DOI: 10.5061/dryad.b8gtht795
title: Data from: A red knot as a black swan: how a single bird shows navigational abilities during repeat crossings of the Greenland Icecap

description: Despite the wealth of studies on seasonal movements of birds between
 southern nonbreeding locations and High Arctic breeding locations, the key
 mechanisms of navigation during these migrations remain elusive. A flight
 along the shortest possible route between pairs of points on a sphere
 (‘orthodrome’) requires a bird to be able to assess its current location
 in relation to its migration goal and to make continuous adjustment of
 heading to reach that goal. Alternatively, birds may navigate along a
 vector with a fixed orientation (‘loxodrome’) based on magnetic and/or
 celestial compass mechanisms. Compass navigation is considered especially
 challenging for summer migrations in Polar regions, as continuous daylight
 and complexity in the geomagnetic field may complicate the use of both
 celestial and magnetic compasses here. We examine the possible use of
 orientation mechanisms during migratory flights across the Greenland
 Icecap. Using a novel 2 g solar-powered satellite transmitter, we
 documented the flight paths travelled by a female red knot (Calidris
 canutus islandica) during two northward and two southward migrations. The
 geometry of the paths suggests that red knots can migrate across the
 Greenland Icecap along the shortest-, orthodrome-like, path instead of the
 previously suggested loxodrome path. This particular bird’s ability to
 return to locations visited in a previous year, together with its sudden
 course changes (which would be appropriate responses to ambient wind
 fields), suggest a map sense that enables red knots to determine location,
 so that they can tailor their route depending on local conditions.
description: Read me Article: A red knot as a black swan:
 how a single bird shows navigational abilities during repeat crossings of
 the Greenland Icecap Journal: Journal of Avian
 Biology Article DOI: 10.1111/jav.02464
 Authors: Eva M. A. Kok*, T. Lee
 Tibbitts, David C. Douglas, Paul W. Howey, Anne Dekinga, Benjamin Gnep
 & Theunis Piersma. *Corresponding author: E-mail: evamakok@gmail.nl,
 ORCID-ID: 0000-0002-3961-008X, ORCID-ID: Theunis Piersma:
 0000-0001-9668-466X. 1. Raw tracking data:
 rekn13_totloc_r130d10lc1.txt All Argos data were
 filtered by the SAS version of the Douglas Argos Filter algorithm using
 the following parameter values: maxredun = 10 km, maxrate = 130 kph, and
 coef = 25. Locations that met the distance-angle-rate filter thresholds
 are labeled '1' in the  weeddist column. 2.
 Identification of departure and arrival locations: lables
 JAB.csv See Material and Methods/Spatial analyses:
 Departure and arrival times and the intervening flights were determined
 from the visual inspection of the tracks (Google Earth ©). Departure
 locations were defined as the last location on land with a ground speed
 &lt; 20 km/h (Chan et al. 2019) and arrival locations as the first
 location on land with ground speed &lt; 20 km/h. Intermediate
 locations were defined as ‘migratory flights’ and were labeled as
 ‘northward’ or ‘southward’ migration together with a unique identifier for
 each migratory flight by year (number of migratory flights per year is 4
 for 2016, and 5 for 2017, see Figure 1 and Supplementary material Appendix
 1, Table A1 for the migration scheme for both years).
 3. R script to extrapolate orthodromes and geographic and
 magnetic loxodromes: Koketal2020 JAB script.R. See Material and
 Methods/Orthodrome or loxodrome routes? : Geographic orthodrome and
 loxodrome paths between Iceland and Ellesmere Island were simulated by
 means of the functions gcIntermediate() and destPointRhumb() of the
 <i>geosphere</i> package (Hijmans 2019), with a resolution of
 1 point per kilometer between previously assigned departure and arrival
 locations. Since Paula’s tracks crossed Iceland without stops during both
 southward migrations (a pattern predicted by Dietz et al. 2010), we
 assigned ‘pseudo-‘ arrival locations and arrival times by means of the
 locations where she first crossed the Icelandic coastline and the average
 groundspeeds of the respective migratory flights.