Among- and within-individual correlations between basal and maximal metabolic rates in birds

The aerobic capacity model proposes that endothermy is a by-product of selection favouring high maximal metabolic rates (MMR) and its mechanistic coupling with basal metabolic rate (BMR). Attempts to validate this model in birds are equivocal and restricted to phenotypic correlations (rP), thus failing to distinguish among- and within-individual correlations (rind and re). We examined 300 paired measurements of BMR and MMR from 60 house sparrows before and after two levels of experimental manipulation - testosterone implants and immune challenge. Overall, repeatability was significant in both BMR (R=0.25±0.06) and MMR (R=0.52±0.06). Only the testosterone treatment altered the rP between BMR and MMR, which resulted from contrasting effects on rind and re. While rind was high and significant (0.62±0.22) in sham-implanted birds, re was negative and marginally non-significant (-0.15±0.09) in testosterone-treated birds. Thus, the expected mechanistic link between BMR and MMR was apparent, but only in birds with low testosterone levels.

Migratory birds reinforce local circulation of avian influenza viruses

Migratory and resident hosts have been hypothesized to fulfil distinct roles in infectious disease dynamics. However, the contribution of resident and migratory hosts to wildlife infectious disease epidemiology, including that of low pathogenic avian influenza virus (LPAIV) in wild birds, has largely remained unstudied. During an autumn H3 LPAIV epizootic in free-living mallards (Anas platyrhynchos) - a partially migratory species - we identified resident and migratory host populations using stable hydrogen isotope analysis of flight feathers. We investigated the role of migratory and resident hosts separately in the introduction and maintenance of H3 LPAIV during the epizootic. To test this we analysed (i) H3 virus kinship, (ii) temporal patterns in H3 virus prevalence and shedding and (iii) H3-specific antibody prevalence in relation to host migratory strategy. We demonstrate that the H3 LPAIV strain causing the epizootic most likely originated from a single introduction, followed by local clonal expansion. The H3 LPAIV strain was genetically unrelated to H3 LPAIV detected both before and after the epizootic at the study site. During the LPAIV epizootic, migratory mallards were more often infected with H3 LPAIV than residents. Low titres of H3-specific antibodies were detected in only a few residents and migrants. Our results suggest that in this LPAIV epizootic, a single H3 virus was present in resident mallards prior to arrival of migratory mallards followed by a period of virus amplification, importantly associated with the influx of migratory mallards. Thus migrants are suggested to act as local amplifiers rather than the often suggested role as vectors importing novel strains from afar. Our study exemplifies that a multifaceted interdisciplinary approach offers promising opportunities to elucidate the role of migratory and resident hosts in infectious disease dynamics in wildlife.

Feeding wild birds in gardens: a test of water versus food

Bird feeding in residential gardens is an increasingly popular human-wildlife interaction. In Australia, the practice is discouraged by most government and nongovernment wildlife conservation agencies, although advice varies and the most common recommendation is to provide water and habitat for birds rather than supplementary food. This study compares bird abundance and diversity when residents in a Melbourne municipality provide water for birds versus food. Bird abundance was greater when food was provided compared with water, but avian assemblages did not differ.

Flying, fasting, and feeding in birds during migration: a nutritional and physiological ecology perspective

Unlike exercising mammals, migratory birds fuel very high intensity exercise (e.g., flight) with fatty acids delivered from the adipose tissue to the working muscles by the circulatory system. Given the primary importance of fatty acids for fueling intense exercise, we discuss the likely limiting steps in lipid transport and oxidation for exercising birds and the ecological factors that affect the quality and quantity of fat stored in wild birds. Most stored lipids in migratory birds are comprised of three fatty acids (16:0, 18:1 and 18:2) even though migratory birds have diverse food habits. Diet selection and selective metabolism of lipids play important roles in determining the fatty acid composition of birds which, in turn, affects energetic performance during intense exercise. As such, migratory birds offer an intriguing model for studying the implications of lipid metabolism and obesity on exercise performance. We conclude with a discussion of the energetic costs of migratory flight and stopover in birds, and its implications for bird migration strategies.

Departure fuel loads in time-minimizing migrating birds can be explained by the energy costs of being heavy

Lindstrom and Alerstam presented a model that predicts optimal departure fuel loads as a function of the rate of fuel deposition in time-minimizing migrants. The basis of the model is that the coverable distance per unit of fuel deposited, diminishes with increasing fuel load. This is an effect of the increasing flight costs associated with increasing body mass. Lindstrom and Alerstam (1992) found that birds left at lower fuel loads than their model predicted for which they considered various ecological explanations. Alternatively, we hypothesize that the difference between prediction and empirical data might be a result of extra resting metabolic and transport costs associated with an increase in fuel load during stopover. We develop a new version of the Lindstrom and Alerstam (1992) model taking fuel load associated costs during stopover into account. We fit empirical data from rufous hummingbirds Selasphorus rufus and bluethroats Luscinia svecica to this new model. Estimated fuel-load costs are discussed in relation to knowledge presently available on variations in basal metabolic costs and transport costs with body mass. We show that fuel-load costs within a reasonable range can explain the observed departure fuel loads when migrating birds are time minimizers.

