Black wildebeest seek shade less and use solar orientation behavior more than do blue wildebeest

Many ungulates, including wildebeest, seek shade and orient their bodies relative to incoming solar radiation in order to reduce environmental heat loads. Blue (Connochaetes taurinus) and black wildebeest (Connochaetes gnou), which co-exist artificially in some reserves in South Africa, are thought to adopt different thermoregulatory behaviors to mitigate high environmental heat loads. However, whether or not blue and black wildebeest use different behaviors to reduce heat loads in regions where they co-occur has never previously been examined. We compared the shade seeking and solar orientation behavior of free-ranging blue and black wildebeest in summer at three locations in South Africa where both species co-occur. We found that blue wildebeest exhibited more shade seeking behavior than did black wildebeest at all times of day, at all study sites. Black wildebeest remained in the sun but were more likely than blue wildebeest to orient their bodies parallel to the sun at all study sites, a behavior which reduces the amount of surface area exposed to incoming radiation. Black wildebeest were most likely to employ parallel solar orientation during the hottest times of the day when the sun was not directly overhead (i.e., solar noon ± 1 hour). We thus demonstrate that co-occurring blue and black wildebeest use different thermoregulatory behaviors to reduce high heat loads. It is possible that the lack of shade in the historical distribution of black wildebeest led to selective pressure for reliance on solar orientation. Differences in thermoregulatory behavior can affect species-specific heat loads, habitat use, body mass, fitness and grazing activity. Such differences may also allow blue and black wildebeest to inhabit separate microclimates within the same habitat, provided there is sufficient heterogeneity in vegetation structure, potentially facilitating reproductive isolation.     

Energy advantages of orientation to solar radiation in three African ruminants

Animal orientation relative to incident solar radiation allows an animal to effectively adjust the amount of radiant heat gained from an environment. Yet recent literature found ruminants to primarily orientate north/south and proposed magnetic alignment as the most parsimonious explanation. To test whether such northerly orientation has an energy advantage, we used heated cylindrical models to estimate energy costs of thermoregulation associated with north and east orientations of three species of African ruminants under cool winter conditions. Concurrent behavioural observations revealed that eland, blue wildebeest and impala did not preferentially orientate north/south during warm summer or cool winter conditions. Instead, all three species preferred to orientate perpendicular to incident solar radiation during winter and parallel to incident solar radiation during summer, throughout the day. On clear winter days with little wind, more than 60% of animal orientation preference could be accounted for by the energy savings associated with that orientation. Thus energy demands are likely to be the primary driver of animal orientation preferences.     

Walking and take-off in Aphis fabae.

ABSTRACT. Illumination either from one side or alternating between the two sides induced aphids to turn towards the light and also delayed their take-off as compared with illumination from the front. Illumination from in front or from both sides simultaneously delayed take-off as compared with dorsal illumination and also increased the rate of walking. Take-off was frequently induced by a change from frontal to dorsal illumination but not from lateral or ventral to dorsal. Ventral illumination delayed take-off as compared with dorsal, but appeared to inhibit walking.
In frontal illumination, rate of walking and time to take-off were positively correlated when aphids walked on a cat-walk, but negatively correlated on a smooth surface. Thus the two locomotory acts, walking and flight, could interact either as 'allies' or as 'antagonists', either one hastening or deferring the other in different conditions. Take-off from a plant is discussed in terms of the interaction between these two locomotory responses, and 'settling' responses.     

Moon and sun compasses in sandhoppers rely on two separate chronometric mechanisms

The relationship between the chronometric system of compensation for the apparent movement of the sun and that for the moon has been the subject of several, never proven, hypotheses. Our studies on sandhoppers have demonstrated that the chronometric mechanism of the moon compass is separate from that of the sun compass. They show (i) that a period of seven days in constant darkness has no influence on the capacity for orientation, either solar or lunar, and indicates the presence of one or more continuously operating timing mechanisms; (ii) that two different shifts in the light–dark phase have no effect on the chronometric mechanism of lunar orientation, but they do affect that of solar orientation; and (iii) that exposure to an artificial moon delayed by seven days with respect to the natural cycle causes the expected change in the mean direction of individuals tested under the natural moon, but not of those tested under the sun.     

Orientation to solar radiation in black wildebeest (<Emphasis Type="Italic">Connochaetes gnou</Emphasis>)

We recorded the body axis orientation of free-living black wildebeest relative to incident solar radiation and wind. Observations were made on three consecutive days, on six occasions over the course of 1 year, in a treeless, predominantly cloudless habitat. Frequency of orientation parallel to incident solar radiation increased, and perpendicular to incident solar radiation decreased, as ambient dry-bulb temperature or solar radiation intensity increased, or wind speed decreased. We believe these changes were mediated via their effect on skin temperature. Parallel orientation behavior was more prominent when the wildebeest were standing without feeding than it was when they were feeding. We calculate that a black wildebeest adopting parallel orientation throughout the diurnal period would absorb 30% less radiant heat than the same animal adopting perpendicular orientation. Parallel orientation was reduced at times when water was freely available, possibly reflecting a shift from behavioral to autonomic thermoregulatory mechanisms. The use of orientation behavior by black wildebeest is well developed and forms part of the suite of adaptations that help them to maintain heat balance while living in a shadeless, often hot, environment.     

How birds use their eyes: Opposite left-right specialization for the lateral and frontal visual hemifield in the domestic chick

Recent evidence has demonstrated that, in animals with laterally placed eyes, functional cerebral asymmetry is revealed by preferential use of either the left or right eye in a range of behaviors (birds: [1, 2, 3]; fish: [4, 5]; reptiles: [6, 7]). These findings pose a theoretical problem. It seems that there would be disadvantages in having a substantial degree of asymmetry in the use of the two eyes; a deficit on one side would leave the organism vulnerable to attack on that side or unable to exploit resources appearing on one side. We here report a possible solution to the problem. We have found that domestic chicks show selective use of the lateral visual field of the left eye and of the right hemifield in the binocular, frontal visual field when they peck at strangers but not at cagemates. Thus, during social recognition, there seems to be opposite and complementary left-right specialization for the lateral and frontal visual fields of the two eyes. These findings can reconcile the computational advantages associated with asymmetry of the left and right sides of the brain with the ecological demands for an animal to perceive and respond equally well to the left and right sides of its midline.     

Central neural coding of sky polarization in insects

Many animals rely on a sun compass for spatial orientation and long-range navigation. In addition to the Sun, insects also exploit the polarization pattern and chromatic gradient of the sky for estimating navigational directions. Analysis of polarization-vision pathways in locusts and crickets has shed first light on brain areas involved in sky compass orientation. Detection of sky polarization relies on specialized photoreceptor cells in a small dorsal rim area of the compound eye. Brain areas involved in polarization processing include parts of the lamina, medulla and lobula of the optic lobe and, in the central brain, the anterior optic tubercle, the lateral accessory lobe and the central complex. In the optic lobe, polarization sensitivity and contrast are enhanced through convergence and opponency. In the anterior optic tubercle, polarized-light signals are integrated with information on the chromatic contrast of the sky. Tubercle neurons combine responses to the UV/green contrast and e-vector orientation of the sky and compensate for diurnal changes of the celestial polarization pattern associated with changes in solar elevation. In the central complex, a topographic representation of e-vector tunings underlies the columnar organization and suggests that this brain area serves as an internal compass coding for spatial directions.     

Seeing sunlit owls in a new light: orienting Snowy Owls may not be displaying

Snowy Owls Bubo scandiacus often face the sun when sitting on the ground or when perched. Such sun‐orienting has been suggested to represent a visual display to conspecifics but other explanations have not been thoroughly examined. We observed the orientation of wintering Snowy Owls to both the sun and the wind, and their perching behaviour during two winters in central Saskatchewan, Canada. We proposed three new explanations for sun orientation in addition to the display hypothesis: thermoregulation, hunting and defence against predators. On sunny days, 44% of 710 Owls faced the sun; this was non‐random because few did so on overcast days. Sun‐ as opposed to wind‐orienting was strongly associated with weather conditions. Logistic regressions indicated that at temperatures below –13 °C and at wind speeds greater than about 18 km/h, Owls tended to orient to the wind rather than to the sun. The likelihood of wind‐orienting increased if the Owl perched above the ground, whereas the likelihood of sun‐orientating increased slightly when the Owl was sitting on the ground. There was no difference between the sexes in orienting behaviour. Snowy Owls seemed to prioritize wind‐orienting for thermoregulation but the results are also consistent with the idea that sun‐orientation can reduce heat loss. Facing into the sun did not support the hunting explanation because the birds would have been blinded and not able to see prey, but was consistent with the protection explanation if it helps to increase vigilance against enemies. Although we cannot completely rule out the display explanation, the spatial context of sunning Owls and a lack of a sex effect makes it unlikely that this is the main function. Instead, Owls seem to trade‐off wind‐ vs. sun‐orienting according to the prevailing weather conditions and do so mainly to thermoregulate and perhaps to maintain vigilance.     

Daytime relapse of the mean radiant temperature based on the six-directional method under unobstructed solar radiation

This study contributes to the knowledge about the capabilities of the popular “six-directional method” describing the radiation fields outdoors. In Taiwan, measurements were carried out with three orthogonally placed net radiometers to determine the mean radiant temperature (T _mrt). The short- and long-wave radiation flux densities from the six perpendicular directions were recorded in the daylight hours of 12 days. During unobstructed direct irradiation, a specific daytime relapse was found in the temporal course of the T _mrt values referring to the reference shapes of a standing man and also of a sphere. This relapse can be related to the short-wave fluxes reaching the body from the lateral directions. Through deeper analysis, an instrumental shortcoming of the six-directional technique was discovered. The pyranometer pairs of the same net radiometer have a 10–15-min long “blind spot” when the sun beams are nearly perpendicular to them. The blind-spot period is supposed to be shorter with steeper solar azimuth curve on the daylight period. This means that the locations with lower geographical latitude, and the summertime measurements, are affected less by this instrumental problem. A methodological shortcoming of the six-directional technique was also demonstrated. Namely, the sum of the short-wave flux densities from the lateral directions is sensitive to the orientation of the radiometers, and therefore by deviating from the original directions, the T _mrt decrease on clear sunny days will occur in different times and will be different in extent.     

The Orientation Behaviour of Chaffinches, Fringilla coelebs, Caught during Active Migratory Flight, in Relation to the Sun

The few orientation studies that have been carried out with day-migrating birds show that they are able to use solar and magnetic orientation cues for orientation. Previous orientation experiments in Emlen funnels have been carried out either with hand-raised birds or with birds caught during resting periods at stop-over sites. The aim of our study was to test whether birds caught during active flight show a higher concentration of migratory activity in the seasonally appropriate migratory direction in the funnels than birds that had not experienced migration just before the funnel experiments. The topography at the alpine pass Col de Bretolet at the border of Switzerland and France allowed us to capture birds during active migratory flight. These birds were in full migration disposition. Orientation experiments with chaffinches suggested an influence of the sun because chaffinches did not orient in the seasonally expected direction, but probably showed positive phototaxis towards the light of the sun at the opposite side of the funnel. Chaffinches tested under overcast conditions oriented to the north-west which probably was a 'nonsense' orientation and not a reverse migration or compensatory behaviour. We conclude that freshly caught birds are too stressed to show appropriate orientation when tested immediately after catching.     

Differences in the response of carbon assimilation to summer stress (water deficits, high light and temperature) in four Mediterranean tree species

Daily changes in photoprotective mechanisms were studied in sun leaves of Quercus suber L., Quercus ilex L., Olea europaea L. and Eucalyptus globulus Labill. trees during the summer in Portugal. Even though stomatal closure explained most of the diurnal variation in carbon assimilation along the summer, a decline in the photochemical yield of photosystem II (F'v/F'm) also occurred, as a result of an excess of intercepted solar radiation when carbon assimilation is limited by stomatal closure due to high vapour pressure deficits and/or soil water deficits. These changes were accompanied by the conversion of violaxanthin to antheraxanthin and zeaxanthin which were correlated with thermal dissipation of excess photon energy. In spite of a common general response, differences between species were observed Olea europaea , which is a slowgrowing tree, had the lowest net photosynthetic rates, the highest proportion of carotenoids in relation to chlorophyll and the highest rates of deepoxidation of violaxanthin. This enabled a large thermal dissipation of the excess intercepted radiation but led to rather small values of light utilisation for photochemistry (ca 20%). In contrast, in E. globulus , a fastgrowing tree, photosynthetic rates were the highest, thermal dissipation of absorbed radiation the lowest and maximal values of light utilisation for photochemistry reached ca 50%. The two Quercus species exhibited an intermediate response. A high degree of coordination is apparent between stomatal behaviour, photosynthetic capacity and photoprotection mechanisms.     

Activity in Heodes virgaureae (Lep., Lycaenidae) in relation to air temperature,solar radiation,and time of day

Summary The degree of activity of H. virgaureae in the field is largely dependent on air temperature, solar radiation, and wind velocity. Solar radiation increases body temperature above ambient. The butterfly orientates its back towards the sun and exposes the dorsal surface of the wings. At high temperatures they close the wings thereby minimizing the surface exposed to the sun. The optimal body temperature lies around 35°C as was indicated by laboratory experiments. In cloudy and cool to fairly warm conditions the butterfly is inactive. In sunshine the butterfly basks at low radiation intensities or low air temperatures while feeding (in males also flying) predominates at full sunshine or very high air temperatures (around 30°C). Males fly 5–10 times as much as females. A change from unfavourable to favourable weather is followed by an immediate increase in activity of the butterfly, which enables the butterfly to utilize short periods of sunshine.     

Sex differences in cell migration in the preoptic area/anterior hypothalamus of mice

The preoptic area/anterior hypothalamus (POA/AH) sits as a boundary region rostral to the classical diencephalic hypothalamus and ventral to the telencephalic septal region. Numerous studies have pointed to the region's importance for sex‐dependent functions. Previous studies suggested that migratory guidance cues within this region might be particularly unique in their diversity. To better understand the early development and differentiation of the POA/AH, cytoarchitectural, birthdate, immunocytochemical, and cell migration studies were conducted in vivo and in vitro using embryonic C57BL/6J mice. A medial preoptic nucleus became discernible using Nissl stain in males and females between embryonic days (E) E15 and E17. Cells containing immunoreactive estrogen receptor‐α were detected in the POA/AH by E13, and increased in number with age in both sexes. From E15 to E17, examination of the radial glial fiber pattern by immunocytochemistry confirmed the presence of dual orientations for migratory guidance ventral to the anterior commissure (medial‐lateral and dorsal‐ventral) and uniform orientation more caudally (medial‐lateral). Video microscopy studies followed the migration of DiI‐labeled cells in coronal 250‐μm brain slices from E15 mice maintained in serum‐free media for 1–3 days. Analyses showed significant migration along a dorsal‐ventral orientation in addition to medial‐lateral. The video analyses showed significantly more medial‐lateral migration in males than females in the caudal POA/AH. In vivo, changes in the distribution of cells labeled by the mitotic indicator bromodeoxyuridine (BrdU) suggested their progressive migration through the POA/AH. BrdU analyses also indicated significant movement from dorsal to ventral regions ventral to the anterior commissure. The significant dorsal‐ventral migration of cells in the POA/AH provides additional support for the notion that the region integrates developmental information from both telencephalic and diencephalic compartments. The sex difference in the orientation of migration of cells in the caudal POA/AH suggests one locus for the influence of gonadal steroids in the embryonic mouse forebrain. © 1999 John Wiley & Sons, Inc. J Neurobiol 41: 252–266, 1999     

Ground monitoring the light–shadow windows of a tree canopy to yield canopy light interception and morphological traits

Monitoring the light–shadow windows of a tree via a grid system on the ground was performed on sunny summer days at high spatial resolution using a custom‐built, inexpensive scanner. The measurements were taken with two goals: (1) to quickly and remotely quantify the overall, short‐wave solar radiation (300–1100 nm) intercepted by the tree canopy, and (2) to yield such crown geometric traits as shape, size and the number of theoretical canopy leaf layers (leaf layer index, LLI) in relation to the section orthogonal to sunbeam direction (sun window). The ground readings at each measurement over the day were used to project a digitized shadow image. Image processing was applied and the intercepted radiation was calculated as the difference from the corresponding incoming radiation above the canopy. Tree‐crown size and shape were profiled via computer imaging by analysing the different shadow images acquired at the various solar positions during the day. It is notable that these combined images yielded the crown features without having to parameterize such canopy characteristics as foliage extension and spatial distribution.     

Nest orientation and hatching success in the tree pipit Anthus trivialis

Many open-nesting bird species orient their nests relative to surrounding vegetation to avoid adverse environmental conditions. In eastern England, tree pipit Anthus trivialis nests predominantly faced east, an orientation that provided shelter from prevailing WSW winds, allowed warming by the morning sun and which, together with relatively high field layer cover, shaded nest contents from the midday sun. Mean orientation moved from south to north through the breeding season as temperatures increased, suggesting that solar radiation was a key influence on nest placement for tree pipits in the study area. Tree pipit nests with eastward orientations experienced better hatching success than those in less-preferred orientations and it is suggested that this was due to their thermal advantages. In contrast, nest orientation had no influence on nestling survival.     

The influence of axial rotation upon interception of solar radiation by plant leaves

Axial rotation of a plant leaf about the midrib is an important factor which permits effective maximization or minimization of the interception of direct solar radiation. Through use of matrix rotations of coordinate systems, the cosine of the angle of incidence, a measure of the fraction of solar radiation intercepted by the leaf, is described as a function of angles which specify the relative orientation of the leaf to the sun. All of these angles can be measured directly except for the axial rotation angle, which may be calculated from more easily measured quantities. Computer modeling and theoretical calculations demonstrate that relatively large amounts of average axial rotation permit a plant to reduce the cosine of angle of incidence of each flat leaf to zero, resulting in no interception of direct solar radiation, while smaller amounts of average axial rotation allow a plant to intercept as much as 80% of direct radiation, even if leaves are distributed uniformly over 360° of azimuth.     

Effect of solar radiation and predacious microorganisms on survival of fecal and other bacteria.

The effect of solar radiation and predacious microorganisms on the survival of bacteria of fecal and plant origin was studied. The decline in the numbers of Escherichia coli cells in estuarine water samples was found to be significantly greater in the presence of both naturally occurring microbial predators and solar radiation than when each of these factors was acting independently. The effect of solar radiation on microbial predators was negligible, whereas the susceptibility of bacteria to light-induced decay varied from one organism to another, as follows: Klebsiella pneumoniae greater than E. coli greater than Salmonella typhimurium, Streptococcus faecium, Enterobacter aerogenes, Erwinia herbicola.     

Distinctions between dorsal and ventral premotor areas: anatomical connectivity and functional properties

The dorsal and ventral premotor areas, together with the primary motor cortex, are believed to have major roles in preparing and executing limb movements. Recent studies have expanded our knowledge of the dorsal and ventral premotor areas, which occupy the lateral part of area 6 in the frontal cortex. It is becoming clear that these two premotor areas, through involvement in distinct cortical networks, take part in unique aspects of motor planning and decision making. New lines of evidence also implicate the lateral premotor areas in planning motor behavior and selecting actions.     

Effects of summer microclimates on behavior of lions and tigers in zoos

The surrounding thermal environment has a direct influence on the well-being of an animal. However, few studies have investigated the microclimatic conditions that result from outdoor zoo enclosure designs and whether this affects where animals choose to spend time. Two African lions (Panthera leo) and two Siberian/Amur tigers (Panthera tigris altaica) were observed for a total of 18 full days during the summer and fall of 2009. Their activities and locations were recorded to the nearest minute of each test day. Simultaneous on-site microclimate measurements were taken of air temperature, relative humidity, solar radiation, and wind. Observations indicated that the locations where the animals chose to spend time were influenced by the microclimatic conditions. All subjects spent more time in the shade on their sunny warm days than on other days and differed from one another in their choice of shade source on all days. Temperature-comparable sunny and cloudy days showed a greater use of sun on the cloudy days. Species-specific differences between the lions (whose native habitat is hot) and the tigers (whose native habitat is temperate with cold winters) were observed with the tigers displaying more cooling behaviors than the lions in terms of solar radiation input and evaporative heat loss. The tigers were also more active than the lions. The results of this study provide new insight into how lions and tigers respond to microclimatic conditions in a captive environment.     

STEREOTROPISM IN RATS AND MICE

Typical stereotropic orientation toward a lateral surface of contact is obtained in young rats and mice, and with adult mice congenitally blind. Removal of vibrissæ or tail or both does not essentially affect this response. Equal contact on both sides of the body prevents orientation toward either source of contact. Unequal contact areas on the two sides leads to orientation toward the more extensive contact. This behavior very exactly parallels the stereotropic conduct of arthropods, and thus provides a fairly complete instance of a tropism in mammals.