Animal Biodiversity and Conservation 34.1 (2011) 11 Bird community patterns in sub–Mediterranean pastures: the effects of shrub cover and grazing intensity S. C. Nikolov, D. A. Demerdzhiev, G. S. Popgeorgiev & D. G. Plachiyski Nikolov, S. C., Demerdzhiev, D. A., Popgeorgiev, G. S. & Plachiyski, D. G., 2011. Bird community patterns in sub–Mediterranean pastures: the effects of shrub cover and grazing intensity. Animal Biodiversity and Conservation, 34.1: 11–21. Abstract Bird community patterns in sub–Mediterranean pastures: the effects of shrub cover and grazing intensity.— Shrubs are widely considered a threat to grassland biodiversity. We investigated the effects of shrub cover and grazing intensity on bird communities in sub–Mediterranean pastures in Bulgaria. The point–count method was used on 80 plots in open (< 10% shrub cover) and shrubby (approx. 20% cover) pastures under either intensive or extensive management (grazing intensity) from 2008 to 2009. We recorded a total of 1,956 observations of birds from 53 species. Main environmental gradients accounting for the bird community pattern were related to vegeta- tion succession and land productivity. Bird species richness was higher in shrubby pastures than in open sites, while no effect was found in respect to total bird abundance. Bird species diversity (i.e. H’ index) was highest in extensive shrubby pastures. Shrubland specialists were positively affected by shrub cover and extensive manage- ment of pastures while grassland and woodland specialists showed no significant response to these factors. We conclude that a small proportion of shrubs within pastures may be beneficial for farmland birds and sustainable management of pastures could be achieved by greater flexibility of national agri–environmental schemes. Key words: Agri–environmental scheme, Farmland birds, Grassland management, Semi–natural habitats, Shrubby vegetation. Resumen Patrones de las comunidades de aves en los pastos submediterráneos: el efecto de la cubierta arbustiva y la intensidad de pastoreo.— Se suele considerar a los arbustos como una amenaza a la biodiversidad de los pastos. Investigamos los efectos de la cubierta arbustiva y la intensidad del pastoreo sobre las comunidades de aves en los pastos submediterráneos de Bulgaria. Se utilizó el método de estaciones de escucha en 80 puntos de registro en pastos abiertos (cubierta arbustiva < 10%) y arbustivos (aproximadamente un 20% de la superficie cubierta), con una gestión de pastoreo tanto intensiva como extensiva desde 2008 a 2009. Registramos un total de 1.956 observaciones de aves pertenecientes a 53 especies distintas. Los gradientes ambientales principales responsables de los patrones de las comunidades de aves se relacionaron con la sucesión de la vegetación y la productividad de la tierra. La riqueza de especies de aves era mayor en los pastos arbustivos que en los lugares abiertos, aunque no se observó efecto alguno con respecto a la abundancia total de aves. La mayor diversidad de especies de aves (índice H’) se daba en los pastos arbustivos con gestión extensiva. Los especialistas en zonas arbustivas se veían afectados positivamente por la cubierta arbustiva y la gestión extensiva de los pastos, mientras que los especialistas de praderas y bosques no presentaron ninguna respuesta positiva a dichos factores. Nuestra conclusión es que una pequeña proporción de arbustos dentro de los pastos puede ser beneficiosa para las aves de tierras de labrantío, y la gestión sostenible de los pastos podría alcanzarse mediante una mayor flexibilidad de los esquemas agroambientales nacionales. Palabras clave: Esquema agroambiental, Aves de labrantío, Gestión de prados, Hábitats seminaturales, Vegetación arbustiva. (Received: 14 VI 10; Conditional acceptance: 6 IX 10; Final acceptance: 10 II 11) Stoyan C. Nikolov, Inst. of Biodiversity and Ecosystem Research–BAS, 2 Yurii Gagarin Str., 1113 Sofia, Bul- garia.– Dimitar A. Demerdzhiev, Georgi S. Popgeorgiev & Dimitar G. Plachiyski, Bulgarian Society for the Protection of Birds–BirdLife Bulgaria, 27A P. Todorov Str., 4000 Plovdiv, Bulgaria. Corresponding author: S. C. Nikolov. E–mail: [email protected] ISSN: 1578–665X © 2011 Museu de Ciències Naturals 12 Nikolov et al. Introduction Methods Semi–natural grasslands are among the high nature Study area value farming systems of conservation concern as they are biodiversity–rich and provide agricultural The study area covers the territory of the Special benefits through stock grazing and haymaking (Henle Protected Area (SPA) Besaparski Hills (147.7 km2) et al., 2008). These habitats were created under in southern Bulgaria (42° 7' N–24° 23' E; fig. 1). The traditional agricultural practices but currently, due landscape represents sub–Mediterranean