Abstract: The Cream-coloured Courser Cursorius cursor is a poorly known species inhabiting arid environments of the Western Palaearctic. The easternmost main islands of the Canary archipelago (Fuerteventura and Lanzarote, North Atlantic Ocean, Spain) harbour a stable population. The species showed an intense habitat selection pattern in these islands. Its probability of occurrence was highest in locations of relatively flat terrain (maximum slope steepness o11%), below 197m a.s.l., with scarce shrub cover less than 16%, and a rock cover less than 23%. Roads were the only human disturbance among those considered in the study (i.e., dirt tracks, urban developments, agriculture), having a clear negative effect on the occurrence of the Cream-coloured Courser. This paper highlights the importance of an issue deserving greater attention in future studies: fine-grained habitat features, which are not directly related to vegetation structure, but are relative to topographic and lithological traits, largely determine habitat selection of birds inhabiting arid environments.

Abstract: This paper deals with the population size and the distribution pattern of the houbara bustard in Fuerteventura (the largest island occupied by the species in the Canary archipelago), and analyzes its habitat use according to topographic, soil, vegetation and human impact variables. We employ distance sampling on 1471 (early spring) and 602 (summer) 500-m transects and measure habitat characteristics within the transects. Topographic and anthropic features are the main determinants of the habitat use of the species, while other descriptors related to vegetation structure play a minor role in its habitat preferences. The slope of the terrain is the most important habitat feature constraining the occurrence of the houbara bustard. The proximity of urban areas, the density of paved roads and rural tracks, and the extension of agricultural fields also adversely influence its distribution pattern in Fuerteventura. These habitat patterns do not change between summer and early spring considering the whole population of the species. Population size is estimated at 177 birds for the whole Fuerteventura island during the breeding season (90% confidence interval: 108 � 258 birds). Only five areas comprising 247 km2 include 80.8% of the total population in this island.

Abstract: Aim To explore the determinants of island occupancy of 48 terrestrial bird species in an oceanic archipelago, accounting for ecological components while controlling for phylogenetic effects. Location The seven main islands of the Canary archipelago. Methods We obtained field data on density, habitat breadth and landscape distribution in Tenerife, Fuerteventura and La Palma, trying to sample the whole availability of habitats and the gradient of altitudes. A total number of 1,715 line transects of 0.5 km were carried out in these islands during the breeding season. We also reviewed the literature for data on occupancy, the distance between the Canary Islands and the nearest distribution border in the mainland, body size and endemicity of the 48 terrestrial bird species studied. Phylogenetic eigenvector regression was used to quantify (and to control for) the amount of phylogenetic signal. Results The two measurements of occupancy (number of occupied islands or 10x10 km UTM squares) were tightly correlated and produced very similar results. The occupancy of the terrestrial birds of the Canary Islands during the breeding season had a very low phylogenetic effect. Species with broader habitat breadth, more intense preferences for urban environments, smaller body size, and lower degree of endemicity of the Canary Islands had a broader geographical distribution in the archipelago, occupying a larger number of different islands and 10x10 UTM squares. Main conclusions The habitat generalist species with a tolerance for novel urban environments tend to be present at more islands (or to occupy more area), while largesized species that have genetically differentiated within the islands are less widespread. Therefore, at least part of the range of a species is determined from basic biological features and is irrespective of human alterations. The positive relationship with local abundance, previously uncovered in continental studies, was not found, probably because it relies on free dispersal on continuous landmasses that may be short-circuited in real islands scenarios.

