How the Poyang Lake drought is affecting migratory birds

In the late 1990s and early 2000s, 3,000 or 4,000 white-naped cranes could be seen at Poyang, but that’s fallen to under 1,000. In January 2020, we worked with other organisations to survey wetland waterbirds wintering in the middle and lower reaches of the Yangtze. No white-naped cranes were seen in Hunan, Hubei, Anhui, Jiangsu – only at Poyang. So the health of the lake’s ecosystem has a huge impact on both these species. They have all their eggs in that one basket.

Similarly, 80 per cent or 90 per cent of all oriental storks rely on Poyang over winter. Geese and swans, meanwhile, make up 80–90 per cent of the birds which winter here – hundreds of thousands of them, including the tundra swan, swan goose, taiga bean goose, greater white-fronted goose, greylag goose and even the rare lesser white-fronted goose.

Any major changes at Poyang Lake, such as low water levels or scarcity of food, will force the birds to move on. They will shift to “manmade wetlands” – rice and lotus fields – or even other lakes in the Yangtze basin.

What effect do you think this year’s drought will have on the migratory birds wintering at Poyang?

It’s extremely rare to see a summer drought at Poyang, but it happened this year and was very different to the ordinary autumn and winter dry season. The drought was catastrophic for the lake’s submerged aquatic plants, while wetland plants started their period of rapid growth earlier than usual. During a dry season, Poyang Lake dries up into a hundred or so smaller and shallower lakes, which is where the wintering migratory birds find their food. The Siberian crane, tundra swan and swan goose feed mainly from the stem tubers of the submerged aquatic plants in those shallow lakes. But the drought meant even those shallow lakes dried up and the plants died. There were no stem tubers for the birds to eat.

Many of the other birds eat the young leaves and tubers of sedge and other wetland plants. Usually, those plants are emerging in September and October, just as the water level is falling to create those shallow lakes. When the birds arrive, the plants have been growing for two or three weeks and there’s plenty of food. But the low water levels in summer triggered the plants into growing earlier than usual, in August. Now, two or three months later, they are too tall and tough for the birds to eat.

This has meant severe food shortages for the migratory birds, which move to nearby fields in search of alternatives. Since 2016, we’ve seen species including Siberian cranes and tundra swans feed on rice and lotus fields. We expect to see that happen in large numbers and over a wider area this year, both with those two species and with other waterbirds. Rather than staying concentrated around the lake, the birds will spread out to surrounding areas, leaving the reserve and so making conservation efforts harder.

In a survey on 3 November, we found large numbers of swans, geese and common cranes feeding on rice fields, as well as dozens of Siberian cranes feeding on both rice and lotus fields. This brings the birds into closer proximity with locals, and human activity is very likely to disturb them as they feed or rest. It can also cause conflict – for example, when the migratory birds try to eat grain left out by poultry farmers for their flocks. Some local governments have responded by leaving areas of paddy field unharvested, to serve as food for migratory birds.

That’s a partial solution, but we don’t know if it is adequate. Another problem is that the birds come into closer proximity with each other, as they are feeding from a smaller area. That increases the risk of spreading diseases such as avian flu, either amongst themselves or to poultry. And moving nearer to settlements makes it more likely the birds will be disturbed or even harmed.

There have been news reports of local governments cutting sedge so it sprouts newer and more edible growth for the birds to eat. But what about waders which eat fish or shellfish?

There are even fewer sources of food for them. On 28 October, we found waders were already making use of ponds, riverbeds, ditches – any patch of mud or shallow water.

Why have the migratory birds stopping at Poyang Lake been turning to local crops for food in recent years?

Because their natural sources of food are in decline. Since 1999, we’ve been monitoring four of those shallow lakes that form over winter in the Poyang Nature Reserve. Since 2015, we’ve seen a decrease in sprouts and tubers, both in terms of number and size. That means less food for the Siberian crane, tundra swan, and other waterbirds.

