Graham R. Martin

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1. Time and energy are key currencies in animal ecology, and judicious management of these is a primary focus for natural selection. At present, however, there are only two main methods for estimation of rate of energy expenditure in the field, heart rate and doubly labelled water, both of which have been used with success; but both also have their(More)
Visual fields were determined in alert restrained birds using an ophthalmoscopic reflex technique. The region of binocular overlap is relatively small: maximum width of 20 degrees occurs approximately 15 degrees below the horizontal, and the field extends vertically through 80 degrees with the bill tip placed close to the centre. Monocular field width in(More)
The uniocular retinal field of Strix aluco is highly asymmetrical. The maximum width of 124 degrees is less than that recorded in any other vertebrate. Maximum retinal binocular field width equals 48 degrees and the optic axes diverge by 55 degrees. Maximum binocularity occurs above the bill whose tip lies outside of the visual field. The cyclopean retinal(More)
The European starling,Sturnus vulgaris, is a diurnal, ground feeding bird of the order Passeriformes. Aspects of its visual fields, eye movements and the optical structure of its eye are described. 1. The magnitude of eye movements as a function of elevation in the median sagittal plane of the head was measured (Fig. 1). Maximum eye movement amplitude (32°)(More)
The schematic eye ofStrix aluco, a nocturnal owl species, is described. A comparative and ecological context is used to examine the relationships between optical parameters of the eye and its light gathering and resolving powers. It is concluded that the essentially ‘nocturnal’ feature of the owl eye does not lie in either its light gathering power or the(More)
Among birds there are considerable interspecific differences in all aspects of visual fields. However, it is hypothesised that the topography of the frontal binocular portion of fields are of only three main types, and their principal functions lie in the degree to which vision is used in the guidance of the bill (or feet) towards food objects or for the(More)
BACKGROUND In vision, there is a trade-off between sensitivity and resolution, and any eye which maximises information gain at low light levels needs to be large. This imposes exacting constraints upon vision in nocturnal flying birds. Eyes are essentially heavy, fluid-filled chambers, and in flying birds their increased size is countered by selection for(More)
An ophthalmoscopic reflex technique has shown that in sedated pigeons maximum retinal binocular field width occurs approximately 20 degrees above the bill. The binocular field has a maximum width of 27 degrees and extends vertically by 130 degrees (90 degrees above the bill, 40 degrees below it). Both the bill and cere intrude into the binocular field.(More)
A wave optical model was used to analyse the scattering properties of avian retinal oil droplets. Computations for the near field region showed that oil droplets perform significant light collection in cone photoreceptors and so enhance outer segment photon capture rates. Scattering by the oil droplet of the principal cone of a double cone pair, combined(More)