spacer gif spacer gif spacer gif spacer gif Online submission spacer gif
QUICK SEARCH:   [advanced]


spacer gif
     Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents    

First published online February 29, 2008
Journal of Experimental Biology 211, 866-872 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.014324
This Article
Right arrow Figures Only
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Google Scholar
Right arrow Articles by Strod, T.
Right arrow Articles by Katzir, G.
PubMed
Right arrow PubMed Citation
Right arrow Articles by Strod, T.
Right arrow Articles by Katzir, G.

Prey detection by great cormorant (Phalacrocorax carbo sinensis) in clear and in turbid water

Tamir Strod1, Ido Izhaki2,3, Zeev Arad1 and Gadi Katzir3,*

1 Department of Biology, Technion – Israel Institute of Technology, Haifa 32000, Israel
2 Department of Evolutionary and Environmental Biology, University of Haifa, Haifa 31905, Israel
3 Department of Biology, University of Haifa at Oranim, Tivon 36006, Israel

* Author for correspondence (e-mail: gkatzir{at}research.haifa.ac.il)

Accepted 10 January 2008

The scattering and absorption of light by water molecules and by suspended and dissolved matter (turbidity) degrade image transmission and, thus, underwater perception. We tested the effects on visual detection of prey size and distance (affecting apparent prey size) and of low-level water turbidity in hand-reared great cormorants (Phalacrocorax carbo sinensis) diving for natural prey (fish) in a forced-choice situation. The cormorants' detection of underwater prey relied on vision. The minimal tested subtending visual angle of the prey at detection ranged between ~34.2' (prey size constant; distance varied) and 9.5' (distance constant; prey size varied). For all tested distances (0.8–3.1 m) the mean detection success was significantly higher than the chance level. The probability of a correct choice declined significantly with increased distance, with Detection success=–0.034D+1.021 (where D is distance, r2=0.5, N=70, P<0.001). The combined effect of turbidity and distance on the probability of detection success was significant, with both variables having a negative effect: Detection success=–0.286D–0.224Tu+1.691 (where Tu is turbidity, r2=0.68, N=144, P<0.001). At prey detection threshold, the relationship between distance and turbidity was: D=3.79e–4.55Tu. It is concluded that (i) the subtending angle of natural prey at detection was lower than that of resolution of square-wave, high-contrast grating and (ii) turbidity, at levels significantly lower than commonly used in behavioural experiments, had a pronounced effect on visually mediated behaviour patterns.

Key words: cormorant, aquatic vision, underwater visual resolution, water turbidity, underwater prey detection






© The Company of Biologists Ltd 2008