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 Professor Graham Martin |
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Graham Martin: Research
Within this general theme my work is principally focused upon vision. My particular interests are in the eye structure, visual fields, and visual capacities of birds in relation to ecological and behavioural problems. Below are details of some current papers and a general outline of my approach to these problems.
Visual and energetic determinants of pursuit-dive foraging in birds (Great Cormorants)" ________________________________________________ A sensory ecology approach is used in all of my work and the aim is to seek general principles that underlie the form and function of sensory systems across species groups. This has entailed comparative studies particularly in relation to the tasks of foraging at low light levels, amphibious foraging, and the function of binocular vision in guiding foraging. This approach necessitates investigation of how vision might be used both alone and in conjunction with other sensory functions in the execution of particular tasks. A brief history: My initial work in this area attempted to answer the question, "How is it that owls are nocturnal?". The answer seems to be a complex of interactions and complementary functioning between sensory systems, behaviour, prey type and habitat characteristics, i.e. there is not a simple "super-sensory" solution to being a flying bird within structurally complex habitats at night. Vision and hearing provide high sensitivity but they are not sufficient in themselves to account for the behaviour. This work was summarized in a book
Since that date some of my work has been conducted collaboratively with Dr Gadi Katzir of the University of Haifa , Israel and others. In particular we have been following problems in aquatic foraging (foraging through the water surface or underwater) and in the role of binocular vision in the control of bill position. In pursuit of this I have been conducting a long term comparative study of visual field topography in a range of bird species. To date visual field data in 31 species has been published (as summary paper is in preparation as part of the proceedings of the International Ornithological Congress, Hamburg, 2006). This work has also shown a number of ways in which visual field topography appears to be related to aspects of foraging ecology. Particular examples of such relationships have been found in work with Peter Prince (deceased) of the British Antarctic Survey in White-chinned Petrels and in Antarctic Prions (see below for summary), and with Matthieu Guillemain of The Office National de la Chasse et de la Faune Sauvage (France) in dabbling ducks (see summary below). This work has lead us to hypothesise that visual fields in birds are of three basic types. This is summarized in Visual fields in Short-toed eagles and the function of binocularity in birds. Brain, Behavior and Evolution. 53: 55-66. Other species that have shown some interesting adaptations of visual fields have been Oilbirds, Flamingos, and Kiwi and details of work with these species are given in the sections below. Based upon some of this comparative data base I have also discussed the function of "sunshades" in birds (for reference see below). We have also presented data supporting a possible "convergence" in the characteristics of frontal binocular visual fields and presented a general hypothesis for the function of binocularity in birds (see above reference). In all species that we have examined, the functional binocular field is considerably narrower than it has appeared from casual observation. These two lines of interest came together through an investigation of visual fields in two species of Hornbills. These birds forage using the technique of "precision grasping" in which small items are held in the bill tip prior to being tossed into the mouth. Working in collaboration with Hendri Coetzee of the Ground Hornbill Research & Conservation Project (South Africa) we have found that despite this specialised feeding technique the visual field topography is similar to those found in birds which either peck or lung at items with their bills, or take prey in their feet. We also found that these birds have extensive eye movements and employ their impressive eye lashes as sun shades (see summary below) I have also been interested in understanding the general rules that determine the optical structure of bird eyes. In this work we construct schematic models of the eye's optical system and use these as the basis for comparative analysis. It appears that there may be a common optical design to the eyes of terrestrial birds which is independent of their size or of the ecology and phylogeny of the species. The birds studied mostly recently in this way have been ostriches and this is described in Ostrich Ocular Optics, Brain Behavior and Evolution 58: 115-120 (see below).
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White-chinned petrels and antarctic
prions feed on a similar diet in the same waters, but their foraging behaviour
is quite different. The petrel is visually guided and often makes shallow dives,
the prion feeds at the surface using a filtering technique. This is reflected in
the topography of their visual fields. Details in Visual Fields and Foraging
in Procellariiform Seabirds: Sensory aspects of Dietary Segregation.
Brain Behaviour and
Evolution , 2001, Vol, 57, 33-38.
Although of very different sizes
and overall shapes, the eyes of ostriches, tawny owls and common starlings
actually share a very similar optical design. This is revealed by the
similarity in the ratio of the optical powers of the lens to cornea in each eye.
This suggests that optically these eyes are scaled versions of each other, and
this may reveal a common design in the eyes of terrestrial birds. See,
Ostrich Ocular Optics,
Brain, Behavior and
Evolution , 2001, 58: 115-120.
Shovelers and wigeons employ
different foraging techniques. When feeding wigeons spend more time with their
head up. Also, each feeding bout is shorter in wigeons than in shovelers. We
suggest that this reflects differences in these birds' ability to visually scan
the world around them when feeding. In shovelers there is no blind area behind
their head. In wigeons there is a small blind sector. This small difference may
be enough to explain these differences in foraging behaviour.See Guillemain,
M., Martin, G.R. and Fritz, H. 2002. Feeding methods, visual fields and
vigilance in dabbling ducks (Anatidae) .
Functional Ecology . 16: 522-529.
Click here for a PDF copy of the paper
Martin, G.R. et al. (2004) Binocular vision and nocturnal activity in Oilbirds (Steatornis caripensis) and Pauraques (Nyctidromus albicollis): Caprimulgiformes. Ornitologia Neotropical 15 (Suppl.) 233-242. In this paper we show that although Pauraques (a neotropical species of nightjar) are forage at night on aerial insects their visual fields are similar to those of many day time birds which feed by direct pursuit (pecking, lunging) of individual items. This raises interesting questions about the presumed link between the nocturnal habit and extensive binocular vision.
