Taxonomic and functional diversity of farmland bird communities across Europe:Effects of biogeography and agricultural intensification

In eight European study sites (in Spain, Ireland, Netherlands, Germany, Poland, Estonia and Sweden), abundance of breeding farmland bird territories was obtained from 500 × 500 m survey plots (30 per area, N = 240) using the mapping method. Two analyses were performed: (I) a Canonical Correspondence Analysis of species abundance in relation to geographical location and variables measuring agricultural intensification at field and farm level to identify significant intensification variables and to estimate the fractions of total variance in bird abundance explained by geography and agricultural intensification; (II) several taxonomic and functional community indices were built and analysed using GLM in relation to the intensification variables found significant in the CCA. The geographical location of study sites alone explains nearly one fifth (19. 5%) of total variation in species abundance. The fraction of variance explained by agricultural intensification alone is much smaller (4. 3%), although significant. The intersection explains nearly two fifths (37. 8%) of variance in species abundance. Community indices are negatively affected by correlates of intensification like farm size and yield, whereas correlates of habitat availability and quality have positive effects on taxonomic and functional diversity of assemblages. Most of the purely geographical variation in farmland bird assemblage composition is associated to Mediterranean steppe species, reflecting the bio-geographical singularity of that assemblage and reinforcing the need to preserve this community. Taxonomic and functional diversity of farmland bird communities are negatively affected by agricultural intensification and positively affected by increasing farmland habitat availability and quality. © 2011 Springer Science+Business Media B.V.

Effects of climate and land management changes on conservation : of mediterranean cork oak woodlands and their bird communities

Tese de doutoramento (co-tutela), Biologia (Biologia da Conservação), Faculdade de Ciências da Universidade de Lisboa, University of East Anglia, School of Environmental Sciences, 2014

Effects of Spruce Budworm (Choristoneura fumiferana (Clem.)) Outbreaks on Boreal Mixed-Wood Bird Communities

This study examined the influence of a spruce budworm (Choristoneura fumiferana (Clem.)) outbreak on a boreal mixed-wood bird community in forest stands ranging in age from 0 to 223 yr. We asked if (1) patterns of species response were consistent with the existence of spruce budworm specialists, i.e., species that respond in a stronger quantitative or qualitative way than other species; (2) the superabundance of food made it possible for species to expand their habitat use in age classes that were normally less used; and (3) the response to budworm was limited to specialists or was it more widespread. Results here indicated that three species, specifically the Bay-breasted Warbler (Dendroica castanea), Tennessee Warbler (Vermivora peregrina), and Cape May Warbler (Dendroica tigrina), had a larger numerical response to the budworm outbreak. They responded with increases in density of up to tenfold over 4 or 5 yr. No other species responded with more than a twofold increase in the same time period. These species also showed a functional response by breeding more frequently in young stands aged 1–21 yr and intermediate stands aged 22–36 yr as budworm numbers increased. Our data also suggested that many species profited to a lesser extent from budworm outbreaks, but that this effect may be too subtle to detect in most studies. We found evidence of a positive numerical effect in at least 18 additional species in one or two stand-age categories but never in all three for any one species. Given the numerical response in many species and the potential influence of budworm on bird populations because of the vast extent of outbreaks, we believe that the population cycle of spruce budworm should be considered in any evaluation of population trends in eastern boreal birds.

Shifts in resident bird communities associated with cloud forest patch size in Central Veracruz, Mexico