Summer water levels have been generally high recently – on the high side in 2016 and 2017, normal in 2018, high again in 2019, and then a big flood in 2020. Higher water levels mean less light for submerged aquatic plants, which then grow less. Even though autumn and winter water levels were normal those years, the plants hadn’t sprouted and formed tubers. And it is the tubers that help the plants survive the lower water levels of autumn and winter.

So there’s less food for migratory birds if summer water levels are either too high or too low?

Yes. Over the last decade, summer water levels have been higher than average, but dry seasons have been starting earlier than expected, with water levels falling lower than usual. So we’re seeing larger fluctuations across the year.

So it’s not low water levels in winter that cause problems for the waterbirds? It’s the higher water levels in summer?

That’s right.

If we see this year’s record-breaking drought persist, perhaps even become worse, what will that mean for the birds?

There’s no doubt there’s a food shortage this year, but that doesn’t mean the birds will change their migratory routes. That said, we will see them take food from a wider area. The shortage of food also means their return north will be delayed and they’ll get to their breeding grounds later. This means less time to nest, lay eggs and raise their young. In September and October, when the weather turns and it is time to return south, the young birds won’t be ready to make the trip. This will affect the health of the whole population.

The decade-long ban on fishing in the Yangtze is also affecting food sources and habitat quality for migratory birds. I hear the ICF is doing some work on this. Can you tell us about that?

The ban means fishing on the shallow lakes that form during winter no longer takes place. But the way local people used to manage water levels to suit their fishing actually suited the migratory birds too.

In autumn and winter, Poyang turns from one big lake into 100 or so smaller lakes, ranging from one or two hundred hectares in size, to seven or eight thousand. In the past, locals would build dykes and sluice gates in these smaller lakes to create enclosures.

As the lakes dried out and shrunk further, the fish survived and grew in these enclosures. Then, in October, the locals let the water out and caught the fish in a net at the outlet. That drop in water level roughly coincides with the arrival of the birds. It exposes the plants that swans, geese and ducks feed on, as well as the mud for waders and herons, and creates the shallow waters the cranes need.

That method of catching fish is beneficial for the birds and they became accustomed to it.

Prior to the ban, groups of private individuals would lease the fishing rights to the shallow lakes from the local village committee. That would cost from several hundred thousand yuan to several million, depending on the size of the lake. But the fishing ban stopped that and the water levels of those shallow lakes are no longer managed. It does still happen on a small number of shallow lakes owned by the reserve, but only to provide the habitats the birds need, not to catch fish.

The other shallow lakes are owned by villages or townships and go unmanaged. Last winter, water levels in some shallow lakes were too high, as nobody was managing the sluice gates. And during the drought the water quickly flowed away – again, as nobody was taking care of the sluice gates and dykes. Some of the lakes within the reserve are still managed by local villages and were leased out prior to the fishing ban. But again, these are now left unmanaged.

Experts have informed the provincial government of the problem and the ICF is in touch with these experts.

So what would you propose?

We think that if the government take over management of the shallow lakes during the fishing ban, it could be beneficial, helping protect both migratory birds and fishery stocks. But the ban is only due to last a decade, and the locals are hopeful of resuming fishing. If the lakes return to permanent state ownership, the government will need to provide alternative livelihoods. If that doesn’t happen, there will be opposition.

So, prior to the ban, that fishing method benefited both locals and the migratory birds perfectly?

Overall, it benefited the birds, but there was room for improvement. First, the changes in the water levels weren’t timed to coincide with their arrival. The water was often released prior to Chinese New Year (which usually falls between mid January and late February) as the fish would fetch better prices then. Swans and geese arrive in September and cranes in late October or early November. By the middle of November, all the migratory birds have arrived, but water is still being retained in some of the shallow lakes until Chinese New Year. We’d like to see water released earlier, and for that to continue until after Chinese New Year. But the market for fish falls off after the festival.