Steven Portugal

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Verified

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• PhD
• Associate Professor at University of Oxford

The brain is energetically expensive. Energy availability may, therefore, determine whether costly cognitive processes such as long-term memory can be expressed. However, there is a limited understanding of the metabolic costs associated with long-term memory formation. Here, we explored the potential induced costs of long-term memory formation usi...

Despite the role of many domestic animals as model organisms, our understanding of their undomesticated conspecifics is comparatively poor. This limits our ability to infer the eco-evolutionary context of phenomena studied in the laboratory and to explore domestication. The domestic pigeon's wild form is the Rock Dove (Columba livia). By studying 5...

Subterranean mammals representing a single subspecies occurring along an aridity gradient provide an appropriate model for investigating adaptive variation in thermal physiology with varying levels of precipitation and air temperature (Tair). This study examined the thermal physiological adaptations of common mole-rats (Cryptomys hottentotus hotten...

As the avian embryo grows and develops within the egg, its metabolic rate gradually increases. Obligate avian brood-parasitic birds lay their eggs in the nests of other species to avoid the costs of parental care, and all but one of these brood-parasitic species are altricial at hatching. Yet the chicks of some altricial brood-parasitic species per...

Wide variation in visual field configuration has been recorded among avian species and it is hypothesized that this variation is driven primarily by foraging ecology and predator detection. It has also been shown that visual field configurations can render some species more vulnerable to collisions with human artefacts that extend into open airspac...

Birds’ bills are their main tactile interface with the outside world. Tactile bill-tip organs associated with specialized foraging techniques are present in several bird groups, yet remain understudied in most clades. One example is Austrodyptornithes, the major seabird clade uniting Procellariiformes (albatrosses and petrels) and Sphenisciformes (...

Avian visual fields have been predicted to be highly conserved at the intraspecific level and be repeatable within an individual, yet this has never been previously determined empirically. Typically, only 2–3 individuals of a species are measured during visual field procedures, and these individuals are measured just once. Using the ophthalmoscopic...

The visual field of a bird defines the amount of information that can be extracted from the environment around it, using the eyes. Previous visual field research has left large phylogenetic gaps, where tropical bird species have been comparatively understudied. Using the ophthalmoscopic technique, we measured the visual fields of seven tropical sea...

Genetic adaptation is the change of a population toward a phenotype that best fits the present ecological conditions of the environment it inhabits. As environmental conditions change, allele frequencies shift, resulting in different populations of the same species possessing genetic variation and divergent phenotypes. Cooperatively breeding common...

A vast array of challenging environments are inhabited by mammals, such as living in confined spaces where oxygen levels are likely to be low. Species can exhibit adaptations in basal metabolic rate (BMR) to exploit such unique niches. In this study we use 801 species to determine the relationship between BMR and burrow use in mammals. We included...

Designing conservation interventions for rare species can be hindered by a lack of relevant data. Local ecological knowledge (LEK) has potential to provide rapidly collected, cost‐effective data across large spatio‐temporal scales, but has rarely been used as a source of conservation‐relevant information for the Asian Songbird Crisis. The Blue‐crow...

Morphological adaptation is the change in the form of an organism that benefits the individual in its current habitat. Mole-rats (family Bathyergidae), despite being subterranean , are impacted by both local and broad-scale environmental conditions that occur above ground. Common mole-rats (Cryptomys hottentotus hottentotus) present an ideal mammal...

Two questions guide this seven-year project: First, how can we approach the phenomenon, representation, and interpretation of total solar eclipses? Second, how can we heal the historical divide separating the natural sciences from the humanities, arts, history, and theology? This volume presents Tom McLeish’s and Henrike Lange’s answer to both ques...

The binocular field of vision differs widely in birds depending on ecological traits such as foraging. Owls (Strigiformes) have been considered to have a unique binocular field, but whether it is related to foraging has remained unknown. While taking into account allometry and phylogeny, we hypothesized that both daily activity cycle and diet deter...

Metabolic rate determines life processes and the physiological requirements of an individual, and has recently been implicated as a driver of inter-individual variation in behaviour, with positive correlations associated with boldness, exploration and aggressive behaviours being recorded. While the link between metabolism and personality has been e...

Wide variation in visual field configuration across avian species is hypothesized to be driven primarily by foraging ecology and predator detection. While some studies of selected taxa have identified relationships between foraging ecology and binocular field characteristics in particular species, few have accounted for the relevance of shared ance...

