Basal metabolic rate and risk‐taking behaviour in birds

Basal metabolic rate (BMR) constitutes the minimal metabolic rate in the zone of thermo‐neutrality, where heat production is not elevated for temperature regulation. BMR thus constitutes the minimum metabolic rate that is required for maintenance. Interspecific variation in BMR in birds is correlated with food habits, climate, habitat, flight activity, torpor, altitude, and migration, although the selective forces involved in the evolution of these presumed adaptations are not always obvious. I suggest that BMR constitutes the minimum level required for maintenance, and that variation in this minimum level reflects the fitness costs and benefits in terms of ability to respond to selective agents like predators, implying that an elevated level of BMR is a cost of wariness towards predators. This hypothesis predicts a positive relationship between BMR and measures of risk taking such as flight initiation distance (FID) of individuals approached by a potential predator. Consistent with this suggestion, I show in a comparative analysis of 76 bird species that species with higher BMR for their body mass have longer FID when approached by a potential predator. This effect was independent of potentially confounding variables and similarity among species due to common phylogenetic descent. These results imply that BMR is positively related to risk‐taking behaviour, and that predation constitutes a neglected factor in the evolution of BMR.     

Testosterone and year‐round territoriality in tropical and non‐tropical songbirds

Past studies have suggested a fundamental difference in testosterone concentrations between tropical and northern latitude male birds, with the convention being that males in the tropics express much lower levels of testosterone. However, recent comparative studies have shown that tropical males with a short and synchronous breeding season (i.e. a breeding season typical of northern species) express maximum testosterone levels similar to those of northern latitude birds. Here, we ask the converse: do northern latitude songbirds that express a defining life‐history characteristic typical of the tropics, i.e. year‐round territoriality, have an annual testosterone profile similar to that of tropical songbirds? For the few year‐round territorial species for which data are available, we found that seasonal testosterone profiles and seasonal maxima in plasma testosterone were similar between males of tropical and non‐tropical species. For example, males of both groups expressed seasonal maxima during the period when females were fertile, and testosterone levels at this time were similar. In contrast, this and other studies show that species with seasonal territories typically express maximum testosterone levels earlier in the breeding cycle, when territories are first being established. Taken together, we suggest that specific life‐history traits may play a more important role in determining testosterone profiles of tropical and non‐tropical birds than breeding latitude and encourage further studies to allow for more formal comparisons.     

Seasonality in basal metabolic rate and thermal conductance in a long-distance migrant shorebird,the knot (Calidris canutus)

Knots Calidris canutus live highly seasonal lives, breeding solitarily on high arctic tundra and spending the non-breeding season in large social flocks in temperate to tropical estuaries. Their reproductive activities and physiological preparations for long flights are reflected in pronounced plumage and body mass changes, even in long-term captives of the islandica subspecies (breeding in north Greenland and northeast Canada and wintering in western Europe) studied in outdoor aviaries. The three to four fattening episodes in April-July in connection with the flights to and from the high arctic breeding grounds by free-living birds, are represented by a single period of high body mass, peaking between late May and early July in a sample of ten captive islandica knots studied over four years. There are consistent and synchronized annual variations in basal metabolic rate and thermal conductance in three islandica knots. Basal metabolic rate was highest during the summer body mass peak. Within the examined individuals, basal metabolic rate scales on body mass with an exponent of about 1.4, probably reflecting a general hypertrophy of metabolically expensive muscles and organs. Any potential effect of moult on basal metabolic rate was obscured by the large seasonal mass-associated variations. In breeding plumage, insulation (the inverse of thermal conductance) was a factor of 1.35 lower than in winter plumage. This was paralleled by the dry mass of contour feathers being a factor of 1.17 lower. In this subspecies the breeding season is indeed the period during which the costs of thermoregulation are lowest. In captive knots seasonal changes in basal metabolic rate and thermal conductance likely reflect an anticipatory programme adaptive to the variable demands made by the environment at different times of the year.     