Avian communities in cloud forests have high levels of endemism and are at major risk given the accelerated rate of habitat fragmentation. Nevertheless, the response of these communities to changes in fragment size remains poorly understood. We evaluated species richness, bird community density, community composition, and dominance as indicators of the response to fragment size in a fragmented cloud forest landscape in central Veracruz, Mexico. Medium-sized fragments had statistically higher than expected species richness and more even communities, which may be a reflection of the intermediate disturbance hypothesis, in which medium-sized fragments are exploited by both forest and disturbance-associated species. Bird density also reached higher values in medium-sized fragments, which may indicate a carrying capacity in this habitat. However, large cloud forest fragments had a distinct taxonomic and functional composition, attributable to an increased number of understory insectivore species and canopy frugivores. By comparison, omnivorous species associated with human-altered habitats were more abundant in smaller fragments. Hence, although medium-sized cloud forest fragments had higher species richness and high bird density, large forest tracts maintained a distinct avian community composition, particularly of insectivorous and frugivorous species. Furthermore, the underlying response to fragmentation can only be properly addressed when contrasting several community attributes, such as richness, density, composition, and species dominance. Therefore, cloud forest conservation should aim to preserve the remaining large forest fragments to maintain comprehensive avian communities and avoid local extinctions.

The structure of bird communities in areas revegetated after mining in southern Brazil

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of habitat and climate change on European bird communities

Die Fragmentierung von Waldgebieten, der Verlust geeigneter Habitate, die Invasion exotischer Arten und globale Klimaveränderung haben auf Artengemeinschaften erhebliche Auswirkungen. Vögel dienen in vielen Fällen als Indikatorarten für Umweltveränderungen und, besonders, für Veränderungen im Zusammenhang mit globaler Erwärmung. In meiner Arbeit habe ich zuerst einen Literaturüberblick über die Auswirkungen globaler Klimaveränderung auf die Verbreitungsgebiete, den Artenreichtum und die Zusammensetzung von Vogelgemeinschaften dargestellt. Zahlreiche Untersuchungen zeigen, daß die Grenzen der Verbreitungsgebiete der meisten Vogelarten mit klimatischen Faktoren korrelieren. Verschiebungen der Verbreitungsgebiete in nördliche Richtung oder in höhere Regionen im Gebirge konnten bereits für viele temperate Vogelarten beobachtet werden. Weiterhin wurde ein zunehmender Artenreichtum besonders in nördlichen Breiten und in höheren Lagen für viele temperate Vogelgemeinschaften vorhergesagt. In trockenen Gebieten ist dagegen mit einer Abnahme des Artenreichtums zu rechnen. Im zweiten Teil meiner Arbeit habe ich untersucht, ob beobachtete Veränderungen in der Zusammensetzung europäischer Vogelgemeinschaften tatsächlich durch aktuelle Klimaveränderungen beeinflußt werden. Das Zugverhalten der Arten war dabei ein Schwerpunkt der Untersuchung, weil zu erwarten war, daß Vogelarten mit verschiedenem Zugverhalten unterschiedlich auf Klimaveränderungen reagieren. Ich habe ein Regressionsmodell genutzt, welches die räumliche Beziehung zwischen dem Anteil von Langstreckenziehern, Kurzstreckenziehern und Standvögeln in europäischen Vogelgemeinschaften und verschiedenen Klimavariablen beschreibt. Für 21 Gebiete in Europa habe ich Daten über beobachtete Veränderungen in der Struktur der Vogelgemeinschaften und isochrone Klimaveränderungen zusammengetragen. Mit Hilfe dieser Klimaveränderungen und dem räumlichen Regressionsmodell konnte ich berechnen, welche Veränderungen in den Vogelgemeinschaften aufgrund der veränderten Klimabedingungen zu erwarten wären und sie mit beobachteten Veränderungen vergleichen. Beobachtete und berechnete Veränderungen korrelierten signifikant miteinander. Die beobachteten Veränderungen konnten nicht durch räumliche Autokorrelationseffekte oder durch alternative Faktoren, wie z.B. Veränderungen in der Landnutzung, erklärt werden. Im dritten Teil der Arbeit untersuchte ich für eine mitteleuropäische Vogelgemeinschaft welchen Einfluß Habitatveränderungen, die Invasion exotischer Arten und die Klimaveränderung auf Veränderungen der Häufigkeit und Verbreitungsgröße der 159 Vogelarten am Bodensee zwischen 1980-1981 und 2000-2002 hatten. Dabei konnte gezeigt werden, daß Veränderungen in der regionalen Abundanz sowohl durch Habitatveränderungen als auch durch Klimavänderungen hervorgerufen wurden. Exotische Arten schienen in dieser Zeit keinen bedeutenden Einfluß zu haben. Besonders bei Agrarlandarten, Arten mit nördlicheren Verbreitungsgebieten und bei Langstreckenziehern konnten signifikante Abnahmen in der Abundanz beobachtet werden. Vor allem die anhaltenden negativen Bestandsveränderungen bei Langstreckenziehern und die in den letzten zehn Jahren aufgetretenen Abnahmen nördlicher verbreiteter Vogelarten deuten darauf hin, daß die Klimaveränderung aktuell als der größte Einfluß für Vögel in Europa angesehen werden muß. Insgesamt zeigen die Ergebnisse dieser Arbeit, daß sich der anhaltende Druck auf die Umwelt in erster Linie durch Habitat- und Klimaveränderungen manifestiert.

