DOI: 10.5061/dryad.z8w9ghxq4
title: Fearfulness of geese and swans on cropland in winter: A multi-species Flight Initiation Distance approach

description: 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) &gt; greylag goose (104 m)
 &gt; whooper swan (102 m) &gt; Canada goose (92 m) &gt;
 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 &gt;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.
description: <strong>Study area, seasons, and crop
 availability </strong> This study was carried out
 during three winters (2018/2019 through 2020/2021) in southernmost Sweden
 (Scania province (<em>Skåne</em>);
 55--56<sup>o</sup>N, 12--15<sup>o</sup>E) in open
 landscapes characterized by intensive agriculture. Cereals (wheat, barley,
 oats, rye), potatoes, sugar beet, oil rape seed (canola), and ley/hay are
 the main crops. However, also corn (maize), lettuce, broccoli, cale,
 carrots, beetroot, parsnip, cabbage, quinoa, green peas, yellow peas,
 yellow onion, red onion, leek, beans, spice herbs, and sileage crops such
 as alfalfa and grass-legume mixtures are cultivated in the study
 area. Scaring trials were conducted by walking towards
 a flock of geese and/or swans (see ‘scaring trials’ below for details) and
 were only carried out on agricultural land, including pastures and
 hayfields. Since sampling was done from November through March, geese were
 encountered on growing crops (fall-sown cereals and oil rapeseed (canola),
 or sugar beets or carrots yet to be harvested) as well as in harvested
 fields. In early and mid-winter, some fields had fall-sown (growing)
 intercrops such as grasses, legumes, or oil radish. The seasons of study
 in the winters of 2018--2021 were typical for recent decades in the area
 when it comes to weather; snow cover was rare, thin, and lasted a few days
 or a week at the most. Temperatures were above the monthly means for the
 meteorological reference period 1991—2020 in 14 out of 15 study months
 (Supplementary information). Consequently, fall-sown (winter-green) crops
 and spill from harvested cereals and root crops (mainly potatoes, sugar
 beets, and carrots) were available to grazing birds throughout the winter.
 The study area is the northmost region in Sweden where all goose species
 winter regularly. <strong>Study species and
 species-specific predictions</strong> Greylag
 goose is a common breeder in wetlands near agricultural land throughout
 the study area, whereas Canada goose and barnacle goose are scarce
 breeders. All three breeding species are resident, thus occurring
 throughout winter. Residents of these species are reinforced in numbers by
 conspecifics arriving from the northeast to spend the winter in the study
 area. Bean goose (<em>Anser fabalis</em> (taxa
 <em>fabalis</em> and
 <em>serrirostris/rossicus</em>)) is an abundant non-breeding
 visitor from November through March. Pink-footed goose and greater
 white-fronted goose are regular in fall, winter, and spring, but are not
 as abundant as the aforementioned species. Lesser white-fronted goose and
 red-breasted goose are very rare but annually occurring in the study area
 in the non-breeding season. Whooper swan (<em>Cygnus
 cygnus</em>) and mute swan (<em>Cygnus olor</em>) are
 scarce but widespread local breeders, being more numerous in winter. In
 other words, the study area has a speciose set of large grazing avian
 herbivores present on agricultural land throughout winter, making it well
 suited for studies of the present type. With respect to
 the species later observed during the course of the study, two of the
 general predictions listed in the introduction can be made
 species-specific: 1) FID should be longer in large-bodied than in
 smaller-bodied species. Prediction: FID mute swan &gt; whooper swan
 &gt; Canada goose &gt; greylag goose &gt; bean goose &gt;
 pink-footed goose &gt; white-fronted goose &gt; barnacle goose)
 (cf. Blumstein 2006, body mass data from Cramp and Simmons 1977), and 2)
 FID should be longer in species hunted in the EU. Prediction: FID longer
 in greylag, bean, pink-footed, white-fronted, and Canada geese than in
 barnacle goose and whooper swan. <strong>Scaring
 trials</strong> We drove rural roads slowly by
 car with the purpose of spotting flocks of geese and/or swans foraging in
 agricultural fields. Days with very strong winds and reduced visibility
 due to rain, fog, or snowfall were avoided. Whenever geese and/or swans
 were sighted, we stopped at a discrete distance before they were alarmed
 (stretched necks, wing-flapping, walking away) and made sure that there
 were not any obvious ongoing external disturbances. Next, we ensured that
 sight was free between the observer and the majority of the individuals in
 the flock (cf. Mayer et al. 2019). The distance between the car and the
 flock (‘detection distance’ <em>sensu</em> Weston et al. 2012)
 varied and the primary goal was to park the car so that its presence did
 not initiate agitation in the flock. From immediately
 outside the car, we counted and identified geese and/or swans in the flock
 using a spotting scope. Next, the scaring person started walking slowly,
 calmly, and silently towards the flock, in a straight direction whenever
 possible. We used plain clothing and left the spotting scope behind. When
 the first birds in the flock took off, we stopped to record the observer’s
 GPS position (first GPS fix), while at the same time noting the spot from
 which the first birds had left. Next, we walked to the latter spot to
 obtain a second GPS fix. Flight initiation distance (FID) is the distance
 between the first and second GPS fixes. When a flock
 was scared off a field, we used binoculars to note its flight direction
 and, if possible, where it landed. We did this to avoid scaring the same
 birds more than once the same day. We regard the risk of repeated scaring
 (and hence habituation) as very small. For example, the study area
 typically hosts hundreds of thousands of geese during the winter months
 (Haas and Nilsson 2019), and we tried to visit new areas from day to day.
