Table 1. Environmental and anthropogenic predictors tested for correlation against the presence of hotspot of highly pathogenic avian influenza virus type H5Nx in Taiwan.

Abbreviation	Description	Transform	Remarks
Farm-related variables
rchickenD	Registered chicken farm density	# registered chicken farm/grid*	Removed due to high collinearity
rduckD	Registered duck farm density	# registered duck farm/grid	Removed due to high collinearity
rgooseD	Registered goose farm density	# registered goose farm/grid	Removed due to high collinearity
allrD	Registered farm density	# registered farm/grid	Categorized based on Percentile (0.333, 0.667, 1) = (2, 7, 154)
allnwaterD	Chicken farm density	# chicken farm/grid	Removed due to high collinearity
allwaterD	Waterfowl farm density	# waterfowl farm/grid	Removed due to high collinearity
PHI	Poultry heterogeneity index	1-{|Pc-Pw|/Pc+Pw}§	Continuous
Farm biosecurity-related variables
nrnwaterD	Non-registered non-waterfowl farm density	# non-registered farm/grid	GAM = (19, 29, 48)
nrwaterD	Non-registered waterfowl farm density	# non-registered farm/grid	Percentile (0.333, 0.667, 1) = (0, 1, 506)
rbroilerD	Broiler chicken density (Good biosecurity)	# broiler chicken/grid	GAM = (2, 12)
rlayerD	Layer chicken density (medium biosecurity)	# layer chicken/grid	Percentile (0.333, 0.667, 1) = (0, 1, 84)
rnativeD	Native chicken density (poor biosecurity)	# native chicken/grid	Continuous
butcherD	Slaughter house density	# slaughter house/grid	Continuous
Wildbird-related variables
wetlandA	% wetland coverage	Wetland coverage area/grid	Continuous
allrice	% rice crop coverage	Rice crop coverage area/grid	Continuous
allcrop	% all crop coverage (exclude rice crop)	All cropping area/grid	Continuous
Anthropological variables
popD	Population density	Human population/grid	Categorized based on Percentile (0.333, 0.667, 1) = (371, 842)

§Pc: number of chicken divided by number of poultry; Pw: number of waterfowl/number of poultry

*each grid is equivalent to 9 km² or 3 km x 3 km for each side.