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Table 2 Parameter estimates (β, 95% confidence intervals) for generalized linear mixed models examining the effects of population on autumn migration characteristics of Herring Gulls. Long distance migrants were tracked from Eastern Arctic (NU; n = 8), and short distance migrants were tracked from Newfoundland (NL; n = 9), Sable Island (SI; n = 8), and the Bay of Fundy (n = 8). Individual is included as a random effect in all models except for directness. The intercept is the predicted value for Herring Gulls from Eastern Arctic, which then acts as the reference level for the other parameter estimates, which are relative differences from the intercept. Bold font indicates estimates whose 95% confidence intervals do not cross 0, indicating a significant difference from the Eastern Arctic population, and likelihood ratio test statistics (χ2) where p < 0.05

From: Both short and long distance migrants use energy-minimizing migration strategies in North American herring gulls

Migration characteristic Population β (95% CI) Marginal R2 Conditional R2 χ23 p
Migration Distance (km) Intercept (NU) 6899 (6263, 7536) 0.84 0.94 67.16 <0.01
NL -4652 (-5515, -3778)     
SI -5190 (-6057, -4324)     
BF -5934 (-6822, -5050)     
Duration (days) Intercept (NU) 3.9 (3.4, 4.4) 0.47 0.95 23.33 <0.01
NL -0.9 (-1.6, -0.2)     
SI -1.5 (-2.2, -0.8)     
BF -2.0 (-2.8, -1.3)     
Start Date (day of year) Intercept (NU) 267 (237, 298) 0.10 0.98 2.69 0.44
NL 8 (-33, 50)     
SI -23 (-65, 20)     
BF 6 (-36, 49)     
End Date (day of year) Intercept (NU) 330 (298, 363) 0.25 0.98 9.77 0.02
NL -26 (-70, 18)     
SI -72 (-117, -27)     
BF -48 (-94, -3)     
Directness (∑ km/direct km) Intercept (NU 0.59 (0.47, 0.71) 0.17 - 9.06 0.03
NL 0.23 (0.09, 0.38)     
SI 0.18 (0.03, 0.32)     
BF 0.19 (0.04, 0.34)     
Migration Speed (km/day) Intercept (NU) 185 (94, 275) 0.00 0.84 0.01 0.99
NL -2 (-126,123)     
SI -3 (-130,129)     
BF 1 (-126, 129)     
Travel Speed (km/day) Intercept (NU) 366 (-290, 441) 0.21 0.82 9.67 0.02
NL -104 (-207, -0.3)     
SI -144 (-248, -40)     
BF -160 (-256, -54)     
Total Stopover Days (days) Intercept (NU) 2.9 (1.8, 4.0) 0.37 0.97 14.61 <0.01
NL -0.9 (-2.4, 0.6)     
SI -2.6 (-4.2, -1.1)     
BF -2.8 (-4.6, -1.3)     
Travel:Stopover Ratio (km/day) Intercept (NU) 1187 (473, 1902)     
NL -622 (-1598, 357) 0.07 0.79 2.48 0.48
SI -93 (-1082, 896)     
BF -561 (-1563, 441)     
Stopover Length (days) Intercept (NU 2.4 (1.9, 2.9)     
NL -0.7 (-1.4, 0.1) 0.21 0.80 6.16 0.10
SI -1.0 (-1.8, -0.2)     
BF -0.7 (-1.6, 0.3)