Dispersal of fungi spores by non‐specialized flower‐visiting birds

Birds are important biotic dispersers of a wide range of propagules. Fungi spores are mainly dispersed by wind. Nevertheless there are several animals known to disperse fungi spores, which might be particularly important if spores are delivered to particularly favourable sites i.e. directed dispersal. This may be especially important for fungi that require specific microsites such as flowers. We sampled birds for the presence of fungi spores and pollen grains during one year at two forest sites in central Portugal. We found that out of the 894 birds sampled, 131 individuals from 11 species carried spores from at least 6 morphological types, mainly during winter. The great majority of birds found to carry fungi spores was also found to carry pollen grains, suggesting that they were feeding on flowers which are the main origin of the spores. This co‐dispersion of pollen and fungi spores suggest that the latter are not randomly dispersed on the environment, but are likely to have an increased probability of being deposited on flowers propitious to fungi development. Our results suggest that directed dispersal of fungi by flower‐visiting birds might by a common and under‐appreciated phenomenon with potentially important ecological, biogeographic and even economic outcomes.     

Relative longevity and field metabolic rate in birds

Metabolism is a defining feature of all living organisms, with the metabolic process resulting in the production of free radicals that can cause permanent damage to DNA and other molecules. Surprisingly, birds, bats and other organisms with high metabolic rates have some of the slowest rates of senescence begging the question whether species with high metabolic rates also have evolved mechanisms to cope with damage induced by metabolism. To test whether species with the highest metabolic rates also lived the longest I determined the relationship between relative longevity (maximum lifespan), after adjusting for annual adult survival rate, body mass and sampling effort, and mass-specific field metabolic rate (FMR) in 35 species of birds. There was a strongly positive relationship between relative longevity and FMR, consistent with the hypothesis. This conclusion was robust to statistical control for effects of potentially confounding variables such as age at first reproduction, latitude and migration distance, and similarity in phenotype among species because of common phylogenetic descent. Therefore, species of birds with high metabolic rates senesce more slowly than species with low metabolic rates.     

Identifying forest‐obligate birds in tropical moist cloud forest of Andean Ecuador

ABSTRACT Large‐scale transformation of forested landscapes is a major factor in loss of biological diversity in the American tropics. Investigators examining the responses of species to deforestation rarely control for variation in the amount of forest relative to other habitats at the landscape‐level. Bellavista Reserve on the western slope of the Andes in Ecuador is located between similar‐sized areas of pristine, protected forest, and deforested landscapes. We used strip‐transect counts and mist netting to evaluate habitat use by passerine birds in a habitat mosaic consisting of abandoned pastures, forest edges, forest fragments, and large blocks of interior tropical montane cloud forest (TMCF). During 3600 net hours, we had 1476 captures, including 346 recaptures. Of 78 species captured in mist nets, 30 had sufficient counts for Poison Rate Regression (PRR) modeling (a statistical method for comparing counts). Twelve species (40%) had capture patterns indicative of an affinity for mature TMCF, and 6 species (20%) had significantly higher counts in degraded areas (forest edge, forest fragment, and regenerating pastures) than in interior TMCF. The remaining 40% showed no significant bias in detection among habitats. Combined with strip‐count data, our results suggest that about 38% of the 119 species sampled at the Bellavista Reserve occur primarily in mature TMCF, avoiding edges and early second‐growth forest. Populations of these species may be vulnerable to further loss, fragmentation, and degradation of TMCF and, as such, deserve additional study and a place on lists of species of conservation concern.     

Resting metabolic rate in migratory and non‐migratory geese following range expansion: go south,go low

While many species suffer from human activities, some like geese benefit and may show range expansions. In some cases geese (partially) gave up migration and started breeding at wintering and stopover grounds. Range expansion may be facilitated and accompanied by physiological changes, especially when associated with changes in migratory behaviour. Interspecific comparisons found that migratory tendency is associated with a higher basal or resting metabolic rate (RMR). We compared RMR of individuals belonging to a migratory and a sedentary colony of barnacle geese Branta leucopsis. The migratory colony is situated in the traditional arctic breeding grounds (Russia), whereas the sedentary colony has recently been established in the now shared wintering area (the Netherlands). We measured RMR by oxygen consumption () during two ontogenetic phases (juvenile growth and adult wing moult). We also investigated juvenile growth rates and adult body mass dynamics. Mass‐independent was 13.6% lower in goslings from the sedentary colony than in goslings from the migratory colony. Similarly, in adult geese, mass‐independent was 15.5% lower in sedentary than in migratory conspecifics. Goslings in the Netherlands grew 36.2% slower than goslings in Russia, while we found no differences in body dimensions in adults. Adult geese from both colonies commenced wing moult with similar body stores, but whereas Russian barnacle geese maintained this level throughout moult, body stores in geese from the Netherlands fell, being 8.5% lower half‐way through the moult. We propose that the colony differences in resting metabolic rate, growth rate and body mass dynamics during moult can be explained by environmental and behavioural differences. The less stringent time constraints combined with poorer foraging opportunities allow for a smaller ‘metabolic machinery’ in non‐migratory geese. Our analysis suggests that range expansion may be associated with changes in physiology, especially when paired with changes in migratory tendency.     

