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.     

Long-term trends of heron and egret populations in Italy, and the effects of climate, human-induced mortality, and habitat on population dynamics

Factors affecting bird population dynamics include climate, harvesting by humans, and habitat changes. Here, we describe the long-term (1972–2006) population trends of seven heron species in NW Italy, an area holding important European breeding populations of these species. Grey (Ardea cinerea), purple (Ardea purpurea), and squacco (Ardeola ralloides) herons, and little egrets (Egretta garzetta) exhibited a strong logistic increase, leveling off around year 2000 at 3–23 times their initial level. Black-crowned night herons (Nycticorax nycticorax) began by increasing like the former species but then dropped to initial levels. Such trends were found to be influenced by several candidate ecological factors, as assessed by ARIMA models. Specifically, grey herons increased following a decrease in human-induced mortality, as quantified by an index of hunting pressure, and an increase in winter temperatures. Little egrets increased mainly with the increase of the extent of ricefields, whereas squacco herons increased with increasing rainfall in the African wintering range. Black-crowned night herons were also positively affected by increasing African rainfall, but only during 1972–1988, whereas in later years competition with other herons could have affected the species’ decline. The improved protection of colony sites by special reserves was unlikely to be the primary trigger of the observed increase, although obviously important for the long-term population persistence. In conclusion, our study shows that heron populations of southern Europe are sensitive to environmental and climatic changes, as well as to temporal variation in human disturbance and changes in foraging habitats, though the importance of the different factors differs among species.     

广西防城7种鹭类混群繁殖的空间生态位研究

2002年3~8月对广西防城万鹤山营巢的鹭类繁殖种群进行了调查研究,结果表明:万鹤山栖息有大白鹭(Egretta alba)、中白鹭(Egretta intermedia)、白鹭(Egretta garzetta)、黄嘴白鹭(Egretta eulophotes)、牛背鹭(Bubulcus ibis)、池鹭(Ardeda bacchus)、夜鹭(Nycticorax nycticorax)7种鹭类种群。除黄嘴白鹭为均匀分布之外,其他6种均为成群分布。鹭类在万鹤山上营巢繁殖具有明显的水平分布和垂直分布现象。对影响鹭类混群繁殖时空间分布的因素及各种群间的相互关系进行了探讨。     

Distributions for Key Exposure Factors Controlling the Uptake of Xenobiotic Chemicals by Great Blue Herons (Ardea herodius) through Ingestion of Fish

A variety of exposure factors ultimately control the uptake of xenobiotic chemicals by colonial piscivorous birds, such as herons and egrets. These factors, which include feeding rate for various food sources, feeding territory size, and body weight, are critical to the implementation of models commonly used to predict ecological risks. A critical evaluation of literature on avian behavior, physiology, and ecology was conducted in order to identify those variables that most strongly influence uptake of chemicals by herons and egrets. After developing a database of such exposure factors, we identified each factor's range, central tendency, and distribution. Sufficient information was available to allow the development of statistical distributions for body weight, fraction of diet from fish, prey length, distance to foraging site, and feeding territory size for great blue herons. The five distributions presented in this paper are intended to support probabilistic assessments of potential risks to great blue herons. Distributions of exposure factors for great blue herons have not been previously published. Without such data, application of all but the most simple mechanistic models will require point estimates, most of which will be overly conservative and will not support accurate characterization of actual exposures of herons at hazardous waste sites.     