Abstract: 1. Aim Animal monitoring programs have allowed analyses of population trends, most of which recently comment on the possible effect of global climate change. However, the relationship between the interspecific variation in population trends and species� traits such as habitat preferences, niche breadth or distribution patterns have received little attention, in spite of its usefulness in the construction of ecological generalizations. The objectives of this study were to (1) determine whether there are characteristics shared among species with upwards or downwards trends, and (2) assess whether population changes agree with what could be expected under global warming (a decrease of species typical of cooler environments). 2. Location The Spanish part of the Iberian Peninsula (ca. 500,000 km2) in the south-western part of the Mediterranean Basin. 3. Methods We modelled recent breeding population changes (1996-2004), in areas without aparent land use changes, for fifty-seven common passerine birds with species-specific ecological and distributional patterns as explanatory variables. 4. Results One-half of these species have shown a generalized pattern towards the increase of their populations, while only one-tenth showed a significant decrease. One half (54%) of the interspecific variability in yearly population trends is explained considering species-specific traits. Species showing more marked increases preferred wooded habitats, were habitat generalists and occupied warmer and wetter areas, while moderate decreases were found for open country habitats living in drier areas. 5. Main conclusions The coherent pattern in population trends we found disagree with the proposed detrimental effect of global warming on bird populations of Western Europe, which is expected to be more intense in bird species inhabiting cooler areas and habitats. Such pattern suggests that factors other than the increase in temperature may be brought to discussions on global change as relevant components to explain recent changes in biodiversity.

Abstract: The environmental temperature and the level of body reserves have been described as important regulating factors of the amount of energy used at resting (i.e. nocturnal body mass loss). However, because these variables are associated in natural conditions, previous studies have not made a clear distinction between the separate effect of ambient temperature and body reserves on nightly energy management. To investigate whether ambient temperature acts as a proximate factor on nocturnal body mass regulation in captive coal tits (Periparus ater), the day-to-day and day-to-night changes in environmental temperatures were experimentally manipulated, under unrestricted food availability. The experiment was conducted within the normal autumn range of temperature variation in a mountain area of continental Mediterranean climate in Central Spain. Nocturnal body mass loss depended on the level of body mass at dusk and daily body-mass gain in the previous day. The largest rates of body mass loss at night were recorded when birds ended the previous day-time period with the highest levels of body reserves obtained after high rates of diurnal body mass increase. However, unpredictable changes in current environmental temperatures did not influence night body mass loss in the coal tit, as it would be expected following a pure physiological energetic balance. These results suggest that birds try to maintain body reserves within narrow ranges when some environmental factors, as the ambient temperature, become unpredictable.

Abstract: Urban developments and road networks extend their impacts on the surrounding habitats along a variable distance, affecting birds living in natural environments. This study identifies the threshold distances upon which several cities and roads, located across a large mosaic landscape of ca. 300 km2 in central Spain, alter the abundance patterns of the native avifauna. Total species richness, total bird abundance, and abundance of different guilds of birds which are potentially sensitive to human disturbances were modelled by means of tree regression analyzes. Nearby cities do not affect the total bird species richness in natural habitats of the study region. Total bird abundance increases near urban areas, mainly through its positive influence on urban-exploiter species. The effect of roads is negative and highly generalized, although threshold distances to roads vary among different groups of species. The bird communities of deciduous woodlands (ash groves, oak patches and poplars) show higher resilience to deletereous influences from nearby cities and roads. It would be desirable not to build new scattered urban developments within the remnant natural areas of this heavily fragmented region, because their existence and connection to the nearby cities by new roads would add �invisible� negative effects on the native bird fauna (e.g. on some threatened species from open habitats), considering the buffer distances determining most significant impacts (400m for urban areas, and 300m for roads).

Abstract: The effects of urban sprawl and the associated road network on patterns of land use by diurnal raptors were assessed in a extent mosaic landscape of Sierra de Guadarrama subjected to exurban development (Madrid province; Central Spain), within the buffer area of a planned national park. During three consecutive years, the sightings of raptors per 0.25 km2 were analyzed to identify their habitat preferences according to several vegetation types, urban cover and length of paved roads. Species richness increased with the amount of deciduous forests of Pyrenean oak Quercus pyrenaica and parklands of Narrow-leaved Ash Fraxinus angustifolia in lowland areas, while it decreased with cover of urban/suburban areas. Analyzing the three most abundant species separately, urban development had a negative influence on the Common Buzzard Buteo buteo and the Black Kite Milvus migrans, although positively affected the Booted Eagle Hieraaetus pennatus, probably through an increase in the availability of its potential prey within urban areas. This study did not find a negative influence of the road network, either considering total species richness or the three most abundant species separately. The current levels of urban development diminished the suitability of the study area for the raptor community overall (though particular species can be favoured), notably when residential sprawls are established over ash parklands traditionally devoted to cattle grazing.

