In a 2020 paper, Mark Whittingham and colleagues show that, in one area of northeast England, the decline in Turnstone numbers is more obvious on mainland sites that are subject to human disturbance than on offshore refuges. Whilst national declines are probably linked to factors affecting productivity in breeding areas in Greenland and Canada, it is interesting that Turnstone seem to be withdrawing into areas where they are subject to less winter disturbance.
Turnstones – some background
The Turnstones that we see around the coastline of Britain and Ireland in the winter are almost exclusively birds that fly here from Greenland and eastern Canada, as you can read in this blog about wader migration (Which wader, when and why?). Britain’s wintering Turnstone numbers are falling, as are populations of several other species, such as Curlew, Oystercatcher, Knot and Redshank (see Do population estimates matter?). Turnstones are opportunist feeders; although traditionally thought of as rocky coast specialists, they can also be found on muddy estuaries and around beach-bars in the Caribbean (Why do Turnstones eat chips?).
Assessing the effects of disturbance during the winter is not easy. Feeding waders may be flushed by bait-diggers, kayakers, dog-walkers etc. but is this an issue if the food that they were attempting to eat becomes available later? To demonstrate that disturbance is a real problem, one would ideally demonstrate reductions in fitness measures such as survival, recruitment and/or productivity. This is discussed in a paper by Jenny Gill and colleagues, who studied the potential effects of disturbance on feeding Black-tailed Godwits (paper in Journal of Applied Ecology) and in another paper by Colin Beale and Pat Monaghan that shows that well-fed Turnstones were quicker to respond to disturbance than birds that had not received supplementary food supplies (Animal Behaviour). Birds may be quicker to fly if they are well-fed or there is somewhere else where they can feed. The ones that have no choice and are still hungry may be the last to leave. The issue is discussed more widely in Why behavioural responses may not reflect the population consequences of human disturbance.
Potentially, roosting waders could be more prone to disturbance than feeding birds, because of the wasted energy associated with flying around over the high-tide period or relocating to an alternative roost site (see A place to roost). An interesting modelling paper by Mark Rehfisch and colleagues showed that 90% of Dunlin, Grey Plover and Redshank on the Wash could be serviced by roost sites that were 2 km, 2.5 km and 3.5 km apart, respectively (Applied Ecology). These numbers may or may not be comparable for Turnstone but do suggest that small- to medium-sized waders feed within relatively short distances of their preferred roosting areas.
Turnstone in this study
Turnstone is a species of qualifying interest for the Northumbria Coast Special Protection Area (SPA) and for several Sites of Special Scientific Interest (SSSI) in the region. On this 140 km stretch of coast, the population of Turnstone declined by 27% between 2004/5 and 2009/10, during a period when the wintering number within England declined by 9%. There was concern that human disturbance may be one of the drivers of the population decline of wintering Turmstone within the SPA. Potentially such conditions could become more challenging towards the end of the winter, when food supplies may be less and birds are preparing for migration, or during periods of very cold weather. Given an increase in the local human (and canine) population and a marked rise in tourism within the region, it was suggested that the potential for disturbance may have increased.
The aim of the study was to compare wintering Turnstone densities and changes in counts across time from sites with differing levels of human disturbance. This was possible because long-term Wetland Bird Survey counts of waders had been made in the period between 1998/99 and 2015/16. Counts were available for two offshore refuges and 17 mainland sites that were subject to higher levels of human disturbance. No direct measure of human disturbance was available so questionnaires were used to determine the behaviour of beach users, in terms of distance travelled to visit the coast. The paper contains full detail of this methodology.
After controlling for the extent of preferred habitat (rocky shore) at each site the authors found that:
- The closer each of the 19 sites was to the nearest offshore refuge the higher the density of Turnstones, where density is calculated as birds per hectare of suitable feeding habitat.
- Turnstone counts at the four sites closest to, or containing, offshore refuges showed no significant declines. Despite the national decline in the number of wintering Turnstones, the counts on the Farne Islands and on St. Mary’s Island (both offshore islands) rose during the study period, although the rate of increase was not statistically significant from zero. There were declines at 15 of the 17 non-refuge sites. These results are consistent with the idea that, as populations decline generally, the sites of the highest quality (in this case those subject to less human disturbance) will show no, or slower, declines.
- 65% of the walkers interviewed on beaches were exercising their dogs, 83% having travelled 6 km or less to get to the beach. No relationship was found between Turnstone counts and human population densities. There is more information in the paper about the amount of time that people spend on different types of beaches.
The authors of the Bird Study paper have not sought to explain declines in Turnstone numbers, but they have provided some useful references in the Discussion that highlight how improved water treatment and warmer winters might have affected regional distributions. They also remind us that Turnstone numbers are declining – as is the case for several High Arctic species. Having established that there are declines, they use the pattern of change to ask questions about whether disturbance is an issue for this species.
The results of the research suggest that Turnstones make greater use of relatively undisturbed areas (offshore refuges) than those subject to greater disturbance by humans and their four-legged friends. Previous work has shown that excessive disturbance prevents the use of roosts and that disturbance can have serious energetic consequences (see A place to roost). Although the paper does not distinguish between birds that are foraging or roosting, this study suggests greater provision of undisturbed sites (refuges) within, or close to, protected areas is important for Turnstones, especially if there is also a drive to build more houses and attract more tourists.