Relationship between instream habitat characteristics, emergent insects, and riparian bird communities

Streams and riparian areas can be intricately connected via physical and biotic interactions that influence habitat conditions and supply resource subsidies between these ecosystems. Streambed characteristics such as the size of substrate particles influence the composition and the abundance of emergent aquatic insects, which can be an important resource for riparian breeding birds. We predict fine sediment abundance in small headwater streams directly affects the composition and number of emergent insects while it may indirectly affect riparian bird assemblages. Streams with abundant fine sediments that embed larger substrates should have lower emergence of large insects such as phemeroptera, Plecoptera and Trichoptera. Streams with lower emergent insect abundance are predicted to support fewer breeding birds and may lack certain bird species that specialize on aquatic insects. This study examined relationships between streambed characteristics, and emergent insects (composition, abundance and biomass), and riparian breeding birds (abundance and richness) along headwater streams of the Otter River Watershed. The stream bed habitats of seven stream reaches were characterized using longitudinal surveys. Malaise traps were deployed to sample emergent aquatic insects. Riparian breeding birds were surveyed using fixed-radius point-counts. Streams differed within a wide range of fine sediment abundances. Total emergent aquatic insect abundance increased as coverage by instream substrates increased in diameter, while bird community was unresponsive to insect or stream features. Knowledge of stream and riparian relationships is important for understanding of food webs in these ecosystems, and it is useful for riparian forest conservation and improving land-use management to reduce sediment pollution in these systems.

Distinct carbon sources indicate strong differentiation between tropical forest and farmland bird communities

The conversion of forest into farmland has resulted in mosaic landscapes in many parts of the tropics. From a conservation perspective, it is important to know whether tropical farmlands can buffer species loss caused by deforestation and how different functional groups of birds respond to land-use intensification. To test the degree of differentiation between farmland and forest bird communities across feeding guilds, we analyzed stable C and N isotopes in blood and claws of 101 bird species comprising four feeding guilds along a tropical forest-farmland gradient in Kenya. We additionally assessed the importance of farmland insectivores for pest control in C4 crops by using allometric relationships, C stable isotope ratios and estimates of bird species abundance. Species composition differed strongly between forest and farmland bird communities. Across seasons, forest birds primarily relied on C3 carbon sources, whereas many farmland birds also assimilated C4 carbon. While C sources of frugivores and omnivores did not differ between forest and farmland communities, insectivores used more C4 carbon in the farmland than in the forest. Granivores assimilated more C4 carbon than all other guilds in the farmland. We estimated that insectivorous farmland birds consumed at least 1,000 kg pest invertebrates km−2 year−1. We conclude that tropical forest and farmland understory bird communities are strongly separated and that tropical farmlands cannot compensate forest loss for insectivorous forest understory birds. In tropical farmlands, insectivorous bird species provide a quantitatively important contribution to pest control.