Abstract: We analyzed changes in distribution and abundance of forest birds due to different types of recreational activity in the Madrid province (Guadarrama Range, Central Spain). Census plots were distributed in forest interiors (undisturbed sites), along forest trails (transiently disturbed hiking tracks), and in recreational areas (long-lasting disturbed picnic sites). Parameters describing the overall bird community (i.e. total bird abundance, species richness and diversity), groups of species (i.e. abundance of corvids and nesting or foraging guilds) and individual species abundances were compared. Forest sites with any type of human presence (trails and picnic sites pooled) had higher overall abundances and species richness per sampling plot than undisturbed forest interiors. Furthermore, fourteen species were significantly more abundant in disturbed sites than in forest interiors, while the converse was true only for five species. Anthropogenic sites did not affect forest specialists. Canopy-nesters, trunk and ground-foragers, and corvids were more abundant at recreational sites than in undisturbed forests, while the converse pattern was observed for ground-nesters. These patterns were more distinct in deciduous than in coniferous forest tracts. The positive effects of recreational sites were mostly associated with picnic sites, since forest trails were mostly indistinguishable from undisturbed forest interiors in terms of bird community patterns. Several habitat characteristics of disturbed sites can explain some of these differences: increased maturity of the tree layer, less dense subcanopy vegetation, higher abundance of holes and crevices, and greater predictability and availability of human food waste in picnic areas. So, contrary to expectations, we conclude that these types of nonconsumptive recreation do not decrease habitat suitability for most birds, although it might decrease suitability for ground-nesting birds.

Abstract: Amphibian species are declining at an alarming rate on a global scale in large part due to an infectious disease caused by the chytridiomycete fungus, Batrachochytrium dendrobatidis. This pathogen of amphibians has recently emerged within Europe, but knowledge of its widespread effects on amphibian assemblages remains poor. Importantly, little is known about the environmental envelope that is associated with chytridiomycosis in Europe, and the potential for climate change to drive future disease dynamics. Here, we use long-term observations on amphibian population dynamics in the Peñalara Natural Park, Spain, to investigate the link between climate-change and chytridiomycosis. Our analysis shows a significant association between local climatic variables and the occurrence of chytridiomycosis within this region. Specifically, we show that rising temperature and humidity are linked to the occurrence of chytrid-related disease, and that these local variables are driven by general circulation patterns, such as the North Atlantic oscillation. Given that the chytrid is known to be broadly distributed across Europe, there is now an urgent need to assess how climate-driven epidemics are expected to impact on amphibian species across the wider region.

