Effects of chilling on sampling of bacteria attached to swine carcasses

Two microbiological sampling techniques, excision and sponge swabbing, were compared by determining counts of aerobic bacteria, coliforms and injured coliforms from 20 de-haired swine carcasses before and after chilling. Excised jowl skin produced significantly greater counts of the three types of bacteria than sponge swabs. Aerobic bacteria, coliforms and injured coliforms recovered by sponge swabbing carcasses before chilling were 11.6%, 0.9% and 11.0% of excised samples, respectively; the corresponding percentages recovered after chilling were 23.9%, 11.1% and 5.0%. Numbers of all bacteria present on the post-chill carcasses were substantially lower than on the pre-chill carcasses. Excision usually produced more countable plates for coliforms and injured coliforms on chilled carcasses than sponge swabbing and therefore, is more suitable in estimating low numbers of faecal bacteria on chilled carcasses. To explore the possible structural bases for these findings, skin samples were inoculated with 10(2)-10(7) cfu cm(-2) faecal bacteria and examined by scanning electron microscopy. Chilled samples showed bacteria and biofilm embedded in superficial crevices, which underlies a possible reason for the lower recovery of bacterial cells by the sponge swabbing. The study indicates that the differences between sampling techniques may be a result of the chilling process of swine carcasses.     

The role of visible faecal material as a vehicle for generic Escherichia coli,coliform, and other enterobacteria contaminating poultry carcasses during slaughtering

AIMS: A comparison of Enterobacteriaceae, coliform and Escherichia coli counts in chicken carcasses with and without visible faecal contamination was conducted to evaluate the role of contamination as a vehicle for generic E. coli, coliform and other enterobacteria contaminating broiler chicken carcasses when processed under routine commercial operations. METHODS AND RESULTS: Samples were removed from the processing line immediately after evisceration, inside-outside shower and chilling for microbiological analysis. After evisceration, mean counts were significantly different only for E. coli (P < or = 0.05) in chicken carcasses with and without visible faecal contamination. While the spray wash practice was not efficient enough for complete removal of the visible contamination from carcasses, leading to microbiological reduction percentages lower than expected, 25 ppm chlorinated water chilling did reduce the contamination level considerably in all samples. CONCLUSIONS: Carcasses with and without visible faecal contamination harboured E. coli and other potentially hazardous enterobacteria. E. coli was the predominant strain isolated in all samples, Enterobacter cloacae being next most frequent. SIGNIFICANCE AND IMPACT OF THE STUDY: The zero tolerance of visible faecal contamination requirement alone is not sufficient to assure safety and to improve the microbial quality of carcasses.     

COUNTS OF CALIFORNIA SEA LION (ZALOPHUS CALIFORNIANUS) PUPS FROM AERIAL COLOR PHOTOGRAPHS AND FROM THE GROUND: A COMPARISON OF TWO METHODS

Pups on San Nicolas Island were counted by two methods; counts by observers on the ground were compared to counts from aerial photographs taken with a 126-mm-format camera with image motion compensation. No difference was detected between photographic counts and ground counts (P= 0.367) when ground counters had unobstructed views. However, ground counts were significantly lower when areas with obstructed views were included in the analysis (P < 0.001). For areas with unobstructed viewing conditions, no difference was detected between counts by the two methods for rock substrates (P= 0.140), sand substrates (P= 0.468), or mixed rock-and-sand substrates (P= 0.968). No differences were found among three replicate aerial photographic censuses (P= 0.432), but a significant difference was found between two replicate ground censuses (P= 0.037). Total counts obtained from the aerial photographs were more precise (CV = 0.042) than counts obtained on the ground (CV = 0.078). Less variability in counts was found between photographic counters than for ground counters.     

