Ardeola 54(2), 2007, 205-215 FACTORS RESPONSIBLE FOR THE PRESENCE AND DISTRIBUTION OF BLACK-BELLIED SANDGROUSE PTEROCLES ORIENTALIS IN THE NATURE PARK “VALE DO GUADIANA” Ana Cristina CARDOSO* 1, Ana Sofia POEIRAS** and Carlos CARRAPATO*** SUMMARY.—Factors responsible for the presence and distribution of black bellied sandgrouse Ptero- cles orientalis in the Natura Park “Vale do Guadiana”. Aims: Identify factors that are responsible for the presence and distribution of black-bellied sandgrouse in the nature park of ‘Vale do Guadiana’so that management actions can be undertaken. Localization: Southern Portugal. Methods: Kruskal-Wallis non-parametric tests and Bailey’s tests was used to analyse the preferences among biotopes, while logistic regression analysis was utilized to obtain an explanation model for species distributions during breeding and non-breeding seasons. Variables considered in the analysis included presence or absence of cattle; ground vegetation coverage, height and vertical density; tree density; bush coverage; slope exposition; stone coverage and number of stones; wind direction; habitat; soil capacity; distance to roads, drinking places and villages; and altitude. Results: The results of biotope selection indicated that sandgrouses preferred fields of leguminous plants during both breeding and non-breeding periods and tillage during the breeding period. Montado and fallows older than two years were avoided during the non-breeding season. Cereal fields were used according to their availability. Besides not significantly, fallows were highly used. For the explanation model, six variables that explain the species distribution during the breeding sea- son were selected: cattle presence, stony ground and distance to secondary roads had a positive effect, while vegetation cover, stone cover and distance to the drinking places had a negative effect. During the non-breeding period, the model was not adjusted to validation sample. Conclusions: It was found that the most important biotopes are leguminous cultivations and fallows with extensive pastures. Grazing can have either a positive or a negative effect on these fields, depending on cattle density. Besides the number of small dams, drinking places are still a limiting factor for this species. Dispersion of settlements and roads is also negative to sandgrouse distribution. Finally conser- vation implications, namely management actions such as an enlargement of leguminous fields, cattle graz- ing control and modifications of Territory Management Plans, are discussed. Key words: habitat selection; logistic regression; management actions; Pterocles orientalis; seasonal variation. RESUMEN.—Factores responsables de la presencia y distribución de la ganga ortega Pterocles orien- talis en el Parque Natural “Vale do Guadiana”. * Parque Natural do Vale do Guadiana, Apartado 45, 7750-352 Mértola, Portugal. ** Bairro do Bacelo, Rua dos Altos, nº 6, 7000-693 Évora, Portugal. *** Parque Natural do Vale do Guadiana, Apartado 45, 7750-352 Mértola, Portugal. 1 Corresponding author: [email protected] 206 CARDOSO, A. C., POEIRAS, A. S. and CARRAPATO, C. Objetivos: Identificar los factores que son los responsables de la presencia y distribución de la ganga ortega Pterocles orientalis en el Parque Natural “Vale do Guadiana” para que las acciones de manejo y conservación puedan ser adoptadas. Localización: Sur de Portugal. Métodos: Pruebas no paramétricas de Kruskal-Wallis y de Bailey se utilizaron para analizar las prefe- rencias entre biotopos, mientras que regresiones logísticas lo fueron para obtener modelos que explicaran la distribución de la especie durante el periodo reproductor y durante el resto del año. Las variables que se incluyeron en los análisis fueron: presencia de ganado vacuno, cobertura vegetal, altura y densidad verti- cal, densidad del arbolado, cobertura arbustiva, pendiente, cobertura de rocas y su número, dirección del viento, hábitat, capacidad del suelo, distancias a carreteras, bebederos y pueblos, y la altitud. Resultados: Se muestra que las gangas ortega seleccionan campos de leguminosas durante todo el año y campos labrados durante el periodo reproductor. Montado y barbechos de más de dos años son evita- dos durante el periodo no reproductor, mientras que los campos con cereales eran utilizados de acuerdo a su disponibilidad. A pesar de ser un resultado no significativo, los barbechos eran altamente utilizados. En el modelo explicativo fueron seis las variables que explicaban la distribución de la especie durante el periodo reproductor: presencia de ganado vacuno, presencia de rocas, y la distancia a carreteras secun- darias tenían un efecto positivo, mientras que la cobertura vegetal, la cobertura de rocas y la distancia a bebederos tenían un efecto negativo. Durante el periodo no reproductor, el modelo final no fue adecuado. Conclusiones: El trabajo muestra que el biotopo más importante para esta especie y en el área de es- tudio fueron los campos de leguminosas y los barbechos con extensos pastos. La presencia de ganado pue- de ser tanto positiva