Additional File 1 s6

Additional file 1

Table S1. Model selection for predicting the activity intensity of great knots during northward migration at two stopover sites, Chongming Dongtan Nature Reserve (CMDT) in the south and Yalujiang Estuarine Wetland Nature Reserve (YLE) in the north Yellow Sea. Dependent variables were activity intensity at CMDT and YLE before and after sunset. Models were compared with the second-order-corrected Akaike’s information criterion (AICc, Burnham and Anderson 2002). W = wind effect, D = test date, BM = body mass at capture, BMD = body mass decrease (the deviation of body mass at capture and at test time), C = cloud cover

(three levels: clear, partly cloudy, and overcast), T = tide condition (two levels: HW and LW).

Models are ranked according to the ascending sequence of AICc values. Only the models with

Delta AICc ≤ 2 are listed for each prediction.

2 Model Independent variables K AICc Delta AICc Wi R p at CMDT before sunset 1 W 2 347.84 0 0.39 0.032 0.032 2 W, D 3 348.59 0.75 0.27 0.041 0.052 3 W, BMD 3 349.23 1.39 0.20 0.036 0.022 4 W, BM 3 349.82 1.98 0.15 0.033 0.096 at YLE before sunset 1 W, D, BMD 4 76.56 0 0.19 0.230 0.053 2 D, T 3 76.94 0.38 0.16 0.152 0.084 3 W, D, BMD, T 5 77.30 0.74 0.13 0.281 0.049 4 - 1 77.36 0.80 0.13 - - 5 T 2 77.60 1.04 0.11 0.064 0.155 6 D 2 77.74 1.18 0.11 0.060 0.168 7 BM 2 78.23 1.67 0.08 0.046 0.230 8 W, D, T 4 78.40 1.84 0.08 0.186 0.109

1 Table S2. Comparison of shifted directions of great knots grouped by cloud cover, seasonal timing, wind effect, body mass, tide condition, and restlessness at two stopover sites, Chongming Dongtan Nature Reserve (CMDT) in the south Yellow Sea and Yalujiang Estuarine Wetland Nature Reserve (YLE) in the north Yellow Sea.

Rayleigh’s test Watson’s U2 test Site Time period Group N α r p 95% C. I. U p CMD Before sunset Cloud cover Clear & partly 77 11.1 0.440 < 0.001 351.5 - 30.6 0.063 n.s.

T cloudy Overcast 12 351.0 0.242 0.505 188.5 - 153.4 a Seasonal timing 25 Mar – 14 Apr 56 11.9 0.584 < 0.001 355.6 - 28.2 0.249 < 0.02 15 Apr – 10 May 33 350.4 0.125 0.599 240.5 - 100.2 a Wind effect Headwind 33 30.1 0.279 0.076 341.5 - 78.8 0.153 n.s. Tailwind 56 2.9 0.503 < 0.001 343.3 - 22.5 Body mass ≥ 138 g 50 11.5 0.422 < 0.001 346.2 - 36.9 0.026 n.s. < 138 g 39 6.8 0.398 0.002 336.2 - 37.4 Restlessness ≥ 300 scratches 31 355.1 0.442 0.002 324.5 - 25.7 0.174 n.s. < 300 scratches 58 17.8 0.407 <0.001 353.3 - 42.3 Tide Low water 64 6.8 0.332 < 0.001 337.7 - 35.8 0.216 < 0.05 High water 25 13.3 0.616 < 0.001 350.5 - 36.1 After sunset Cloud cover Clear & partly 34 39.7 0.282 0.066 352.4 - 87.1 b b

cloudy Overcast 3 122.4 0.191 0.911 a Seasonal timing 25 Mar – 14 Apr 24 24.9 0.116 0.728 245.8 - 164.0 a 0.143 n.s. 15 Apr – 10 May 13 50.2 0.544 0.018 11.3 - 89.0 a Wind effect Headwind 22 17.5 0.277 0.186 317.5 - 77.4 a 0.095 n.s. Tailwind 15 75.4 0.33 0.198 4.4 - 146.3 a Body mass ≥ 138 g 22 31.9 0.152 0.607 281.1 - 142.8 a 0.054 n.s.

