in Shetland: a
century of colonisation
This report presents the results of ‘Frogwatch’, a
Shetland Biological Records Centre survey of Shetland’s Frog population in
1999. The survey was designed and organised by Roger Riddington and Mick
Clifton (Shetland Amenity Trust). An information pack was distributed to
all schools (with the help of the Education Department of Shetland Islands
Council) and youth groups in March/April 1999, to all members of Shetland
Bird Club, and to as many interested individuals as possible following a
publicity campaign in the local media. The survey pack aimed to provide
information and awareness about Shetland’s amphibians, and also produce
new records to assess the current distribution of Frogs in Shetland.
Frogs are not native to Shetland,
but have been brought in by humans, initially during the late 19th
century we believe, spreading throughout Mainland and as far north as Unst
by the middle of the 20th century. As well as being the
initial source, humans continue to be a key factor in their distribution
within Shetland (though natural movement doubtless occurs too). Since
children have had (and continue to have) a key role in the spread of Frogs
in Shetland, it is entirely appropriate that this survey was targetted
towards younger age-groups.
An appendix to this report
describes the Frog distribution throughout Shetland in more detail,
treating the main islands individually, and dividing Mainland into four.
Wherever possible, comparison is made with a similar survey in 1982, by M.
G. Richardson on behalf of the Nature Conservancy Council (now Scottish
In summary, 198 records were
received from 64 participants in response to the present survey. The map
on page 2 shows the distribution of Frogs throughout Shetland. It is
clear that, over the course of the 20th century (which has
encompassed the majority of introductions to Shetland), Frogs have spread
across all parts of Shetland, and for the most part live happily in this
northern landscape. Skerries remains the only major inhabited island or
group of islands where Frogs have not established a sustainable
population. Frogs are most abundant in the wetter and richer agricultural
areas of Central and West Mainland. Distribution on some of the larger
uninhabited islands, such as some of the Scalloway islands, is unclear,
and perhaps depends on repeated human introduction. High densities of
nesting seabirds, particularly skuas and gulls, may restrict the
population here (and this may be an important factor on Skerries too).
As might be
expected, Frogs breed somewhat later in Shetland than elsewhere in the
British Isles. Typically, spawn first appears in mid- March, over a month
later than might be expected in SW England. The development of spawn into
tadpoles and then Frogs also takes longer than in southern Britain, with
most tadpoles appearing after the middle of April. In 1999, the first
spawn reported was on 7th March in Unst, and the first tadpoles
on 29th March at Mossbank.
distribution on Shetland
Note: Black symbols indicate records since 1990, grey symbols indicate
contrast to Frogs, there were no confirmed reports of Toads in Shetland
during 1999, and it seems that these may have died out following
introductions during the first half of the 20th century.
Whether this is due to different ecological requirements of Toads, who may
find Shetland a less welcoming environment than Frogs, or whether the
initial introductions were simply on too small a scale to establish a
viable population, is not known.
This survey could not have taken place without the
interest and enthusiasm of all those who participated, and sincere thanks
is due to all those who sent in records. Participants are listed in
Appendix II. Records of Frogs, and indeed any other elements of
Shetland’s wildlife, are always welcomed by the Shetland Biological
Records Centre, and these help to improve knowledge and understanding of
the natural environment. Please send any records to:
Shetland Biological Records Centre, Shetland Amenity
Trust, 22-24 North Road, Lerwick, Shetland, ZE1 0NQ. Tel (01595) 694688.
Appendix I Details of Frog distribution
Breeding was noted in three different areas during
1999: at Uyeasound (the disused quarry and marshy area near the school),
at Baltasound (Trolla Water, the small loch adjacent to the school) and in
the mires at Haroldswick (predominantly along the Feall road). At the
latter site, spawn was first recorded on 7th March, an
exceptionally early date for Unst. At Baltasound, the main spawning
period was mid-March. Observations at Trolla Water revealed 90 ‘spawn
masses’ on 11th March, rising to 160 by the 16th and
a maximum 180 on the 24th.
Baltasound and Haroldswick
would appear to be the main centres of the Frog population on Unst. Apart
from Uyeasound, breeding has also occurred at Loch of Bordastubble
(Richardson, 1982). The Unst population has received regular injections
of frogspawn since the original introduction of Frogs (and Toads) by Saxby
in 1931, mostly to Baltasound and Haroldswick, from Mainland Shetland.
