The following is a redraft of the submission I made for the Orkney Bird Report 2016. Unfortunately the paper as published contains a number of errors (not of my doing, not that my submission did not require an edit). Comments gratefully received.
Stonechats
in Orkney, recent population changes (Revised from the original submission, September 2017).
Population
fluctuations of Stonechat (Saxicola
torquatus) due to weather conditions are well documented. A reference in The
Birds of Scotland is Rintoul L.J and Baxter E.V. (1948) and I think it is worth quoting Leonora Rintoul and Evylyn
Baxter at length as they describe a picture of Stonechat population change, in
their locale, towards the beginning of the last century, which is familiar to us
in Orkney today.
“It is a bird which varies considerably
in numbers, serious diminutions being often correlated with hard winters,
although this appears not to be the only factor. Our experience in our own part
bears this out: prior to 1917 stonechats were common round the coast of east
Fife, but after the winter of 1917 they became very scarce, and it was a
considerable time before they regained their former numbers. On 13th December
1920 we made the following note : “ We never see stonechats in Largo Bay now ;
they used to be there always but we have not seen one for years.” On 14th April
1923 we first note them again in Largo Bay, a pair being seen there, and the
following year two pairs bred. By 1934 they were back to their former numbers
but the hard winter of 1939-40 again wiped them out.”
Stonechat
has undergone a number of population fluctuations in Orkney in the past, these
fluctuations are well documented and well known, for example, during 1939-40 the
breeding population of Orkney was exterminated (Magee J.D. 1965) by the exceptionally harsh winter of that year. In
more recent times Stonechat was a locally common breeding bird in Orkney prior
to the winters of 2009/10 and 2010/2011 as evidenced by the species accounts in
the Orkney Bird Report. The 2006 report states, “ – a full survey of North Hoy revealed 36 pairs and an incomplete
survey of Birsay Moors showed 11 pairs, so the population level is high. Four
pairs bred at Hobbister and two at Cottascarth. Other localities included
Russadale, Stenness (two pairs); Lyde Road, Harray (three pairs); Heldale, Hoy (three
pairs) and Feold, Firth.” The reports for the subsequent years upto 2010 reflect
a similarly healthy population.
However 2010
brought change and in The Orkney Bird Report for that year the species account for
Stonechat states, “The icy weather of
January and February did not affect this species as much as might have been
anticipated.” The report then goes on to detail widely distributed pairs on
Mainland, six pairs on Rousay, five pairs in Orphir and at least 15 pairs on
Hoy. The 2011 Orkney Bird Report paints a less optimistic picture though
stating, “Following the exceptionally
cold winter some traditional breeding areas were devoid of birds and records of
confirmed and probable breeding birds were much fewer than in previous years.
There were only three reports of breeding birds on Mainland but thankfully Hoy
remained a stronghold and pairs were on territory there in at least ten
locations…”
By 2012 the
Orkney Bird Report for that year was reporting a more hopeful picture, “Following the exceptionally poor breeding
year of 2011, it was reassuring to learn that birds had returned to some of
their traditional breeding sites, albeit in very small numbers.” However, the
relative scarcity of Stonechat during 2012, particularly on Mainland, was a
topic of some interest on the Orkbird Yahoo discussion forum with a number of
posts recording sightings and discussing the relative scarcity of the species during
that year (Orkbird 2012).
Since the
autumn of 2009 I have monitored an inland site on the West Mainland around my
home near The Shunan, in Harray. This site is of about 3km2 and has
within it, and close by, a number of sizable clumps of Gorse (Ulex sp) and some areas of open Ling (Calluna vulgaris), plant species closely
associated with Stonechat (Parrinder E.R.
and Parrinder E.D. 1945). The study site is usually monitored at least
weekly, often more frequently. Stonechat was a species I saw regularly on the
study site during the autumn and early winter of 2009, with birds even seen in
our garden on a few occasions, although perhaps just one breeding pair and
their offspring were involved in these records.
Following the 2009/10 winter Stonechat disappeared from the Harray site.
So whilst the 2009/10 winter did not have the same impact as the following
winter on the Stonechat population in the county it did have an impact in this
particular location. Harray is land-locked and winter temperatures may be lower,
and snow fall may be more frequent, or snow may remain longer on the ground,
than elsewhere in the county.
The winters
of 2009/10 and 2010/11 were quite exceptional in recent times for Orkney.
Days Oct - Mar
|
||
Year
|
Ground frost
|
Snow or sleet
|
2007/08
|
65
|
8
|
2008/09
|
62
|
12
|
2009/10
|
91
|
32
|
2010/11
|
88
|
26
|
2011/12
|
57
|
7
|
2012/13
|
109
|
19
|
2013/14
|
53
|
6
|
2014/15
|
74
|
5
|
(Johnson A.K. pers.comm and 2005 to 2016).