Metabolic constraints on long-distance migration in birds

The flight range of migrating birds depends crucially on the amount of fuel stored by the bird prior to migration or taken up en route at stop-over sites. However, an increase in body mass is associated with an increase in energetic costs, counteracting the benefit of fuel stores. Water imbalance, occurring when water loss exceeds metabolic water production, may constitute another less well recognised problem limiting flight range. The main route of water loss during flight is via the lungs; the rate of loss depends on ambient temperature, relative humidity and ventilatory flow and increases with altitude. Metabolite production results in an increased plasma osmolality, also endangering the proper functioning of the organism during flight. Energetic constraints and water-balance problems may interact in determining several aspects of flight behaviour, such as altitude of flight, mode of flight, lap distance and stop-over duration. To circumvent energetic and water-balance problems, a bird could migrate in short hops instead of long leaps if crossing of large ecological barriers can be avoided. However, although necessitating larger fuel stores and being more expensive, migration by long leaps may sometimes be faster than by short hops. Time constraints are also an important factor in explaining why soaring, which conserves energy and water, occurs exclusively in very large species: small birds can soar at low speeds only. Good navigational skills involving accurate orientation and assessment of altitude and air and ground speed assist in avoiding physiological stress during migration.

Flight initiation distances in relation to sexual dichromatism and body size in birds from three continents

Predators exert strong selection pressures on their prey. Prey would therefore benefit by adjusting their behaviour to the risk of predation, while predators conversely would benefit from adjusting their behaviour to that of their prey. Extravagant ornamentation has evolved to attract mates and/or successfully compete with conspecifics of the same sex to secure high mating success, even if that occurs at a cost of increased risk of predation. Thus, sexually dichromatic species may be more susceptible to predation than sexually monochromatic species, and the presence of compensation is indicative of such species being more vulnerable. If extravagant ornamentation is costly in terms of predation risk, then we should expect sexually dichromatic species to have longer flight initiation distances (FID) than sexually monochromatic species. If ornamentation is acquired as a handicap with only individuals in prime condition being able to display with the smallest viability cost, we should expect sexually dichromatic individuals to have shorter FID than sexually monochromatic individuals. Such differences among individuals should, on an evolutionary time scale, translate into differences in FID being related to differences in sexual dichromatism among species. We investigated the relationship between FID and sexual dichromatism in phylogenetic analyses, while accounting for effects of continent (Australia, North America, and Europe), body mass, the interaction between sexual dichromatism and body mass and the interaction between sexual dichromatism and continent. In an analysis of 447 species we found shorter FID in sexually dichromatic than in sexually monochromatic species (consistent with the handicap hypothesis because sexually dichromatic species took greater risks), especially so at large body size. FID differed among continents and the relative difference in FID between sexually monochromatic and sexually dichromatic species was larger in Europe than in Australia and North America. These differences among continents may be attributed to latitudinal effects of predation. These findings are important for current ideas about the evolution of secondary sexual characters because they imply covarying continental differences in predation, especially for large bodied sexually dichromatic species.

Campus Life: In Perkins Arboretum there are birds of all feathers, trees that tell a story, and even romance (especially if you're a frog)

To the uninitiated, Perkins Arboretum is the edge of campus. For those familiar with its flora and fauna, the arboretum is a wondrous classroom and refuge.

Neospora caninum infection in birds: experimental infections in chicken and embryonated eggs

Neospora caninum causes economical impact in cattle-raising farms since it is implicated as the major cause of bovine abortions. Although infection by the parasite has been widely described in mammals, the role of birds in its life-cycle is still obscure. Therefore, this work aimed to evaluate the infection by N. caninum in different chicken models. Experimental infections were conducted in 7-day-old chicks, laying hens and embryonated eggs, where samples were analysed for parasite burden, IgG antibodies and lesions promoted. Chickens demonstrated an asymptomatic infection, although with seroconversion and systemic replication of the parasite. In laying hens, no signs of vertical transmission were observed. However, embryonated eggs inoculated by the allantoic cavity route demonstrated susceptibility to infection, with mortality rates around 50% independent of the inoculum dose. Additionally, dogs became infected after ingestion of different amounts of inoculated eggs, producing either oocysts or specific IgG antibodies. The results herein presented demonstrate that chickens may be intermediate hosts of N. caninum and that embryonated eggs could be a useful model to study the parasite's biology.

Salmonella spp investigation in transport boxes of day-old birds

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Prevention of Salmonella infection by contact using intestinal flora of adult birds and/or a mixture of organic acids

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)