Spotlight: A tale of two study sites with increasing shorebird numbers
Imagine. You are driving very slowly along the coast of Barr Al Hikman, a tropical intertidal ecosystem in Oman. You scan high water line for flocks of shorebirds and marvel at the abundant birdlife. When the vehicle can go no further, you continue your scan on foot. You have even seen turtles, dolphins and whales while studying the birds at this amazing site. Now imagine that you are alone on an ocean beach in northern California. The water laps at the sand as you walk slowly, stopping occasionally to use your binoculars or spotting scope to scan for Snowy Plovers. It’s nesting season and you are visiting two to three times a week because you’ve detected nesting adults.
It was the best of fieldwork.
Of course, I am sure the researchers could tell you that it was also the worst of fieldwork; perhaps on a surprisingly wet day in Barr Al Hikman, when the sabkha – a mixture of sand, salt and mud – was suddenly like quicksand; or perhaps in the pouring rain on a northern California beach full of nests destroyed by predators, unleashed dogs or vehicles.
For many shorebird biologists, fieldwork can be the best of times and the worst of times. This issue of Wader Study contains articles about two very different field sites on nearly opposite sides of the northern hemisphere. In their study, de Fouw and colleagues1 report on broad waterbird surveys conducted during the winters of 2007/08, 2013/14 and 2015/16 in Barr Al Hikmann – a study area that had last been surveyed in 1990. In a very different study, Colwell and colleagues2 summarize 16 years of data focused on a color-marked breeding population of Snowy Plovers in northern California. At their site annual surveys are required as part of a species’ recovery plan.
At both sites the researchers were counting shorebirds and looking at how their numbers were changing over time. And in both studies, the researchers found that shorebird numbers increased.
For years, shorebird conservationists have been reporting decreases in shorebird numbers worldwide3. So increases are good news, right? Well, yes and no. Increases in at least some sites are undoubtedly better than decreases at all sites across a flyway or within a population. However, the studies under the spotlight here remind us that increases in shorebird numbers at one site don’t necessarily mean all is well in the flyway – or even at the site.
Researchers studying at Barr Al Hikman wanted to update data on the number of birds using the site and confirm the area’s importance within the network of intertidal ecosystems that make up the Asian-East African migratory flyway. They found that at least 42 species of waterbirds use the site regularly and they counted more than half a million birds. Shorebirds were by far the most dominant species group with total numbers of 300 to 400 thousand in each survey year across 23 species. Impressively, for 18 of the 23 shorebird species, the numbers wintering at Barr Al Hikman exceeded 1% of their flyway population (the critical minimum threshold value that defines an area of conservation concern) and for nine of these species, at least 10% of the flyway population was found at Barr Al Hikman. The study clearly confirmed that Barr Al Hikman is the single most important wetland for wintering birds in the Middle East, not only with respect to the number of birds, but also in terms of species diversity.
Additionally, the surveys revealed that the number of birds wintering at Barr Al Hikman has increased. Compared to the numbers seen during surveys in 1989/90, the researchers found that general waterbird numbers had almost tripled, with large shorebirds increasing two-fold and small shorebirds increasing five-fold.
What is causing the increases? Perhaps conditions have improved throughout the Asian-East African flyway and shorebird populations are increasing everywhere. For shorebirds that breed in the difficult-to-reach High Arctic, this question is usually examined by monitoring numbers in wintering areas. If increases are found in a number of wintering areas, then it’s a good-news story. Unfortunately, as de Fouw and colleagues discuss, the Arabian Gulf is developing rapidly and human impact on marine systems is high. Increased shorebird numbers are not being seen throughout the flyway. For example, a 2008 study in the United Arab Emirates paints a picture of shorebird decline as a result of major loss of wetlands due to coastal development4. Perhaps birds from that site now find a haven at Barr Al Hikman – one of the remaining sites for shorebirds in the Middle East. Barr Al Hikman is still relatively pristine, but is under threat from export-driven fisheries including plans for a large aquaculture shrimp facility. If the increased numbers at Barr Al Hikman stem from the redistribution of shorebirds due to the loss of their original wintering habitat at other sites in the flyway, then the increase actually indicates that the flyway populations are threatened. This makes long-term conservation of Barr Al Hikman all the more important.
In northern California the story is very different. Colwell and colleagues have solid data not only on population size, but also on population productivity and immigration rates. Over 16 years, they kept detailed histories of 353 marked and breeding individuals (159 males; 194 females). The population at their site decreased dramatically from 74 to a low of only 19 between the years of 2001 to 2009. Then from 2010 to 2016 the population rebounded, growing at an annual rate of 22% to 72 birds in 2016. Had things turned around? Was the site now productive? Unfortunately not, productivity averaged around 0.85 of a chick fledged per male, which is below what is needed to even maintain, never mind increase a population. Instead, the authors argue that, much like at Barr Al Hikman, recent growth stems from immigration. Their data showed that over the past 12 years, immigrants from more northerly sites comprised about 65% of the population. But unlike Barr Al Hikman, the authors do not think the site is a haven; rather, based on the productivity and immigration data, the authors conclude that the Snowy Plover subpopulation in coastal northern California (Recovery Unit 2) is a demographic sink. Not the best of sites, even if it might be the best of fieldwork at times.
Colwell and colleagues point out that no predator management occurs on their site, despite evidence that predation is the main cause of low reproductive success. They further point out that most immigrants to their site come from areas where active predator management has resulted in consistently higher productivity (as also highlighted for Red-necked Phalaropes in Nome, Alaska in a paper by English and colleagues, also in this issue of Wader Study5). They urge agencies responsible for the Snowy Plover in northern California to expand predator management and also note that that management of human recreational use of plover habitats is most effective on federal and state lands where enforcement also occurs.
This tale of two sites and these two important studies emphasize the importance of thorough and nuanced research on shorebird demographics within the context of conservation within the flyway or the larger threatened population as a whole. There is often more to increasing numbers than meets the eye.
- de Fouw, J., A. W. Thorpe, R. A. Bom, S. de Bie, K. Camphuysen, B. Etheridge, W. Hagemeijer, L. Hofstee, T. Jager, L. Kelder, R. Kleefstra, M. Kersten, S. Nagy & R. H.G. Klaassen. 2017. Barr Al Hikman, a major shorebird hotspot within the Asian-East African flyway; results of three winter surveys. Wader Study 124(1): 5-16.
- Colwell, M. A., E. J. Feucht, M. J. Lau, D. J. Orluck, S. E. McAllister & A. N. Transou. 2017. Recent Snowy Plover population increase arises from high immigration rate in coastal northern California. Wader Study 124(1): 21-29.
- Wetlands International. 2012. Waterbird Population Estimates, Fifth Edition. Summary Report. Wetlands International, Wageningen, The Netherlands. Available from wpe.wetlands.org.
- Green, M., & C. Richardson. 2008. Loss of wader habitats in the United Arab Emirates. Wader Study Group Bulletin 115(1):50-51.
- English, W.B., E. Kwon, B. K. Sandercock & D. B. Lank. 2017. Effects of predator exclosures on reproductive success in Red-necked Phalaropes. Wader Study 124(1): 26-32.
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