Javier Seoane

The effects of land use and climate on red kite distribution in the Iberian peninsula

The main breeding populations of the red kite (Milvus milvus L.), have been declining in the Iberian peninsula during the last decade. However, there is a lack of regional assessments of habitat suitability that identifies limiting ecological factors for the species and areas with conservation problems. In this work we present a regional model for the distribution and abundance of breeding red kites in the Iberian peninsula. The occurrence and estimated abundance in 100 km 2 UTM squares resulting from road censuses were modelled with broad-scale explanatory variables obtained from satellite imagery, thematic digital cartography, climatic data and spatial coordinates. The occurrence model incorporated mainly climatic variables and had a good discrimination ability, while the abundance model incorporated mainly land-use variables and had a lower explanatory power (r 2 =0.14). The predictions somewhat overestimated the results of the censuses, and this agrees with the decline of population size and range observed for this species in the Iberian peninsula. These models are relevant in the conservation of the species: first, they suggest the limiting factors for red kite in the Iberian peninsula, and, second, they generate predictive maps pointing out both areas in which conservation problems may be acute (suitable locations that are unoccupied), and areas where no data is available but the red kite is likely to be present (thus guiding further survey and research). # 2003 Elsevier Science Ltd. All rights reserved.

Thermal, food and vegetation effects on winter bird species richness of Mediterranean oakwoods

A better understanding of species–energy relationships needs to be developed using fine-grained approaches that involve the use of small geographical scales of known characteristics, such as habitat heterogeneity, food availability, direct measures of temperature, and functional groups of species. We carried out a 2-year study to analyze the effects of the thermal environment and food availability, while controlling for the influence of habitat structure, on winter species richness of birds living in oakwoods of a mountanious region of Central Spain of Mediterranean continental climate. The guild of ground-foraging birds was selected as model organisms considering its susceptibility to winter conditions associated with unpredictable snowfalls. The spatial variation in species richness of this guild was determined by food availability, but only for those stable and predictable resources not affected by frequent snowfall (shrubs producing fruits; a complete lack of association was found with arthropod abundance on the ground). Thermal effects associated directly with air temperature, and mediated indirectly by vegetation structure providing a mosaic of sun-shade patches, were also very influential. These patterns were highly repeatable across years. Daytime temperature had no influence on determining spatial variation in species richness, but night (minimum) temperature was a very important predictor (explained considering the lower temperatures at night, the longer duration of night, and the inability of diurnal birds to develop active behavioral thermoregulation during nighttime). This result highlights the need to consider physiological processes mediating species–environment relationships when analyzing the relationship between climatic variables and biodiversity phenomena.

Factors affecting large-scale distribution of the Bonelli’s eagle Aquila fasciata in Spain

We analyzed the environmental determinants of the regional distribution of Bonelli’s eagle (Aquila fasciata) in Spain (ca. 500,000 km2), taking into account its frequency of occurrence on UTM blocks of 50 × 50 km. We found that the distribution pattern of Bonelli’s eagle was a highly predictable phenomenon based on climate, vegetation and interspecific relationships. The proportion of sunny, anticyclonic days, per year (i.e., high levels of solar radiation) was the main environmental predictor explaining the distribution and abundance pattern of the Bonelli’s eagle. Sparse plant formations (mainly shrublands) had also a positive effect, while altitude, agricultural land and deciduous forests had a negative influence. The relative abundance of one of its main preys, the Red Partridge (Alectoris rufa), favored the probability of occurrence of Bonelli’s eagle, but only in the less sunny areas located in the north of Spain. The relative abundance of its main competitor, the Golden eagle (Aquila chrysaetos), was slightly but positively correlated with both the distribution and the abundance of the Bonelli’s eagle in the Spanish portion of the Iberian Peninsula, probably due to similarities in their habitat preferences. Finally, we did not find further regional effects of the variables describing the degree of human pressure (density of roads, urban cover, and length of power lines).

Foraging patch selection in winter: a balance between predation risk and thermoregulation benefit.

In winter, foraging activity is intended to optimize food search while minimizing both thermoregulation costs and predation risk. Here we quantify the relative importance of thermoregulation and predation in foraging patch selection of woodland birds wintering in a Mediterranean montane forest. Specifically, we account for thermoregulation benefits related to temperature, and predation risk associated with both illumination of the feeding patch and distance to the nearest refuge provided by vegetation. We measured the amount of time that 38 marked individual birds belonging to five small passerine species spent foraging at artificial feeders. Feeders were located in forest patches that vary in distance to protective cover and exposure to sun radiation; temperature and illumination were registered locally by data loggers. Our results support the influence of both thermoregulation benefits and predation costs on feeding patch choice. The influence of distance to refuge (negative relationship) was nearly three times higher than that of temperature (positive relationship) in determining total foraging time spent at a patch. Light intensity had a negligible and no significant effect. This pattern was generalizable among species and individuals within species, and highlights the preponderance of latent predation risk over thermoregulation benefits on foraging decisions of birds wintering in temperate Mediterranean forests.

