Aim: Animal migrations influence ecosystem structure, dynamics, and persistence of predator and prey populations. The theory of migratory coupling postulates that aggregations of migrant prey can induce large-scale synchronized movements in predators, and this coupling is consequential for the dynamics of ecological communities. The degree to which humans influence these interactions remains largely unknown. We tested whether the creation of large resource pulses by humans such as seasonal herding of reindeer Rangifer tarandus and hunting of moose, Alces alces, can induce migratory coupling with Golden Eagles, Aquila chrysaetos, and if these lead to demographic consequences for the eagles.


Location: Fennoscandia

Methods: We used movement data from 32 tracked Golden Eagles spanning 125 annual migratory cycles over eight years. We obtained reindeer distribution data through collaboration with reindeer herders based on satellite tracking of reindeer, and moose harvest data from the national hunting statistics for Sweden. We assessed demographic consequences for eagles from ingesting lead from ammunition fragments in moose carcasses through survival estimates and their links with lead concentrations in eagles’ blood.

Results: In spring, eagles migrated hundreds of kilometers to be spatially and temporally coupled with calving reindeer, whereas in autumn, eagles matched their distribution with the location and timing of moose hunt. Juveniles were more likely to couple with reindeer calving, whereas adults were particularly drawn to areas of higher moose harvest. Due to this coupling, eagles ingested lead from spent ammunition in moose offal and carcasses and the resulting lead-toxicity increased the risk of mortality by 3.4 times.

Main conclusions: We show how migratory coupling connects landscape processes and that human actions can influence migratory coupling over large spatial scales and increase demographic risks for predators. We provide vital knowledge towards resolving human wildlife conflicts and the conservation of protected species over a large spatial and temporal scale.

GPS tracking of Golden Eagles, Spatial Mapping of Semi domestic Reindeer Calving areas, National Hunting Statistics for Moose

In Data file data.csv

date - date and time of eagle position (YYYY-MM-DD HH:MM:SS)
Distance - net squared distance between consecutive golden eagle locations  = (sqrt(distance/1000000))       
Object_ID - Individual eagle ID       
CalvingOrNot - Whether a position is within the calving period or not
CalvingPresence - Whether a position is within a calving area or not         
mooseDenVals - value of moose harvest encountered at a eagle's position in terms of No. of moose harvested / 1000 ha. (note that this value turns to 0 outside the moose hunting season)        
MooseHuntOrNot - Whether a position is within the moose hunting period or not    
AgeClass - Whether an individual was a juvenile or adult

Reindeer calving areas polygons are available at https://ext-geodatakatalog.lansstyrelsen.se/GeodataKatalogen/ 

National moose hunting statistics can be downloaded from https://rapport.viltdata.se/statistik/