Abstract: 1. Cyclic daily fattening routines are very common in wintering small wild birds, and are thought to be the consequence of a trade-off between different environmental and intrinsic factors. According to theory, these trajectories should range from accelerated (i.e. mass increases exponentially towards dusk) when mass-dependent costs are the most important cause of mortality, to decelerated (i.e. the rate of mass gain is highest at dawn and decreases afterward) when starvation is the greater risk. 2. We examine if geographically separate populations of coal tits, wintering in Scotland and Central Spain under contrasting photoperiods, show differences in their strategies of daily mass regulation. We describe population differences in wild birds under natural conditions, and experimentally search for intrinsic interpopulation variation in diurnal body mass increase under common, manipulated, photoperiod conditions (9 h Light:15 h Dark vs 7L:17D) , controlling for temperature, food availability, predator pressure and foraging arena. 3. Winter diurnal mass gain of wild coal tits was more delayed towards the latter part of the daylight period in Central Spain (i.e., the locality with longer winter days) than in Scotland. In both localities, the pattern was linked to the average mass at dawn, with mass increasing more rapidly in lighter birds. However, under the controlled photoperiod situation the pattern of daily mass gain was similar in both populations. Diurnal body mass gain was more accelerated at the end of the day, and the increase in body mass in the first hour of the day was considerably lower under the long (9 hours) than under the short (7 hours) photoperiod in both populations. 4. Wintering coal tits show patterns of mass gain through the day that are compatible with current theories of the costs and benefits of fat storage, with birds at lower latitudes (with longer winter days) having a greater tendency to delay mass gain until late in the day. The experimental study revealed that these patterns are plastic, with birds responding directly to the photoperiod that they experience, suggesting that they are continually making fine-scale adjustments to energy reserves on the basis of both intrinsic (e.g. state-dependent) and extrinsic cues.

Abstract: Aims: To study the habitat features affecting the risk of nest predation of birds nesting on the ground or the shrub layer in pyrenean oakwood forests of central Spain, and the variation across different forest areas. Location: Four pyrenean oak Quercus pyrenaica forests in the Sistema Central (Madrid, Spain). Methods: Estimation of predation rates of artificial wicker nests baited with two quail eggs in four oakwood sites spanning over 700 km2. Predation rates of individual nests were related, by means of generalized logistic regression models, to different forest locations, habitat features in nest surroundings, and shrub species characteristics where artificial nests were placed. Results: Variation in predation pressure was explainable to a low extent by predictor variables (less than 33 % of the original deviance). The most remarkable differences in predation pressure were attributable to forest location. Predation risk of artificial nests placed on shrubs decreased with the development of the shrub layer around the nests, and increased in places with a high density of young trees and a large cover of the herbaceous layer. Shrub characteristics related to the probable accessibility of nests did not influence predation risk. Conclusions: This study demonstrates a small effect of habitat structure of the nest surroundings on the predation risk of nests placed on the ground or shrubs within pyrenean oakwood areas. A trend towards a lower predation pressure was observed in areas with less immature trees and a large shrub cover 10 m around the shrub nests. However, forest tracts where the nests were placed largely determined the predation risk they suffered to an extent not directly associated with habitat structure.

Abstract: Bird fauna of the Madrid province (Central Spain) was analyzed according to urban development in a landscape mosaic of 700 km2. Bird distribution and abundance was studied in urban versus several rural habitats and along a gradient of urban typologies. By means of tree regression analyses we identified the most important habitat structure variables affecting bird species richness and density in urban environments. Bird communities in urban environments were globally less diverse and had higher densities than any natural habitat of the study region. The number of urban-avoider species (n = 37) was greater than the number of species favoured by urban habitats (n = 8). Current housing developments of extense crowded terraced-houses, with shortage of gardens, supported the least diverse and dense bird populations. Nevertheless, differences in bird species abundance between urban and natural habitats mitigated in many species when considering the older gardened developments. The plots with the highest species richness (average of 14.5 spp./0.8 ha) were those with 15�28% of building cover, more than 43 medium-sized trees/ha (10�30 cm dbh), and 13�54 small trees/ha (less than 10 cm dbh). Subsequently, future land-use planning should stress the exclusion of urban developments from the most valuable habitats, such as open wooded valley areas devoted to cattle-grazing (mainly ash-groves), and the negative effect of dense, low-gardened housing developments.