2 < 138 g 15 48.9 0.428 0.061 359.6 - 98.2 a Restlessness ≥ 300 scratches 9 15.4 0.740 0.004 340.8 – 50.0 a 0.251 < 0.02 < 300 scratches 28 82.5 0.174 0.430 357.1 - 167.9 a Tide Low water 31 56.6 0.219 0.226 352.4 - 120.9 0.089 n.s. High water 6 15.7 0.575 0.138 319.8 - 71.5 a YLE Before sunset Cloud cover Clear &partly cloudy 12 319.2 0.550 0.023 279.2 - 359.2 a 0.037 n.s. Overcast 11 320.0 0.342 0.283 236.2 - 43.8 a Seasonal timing 30 Mar – 14 May 13 348.6 0.415 0.106 292.5 - 44.7 a 0.147 n.s. 15 May – 20 May 10 294.6 0.623 0.016 257.7 - 331.6 a Wind effect Headwind 6 10.3 0.870 0.005 338.2 - 42.4 0.223 < 0.02 Tailwind 17 289.7 0.479 0.018 252.0 - 327.4 Body mass ≥ 215 g 10 275.0 0.526 0.059 227.6 - 322.3 a 0.103 n.s. < 215 g 13 348.6 0.582 0.010 313.3 - 24.0 a Restlessness ≥ 300 scratches 17 314. 9 0.439 0.035 273.2 - 356.5 a 0.043 n.s. < 300 scratches 6 331.1 0.499 0.233 260.9 - 41.2 a Tide Low water 13 315.4 0.577 0.011 279.5 - 351.3 a 0.053 n.s. High water 10 330.0 0.294 0.432 208.4 - 91.7 a After sunset Cloud cover Clear & partly 14 305.2 0.591 0.006 271.9 - 338.5 a 0.125 n.s.

cloudy Overcast 5 32.1 0.693 0.085 346.6 - 77.5 a Seasonal timing 30 Mar – 14 May 19 327.5 0.481 0.010 292.0 – 3.0 b b 15 May – 20 May 0 Wind effect Headwind 8 316.3 0.551 0.085 266.0 - 6.5 a 0.025 n.s. Tailwind 11 337.6 0.445 0.112 281.2 – 34.0 a Body mass ≥ 215 g 8 283.1 0.647 0.030 243.7 - 322.5 a 0.182 n.s. < 215 g 11 1.1 0.594 0.017 323.5 - 38.7 a Restlessness ≥ 300 scratches 8 292.1 0.561 0.077 243.2 - 341.0 a 0.065 n.s. < 300 scratches 11 352.8 0.552 0.031 311.0 - 34.6 a Tide Low water 17 324.4 0.434 0.038 282.3 - 6.5 a b b High water 2 340.0 0.906 0.215 228.8 - 91.2 a

3 Notes: Seasonal timing is divided in the middle of the stopover period at CMDT but just before the departure time window at YLE, because departures are unsynchronized at CMDT but highly synchronized at YLE. Body mass is grouped according to the maximum flight distance estimated by Flight program: birds weighing 138 g are able to fly from CMDT to YLE and those weighing 215 g are able to fly from YLE to the breeding area (Ma et al., 2013). a: the confidence interval is unreliable due to small sample size or low degree of concentration. b: the calculation could not be completed because one sample had fewer than five observations.

4 Table S3. Comparison of natural directions of great knots grouped by cloud cover, seasonal timing, wind effect, body mass, tide condition, and restlessness at two stopover sites, Chongming Dongtan Nature Reserve (CMDT) in the south Yellow Sea and Yalujiang Estuarine Wetland Nature Reserve (YLE) in the north Yellow Sea.

Rayleigh’s test Watson’s U2 test Site Time period Group N α r p 95% C. I. U p CMD Before sunset Cloud cover Clear & partly 77 147.7 0.282 0.002 116.2 - 179.1 0.015 n.s.

