Table 3.

Relative Importance of the Different Hypotheses of Introduction, Amplification/Dispersal and Spillover of West Nile Virus Explaining Variations in Magpies and Horses Seroprevalence Data, Camargue Area, Southern France, Based on Their Normalized Akaike Weights (w _AIC).

Step	Hypothesis		Code	Magpies seroprevalence data Σw AIC (n)		Horses seroprevalence data Σw AIC (n)
Introduction	Introduction by migratory birds	Southern spring migrants	I 1a	0.64 (30)	0.25 (15)	0.95	0.662 (21)
		Eastern summer migrants	I 1b		0.39 (15)		0.288 (18)
	Virus overwintering	Culex modestus only	I 2a	0.36 (45)	<10−3 (15)	0.053	0.046 (27)
		Culex pipiens only	I 2b		0.13 (15)		0.002 (12)
		Both species	I 2c		0.23 (15)		0.002 (15)
Amplification	Vector amplification	Culex modestus only	A 1xx	0.37 (25)		0.85 (42)
		Culex pipiens only	A 2xx	0.13 (25)		<10−4 (27)
		Both species	A 3xx	0.50 (25)		0.15 (24)
	Host amplification	Magpies and sparrows only	A x1x	<10−5 (30)		<10−3 (0)
		All bird species, heterogeneous competences	A x2x	1 (30)		0.63 (69)
		All bird species, homogenous competences	A x3x	<10−3 (15)		0.37 (24)
	Diversity effects	Absence of ‘dilution effect’	A xx1	0.81 (45)		0.97 (60)
		‘Dilution effect’	A xx2	0.19 (30)		0.03 (33)
Spillover	Spillover	Culex modestus only	S 1	-		0.01 (31)
		Culex pipiens only	S 2	-		0.01 (31)
		Both species	S 3	-		0.98 (31)

Bold text depicts the hypothesis with the higher support from the data.

n number of scenarios including the tested hypothesis.