From this we have been able to model visual prey detectability in cormorants under a range of viewing conditions.
The actual visual prey detectability in cormorants is therefore likely to be far lower than the upper limits modelled in Figs. 5 and 6 based upon simple contrast parameters.
We have modelled prey detectability in cormorants using a relatively high contrast prey item stimulus based upon a pelagic fish which would be taken from a water column with low turbidity.
To provide a perspective on this relatively poor visual acuity in cormorants it should be noted that the cormorants' highest visual performance is only equal to that of unaided humans in water [19], and approximately 60 times lower than that of visually-guided terrestrial avian predators, such as eagles, whose acuity threshold lies between 0.2 0.8 min of arc [20] [23].
Therefore, we propose that an advantage in cormorants - as in other families of diving seabirds - of respiratory air volume adjustment upon diving could be related less to increasing time of submergence, through an increased volume of body oxygen stores, than to reducing the locomotor costs of buoyancy control.
Consequently, unless previous estimates of blood and skeletal O2 stores and diving metabolic rates in avian divers are highly over-estimated, a more important advantage of respiratory air volume adjustment in cormorants, as in perhaps other families of diving seabirds, would be to reduce the costs of buoyancy control.
Though it occurs in many places in Japan, cormorant fishing on the Nagara River dates back more than 1,300 years.
In winter cormorant roosts are boosted by continental visitors, with some roosts numbering several hundred birds.
We propose that these kinds of specialised behavioural strategies play an important role in all cormorant foraging.
Those who follow Finney are able to see the highly detailed and impressionistic artwork alongside the text of his work-in-progress, The Cormorant.