Spatial ability is impaired and hippocampal mineralocorticoid receptor mRNA expression reduced in zebra finches (Taeniopygia guttata) selected for acute high corticosterone response to stress

In mammals, stress hormones have profound influences on spatial learning and memory. Here, we investigated whether glucocorticoids influence cognitive abilities in birds by testing a line of zebra finches selectively bred to respond to an acute stressor with high plasma corticosterone (CORT) levels. Cognitive performance was assessed by spatial and visual one-trial associative memory tasks. Task performance in the high CORT birds was compared with that of the random-bred birds from a control breeding line. The birds selected for high CORT in response to an acute stressor performed less well than the controls in the spatial task, but there were no significant differences between the lines in performance during the visual task. The birds from the two lines did not differ in their plasma CORT levels immediately after the performance of the memory tasks; nevertheless, there were significant differences in peak plasma CORT between the lines. The high CORT birds also had significantly lower mineralocorticoid receptor mRNA expression in the hippocampus than the control birds. There was no measurable difference between the lines in glucocorticoid receptor mRNA density in either the hippocampus or the paraventricular nucleus. Together, these findings provide evidence to suggest that stress hormones have important regulatory roles in avian spatial cognition.     

Comparison of hematologic and biochemical reference ranges between captive populations of northern bald ibises (Geronticus eremita)

Hematologic and biochemical reference ranges for two captive populations of northern bald ibises (Geronticus eremita) were compared. The first consisted of 11 birds at an in-situ breeding colony in Bire?ik, southern Turkey. The second consisted of 27 birds housed at the Durrell Wildlife Conservation Trust in Jersey, British Channel Isles (UK). Blood samples were collected in February 1992 by basilic venipuncture under manual restraint. Bire?ik birds had higher packed cell volumes and red blood counts but lower white blood cell and lymphocyte counts than Jersey birds. Bire?ik birds also had higher total protein, albumin, total globulin, calcium, phosphorus, blood urea nitrogen, and total bilirubin values; higher albumin to globulin ratios; but lower uric acid values and calcium to phosphorus ratios than Jersey birds. Finally, Bire?ik birds had higher lactate dehydrogenase but lower gamma glutamyl transferase values than Jersey birds. Male Jersey birds had higher calcium and alkaline phosphatase values, but lower white blood cell and heterophil counts than female Jersey birds. The apparent differences between the two populations are not thought to be biologically significant and may be related to diet and state of hydration.     

The influence of scald water pH on the death rates of Salmonella typhimurium and other bacteria attached to chicken skin

Factory trials where scald tank water was maintained at pH 9.0 +/- 0.2 showed that compared with the usual system of scalding when the water is at pH 6.0 for much of the working day the bacterial counts on carcases post scalding and plucking were significantly lower. In laboratory experiments, attached Salmonella typhimurium and the naturally occurring skin flora were found to be killed significantly more quickly in water at pH 9.0 +/- 0.2.     

The influence of scald water pH on the death rates of Salmonella typhimurium and other bacteria attached to chicken skin

Factory trials where scald tank water was maintained at pH 9.0± 0.2 showed that compared with the usual system of scalding when the water is at pH 6.0 for much of the working day the bacterial counts on carcases post scalding and plucking were significantly lower. In laboratory experiments, attached Salmonella typhimurium and the naturally occurring skin flora were found to be killed significantly more quickly in water at pH 9.0±0.2.     

Estimating impacts of poison operations using mark-recapture analysis and population viability analysis: an example with New Zealand robins (

