All signals are not equal: acoustic signalling of individuality, sex and breeding status in a cooperative breeder

Repeated interactions between individuals in socially living animals select for the evolution of signals that convey information identifying individuals or categories of individuals, which may enable the discrimination of familiar versus unfamiliar individuals. Such information may help animals maximize their inclusive fitness by adjusting their own behaviour, allowing them to avoid conflict, preferentially direct help and/or ignore unreliable individuals. Acoustic signals in birds provide the potential to encode individual-specific information. We examined the degree to which individual identity, sex, breeding status, group membership and genetic relatedness were related to variability in six different call types, which occurred across a variety of different behavioural contexts in the apostlebird, Struthidea cinerea, a socially living and cooperatively breeding Australian passerine. We demonstrated that not all calls reflected the same extent of information. Of the six call types, call variation was related to individual identity in three call types, breeding status in two call types and sex and group relatedness in one call type. Finally, variation in two call types was not related to any of the measured variables. Our results suggest that some, but not all, acoustic signals in apostlebirds may be selected for individual distinctiveness between individuals and categories of individuals (male versus female, breeder versus nonbreeder), and these signals may be important in determining levels of cooperation and interaction between individuals in this cooperatively breeding society. © 2014 The Association for the Study of Animal Behaviour.

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.

Birds of a feather: the geographic interconnection of Australian universities on Twitter

Purpose
Regardless of their virtual nature, research suggests that social media networks are still influenced by geography. This research investigates the connections between Australian universities on the Twitter social media system.

Design/methodology/approach
This research employs network analysis and visualisation to characterise the connections between Australian universities on Twitter.

Findings
A strong relationship to geography, both at the intra-state level and the inter-state level, was observed in the connections between Australian universities on Twitter. A relationship between number of followers and time since joining Twitter was also observed.

Research limitations/implications
The research presented is limited to Australian universities only and represents a snapshot in time only.

Practical implications
Australian universities have the opportunity to reach beyond the geographically restricted connections observed here, to actively seek new audiences, and to realise the cited benefits of online social media relating to increased connection across physical and digital frontiers. By capitalising on the strong ‘locality’ observed in social media connections, a university could become a desirable source of information that is likely to be of interest to, and valued by, local constituents.

Originality/value
This paper contributes to the research literature on university use of social media by addressing the so far largely silent area of inter-institutional connections via social media, and the influence of physical geography on the connections between universities on Twitter. It also offers a practical methodology for those interested in further research in this area.

Complex responses of birds to landscape-level fire extent, fire severity and environmental drivers

Aim: To quantify bird responses to a large unplanned fire, taking into consideration landscape-level fire severity and extent, pre-fire site detection frequency and environmental gradients. Location: South-eastern Australia. Methods: A major wildfire in 2009 coincided with a long-term study of birds and provided a rare opportunity to quantify bird responses to wildfire. Using hierarchical Bayesian analysis, we modelled bird species richness and the detection frequency of individual species in response to a suite of explanatory variables, including (1) landscape-level fire severity and extent (2) pre-fire detection frequency, (3) site-level vegetation density and (4) environmental variables (e.g. elevation and topography). Results: Landscape-level fire severity had strong effects on bird species richness and the detection frequency of the majority of bird species. These effects varied markedly between species; most responded negatively to amount of severely burned forest in the landscape, one negatively to the amount of moderately burned forest and one responded negatively to the total area of burned forest. Only one species - the Flame Robin - responded positively to the amount of burned forest. Relationships with landscape-scale fire extent changed over time for one species - the Brown Thornbill - with initially depressed rates of detection recovering after just 2 years. The majority of species were significantly more likely to be detected in burned areas if they have been recorded there prior to the fire. Main conclusions: Birds responded strongly to the severity and spatial extent of fire. They also exhibited strong site fidelity even after severe wildfire which causes profound changes in vegetation cover - a response likely influenced by environmental features such as elevation and topography.

Regional drivers of clutch loss reveal important trade-offs for beach-nesting birds

Coastal birds are critical ecosystem constituents on sandy shores, yet are threatened by depressed reproductive success resulting from direct and indirect anthropogenic and natural pressures. Few studies examine clutch fate across the wide range of environments experienced by birds; instead, most focus at the small site scale. We examine survival of model shorebird clutches as an index of true clutch survival at a regional scale (∼200 km), encompassing a variety of geomorphologies, predator communities, and human use regimes in southeast Queensland, Australia. Of the 132 model nests deployed and monitored with cameras, 45 (34%) survived the experimental exposure period. Thirty-five (27%) were lost to flooding, 32 (24%) were depredated, nine (7%) buried by sand, seven (5%) destroyed by people, three (2%) failed by unknown causes, and one (1%) was destroyed by a dog. Clutch fate differed substantially among regions, particularly with respect to losses from flooding and predation. ‘Topographic’ exposure was the main driver of mortality of nests placed close to the drift line near the base of dunes, which were lost to waves (particularly during storms) and to a lesser extent depredation. Predators determined the fate of clutches not lost to waves, with the depredation probability largely influenced by region. Depredation probability declined as nests were backed by higher dunes and were placed closer to vegetation. This study emphasizes the scale at which clutch fate and survival varies within a regional context, the prominence of corvids as egg predators, the significant role of flooding as a source of nest loss, and the multiple trade-offs faced by beach-nesting birds and those that manage them.

Time since urbanization but not encephalisation is associated with increased tolerance of human proximity in birds

The examination of links between a high degree of encephalisation (i.e., a large brain mass relative to body size) and the capacity of wildlife to inhabit anthropogenic habitats has formed the basis of several recent studies, although typically they have not uncovered any relationship. It, however, remains unclear whether encephalisation is directly related to a species' capacity to develop tolerance to human proximity (i.e., a reduction in response to approaching humans). It is also unknown whether such a relationship is related to the size of specific areas of the brain. Using published data on flight-initiation distance (FID), the distance at which animals flee from an approaching human, we estimate the degree of tolerance of human proximity for 42 bird species by comparing FIDs in urban and rural areas, with relatively high and low exposure to humans, respectively. We used a phylogenetic, comparative approach to analyse the relationship of degree of tolerance, and of FID in urban and rural populations more directly, to relative sizes of whole brains (42 species) and brain components (25 species) for the species, and examine the effect of the year that the bird species was first recorded in an urban area (year of urbanization). We demonstrate an interaction between bird habitat and year of urbanization on FIDs. Urban populations of species that have a longer history of inhabiting urban areas have lower FIDs (i.e., birds that were urbanized earlier are more tolerant), which may suggest local selection for birds with reduced responsiveness to humans in urban areas. The pattern is not seen in rural populations of the same species, providing additional evidence that it is greater exposure to humans that has resulted in this tolerance. While we found that forebrain mass and optic lobe mass are influential positive predictors of FID there was no indication that degree of tolerance itself was related to any brain size metric and hence no support for the idea that urban populations of species with larger brains are better able to habituate to human presence. This suggests that processes other than encephalisation explain the high degree of tolerance evident in urban-dwelling birds.