limestone to agricultural intensification or land abandonment, hills with an average altitude of 350 m a.s.l. (rang- they have now become significantly reduced in area ing from 184 m a.s.l. to 536 m a.s.l.) (Demerdzhiev, in northern European (Pärt & Söderström, 1999), 2007). Most of the area is covered by arable land western European (Tucker & Heath, 1994; Fuller et (about 50% of the territory) and by dry grasslands al., 1995) and eastern European countries (Meshinev with some shrub heath (about 33% of the territory) et al., 2005). and the rest of the territory is covered by vineyards In the European Union, semi–natural grasslands and orchards (6%), wetlands (3%), stone pits (3%), are under the regulation of the Common Agricultural urban areas and roads (3%) and small forests (1%). Policy (CAP) which was adopted in 1957 to increase Grasslands are not fertilized and most of them are agricultural production by ensuring sufficient food used for pastures (mainly for sheep and cattle). for all inhabitants and a fair standard of living for farmers (Verhulst et al., 2004). Implementation of Study design the CAP resulted in a polarization of production areas by stimulating land use intensification in Based on a digital map of the area (Bulgarian Society some areas (Donald et al., 2002) and leading to for the Protection of Birds, unpublished data), a total abandonment of other, marginally profitable areas of 80 point–count stations were equally distributed (Bignal, 1998). It was found that intensification or and located randomly within two categories of pas- abandonment of land management can greatly re- tures (open pastures with up to 10% shrub cover and duce biodiversity by threatening the survival of many shrubby pastures with more than 10% shrub cover) species adapted to the diversity of structures and with the restriction that any two adjacent point–count resources of high nature value farmlands (Sirami et stations should be a minimum of 250 m apart (Ralph al., 2007; Kleijn et al., 2009; Nikolov, 2010). Grass- et al., 1995). All study plots with difficult accessibility land bird populations for instance, declined sharply to the field were replaced using a second random due to agricultural intensification in Europe over the selection. As a result, an aggregation of study plots past half century (Gregory et al., 2004; Donald et in the eastern part of the study area appeared, but al., 2006). On the other hand, abandonment of as the study plots were equally distributed between land management benefits vegetation succession the studied pastureland categories (25 vs. 25 study through the development of woody vegetation, plots in shrubby and open pastures, respectively) providing benefits to shrubland and woodland birds within the area of aggregation, we assumed that whilst negatively affecting open–habitat special- our data were not biased by spatial autocorrelation ists (Preiss et al., 1997; Suárez–Seoane et al., effects. After a pilot visit to the study area, we found 2002; Pons et al., 2003; Verhulst et al., 2004). As that 41 point–count stations were located within open a result, the development of shrubby and woody pastures and 39 in shrubby pastures. Supplementary vegetation was considered a potential threat to data on grazing intensity within the studied areas grassland biodiversity, and the CAP strongly ad- was collected from the local agricultural authorities vised removal of these habitat features as a man- and studied plots were classified according to their agement recommendation (Boccaccio et al., 2009). grazing regime as intensively grazed (0.8 AU ha–1; In many countries (e.g. France, Sweden, Greece n = 30 study plots) and extensively grazed pastures and Bulgaria), this measure was not tested but (0.2 AU ha–1; n = 50 study plots). Finally, we used 31 applied directly in the national agri–environmental study plots in open and extensive pastures, 10 in open schemes (Lefranc, 1997; Pärt & Söderström, 1999; and intensive pastures, 19 in shrubby and extensive Söderström et al., 2001; Kati & Sekercioglu, 2006; pastures and 20 in shrubby and intensive pastures. Nikolov, 2010). Indeed, in northern and southeast- Fieldwork was carried out during the breeding ern Europe small covers of woody vegetation (≤ seasons of 2008 and 2009. Birds were sampled twice 20%) were found to increase avian species rich- per year (in May and June), in the mornings (6:00– ness and diversity by favouring some threatened 10:00 a.m.), under appropriate weather conditions and species (Pärt & Söderström, 1999; Söderström et by the same observer (D. D.). The point count method al., 2001; Nikolov, 2010). (Gibbons & Gregory, 2006) was applied, with a count- The main objective of this study was to test the ing period of 5 min and a radial distance