Minimum monthly temperatures
Oct
|
Nov
|
Dec
|
Jan
|
Feb
|
Mar
|
|
2007/08
|
3
|
-0.8
|
-3.9
|
-3.6
|
-3.8
|
-5
|
2008/09
|
-2.1
|
-4
|
-5.1
|
-5.8
|
-8.8
|
-2.8
|
2009/10
|
-1
|
-1.1
|
-5
|
-8.5
|
-8.1
|
-4.2
|
2010/11
|
-0.1
|
-6.5
|
-10.8
|
-3.2
|
-3.2
|
-2.8
|
2011/12
|
2.7
|
-3.5
|
-3.5
|
-3.2
|
-2.5
|
0
|
2012/13
|
-0.9
|
-2
|
-6
|
-6.4
|
-5.5
|
-6.7
|
2013/14
|
2.2
|
-2.5
|
-2
|
-0.2
|
-1.1
|
0
|
2014/15
|
0.1
|
1.1
|
-0.7
|
-3.1
|
-1
|
-2.5
|
(Johnson
A.K. pers.comm and 2005 to 2016).
The winter
of 2012/13, although considered locally not nearly as harsh as 2009/10 and
2010/11, may have had an impact on Stonechat populations and further hindered recolonisation.
Following
the winter of 2009/10 no Stonechats were recorded in the Harray study area
until 2nd Nov 2014 when a single bird was found near Loch of
Bosquoy. Following this initial sighting three were seen a few days later on 9th
Nov and then there was one on 13th Dec. There were no further
sightings in the Harray study area until autumn 2015 when a single bird was
recorded by The Shunan on 8th Aug. There followed a series of fourteen
sightings of up to three individual birds through that autumn and into the
winter with the final record being a
single bird on 2nd Jan 2016. No further sightings were made until
the autumn of 2016 when a single bird was located on 3rd Aug. The
autumn and early winter of 2016 produced ten further sightings of up to two
individual birds but in contrast to the previous years these birds continued to
be seen into the early spring of 2017 and one pair, if not two, appeared to be
holding territory.
Bird days, Stonechat recorded The
Shunan, Harray study area.
Bird days, Stonechat recorded The
Shunan, Harray study area.
Bird days per six month
period Jan-Jun (a) and Jul – Dec (b)
(Bird day data collected only for Dec
2009 (3), occurrence estimated Aug-Nov 2009
).
It is not
unexpected that autumn sightings signalled the initial return of Stonechat to
the Harray site. Indeed the pattern of occurrence here reflects the description
in The Birds of Scotland, “Young from
early broods start to disperse locally from June, but it is not until August
that migrating birds are first found…” I consider that recolonization takes
place via the wide dispersal of young from surviving local successful breeding
pairs, and that this dispersal may also involve birds from quite distant
successful nesting. Ringing data indicate that Scottish birds can move
considerable distances in autumn (Forrester
R.W. and Andrews I.J. 2007), a bird fledged in Ayr was recovered in Spain
in the year of its fledging, 1,924km south. A colour ringing study in
North-east Scotland in the 1990s produced recoveries that suggested that some
birds also moved north in the post-fledging period. However, the provenance of
our recolonising birds on Mainland may be from nearby Hoy where the population
was less dramatically reduced by the winters of 2009/10 and 2010/11 (Williams E.J. and Branscombe J. 2005-2015).
Stonechat is
a species that may gain advantage in Orkney from climate change. Milder
winters, less snow cover and frozen ground, are likely to be beneficial to the
species. However, habitat is also influenced by climate change, and may well
lead to increases in Downy Birch (Betula
pubescens) and Sallow (Salix cinerea)
ground cover, which will have a
detrimental impact on the species as it requires open ground over which to feed
(McGee J.D. 1965). Continued
monitoring of weather data, and Stonechat occurrence and breeding success, will
in the future tell us an interesting tale in relation to this, small, colourful
and enigmatic bird.
Post script –
during the 2017 breeding season one pair bred on the study site, young birds
were in another area of the study site in late summer and two pairs bred in an
area adjoining the study site.
References
Forrester
R.W. and Andrews I.J. (editors), The Birds of Scotland, 2007.
Johnson A.K.
pers.comm. www.orkneyweather.co.uk and published in the Orkney Bird
Report, 2005 to 2016.
Magee J.D. The
breeding distribution of the Stonechat in Britain and the causes of its
decline, Bird Study, 12:2, 83-89, 1965.
Parrinder
E.R. and E.D. Some observations on
Stonechats in North Cornwall, British Birds, 38:362-369, 1945.
Rintoul L.J.
and Baxter E.V. On the present status of the Stonechat in Scotland, The
Scottish Naturalist, 60:164-170, 1948.
Williams
E.J. and Branscombe J. (editors), The Orkney Bird Report 2006-2015 (publication
dates 2007-2016).
My thanks go
to Keith Johnson for his help with Orkney weather data and to the various and
anonymous folk at British Birds, at the BTO and at the Biodiversity Heritage
Library who made the references for this short paper freely available online.
Alastair
Forsyth, March 2017 (revised September 2017).
2 comments:
Thanks for this illuminating article, Alastair, and please accept my apologies for only just noticing the page tabs for Redpoll and Stonechat!
Glad you enjoyed it, it's been a nice story to tell.
Post a Comment