Anecdotal evidence suggests that Hazel Laurenson, a teacher at Baltasound
school in the early 1970’s, brought in spawn on a regular basis from Sandy
Loch in Lerwick. Frogs were so unusual in Unst at this time that one
elderly woman, working on her croft, chased and killed one unfortunate
Frog because she was so alarmed by its appearance!
The only breeding records received for Yell in 1999
were at Burravoe (where spawn was reported in March), and at Basta, where
spawn appeared as usual in March/April. Adult Frogs were reported
regularly from Cullivoe between March and May, from Mid Yell in March,
Aywick in April and near the Loch of Neapaback (north of Burravoe) in the
Older records suggest that spawning grounds have
been known in the south of Yell (including Coppister, Ulsta and West
Sandwick) since the early 1960’s at least (Richardson, 1982 and this
survey). It is believed that spawn was first brought to Basta (see above)
in 1963, from stocks at West Sandwick, possibly from the Loch of
Scattlands. Records from North Yell and the crofting areas of East Yell
were more frequent in 1999 than reported in the previous survey. It seems
reasonable to assume that Frogs are widely but thinly distributed across
The sole record from Fetlar in 1999 was a single
adult in the Mires of Houbie in July.
The only known breeding area for Frogs on Fetlar is
around the croft at Velzie, north of Papil Water. The record from Houbie
perhaps indicates that Frogs are slowly colonizing the wetter areas of
Whalsay & Skerries
No records were received from Skerries, where there
have apparently been no successful introduction attempts.
There were no sightings from Whalsay in 1999, but
the survey revealed previous records of adult Frogs at both the Loch of
Livister and the Loch of Huxter in the late 1990’s.
A fascinating historical account was provided by
Robert Sandison, via his uncle, of a lady in Whalsay named Joan Robertson,
born in 1861. Joan Robertson would recount how, as a young girl, she and
her family frequently heard the croaking of Frogs whilst working hay in
the meadow of Hamister, behind North Voe beach. This places the record in
the late 1860’s or early 1870’s; well before the previous earliest record
of Frogs in Shetland (Brough Lodge, Fetlar, 1895). There seems no real
reason to doubt this record. Perhaps the only possible confusion might
have been the ‘crexing’ of Corncrakes; however, these would have been
familiar birds to the crofting community at this time, and anyway they
would presumably have been largely silent by hay-making time. Robert
Sandison remarks also that at the end of the 19th century,
Hamister meadow was a very wet place with no drainage or ditching.
Breeding was reported from only four locations in
1999: by the Hillswick/Ollaberry road junction, Assater (north of
Urafirth), Ollaberry (the school), and at Nissetter, by Gluss. The
earliest report of spawn in this part of Shetland came from the
Hillswick/Ollaberry junction on March 22nd. However, reports
of adult Frogs were much more widespread. In particular, there were a
number of reports from the Eshaness area, whilst records from the more
remote parts of north mainland Shetland (such as Tingon, the Beorgs of
Skelberry and the North Roe plateau) suggest that Frogs are have now
spread throughout the more inhospitable parts of Mainland Shetland.
Richardson (1982) gives a more comprehensive list of
areas where breeding was reported, though he too cites Hillswick and
Eshaness as areas from which records were more abundant.
Adult frogs have been seen occasionally in the
Muckle Roe meadows, just south of the bridge, for the past 20 years or so,
with the latest sighting being a large adult in the autumn of 1998. These
are the first documented sightings of Frogs in Muckle Roe; whilst no
evidence of breeding was reported, it seems very likely that they do breed
successfully on the island.
The children of Mossbank primary school sent in
comprehensive details about their Frog sightings in the Mossbank area,
proving beyond all doubt that Mossbank has a healthy population! Date of
first spawn recorded was not until March 27th (this may have
been due to distribution of survey forms at about this time); the first
tadpoles were recorded on March 29th, the earliest in Shetland
Elsewhere, breeding was reported from Brae, Voe,
Eswick and Stromfirth. Adults were seen at Billister, North Nesting, and
young frogs by Sand Water in August, at peat-cutting time. This was a
very typical sighting, and many folk encounter Frogs in the Shetland
landscape when working at the peat banks during the summer.
In 1982, Richardson reported only two records from
the northern parts of central Mainland (Voe, and Setter Voe), and
suggested that the moorland area of the Kames might act as a natural
barrier to amphibians (given the vibrant population centres in southern
central and west mainland). The batch of records this year from Mossbank,
and the widely dispersed sightings elsewhere from this region, suggest
that whilst the Kames might act as a barrier to natural dispersal,
human-assisted movements are clearly not affected!