Environmental determinants of seasonal changes in bird diversity of Mediterranean oakwoods

The strong season-to-season variation (seasonality) in abiotic factors and productivity shape the changing patterns of species distribution and diversity throughout the year in temperate ecosystems. However, the determinants of seasonal changes within animal communities have rarely been explored, and the prognosis of community variation typically relies on identifying simple factors (e.g., mean temperature) that are assumed to have a constant effect throughout the year. Here we analyze the competing and changing roles of biotic (vegetation structure and phenology) and abiotic (temperature and elevation) factors in determining the richness and nestedness of montane Mediterranean oakwoods (central Spain) bird species in winter and spring. In winter, the most energy-demanding period, birds prefer mature forests with higher nocturnal temperatures where they can minimize thermoregulation costs during the long winter nights. In spring, which is the breeding season, spatial variation of species richness and nestedness is more deterministic than in winter. Breeding birds prefer lower forests with cooler temperatures at midday (presumably to avoid summer overheating stress), less unpredictable weather, and where trees develop leaves earlier (suggesting that birds, particularly those that prey on folivorous insects, would be able to breed early in the season). Thus, although both biotic and abiotic factors take part in the assemblage of local communities, the intervening specific components vary between seasons. For example, temperature—the factor most widely used to forecast future community changes—had opposite effects in winter than in spring. These results highlight the importance of fine-grained scale studies in accounting for temporal variation to understand both current and future regional biodiversity patterns.

Population size and habitat relationships of Black-bellied Sandgrouse Pterocles orientalis in the Canary Islands, Spain

Summary We estimated the breeding population size and assess the habitat relationships of Black-bellied Sandgrouse in the Eastern Canary Islands (Fuerteventura, Lanzarote and La Graciosa, Spain) by means of a survey based on 1,787 0.5-km line transects and distance sampling done in 2005 and 2006. The population comprised 2,906 individuals (90% CI: 2,363–3,562), which is much higher than the numbers estimated in previous reports based on partial surveys, and constitutes 20 %o f the total Spanish population. Sandgrouse in the Canaries are currently restricted to Fuerteventura, where 70% of the population gathers in four areas that encompass just 16.7 % of the island and are largely within Special Protection Areas classified under the EU Birds Directive (except the area of Tefia-Ampuyenta, first in absolute number of individuals). The environmental characteristics that maximize the probability of occurrence of the sandgrouse in Fuerteventura (probability 5 0.196) are: treeless non-cultivated areas of sandy soils without bare bedrock, with a rock cover less than 44%, located in non-coastal areas with an average terrain slope less than 27.5%, at more than 400 m from the nearest urban area, with less than 795 m of dirt roads per 20 ha, with at least 0.9% of shrub cover and a NDVI index higher than 53. Sandgrouse were closer to human settlements in midsummer than in March, perhaps being attracted to artificial pools surrounding villages. Similar habitat characteristics exist in nearby Lanzarote, where the species could hypothetically reach densities as high as 4–5 birds km 2 . Possible reasons for the absence of sandgrouse in this island are discussed.

The intensity of male-male interactions declines in highland songbird populations

Elevation gradients are associated with sharp environmental clines that play a crucial role in the phenotypic diversification of animal populations. In a variety of organisms, the reproductive output of females declines with elevation in parallel to the drop in environmental productivity and shortening of the breeding season. Little evidence is available on male traits associated with reproductive activities, such as territorial defence and signalling, which may decline because of the low economic defendability of resources and the selective advantage of investing in parental rather than mating (e.g. signalling, chasing intruders) effort in such conditions. Along a broad elevational gradient, we investigated variation in the intensity of territorial defence and sexual signalling in males of the water pipit Anthus spinoletta exposed to song playbacks simulating the territorial intrusion of a conspecific. We found that birds from the lower limits of the species distribution approached song stimuli more closely than those from the upper limits. Moreover, physically challenging songs (broad frequency bandwidths and fast trills) elicited a closer approach, and low elevation birds uttered songs ending with the broadest bandwidths. Other responses to the intrusion, such as the number of songs uttered or the latency to approach, exhibited seasonal or spatial variation irrespective of elevation. This study illustrates the decline of some trait associated with aggressive territorial behaviours during male-male conflicts along elevation, and points to the allocation in sexual signalling and motor constraints to signal production, as potential mechanisms underlying it.