 When possible, we recorded the flight order of the different species in
 multi-species flocks. We discarded cases during which
 geese or swans were disturbed by something else after the start of our
 approach (e.g., cars, airplanes, dogs, noises). We also discarded three
 trials for which a totally unrealistic FID was obtained, most likely due
 to handwriting errors when filling out the field protocol. This left us
 with a total of 408 successful scaring trials, of which 146 were carried
 out before noon and 262 in the afternoon (Table 1). To
 test the last of the hypotheses (see Introduction), scaring trials were
 grouped as either ‘morning’ (before 12 AM) or ‘afternoon trials’ (after 12
 AM) (Table 1). Although geese may forage at night under some
 circumstances, most if not all geese in our study area in winter spend
 nights in roost sites where they cannot forage much (lakes, iced-over
 wetlands, sheltered sea bays; Olsson, Månsson and Elmberg,
 unpublished). We also noted crop stage and crop type in
 fields from which geese were scared, but due to sample size restrictions
 it was not possible to analyze these data statistically when broken down
 by species, flock type, flock size, and time of day. Data from all three
 winters of study were pooled before subsequent analyses, as they were all
 benign for geese weather-wise.
 <strong>Restrictions: bean geese, pink-footed goose, and
 mute swan</strong> Although the two bean goose
 taxa <em>fabalis</em> and <em>serrirostris</em>
 (here regarded as subspecies) can be identified when seen well, the latter
 is not always the case. During our field work there were individuals that
 could not be identified to subspecies in 41 of the 102 trials involving
 bean geese. Out of the 102 bean goose trials there were 53 that positively
 had <em>fabalis</em> in the flock and 41 that had
 <em>serrirostris</em>. In many cases flocks contained both
 subspecies. For these reasons we subsequently did not treat the two
 subspecies separately; hence all trials involving bean geese are termed as
 concerning bean goose in the wide sense (<em>Anser
 fabalis</em> sensu latu) (Table 2). Mute swan and pink-footed goose
 were recorded in just one trial each and were excluded from further
 analyses.
description: # Fearfulness of geese and swans on cropland in winter: A multi-species
 Flight Initiation Distance approach
 [https://doi.org/10.5061/dryad.z8w9ghxq4](https://doi.org/10.5061/dryad.z8w9ghxq4) ## Description of the data and file structure ### Files and variables #### File: Elmberg-et-al-Wildlife-Biology-Fearfulness-of-geese.xlsx **Description:**  ##### Variables * DATE = day of trial * MONTH = month of trial * BEFORE/AFTER NOON = trial before or after 12 AM * TIME = European Central Time (hr,min) * WHOOPER SWAN = number of whooper swans * MUTE SWAN = number of mute swans * GREYLAG GOOSE = number of greylag geese * BARNACLE GOOSE = number of barnacle geese * BEAN GOOSE SENSU LATU = number of bean geese (taxon fabalis, rossicus/serrirostris, or unidentified to subspecies) * CANADA GOOSE = number of Canada geese * GREATER WHITE-FRONTED GOOSE = number of greater white-fronted geese * PINK-FOOTED GOOSE = number of pink-footed geese * TOTAL NUMBER OF GEESE = sum of geese in trail * TOTAL NUMBER OF GEESE AND SWANS = total number of geese and swans in trial * SINGLE SPECIES FLOCKS = names of the sole species in trials with just one species (trials with more than one species present are denoted by "n/a") * FLIGHT ORDER = the sequence in which species took flight in trials with two species or more (trials where this information was not collected are denoted by "n/a") * FLIGHT INITIATION DISTANCE (FID) = the distance (m) from the approaching observer at which the first geese in a flock took flight.