As in the previous survey of 1982, more records were
received from the West Mainland than anywhere else in Shetland. Whilst
the majority of records in 1999 came from Walls and its environs
(including Mid-Walls, Brough, Burrastow, Brunatwatt etc.), the grandfather
of one young recorder remarked that it would be no surprise to find Frogs
in any area of suitable habitat throughout the West Mainland. Besides
Walls, breeding was reported from Aith, West Houlland, West Burrafirth,
Clousta, Tresta, Selivoe and Gruting. The appearance of spawn was
remarkably synchronous throughout the region. Clousta narrowly scraped
into first place with spawn at Flawton on March 15th, closely
followed by Brunatwatt on the 16th, then West Houlland and Troni Shun on
the 18th. Almost all the main breeding areas first reported
spawn between the 15th and the 25th. The first
tadpoles were at West Burrafirth and Selivoe on April 23rd.
In addition to breeding records, adults were
reported from Bridge of Walls, Bruntskerry, Sandsound and Effirth. An
interesting record from the early times of Frogs in Shetland came from
Harold Bowie, now living in the West Midlands, who remembers releasing 24
young frogs at Upperskule, Twatt, in July 1937. The young froglets were
carefully brought north from Scotstown Moor, Aberdeen, and existing
records suggest these would have been some of the earliest introductions
to the West Mainland.
The results of the 1982 enquiry were broadly similar to
the current one, though it is perhaps surprising that no records were
received this year from Sandness.
Central & South Mainland
After the West Mainland, it is Central and South
Mainland (including Lerwick and Scalloway) that scores best for Frogs in
Shetland. In fact, the widespread distribution throughout South Mainland
was illustrated well by this year’s survey. Breeding reports were
received from South Whiteness, Califf and Hamars (Gott), Gremista, Staney
Hill, Lerwick town centre (various localities), Lerwick Observatory and
the hill area to the south, Gulberwick, Wester Quarff, Easter Quarff,
Fladdabister, Cunningsburgh, Sandwick, Hoswick and Dunrossness.
Additional sightings of adults came from Scalloway, the Tingwall Valley,
Clumlie, Exnaboe and Quendale. In some areas, Frogs are clearly very
abundant, such as Gulberwick, where a small garden pond at Shurton Brae
was almost jammed solid with adult Frogs and spawn at the end of March,
whilst another householder commented that he was feared to mow his lawn
because of the inevitable carnage! At Gulberwick, the first adult was
recorded back at a well-watched pond on February 14th 1999,
whilst the first records of spawn were March 14th at Gremista
and March 15th in Lerwick (i.e. similar to the West Mainland).
Again, the overall results of the present survey are
quite similar to the previous one in 1982, though with perhaps more
records from the southernmost part of South Mainland.
In contrast to the 1982 survey (when no records were
received from Bressay), a number of records were received from the island
in 1999, confirming that the suitable habitat here does indeed support
Frogs. Spawn was recorded in 1999 at Voehead, and on both sides of the
track up to the Ward of Bressay (on the north-west side). At the latter
site, at least some of the spawn is known to have been introduced to the
area from Gulberwick, approximately 10-15 years ago. In addition, adult
animals were reported from Cruetoun (perhaps originating from spawn
collected in past years from pools on the Hill of Setter), and to the
north of Grindiscol.
Burra, Trondra and surrounding islands
Breeding was reported from West Burra, at Hamnavoe
school and the ‘Boggy Loch’, near Hamnavoe (where spawn was present by
March 18th). An adult was seen on Trondra in the summer. No
records were received from any of the uninhabited Scalloway islands (in
1982, there were reports from Hildasay, Oxna and Papa), though of course
this may reflect observer bias rather than a real demise of the
The previous survey found Frogs to be relatively
common on Foula, an assessment confirmed by this year’s survey. Spawn was
reported from three sites in the Hametoun area on March 10th,
with 200 adults in one pool on this date! Spawn was also recorded along
the road north of the school.
Spawn was reported from two adjacent crofts in the
centre of the island, Field and Pund. Adults were reported at two further
sites not far from here, at Setter and at the school. Frogs now seem
well-established on Fair Isle (they were not recorded as present here in
the 1982 survey).
List of participants in the 1999 survey.
Mrs S. Brown
Holly Ann Nicolson
Hannah & Kirsty Uttley
Susan & Gordon Wilson
Alice & Jack Jamieson