Temporal Changes in Randomness of Bird Communities across Central Europe

Many studies have examined whether communities are structured by random or deterministic processes, and both are likely to play a role, but relatively few studies have attempted to quantify the degree of randomness in species composition. We quantified, for the first time, the degree of randomness in forest bird communities based on an analysis of spatial autocorrelation in three regions of Germany. The compositional dissimilarity between pairs of forest patches was regressed against the distance between them. We then calculated the y-intercept of the curve, i.e. the ‘nugget’, which represents the compositional dissimilarity at zero spatial distance. We therefore assume, following similar work on plant communities, that this represents the degree of randomness in species composition. We then analysed how the degree of randomness in community composition varied over time and with forest management intensity, which we expected to reduce the importance of random processes by increasing the strength of environmental drivers. We found that a high portion of the bird community composition could be explained by chance (overall mean of 0.63), implying that most of the variation in local bird community composition is driven by stochastic processes. Forest management intensity did not consistently affect the mean degree of randomness in community composition, perhaps because the bird communities were relatively insensitive to management intensity. We found a high temporal variation in the degree of randomness, which may indicate temporal variation in assembly processes and in the importance of key environmental drivers. We conclude that the degree of randomness in community composition should be considered in bird community studies, and the high values we find may indicate that bird community composition is relatively hard to predict at the regional scale.

Higher temporal variability of forest breeding bird communities in fragmented landscapes

Understanding the relationship between animal community dynamics and landscape structure has become a priority for biodiversity conservation. In particular, predicting the effects of habitat destruction that confine species to networks of small patches is an important prerequisite to conservation plan development. Theoretical models that predict the occurrence of species in fragmented landscapes, and relationships between stability and diversity do exist. However, reliable empirical investigations of the dynamics of biodiversity have been prevented by differences in species detection probabilities among landscapes. Using long-term data sampled at a large spatial scale in conjunction with a capture-recapture approach, we developed estimates of parameters of community changes over a 22-year period for forest breeding birds in selected areas of the eastern United States. We show that forest fragmentation was associated not only with a reduced number of forest bird species, but also with increased temporal variability in the number of species. This higher temporal variability was associated with higher local extinction and turnover rates. These results have major conservation implications. Moreover, the approach used provides a practical tool for the study of the dynamics of biodiversity.

The influence of forest management on bird communities of portuguese montados

The world distribution of cork oak Quercus suber and holm oak Q. rotundifolia is basically restricted to the western Mediterranean basin. These two evergreen oaks are the base of the Portuguese montado and the Spanish dehesa. This thesis aims to analyse how bird communities of the montado are influenced by management practices. We used different approaches to study this relationship, and to evaluate which features are responsible for species distribution in different typologies of montado. First, we reviewed the concept of montado in order to better understand the system and to set thresholds on what can be considered as montado. Afterwards, we studied the elements that promote higher species diversity and individual species, or group of species, that can act as indicators of High Nature Value for montados. Finally, we evaluated how the bird communities are structured, and the influence of the main management actions (e.g. cattle and cork exploitation) on those communities; Resumo: A distribuição mundial do sobreiro Quercus suber e da azinheira Quercus rotundifolia é praticamente restrita à bacia do Mediterrâneo. Estas duas espécies de carvalhos são a base dos montados em Portugal e das dehesas em Espanha. No âmbito desta tese analisamos como as comunidades de aves do montado são influenciadas pela gestão florestal. Para este efeito usámos diferentes abordagens e avaliámos quais as características do montado responsáveis pela distribuição das espécies ao longo das suas diferentes tipologias. Fizemos uma revisão do conceito de montado e proposemos uma definição para o sistema, englobando a sua multifuncionalidade. Estudámos os elementos singulares que promovem a diversidade de aves e que podem ser simultaneamente indicadores de áreas de Alto Valor Natural (HNV). Por fim, avaliámos qual a influência da gestão (p. ex. pastoreio e descortiçamento) na estruturação das comunidades de aves.

