Body size trends in a Holocene island bird assemblage

Despite the robust observation in macroecology that there are many small-bodied species, recent comparative studies have found little evidence for elevated net rates of diversification among small-bodied species within taxa. Here we examine the relationship between body size and species richness using the New Zealand land bird fauna, a well resolved palaeoecological Holocene assemblage. We test whether there is any evidence that net cladogenesis depended on body size in an assemblage prior to the impact of human-induced extinction. We also test whether net cladogenesis depends on the level at which taxa are endemic to New Zealand, to see whether there is evidence for bursts of cladogenesis following taxon establishment, and examine how the body sizes of New Zealand land birds relate to those in Australia, the most likely source pool for colonising taxa. Most New Zealand land bird species are small-bodied. We find no evidence, however, that this is due to higher net cladogenesis in small-bodied taxa. The body mass distributions of endemic and recent colonist species do not differ statistically, but recent colonists tend to be smaller-bodied than their closest endemic relative. This tendency is more marked for small-bodied than large-bodied taxa. More endemic taxa do not tend to be more species rich in New Zealand, although there is a positive relationship between level of endemism and species richness for forest taxa. The body mass distribution of New Zealand birds is very similar to that for Australia. Body mass does not dictate the likelihood that a family has colonised New Zealand from Australia, but the number of species in the family does: it is the species rich Australian families that have successfully colonised. We discuss the implications of these results for the evolution of body size distributions, and for the "island rule" of body size evolution on islands.     

A meta-analysis of spatial relationships in species richness across taxa: Birds as indicators of wider biodiversity in temperate regions

AimIndicators are an important tool by which conservationists monitor biodiversity because resources and expertise needed to survey biodiversity in a more direct way are often lacking. We aim to examine the effectiveness of species richness in birds as an indicator of species richness in other taxa. Birds are perhaps the most widely monitored species group so it is important to understand whether they can act as surrogates for distribution and abundance of other taxa.MethodsWe use a meta-analytical approach to assess the effectiveness of birds as indicators of cross-taxonomic species richness on spatial data from terrestrial temperate studies.ResultsThe literature showed mixed results but, in general, species richness in birds only weakly reflected species richness in other taxa. On average 19% of the variation in total species richness in other taxa was explained by species richness in birds. This is marginally higher than results found in a previous meta-analysis of species richness correlations between all taxa. Birds were more effective at reflecting cross-taxa species richness in study areas that were dominated by agricultural mosaics or mixtures of habitat types; they were less effective in forests and grassland environments. Overall, birds were better at reflecting species richness in mammals than other taxa, and relationships were more effective at larger spatial scales.Main conclusionsSpecies richness in birds only weakly reflected that of other taxa. Birds might be most useful as indicators of spatial variation in wider biodiversity in relatively patchy environments and for taxa that have similar spatial requirements. Species richness is one of many potential metrics for measuring biodiversity. There is a need to assess whether temporal change in bird populations and assemblages, as opposed to spatial variation, reflects change in other taxa and to identify elements of biodiversity for which birds could be the most effective surrogates.     

Vocal plasticity in mallards: multiple signal changes in noise and the evolution of the Lombard effect in birds

Signal plasticity is a building block of complex animal communication systems. A particular form of signal plasticity is the Lombard effect, in which a signaler increases its vocal amplitude in response to an increase in the background noise. The Lombard effect is a basic mechanism for communication in noise that is well‐studied in human speech and which has also been reported in other mammals and several bird species. Sometimes, but not always, the Lombard effect is accompanied by additional changes in signal parameters. However, the evolution of the Lombard effect and related vocal adjustments in birds are still unclear because so far only three major avian clades have been studied. We report the first evidence for the Lombard effect in an anseriform bird, the mallard Anas platyrhynchos. In association with the Lombard effect, the fifteen ducklings in our experiment also increased the peak frequency of their calls in noise. However, they did not change the duration of call syllables or their call rates as has been found in other bird species. Our findings support the notion that all extant birds use the Lombard effect to solve the common problem of maintaining communication in noise, i.e. it is an ancestral trait shared among all living avian taxa, which means that it has evolved more than 70 million yr ago. At the same time, our data suggest that parameter changes associated with the Lombard effect follow more complex patterns, with marked differences between taxa, some of which might be related to proximate constraints.     