长江口滩涂围垦后水鸟群落结构的变化——以南汇东滩为例

近年来长江口滩涂湿地高强度的促淤围垦对生物多样性保育造成了严重影响。本研究于2006至2010年在南汇东滩进行了水鸟调查,研究围垦后堤内环境的快速演替过程对水鸟的群落结构的影响。通过分析鸻鹬类、雁鸭类和鹭类三类主要水鸟类群,结果表明鸻鹬类的总数呈严重下降趋势（ANOVA, p=0.009）,而雁鸭类和鹭类总数在上升（ANOVA,p=0.015;p=0.00）;在种类数量方面,鸻鹬类和雁鸭类差异不显著（ANOVA,p=0.597;p=0.523）,鹭类种类数变化极显著（ANOVA ,p=0.00）。同时,通过对水鸟的栖息地选择因子偏好的分析, 发现滩涂减少是鸻鹬类减少的主要因素,而大型鱼塘和芦苇增加是雁鸭类和鹭类增加的重要原因。为此我们提出相应海岸带湿地管理建议。     

Mechanism of suppression of sustained neuronal spiking under high-frequency stimulation

Using Hodgkin–Huxley and isolated subthalamic nucleus (STN) model neurons as examples, we show that electrical high-frequency stimulation (HFS) suppresses sustained neuronal spiking. The mechanism of suppression is explained on the basis of averaged equations derived from the original neuron equations in the limit of high frequencies. We show that for frequencies considerably greater than the reciprocal of the neuron’s characteristic time scale, the result of action of HFS is defined by the ratio between the amplitude and the frequency of the stimulating signal. The effect of suppression emerges due to a stabilization of the neuron’s resting state or due to a stabilization of a low-amplitude subthreshold oscillation of its membrane potential. Intriguingly, although we neglect synaptic dynamics, neural circuity as well as contribution of glial cells, the results obtained with the isolated high-frequency stimulated STN model neuron resemble the clinically observed relations between stimulation amplitude and stimulation frequency required to suppress Parkinsonian tremor.     

Natural infections of Clinostomum complanatum (Trematoda: Clinostomatidae) in wild herons and egrets, Tottori Prefecture, Japan.

Nycticorax nycticorax, Ardea cinerea, Egretta garzetta, and Egretta intermedia were naturally infected with Clinostomum complanatum (Trematoda: Clinostomatidae) among fourteen wild herons, seven wild egrets and one wild bittern evaluated at the Veterinary Hospital of Tottori University, Tottori, Japan. The latter three species of heron and egrets are reported for the first time as definitive hosts of this parasite in Japan.     

Effects of Long Piers on Birds in Tidal Wetlands

ABSTRACT As human development continues in coastal areas, shoreline properties adjacent to expansive tidal marsh habitat are increasingly used for access to coastal waterways via long piers (>30 m) over marsh habitat. These tidal wetlands provide breeding and foraging habitat for many marsh birds, which may be affected by the human disturbance associated with long piers. Our objectives were to determine the effect of long piers over vegetated tidal marshes on the relative abundance and species richness of marsh birds. We completed combined passive and callback surveys in tidal marsh habitat at 22 sites with long piers and 24 sites without long piers, May-July 2005–2006 in Worcester County, Maryland, USA. Pier sites had lower relative abundance and species richness of obligate marsh birds than nonpier sites. Pier sites had a greater relative abundance of gulls, terns, herons, and egrets than nonpier sites. Pier sites had fewer species of herons and egrets than at nonpier sites. The presence of long piers had no affect on facultative marsh birds. Long pier density was negatively related to obligate marsh bird relative abundance and species richness, and facultative marsh bird species richness, whereas it was positively related to the relative abundance and species richness of gulls and terns. Herons and egrets relative abundance and species richness were not related to long pier density. Obligate marsh birds were negatively affected by long piers, whereas herons, egrets, gulls, and terns appeared to benefit from perching opportunities. Based on the negative effects of long piers on obligate marsh birds, management should focus on reducing the presence and density of long piers in tidal marshes by requiring the removal of existing long piers, or reducing or eliminating permits for construction of new long piers.     

