Fearfulness of geese and swans on cropland in winter: a multi-species
Flight Initiation Distance approach
Abstract
Geese and swans are focal species in conservation and in management
aimed at reducing crop damage. In the former disturbance should be
minimized, and in the latter it is important to know how different
species react to scaring activities. Previous research about trade-offs
between predation risk and foraging in birds often use ‘Flight
Initiation Distance’ (FID) as a proxy to compare fearfulness under
different circumstances and among species. We studied variation in FID
in geese and swans by species, flock size and composition, time of day,
and body size (408 scaring trials on agricultural land in the winters
2018—2021). In single-species flocks mean FID decreased in the order:
bean goose (171 m) > greylag goose (104 m) >
whooper swan (102 m) > Canada goose (92 m) >
barnacle goose (77 m). In line with predictions based on body mass, the
lightest species (barnacle goose) was the least fearful, but contrary to
prediction neither of the two heaviest species (whooper swan, Canada
goose) was the most fearful. FID was negatively correlated with flock
size in bean goose. Flock size and FID did not correlate in greylag,
Canada, and barnacle geese. FID did not differ between morning and
afternoon in the 4 species with a sample of >20
single-species trials. When in multi-species flocks, FID differed less
among species, converging in the 108—138 m range. Accordingly, bean
goose FID decreased significantly whereas it increased significantly in
barnacle and greylag geese. Barnacle goose (protected from hunting by
the EU bird directive) was less fearful than species with an open
hunting season in the EU, implying that exposure to hunting affect
species-specific FID. We show that the level of fearfulness varied among
swan and goose species, making it necessary to adopt diverse strategies
in conservation as well as crop protection.