Noe and Derwent from Edale to Baslow and the Wye
between Buxton and Bakewell. Both are about 15 miles long and flow
south-east; they are of similar altitude, width and depth, and have about
the same number of weirs. The first (on gritstone) held 13 territories
and the second (on limestone) held 14 during each year of the survey.
These figures are, of course, for the main river only, excluding tributaries. In each case, weirs account for about two miles of water which
Dipper population of Derbyshire
161
Dippers do not normally use, so the average density on both stretches
of river was about one territory per mile.
A survey carried out during 1962-67 by George Wigglesworth and
students at Matlock College of Further Education (unpublished)
showed that the limestone rivers of the Peak District contain over three
times as much potential Dipper food as those on gritstone at the same
altitude. It is thought, however, that it is not the length or breadth
of a stream, nor even the quantity of food in the water, which governs
territory size, but the accessibility of the food. Dippers can dive and
swim in quite deep water to obtain their food, but they very much
prefer water only a few inches deep, and it seems that territory size
is principally controlled by the area of such shallow water. This is very
difficult to express quantitatively and varies with rainfall, but during
the breeding season it appears to be about an acre. Applying this to
the two lengths of river mentioned previously gives a minimum
territory length of about a third of a mile. In practice, this area of
favoured feeding-ground is often broken by several stretches of much
deeper water, which presumably explains the average density of one
territory per mile. The deep, clear, alkaline waters of the River Lathkill,
seven miles long, support only two pairs of Dippers, but they probably
contain more potential Dipper food per mile than any other river in
Derbyshire.
BREEDING
More than 100 nest records were obtained during the survey from
British Trust for Ornithology nest record cards and other sources.
About 25% relate to nests over 800 feet above sea-level, which is
about the altitude at which moorland tributaries join to form the
main rivers. Here the breeding season is short; the earliest date of
finding a nest with eggs was 29th April, a clutch of five, and the
latest nest with eggs was a clutch of four on 2nd June; the largest
clutch was five and the average 3.7, Below 800 feet, a clutch of five
was found as early as 19th March and young were sometimes still in
the nest at the end of June; the largest clutch was six and the average 4.3.
Four territories, thought to represent a good cross-section, were
kept under close observation during 1960-68. The first was on a
tributary of the Derwent, among wooded pasture at around 550 feet
above sea-level. It was unoccupied in 196} and 1964, but during the
other seven breeding seasons eight clutches totalling 35 eggs were
laid, and 26 or 27 young fledged; the largest clutch was five. The
second was also among wooded pasture at the same altitude, but on a
tributary of the Wye. It was occupied for all nine breeding seasons,
but two clutches of eggs were taken and one nest with eggs disappeared.
From twelve clutches, totalling 49 eggs, 27 or 28 young fledged; the
largest clutch was again five. The third was on gritstone moorland at
i6z
Dipper population of Derbyshire
1,200 feet above sea-level. During 1960-68, from six clutches totalling
28 eggs, 15 young fledged, but the fate of one clutch was unknown;
the largest clutch was four. In spring 196} only one bird was seen,
but a half-built nest was found; in 1968 a nest was built, but apparently
no eggs were laid. The fourth and last territory was on a limestone
river alongside a village; this site was chosen to see whether Dipper
nests suffer the same fate as many others near a village. Between
i960 and 1968 at least 16 nests were built, wholly or partly, but most
were pulled apart by children before the clutch was complete; probably
no more than ten young fledged during the whole period. The total
number of eggs laid in territories one, two and three was 112, from
which 68-70 young fledged, about 62%.
RINGING
AND
MOVEMENT
Jeremy Sorensen and other members of the Buxton Field Club ringed
136 Dippers in the Goyt Valley during 1959-66; two were later
controlled only a mile from their place of ringing, and a third was
found dying after moving four miles. The Sorby Natural History
Society ringed 34 Dippers in the Derwent Valley during 1959-67; one
was picked up dead only three miles from its birthplace. I colourringed 45 nestling Dippers during 1962-67, broadly distributed as
follows: Derwent 18, Wye eleven, Dove ten, Goyt three and Hipper
three. One which I ringed on the Dove in May 1963 has held territory
two miles north since spring 1964 and was still present in 1968; two
others (Dove and Bradford) each replaced one of their parents during
the following breeding season and two more (Wye and Hipper) bred
in their second summer on an adjacent territory. Clearly the Dippers
of the Peak District move very little, and the only conditions under
which they vacate their territories are severe frost and drought. The
high gritstone moorland has the severest winter climate, and the Dippers
of this area are those most likely to move downstream.
AC KNOWLEDGEMENTS
I would like to thank the many observers who have sent me notes on their Dipper
observations in Derbyshire, and in particular David Wilson and Ray Hawley who
gave me much help and encouragement in the early days and Derek Allsop, Peter
Lomas, Grace and George Wheeldon and George Wigglesworth who helped me
draw the work to a close.
SUMMARY
A study of the Dipper Cinclm einclus in Derbyshire was carried out during the years
1958 to 1968. About 9 0 % of the population of 97 to 112 pairs were breeding
within the Peak District National Park in the north-west of the county. The rivers
and streams occupied by Dippers, together with the general topography and geology
of the area, are described and illustrated. Factors affecting the population from
year to year in different parts of the county are discussed: in the gritstone area
the most important appears to be the severity of winter weather, while limitations
Dipper population of Derbyshire
163
on territorial space may play a larger part on the warmer limestone rivers.
Dipper territories on similar stretches of river in the gritstone and limestone
areas are compared; in each case the average density is about one pair per mile of
river. Territory size is principally controlled by the area (about one acre) of shallow
water in which Dippers prefer to obtain their food.
Data on clutch size and breeding success are given for four representative territories; the least successful are those on headwater streams in high gritstone
moorland, and also those liable to excessive human disturbance. Finally, evidence
from ringing has shown that the Dipper population of north-west Derbyshire is
very sedentary except during periods of severe frost and drought.
Philip Shooter, ijj
Derbyshire
Lower Market
Street, Clay Cross,
Chesterfield,