Animals rely on movement to explore and exploit resources in their environment. While movement can provide energetic benefits, it also comes with energetic costs. This study examines how group phenotypic composition individual speed and energy expenditure during group travel in homing pigeons. We manipulated the composition of pigeon groups based o...

The eggs of avian obligate brood-parasitic species have multiple adaptations to deceive hosts and optimize development in host nests. While the structure and composition of the eggshell in all birds is essential for embryo growth and protection from external threats, parasitic eggs may face specific challenges such as high microbial loads, rapid la...

Steven Portugal introduces the Siamese fighting fish (Betta splendens).

A single sheepdog can bring together and manoeuvre hundreds of sheep from one location to another. Engineers and ecologists are fascinated by this sheepdog herding because of the potential it provides for ‘bio‐herding’: a biologically inspired herding of animal groups by robots. Although many herding algorithms have been proposed, most are studied...

Climate change has caused aridification which can alter habitat vegetation, soil and precipitation profiles potentially affecting resident species. Vegetation and soil profiles are important for subterranean mole-rats as increasing aridity causes soils to become harder and geophytes less evenly distributed, and the inter-geophyte distance increases...

Portugal describes the unique morphology and habits of the secretary bird, which kills its prey with lightning-quick kicks to the head.

Animals are characterised, in part, by their use of voluntary movement, which is used to explore and exploit resources from their surrounding environment. Movement can therefore benefit animals, but will cost them their energetic reserves. Thus, adaptations for faster movements with negligible increases in energy expenditure will likely evolve via...

The amniote eggshell is a fundamental aspect of the embryo life‐support system, protecting it from UV light, microbes and mechanical damage, while regulating gas exchange and providing calcium for growth. The thickness of eggshells is highly diverse across modern birds and influences multiple eggshell functions, yet the selective pressures driving...

Dominance hierarchies are a social dynamic common in many species, which help balance the costs and benefits of social living. Which individuals in a group occupy high ranking positions is influenced by a multitude of different intrinsic and/or extrinsic factors. While homing pigeons ( Columba livia ) have been a model system for their navigational...

Remaining cohesive on the move can be beneficial for animal groups. As such, animal groups have evolved coordination mechanisms such as leadership to resolve navigational conflicts of interest. Consistent "leaders" may have an intrinsic advantage over "followers" which compromise on their preferred route to retain cohesion, which highlights the que...

Complex patterns of collective behaviour may emerge through self-organization, from local interactions among individuals in a group. To understand what behavioural rules underlie these patterns, computational models are often necessary. These rules have not yet been systematically studied for bird flocks under predation. Here, we study airborne flo...

Bird flocks under predation demonstrate complex patterns of collective escape. These patterns may emerge by self-organization from local interactions among group-members. Computational models have been shown to be valuable for identifying what behavioral rules may govern such interactions among individuals during collective motion. However, our kno...

Animal‐borne logging devices are now commonly used to record and monitor the movements, physiology and behaviours of free‐living animals. It is imperative that the impacts these devices have on the animals themselves are minimised. One important consideration is the interaction between the body mass of the animal and the mass of the device. Using c...

Movement of the embryo is essential for musculoskeletal development in vertebrates, yet little is known about whether, and why, species vary. Avian brood parasites exhibit feats of strength in early life as adaptations to exploit the hosts that rear them. We hypothesized that an increase in embryonic movement could allow brood parasites to develop...

Complex and at times extreme environments have pushed many bird species to develop unique eggshell surface properties to protect the embryo from external threats. Because microbes are usually transmitted into eggs by moisture, some species have evolved hydrophobic shell surfaces that resist water absorption, while also regulating heat loss and the...

The avian eggshell is a bio-ceramic structure that protects the embryo. It is composed almost entirely of calcium carbonate and a small amount of organic material. An optimal amount of calcium carbonate in the eggshell is essential for the embryo's development, yet how the ratio of calcium carbonate to organic matter varies between species has not...

The benefits of dominance are well known and numerous, including first access to resources such as food, mates and nesting sites. Less well studied are the potential costs associated with being dominant. Here, the movement of two flocks of domestic homing pigeons Columba livia – measured via accelerometry loggers – was recorded over a period of two...

Bird flocks under predation demonstrate complex patterns of collective escape. These patterns may emerge by self-organization from simple interactions among group-members. Computational models have been shown to be valuable for identifying the behavioral rules that may govern these interactions among individuals during collective motion. However, o...