Positive Relationships between Association Strength and Phenotypic Similarity Characterize the Assembly of Mixed-Species Bird Flocks Worldwide

Competition theory predicts that local communities should consist of species that are more dissimilar than expected by chance. We find a strikingly different pattern in a multicontinent data set (55 presence-absence matrices from 24 locations) on the composition of mixed-species bird flocks, which are important sub-units of local bird communities the world over. By using null models and randomization tests followed by meta-analysis, we find the association strengths of species in flocks to be strongly related to similarity in body size and foraging behavior and higher for congeneric compared with noncongeneric species pairs. Given the local spatial scales of our individual analyses, differences in the habitat preferences of species are unlikely to have caused these association patterns; the patterns observed are most likely the outcome of species interactions. Extending group-living and social-information-use theory to a heterospecific context, we discuss potential behavioral mechanisms that lead to positive interactions among similar species in flocks, as well as ways in which competition costs are reduced. Our findings highlight the need to consider positive interactions along with competition when seeking to explain community assembly.

Off-road sampling reveals a different grassland bird community than roadside sampling: implications for survey design and estimates to guide conservation

Grassland bird species continue to decline steeply across North America. Road-based surveys such as the North American Breeding Bird Survey (BBS) are often used to estimate trends and population sizes and to build species distribution models for grassland birds, although roadside survey counts may introduce bias in estimates because of differences in habitats along roadsides and in off-road surveys. We tested for differences in land cover composition and in the avian community on 21 roadside-based survey routes and in an equal number of adjacent off-road walking routes in the grasslands of southern Alberta, Canada. Off-road routes (n = 225 point counts) had more native grassland and short shrubs and less fallow land and road area than the roadside routes (n = 225 point counts). Consequently, 17 of the 39 bird species differed between the two route types in frequency of occurrence and relative abundance, measured using an indicator species analysis. Six species, including five obligate grassland species, were more prevalent at off-road sites; they included four species listed under the Canadian federal Species At Risk Act or listed by the Committee on the Status of Endangered Wildlife in Canada: Sprague’s Pipit (Anthus spragueii), Baird’s Sparrow (Ammodramus bairdii), the Chestnut-collared Longspur (Calcarius ornatus), and McCown’s Longspur (Rhynchophanes mccownii). The six species were as much as four times more abundant on off-road sites. Species more prevalent along roadside routes included common species and those typical of farmland and other human-modified habitats, e.g., the European Starling (Sturnus vulgaris), the Black-billed Magpie (Pica hudsonia), and the House Sparrow (Passer domesticus). Differences in avian community composition between roadside and off-road surveys suggest that the use of BBS data when generating population estimates or distribution models may overestimate certain common species and underestimate others of conservation concern. Our results highlight the need to develop appropriate corrections for bias in estimates derived from roadside sampling, and the need to design surveys that sample bird communities across a more representative cross-section of the landscape, both near and far from roads. 

Habitat associations and breeding bird community composition within the city of Bristol, UK

Capsule: Different urban breeding bird communities are associated with different habitat types, but, although community species diversity varies significantly, total bird density does not. Aims: To investigate the association between breeding bird communities and habitats within Bristol, UK and how these communities vary in terms of species diversity and total bird abundance. Methods: Breeding density data for 70 species in the metropolitan area of Bristol, UK were subjected to de-trended correspondence analysis to identify the number of different communities present and their indicator species. These data were then used to identify patterns of habitat association with each community and differences in species richness and total bird density. Results: Three communities were identified: a rural community associated with woodland, managed grassland and inland water; a suburban community associated with buildings and residential gardens; and an intermediate community that shared some of these habitat characteristics. Species richness, but not total bird abundance, was lowest in the suburban community. Conclusion: The diversity of species in urban areas appears to be most dependent upon the availability of patches of natural and semi-natural habitats. Residential gardens support fewer species, but those species that are present may be found at high densities.