Ecological Modelling 221 (2010) 1954–1963 Contents lists available at ScienceDirect Ecological Modelling journal homepage: www.elsevier.com/locate/ecolmodel Estimating the influence of overhead transmission power lines and landscape context on the density of little bustard Tetrax tetrax breeding populations João Paulo Silva a,b,c,∗ , Mário Santos d , Luís Queirós d , Domingos Leitão e , Francisco Moreira c , Márcia Pinto a , Miguel Leqoc e , João Alexandre Cabral d a Institute for Nature Conservation and Biodiversity, Rua de Santa Marta, 55, 1150-294 Lisbon, Portugal b Centre for Environmental Biology, Faculty of Sciences, University of Lisbon, 1749-016 Lisbon, Portugal c Centre for Applied Ecology “Prof. Baeta Neves”, Institute of Agronomy, Technical University of Lisbon, Tapada da Ajuda, 1349-017 Lisbon, Portugal d Laboratory of Applied Ecology, CITAB – Centre for the Research and Technology of Agro-Environment and Biological Sciences, University of Trás-os-Montes e Alto Douro, 5000-911 Vila Real, Portugal e SPEA – Society for the Protection and Study of Birds, Avenida da Liberdade, n ◦ 105, 2 ◦ Esq., 1250-140 Lisbon, Portugal article info Article history: Received 18 January 2010 Received in revised form 23 March 2010 Accepted 30 March 2010 Available online 20 May 2010 Keywords: Tetrax tetrax Transmission power lines Stochastic Dynamic Methodology Avoidance Displacement Land use changes abstract Collision with conductors and earth cables is a known impact generated by transmission power lines, however there is virtually no information on how these infrastructures might affect bird distribution in a landscape context. With this work we specifically hypothesise that transmission power lines may affect the occurrence of a threatened bird, the little bustard (Tetrax tetrax). To test this hypothesis we used a Stochastic Dynamic Methodology (StDM), analysing the effects of power lines in a landscape perspective and simulating population trends as a response to power line installation and habitat changes induced by agricultural shifts in southern Portugal. The data used in the dynamic model construction included rele- vant gradients of environmental conditions and was sampled during the breeding seasons of 2003–2006. Transmission power lines were significantly avoided by the little bustard and the developed StDM model showed that the distance to these utility structures is the most important factor determining breeding densities in sites with suitable habitat for the species, which possibly leads to displacement of popula- tions and habitat fragmentation. The model simulations also provided the base to analyse the cumulative effects caused by the habitat degradation that can ultimately lead to the extinction of local populations. Within priority conservation sites, the dismantling of existing transmission lines should be considered whenever possible, in order to ensure adequate breeding habitat. The model is considered useful as an auxiliary tool to be used in environmental impact assessments, management and conservation studies. © 2010 Elsevier B.V. All rights reserved. 1. Introduction From the middle of the last century there has been a generalized expansion of the power grids, as a result of increasing consumption of electricity, mostly motivated by economic growth. The develop- ment of new electric production facilities, such as wind and solar farms, normally installed at a considerable distance from the energy users, and the need to implement transnational energy markets are presently the most important factors driving the construction of new overhead high tension power lines (REN, 2008). As a result, power lines are a common element in the landscape, crossing a significant number of habitats, including priority areas for the con- ∗ Corresponding author at: Centre for Environmental Biology, Faculty of Sciences, University of Lisbon, 1749-016 Lisbon, Portugal. Tel.: +351 217500000; fax: +351 217500028. E-mail address: silvaj@sapo.pt (J.P. Silva). servation of birds. The impact of these structures has been almost exclusively attributed to the direct effects of mortality by collision of birds with phase conductors or earth cables. In open-country, overhead high tension power lines, because of their large size and prominence, might also constitute a barrier effect for bird species (Ballasus and Sossinka, 1997; Pruett et al., 2009). Additionally, the presence of electric poles in open-country habitats is beneficial to some raptors by providing perches with commanding views of hunting areas (Stahlecker, 1978; Graul, 1980; Lammers and Collopy, 2007). Therefore, the hunting efficiency might be greater and predation pressure is likely to be higher for some more vulner- able prey (Plumpton and Andersen, 1997; Lammers and Collopy, 2007). However, virtually nothing is known about how these struc- tures influence open-country species in their habitat requirements, use or avoidance (Pruett et al., 2009). Although South European landscapes have evolved over thou- sands of years with a gradual and increasing role played by human activity (Naveh, 1998), recent agricultural intensification, habitat 0304-3800/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2010.03.027