Woody plants and the prediction of climate-change impacts on bird diversity

Current methods of assessing climate-induced shifts of species distributions rarely account for species interactions and usually ignore potential differences in response times of interacting taxa to climate change. Here, we used species-richness data from 1005 breeding bird and 1417 woody plant species in Kenya and employed model-averaged coefficients from regression models and median climatic forecasts assembled across 15 climate-change scenarios to predict bird species richness under climate change. Forecasts assuming an instantaneous response of woody plants and birds to climate change suggested increases in future bird species richness across most of Kenya whereas forecasts assuming strongly lagged woody plant responses to climate change indicated a reversed trend, i.e. reduced bird species richness. Uncertainties in predictions of future bird species richness were geographically structured, mainly owing to uncertainties in projected precipitation changes. We conclude that assessments of future species responses to climate change are very sensitive to current uncertainties in regional climate-change projections, and to the inclusion or not of time-lagged interacting taxa. We expect even stronger effects for more specialized plant–animal associations. Given the slow response time of woody plant distributions to climate change, current estimates of future biodiversity of many animal taxa may be both biased and too optimistic.     

Does polymorphism predict physiological connectedness? A test using two encrusting bryozoans

A colonial lifestyle necessitates communication between colony members to coordinate functions and enable resource sharing through physiological integration. Colonial integration is predicted to increase with both the size of the colony and the level of specialization (polymorphism). In modular colonies, although integration might be reflected in structural characteristics such as module spacing or branching patterns, physiological integration is fundamentally dependent on the level of connectedness between modules. In cheilostome bryozoans, funicular tissue links adjacent zooids through pores within zooid walls and is the most likely means of nutrient transport within colonies. We sought to determine whether the relative numbers of pores (septulae) and pore plates (septal chambers) per zooid differed across colony regions in a monomorphic species, Watersipora subtorquata, and one showing some polymorphism, Mucropetraliella ellerii. Within each species, the morphology of pore plates corresponded to functional predictions based on their position within the zooid, and connection numbers per zooid increased with colony size. Contrary to expectations, however, the more complex species, M. ellerii, had significantly fewer porous connections per zooid than W. subtorquata. Physiological connectedness was therefore not predicted by simple assessment of polymorphism in these species and may not be sufficient to infer colonial integration in related taxa.     

Geographical patterns of old and young species in African forest biota: the significance of specific montane areas as evolutionary centres

A widely accepted paradigm for speciation in tropical forests, the refuge theory, requires periodic habitat fragmentation driven by global climatic fluctuations to provide conditions for allopatric speciation. This implies that comparative species richness in refugia is due to loss of diverse communities in areas affected by climatic cycles. In this study we compare distribution patterns of bird and plant taxa which we consider to be of either deep phylogenetic lineages or recent radiations. It is demonstrated that lowland areas which have been postulated as Pleistocene refugia are dominated by species which represent lineages of pre-Pleistocene age. Since variations in species richness within these forest tracts reflect currently apparent environmental variables which might be considered to determine carrying capacity, we do not need to postulate that richness is the result of changes in forest cover in the past. Recently diversified taxa of plants and birds are found mainly at the periphery of the main rain forest blocks and in habitat islands outside them. Here, peak concentrations of young restricted-range species are often congruent with clusters of old and biogeographically relictual species. It is suggested that this reflects special intrinsic environmental properties of these areas, in the form of long-term environmental stability caused mainly by persistent orographic rain or mist. In this case, richness is not necessarily due to extinction outside these areas. Stability not only enables survival of relictual taxa, but also promotes morphological differentiation of radiating taxa, leading to aggregates of taxa of restricted distribution.     

