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North York Moors

The North York Moors are located in north-east England, to the south-east of Middlesbrough and to the north-east of York. It is predominantly an upland area, dominated by open heather moorland that is intersected by long valleys (dales) that are largely orientated north-west to south-east. The North York Moors contain the largest continuous tract of open heather moorland in England and Wales and has SSSI and SPA status. The habitat favoured by the Ring Ouzel lies in the western half of the upland area, where land elevation rises significantly above the 250 metres contour. The moorland area covers around 490 km² of which up to 288 km² (59%) could contain suitable breeding habitat for the Ring Ouzel. The North York Moors is the most easterly breeding ground for the Ring Ouzel in Great Britain and stands isolated from the nearest population in the Yorkshire Dales some 50 km to the west.

National Population and Trend

The British breeding population of Ring Ouzels has been in decline since the early twentieth century and a 27% reduction in the British breeding range was apparent between the two national atlases of 1968-72 and 1988-91 (Sharrock 1976; Gibbons et al. 1993). The first national Ring Ouzel survey in 1999 estimated the UK population at 6,157-7,549 pairs (1,523-1,654 pairs in England), with further range contraction and a likely 58% decline in population numbers since the 2nd atlas (Wotton et al. 2002). This resulted in the Ring Ouzel being Red-listed in 2003 and made a priority Bio-diversity Action Plan species in the UK.

North York Moors Population and Trend

The national survey data indicated that there was a North York Moors decrease in distribution between the two atlases of 38% with the number of 10km squares where confirmed and probable breeding had been recorded falling from 9 to 5. Provisional data from the 2007-11 3rd atlas suggests a continuing downward trend.

There are a number of problems in trying to arrive at a reliable estimate of Ring Ouzel population and trends on the North York Moors.

There is a surprising shortage of published accounts of Ring Ouzel records from the North York Moors and no dedicated study to use as a benchmark. Survey work for the two national atlases required field workers to record data for all bird species during their visits and data was published only at the 10km square level. Whilst appropriate and the only viable approach for a national survey, this methodology provides an incomplete local picture.

The first national Ring Ouzel survey in 1999 was inevitably restricted to a random selection of squares so coverage on the North York Moors was quite limited and not all squares selected were surveyed.

An elusive upland species like the Ring Ouzel which frequently nests in remote areas, often not easy to access, is a difficult and time consuming species to monitor. A dedicated survey, preferably by a field worker with experience of the species is clearly beneficial if a reliable population estimate is to be obtained.

North York Moors Study

In view of the national decline and the paucity of data on Ring Ouzel numbers and distribution on the North York Moors a local study was commenced in 1999. Records were sought in tetrads containing suitable habitat throughout the area but a core study area was identified in Rosedale in order to monitor this discrete population more intensively over a long time period.

This approach produced extensive and detailed records for 5 tetrads but information on distribution and numbers for the remaining tetrads in the North York Moors was limited to and dependent on a smaller number of occasional records from the study members and casual records from interested contacts.

The offer of help from a volunteer seeking a sabbatical project in 2010 provided an opportunity to significantly enhance the wider records. Provided with grid references of all previous locations a detailed search was carried out across the North York Moors to identify suitable breeding sites and to record Ring Ouzel sightings and breeding status (Tyas 2010). This effort updated and added considerably to existing tetrad records and provided an excellent opportunity to produce a realistic estimate of the Ring Ouzel population on the North York Moors for the first time.

Findings of the 2010 Survey

Annex 1 shows the criteria used to assess the breeding status.

Annex 2 shows all Ring Ouzel records for the North York Moors between 1999 and 2011 combined with data from the 2010 survey.

The map at Annex 3 shows the tetrads that contain suitable breeding habitat and where Ring Ouzel sightings were recorded in 2010. From this it can be seen that in 2010 Ring Ouzels were recorded in 25 of the 72 tetrads (35%) assessed as having some suitable breeding habitat. Breeding was Confirmed in 6 (24%) of the 25 tetrads, Probable in 9 (36%) and Possible in 10 (40%). The map also shows those tetrads where nothing was found during the 2010 survey but where records show breeding had taken place over a number of years between 1999 and 2011.

Annex 4 shows the location of all the territories recorded in Rosedale between 1999 and 2011.

