Tracing the origin of migratory pests using geochemical fingerprinting : application to European starling in the Okanagan Valley of British Columbia, Canada

The European starling (EUST) (Sturnidae: Sturnus vulgaris L.) is an invasive bird in North America where it is an agricultural pest. In British Columbia (Canada), the EUST population increases in orchards and vineyards in autumn, coinciding with ripening fruits. Starlings also create damage in dairy farms and feedlots by eating and contaminating food, and spreading diseases. Damage can be partly mitigated by the use of scare deterrents. However, scare techniques mainly serve to divert flocks until they become acclimated. Large-scale trapping and euthanizing before they move to fields and farms is the most practical means of preventing damage, but requires knowledge of natal origin. Within a small (20,831 km²), agriculturally significant portion of south-central British Columbia, the Okanagan Valley, I employed analyses of 21 trace elements in bone tissue to discriminate the spatial distribution of juvenile EUST and to reveal the geographic origin of the problem birds. Stepwise discriminant analysis of trace elements classified juveniles from 64-79 % accurately to their natal origin, including sites that are 12 km apart. The elemental fingerprint of juveniles collected in the same area was different in two consecutive years (2015 and 2016). In both years, the majority of problem birds (55% in 2015 and 79 % in 2016) caught in vineyards and orchards were derived from the North Okanagan. In contrast, 89% of problem birds caught at dairy farms and feedlots were not from Okanagan and 11% were local in 2015; 100% of problem birds were local in 2016. It is unlikely that starlings from outside the region were misidentified as Okanagan Valley starlings because the geochemical fingerprints of those outside of the valley are very distinct. Thus, elemental signatures can separate populations with a high degree of spatial accuracy within several 10s of km, yielding a promising tool for identifying the geographic origin of migratory birds even over small geographic scales. These findings suggested that further control of starlings in vineyards and orchards, be targeted to the northern and southern regions of the valley; control in dairy farms and feedlots will require an expansion of the trapping program outside the region.Arts and Sciences, Irving K. Barber School of (Okanagan)Earth, Environmental and Geographic Sciences, Department of (Okanagan)Graduat