The evolution of plumage polymorphism in birds of prey and owls: the apostatic selection hypothesis revisited

Co-evolution between phenotypic variation and other traits is of paramount importance for our understanding of the origin and maintenance of polymorphism in natural populations. We tested whether the evolution of plumage polymorphism in birds of prey and owls was supported by the apostatic selection hypothesis using ecological and life-history variables in birds of prey and owls and performing both cross taxa and independent contrast analyses. For both bird groups, we did not find any support for the apostatic selection hypothesis being the maintaining factor for the polymorphism: plumage polymorphism was not more common in taxa hunting avian or mammalian prey, nor in migratory species. In contrast, we found that polymorphism was related to variables such as sexual plumage dimorphism, population size and range size, as well as breeding altitude and breeding latitude. These results imply that the most likely evolutionary correlate of polymorphism in both bird groups is population size, different plumage morphs might simply arise in larger populations most likely because of a higher probability of mutations and then be maintained by sexual selection.     

The evolutionary transition to coloniality promotes higher blood parasitism in birds

Parasitism has been argued as one of the major costs of breeding sociality in birds. However, there is no clear evidence for an increased parasite pressure associated with the evolutionary transition from solitary to colonial breeding. I used the pairwise comparative method to test whether colonial bird species incur in a greater risk of infection and if they must to face with a greater diversity of blood parasites (Haematozoa), by comparing pairs of congeners that included one solitary and one colonial breeding species. The richness, both in terms of number of species and number of genera, as well as the prevalence of blood parasites resulted higher in colonial species than in their solitary breeding sisters, while controlling for differences in research effort and other potentially confounding effects. These results point towards higher transmission rates of blood parasites among colonial hosts. Given the detrimental effects of blood parasites on their host fitness, the higher risk of infection and the exposition to a more diverse parasite fauna may have imposed an important cost associated to the evolution of avian coloniality. This may help to explain why colonial species have larger immune system organs, as well as to explore differences in other host life history traits potentially shaped by blood parasites.     

A new species of shrike (Laniidae: Laniarius) from Somalia, verified by DNA sequence data from the only known individual

A new species of bush-shrike is described on the basis of the only known individual. The bird was captured in a disturbed Acacia thicket near the town of Bulo Burti by the Shabeelle River in central Somalia. Believed to represent a species near extinction, the bird was kept alive, studied in captivity and then released. The type material comprises moulted feathers, blood samples and DNA extracted from feather quills. For comparison, DNA from other bush-shrikes was obtained from old museum skins and three live birds. Comparisons of base sequences from the cyt-b gene of mitochondrial DNA support the judgement that the bird represents a full species and is not a colour morph or hybrid of examined taxa. This procedure confirms that, in situations where collecting is not desirable, tissue from live individuals can be used to define taxa, and for comparisons with DNA from museum specimens of other taxa.     

BIODIVERSITY RESEARCH: When is a species really extinct? Testing extinction inference from a sighting record to inform conservation assessment

Aim The global extinction of a species typically represents the end point in a series of population extinctions, during which unique evolutionary history is lost at every stage. Insight into the process of extinction can provide the means to identify species at high risk, but the number of extinctions being identified languishes far behind true totals. More proactive ways of inferring extinction from limited data are required. Location Historic sightings, collections and specimen data from Australia and Asia. Method We used a technique called optimal linear estimation to analyse the sightings record of mammal and bird species of varying ecology, life history and population demography. The mammal species chosen were all considered regionally extinct in the literature, while the bird species chosen had all been highlighted as candidates for the new IUCN Red List category flag: Critically Endangered (Possibly Extinct). Results Nine of the ten mammal species were predicted to be probably extinct, but only two with 95% certainty. Seven of the ten bird species were predicted to be probably extinct, four with 95% certainty. Main conclusions Superficially, determining whether a species is extinct might seem a simple task, whereby we either find a species extant, or it is extinct. In reality, however, the task is much more complex. Techniques such as optimal linear estimation, in combination with other data sources, and knowledge of recording effort, may prove useful in inferring extinction across a variety of taxa but should not be used in isolation.     

Phylogeny of the colonial green flagellates: a study of 18S and 26S rRNA sequence data.