Abstract: Theoretical and experimental evidence suggests that an increase in flight costs will cause a decrease in flight performance, and that birds should trade-off the benefits of body reserves to minimize these costs. However, an alternative strategy could be to avoid the dangers of starvation by increasing food intake, thereby maintaining body reserves, and/or decreasing flight activity to compensate for the greater per unit flight costs. To test the effect of increased flight costs on body mass regulation and on flying and feeding activity, we experimentally manipulated wing area in a free-ranging wintering population of coal tits (Parus ater), and in captive birds living in a less restrictive environment (large outdoor aviaries). In the field, there was a clear trend towards body mass decrease when wing area was experimentally reduced, although it was not homogeneous: heavier birds lost more weight than lighter birds as a consequence of an allometric increase in flying costs. However, the experimental reduction of wing area had a non-significant, negligible, effect on body mass in the aviaries. Flight and feeding frequency were significantly affected by the experimental reduction of wing area: birds flew less and ate more when wing area was reduced. Birds with higher wing loads decreased more markedly flying frequency when wing area was reduced. We suggest that the goal of small resident birds living in Mediterranean montane climate would be to maintain daily fat reserves within some narrow limits during autumn and winter, even under contrasting ecological conditions. Our results show a trade-off between wing area reduction and body mass (in the field) and a trade-off between wing area and flying frequency (in the aviaries), both mediated by allometric effects of body size.

Abstract: We identify autoecological traits of bird species that influence the accuracy of predictive models of species distribution based on census data obtained from stratified sampling. These models would serve as a complementary approach to the development of regional bird atlases. We model the winter bird abundance of 64 terrestrial bird species in 77 census plots in Central Spain (Madrid province), using regression tree analyses. The predicted distribution of species density derived from statistical models (birds/10 ha) was compared with the published relative abundances depicted by a very accurate regional atlas of wintering birds (birds observed per 10 h). Statistical models explained an average of 41.7% of the original deviance observed in the local bird distribution (range 19.6�79.3%). Significant associations between observed relative abundances (atlas data) and predicted average densities in 1·1 km squares within 10·10 km UTMs were attained for 44 out of 64 species. Interspecific discrepancies between predicted and observed distribution maps decreased with between-year constancy in regional bird distribution and the degree of ecological specialization of species. Therefore, statistical modeling using census localities allowed us to depict geographical variations in bird abundance that were similar to those in the quantitative atlas maps. Nevertheless, bird distributions derived from statistical models are less reproducible in some species than in others, depending on their autoecological traits.

Abstract: The conservation status of bird species of Comunidad de Madrid is analysed using the ecological breadth of the species, the distribution area, their habitat preferences, and maximum ecological densities in the region. The species which are less widely distributed in Madrid are characterized by their low maximum ecological densities, narrow habitat breadths, and limited distribution in the Iberian peninsular. Another component defining regional rarity shows that large-sized species tend to reach lower densities than small-sized birds. These two gradients of ecological rarity are closely associated with the current categories of threat status in Madrid, and allow the proposal and justification of possible modifications of the regional catalogue for 11 species.

Abstract: Aims:To analyze the environmental factors influencing the large-scale distribution of 17 breeding species of Turdidae in the Iberian Peninsula. To test the predictions of global climatic change and the hypothesis of �abundance centers� on the frequency of occurrence of these species within the Iberian Peninsula. Methods: The frequency of occurrence of each species in UTM squares of 10 x 10 km within blocks of 50 x 50 km was modeled by means of regression tree analyses using 26 geographic, climatological and land-use variables. Residuals of these models in each one of the 190 blocks of 50 x 50 km (i.e., distribution patterns in Iberia not related to autoecological-environmental preferences) were related to the distances to the European barycenter of each species. Results: The models summarizing the basic environmental preferences of the 17 species accounted for an average 78.3 % of variation in the frequency of occurrence within the Iberian Peninsula. There was a common selection for areas located at higher altitudes or in mountains, the avoidance of agricultural landscapes, and a tight relationship with climatic variables (especially insolation). The frequency of occurrence of the 17 turdid species in Spain was not markedly influenced by the distances to their European distribution barycenters. Conclusions: The large-scale distribution patterns of the 17 turdid species in the Iberian Peninsula can be adequately explained considering coarse-grained environmental variables. Climatic variables were highly influential, although their effects do not support current predictions on alteration of distribution patterns due to global warming. After controlling for autoecological-environmental preferences, the hypothesis of �centers of abundance� did not play any role in determining the distribution patterns in the Iberian Peninsula.

