Birds Near and Far
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A blog by Dave Gosney about some of the birds and places that feature in his books and DVDs but also about the state of birds in the Sheffield area
10th November 2016
Breeding birds in SK29 - changes in bird numbers in a Sheffield 10km square since 1988-90
Introduction
During 1988-90, SBSG members carried out 1-hour bird counts in almost every tetrad in the SBSG study area, providing a baseline against which future studies could be compared. For example, Gosney (2015) studied the results for the whole SBSG area, comparing these 1988-90 counts with similar 1-hour counts (TTVs) carried out on behalf of the BTO during 2008-11. These highlighted many changes in bird numbers but also warned that some of the results may be influenced by the relatively poor coverage of some tetrads during 2008-11. In SK29 (Bradfield), for example, the observers recorded less than 40% of the 'expected species' in 9 tetrads. The aim of the current study was to redo all the 1-hour counts in SK29 to provide a more reliable comparison with the 1988-90 data.
Methods
24 of the 25 tetrads were visited by the author during May 2016 and counts were made of all species found by sight or sound during timed 1-hour periods. Any species recorded outside of that hour were noted as merely 'present'. Only adults were counted and species were only counted if they were deemed to be using the available habitat - hence birds flying high overhead such as gulls or swifts were ignored. The results from these 24 1-hour counts are compared with an equivalent 24 1-hour counts made during 1988-90. Where several 1-hour counts were made, the data used for comparison is only what was counted during the 'best' hour - that is the hour in which the most species were recorded. One tetrad, SK29 D (Pike Lowe Stones), was not visited during either survey due to its remote location. On average, 53% of the 'expected species' were found in each timed tetrad visit in 2016 (The number of 'expected species' is largely based on the number of species found in each tetrad during 2003-08, given unlimited time).
The 10 km square SK29 (Bradfield) is located immediately north-west of the City of Sheffield (see map). It comprises several upland valleys (Don, Ewden and Bradfield) and interceding plateaux leading down from the grouse moors which make up the western quarter of the square. Almost all of the square lies between 300-400 metres asl.
Results
Species not found in 2016
The following 11 species were found in 1988-90 but not in 2016. Some of these species probably no longer breed in SK29 but that cannot be concluded from these results alone; they merely demonstrate that in 2016 these species were sufficiently scarce to be unrecorded in at least 24 hours of intensive birding. The numbers given show how many were found in 1988-90 followed by the number of tetrads in which they were recorded (during the 'best' 1-hour count only).
Little Grebe (1,1), Tufted Duck (14,3), Goshawk (1,1), Sparrowhawk (3,3), Short-eared Owl (1,1), Green Woodpecker (3,3), Yellow Wagtail (1,1), Whinchat (16,7), Wood Warbler (11,7), Willow Tit (3,2), Twite (1,1)
Local declines in Whinchat and Wood Warbler have been well documented in the Sheffield Bird Reports and in Gosney (2015) but it was still a surprise to find NONE AT ALL of these formerly quite widespread species in SK29. It was no surprise to find no Twite or Willow Tit as these are almost certainly locally extinct; the same may also be true of Goshawk.
However, the failure to find any Tufted Ducks and Green Woodpeckers is surprising and points, at least, to a decline in these species. Sparrowhawk is certainly not extinct as they were found in the area in 2016 but outside of the 1-hour counts. It's still quite shocking to note that none were recorded in 24 hours in what was formerly one of their Sheffield strongholds; in 1975-80 they were more widespread in this 10km square than any other (Hornbuckle and Herringshaw 1985). It's not known whether Little Grebe, Yellow Wagtail and Short-eared Owl were genuinely absent in 2016 or simply overlooked.
'New' species found in 2016
The following 15 species were found in 2016 but not during the equivalent 1-hour counts in 1988-90. The numbers given show how many were found in 2016 followed by the number of tetrads in which they were recorded.
