Regional differences in crippling rate in greylag geese Anser anser in Sweden

Goose populations across Europe have been subjected to long-standing harvest practices, which include shotgun hunting. In addition to immediate mortality, hunting can affect an animal’s fitness by inflicting non-lethal injuries, often referred to as ‘crippling’ or ‘wounding’. This could subsequently have negative effects on the population level and causes ethical concerns, ultimately challenging the legitimacy of hunting as a management tool. Understanding spatial variation in crippling rate can assist management to prioritize regions for enhancing awareness and implementing measures aimed at reducing crippling. We examined greylag geese from three subpopulations (Nyköping, Örebro, and Hudiksvall) breeding in three regions in Sweden (Södermanland, Örebro, and Gävleborg) to record prevalence of imbedded shotgun pellets and to quantify crippling impact. Our approach excludes birds that were wounded and subsequently died without being retrieved. We found that across the three subpopulations, 21% of the 176 x-rayed greylag geese were carrying imbedded pellets (average 2.33 pellets, range 1–16). Crippling rate varied among the subpopulations, being twice as high in Örebro and Nyköping (26.4 and 25.0%, respectively) compared to Hudiksvall (11.7%). However, the probability of being crippled differed significantly only between Nyköping and Hudiksvall (p=0.04), but not between Örebro and Hudiksvall (p>0.05) or between Nyköping and Örebro (p>0.05). This study could not elucidate the mechanisms underlying the observed regional variations in crippling rate. Nevertheless, the regional disparities in these rates, and the potential links between crippling rate, levels of crop damage, attitudes, and hunting behaviors, present intriguing avenues for future exploration.

Methods
Greylag geese were captured and x-rayed in three study sites in Sweden. In June 2019–2022, breeding and moulting (flightless) greylag geese were caught when foraging in fields near water. They were herded by foot and canoes towards standing nets and corrals. The birds were kept in gunny bags until further handling. During ringing, geese were aged (juvenile versus adult) based on plumage, and the adult birds were x-rayed for the purpose of the present study. Juveniles were not yet fledged and had not yet been exposed to hunting; hence they were not x-rayed. After ringing, adult birds were again placed in gunny bags and fitted in a plastic box so that they would not move during the x-ray examination. In total, we x-rayed 176 individuals and they were released immediately after examination. In 2019, 103 geese were x-rayed using a Mars1417V-TSI detector plate from iRay Technology combined with a portable ACOMA PX-15HF. In 2021, 25 were x-rayed using a VIVIX-S 1417N detector combined with a portable Econet Vet20BT x-ray unit. In 2022, 48 individuals were x-rayed using a Sedecal SP-VET-4.0 with Beam device r 72/170A DHHS. The x-ray was set at 50 kW and 3 mAs.