Ectoparasite‐induced increase in Drosophila host metabolic rate

Parasites exert numerous effects upon their hosts, including physiological and metabolic changes that can in turn influence various aspects of host life history. Using flow‐through respirometry, we investigated how infection intensity of an ectoparasitic mite (Macrocheles subbadius) affects the respiratory rate (CO₂ production) of its host Drosophila nigrospiracula. Mean fly respiratory rate increased with infection intensity with the strongest effect, a 40% increase relative to uninfected controls, occurring with three mites attached. We also verified the causal relationship between elevated respiration rate and mite attachment by examining changes in host respiration before and after mite exposure. We found that the rate of CO₂ production increased by 11% for individual flies following parasite attachment. Fly locomotor activity was not significantly different between infected and uninfected individuals. Metabolic rate of hosts increased as a result of infection in an intensity dependent manner and was not simply due to changes in host activity. These results demonstrate that parasites can have a significant influence on the energy requirements of their host, which may account for the parasite‐mediated loss in host fitness.     

Recent population declines in Afro‐Palaearctic migratory birds: the influence of breeding and non‐breeding seasons

Aim

Recent, rapid population declines in many Afro‐Palaearctic migratory bird species have focussed attention on changing conditions within Africa. However, processes influencing population change can operate throughout the annual cycle and throughout migratory ranges. Here, we explore the evidence for impacts of breeding and non‐breeding conditions on population trends of British breeding birds of varying migratory status and wintering ecology.

Location

Great Britain (England & Scotland).

Methods

Within‐ and between‐species variation in population trends is quantified for 46 bird species with differing migration strategies.

Results

Between 1994 and 2007, rates of population change in Scotland and England differed significantly for 19 resident and 15 long‐distance migrant species, but were similar for 12 short‐distance migrant species. Of the six long‐distance migrant species that winter in the arid zone of Africa, five are increasing in abundance throughout Britain. In contrast, the seven species wintering in the humid zone of Africa are all declining in England, but five of these are increasing in Scotland. Consequently, populations of both arid and humid zone species are increasing significantly faster in Scotland than England, and only the English breeding populations of species wintering in the humid zone are declining.

Main conclusions

Population declines in long‐distance migrants, especially those wintering in the humid zone, but not residents or short‐distance migrants suggest an influence of non‐breeding season conditions on population trends. However, the consistently less favourable population trends in England than Scotland of long‐distance migrant and resident species strongly suggest that variation in the quality of breeding grounds is influencing recent population changes. The declines in humid zone species in England, but not Scotland, may result from poorer breeding conditions in England exacerbating the impacts of non‐breeding conditions or the costs associated with a longer migration, while better conditions in Scotland may be buffering these impacts.

     

Effects of metabolic level on the body size scaling of metabolic rate in birds and mammals

Metabolic rate is traditionally assumed to scale with body mass to the 3/4-power, but significant deviations from the '3/4-power law' have been observed for several different taxa of animals and plants, and for different physiological states. The recently proposed 'metabolic-level boundaries hypothesis' represents one of the attempts to explain this variation. It predicts that the power (log-log slope) of metabolic scaling relationships should vary between 2/3 and 1, in a systematic way with metabolic level. Here, this hypothesis is tested using data from birds and mammals. As predicted, in both of these independently evolved endothermic taxa, the scaling slope approaches 1 at the lowest and highest metabolic levels (as observed during torpor and strenuous exercise, respectively), whereas it is near 2/3 at intermediate resting and cold-induced metabolic levels. Remarkably, both taxa show similar, approximately U-shaped relationships between the scaling slope and the metabolic (activity) level. These predictable patterns strongly support the view that variation of the scaling slope is not merely noise obscuring the signal of a universal scaling law, but rather is the result of multiple physical constraints whose relative influence depends on the metabolic state of the organisms being analysed.     

