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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)
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)
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)
It is proposed that with the possible exception of owls, binocularity in birds does not have a higher order function that results in the perception of solidity and relative depth. Rather, binocularity is a consequence of the requirement of having a portion of the visual field that looks in the direction of travel; hence, each eye must have a contralateral(More)
A classic example of ecophysiological adaptation is the observation that animals from hot arid environments have lower basal metabolic rates (BMRs, ml O2min-1) than those from non-arid (luxuriant) ones. However, the term 'arid' conceals within it a multitude of characteristics including extreme ambient temperatures (Ta, degrees C) and low annual net primary(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 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)