An avian detection system for determining risks of collision between a collision object, such as an air plane, and bird objects that may pose a collision risk with the collision object, the system comprising: one or more avian radar systems (2, 19, 20, 21, 301, 302) providing a first type of information data relating to objects (4, 5) detected by the avian radar system(s) (2, 19, 20, 21, 301, 302); and one or more processors (9, 24) configured to: receive first type of information data corresponding to one or more detected objects (4, 5) and provide radar plots (304, 305) based on the first type of information data; characterised in that the system further comprises an Automatic Dependent Surveillance-Broadcast transponder receiver (8,23, 303), ADS-B transponder receiver, receiving ADS-B transponder data transmitted or broadcasted by one or more ADS-B transponders provided at one or more corresponding collision objects; and in that the one or more processors (9, 24) are further configured to: receive the transponder data corresponding to one or more collision objects and provide ADS-B transponder plots based on the transponder data; create and store a number of object tracks (310, 311) based on the provided radar plots (304, 305) and transponder plots, each track (310, 311) holding object data corresponding to or determined from data of matching plots (304, 305, 306), with at least part of the object tracks (310, 311) holding a combination of data obtained from both the radar plots (304, 305) and the transponder plots; and determine one or more risks of collision or collision risk levels for at least one collision object based on object data of a plurality of the obtained object tracks (310, 311). one or more avian radar systems (2, 19, 20, 21, 301, 302) providing a first type of information data relating to objects (4, 5) detected by the avian radar system(s) (2, 19, 20, 21, 301, 302); and one or more processors (9, 24) configured to: receive first type of information data corresponding to one or more detected objects (4, 5) and provide radar plots (304, 305) based on the first type of information data; characterised in that the system further comprises an Automatic Dependent Surveillance-Broadcast transponder receiver (8,23, 303), ADS-B transponder receiver, receiving ADS-B transponder data transmitted or broadcasted by one or more ADS-B transponders provided at one or more corresponding collision objects; and in that the one or more processors (9, 24) are further configured to: receive the transponder data corresponding to one or more collision objects and provide ADS-B transponder plots based on the transponder data; create and store a number of object tracks (310, 311) based on the provided radar plots (304, 305) and transponder plots, each track (310, 311) holding object data corresponding to or determined from data of matching plots (304, 305, 306), with at least part of the object tracks (310, 311) holding a combination of data obtained from both the radar plots (304, 305) and the transponder plots; and determine one or more risks of collision or collision risk levels for at least one collision object based on object data of a plurality of the obtained object tracks (310, 311). receive first type of information data corresponding to one or more detected objects (4, 5) and provide radar plots (304, 305) based on the first type of information data; characterised in that the system further comprises an Automatic Dependent Surveillance-Broadcast transponder receiver (8,23, 303), ADS-B transponder receiver, receiving ADS-B transponder data transmitted or broadcasted by one or more ADS-B transponders provided at one or more corresponding collision objects; and in that the one or more processors (9, 24) are further configured to: receive the transponder data corresponding to one or more collision objects and provide ADS-B transponder plots based on the transponder data; create and store a number of object tracks (310, 311) based on the provided radar plots (304, 305) and transponder plots, each track (310, 311) holding object data corresponding to or determined from data of matching plots (304, 305, 306), with at least part of the object tracks (310, 311) holding a combination of data obtained from both the radar plots (304, 305) and the transponder plots; and determine one or more risks of collision or collision risk levels for at least one collision object based on object data of a plurality of the obtained object tracks (310, 311). receive the transponder data corresponding to one or more collision objects and provide ADS-B transponder plots based on the transponder data; create and store a number of object tracks (310, 311) based on the provided radar plots (304, 305) and transponder plots, each track (310, 311) holding object data corresponding to or determined from data of matching plots (304, 305, 306), with at least part of the object tracks (310, 311) holding a combination of data obtained from both the radar plots (304, 305) and the transponder plots; and determine one or more risks of collision or collision risk levels for at least one collision object based on object data of a plurality of the obtained object tracks (310, 311).