title: Upside-down swimming behaviour of free-ranging narwhals.
abstract: BACKGROUND
  Free-ranging narwhals (Monodon monoceros) were instrumented in Admiralty Inlet, Canada with both satellite tags to study migration and stock separation and short-term, high-resolution digital archival tags to explore diving and feeding behaviour. Three narwhals were equipped with an underwater camera pod (Crittercam), another individual was equipped with a digital archival tag (DTAG), and a fifth with both units during August 2003 and 2004.
  
  
  RESULTS
  Crittercam footage indicated that of the combined 286 minutes of recordings, 12% of the time was spent along the bottom. When the bottom was visible in the camera footage, the narwhals were oriented upside-down 80% of the time (range: 61 100%). The DTAG data (14.6 hours of recordings) revealed that during time spent below the surface, the two tagged narwhals were supine an average of 13% (range: 9-18%) of the time. Roughly 70% of this time spent in a supine posture occurred during the descent.
  
  
  CONCLUSIONS
  Possible reasons for this upside-down swimming behaviour are discussed. No preference for a clockwise or counter-clockwise direction of roll was observed, discounting the possibility that rolling movements contribute to the asymmetric left-handed helical turns of the tusk.
authors.affiliation: Department of Arctic Environment, National Environmental Research Institute, University of Aarhus, Frederiksborgvej 399, Postbox 358, DK-4000 Roskilde, Denmark. rdi@dmu.dk
authors.forename: Rune
authors.initials: R
authors.lastname: Dietz
authors.forename: Ari D
authors.initials: AD
authors.lastname: Shapiro
authors.forename: Mehdi
authors.initials: M
authors.lastname: Bakhtiari
authors.forename: Jack
authors.initials: J
authors.lastname: Orr
authors.forename: Peter L
authors.initials: PL
authors.lastname: Tyack
authors.forename: Pierre
authors.initials: P
authors.lastname: Richard
authors.forename: Ida Grønborg
authors.initials: IG
authors.lastname: Eskesen
authors.forename: Greg
authors.initials: G
authors.lastname: Marshall
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D005260:Female; D008297:Male; D009949:Orientation; D011187:Posture; D013550:Swimming / Q000502:physiology*; D014907:Whales / Q000502:physiology*