Bohai 2021 – Update 4

Update 4 – Farewell Knots!

Bohai spring season 2021 concluded on 7 June with the season ending “typically” like previous years. At the end, we have a number of days with higher count of over 5000 Red Knots, but did not encountered any large number over 10 thousand. We finished the season with 411 sightings of 208 North-west Australia colour banded Red Knot individuals.

The missing birds

Since late May our team has tried to contact birders along China coast (via the China Coastal Waterbird Census network https://www.eaaflyway.net/ccwc-2012-2019-report/)  to see if anyone saw any large flock of Red Knots. Unfortunately, we did not find much clue except knowing that Red Knot numbers have increased slightly at 2 sites in Jiangsu compare to same period in 2020, and that no big flock has been seen along Bohai coast this year. Table below shows the daily number of Red Knot presented at our study sites during our last twelve days in the field compare to the past 2 years:

Table 1: Daily count of Red Knot from late May to early June

Date 2019 2020 2021
27-May   10,000 7,000
28-May   6,000 2,500
29-May 27,500 5,000 1,932
30-May   4,000 6,404
31-May 16,000 4,000 5,450
1-Jun 10,000 500 3,500
2-Jun 8,370 2,500 1,224
3-Jun 6,550 2,500 1,200
4-Jun 4,720 1,500 1,494
5-Jun 4,213 1,500 2,307
6-Jun 1,765 751 763
7-Jun   490 700
Season peak count: 47,537 (22-May) 20,000 (24-May) 9,000 (12-May)

We had our best colour band resighting day on 27-May with 29 Red Knot individuals plus one Great Knot individual. Then scanning become increasingly difficult on the Nanpu mudflat with birds foraging far along tide line, heat haze as tide falling later each day and some extreme weather (see next section).

Red Knot flock feeding right at the tide line as the tide recede (photo by Katherine on 28-May)

As per previous year experience, we know that Red Knots tend to rely on brine shrimp eggs in the salt ponds when they are about to depart in late May/early June, thus we focus our effort in the salt pond in our last week. What’s different from previous years was that regardless of suitable water levels at several places, there wasn’t many ponds that the Red Knots were using. This was probably because of the small number of birds presented. Even so, we had some luck resighting the “usual” late arriving individuals at the ponds for a couple of days, which gave us the clue that migration season was getting close to the end.

   Left: Brine shrimp and eggs under microscope (photo by Zhang Wei).
Tong and Rainy scanning at the salt pond in strong wind (photo by Katherine).

Crazy weather

If you are a fan of extreme weather, Nanpu is obviously an interesting place to visit. Earlier in April, I have been running on the street in the middle of a dust storm followed by heavy rain and thunder. In the last 12 days in the field, we had experienced super strong wind, misty and hazy mornings and thunder storm with hail in size of marbles. All these added on to the difficulties in scanning and finding Red Knots, and may have pushed some of the birds to move on earlier. 


Scanning in super strong wind and dust can only be carried out inside our car
(photo by Tong on 29-May)
Feeding Red Knots in Tong’s telescope during dust storm (photo by Tong on 29-May)
Katherine and roosting Red Knot flock on salt pond bund in morning mist and haze
(photo by Zhang Wei on 3 June).

Lightening hit the Nanpu mudflat photographed from salt pond (photo by Tong on 7 June).

Food supply

For a few days we had a film crew with us which was appointed by the National Forestry and Grassland Administration to produce a series of documentary on China’s natural environment to be broadcast on China Central Television, including 10 minutes featuring Red Knot as an “international bird” in the wetland episode. Other than filming us scanning and doing interviews, they were also interested to complete their story with what Red Knots feed on at Nanpu. Thus, we took the chance to demonstrate mud sampling and explained Red Knot’s reliance on Potamocorbula laevis.

We had already heard from our colleague Hebo that P. laevis density was low at Nanpu this year along his long-term monitoring transect. Tong and Rainy, who had carried out sampling at Nanpu in 2017-2019, agreed with Hebo’s finding. Very few P. laevis were found in a standard sample about 50m away from the seawall. We found slightly more but still low number of P. laevis close to the seawall, where birds were less likely to feed to avoid disturbance. Maybe this explains why we seldom saw Red Knot spreading along the 7km long mudflat to feed this year.

Left: Director Zhang filming closely how mud sampling was carried our
(photo by Katherine).

Small number of P. laevis collected from a “standard” sample, comparing to >200 individuals in past years (photo by Zhang Wei).

All these clues seem to suggest that maybe the Red Knots choose to spread out more widely along China coast this year and did not concentrate at “traditional” sites in Bohai (?). I can’t wait to find out what they will do next Spring already!

Last but not least, some positive news

After our field work ended, on 8-10 June, I attended a workshop organised by WWF-China in Luannan Town, which brought together stakeholders of the newly established Luannan Nanpu Zuidong Provincial Wetland Park. The meeting was very fruitful and I found it great to be able to listen to the local people from Beipu village (shellfish harvesting on mudflat) and from the salt pond (salt, brine shrimp and salt pond shrimp production) about their work routine and local knowledge, which help us better understand Red Knot movement around the site. More importantly, we explored possibility to further improve the shellfish, salt and shrimp production in a bird-friendly and sustainable way. As such, aqua products from the Wetland Park could be sold at the market at higher price with accreditation in future. This would be a win-win situation for both the local communities and the birds. More details of this workshop will be included in the 2021 final report.

Young village head from Beipu village (2nd person at the back row) explaining their harvesting routine and expectation to keep harvesting at the Nanpu mudflat, which is now part of the Wetland Park (photo by WWF-China Shanghai Office).

Imagine you can choose to buy “Nanpu Wetland Park Red Knot friendly shellfish” in the market in future? (photo by Katherine)

That’s all for 2021 updates, please don’t miss our final report with all the results from this year field work.

Katherine Leung 15-Jun-2021

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