Several recent studies have used "roll calls"—searches for individually-marked birds—to assess impacts of aerial poison operations on non-target species. Roll calls have advantages over methods such as 5-minute bird counts, call counts, and dead body counts, but roll calls are based on the assumption that detection rates are 100%, or that detection rates are constant over time and space. They also require more than one group of birds, at a poisoned and unpoisoned site for example, for valid statistical comparisons. With minor adjustment of field methods, however, a series of surveys can be treated as a mark-recapture experiment, allowing powerful analysis without such restrictive assumptions. Survival and detection rates can be estimated independently for each time interval, and alternative models fitted to the data for factors affecting those rates. Using the software package MARK, we analyzed data for New Zealand robins (Petroica australis) on Tiritiri Matangi Island to estimate impact of an aerial brodifacoum operation conducted in September 1993 to eradicate kiore (Rattus exulans). The population was established by translocations in 1992 and 1993, and consisted of 40 birds at the time of the operation. Taking seasonal and yearly variation in detection and survival rates into account, we estimate that 11% of robins (4-5 birds) died as a result of the poison. There was strong evidence that survival probability was lower immediately after the operation, despite the small number of birds disappearing. The poison effect was confined to the interval from September-October 1993, including the first two weeks after the poison drop, and survival for subsequent monthly intervals was consistent with the normal summer rate. Using simulation modelling based on our data from the population, we predict that the operation set population growth back by about one year but had no longer-term impact.     

Comparison of blood values and health status of Floreana Mockingbirds (Mimus trifasciatus) on the islands of Champion and Gardner-by-Floreana, Galápagos Islands

The Floreana Mockingbird (Mimus trifasciatus) is one of the rarest bird species in the world, with an estimated 550 individuals remaining on two rocky islets off the coast of Floreana, Galápagos, Ecuador, from which the main population was extirpated more than 100 yr ago. Because they have been listed in critical danger of extinction, a plan to reintroduce this species to Floreana has been initiated. Determining the health status of the source mockingbird populations is a top priority within the reintroduction plan. We report the health status, over the course of 4 yr, of 75 Floreana Mockingbirds on Champion Island and 160 Floreana Mockingbirds on Gardner-by-Floreana, based on physical examinations, hematology, hemolysis-hemagglutination assay, exposure to selected infectious disease agents, and ecto- and endoparasite counts. Birds on Gardner-by-Floreana had higher body condition index scores, packed cell volumes, total solids, and lymphocyte counts. Additionally, Gardner-by-Floreana birds had lower heterophil counts, eosinophil counts, and heterophil:lymphocyte ratios. No Chlamydophila psittaci DNA or antibodies to paramyxovirus-I, adenovirus-II, or Mycoplasma gallisepticum were found in any of the mockingbirds tested. Ectoparasites were present on birds from both islands, although species varied between islands. A coccidian species was found in eight of the 45 fecal samples from birds on Gardner-by-Floreana, but none of 33 birds examined from Champion. Birds on Gardner-by-Floreana were classified as healthier than those on Champion based on clinical and laboratory findings. These health data will be analyzed in conjunction with genetics, population structure, and disease presence on Floreana for developing recommendations for the Floreana Mockingbird reintroduction plan.     

Trichomonas gallinae in wintering Common Wood Pigeons Columba palumbus in Spain

We studied the prevalence and potential subclinical effects of infestation by Trichomonas gallinae in 91 hunter-harvested Common Wood Pigeons Columba palumbus from northern ( n  = 30) and southern ( n  = 61) Spain during the winter period. All animals were measured, sexed, aged, necropsied and their organs were weighed. Infestation with T. gallinae was diagnosed using three different methods: direct inspection for the presence of lesions, direct microscopic observation and culture. Of the sampled birds, 34.2% were positive for the presence of T. gallinae . Prevalence was significantly higher in adult Wood Pigeons than in the juvenile group, and prevalence was significantly lower in birds sampled from the north. No significant differences in prevalence were found between males and females. Culture was significantly more sensitive than the other methods of diagnosis. Parasitized birds were in poorer body condition, as revealed by their lower body mass and fat reserves. No significant variation could be detected in heart or spleen weight between parasitized and healthy birds. However, juvenile Wood Pigeons in which T. gallinae was detected had a significantly larger bursa of Fabricius. Variations in the prevalence of T. gallinae in Wood Pigeons could be related to migration as well as increased exposure through shared feed and water where these are artificially provided. We also discuss the potential effect of T. gallinae on body condition and the eventual risk for endangered predators through increased exposure to infected prey.     