A study of phylogenetic relationships of the colonial green algal flagellates based on nuclear 18S and 26S rRNA sequence data suggests that the colonial habit has had at least two independent origins. All colonial taxa included in the analysis, except Stephanosphaera, are allied in a clade with Chlamydomonas reinhardtii and other Chlamydomonas taxa ascribed to the Euchlamydomonas group by Ettl. In contrast, Stephanosphaera is allied with other unicellular flagellates including Haematococcus. Comparison of the 18S and 26S data shows that the two sets of data yield different results following cladistic analysis. The 18S data provide the principal signal that supports the more basal divergences, but the data do not unambiguously address relationships among taxa in the clade that includes most colonial flagellates and Chlamydomonas taxa representative of the Euchlamydomonas group (sensu Ettl). In contrast, the 26S data have fewer informative sites that support basal divergences than the 18S data, but provide much of the signal that supports resolution of taxa in the colonial flagellate clade in an analysis of the combined 18S and 26S rRNA sequence data. Additional sequence data from the 26S molecule and additional taxa may reduce the topological ambiguity inferred from the sequence data for the colonial flagellates. Alternatively, an ancient and rapid radiation of taxa in the colonial lineage could account for the topological ambiguity. Despite some unresolved questions of relationships, cladistic analysis of the combined data sets provides some robustly supported concepts of evolution in these flagellates.     

The culture of bird conservation: Australian stakeholder values regarding iconic,flagship and rare birds

Iconic, flagship and rare threatened bird taxa attract disproportionate amounts of public attention, and are often used to enable broader conservation strategies. Yet, little is known about why certain taxa achieve iconic or flagship status. Also unclear is whether the perception of rarity among those acting to conserve threatened birds is sufficient to influence attitudes and behaviour that lead to effective conservation action and, if so, which characteristics of rare birds are important to their conservation. We interviewed 74 threatened bird conservation stakeholders to explore perceptions about iconic, flagship and rare threatened birds and classified their attitudes using a new typology of avifaunal attitudes. There was a relationship between societal interest and conservation effort for threatened species characterised as iconic, flagship and rare. Iconic species tended to arouse interest or emotion in people due to being appealing and readily encountered, thereby attracting conservation interest that can benefit other biodiversity. Flagships tended to have distinguishing physical or cultural characteristics and were used to convey conservation messages about associated biodiversity. Attitudes about rarity mostly related to a taxon’s threatened status and small population size. Rarity was important for threatened bird conservation but not always associated with attitudes and behaviour that lead to effective conservation action. We conclude that conservation action for individual threatened bird taxa is biased and directly influenced by the ways taxa are socially constructed by stakeholders, which is specific to prevailing culture and stakeholder knowledge.     

The formation of “mega‐flocks” depends on vegetation structure in montane coniferous forests of Taiwan

A mixed‐species bird flock is a social assemblage where two or more bird species are moving together while foraging and might benefit from increased foraging efficiency and antipredator vigilance. A “mega‐flock,” which includes flocking species from different vegetation strata, often exhibits high species diversity. Mechanisms for the formation of mega‐flocks have not yet been explored. In this study, we evaluated the influence of vegetation structure and bird species diversity in driving the occurrence of mega‐flocks. We investigated the composition of mixed‐species flocks, local bird communities, and vegetation structure in five vegetation types of two high‐elevation sites in central Taiwan. Mega‐flocks occurred more frequently in pine woodland than later successional stages of coniferous forests. However, species richness/diversity of local bird communities increased along successional stages. Therefore, vegetation variables exhibit more influence on the occurrence of mega‐flocks than local bird communities. Besides foliage height diversity, understory coverage also showed positive effects on flock size of mixed‐species flocks. Our results indicated that pine woodlands with more evenly distributed vegetation layers could facilitate the interactions of canopy and understory flocks and increase the formation of mega‐flocks and thus the complexity of mixed‐species flocks.     

