title: Crocodylus niloticus (Crocodilia) is highly sensitive to water surface waves.
abstract: Crocodiles show oriented responses to water surface wave stimuli but up to now behavioral thresholds are missing. This study determines the behavioral thresholds of crocodilians to water surface waves. Nile crocodiles (Crocodylus niloticus) were conditioned to respond to single-frequency water surface wave stimuli (duration 1150 ms, frequency 15, 30, 40, 60 and 80 Hz), produced by blowing air onto the water surface. Our study shows that C. niloticus is highly sensitive to capillary water surface waves. Threshold values decreased with increasing frequency and ranged between 10.3 μm (15 Hz) and 0.5 μm (80 Hz) peak-to-peak wave amplitude. For the frequencies 15 Hz and 30 Hz the sensitivity of one spectacled caiman (Caiman crocodilus) to water surface waves was also tested. Threshold values were 12.8 μm (15 Hz) down to 1.76 μm (30 Hz), i.e. close to the threshold values of C. niloticus. The surface wave sensitivity of crocodiles is similar to the surface wave sensitivity of semi-aquatic insects and fishing spiders but does not match the sensitivity of surface-feeding fishes which is higher by one to two orders of magnitude.
authors.affiliation: Institute of Zoology, University of Bonn, Meckenheimer Allee 169, D-53115 Bonn, Germany. Electronic address: ngrap@uni-bonn.de.
authors.forename: Nadja J
authors.initials: NJ
authors.lastname: Grap
authors.affiliation: Institute of Zoology, University of Bonn, Meckenheimer Allee 169, D-53115 Bonn, Germany.
authors.forename: Anna S
authors.initials: AS
authors.lastname: Monzel
authors.affiliation: Institute of Zoology, University of Bonn, Meckenheimer Allee 169, D-53115 Bonn, Germany; Chair of Zoology, Technische Universität München, Liesel-Beckmann-Straße 2, D-85350 Freising-Weihenstephan, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Kohl
authors.affiliation: Institute of Zoology, University of Bonn, Meckenheimer Allee 169, D-53115 Bonn, Germany.
authors.forename: Horst
authors.initials: H
authors.lastname: Bleckmann
mesh_terms: D000489:Alligators and Crocodiles / Q000502:physiology*; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D014872:Water Movements
keywords: Crocodile; Integumentary sensory organs; Mechanoreception; Water surface waves