Abstract: We test the prediction that predation risk is a foraging cost affecting the spatial distribution of birds within habitat. The work was carried out in a montane mixed forest of Central Spain with four Parus species, the Long-tailed tit (Aegithalos caudatus) and the Nuthatch (Sitta europaea). Using specially designed feeders containing the same amount and kind of food, we control for interspecific differences in food preferences and in foraging postures related to ecomorphological constraints, and for differences in natural food availability among foraging substrata. Small tree gleaning passerines avoided feeding on dark inner forest places far from edges, distant from protective cover, outside the tree canopy and near the ground; they preferred deciduous, relatively clear forest plots. These effects remained invariable across years and weather conditions. There was a common pattern of selection of foraging locations by the four Parus species: distance to cover (negatively), and height above ground and over the lowest branches of the tree canopy (positively) markedly determined the use of feeding places. According to these patterns, the vigilance proportion of species was significantly higher when feeding far from cover than when birds were feeding near pine foliage. This pattern was also common for the four studied Parus species. Nevertheless, the interspecific dominance hierarchy of the species was negatively correlated with the use of the most exposed feeders (feeders nearer the ground and more distant from cover and below the lower branches of tree canopy), being the converse with the safest ones. Therefore, the results of this paper demonstrate that the selection of feeding locations within habitat follows a pattern minimizing predation risk. Interspecific dominance hyerarchies can lead to the exploitation of unfavourable risky patches by subordinate species.

Abstract: Aims:To quantify the population size and the distribution patterns of the houbara bustard (Chlamydotis undulata fuertaventurae) in Lanzarote and La Graciosa islands (Canary Islands). To analyze habitat preferences of the species according to topographic, soil, vegetation and human impact variables. Location: Lanzarote and La Graciosa islands (Canary Islands). Methods: Bird censuses using the line transect method and the estimation of detection probabilities. Bootstrap to calculate the confidence interval of population size estimations. Classification trees were used to analyze the effect of habitat descriptors on bird species occurrence in 671 0.5 km-transects. Results: The population size of the houbara bustard was 500 birds (90 % confidence interval: 272- 801) in Lanzarote and 6 birds (3 - 10) in La Graciosa. The average density in the occupied semiarid environments was 1.63 birds/km2 in Lanzarote and 0.32 birds/km2 in La Graciosa. The maximum ecological density recorded was 3 birds/km2. The most important areas for the species were the steppe plains of Famara- Soo-Zonzamas, Guatiza and Teguise (202 km2), where 85 % of the whole population of Lanzarote is included. Slope of the terrain, rock cover on the ground and the density of roads and unpaved tracks had a highly negative influence on the habitat preferences of the houbara bustard. The probability of occurrence of the species increased as the distance to the nearest urban area also increased. Habitat descriptors related to vegetation structure played a minor role in the distribution of the houbara bustard. Conclusions: According to the data provided by this paper, and those previously published in 1990 decade, the population of houbara bustard in Lanzarote has shown a 40 % increase in the last 10-15 years. Only 20 % of this population is included in protected areas. The density of the species in Lanzarote is the highest recorded in the whole geographic range of the species in northern Africa and central Asia. Although the species has a favourable protection status in Lanzarote and La Graciosa, conservation efforts should be reinforced in order to preserve semiarid grasslands and shrublands with a steepness of the terrain lower than 15 %, a rock cover less than 60 %, a low density of roads and tracks (less than 0.5 km/20 ha) and away from urban sprawls (at least further than 650 m).

