Jeroen Reneerkens studies how temperatures affect breeding success of sanderlings in Greenland. Together with other researchers, he’s noted both steadily increasing summer temperatures at the Zackenberg study site and witnessed almost no sanderlings breeding this summer.
A sanderling in the long-term study in Greenland. Photo: Jeroen Reneerkens
The warming Arctic summers are creating a mismatch in timing between insects and spiders and their shorebird predators. Crawly creatures in the pitfall traps in Zackenberg are emerging earlier over the last two decades, yet the sanderlings have not adjusted their egg laying, prompting further studies this year.
But 2018 has been an exceptional summer. Heavier winter snowfall more than counteracted the warmer spring season, and the sanderlings and other Arctic shorebirds arrived to find extensive snow cover, forcing the birds to congregate in small snow-free areas where they are able to feed.
These sanderlings are usually mostly on their nests in the last two weeks of June. But this year most of the shorebirds in the Zackenberg valley were flocked together in the snow-free area around the field station. Very lean birds were walking between the station's wooden buildings, approachable to a few meters, likely saving energy for foraging rather than escaping from human researchers. It was clear that no shorebirds were going to nest within the next few weeks, if at all this summer. But it did allow the researchers to document the effects of late snow cover on the behavior of shorebirds and their condition.
Capturing and re-capturing sanderlings, turnstones and red knots showed that most individuals were in poor condition. Some birds managed to maintain weight from the food waste outlet of the field station, but other birds were underweight, and some were found dead apparently of starvation. The sewage outlet was also a magnet for gyrfalcons, and possibly Arctic foxes, seeking prey.
Over the two-week period of Jeroen's visit, he did not hear a single singing sanderling and only a few times heard a singing red knot or dunlin. Just two Sanderling pairs were seen, and these appeared not to stay together, or at least could not be found again, during the following days.
With deep snow still present well into the time the sanderlings would normally be starting to hatch, it’s very unlikely that they, or other shorebirds, will have been able to breed at Zackenberg this year. And with similar snow conditions across north-eastern Greenland, most of the area's shorebirds probably never reached their breeding grounds, staying in more southerly regions with better feeding possibilities.
Snow covering the tundra of Zackenberg valley at the end of June. Photo: Jeroen Reneerkens
Jeroen asks for your help to assess the failure of shorebirds breeding in this area of Greenland on species’ populations. He encourages you to score the percentage of juvenile sanderlings in flocks at beaches through August to November, ideally repeating the counts in the same area over this period. There’s more information on the monitoring protocol, and a more detailed account of the research.
The work of Jan van Gils gives an even more complex insight into how climate change is affecting northern breeding shorebirds. Reduced body size is often associated with climate change, likely the result of poor nutrition. In the case of the red knot, Jan's team has found that this is also leading to shorter bill size, and seems to be the result of early snow melt. At their tropical wintering grounds, these short-billed birds are feeding increasingly on nutritionally poorer seagrass rhizomes in the shallow mud, rather than on deeper dwelling molluscs. These seasonal migrants are experiencing reduced fitness at one end of their range due to climate change at the other end.
So it’s a rather gloomy outlook:, we can expect that we’ll soon see numbers of migrating waders declining fast. The situation is similar to that of seabirds like kittiwakes: they can’t keep breeding unsuccessfully year after year without an eventual impact on populations, only visible once the impact has worked through masking by adult longevity. Worryingly, that’s both the groups for which the UK is internationally important now threatened by climate change.
What to do? Research is vital, to understand the ecological and biological mechanisms affected by climate change. Only then, might we have a chance of developing adaptation responses and conservation measures that can address the problem.
And of course with climate change, we must renew our vigour in reducing greenhouse gas pollution, in our own lives, and in our national and international commitments. It’s a massive challenge, which the RSPB is addressing on several fronts.