Secondary phytohaemagglutinin (PHA) swelling response is a good indicator of T‐cell‐mediated immunity in free‐living birds

The validity of using the phytohaemagglutinin (PHA) test to measure acquired immunity, one of the most widely used methods, is currently being debated due to new knowledge on the complex physiology of the process. As a greater secondary response to repeated challenges linked to increases of circulating lymphocyte levels would be indicative of a T‐cell‐mediated immune response, we performed for the first time an experiment under natural conditions with repeated PHA challenges in free‐living adult birds and chicks to shed light on this topic. We found significantly stronger secondary response to PHA injection independent of sex or age, while controlling for body condition, the second response being on average 90% larger than the first. Likewise, lymphocyte counts were significantly higher in the second PHA challenge, whereas no significant differences were found among untreated birds. Significant positive correlations between the PHA response and both lymphocyte counts and plasma protein levels (mainly albumin, globulin precursor) were recovered, whereas no significant differences were recovered in plasma protein levels between challenges. Our results are consistent with those from captive birds, supporting the validity of the PHA skin‐swelling test as an accurate gauge of acquired T‐cell‐mediated immunity in birds.     

Chilling injury in coleus as influenced by photosynthetically active radiation, temperature and abscisic acid pretreatment. I. Morphological and physiological responses

Abstract. Coleus blumei Benth. (PI No. 354190), a green-leafed cultivar, was exposed to 5°C for 48 or 72 h after pretreatment for 48 h at two levels of photosynthetically active radiation (PAR) (8 and 320 μmol s⁻¹ m⁻²), two temperatures (13 and 20°C), and two abscisic acid (ABA) levels (0 and 200 g m⁻³ of the racemic mixture). Plants given low PAR for only 48 h prior to chilling treatment (48 or 72 h at 5°C) showed increased protection against chilling injury while those given high PAR were severely injured. The former plants were darker green, contained greater concentrations of chlorophyll- a , chlorophyll- b , total chlorophyll and anthocyanin and generally had a lower abscission rate than the latter plants. There were no differences, however, in chlorophyll- a/b ratio among plants grown at the two PAR levels, two temperatures or two ABA concentrations. Temperature and ABA pretreatment and number of hours at 5°C had no significant effect on chilling injury as measured by leaf chlorosis, but generally had a significant effect on leaf abcission, especially at 3 and 7 d after returning the plants to the greenhouse. Enclosing intact plants or excised shoots in plastic bags to maintain 100% relative humidity during 72 h chilling treatment failed to provide protection against chilling injury. These findings indicate that the protective effects of low PAR applied prior to chilling treatment may be as important or more important than that applied during chilling. They also indicate the importance of making careful measurements of PAR levels when conducting studies on chilling injury.     

Genotype-specific differences in chilling tolerance of maize in relation to chilling-induced changes in water status and abscisic acid accumulation

Four inbred maize lines differing in chilling tolerance were used to study changes in water status and abscisic acid (ABA) levels before, during and after a chilling period. Seedlings were raised in fertilized soil at 24/22°C (day/night), 70% relative humidity. and a 12-h photoperiod with 200 μmol m⁻² s⁻¹ from fluorescent tubes. At an age of 2 weeks the plants were conditioned at 14/12°C for 4 days and then chilled for 5 days at 5/3°C. The other conditions (relative humidity, quantum flux, photoperiod) were unchanged. After the chilling period the plants were transferred to the original conditions for recovery. The third leaves were used to study changes in leaf necrosis, ion efflux, transpiration, water status and ABA accumulation. Pronounced differences in chilling tolerance between the 4 lines as estimated by necrotic leaf areas, ion efflux and whole plant survival were observed. Conditioning significantly increased tolerance against chilling at 5/3°C in all genotypes. The genotypes with low chilling tolerance had lower water and osmotic potentials than the more tolerant genotypes during a chilling period at 5/3°C. These differences were related to higher transpiration rates and lower diffusive resistance values of the more susceptible lines. During chilling stress at 5/3°C ABA levels were quadrupled. Only a small rise was measurable during conditioning at 14/12°C. However, conditioning enhanced the rise of ABA during subsequent chilling. ABA accumulation in the two lines with a higher chilling tolerance was triggered at a higher leaf water potential and reached higher levels than in the less tolerant lines. We conclude that chilling tolerance in maize is related to the ability for fast and pronounced formation of ABA as a protective agent against chilling injury.     