The use of body mass loss to estimate metabolic rate in birds

During starvation, energy production occurs at the expense of body reserve utilisation which results in body mass loss. Knowing the role of the fuels involved in this body mass loss, along with their energy density, can allow an energy equivalent of mass loss to be calculated. Therefore, it is possible to determine daily energy expenditure (DEE) if two body mass loss measurements at an interval of a few days are obtained. The technique can be cheap, minimally stressful for the animals involved, and the data relatively simple to gather. Here we review the use of body mass loss to estimate DEE in birds through critiquing the strengths and weaknesses of the technique, and detail the methodology and considerations that must be adhered to for accurate measures of DEE to be obtained. Owing to the biology of the species, the use of the technique has been used predominantly in Antarctic seabirds, particularly penguins and albatrosses. We demonstrate how reliable the technique can be in predicting DEE in a non-Antarctic species, common eiders (Somateria mollissima), the female of which undergoes a fasting period during incubation. We conclude that using daily body mass loss to estimate DEE can be a useful and effective approach provided that (1) the substrate being consumed during mass loss is known, (2) the kinetics of body mass loss are understood for the species in question and (3) only species that enter a full phase II of a fast (where substrate catabolism reaches a steady state) and are not feeding for a period of time are appropriate for this method.     

Roles of non‐native species in large‐scale regeneration of moist tropical forests on anthropogenic grassland

This paper presents a new synthesis of the role of native and non‐native species in diverse pathways and processes that influence forest regeneration on anthropogenic grassland in the moist tropics. Because of altered species composition, abiotic conditions and landscape habitat mosaics, together with human interventions, these successional pathways differ from those seen in pre‐clearing forests. However, representation of different functional life forms of plant (tree, vine, grass, herb and fern) and animal (frugivorous seed disperser, granivorous seed predator, seedling herbivore and carnivore) shows consistent global variation among areas of pasture, intact forest, and post‐grassland regrowth. Biotic webs of interaction involve complex indirect influences and feedbacks, which can account for wide observed variation in regeneration trajectories over time. Important processes include: limitation of tree establishment by dense grasses; recruitment and growth of pioneer pasture trees (shading grasses and facilitating bird‐assisted seed dispersal); and smothering of trees by vines. In these interactions, species’ functional roles are more important than their biogeographic origins. Case studies in eastern Australia show native rain forest plant species diversity in all life forms increasing over time when pioneer trees are non‐native (e.g., Cinnamomum camphora, Solanum mauritianum), concurrent with decreased grass and fern cover and increased abundance of trees and vine tangles. The global literature shows both native and non‐native species facilitating and inhibiting regeneration. However conservation goals are often targeted at removing non‐native species. Achieving large‐scale tropical forest restoration will require increased recognition of their multiple roles, and compromises about allocating resources to their removal.     

A non‐lethal biopsy technique for sampling subcutaneous adipose tissue of small and medium‐sized birds

Analysis of fatty acids from adipose tissue can provide important information about the physiological and nutritional condition of birds. However, non‐lethal biopsy procedures and their potential negative effects on small and medium‐sized birds have not been adequately assessed. We developed a biopsy procedure for collecting small amounts of adipose tissue from the furcular area of small and medium‐sized birds (13–62 g) without adverse effects. The biopsy procedure was performed on Dunlins (Calidris alpina), a medium‐sized migratory shorebird, and small hybrid songbirds (European Goldfinch [Carduelis carduelis] × Atlantic Canary [Serinus canaria]). The biopsy involved making a skin incision 2–3 mm long on one side of the furcular region to collect 2–16 mg of adipose tissue. All birds were monitored for 2 weeks after biopsies to examine potential effects of the procedure on body mass, visible fat deposition, time for wound healing, hematocrit levels, total white blood cell counts, and heterophil:lymphocyte ratios. Visible scars were apparent for 10 d for hybrids and 6 d for Dunlins, with no evidence of infection or abnormal scar tissue formation. Body mass of songbirds did not differ before and after the biopsy, but Dunlins increased body mass and visible fat deposition after biopsy. The collection of adipose tissue in the furcular region was performed only for birds with fat scores ≥2, and the tissue collected never represented more than 0.07% of a bird's body mass; we recommend both these values to avoid any possible unknown negative effects. Our non‐lethal biopsy technique is relatively simple to perform, and we recommend it as an alternative to lethal methods for sampling adipose tissue in studies of wild and captive birds.     