The detection threshold for extremely low frequency magnetic fields may be below 1000 nT-Hz in mice

Previous experiments with mice have shown that a repeated 1 h daily exposure to an ambient magnetic field shielded environment induces analgesia (anti-nociception). This shielding reduces ambient static and extremely low frequency magnetic fields (ELF-MF) by approximately 100 times for frequencies below 120 Hz. To determine the threshold of ELF-MF amplitude that would attenuate or abolish this effect, 30 and 120 Hz magnetic fields were introduced into the shielded environment at peak amplitudes of 25, 50, 100 and 500 nT. At 30 Hz, peak amplitudes of 50, 100, and 500 nT attenuated this effect in proportion to the amplitude magnitude. At 120 Hz, significant attenuation was observed at all amplitudes. Exposures at 10, 60, 100, and 240 Hz with peak amplitudes of 500, 300, 500, and 300 nT, respectively, also attenuated the induced analgesia. No exposure abolished this effect except perhaps at 120 Hz, 500 nT. If the peak amplitude frequency product was kept constant at 6000 nT-Hz for frequencies of 12.5, 25, 50, and 100 Hz, the extent of attenuation was constant, indicating that the detection mechanism is dependent on the nT-Hz product. A plot of effect versus the induced current metric nT-Hz suggests a threshold of ELF-MF detection in mice at or below 1000 nT-Hz.     

Extrapolation of random forest models shows scale adaptation in egret colony site selection against landscape complexity

Availability of certain habitats or landscape configurations can cause differential habitat selection in animal species. Landscape complexity can affect foraging scales, home ranges and movement, but its effect on habitat selection is not well documented. We aimed to examine differences in colony site selection of herons and egrets in different regions. We studied whether landscape complexities could affect their scale of selection and habitat preferences. We used colony distribution data and land-use maps for two neighboring regions, Ibaraki and Chiba prefectures in Japan, to create random forest models for analyzing habitat preferences and important scales of selection. We did cross-validation of the models, adjusted for its respective region's land-use maps with changing scales. The scales that best explained colony distribution were 1-, 4-, 10- and 15-km in the Ibaraki region, and 1- and 10-km in the Chiba region. Evergreen forest was the most important variable for Ibaraki at 4-km and for the Chiba at 1-km. The importance of other variables differed for other models. Cross-validation showed that herons and egrets had the same habitat preferences at a 4-km scale in Ibaraki and at a 1-km scale in Chiba. The scale of selection was reduced in Chiba, where the main foraging resources for herons and egrets was more complex. Differences in landscape complexities did not affect habitat preferences but resulted in differences in the scale of selection. Habitat selection models created at the landscape level can be useful to study behavioral aspects difficult to describe with direct observation in detail.     

The effect of the amplitude of motor action on anticipatory postural adjustments.

The purpose of this study was to determine whether changes in the amplitude of a motor action triggering the same perturbation affect anticipatory postural adjustments (APAs). Healthy subjects performed releases of the same load with shoulder abduction movements of different amplitudes. Changes in the electrical activity of trunk and leg muscles, as well as displacements of the center of pressure were recorded. Generally, there were no differences in anticipatory activity of muscles and displacements of the center of pressure between series of load releases induced by motor actions of different amplitudes. We suggest that the CNS arranges APAs based on the magnitude of the perturbation if the same muscle groups generate motor actions of different amplitudes.     

Gender differences in active musculoskeletal stiffness. Part II. Quantification of leg stiffness during functional hopping tasks.

Leg stiffness was compared between age-matched males and females during hopping at preferred and controlled frequencies. Stiffness was defined as the linear regression slope between the vertical center of mass (COM) displacement and ground-reaction forces recorded from a force plate during the stance phase of the hopping task. Results demonstrate that subjects modulated the vertical displacement of the COM during ground contact in relation to the square of hopping frequency. This supports the accuracy of the spring-mass oscillator as a representative model of hopping. It also maintained peak vertical ground-reaction load at approximately three times body weight. Leg stiffness values in males (33.9+/-8.7 kN/m) were significantly (p<0.01) greater than in females (26.3+/-6.5 kN/m) at each of three hopping frequencies, 3.0, 2.5 Hz, and a preferred hopping rate. In the spring-mass oscillator model leg stiffness and body mass are related to the frequency of motion. Thus male subjects necessarily recruited greater leg stiffness to drive their heavier body mass at the same frequency as the lighter female subjects during the controlled frequency trials. However, in the preferred hopping condition the stiffness was not constrained by the task because frequency was self-selected. Nonetheless, both male and female subjects hopped at statistically similar preferred frequencies (2.34+/-0.22 Hz), therefore, the females continued to demonstrate less leg stiffness. Recognizing the active muscle stiffness contributes to biomechanical stability as well as leg stiffness, these results may provide insight into the gender bias in risk of musculoskeletal knee injury.     