Quantifying observer heterogeneity in bird counts

An essential pilot study was designed to quantify observer heterogeneity and to compare observation methods for the detectability of forest birds in stands of Eucalyptus and Pinus radiata forest as a basis for a major research project on habitat fragmentation near Tumut, southern New South Wales. Twelve experienced observers participated in the investigation. Point interval counts, zig-zag walks and strip transects were used to count birds in both eucalypt and pine forests. The 65 species of birds recorded in the study were assigned to one of nine groups classified by a set of attributes that characterized bird detection by field observers (e.g. body size, colour and calling patterns). Observer heterogeneity varied between groups of birds and was most apparent for small birds foraging in low shrubs (species such as the white-browed scrub wren, assigned to group 2), frequent calling, active birds (species such as the golden whistler, assigned to group 7), and midstorey, undercanopy foragers with distinctive behaviour (species such as the grey fantail assigned to group 4). For bird groups 2, 4 and 7, additional variability due to observer differences resulted in an average increase of ~ 40% in the width of a 95% confidence interval for the logarithm of bird abundance generated from a 20 minute count. Our analysis shows that taking the average of counts obtained by two or more observers would negate the increase in variance of counts due to observer heterogeneity. Few differences between methods of field observation were found. However, for frequent calling, active birds (group 7) there was evidence that more birds were heard using the point interval count method. Our study clearly demonstrated a need to either control for observer differences or to assign at least two observers to individual sites when designing bird surveys for comparative studies. Failure to do so will result in a decrease in precision of bird counts.     

Effects of whole wheat feeding on the development of the digestive tract of broiler chickens

The objective of the current study was to investigate the impact of including whole wheat in broiler diets on the development of the digestive tract. Chickens were fed a standard feed containing 400 g ground wheat/kg or the same diet with a part of the wheat given separately as whole grains that increased progressively from 200 g/kg at 8 d to 400 g/kg at 22 d. Every week, from 16 to 44 d, growth performance, modifications of the size of the digestive tract organs and intestinal enzyme activities were investigated. Morphology of villi and crypts in the small intestinal segments (duodenum, jejunum, ileum) were analyzed at 23 and 44 d. Microbacterial counts were performed in jejunal, ileal and caecal contents weekly from 16 to 44 d.During the adaptation period from 8 to 15 d, the birds fed the whole wheat diet had lower feed intake and lower weight gain. Thereafter, they showed improved growth performance so that by the end of the experiment, they had higher body weight compared to the standard-fed birds, 2430 ± 29 versus 2331 ± 36 g.Higher relative weights of gizzard (+26%) and pancreas (+12%) were observed from 16 to 44 d for whole wheat-fed birds compared to standard-fed birds. No differences in relative size of the different intestinal segments were observed, except that the jejunum was shorter. Increased villus to crypt length and surface ratios were observed at 23 d in the duodenum of whole wheat-fed birds, with no differences in morphometry between groups thereafter. Alkaline phosphatase activity was higher from 16 to 44 d in the duodenum and jejunum of whole wheat-fed birds. However, the activities of the digestive enzymes, leucine aminopeptidase and maltase, were similar between the two diets in the measured intestinal segments.A lower number of facultative anaerobic bacteria was found in the ileum of the whole wheat-fed birds, with no differences between treatments for Escherichia coli and for Lactobacillus counts. In the jejunum and the caeca, no differences in microflora counts were observed.The present results showed that feeding whole grains to broilers led mainly to modifications in the upper part of the digestive tract (gizzard, pancreas) and had little influence on the small and large intestine.     