Embryo survival in birds depends on a controlled transfer of water vapour and respiratory gases through the eggshell, and this exchange is critically sensitive to the surrounding physical environment. As birds breed in most terrestrial habitats worldwide, we proposed that variation in eggshell conductance has evolved to optimize embryonic developme...

The “selfish herd” hypothesis¹ provides a potential mechanism to explain a ubiquitous phenomenon in nature: that of non-kin aggregations. Individuals in selfish herds are thought to benefit by reducing their own risk at the expense of conspecifics by attracting toward their neighbors’ positions¹,² or central locations in the aggregation.3, 4, 5 Alt...

The power curve provides a basis for predicting adjustments that animals make in flight speed, for example in relation to wind, distance, habitat foraging quality and objective. However, relatively few studies have examined how animals respond to the landscape below them, which could affect speed and power allocation through modifications in climb...

The power curve provides a basis for predicting adjustments that animals make in flight speed, for example in relation to wind, distance, habitat foraging quality and objective. However, relatively few studies have examined how animals respond to the landscape below them, which could affect speed and power allocation through modifications in climb...

Climate affects all aspects of biology. Physiological traits play a key role in mediating these effects, because they define the fundamental niche of each organism. Climate change is likely to shift environmental conditions away from physiological optima. The consequences for species are significant: they must alter their physiology through plastic...

The flight speeds that animals should adopt to minimise energy expenditure in different scenarios can be predicted by the curve of power against speed. However, relatively few studies have examined how animals respond to the landscape below them, which could affect speed through modifications in climb rate and perceived predation risk. We equipped...

Dominance hierarchies confer benefits to group members by decreasing the incidences of physical conflict, but may result in certain lower ranked individuals consistently missing out on access to resources. Here, we report a linear dominance hierarchy remaining stable over time in a closed population of birds. We show that this stability can be disr...

Dominance hierarchies confer benefits to group members by decreasing the incidences of physical conflict, but may result in certain lower ranked individuals consistently missing out on access to resources. Here, we report a linear dominance hierarchy remaining stable over time in a closed population of birds. We show that this stability can be disr...

Gillnet bycatch accounts for over 400,000 bird mortalities worldwide every year, affecting a wide variety of species, especially those birds that dive when foraging. Technological solutions to improve gillnet visibility or deter birds from approaching nets, such as LED lights, are essential for aiding diving birds to perceive nets as a hazard. Desi...

Many different physiological changes have been observed in wild waterfowl during the flightless stage of wing moult, including a loss of body mass. Previously we established that captive barnacle geese (Branta leucopsis) underwent this characteristic decrease in body mass during their wing moult, even though they had unlimited and unrestricted acce...

Feathers act as aerodynamic cantilevers, and to withstand the prolonged cyclical loading that occurs during flight, feathers must be stiff, lightweight and strong. We experimentally tested the differences in feather structure, primarily stiffness and size, between (a) wild and captive Barnacle Geese Branta leucopsis, and (b) primary feathers droppe...

Siamese fighting fish, Betta splendens, have been extensively studied due to their aggression and stereotypical displays. Many studies have focused on their characteristic opercular flaring, while the less aggressive and less energetically costly lateral display have been comparatively understudied. Many factors have been shown to influence aggress...

The benefits of dominance are well known and numerous, including first access to resources such as food, mates and nesting sites. Less well studied are the potential costs associated with being dominant. Here, the movement of two flocks of domestic homing pigeons ( Columba livia ) – measured via accelerometry loggers – was recorded over a period of...

Feathers act as aerodynamic cantilevers, and to withstand the prolonged cyclical loading that occurs during flight, feathers must be stiff, lightweight and strong. We experimentally tested the differences in feather structure, primarily stiffness and size, between (a) wild and captive Barnacle Geese Branta leucopsis, and (b) primary feathers droppe...

Steven Portugal introduces the behavioral and aerodynamic underpinnings of aerial flocking in birds.

Closely related tropical bird species often occupy mutually exclusive elevational ranges, but the mechanisms generating and maintaining this pattern remain poorly understood. One hypothesis is that replacement species are segregated by interference competition (e.g. territorial aggression), but the extent to which competition combines with other ke...

The evolution of group living transformed the history of animal life on earth, yielding substantial selective benefits. Yet, without overcoming fundamental challenges such as how to coordinate movements with conspecifics, animals cannot maintain cohesion, and coordination is thus a prerequisite for the evolution of sociality in nonstationary animal...

Birds which fly in coordinated cluster-flocks can benefit through the formation of group-level structures and patterns which can deter predators by visual confusion. Though unlike V-formation flight, cluster-flocking increases the energetic cost of flight, particularly in denser flocks. Cluster formations therefore provide a unique opportunity to i...

