ePrints Repository

Vision and Foraging in Cormorants: More like Herons than Hawks?

White, Craig R. and Day, Norman and Butler, Patrick J. and Martin, Graham R. (2007) Vision and Foraging in Cormorants: More like Herons than Hawks? PLoS ONE, 2 (7).

Loading
PDF (490Kb)

Available under License : Creative Commons Attribution

Identification Number/DOI: e639.doi:10.1371/journal.pone.0000639

Background
Great cormorants (Phalacrocorax carbo L.) show the highest known foraging yield for a marine predator and they are often perceived to be in conflict with human economic interests. They are generally regarded as visually-guided, pursuit-dive foragers, so it would be expected that cormorants have excellent vision much like aerial predators, such as hawks which detect and pursue prey from a distance. Indeed cormorant eyes appear to show some specific adaptations to the amphibious life style. They are reported to have a highly pliable lens and powerful intraocular muscles which are thought to accommodate for the loss of corneal refractive power that accompanies immersion and ensures a well focussed image on the retina. However, nothing is known of the visual performance of these birds and how this might influence their prey capture technique.

Methodology/Principal Findings
We measured the aquatic visual acuity of great cormorants under a range of viewing conditions (illuminance, target contrast, viewing distance) and found it to be unexpectedly poor. Cormorant visual acuity under a range of viewing conditions is in fact comparable to unaided humans under water, and very inferior to that of aerial predators. We present a prey detectability model based upon the known acuity of cormorants at different illuminances, target contrasts and viewing distances. This shows that cormorants are able to detect individual prey only at close range (less than 1 m).

Conclusions/Significance
We conclude that cormorants are not the aquatic equivalent of hawks. Their efficient hunting involves the use of specialised foraging techniques which employ brief short-distance pursuit and/or rapid neck extension to capture prey that is visually detected or flushed only at short range. This technique appears to be driven proximately by the cormorant's limited visual capacities, and is analogous to the foraging techniques employed by herons.

Type of Work:Article
Date:25 July 2007 (Publication)
School/Faculty:Schools (1998 to 2008) > School of Biosciences
Department:Centre for Ornithology, Biosciences
Subjects:QL Zoology
Institution:University of Birmingham
Copyright Holders:White et al.
ID Code:55
Refereed:YES
Export Reference As : ASCII + BibTeX + Dublin Core + EndNote + HTML + METS + MODS + OpenURL Object + Reference Manager + Refer + RefWorks
Share this item :
QR Code for this page

Repository Staff Only: item control page