Abscisic Acid-induced chilling tolerance in maize suspension-cultured cells

The induction of chilling tolerance by abscisic acid (ABA) in maize (Zea mays L. cv Black Mexican Sweet) suspension cultured cells was examined. Cell viability during exposure to chilling was estimated by triphenyl tetrazolium chloride reduction immediately after chilling and a filter paper growth assay. Both methods yielded comparable results. Chilling tolerance was induced by transferring 5-day-old cultures (late log phase) to a fresh medium containing ABA (10 to 100 micromolar). The greatest chilling tolerance was achieved with ABA at 100 micromolar. Growth of cells was inhibited at this concentration. After a 7-day exposure to 4°C in the dark, the survival of ABA-treated cells (100 micromolar ABA, 28°C for 24 h in the dark) was sevenfold greater than untreated cells. Effective induction of chilling tolerance was first observed when cells were held at 28°C for 6 hours after adding ABA. No tolerance was induced if the culture was chilled at the inception of ABA treatment. Induction of chilling tolerance was inhibited by cycloheximide. These results indicate that ABA is capable of inducing chilling tolerance when ABA-treated cells are incubated at a warm temperature before exposure to chilling, and this induction requires de novo synthesis of proteins.     

Prevalence, enumeration, serotypes, and antimicrobial resistance phenotypes of salmonella enterica isolates from carcasses at two large United States pork processing plants

The objective of this study was to characterize Salmonella enterica contamination on carcasses in two large U.S. commercial pork processing plants. The carcasses were sampled at three points, before scalding (prescald), after dehairing/polishing but before evisceration (preevisceration), and after chilling (chilled final). The overall prevalences of Salmonella on carcasses at these three sampling points, prescald, preevisceration, and after chilling, were 91.2%, 19.1%, and 3.7%, respectively. At one of the two plants, the prevalence of Salmonella was significantly higher (P < 0.01) for each of the carcass sampling points. The prevalences of carcasses with enumerable Salmonella at prescald, preevisceration, and after chilling were 37.7%, 4.8%, and 0.6%, respectively. A total of 294 prescald carcasses had Salmonella loads of >1.9 log CFU/100 cm(2), but these carcasses were not equally distributed between the two plants, as 234 occurred at the plant with higher Salmonella prevalences. Forty-one serotypes were identified on prescald carcasses with Salmonella enterica serotypes Derby, Typhimurium, and Anatum predominating. S. enterica serotypes Typhimurium and London were the most common of the 24 serotypes isolated from preevisceration carcasses. The Salmonella serotypes Johannesburg and Typhimurium were the most frequently isolated serotypes of the 9 serotypes identified from chilled final carcasses. Antimicrobial susceptibility was determined for selected isolates from each carcass sampling point. Multiple drug resistance (MDR), defined as resistance to three or more classes of antimicrobial agents, was identified for 71.2%, 47.8%, and 77.5% of the tested isolates from prescald, preevisceration, and chilled final carcasses, respectively. The results of this study indicate that the interventions used by pork processing plants greatly reduce the prevalence of Salmonella on carcasses, but MDR Salmonella was isolated from 3.2% of the final carcasses sampled.     

Sex, diet and feeding method-related differences in body condition in the Oystercatcher Haematopus ostralegus

Measurements were made of Oystercatcher corpses to find the most reliable measure of body condition in live birds. Total body weight was as accurate as muscle thickness in assessing the weight of the pectoral muscles, a major store of protein reserves. Total body weight was also a good indicator of fat reserves. Wing‐length was the most reliable measure of body size. Body condition in live birds was measured as an individual's residual weight derived from a general linear model of (loge) body weight against age, month, (loge) wing‐length and time since capture. On the Exe estuary in autumn, there was no significant difference in body condition between same‐age Oystercatchers of different diets and feeding methods. In the winter months, however, body condition differed significantly between mussel feeders using different feeding methods, and between mussel feeders and birds that fed on worms and clams. Differences between diet/feeding methods were not the same for each age group. Birds with the highest mean body condition index in adults were mussel hammerers, in immatures mussel stabbers and in juveniles, worm/clam feeders. No significant difference in body condition was found between the sexes in any age group in autumn. In winter, when birds with the same diet/feeding method were considered, females were significantly heavier than males. However, when birds of all diets and feeding methods were combined, weight differences between the sexes were not apparent. We examine reasons why birds with certain diets and feeding methods may be heavier than others in winter, and why females are sometimes heavier than males. We conclude that, in most cases, it is due to differences between birds in their ability to achieve a common target weight. However, we conclude that adult females try to achieve a higher target weight than males, probably as a premigratory and prebreeding strategy. In the light of this, we consider the consequences for adult females, in terms of reproductive success and survival, of specializing in diets and feeding methods associated with lower body weights in winter.     

Chilling-induced ultrastructural changes to mesophyll cells of Arabidopsis grown under short days are almost completely reversible by plant re-warming

Exposure of plants to chilling (low temperatures above freezing) limits growth and development in all environments outside the lowest latitudes. Cell ultrastructure and morphometric studies may allow associations to be made between chilling-induced changes at the ultrastructural level, molecular events and their physiological consequences. We examined changes in the shape, size and membrane organization of the organelles of mesophyll cells in Arabidopsis thaliana (Col 0), a cold-resistant species, after subjecting 6-week-old plants grown at normal growth temperatures to chilling (2.5–4°C; 14-h dark/10-h light cycle) for 6, 24 and 72 h and after a re-warming period of 50 h. No ultrastructural differences were seen in the first 6 h of chilling but after 24 h we observed swollen and rounded chloroplasts with larger starch grains and dilated thylakoids compared to control plants. By 72 h, chilling had resulted in a large accumulation of starch in chloroplasts, an apparent crowding of the cytosol and a lower abundance of peripheral reticulum than in the controls. The average area per chloroplast in cell sections increased after 72-h chilling while the number of chloroplasts remained the same. Ring-shaped and other morphologically aberrant mitochondria were present in significantly higher abundance in plants given 72 h chilling than in the controls. Plant re-warming for 50 h reduced chloroplast size to those of the controls and returned mitochondria to standard morphology, but peripheral reticulum remained less abundant than in plants never given a cold treatment. The near full return to normal ultrastructure upon plant re-warming indicates that the morphological changes may be part of acclimation to cold.     

Composition of mixed‐species flocks and shifts in foraging location of flocking species on Hainan Island,China

A total of 134 bird species were recorded at Jianfengling, Hainan Island, in China from May 2000 to September 2004, of which 44 participated in one or more of 134 mixed‐species flocks. These flocks averaged 3.8 ± 0.2 species and 20.3 ± 1.2 individuals. Flocking propensity in a given species ranged from 1.5 to 100%. For flocking species, frequency of flocking and number of individuals in flocks was positively correlated with frequency and number in point counts. Among all species pairs with flocking frequency above 5%, cluster and correlation analysis indicated there were two principal groups of flocking birds – canopy species and understorey species: associations were positive within a group, but negative between groups. Canopy birds had a higher flocking propensity than understorey birds. They also made significantly less use of inner branches and trunks and greater use of middle branches, and foraged at a significantly greater height when in mixed‐species flocks than when solitary. For understorey bird species, there were no significant differences in foraging locations between solitary and mixed‐species flocks. Higher flocking frequency occurred in the wet season for canopy birds, but in the dry season for understorey birds. Overall patterns were consistent with the explanation that flocking enables an expansion of foraging niche by reducing the risk of predation.