A multi-scale analysis of habitat selection in peripheral populations of the endangered Dupont’s Lark Chersophilus duponti

Habitat selection of endangered species in peripheral populations must be considered when designing effective conservation plans, as these populations tend to occupy atypical habitats where species-environment relationships are not well understood. We examined patterns of habitat use in peripheral populations of the endangered Dupont’s Lark Chersophilus duplonti using a multi-scale approach and assessed the spatiotemporal transferability of these models to test for their generality. Our results show that at microhabitat (circles of 50-m diameter used by the species versus random points) and macrohabitat (occupied/unoccupied squares of 1 ha) scales the species selected flat and non-forested areas, but at the microhabitat scale the cover of small shrubs was also important. Models developed at patch scale (occupied /unoccupied sites) identified only site size as an important predictor of species occurrence. Habitat models transferred successfully among sites and years, which suggests that these models and our recommendations may be extrapolated over a larger geographic area. A multi-scale approach was used for identifying conservation requirements at different spatial scales. At the patch scale our models confirm it is a priority to maintain or enlarge the extent of habitat patches to ensure the viability of the studied metapopulation. At the macrohabitat scale our results suggest that reducing tree density in low slope areas would be the most effective management action. At the microhabitat scale, encouraging the presence of small and medium-sized shrubs, by clearing certain scrubs (e.g. large brooms Genista spp. and rosemary Rosmarinus officinalis ) or promoting traditional low-level extensive grazing, should increase the availability of high-quality habitats for the species, and thus the number of potential territories within a patch. These recommendations largely coincide with the ones given for core populations at specific scales elsewhere.

The use of primary abrasion for ageing reed buntings emberiza schoeniclus

T Reed Bunting Emberiza schoeniclus is a scarce breeding bird in the Iberian Peninsula, but large numbers of birds arrive from Scandinavia and Central Europe to winter at different Spanish wetlands (Saez-Royuela 1990). At this time the species gathers in roost sites and many are ringed during this period, making it one of the most commonly ringed species in Spain, about 2% of total birds ringed in 1995 (Cantos & Gomez-Manzaneque 1996). Similar to many passerine species, adult Reed Buntings undergo a complete post-breeding moult, before the autumn migration, while firstyear birds undertake a partial moult (Ginn & Melville 1983, Jenni & Winkler 1994). This moult strategy enables the use of differences in the abrasion of rectrices and remiges (Svensson 1996) and of moult limits in wing and tail (Jenni & Winkler 1994) to age individuals. Firstyear birds of the intermedia form, located in Italy, have been shown to undergo a primary moult (Pesente et al. 1997). This form belongs to the pyrrhuloides group, which is considered sedentary (Cramp 1994). The wintering population in the study area belongs to the schoeniclus form, representing the widest distribution in Western Europe. The witherby form breeds scarcely in the Iberian Peninsula (Purroy 1997) and it is also sedentary, not wintering in the study area. Flight feather abrasion, especially primaries, is used extensively for ageing birds, however little has been published in this respect (eg Martin 1996). This paper presents this method in Reed Buntings during the winter period in Central Spain.

Species partitioning in a temperate mountain chain: Segregation by habitat vs. interspecific competition

Abstract Disentangling the relative influence of the environment and biotic interactions in determining species coexistence patterns is a major challenge in ecology. The zonation occurring along elevation gradients, or at bioclimatic contact zones, offers a good opportunity to improve such understanding because the small scale at which the partitioning occurs facilitates inference based on experiments and ecological modelling. We studied the influence of abiotic gradients, habitat types, and interspecific competition in determining the spatial turnover between two pipit and two bunting species in NW Spain. We explored two independent lines of evidence to draw inference about the relative importance of environment and biotic interactions in driving range partitioning along elevation, latitude, and longitude. We combined occurrence data with environmental data to develop joint species distribution models (JSDM), in order to attribute co‐occurrence (or exclusion) to shared (or divergent) environmental responses and to interactions (attraction or exclusion). In the same region, we tested for interference competition by means of playback experiments in the contact zone. The JSDMs highlighted different responses for the two species pairs, although we did not find direct evidence of interspecific aggressiveness in our playback experiments. In pipits, partitioning was explained by divergent climate and habitat requirements and also by the negative correlations between species not explained by the environment. This significant residual correlation may reflect forms of competition others than direct interference, although we could not completely exclude the influence of unmeasured environmental predictors. When bunting species co‐occurred, it was because of shared habitat preferences, and a possible limitation to dispersal might cause their partitioning. Our results indicate that no single mechanism dominates in driving the distribution of our study species, but rather distributions are determined by the combination of many small forces including biotic and abiotic determinants of niche, whose relative strengths varied among species.