Group size affects the metabolic rate of a tropical beetle

ABSTRACT. . Dormancy is metabolically very costly for insects and other poikilotherms of the tropics because energy reserves are rapidly utilized at high temperature. Yet, the beetle Stenotarsus rotundus Arrow spends up to 10 months each year in a tropical lowland forest as a non-feeding adult, dependent upon its fat reserve as an energy source. While in this dormant state, the beetles aggregate in huge numbers and the size of the group greatly influences the metabolic rate. As group size increases, the metabolic rate decreases, and the minimum rate observed in the field (22 μ l O₂ g^-1 h^-1) is estimated to occur when group size reaches about 300 individuals. A decrease in metabolic rate can also be achieved by elevating relative humidity, thus suggesting that one function of the aggregation is to increase humidity within the group and thereby decrease metabolic rate.     

Environment, migratory tendency, phylogeny and basal metabolic rate in birds

Basal metabolic rate (BMR) represents the minimum maintenance energy requirement of an endotherm and has far-reaching consequences for interactions between animals and their environments. Avian BMR exhibits considerable variation that is independent of body mass. Some long-distance migrants have been found to exhibit particularly high BMR, traditionally interpreted as being related to the energetic demands of long-distance migration. Here we use a global dataset to evaluate differences in BMR between migrants and non-migrants, and to examine the effects of environmental variables. The BMR of migrant species is significantly higher than that of non-migrants. Intriguingly, while the elevated BMR of migrants on their breeding grounds may reflect the metabolic machinery required for long-distance movements, an alternative (and statistically stronger) explanation is their occupation of predominantly cold high-latitude breeding areas. Among several environmental predictors, average annual temperature has the strongest effect on BMR, with a 50% reduction associated with a 20 degrees C gradient. The negative effects of temperature variables on BMR hold separately for migrants and non-migrants and are not due their different climatic associations. BMR in migrants shows a much lower degree of phylogenetic inertia. Our findings indicate that migratory tendency need not necessarily be invoked to explain the higher BMR of migrants. A weaker phylogenetic signal observed in migrants supports the notion of strong phenotypic flexibility in this group which facilitates migration-related BMR adjustments that occur above and beyond environmental conditions. In contrast to the findings of previous analyses of mammalian BMR, primary productivity, aridity or precipitation variability do not appear to be important environmental correlates of avian BMR. The strong effects of temperature-related variables and varying phylogenetic effects reiterate the importance of addressing both broad-scale and individual-scale variation for understanding the determinants of BMR.     

Long-term population declines in Danish trans-Saharan migrant birds

Capsule Long-distance migrant birds show less favourable trends than sedentary/short-distance species.

Aims To use breeding bird surveys to contrast population trends amongst common species according to their migration pattern.

Methods Changes in abundance of 62 Danish breeding sedentary, short-distance (Europe/North Africa) or long-distance (trans-Saharan) migrants were described by fitting log linear regression models to point-count census data gathered during 1976–2005.

Results Trans-Saharan migrants declined by 1.3% per annum during this period, while short-distance migrants and sedentary species increased by 1.4% and 1.0% per annum, respectively. There were no significant decadal declines amongst species using different summer breeding habitats, except for wetlands, and there was no consistent variation in trends associated with wintering regions or habitats or diet.

Conclusions More information is urgently needed on diet, feeding ecology, habitat requirements, winter distribution and intra-African movements of the commoner European summer visitors to identify causes of the declines and highlight when in the annual cycle detrimental effects occur. Studies linking individuals on their breeding, staging and wintering grounds are especially needed. Danish trends resemble those from elsewhere in Europe, confirming that restoration to favourable conservation status requires inter-continental action to meet European and global targets to reduce or halt biodiversity loss.