o negativa, dependiendo de la densidad de cabezas vacunas. A pesar del bajo núme- ro de zonas con agua, los bebederos son un factor limitante para esta especie. La fragmentación del hábitat y las carreteras actúan de forma negativa. Finalmente, se discute las implicaciones en la conservación de la especie que tendrían el aumento de los campos de leguminosas, el control del tamaño del ganado va- cuno y las modificaciones en los planes de manejo del territorio. Palabras clave: selección de hábitat; regresión logística; acciones de manejo, Pterocles orientalis; variación estacional. INTRODUCTION due to changes in agricultural practices and the loss of habitat (Tucker and Heath, 1994). Steppe-land birds are one of the most en- There are no more than 300 individuals in Por- dangered groups of species in the world, espe- tugal - a reason why the bird has an un- cially in developed countries (Bota et al., 2005). favourable status ‘Endangered’ in Portugal The black-bellied sandgrouse Pterocles orien- (Almeida et al., 2005). The European popula- talis is a steppe-land species whose distribu- tion is classified as ‘Vulnerable’, and it is list- tion in Europe is limited mainly to Turkey ed as SPEC 3 – a species whose global popu- and the Iberian Peninsula (Cramp and Sim- lations are not concentrated in Europe, but mons, 1983; Tucker and Heath, 1994; De which has an unfavourable status in Europe Juana, 1999). (Tucker and Heath, 1994). Major changes in EU Common Agriculture In Portugal, the main threat to steppe-land Policy have occurred in the last few decades, birds is the abandonment of traditional farm- causing significant alterations in agricultural ing and replacement by intensive agriculture and grassland habitats (Tucker and Evans, or forestation (Moreira et al., 2004; Silva et al., 1997; Donald et al., 2001). The black-bellied 2004; Pinto et al., 2005). In southern Portu- sandgrouse European population has suffered gal since the launch of wheat campaign, agri- a clear decline in the last thirty years mainly culture has been supported by European Union Ardeola 54(2), 2007, 205-215 BLACK-BELLIED SANDGROUSE IN THE NATURE PARK “VALE DO GUADIANA” 207 subsidies. Actually, abandonment of land due the species. Fieldwork was carried out between to the soil depletion and forestation, which is April 2002 and March 2003. also funded by the European Union, can be During the non-breeding period (October - negative to steppe-land birds. May), the study area was intensively surveyed The objective of this study was to collect for two days once a month. The whole study area information on the ecology of the black-bel- was visited by car and by foot. Each flock or iso- lied sandgrouse that could be used to support lated bird detected at the ground was defined as management measures in a nature park. In a presence point. Drinking places and flying particular, there was a focus on evaluating birds were not considered in the analysis. habitat use and understanding the role of habi- During the breeding period (June - Septem- tat characteristics in determining the sand- ber), observation of black-bellied sandgrouse grouse distribution in the nature park of ‘Vale was difficult because the birds stayed in cou- do Guadiana’. ples, choosing and occupying breeding places. With the purpose of finding breeding and feed- ing areas, observation points were selected near MATERIAL AND METHODS drinking places, where departure and arrival directions of the birds could be recorded and Study area their point of origin and destination estimated. Later, these areas were explored more inten- The study took place in an area of 24000 ha sively by foot. During this season, field work in the nature park of ‘Vale do Guadiana’(to- lasted for four consecutive mornings each tal area: 70000 ha; 37º42’ N 07º39’ W). The month due to hot temperatures. park is also a Special Protection Area under The main biotopes were mapped at differ- Birds Directive CE/79/409. The region is un- ent periods: spring - summer and autumn - win- der Mediterranean influence, with hot sum- ter (Table 1). Absence points were marked on mers and cold and rainy winters. Average an- the corners of a 1 x 1 Km UTM system map. nual rainfall is 455 mm. The area is crossed by These were later visited in the field and took the the Guadiana River and includes hills and same variables rather than the presence points. plains, cultivated areas, fallows and cereal The same number of observations for presences fields, scrubland and open woodland. Cereal and absences were used: 50 for the breeding pe- cultivation follows traditionally a cycle of 3 - riod and 45 for the non-breeding-period. 9 years: wheat (1st year), oats or barley (2nd Nineteen variables were included in the ini- year) and fallow (3rd to 9th years). Older fal- tial logistic regression model (Table 2). Biotope lows are occupied by shrubs, mostly cistus, composition was determined using a 1 000-m Cistus ladanifer. buffer and Table 1 shows the classification. Coordinates of measuring points were taken with an error rate of 3-12 meters using a GPS.