Great Crested Grebe* (1,1), Cormorant (1,1), Mute Swan (1,1), Greylag Goose (3,1), Mandarin (3,1), Muscovy Duck (1,1), Buzzard (7,5), Hobby (2,1), Oystercatcher (3,2), Woodcock* (1,1), Black-headed Gull* (2,1), Ring Ousel* (1,1), Nuthatch* (4,4), Raven (8,3), Tree Sparrow* (1,1).
Those species marked with a * were known to be present in 1988-90 but just not counted during the timed visits. Of the rest, Cormorant, Mute Swan, Greylag, Mandarin, Buzzard, Hobby, Oystercatcher, Raven and, possibly, Muscovy Duck are genuine additions to the avifauna. Nuthatch is clearly more numerous now than in the 80's but still rather scarce here compared with other parts of the Sheffield area.
Species counted in smaller numbers in 2016
Fig 1 Numbers of each species counted during 24 1-hour counts in 1988-90 and 2016: a) Species showing an apparent decline of over 33%
Decreases in many species were highlighted in Gosney (2015) but some of the apparent declines might have been because species were overlooked by relatively inexperienced observers in 2008-11. These figures, in which none of tetrads were under-recorded, confirm we have lost about 3/4 of our Redpolls, Tree Pipits and Cuckoos. They are in line with familiar national and local observations but notice that Kestrel seems to have experienced a decline of similar proportions. Kestrel was not listed as a declining species by Gosney (2015) because the data for the whole of the Sheffield Area showed only a 13% decline between 1988-90 and 2008-11; however taking the data for SK29 only, the number counted in 2008-11 had fallen from 9 to 3; no other 10km square showed such a marked change. Maybe the data for SK29 is the first local evidence of the national decline (by 52% since 1970 - RSPB 2015). The figures for Swift are unreliable; the presence of airborne swifts can be rather random and not indicative of breeding numbers. Even so, surprisingly few were seen in 2016.
Of the remaining species that seem to be declining in SK29, Yellowhammer, Skylark and, to a lesser extent, Meadow Pipit have been widely identified as declining both locally and nationally (RSPB 2015, Wood and Hill 2013) but the same is not true of Treecreeper, Magpie, Goldcrest, Coal Tit and Jay.
In Gosney's (2015) analysis Treecreeper, Magpie and Jay all seemed to show a decline in the Sheffield area as a whole but, since this was contrary to other national and local data, perhaps such apparent declines were due to relatively poor coverage in 2008-11.
The current study shows that, at least with regard to these species, the declines are more likely to be genuine - perhaps the first indication that these species are in trouble. It also suggests that Goldcrest (and Meadow Pipit) have shown a greater decline locally than has so far been noted nationally. The lack of Coal Tits in 2016 is remarkable as it contradicts all other data; what is certain is that it is not due to them being overlooked by the observer in 2016. Has there been a particular change in the composition of the plantations in SK29 that has caused this change? Note that Goldcrest, Meadow Pipit and Coal Tit were all found in a similar number of tetrads in each survey; it is only the numbers within each tetrad that seems to have changed. These changes would be overlooked by a standard distribution survey.
Not as bad as feared
Of the other species listed in Gosney (2015) as showing a decline of 33% or more in the Sheffield area as a whole, some, such as Spotted Flycatcher, House Sparrow, Snipe, Lapwing and Stock Dove, actually seem to have increased in SK29 (see below). This study shows no clear evidence of declines in Redstart, Mistle Thrush or Linnet although both Starling and Willow Warbler showed declines in SK29 of about 30%, not quite as great a change as reported for the area as a whole but still of concern.
Species counted in greater numbers in 2016
In addition to the 15 species counted in 2016 but not 1988-90, the following species showed a marked increase since 1988-90
Fig 3 Numbers of each species counted during 24 1-hour counts in 1988-90 and 2016: b) Species showing an apparent increase of over 60%
The results for Tawny Owl, Bullfinch, Grey Heron and Reed Bunting are based on so few tetrads that they may be misleading. The same might also be true of Spotted Flycatcher and Golden Plover but, given that they are declining nationally, it was encouraging to find so many in 2016. The discovery of Spotted Flycatchers on the edges of the moorlands in 2016 could be linked to the observation in Gosney (2015) that this species had declined in all parts of the Sheffield area except SK19 (Derwentdale) - another relatively high-altitude area with lots of moorland fringes - where they had noticeably increased.
