Age bias in the bag of pink-footed geese : influence of flocking behaviour on vulnerability

Jesper Madsen (1)

1 Department of Arctic Environment [Rockilde]

In pink-footed goose () wintering in Denmark, The Netherlands and Belgium, the proportion of juveniles in the hunting bag is consistently higher than that observed in the autumn population. Such juvenile bias in the bag is usually ascribed to young geese lacking experience with hunting or disruption of juveniles from families. An alternative explanation may be that flocking behaviour of families make juveniles more vulnerable. Observations of morning flights of pink-footed geese to the feeding grounds from two of the major autumn-staging areas showed that geese were distributed in many small flocks (median flock size = 9). This was not significantly different from the flock size distribution shot at by hunters (median = 8), suggesting that hunters targeted goose flock size in proportion to the general probability of encounter. The rate at which hunters downed geese was independent of flock size. The ratio between juveniles and adults in flocks decreased with flock size and flocks of <60 individuals primarily comprised family groups. The likelihood of being shot at was 2.4 times higher for juveniles and 3.4 times higher for older birds in small flocks (<10 individuals) compared to larger flocks. The observations suggest that both juveniles as well as successful adult breeding birds were more vulnerable than non-breeding/failed breeding birds as a result of flocking behaviour.

Mots clés: Flocking; Juvenile mortality; Harvest; Predation risk; Predator swamping

Jesper Madsen. Age bias in the bag of pink-footed geese : influence of flocking behaviour on vulnerability. European Journal of Wildlife Research, 2009, 56 (4), pp.577-582. ⟨10.1007/s10344-009-0349-1⟩. ⟨hal-00548161⟩