Fearfulness of geese and swans on cropland in winter: A multi-species Flight Initiation Distance approach

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-off 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 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 >20 single-species trials (i.e., supposedly
hungry versus satiated geese). When in multi-species flocks, FID differed
less among species, converging in the 108—138 m range. For example, bean
goose FID decreased significantly whereas it increased significantly in
barnacle and greylag geese. Barnacle goose (protected from open hunting in
EU) 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.