Temporal tuning and nonlinearity of intraretinal pathways in turtle: Effects of temperature,stimulus intensity,and size

Flash responses, amplitude and phase transfer functions, and nonlinearities were measured in turtle retina for pathways with photoreceptor inputs and outputs from horizontal (HC), hyperpolarizing bipolar (HBC), sustained amacrine (AC), and on-off ganglion (GC) cells. Flash responses slowed and attenuated in all cells as temperature decreased. Whitenoise transfer properties of sustained-type cells (HC, HBC, AC) were of low- or bandpass type; highfrequency cut-off (f _c) and phase crossover frequency decreased with temperature. f _c increased as spot diameter was increased. Nonlinearity of these sustained-response pathways (distortion product frequencies in response to a sum-of-sinusoids input probe) increases with intensity and may depend on amplitude saturation limiting. On/off GC synaptic and spike activity increased as spot diameter decreased and intensity increased. Amplitude transfer functions had a low-frequency peak (PSP activity) and monotonically decreasing amplitude vs. frequency shape (spikes and transient PSP activity). Nonlinearity increased with stimulus intensity; it was maximal with 1 mm spot size, less with smaller (500 m) and larger (5 mm) spots. It may depend on the functional equivalent of full-wave rectification (on-off response).This work was supported by NEI grant R01 EY03383     

ADVANTAGES AND DISADVANTAGES OF EGRET AND HERON BROOD REDUCTION

Data from great egrets and great blue herons were used to test a fundamental assumption of Lack's brood-reduction hypothesis, that mortality is brood-size dependent. This was confirmed for the largest brood sizes (4 and 3), which, in egrets, also have the highest sib-fighting rates. Broods of one, however, experienced paradoxically high mortality, especially early in the season. The hypothesis is advanced that parents desert unprofitably small broods when sufficient time remains for production of a larger brood. A simple game-theory model shows that this parental desertion may hinge primarily on the overall costs of renesting. Egret brood reduction caused by sibling aggression (siblicide) occurred later than less aggressive forms of brood reduction. The inclusive fitness of senior broodmates is maximized by the successful fledging of all sibs, and the physical superiority of seniors (in food-handling for herons; food-handling and aggression for egrets) usually suffices to guarantee their own welfare in brood competitions. Finally, it is shown that the last chick in asynchronously hatching broods represents two kinds of reproductive value (RV) to the parents—“extra RV” (obtained despite the survival of elder sibs) and “insurance RV” (obtained only when at least one elder sib dies first)—which can be distinguished from field data. This approach can be used in comparisons with other asynchronous species for partitioning the fitness contributions of marginal offspring.     

Comparison of whole-body vertical stiffness and leg stiffness during single-leg hopping in place in children and adults

In the hopping literature, whole-body vertical stiffness and leg stiffness are used interchangeably, due to most of the movement occurring in the vertical direction. However, there is some anterior/posterior movement of the center of mass and displacements of the foot during hopping in place in both children and adults. Further it is not understood if leg stiffness show a similar pattern as whole-body vertical stiffness when increasing hopping frequency. The purpose of this study was to test if whole-body vertical stiffness and leg stiffness are different during single-leg hopping in-place in children and adults, across a range of frequencies. Seventeen children aged 5–11 years and 16 young adults participated in this study. The subjects hopped at their preferred frequency as well as 20% below, 20% above and 40% above preferred frequency. Our results demonstrate that both whole-body vertical stiffness and leg stiffness increase when increasing hopping frequency for children and adults. However, whole-body vertical stiffness consistently overestimates leg stiffness due to a similar peak force but a greater leg length change compared to vertical COM displacement. This suggests a considerable horizontal COM movement from landing to mid-stance during hopping. Children aged 5–11 years old showed lower absolute values but higher normalized values of two stiffness measures than adults. This suggests somewhat adult-like stiffness control in children, but a reduced ability to manipulate the horizontal movement during single-leg hopping in place when compared to adults.     