Changes in non-randomness in the expanding introduced avifauna of the world

The identities of bird species introduced to areas beyond the limits of their native geographic ranges have historically depended on a combination of societal demands for species with certain characteristics, and the availability of species for capture, transport and release. However, both societal demands and availability have changed over time, which should also change the characteristics of species more recently added to the list of introduced birds. Here, we quantify temporal changes in selectivity of introduced bird species by comparing the characteristics of 423 species listed in the seminal catalogue of introduced birds (Long, J. L. 1981 . Introduced birds of the world. – David and Charles, London) with those of 122 species that have been introduced but are not listed in Long (1981) . We demonstrate differences between these two groups of species in the frequencies with which different taxa are represented, in the geographic range sizes of species, and in their biogeographic regions of origin, but not in body mass. Both groups also differ from bird species in general in terms of geographic range sizes, body masses, and taxonomic composition. We relate the observed differences in the characteristics of species listed or unlisted in Long (1981) to changes in the changes in attitudes, legislation and vectors of transport relating to exotic species. We conclude by noting that the utility of published catalogues of introduced bird species is increasingly being eroded by the continued liberation and establishment of bird species.     

Angola’s central scarp forests: patterns of bird diversity and conservation threats

Despite Angola’s central scarp forests being recognised as a critical global priority for bird conservation, fine-scale information on threatened bird distributions and patterns of bird diversity are lacking. These data are essential to identify sites within the Western Angola Endemic Bird Area that should be targeted for conservation. First endemic and near-endemic species and subspecies, and species with isolated populations along the Angolan scarp were identified to highlight taxa of greatest priority for conservation and for use in studying the evolutionary origins of the region. Thereafter survey data collected during 2005 from 13 forest sites along the central scarp was analysed. These data show that there are three distinct bird communities across the width of the escarpment, each associated with a distinctive forest type. Of note is the finding that threatened and Near Threatened endemic species occur almost exclusively in the dry forests adjacent to the main escarpment, rather than in the moistest forests found on the main escarpment, which instead are richer in Congo Basin forest birds. Based on these data, summaries of ranges, populations and conservation threats are given for the seven most threatened bird species. Attention is drawn to threats to the habitats of greatest importance to these species. A conservation area network should be established that encompasses the full spectrum of bird diversity described, to ensure survival of current unique taxa and the future evolutionary potential of the area.     

Evidence for Convergent Evolution in Gape Morphology of the Bat Hawk (Macheiramphus alcinus) with Swifts,Swallows, and Goatsuckers

Gape morphology has been linked to feeding and breeding ecology in raptors, according to the ingestion rate hypothesis. Mammal feeding raptors have larger gapes, allowing them to ingest prey more rapidly than bird feeders, which have evolved smaller average body sizes and gapes to capture more agile prey. One highly derived raptor, however, the Bat Hawk (Macheiramphus alcinus), specializes on colonial bats and swiftlets concentrated daily in a limited temporal window by capturing and swallowing them whole in flight. We hypothesized that the gape of the Bat Hawk evolved to feed rapidly on agile vertebrates limited temporally. We predicted that the gape of the Bat Hawk would be significantly larger than the gape of other raptors, more closely resembling the gapes of swifts (Apodidae), swallows (Hirundinidae), and goatsuckers (Caprimulgiformes). We measured gape area of the lower mandible in museum specimens representing 138 bird species in six orders. We also compared gape area by prey type in over 100 raptor species in three orders. We predicted that insectivorous raptors would exhibit gapes similar to mammal feeders but would differ from bird feeders because insects are not agile prey. The Bat Hawk had the largest gape of any raptor and more closely resembled the gape of insectivorous birds, which also swallow prey whole in flight. The evolution of an enlarged gape may have permitted the Bat Hawk to exploit a previously unrealized ecological niche. Gapes of bird feeding raptors were smaller than in mammal and insect feeders, supporting the ingestion rate hypothesis.     