For a PDF copy of the
paper click here
Martin, G.R. et al. (2005) Visual fields in Flamingos: chick-feeding versus filter-feeding Naturwissenschaften, 92: 351-354. Flamingos Phoenicopteridae are highly specialised filter-feeders and employ a unique technique that does not require accurate bill positioning in which the inverted head is placed between the feet. Feeding flamingos often walk forwards with the head pointing “backwards”. In this paper we show that in Lesser Flamingos Phoeniconaias minor visual fields are in fact the same as those of birds that feed by precision pecking and that feeding flamingos are blind in the direction of their walking. We suggest that this is due to the requirement for accurate bill placement when flamingos feed their chicks with “crop-milk”, and possibly when building their nest. We propose that chick feeding may be the ultimate determinant of visual field topography in birds, not feeding ecology. Click here for a PDF copy of the paper _____________________________________________________________
Martin, G.R. , Jarret, N, Williams, M (2007) Visual fields in Blue Ducks Hymenolaimus malacorhynchos and Pink-eared Ducks Malacorhynchus membranaceus: visual and tactile foraging. Ibis, 149: 112-120 Blue Ducks Hymenolaimus malacorhynchos (Anatidae) reside in headwaters of New Zealand rivers and feed primarily on aquatic insects. However, whether such food items are detected by tactile or visual cues is unknown. That Blue Ducks may use tactile cues when foraging is suggested by the presence of specialised flaps of thickened, keratinised epidermis containing Herbst’s corpuscles along the ventral margins of the upper mandibles near the bill tip. Similar bill flaps are found only in one other duck species, Pink-eared Ducks Malacorhynchus membranaceus that surface filter-feed in turbid waters on a range of planktonic organisms. Using an ophthalmoscopic reflex technique we determined the visual fields of both species. We conclude that Blue Ducks are primarily visually-guided foragers. The eyes are frontally placed resulting in a wide binocular field into which the narrow tapering bill intrudes. There is a large blind area to the rear of the head. This visual field topography is similar to that of other visually-guided amphibious bird species that take mobile prey e.g. penguins (Spheniscidae). In contrast, Pink-eared Duck visual fields show features found in other tactile feeding ducks: a narrow frontal binocular field with the bill falling at the periphery, and comprehensive visual coverage of the celestial hemisphere. Since Blue Ducks are primarily visual feeders their foraging may be significantly disrupted by changes to water clarity. This introduces a previously unconsidered factor into the selection of sites for population enhancement or re-introductions; a current conservation focus.
Click here for a PDF copy of the paper ___________________________________________________________________________
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 both reduced body mass and the distribution of mass towards the body core. Freed from these mass constraints, it would be predicted that in flightless birds nocturnality should favour the evolution of large eyes and reliance upon visual cues for the guidance of activity. In this paper we show that in Kiwi (Apterygidae), flightlessness and nocturnality have, in fact, resulted in the opposite outcome. Kiwi show minimal reliance upon vision indicated by eye structure, visual field topography, and brain structures, and increased reliance upon tactile and olfactory information. A PDF of this paper is available from the PLosONE web site, click here ____________________________________________________________________________ This page is maintained by Graham Martin. |
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"Birds by Night" published in 1990, Poyser (Academic Press).
Hornbills (Coraciiformes, Bucerotidae) employ a precision grasping foraging
technique in which the large decurved bill is used like a pair of forceps to
pick up items with great precision in the tips. Food items are then thrown
further back into the mouth . Visual field measurements in two species: Southern
Ground Hornbills Bucorvus leadbeateri and Southern Yellow-billed
Hornbills Tockus leucomelas show that the bill intrudes into the frontal
binocular field but that the overall size and shape of the field is very much
like that of birds which either peck or lung at items.This
finding reinforces the idea that visual fields among birds are of a limited
number of types. However, intrusion of the bill into the field suggests that the
birds are able to examine items in their bill tips binocularly and this may aid
the precision grasping technique. Hornbills also have large eye movements which
seem to be used for visual scanning. Hornbills' extensive eye lashes appear to
be used as sunshades. Martin G.R. and Coetzee, H. Visual fields in
hornbills: precision grasping and sunshades. 
Oilbirds
and
hence high light gathering capacity. These adaptations of both the image
producing and image analysis sections of the eye suggest that visual sensitivity
must be very high, but visual resolution is poor. However, the frontal binocular
fields of Oilbirds are similar to those of many other diurnally active species.
Despite appearances, therefore, Oilbirds do not have a large functional frontal
binocular field, and hence we conclude that the large biocular fields of owls
are not necessarily associated with the nocturnal habit. Find out more: Martin,
G.R., Rojas, L.M., Ramirez, Y., McNeil, R. 2004. 
Kiwi Forego Vision in the
Guidance of their Nocturnal Activities (2007). Graham R. Martin, Kerry-Jayne
Wilson, J. Martin Wild, 
We argue that this lack
of reliance upon vision and increased reliance upon tactile and olfactory
information in Kiwi is markedly
similar to the situation in nocturnal mammals
that exploit the forest floor. That Kiwi and mammals evolved to exploit these
habitats quite independently provides evidence for convergent evolution in their
sensory capacities that are tuned to a common set of perceptual challenges found
in forest floor habitats at night and which cannot be met by the vertebrate
visual system. We propose that the Kiwi visual system has undergone adaptive
regressive evolution driven by the trade-off between the relatively low rate of
gain of visual information that is possible at low light levels and the
metabolic costs of extracting that information.