The position of the Moon in relation to the Earth and the Sun gives rise to several predictable cycles, and natural changes in nighttime light intensity are known to cause alterations to physiological processes and behaviors in many animals. The limited research undertaken to date on the physiological responses of animals to the lunar illumination...

Flapping flight is the most energetically demanding form of sustained forwards locomotion that vertebrates perform. Flock dynamics therefore have significant implications for energy expenditure. Despite this, no studies have quantified the biomechanical consequences of flying in a cluster flock or pair relative to flying solo. Here, we compared the...

Organisms vary widely in size, from microbes weighing 0.1 pg to trees weighing thousands of megagrams — a 1021-fold range similar to the difference in mass between an elephant and the Earth. Mass has a pervasive influence on biological processes, but the effect is usually non-proportional; for example, a tenfold increase in mass is typically accomp...

The visual fields of Blacksmith Lapwings Vanellus armatus show the characteristics of visual guided foragers that use precision pecking for prey capture ‐ a binocular field of narrow width and limited vertical extent, with the projection of the bill close to its centre and a large blind area above and behind the head. The topography of the total fi...

Obligate brood-parasitic cheats have fascinated natural historians since ancient times. Passing on the costs of parental care to others occurs widely in birds, insects and fish, and often exerts selection pressure on hosts that in turn evolve defences. Brood parasites have therefore provided an illuminating system for researching coevolution. Never...

Brood parasitism has evolved independently in several bird lineages, giving rise to strikingly similar behavioural adaptations that suggest convergent evolution. By comparison, convergence of physiological traits that optimize this breeding strategy has received much less attention, yet these species share many similar physiological traits that opt...

Flapping flight is the most energetically demanding form of sustained forwards locomotion that vertebrates perform. Flock dynamics therefore have significant implications for energy expenditure. Despite this, no studies have quantified the biomechanical consequences of flying in a cluster flock relative to flying solo. Here, we compared the flight...

Waterfowl undergo an annual simultaneous flight-feather moult that renders them flightless for the duration of the regrowth of the flight feathers. In the wild, this period of flightlessness could restrict the capacity of moulting birds to forage and escape predation. Selection might therefore favour a short moult, but feather growth is constrained...

The use of biologging technology has increased exponentially over the last decade, allowing us to study animal behaviour at a level of detail not previously possible. It is clear from recent meta‐analyses that the attachment of such devices can have negative effects on individual animals, particularly their behaviour and physiology. In recognition...

Mechanisms of avian navigation have received considerable attention, but whether different navigational strategies are accompanied by different flight characteristics is unknown. Managing energy expenditure is critical for survival; therefore, understanding how flight characteristics, and hence energy allocation, potentially change with birds' fami...

Birds’ eggshells are primarily composed of calcite, an abundant polymorph of calcium carbonate (CaCO3). However, the eggshells of some species are coated with spherules of vaterite, a rare and thermodynamically unstable polymorph of CaCO3, the function of which remains unknown. We experimentally test the mechanical and physiological effects of the...

The large amount of energy expended during flapping flight is associated with heat generated through the increased work of the flight muscles. This increased muscle work rate can manifest itself in core body temperature (Tb) increase of 1–2°C in birds during flight. Therefore, episodic body cooling may be mandatory in migratory birds. To elucidate...

One contribution of 13 to a theme issue 'Physiological determinants of social behaviour in animals'. Group living has been proposed to yield benefits that enhance fitness above the level that would be achieved through living as solitary individuals. Dominance hierarchies occur commonly in these social assemblages, and result, by definition, in reso...

The visual fields of the Aegypiinae vultures have been shown to be adapted primarily to meet two key perceptual challenges of their obligate carrion-feeding behaviour: scanning the ground and preventing the sun's image falling upon the retina. However, field observations have shown that foraging White-headed Vultures Trigonoceps occipitalis are not...

Dominant individuals within animal groups will frequently place themselves in the most beneficial position for maximal protection against predation. Higher perches are generally associated with reduced predation risk in birds, so we predicted that dominant birds will preferentially place themselves on higher perches. We tested this by determining t...

One of the defining features of the aerial environment is its variability; air is almost never still. This has profound consequences for flying animals, affecting their flight stability, speed selection, energy expenditure and choice of flight path. All these factors have important implications for the ecology of flying animals, and the ecosystems...

While some migratory birds perform non-stop flights of over 11 000 km, many species only spend around 15% of the day in flight during migration, posing a question as to why flight times for many species are so short. Here, we test the idea that hyperthermia might constrain flight duration (FD) in a short-distance migrant using remote biologging tec...

![Figure][1] Steven Portugal discusses the impact of Peter Lissaman and Carl Shollenberger's classic paper ‘Formation flight of birds’, published in Science in 1970. For centuries, mankind has been fascinated by V-formation flight in birds. Back in AD 79, Pliny the Elder noted that

ABSTRACT Avian embryos are a commonly used model system for developmental studies, but monitoring of physiological parameters such as heart rate (HR) and movement in ovo poses a challenge to researchers. These are also increasingly common research objectives for ecological and embryo behavior studies in oviparous species. We therefore explored the...

The field of collective animal behaviour examines how relatively simple, local interactions between individuals in groups combine to produce global-level outcomes. Existing mathematical models and empirical work have identified candidate mechanisms for numerous collective phenomena but have typically focused on one-off or short-term performance. We...

Energy management models provide theories and predictions for how animals manage their energy budgets within their energetic constraints, in terms of their resting metabolic rate (RMR) and daily energy expenditure (DEE). Thus, uncovering what associations exist between DEE and RMR is key to testing these models. Accordingly, there is considerable i...

No single hypothesis is likely to explain the diversity in eggshell coloration and patterning across birds, suggesting that eggshell appearance is most likely to have evolved to fulfill many nonexclusive functions. By controlling for nonindependent phylogenetic associations between related species, we describe this diversity using museum eggshells...

The study of animal locomotion has uncovered principles that can be applied to bio-inspired robotics, prosthetics and rehabilitation medicine, while also providing insight into musculoskeletal form and function [1-4]. In particular, study of extreme behaviors can reveal mechanical constraints and trade-offs that have influenced evolution of limb fo...

![Graphic][1] Many people go to great lengths to make sure they smell good. Aftershaves and perfumes may smell great, but they don't tell you too much about the individual's health, hometown or how friendly they are likely to be. In the animal kingdom, however, things are slightly different.

![Figure][1] While some people enjoy throwing themselves out of aeroplanes or abseiling down cliffs, other folk are happier staying at home with a nice cup of tea. These differences in personality type have fascinated scientists for decades and, more recently, these interests have spread to

![Figure][1] Although the majority of amphibians lay their eggs in water, some species choose to breed in a more terrestrial environment. For these land-loving species, their eggs have to contend with more extreme fluctuations in environmental conditions than their aquatic-based friends,

Significance Cooperation in animals is an enigma because it contravenes the basic notion that evolution favors selfish genes that promote only their own well-being. Bird migration in organized V-shaped or echelon formations constitutes such a cooperation dilemma. We show that juvenile Northern bald ibis ( Geronticus eremita ) cooperate by taking tu...

Carefully controlled gas exchange across the eggshell is essential for the development of the avian embryo. Water vapour conductance (GH2O) across the shell, typically measured as mass loss during incubation, has been demonstrated to optimally ensure the healthy development of the embryo while avoiding desiccation. Accordingly, eggs exposed to sub-...

![Figure][1] It can be complicated enough co-ordinating four limbs, but imagine how bewildering life would become trying to control eight. This is the predicament octopuses contend with on a daily basis. They avoid this potential confusion to some extent by not having proprioception – they

Obligate avian brood parasites lay their eggs in hosts' nests and play no role in the provisioning of the progeny. Many parasites, including Cuculus cuckoos, hatch before their hosts and the altricial chick evicts hosts eggs and nestlings. A hypothesized, but so far untested parasite adaptation is that the embryos of cuckoos develop more quickly th...

Eggshell pattern scoring, a method to quantify the degree of surface maculation, can potentially be a quick, inexpensive and reliable method to obtain information on eggshell appearance and spot patterns. The key pigment responsible for red-brownish hues, protoporphyrin IX, is often localized as spots, either on the surface or in distinct layers wi...

The avian embryo's development is influenced by both the amount and the wavelength of the light that passes through the eggshell. Commercial poultry breeders use light of specific wavelengths to accelerate embryonic growth, yet the effects of the variably patterned eggshells of wild bird species on light transmission and embryonic development remai...

![][1] Throughout the world, invasive species remain one of the most serious threats to native wildlife. Perhaps the most infamous example of such an alien invasion is that of the cane toad ( Bufo marinus ) in Australia. Released in 1935 to combat sugarcane pests, cane toads proved