Stonechats in Orkney


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:

Imperfect and Tense said...

Thanks for this illuminating article, Alastair, and please accept my apologies for only just noticing the page tabs for Redpoll and Stonechat!

Alastair said...

Glad you enjoyed it, it's been a nice story to tell.