T cloudy Overcast 12 151.3 0.390 0.162 87.0 - 215.6 a Seasonal timing 25 Mar – 14 Apr 56 157.3 0.309 0.005 123.8 - 190.8 0.087 n.s. 15 Apr – 10 May 33 132.1 0.293 0.058 86.0 - 178.3 Wind effect Headwind 33 59.6 0.251 0.126 5.3 - 113.9 0.424 < 0.001 Tailwind 56 165.8 0.490 < 0.001 145.6 - 186.1 Body mass ≥ 138 g 50 157.0 0.256 0.038 113.8 - 200.2 0.057 n.s. < 138 g 39 140.3 0.356 0.007 105.8 - 174.9 Restlessness ≥ 300 scratches 31 162.6 0.344 0.024 122.4 - 202.8 0.171 n.s. < 300 scratches 58 139.0 0.280 0.010 102.6 - 175.5 Tide Low water 64 137.3 0.283 0.006 102.8 - 171.7 0.117 n.s. High water 25 170.2 0.372 0.030 129.1 - 211.3 After sunset Cloud cover Clear & partly 34 102.9 0.072 0.840 274.0 - 291.7 a b b

cloudy Overcast 3 122.4 0.191 0.911 a Seasonal timing 25 Mar – 14 Apr 24 102.2 0.105 0.771 308.4 - 255.9 a 0.024 n.s. 15 Apr – 10 May 13 128.4 0.040 0.980 a Wind effect Headwind 22 57.6 0.289 0.159 0.3 - 114.9 a 0.216 < 0.05 Tailwind 15 210.4 0.33 0.198 139.4 - 281.3 a Body mass ≥ 138 g 22 17.0 0.167 0.545 276.6 - 117.4 a 0.118 n.s.

5 < 138 g 15 157.7 0.315 0.228 81.9 - 233.5 a Restlessness ≥ 300 scratches 9 85.9 0.474 0.132 27.5 - 144.3 a 0.136 n.s. < 300 scratches 28 230.1 0.064 0.892 357.3 - 102.9 a Tide Low water 31 171.1 0.163 0.443 84.0 - 258.1 a 0.265 < 0.02 High water 6 26.8 0.772 0.020 343.3 - 70.3 a YLE Before sunset Cloud cover Clear & partly 12 158.9 0.391 0.160 94.8 – 223.0 a 0.234 < 0.02

cloudy Overcast 11 93.2 0.502 0.060 45.3 - 141.1 a Seasonal timing 30 Mar – 14 May 13 90.2 0.363 0.183 22.3 - 158.1 a 0.131 n.s. 15 May – 20 May 10 152.0 0.529 0.057 104.9 – 199.0 a Wind effect Headwind 6 68.5 0.487 0.251 355.6 - 141.5 a 0.115 n.s. Tailwind 17 142.1 0.429 0.041 99.4 - 184.8 a Body mass ≥ 215 g 10 120.3 0.416 0.179 54.3 - 186.2 a 0.027 n.s. < 215 g 13 125.7 0.341 0.223 51.3 - 200.1 a Restlessness ≥ 300 scratches 17 129.2 0.374 0.092 79.6 - 178.9 a 0.027 n.s. < 300 scratches 6 106.3 0.396 0.409 0.4 - 212.2 a Tide Low water 13 156.6 0.308 0.296 69.1 - 244.1 a 0.212 < 0.05 High water 10 100.2 0.570 0.035 58.1 - 142.3 a After sunset Cloud cover Clear & partly 14 185.5 0.193 0.603 a 0.035 n.s.

cloudy Overcast 9 171.1 0.268 0.537 348.4 - 353.8 a Seasonal timing 30 Mar – 14 May 23 178.7 0.220 0.331 104.5 - 252.9 a b b 15 May – 20 May 0 Wind effect Headwind 12 282.8 0.411 0.132 223.0 - 342.6 a 0.2 < 0.05 Tailwind 11 141.4 0.717 0.002 109.5 - 173.2 Body mass ≥ 215 g 8 182.7 0.292 0.521 18.7 - 346.8 a 0.022 n.s. < 215 g 15 175.3 0.183 0.613 a

6 Restlessness ≥ 300 scratches 9 187.1 0.234 0.623 a 0.032 n.s. < 300 scratches 14 172.9 0.214 0.534 340.0 - 5.8 a Tide Low water 17 162.5 0.421 0.047 118.9 - 206.0 a 0.102 n.s. High water 6 310.7 0.450 0.310 227.6 - 33.9 a Notes: Grouping method is the same as in Table S2. a: the confidence interval is unreliable due to small sample size or low concentration. b: the calculation could not be completed because one sample had fewer than five observations.