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.     

Immobile and tough versus mobile and weak: effects of ultraviolet B radiation on eggs and larvae of Manduca sexta

Although indirect effects of solar ultraviolet (UV) radiation on insects are well known (e.g. UV radiation can modify plant chemistry), direct effects of solar radiation on insects have received little attention. Radiation in the UVB range (300–320 nm) is damaging because it is absorbed directly by proteins and DNA. UVB should be toughest on immobile or small life stages, such as eggs or early larval instars. In the present study, the effects of UVB radiation on eggs and larvae of the tobacco hornworm Manduca sexta L. (Lepidoptera: Sphingidae) are examined. The present study aimed to address: what natural levels of UV do they experience; how does UVB affect the performance of eggs; and how does it affect the performance of larvae? In addition, do M. sexta larvae use behaviour to avoid UVB exposure and, consequently, are they physiologically less robust to UVB? In these experiments, eggs and late larval instars of M. sexta are found to be robust to natural levels of UV radiation. By contrast, young larvae are not only more susceptible to damage from UVB, but also they use behavioural means to avoid it. The strategy of using behaviour may relax selection pressures on morphological and physiological mechanisms for preventing (or recovering from) damage by environmental UV radiation.     

Translation of Rabbit Haemoglobin Messenger RNA by Thalassaemic and Non-thalassaemic Ribosomes

Globin mRNA from rabbit reticulocytes can be translated equally well by human ribosomes from thalassaemic and normal reticulocytes. This implies that the defect in β-thalassaemia is not in the ability of ribosomes to translate mRNA but is probably in the mRNA itself.     

A developmental approach to the problem of variation in evolutionary rates

Certain general features are widely recognized in evolution, one of which is the variability in the rate at which morphological characters evolve and taxa are replaced by others. Although some rate-variability in evolution no doubt arises because of different rates of ecological change, it is proposed that some of the variability also arises from developmental, rather than ecological, sources. A theory is outlined whereby early-acting genes influencing the course of development evolve more slowly, but have individually larger effects, than genes affecting development at a later stage in the life-cycle. The erratic course of morphological evolution that results is illustrated by computer simulation. It is suggested that the applicability of the theory is restricted to long-term evolution and that variability in the rate of evolution over shorter periods may be of an entirely different nature.     

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.     

Relative influence of habitat structure,species interactions and rainfall on the post‐fire population dynamics of ground‐dwelling vertebrates

The long‐term impacts of wildfires on animal populations are largely unknown. We used time‐series data based on a tracking index, from coastal NSW spanning 28 years after a wildfire, to investigate the relative influence of habitat structure, species interactions and climate on post‐fire animal population dynamics. The fire had an immediate impact on habitat structure, reducing and simplifying vegetation cover, which then underwent post‐fire successional change including an increase and plateau in tree canopy cover; an increase, stabilization and then decline in shrub cover; and an increase in ground litter cover. Population changes of different animal species were influenced by different components of successional change, but there was also evidence that species interactions were important. For example, bandicoots (Isoodon obesulus and Perameles nasuta combined) increased concurrent with an increase in shrub cover then declined at a faster rate than a direct association with senescing shrub cover would suggest, while the feral cat (Felis catus) population changed with the bandicoot population, suggesting a link between these species. Potoroos (Potorous tridactylus) increased 10 years after the fire concurrent with the closing tree canopy, but there was also evidence of a negative association with feral foxes (Vulpes vulpes). Variation in rainfall did not have significant effects on the population dynamics of any species. Our results suggest that changes in habitat structure play a key role in the post‐fire dynamics of many ground‐dwelling animals and hence different fire regimes are likely to influence animal dynamics through their effects on habitat structure. However, the role of predator–prey interactions, particularly with feral predators, is less clear and further study will require manipulative experiments of predators in conjunction with fire treatments to determine whether feral predator control should be integrated with fire management to improve outcomes for some native species.