Relative influence of habitat heterogeneity, climate, human disturbance, and spatial structure on vertebrate species richness in Spain

Many factors affect the distribution of species richness. This study examines the relative influence of habitat heterogeneity, climate, human disturbance, and spatial structure on the species-richness distribution of terrestrial vertebrates (amphibians, reptiles, birds and mammals) in mainland Spain. The results indicate that spatial structure and environment exert similar influences on species richness. For all four taxa, species richness increases southward and northward, being lower in the center of the country, when controlled for other variables. This may be the result of a peninsular effect, as found in other studies, and reflect the importance of historical events on species richness in the Iberian Peninsula. Climate is more important than habitat heterogeneity in determining species richness. Temperature is positively correlated with amphibian, reptile, and bird species richness, while mammalian species richness is highest at intermediate temperatures. This effect is stronger in ectotherms than among endotherms, perhaps reflecting physiological differences. Precipitation positively correlates with bird and mammalian species richness, but has no effect on ectotherm species richness. Amphibian species richness increases with altitudinal range, and bird species richness with habitat diversity. Human population density is positively correlated with bird and mammalian species richness, but does not affect ectotherm species richness, while amphibian and bird species richness is highest at moderate levels of human land alteration (farmland). However, unexplained variance remains, and we discuss that the effects of environmental variables on species richness may vary geographically, causing different effects to be obscured on a national scale, diminishing the explanatory power of environmental variables.     

Conservation planning and viability: problems associated with identifying priority sites in Swaziland using species list data

Conservation planning assessments based on species atlas data are known to select planning units containing ecotones because these areas are relatively species‐rich. However, this richness is often dependent on the presence of adjoining core habitat, so populations within these ecotones might not be viable. This suggests that atlas data may also fail to distinguish between planning units that are highly transformed by agriculture or urbanization with those from neighbouring untransformed units. These highly transformed units could also be identified as priority sites, based solely on the presence of species that require adjoining habitat patches to persist. This potential problem was investigated using bird and mammal atlas data from Swaziland and a landcover map and found that: (i) there was no correlation between planning unit species richness and proportion of natural landcover for both taxa; (ii) the priority areas that were identified for both birds and mammals were no less transformed than if the units had been chosen at random and (iii) an approach that aimed to meet conservation targets and minimize transformation levels failed to identify more viable priority areas. This third result probably arose because 4.8% of the bird species and 22% of the mammal species were recorded in only one planning unit, reducing the opportunity to choose between units when aiming to represent each species. Therefore, it is suggested that using species lists to design protected area networks at a fine spatial scale may not conserve species effectively unless population viability data are explicitly included in the analysis.     

PARASITE VIRULENCE AND HOST IMMUNE DEFENSE: HOST IMMUNE RESPONSE IS RELATED TO NEST REUSE IN BIRDS

The evolution of parasite virulence has been hypothesized to be related to the mode of parasite transmission; horizontally transmitted parasites can afford to damage their hosts more than vertically transmitted parasites because increased virulence does not reduce the probability of transmission to new hosts. This relationship between mode of transmission and virulence would particularly select for improved immune defense in hosts that are subject to horizontally transmitted parasites. Among avian hosts, hole nesters and colonial nesters frequently reuse nest sites because of nest-site limitation, and this results in an increased frequency of horizontal transmission. Comparison of the size of two organs involved in the immune defense between pairs of bird species being either hole or open nesters, or colonially or solitarily nesting birds, respectively, revealed that the size of the bursa of Fabricius and the spleen were consistently larger in hole nesters than in open nesters, and similarly in colonially breeding bird species than in solitarily breeding species. These results support the hypothesis that mode of parasite transmission affects the evolution of immune defence in hosts.     

Distributions of forest birds and butterflies in the Andaman islands, Bay of Bengal: nested patterns and processes

The distributional patterns of forest birds and butterflies in the Andaman islands, an oceanic chain located off SE Asia, were tested for nestedness. Both taxa were highly nested. Nestedness could be due to colonization or extinction processes, area or distance effects or nestedness of habitats. Nestedness in forest bird distributions were strongly influenced by area and habitat related factors. Habitats were significantly nested in all three island groups, however most strongly for the North Andamans. However forest bird distributions in the North Andamans, as indicated by row order in the packed matrix, was not correlated with habitat diversity, suggesting that habitat related factors alone cannot account for these patterns. Other causal influences could be passive sampling, where common and abundant species and habitats are more likely to have a widespread distribution than rare species and habitats. The nested subset pattern seen in two unrelated taxa suggests that the Andamans are extinction dominated and that the protection of forests on large islands is critical for the conservation of its biodiversity.