North York Moors Population Estimate

A total of 28 Confirmed and Probable breeding pairs were recorded in 15 tetrads during 2010 - an average breeding density of 1.86 pairs per tetrad. When the records of Possible breeding in 2010 are considered, then a further 16 pairs could be added putting the total number of breeding pairs at 44.

In the 2010 survey it was not possible to visit or conduct a thorough search of all tetrads containing suitable habitat and many tetrads only received one visit. As a consequence some breeding pairs may have escaped detection. Given the 2010 survey found nothing in 47 (65%) of the tetrads considered to have suitable breeding habitat, the population estimate is likely to be higher than the above suggests.

If those tetrads are taken into consideration where nothing was found in 2010 but where breeding has been evident for a number of years during the study period, then a further 10 occupied tetrads could be considered. At a density of 1.86 pairs per tetrad this would increase the number of breeding pairs by 19 to 63.

Combining the data obtained in 2010 with the data and experience gained over the 13 years of the study then a conservative …

… representing about 1% of the breeding population in Great Britain and 4% of the population in England.

Discussion

The 12 territories recorded in the Rosedale core study area in 2010 were slightly higher than the average of 11.5 recorded between 2004 and 2010.

A breeding density of 0.47 pairs/km2 (1.86 pairs per tetrad) recorded in 2010 is low compared to figures given for populations in Scotland where densities of 4.2 to 6.4 pairs/km2 were recorded in Glen Esk and 0.9 to 1.2 pairs/km2 in the contrasting Moorfoots between 1998-2000 (Burfield 2002).

In Wales an average density of 1.2 to1.4 pairs/km2 were recorded in the more recent 2009/10 Snowdonia survey (Driver 2011).

The greatest density found in the Rosedale core study area was 3 pairs/km2 recorded in 2010 and 2011; this was confined to just one 1km square in the north of the dale. Similar density levels of 2-4 pairs/km2 were found in some areas of Snowdonia.

Due to the low-lying nature of the terrain when compared with other study areas, most territories in the North York Moors are confined to a narrow altitudinal band lying between the 250 and 400 metre contours. The highest point lies at 454 metres on Urra Moor. In the Rosedale study area the lowest nest was found at 245 metres and the highest at 362 metres with the mean altitude being 313 metres. Climate change is likely to pose serious problems for the North York Moors population.

Finally, it is instructive to consider the ring ouzel carrying capacity of the North York Moors based on the above data. Taking the 72 tetrads identified as having suitable breeding habitat, then at a breeding density of 1.86 pairs per tetrad the minimum number of breeding ring ouzels that the North York Moors could support is put at 134 pairs. However, if it is assumed that the 37 currently unoccupied tetrads are somewhat less suitable for breeding than the occupied tetrads then the breeding density in these squares may be less than the current average of 1.86 pairs. In that case an estimated carrying capacity of 134 pairs would be a little high. Conversely and to offset this, there is no evidence to suggest that the occupied territories have reached full capacity, even in the more densely populated tetrads found in Rosedale. Evidence from other studies suggests that there could still be additional capacity in the occupied tetrads and if the marginal outlying tetrads which have held breeding pairs in the past but were not included in the current population estimate are taken into consideration, then the potential carrying capacity could conceivably be greater than the estimated 134 pairs. To conclude, the above evidence suggests that in the North York Moors the breeding habitat is unlikely to be a restraining factor to an expanding ring ouzel population.

Acknowledgement

The authors wish to acknowledge the considerable help given by Chris Tyas.

References

Burfield, I.J. 2002. The breeding ecology and conservation of the Ring Ouzel Turdus torquatus in Britain. Unpublished PhD thesis, University of Cambridge.

Driver, J. 2011. Population census of Ring Ouzels Turdus torquatus breeding in Snowdonia, 2009-10. Birds in Wales 8/1 September 2011.

Gibbons,D.W., Reid J.B. & Chapman R.A. 1993. The New atlas of Breeding Birds in Britain and Ireland. 1988-1991. Poyser. London.

Sharrock, J.T.R. (ed.) 1976. The Atlas of Breeding Birds in Britain and Ireland. Poyser, Calton.

Wotton, S.R., Langston, R.H. & Gregory, R.D. 2002. The breeding status of the Ring Ouzel Turdus torquatus in the UK in 1999. Bird Study 49: 26-34.

Annex 3

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Annex 4

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© 2012 Ken Hitchinson and Vic Fairbrother

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