Dynamic properties of Renshaw cells: Frequency response characteristics

The dynamic properties of Renshaw cells located in the lumbar spinal cord of intercollicular decerebrate cats were measured. The responses of these interneurones were recorded extracellularly, while the ventral root was stimulated with sinusoidally frequency-modulated trains of electrical pulses. The frequency of the Renshaw cell discharges resulting from such stimulation varied sinusoidally. The amplitude of modulation about the average (or carrier) rate of discharge exhibited a linear dependence on the modulation amplitude of the stimulus pulse train. Renshaw cells were able to follow modulated stimulus trains in the entire range of modulation frequencies (0.2 to 80 Hz) encompassed by the present study. Above modulation frequencies between 20 and 50 Hz, the amplitude of modulation of the responses declined. Frequency responses measured at low average frequencies of the stimulus pulse train (centre frequencies 30 and 40 Hz) showed comparatively little dependence on modulation frequency. The higher the centre frequency, however, the greater was the enhancement of the modulation amplitudes at high modulation frequencies compared with those observed at low modulation frequencies. Some aspects of the functional implications of these results are considered and an approximate formula for the transfer function of Renshaw cells is presented.     

Steatitis in egrets and herons from Japan

More than 70 egrets and herons were found sick or dead at an agricultural water reservoir in Kanagawa Prefecture, Japan between September and October 2008. The birds showed weakness, lethargy, and inability to fly before death. Postmortem findings included large amounts of firm subcutaneous and cavitary fat comprised of necrotic adipose tissues with infiltrates of heterophils and macrophages. The birds were diagnosed with steatitis on the basis of the gross lesions and histopathology. Egrets with steatitis had low blood levels of vitamin E. High counts of cyanobacteria (Microcystis aeruginosa) were found in the reservoir concurrent with the outbreak of steatitis. No microcystin was detected in the reservoir water or the livers from the egrets. This is the first report of steatitis in wild birds in Japan.     

Neuromuscular fatigue during maximal concurrent hand grip and elbow flexion or extension.

The objective was to investigate muscle fatigue measuring changes in force output and force tremor and electromyographic activity (EMG) during two sustained maximal isometric contractions for 60s: (1) concurrent hand grip and elbow flexion (HG and EF); or (2) hand grip and elbow extension (HG and EE). Each force tremor amplitude was decomposed into four frequency bands (1-3, 4-10, 11-20, and 21-50Hz). Surface EMGs were recorded from the flexor digitorum superficialis (FDS), extensor digitorum (ED), biceps brachii (BB) and lateral head of triceps brachii (TB). The HG and EF forces for the HG and EF and the HG force for the HG and EE declined rapidly, whereas the EE force remained almost constant near to the initial value for the first 40s and then declined. The decrease in EMG amplitude was observed not for the FDS muscle but for the ED muscle. The HG tremor amplitude for each frequency band showed similar decreasing rate, whereas the decreases in EF and EE tremor amplitudes for the lower band (below 10Hz) were slower than those for the higher band (above 11Hz). The neuromuscular mechanisms underlying muscle fatigue during sustained maximal concurrent contractions of hand grip and elbow flexion or extension are discussed.     

An application of autocorrelation methods to the interpretation of intestinal motility records

The application of statistical communication techniques to the analysis of intestinal motility records has made available certain information that has heretofore been obscure. This information is: 1. A measure of total activity expressed in square millimeters of Hg. 2. The frequency and amplitude of segmental activity. 3. A measure of the random variations in the amplitude of the "segmental" waves. 4. A measure of random activity and the range and relative amplitudes of the frequencies making up this component.