When looking at the planning process for developments close to SPAs, Mark Whittingham and his colleagues suggest that three issues need to be considered in some detail:
- While it is valuable to consider the SPA as a whole, it is also important for decision-makers to consider the vulnerabilities of constituent parts of the site. Thus, for planning decisions based upon environmental impact assessments, there is clearly a need to consider pressures on particularly vulnerable areas, e.g. those used for roosting.
Studying the behaviour of marked individuals might help to pinpoint areas that are of critical importance. A separate, small-sample study of radio-tagged Turnstones in the area showed that these birds avoided mainland feeding and roosting areas at night, with at least some of the tagged Turnstones being found on offshore sites.
- Species need to be considered separately when assessing disturbance issues because habitat use and resource distribution varies widely. The focus for Turnstones is on rocky coasts and this determines their choice of roosting sites. The requirements of red-listed Ringed Plover (for instance) may be very different, especially as they spend a lot of time feeding on the sort of open beaches that look great for exercising dogs.
The paper at the heart of this blog is:
Offshore refuges support higher densities and show slower population declines of wintering turnstones by Mark J. Whittingham, Ailsa J. McKenzie, Richard M. Francksen, David Feige, Tom Cadwallender, Matthew Grainger, Nadheer Fazaa, Caroline Rhymer, Catherine Wilkinson, Pauline Lloyd, Ben Smurthwaite, Steve M. Percival, Tammy Morris-Hale, Clare Rawcliffe, Claire Dewson, Sarah Woods, Gavin B. Stewart & Elizabeth Oughton. Bird Study DOI 10.1080/00063657.2020.1713725
Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland. He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.
18 thoughts on “Disturbed Turnstones”
These findings help drive an understanding of the need for integrated management and planning of not only marine but also freshwater environments, and make a clear case for wider (beyond-site) awareness of habitat impacts in planning decision making. A very welcome study.
I have real trouble with the straight line put through the plot showing turnstone density vs. distance to refuge. I have not read the paper (£39!), so maybe I’m missing some extra info, but it seems like the assumption is made it will be a straight line to begin with? The Turnstones I see on the south humber bank roost on New Holland pier and on an offshore platform. As the tide lowers, they tend to start feeding on adjacent bits of shore first, possibly because they are simply closer to the roost site or possibly because these parts of the shore are exposed first on a dropping tide – which may be one of the reasons why the birds choose particular roost sites in the first place? Apart from the one count site that showed a higher density around 2km from the refuge (is there something special about it?), considering that you cannot fully compensate for how one feeding site will be slightly more favourable than the next in the eyes of a turnstone, personally I’d have put a straight, horizontal line through the data and come to the surprising conclusion that turnstone density is independent of distance from the refuge.
“Thanks a lot for the interest in our study. The turnstone data conformed to a normal distribution so least squares regression was used which plots a ‘best fit line’ through the data and compares it with a flat (horizontal) line that the poster mentions. We found a statistically significant relationship that the downward sloped line was a better fit (to the data) than the horizontal line (this is a standard approach used in parametric statistics). We are slightly confused by the statement that only one site at 2km had higher densities of turnstone. At 0km (i.e. at the refuges themselves) there were two sites both with high turnstone densities: therefore taken with the site at c2km there are three sites with high densities all at the left hand side of the graph.
We used sites as a whole as replicates in our study and did not look at movement within an individual site. In the example the poster gives (New Hollland Pier and an offshore platform – presumably close by) we would have treated all of that area as one site. As the poster points out birds are likely to move out from roosting sites to feed but not all birds do roost on offshore refuges.
Hope this makes things a bit clearer
Mark Whittingham and Richard Francksen”
Interesting. I’m unable to make a learned comment but can observe that one of the easiest places to see turnstones in Essex is on the end of Southend pier, where they come for crumbs from folk eating at the cafe. Learned behaviour? Maybe there is regional variation in boldness?
It might just be individual variation – some birds behave differently. This blog may be of interest. https://wadertales.wordpress.com/2016/02/17/why-do-turnstones-eat-chips/
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This is a great article and your blog on wadertales a pleasure to read Graham. Many thanks for all the detailed information.
Though I can’t read the paper by Mark Whittingham et al. I totally agree with the issues they talk about for those areas of natural interest. Human disturbance is probably one of the greatest causes of decline in wildlife but still not discussed well enough nor fully understood by the general public.
I am currently supporting another biologist and local people to save a small natural beach in the North West of Spain from the damage caused by domestic dogs and their owners. Sadly, nearly two years ago the local government converted this area rich in birds biodiversity with species such as turnstones (Arenaria interpres), little egret ( Egretta garzetta) or ringed plover (Charadrius hiaticula) among many others into a dog friendly beach.
As a result, the impact done by human disturbance on this small refuge for both migratory and resident species has been dramatic as shown by the latest bird surveys. Could you provide other sources of information that show how domestic dogs can really have a dramatic impact on wildlife? Thank you very much in anticipation, all the best.
Thank you for the kind comments. The reason that I wrote the blog was to highlight a paper that measures an effect – in this case, change of distribution. There is a lot of ‘they flew away’ research which actually tells you very little. Potentially, having one dog-friendly beach and taking the pressure off other areas may be a positive thing; it all depends upon circumstances. If you write to the lead author (Mark Whittingham, Newcastle Uni) I am sure that he will send you a copy of the paper, for research purposes. The reference list will help you, I’m sure.
Reblogged this on Wolf's Birding and Bonsai Blog.
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