Abstract: The influence of habitat structure and abiotic factors on winter bird distribution was studied at the within-habitat level, in the montane Pyrenean oakwoods of Central Spain. Abiotic factors associated with thermal stress were estimated considering altitude and solar radiation received by woodlands (calculated by the steepness and orientation of the terrain). This paper demonstrates the great importance of abiotic factors influencing bird distribution. Several bird community parameters related to density and species richness decreased with altitude while they increased with radiation incidence of oakwood plots (i.e., birds avoided northern orientations where solar radiation is minimal in winter). The most important habitat structure variables related to bird distribution were the density of young and mature oaks. A thick undergrowth of thin oaks negatively influenced total bird abundance and species richness, and the number of species of the ground searchers guild. Conversely, oak maturity played a positive role on total bird density and species richness, and on the number of species of tree canopy gleaners and trunk foragers. Bird density and species richness were worse explained by general linear regression analyses than by tree regression models considering complex interactions between variables. To enhance winter survival and habitat suitability for birds, forest management in these mediterranean endemic oakwoods should preserve the maturest forests at lower altitudes exposed to the south.

Abstract: Aims :To investigate the sources of spatial bias in the bird records of Catalonia from 1900 to 2002, with the aim of providing generalized recommendations for using other databases, and setting up broad inventory projects. The paper examines the influence of environmental variables, human distribution and ornithological preferences of birdwatchers on past avian sampling effort in Catalonia, a contrasting region in the north east of Spain. Location: Catalonia (Spain). Methods: The relationship between time (field days) devoted to sampling birds in 10 x 10 Km UTM squares (from the records of VertebraCat database, across 5 study periods from 1900 to 2002) and a set of environmental, human distribution and bird species richness variables was analysed. These relationships were analyzed by means of Partial Least Squares Regression (PLSR) and multiple regression analyses. Results: A partial least squares regression analysis accounted for 39.4 % of the spatial variation in time devoted to avian sampling per UTM 10 x 10 km square in the most recent (1983 - 2002) period. The major pattern shows that large visit frequencies were mainly associated with coastal areas with a large cover of wetlands, marshes and sand dunes, high human population density, dense transportation, and also high covers of irrigated croplands, urban and industrial environments. Another group of highly visited UTM squares was also covered with a large surface of protected areas, mostly located in mountainous Catalonian sectors, as opposed to those UTM squares in lowland areas mainly covered by non-irrigated extensive croplands. Catalonian ornithologists and birdwatchers also showed an uneven preference for different groups of bird species, as they mainly relied on migratory and endangered species. Conclusions: The illustrated biased pattern of ornithological field work in Catalonia casts doubts about the usefulness of biodiversity indices obtainable from databases of observation records without a randomstratified sampling approach. However, these problems might be overcome by including a variable of sampling bias such as the number of records or days of field work.

Abstract: 1. Land owners in some European Mediterranean regions receive subsidies to thin dense maquis. This practice consists in the elimination of most shrubs and saplings and the pruning of the tallest trees to favour more opened woodland stands. We investigated how this practice affects the structure of bird communities. 2. We designed a large scale �natural experiment� that included 21 paired thinned and un-thinned maquis stands in Central Spain. Every stand was sampled by means of 5 point counts, each consisting of a 50-m radius plot, in two consecutive years and in winter and spring. The vegetation structure was characterized after bird censuses in 10-m radius plots that coincided with the centers of the bird point counts. Data analyses were based on repeated-measures ANOVAs. 3. Thinning was responsible for a significant increase in species richness, but did not have any effect on total bird density. Average body mass of species in thinned stands was significantly larger than in un-thinned, more densely vegetated, stands. Density of ground searchers was undistinguishable in thinned and in un-thinned stands, whereas density of foliage gleaners was higher in un-thinned stands. Winter density of granivorous species was marginally higher in thinned stands, whereas insectivorous and frugivorous species were marginally more abundant in un-thinned stands. 4. Thinned areas allow the occupation with higher densities of bird species whose European conservation status is of higher concern. Winter density of game birds was higher in thinned stands. 5. Synthesis and application. This is the first time that a large-scale experimental manipulation of habitat structure and vegetation volume demonstrates the predicted allometric effect of habitat structural complexity on the average body mass of a bird community. Thinning of dense Mediterranean woodland enhances habitat heterogeneity and suitability for several bird species and increased species richness. This practice was also beneficial for species of conservation concern and the hunting of non-threatened game birds. However, some un-thinned patches should be preserved to provide refuge for the few species that are impacted by thinning.

