Rolf Åke Norberg

University of Gothenburg | GU · Department of Biological & Environmental Sciences

The wings, legs, and tail in Darwin’s finches show many clear adaptations to different types of locomotion used during foraging. We use size scaling to analyse how various characters vary with body mass to clarify dimensional relationships. The selective advantage of a character is judged in terms of energy savings. The wing aspect ratio (4.6–4.9)...

Here, we report that on six widely separated Scandinavian islands, the coal tit Parus ater has evolved morphologically in the direction of two absent competitors, the crested tit P. cristatus and the willow tit P. montanus, to the effect that it is up to 10% larger in linear dimensions than conspecifics on the adjacent Swedish mainland, where all t...

The ability to fly opens up ecological opportunities but flight mechanics and muscle energetics impose constraints, one of which is that the maximum body size must be kept below a rather low limit. The muscle power available for flight increases in proportion to flight muscle mass and wingbeat frequency. The maximum wingbeat frequency attainable am...

When geometric similarity, or isometry, prevails among animals of different sizes their form and proportions are similar. Weight increases as the cube of the length dimension, while cross-sectional areas increase as its square, so in load-bearing structural elements the stress, caused by the body weight, increases in direct proportion to the length...

Most foot-propelled swimming birds sweep their webbed feet backwards in a curved path that lies in a plane aligned with the swimming direction. When the foot passes the most outward position, near the beginning of the power stroke, a tangent to the foot trajectory is parallel with the line of swimming and the foot web is perpendicular to it. But la...

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In some birds, sexual selection, owing to female preference for long tails in mate choice, has led to tails large enough to constitute serious handicaps in flight, incurring a cost in terms of natural selection. Elongated tails also occur among species that depend heavily on flight for foraging, but then usually only the outer tail feathers are lon...

Clarifies misunderstandings in previous discussions about relationships between volumetric growth and growth in linear dimensions, and explores the causal basis for the -3/2 law and for deviations from it. Different plant parts must often exhibit different growth modes (for functional reasons); therefore, the thinning function for whole plants must...

When individual plants grow in an uncrowded population there is little or no mortality from competition. In a diagram displaying the logarithm of the volume of an average plant against the logarithm of population density, growth trajectories therefore are nearly vertical. But as plants begin to fill up the available space, crowding commences, and t...

The mechanics and energetics of tail-supported clinging and climbing by Certhia familiaris on vertical trunks were analysed from still photographs and cine films. A complete movement cycle, or stride, consists of the power stroke and a floating phase. One stride analyzed in detail was 66 mm long and took 0.1375 s. The bird moved about half the stri...

This paper compares the energy costs of various modes of locomotion of birds foraging in trees. For birds moving vertically in trees by climbing and hopping (but not by flying) the best choice of locomotion mode depends on the distance between visited trees in relation to the height h of the zone searched for food in trees. When the distance betwee...

The lowered weight in adult birds rearing young should result in energy savings during locomotion. Furthermore, the parents may live partly off the energy released during weight loss. For these reasons the parents could eat a smaller proportion of the food collected themselves and give a larger proportion to the young, potentially leading to more f...

(1) From the theory of bird flight energetics (due mainly to Pennycuick) I derive a simple model which identifies the flight speed of breeding birds that results in most food for the young. I consider only flights between foraging areas and the young, with no foraging during travel flights. (2) A parent bird trying to maximize amount of food delive...

This paper describes the energy cost of locomotion in birds foraging over vertical zones in trees. In particular, the energetically cheapest pattern for a bird flying among trees and moving within them is explored. For birds moving vertically by climbing and hopping (but not by flying) it should take less energy to climb and hop upwards in a tree a...

To explain the adaptive significance of sex role partitioning and reversed sexual size dimorphism among raptors, owls and skuas, where females are usually larger than males, we combine several previous hypotheses with some new ideas. Owing to their structural and behavioural adaptations for prey capture, predatory birds have better prospects than o...

The ear apertures in the skin of Tengmalm's owl, Aegolius funereus (Linne) (Strigiformes), are slit-like and ca. 24 mm long. This equals the height of the skull. The ear opening in the skin is bounded by a continuous fold of skin that is developed into a preaural and a postaural flap. The preaural flap carries the facial disk feathers that are stru...

Spiders and some insects were collected from branches of spruce, Picea abies, in September-October and February-March in southwest Sweden. At least 19 species of spiders were present. Spiders of family Thomisidae were most common with 37-45% by number, and the species-group Philodromus aureolus alone made up 35-39%. Family Linyphiidae came second w...

On the basis of the literature and my own examination of living and/or dead but fresh owls of 16 species, bilateral asymmetry of external ears in owls is surveyed and ear structure briefly described. Consideration of the probability of origin of various structural similarities and dissimilarities in the ear leads to the conclusion that ear asymmetr...

(1) A deductive, theoretical model is developed to allow calculation of a minimum energy budget and the corresponding time budget for foraging, both based on a diel (24 h) cycle. The model refers to animals with relatively high energetic costs of foraging, such as birds and mammals. (2) Various contributions to the daily time budget for foraging of...

The kinematics of free unimpeded hovering flight of Aeschna juncea L. was analysed from films taken in the field with 80 frames sec−1, and from still pictures taken with a motorized camera. The body is held almost horizontal, and the wing stroke plane is tilted 60° relative to the horizontal. In these respects the dragonfly differs strongly from mo...

A samara is a winged fruit or seed that autorotates when falling, thereby reducing the sinking speed of the diaspore and increasing the distance it may be transported by winds. Samaras have evolved independently in a large number of plants. Aerodynamical, mechanical, and structural properties crucial for the inherent self‐stability are analysed, an...

Norberg, R. Å. (Department of Zoology, University of Gothenburg, Göteborg, Sweden.) Evolution of flight in insects. Zool. Scripta 1 (6): 247–250, 1972.–Two hypotheses on the origin of flight in insects are discussed. 1. Gliding hypothesis. If wings and flight originated in ca. 1 cm large, or larger, insects, a leaping type seems to be a more probab...

Norberg, R. Å. (Department of Zoology, University of Gothenburg, Göteborg, Sweden.) Flight characteristics of two plume moths, Alucita pentadactyla L. and Orneodes hexadactyla L. (Microlepidoptera). Zool. Scripta 1 (6): 241–246,1972.–Multiple exposure photographs of up to 100 exposures/sec were taken on two plume moth species in free, unrestrained...

1. The pterostigma of insect wings usually is a pigmented spot close to the leading edge far out on the wing, having a greater mass than an equally large wing piece in adjacent wing regions. 2. In several dragonfly (Odonata) species the position of the spanwise torsion axis of the wings, the mass distribution of the wings, and the position of the c...

Take-off and landing of Gavia stellata were studied at nesting tarns. At take-off divers had to skitter to obtain the necessary relative airspeed at the wings, the feet contributing the extra vertical force necessary to keep the diver out of water while acceleration was accomplished by feet and wings. They skittered 15-40 m, their feet moving synch...

Hunting by Aegolius funereus (L.) was studied by direct observation, and various phases of the prey capture were photographed. The owls hunted in forest land and frequented dense parts of the forest where they flew skilfully. They searched for prey from low perches, mean height 1.7 m, and waited a short time at each perch, mean 1 4/5 min. Mean dist...