Biomedical subjects

G Katzir

Publications and source records attributed to G Katzir.

8 recordsLinked to original sources

PubMed2001

Head stabilization in herons.

We examined head stabilization in relation to body mass and length of legs in four heron species (little egrets, Egretta garzetta; night herons, Nycticorax nycticorax; squacco herons, Ardeola ralloides; and cattle egrets, Bubulcus ibis: Aves: Ardeidae). Head stabilization, under controlled, sinusoidal, perch perturbations was mostly elicited at frequencies lower than 1 Hz. Maximal perturbation amplitudes sustained were positively correlated with leg length and maximal perturbation frequencies sustained were negatively correlated with body mass and with leg length. The species differed significantly in average maximal perturbation amplitudes sustained. Combinations of amplitude and frequency for which stabilization was achieved were bounded by a decreasing concave "envelope" curve in the frequency-amplitude plane, with inter specific differences in "envelope". As physical constraints, we tested maximal vertical acceleration, which translates into a line defined by the product of frequency2 x amplitude, and maximal vertical velocity, which translates into a line defined by the product of frequency x amplitude. Both relations were in good agreement with the experimental results for all but squacco herons. The results support predictions based on mechanical considerations and may explain the predominance of motor patterns employed by herons while foraging.

Animals↗

PubMed2001

Ostrich ocular optics.

The optical structure of the eyes of ostriches (Struthio camelus; Struthionidae; Struthioniformes) was determined by the construction of a schematic eye model for paraxial optics. The eye is large (axial length = 38 mm) and of globose shape with an anterior focal length (posterior nodal distance) of 21.8 mm. The optical design of the eye is such that the lens and cornea contribute equally to its total optical power. Interspecific comparison shows that optically the ostrich eye is a larger scaled version of the eyes of common starlings (Sturnus vulgaris) and an owl (Strix aluco).

Animals↗

PubMed2000

Sun shades and eye size in birds.

Visual field width above the head is significantly correlated (r(s) = 0.92, n = 11, p < 0.001) with eye size in a sample of terrestrial birds that differ in their phylogeny and ecology. These species can be divided into two groups. Smaller-eyed sun-observers (axial length <18 mm) have comprehensive or near comprehensive visual coverage of the celestial hemisphere and are thus unable to avoid viewing the sun. Larger-eyed sun-avoiders (axial length >18 mm) have restricted visual fields and various types of optical adnexa (enlarged brows, hair like feathers on the eye lids and around the eye) which can prevent solar illumination of the cornea. We suggest that these differences relate to visual rather than pathological problems and argue that the reduction of disability glare, produced by sunlight falling directly upon the eye, becomes increasingly significant as eye size increases. We propose that the reduced visual fields and optical adnexa of the larger-eyed birds are primarily concerned with the maintenance of high spatial resolution.

Animals↗

PubMed1999

Cattle egrets are less able to cope with light refraction than are other herons.

The majority of heron species (Aves, Ardeidae) forage on aquatic prey in shallow water. Prey detection, aiming and the beginning of the capture strikes are performed while the heron's eyes are above water. For most angles, as a result of air/water light refraction, the apparent image available to a heron is vertically displaced from the prey's real position. Herons must therefore correct for refraction. We tested the hypothesis that species that forage in aquatic habitats should be more able to correct for image disparity than those of terrestrial habitats. The ability of hand-reared herons of four species to capture stationary prey (fish) underwater (submerged) or in air (aerial) was tested. Three species (little egret Egretta garzetta, squacco heron Ardeola ralloides, and night heron Nycticorax nycticorax) normally forage in aquatic habitats while the fourth (cattle egret Bubulcus ibis) forages in terrestrial habitats. No individuals missed aerial prey. Success rates of little egrets and of squacco herons with submerged prey were high, while night herons became less successful with increased prey depth and/or distance. In cattle egrets, success rate was low and negatively correlated with prey depth. The observed interspecific differences may thus be related to (1) differential ability to correct for air/water light refraction and (2) the species' foraging behaviour. We suggest that cattle egrets are in the process of losing their ability to cope with submerged prey. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1999

Visual fields in Short-toed Eagles, Circaetus gallicus (Accipitridae), and the function of binocularity in birds.

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 the horizontal plane is 139 degrees, and the field is asymmetric about the optic axis. The cyclopean field extends through 260 degrees, and the blind area above and behind the head reaches maximum width of 100 degrees close to the horizontal. At the frontal margins of the monocular field the retinal and optical fields do not coincide; the retinal field margin lies approximately 10 degrees inside the optical margin. This gives rise to an apparent binocular field that is twice the width of the functional binocular field. Interspecific comparisons show that the binocular field of Short-toed Eagles is similar in shape and size to those of bird species that differ markedly in phylogeny, ecology, foraging technique, and eye size. This suggests that these relatively narrow binocular fields are a convergent feature of birds whose foraging is guided by visual cues irrespective of whether items are taken directly in the bill or in the feet, as in eagles, and irrespective of the size and shape of the monocular and cyclopean visual fields. It is argued that binocular vision in birds results from the requirement for each monocular field to extend contralaterally to embody a portion of the optical flow field which is radially symmetrical about the direction of travel. This is in contrast to functional explanations of binocularity, such as those concerned with stereopsis, which present it as a means of extracting higher order information through the combination of two monocular images of the same portion of a scene.

Animals↗

PubMed1994

Visual fields and eye movements in herons (Ardeidae).

The visual fields and eye movements of three heron species (Ardeidae; Ciconiiformes): the cattle egret (Bubulcus ibis), the squacco heron (Ardeola ralloides), the western reef heron (Egretta gularis schistacea) were determined in alert, restrained birds using an ophthalmoscopic technique. All three species can gain panoramic visual coverage of the frontal field around the bill, and a bird standing with its bill horizontal can view its own feet binocularly. The region in which binocular overlap is possible is long (approximately 170 degrees) and narrow (maximum width approximately 20 degrees). Monocular field width in a horizontal plane is approximately 170 degrees. Retinal binocular overlap can be abolished by eye movements at all elevations in the frontal field. At the frontal margins of the monocular fields the retinal and optical field margins do not coincide; the retinal field margin lies between 9 degrees and 12.5 degrees inside the optical field margin. This results in a blind sector at the margin of each eye's optical field. Consequently the visually functional retinal binocular field widths are significantly narrower than the optical binocular fields. When retinal binocularity is abolished by eye movements, optical binocular fields are still retained. Thus, estimates of binocular overlap based only upon the appearance of the pupils will be erroneous. The comprehensive nature of vision beneath the bill is probably closely associated with the herons' visually guided, stealthy, foraging techniques, which result in the single-strike capture of mobile, highly evasive prey.

Animals↗

PubMed1988

Two sequential outbreaks of rotavirus gastroenteritis: evidence for symptomatic and asymptomatic reinfections.

In two sequential outbreaks of rotavirus gastroenteritis that occurred in a kibbutz in southern Israel (the Negev), 32 persons (9% of the population) were ill in the first and 45 (13% of the population) in the second. Excretion of virus, changes in titers of rotavirus-specific serum IgG, or both implicated rotavirus in 72% of the illnesses in outbreak 1 and in 56% of the illnesses in outbreak 2. In both outbreaks the age-specific morbidity rate decreased with increasing age. Half (six of 12) of the children six to 27 months of age who were ill with rotavirus in outbreak 1 were ill with rotavirus again in outbreak 2, whereas two were asymptomatically infected; older children who were ill in outbreak 1 were not ill in outbreak 2. Serotype determination by enzyme-linked immunosorbent assay using monoclonal antibodies to VP7 implicated a serotype 3 virus in outbreak 1 and a serotype 1 virus in outbreak 2.

Adolescent↗

PubMed1986

Involvement of infants, children, and adults in a rotavirus gastroenteritis outbreak in a kibbutz in southern Israel.

An outbreak of acute gastroenteritis in a kibbutz in southern Israel, characterized by diarrhea, fever, vomiting, and abdominal pain, involved 32 kibbutz members of all ages. Nineteen percent of the children and 3.5% of the adults were ill. Transmission of the illness occurred in direct proportion to the degree of close contact, involving first infants, then mothers and nursery staff, and only later youngsters, adolescents, and fathers. Stool samples obtained from 32 kibbutz members with clinical illness and from 44 asymptomatic close contacts were examined for the presence of rotavirus antigen. Fifty-six percent of symptomatic members were positive for rotavirus antigen as compared with 4.5% of asymptomatic close contacts. Positivity of stool samples correlated inversely with the number of days elapsed after onset of illness until the sample was obtained. Serologic studies carried out on acute and convalescent sera of symptomatic and asymptomatic subjects further supported a rotavirus etiology for the outbreak. RNA profiles of stool sample extracts obtained by polyacrylamide gel electrophoresis and silver staining indicate that one electropherotype may have been responsible for the outbreak.

Adolescent↗