Abstract: Bird distribution and abundance are described and analyzed in Teneriffe (Canary Islands). Inter� habitat differences in density, diversity and species richness are shown in table 1. Figure 2 shows the main determinants of bird species richness in Teneriffe, and tables 2 and 3 and figure 3 show the species�specific patterns of spatial variation abundance (more detailed for Anthus berthelotii, Fringilla coelebs canariensis, Fringilla teydea, Parus caeruleus teneriffae, Phylloscopus canariensis, Regulus teneriffae, Serinus canarius and Turdus merula cabrerae). Deeply transformed environments due to human impact (urban habitats, agricultural mosaics, banana plantations) have high bird densities and species richness, even higher than those measured in native, unmodified habitats such as laurel forests or mature pinewoods. Urban environments in Teneriffe are very permeable to native bird fauna, as they have been occupied by many widespread endemic species/subspecies. Many of the endemic, well defined species or subspecies of island birds have high population densities within native, untransformed habitats. Density compensation and niche expansion is not a common phenomenon in the avifauna of Teneriffe. Nevertheless, all species/subspecies broadening the inter�habitat or altitudinal distribution are endemic of the Canary Islands.

Abstract: We analyzed the variation in island bird communities of urban environments related to habitat characteristics, using regression/classification tree analyses. Data from field censuses in cities/towns representing the urban heterogeneity of the whole island were obtained in Tenerife (Canary Islands, Spain). Urban bird abundance in Tenerife was negatively affected by altitude and the cover of dry Euphorbia shrubs and positively influenced by the height and cover of the tree layer. Species richness was negatively associated with building cover and positively related to tree height and altitude. Data from field censuses in Tenerife were compared with that of similar urban environments in the mainland (Madrid Province, central Spain). Species diversity was higher in the urban sample of Tenerife than in that of Madrid and the proportion of bird species from the regional pool �captured� by urban environments was higher in the island than in the mainland. Nine native species and three alien species were more abundant in island urban environments than in the continent (densities, at least, 100% higher), the converse occurring for only five species. At a biogeographic scale, we conclude that the avifauna of Tenerife Island is more prone to occupy a new artificial environment than the mainland bird fauna of central Spain.

Abstract: Although there is a wide range of empirical models applied to predict the distribution and abundance of organisms, we lack an understanding of which ecological characteristics of the species being predicted affect the accuracy of those models. However, if we knew the effect of specific traits on modelling results, we could both improve the sampling design for particular species and properly judge model performance. In this study, we first model spatial variation in winter bird density in a large region (Central Spain) applying regression trees to 64 species. Then we associate model accuracy to characteristics of species describing their habitat selection, environmental specialization, maximum densities in the study region, gregariousness, detectability and body size.Predictive power of models covaried with model characteristics (i.e., sample size) and autoecological traits of species, with 48% of interspecific variability being explained by two partial least regression components. There are species-specific characteristics constraining abundance forecasting that are rooted in the natural history of organisms. Controlling for the positive effect of prevalence, the better predicted species had high environmental specialization and reached higher maximum densities. We also detected a measurable positive effect of species detectability. Thus, generalist species and those locally scarce and inconspicuous are unlikely to be modelled with great accuracy. Our results suggest that the limitations caused by those species-specific traits associated with survey work (e.g., conspicuousness, gregariousness or maximum ecological densities) will be difficult to circumvent by either statistical approaches or increasing sampling effort while recording biodiversity in extensive programs.

Abstract: