Flock feeding and food intake in Little Egrets Egretta garzetta and their effects on food provisioning and reproductive success

Food provisioning to chicks of Little Egret Egretta garzetta in a colony at Ligagneau in the Camargue, southern France, was measured using electronic nest balances. Both pair members supplied food to the chicks, and each performed three to five alternating foraging trips. The loading rate during the first trip of the day (1.09 g/min) was more than three times as high as that during later trips (0.32 g/min) and accounted for 20% of the daily amount of food delivered. This food was collected while the birds were feeding in dense aggregations on mosquitofish which had become temporarily concentrated due to hypoxic conditions overnight in the surrounding marsh. Later in the day, when this concentrated food source was no longer available, the birds fed solitarily. The total amount of food delivered per day remained constant at 385 g as chick age increased from 10 to 20 days. Given the observed loading rates, 385 g is near the maximum amount of food the pair can deliver during a 16.5-h daylight period when they forage continuously throughout the day but only one parent at a time. This indicates that a time constraint limits the amount of food delivered to a brood during this stage of the breeding cycle. Given this time constraint, the total amount of food delivered per day would have been reduced by 25% if the birds had not been able to benefit from the concentrations of mosquitofish during the early morning. Breeding success was significantly higher at Ligagneau (3.25 chicks/nest) than in other Camargue colonies (2.69 chicks/nest). In addition, post-fledging survival of chicks with a low rank in the brood hierarchy was probably better at Ligagneau than elsewhere in the Camargue. We attribute this elevated reproductive output at Ligagneau to the exceptionally large amount of food collected by egrets during the early morning aggregations, which were probably formed in response to predictable concentrations of mosquitofish in the permanent marshes surrounding this colony. Such aggregations were rarely observed in the temporary marshes surrounding the other colonies, probably because the occurrence and location of fish concentrations are difficult to predict in this habitat due to rapidly falling water levels.     

Effect of Ammonia Concentration on the Composition, Hydrolytic Activity and Nitrogen Metabolism of the Microbial Flora of the Rumen

The mean NH₃ concentration in the rumen of sheep fed whole barley (08 kg/d) by continuous feeders was increased from 61 to 134 HIM by supplementing the feed with urea (30 g/kg). This change caused a 90% increase in the rate of degradation of rolled barley, and smaller increases in the rates of degradation of protein and plant fibre in the rumen. The total viable count and numbers of pectinolytic bacteria in rumen fluid increased with the urea supplement. Enzyme studies indicated that NAD-linked glutamate dehydrogenase was the main pathway of NH₃ assimilation by rumen bacteria at both NH₃ concentrations. Glutamate was the main free amino acid found in the rumen at low NH₃ but, despite the low activity of alanine dehydrogenase and glutamate-pyruvate aminotransferase, alanine was the principal amino acid at high NH₃ concentrations. Hydrolytic rumen bacteria may require the higher NH₃ concentration either for effective NH₃ assimilation by an unknown mechanism involving alanine or for full expression of enzyme activity.     

Habitat Use and Survival of Preflight Wild Turkey Broods

Abstract: Wild turkey (Meleagris gallopavo) broods spend the first several days of life on the ground until poult flight capabilities are attained. This is a critical period of wild turkey life history, with poult survival ranging from 12% to 52%. We measured vegetation in plots used by Rio Grande wild turkey (M. g. intermedia) preflight broods at 4 sites in southwest Kansas and the Texas Panhandle, USA, to determine microhabitat selection for ground roosting and to determine if microhabitat was related to poult survival. Hens selected ground-roost locations with more visual obstruction from multiple observation heights than random sites. Plots surrounding ground roosts had 1) greater visual obstruction; 2) increased tree decay; 3) higher percent grass, shrub, litter, and forb cover; and 4) lower percent bare ground cover than random sites. Grass, shrubs, and downed trees appeared to provide desired cover for ground-roosting broods. Poult survival increased with age of poult, size of brood, and density of shrubs 1–2 m tall. Plots used by broods <10 days old with above average survival contained more visual obstruction and shrubs than plots used by broods 10–16 days old with above average survival, signifying a shift in habitat use by successful broods as poults attain flight abilities. Density of shrubs 1–2 m tall in brood-use areas appears to be important for poult survival to 16 days of age on southern Great Plains rangeland habitats. Ground-level vegetative cover appears to be a significant factor in preflight poult survival. Provisions of ground-level vegetative cover should be considered during wild turkey brooding periods where increased poult survival is desired.     

Isolation of polymorphic microsatellite loci in Crossosoma californicum (Crossosomataceae)

Crossosoma californicum (Crossosomataceae) is a rare shrub species endemic to the California Channel Islands. Previous studies based on allozymes revealed little genetic variability in this plant species. We have isolated 13 polymorphic microsatellite loci from C. californicum. These loci show intermediate levels of variability, averaging 4.2 alleles per locus and expected heterozygosity of 0.376. Two loci did not fit Hardy–Weinberg expectations with significant deficits of heterozygous genotypes consistent with the presence of null alleles or population subdivision.     

THE EMERGENCE OF LARVAE FROM CYSTS OF THE BEET EELWORM, HETERODERA SCHACHTII SCHMIDT, IN AQUEOUS SOLUTIONS OF ORGANIC AND INORGANIC SUBSTANCES

The rate of larval emergence from cysts of the beet eelworm in a variety of aqueous solutions containing organic and inorganic substances is significantly higher than the emergence rate in water. It is suggested that differences between larval emergence rates in monoamino-monocarboxylic amino-acids may be related to the lipid solubility of these substances and their ability to penetrate the egg membranes. The larval emergence rate in fructose, glucose, sucrose and maltose was significantly higher than that in water, but in raffinose, arabinose and xylose the rate of emergence was no higher than in water. A high rate of larval emergence occurred in sodium chloride, potassium chloride and mercuric chloride, but not in magnesium chloride or calcium chloride. Experiments with several other organic solutions are described. There is an optimum concentration for larval emergence in beet diffusate. The osmotic pressure of the diffusate when maximum emergence occurred was 0·48 atm. Measurements of shrinkage of unhatched larvae in various concentrations of urea, sodium chloride and sucrose showed that decreasing rates of emergence at higher concentrations may be due to changes in the unhatched larvae brought about: by an osmotic effect. High concentrations of beet diffusate may have a similar effect.     

Laboratory experiments on factors affecting the activity of Gammarus pseudolimnaeus Bousfield

Factors such as current, light, food, substrate and time of year were found to influence the activity of specimens of Gammarus pseudolimnaeus maintained in stream tanks in the laboratory. Although there was seasonal variation, levels of diurnal and nocturnal activity were generally much higher when there was no current than when the water was running. Diurnal periodicity occurred but was not as pronounced as had been indicated in the field studies of previous workers. Although there was activity during the day, nocturnal levels were higher especially in specimens collected during the summer. When there was no current, and the lights were left on for 24 h, peak activity occurred at precisely the times when the lights normally would have been off. This strongly suggests that there is an endogenous component in the activity. The nocturnal activity showed a bigeminus pattern, and there was a seasonal change, with the general activity at its highest levels in summer. Activity was significantly greater during daylight both with and without current when there was no substrate present in the tanks. The behaviour of Gammarus appears to be complex and greatly influenced by combinations of the various factors.     

Photosynthetic Response to Water Stress in Phaseolus vulgaris

Water stressed Phaseolus vulgaris L. plants were monitored to detect the relationships between net photosynthesis, transpiration, boundary layer plus stomatal resistance, mesophyll resistance, CO₂ compensation point, ribulose, 1,5-diphosphate carboxylase activity and leaf water potential. At full expansion, the first trifoliate leaves of greenhouse grown bean plants were subjected to water stress by withholding irrigation. Gas exchange and enzyme activity of the central trifoliolate leaflets were monitored as leaf water potential decreased. Although increased stomatal resistance appeared to be the primary causal factor of reduced net photosynthesis, increased mesophyll resistance and decreased ribulose 1,5-diphosphate carboxylase activity further documented the role of non-stomatal factors.