The results for Chiffchaff, Siskin, Goldfinch, Jackdaw, Great Spotted Woodpecker and Blackcap all reflect the national picture (all have increased by over 50% since 1995 - RSPB). In the same period, Whitethroat, Pheasant, Red Grouse, Mallard, Garden Warbler, Collared Dove and Stock Dove have also increased nationally but not to the extent shown here.
The increase in Whitethroats shows the extent to which this species has spread to more upland areas. Although this analysis compares only the 'best' 1 hour counts (ie 24 hours per survey), we actually have data for 192 hours in SK29 during 1988-90, yet Whitethroats were still found in only 2 tetrads; they've increased from 2 tetrads in 192 hours to 8 tetrads in 24 hours.
The most encouraging and surprising outcomes have been for the breeding waders; nationally Lapwing have declined by 45% since 1990 and Curlews by 46% yet in this study they seem to have increased significantly, along with Snipe, Golden Plover and the newly colonising Oystercatcher. It's possible that the numbers of waders counted were unusually high in 2016 due to a particularly wet spring.
It was also encouraging that numbers of Moorhens were higher, despite a national decline of 15% since 1995. The increase in Pied Wagtails seems likely to be genuine but House Sparrow is a species whose numbers in these counts depend very largely on the amount of time within the dedicated hour that is spent in built-up areas. Hence the increase may, or may not, be an artefact but at least there is no evidence of a decline.
Species diversity
The mean number of species counted per hour increased from 28.9 in 1988-90 to 30.8 in 2016; this may be a reflection of greater species diversity (more new species added than species lost) but may also be a reflection of even more comprehensive coverage in 2016 than 1988-90. Comparing only the 14 tetrads covered by the author in both surveys, there was still a slight improvement (from 30.0 species per hour in 1988-90 to 31.1 in 2016).
Discussion
These 1-hour counts provide a quick method of comparing numbers in different time periods. Any of Sheffield's 10km squares could be studied in a similar way by carrying out a 1-hour count in each of the 25 tetrads and comparing the results with those found in 1988-90 (or, indeed, 2008-11). Even if all the counts are done in May (which gives the best results) this is still achievable by a single observer in one, albeit busy, month. Which 10km square do you want to take on?
Summary
The results of 24 1-hour bird counts carried out in 2016 are compared with equivalent counts in 1988-90 and show many changes that reflect previously highlighted national or local increases or declines. However the decreases in Treecreeper, Magpie, Goldcrest, Coal Tit and Jay and the increases in Whitethroat, Red Grouse, Mallard, Moorhen, Garden Warbler and, especially the waders Lapwing, Curlew, Snipe and Golden Plover were all somewhat surprising. Eleven of the species found during the 1988-90 counts were not found in 2016; of these Twite and Willow Tit are almost certainly extinct in SK29 and Wood Warbler and Whinchat are, at best, extremely scarce despite being formerly widespread. On the other hand, 15 species were found in 2016 but not during the 1988-90 1-hour counts. Of these, Cormorant, Mute Swan, Greylag, Mandarin, Buzzard, Hobby, Oystercatcher and Raven were not found at all during 192 hours birding in 1988-90 and so are genuine additions to the local avifauna.
Acknowledgements
Thanks to all the SBSG members who contributed to the original 1988-90 survey.
References
Gosney, D. 2015 Changing numbers of breeding birds in the Sheffield area Brit. Birds. 108:66-79
Hornbuckle, J., & Herringshaw, D. 1985. Birds of the Sheffield Area. Sheffield Bird Study Group, Sheffield
RSPB. 2015 The State of UK's Birds 2015. RSPB, Sandy
Wood, D., and Hill, R. D. 2013. Breeding Birds in the Sheffield Area. Sheffield Bird Study Group, Sheffield
Postscript
Clearly there have been many changes in the last 25 years but maybe they are taking place over much shorter time spans. Look here to see what evidence there is for changes in bird numbers in SK29 within the last decade.
