Knowledge of habitat preferences applied to habitat management: the case of an endangered tortoise population

Abstract

To avoid the possible extinction of the last native population of western Hermann’s tortoise in the Iberian Peninsula it is essential to make sound management decisions. Knowledge of macro and microhabitat use and home range size has considerable practical value for land managers. With this aim we first studied the home range and habitat preferences in western Hermann’s tortoises by radio tracking 15 adults weekly from March 2008 to May 2009 in three localities within the Albera population range (NE Iberian Peninsula). We estimated home ranges with Fixed Kernel estimator (FK) and Minimum Convex Polygon (MCP) after checking tortoise site fidelity. We observed that home range size did not differ significantly between males and females (mean FK = 2.01 ha, mean MCP = 3.01 ha). Secondly, we studied macrohabitat selection using a vegetation map. Preferred habitats were open shrubland, open forest and barren land during the activity period, and dense forest, dense shrubland and open shrubland during the hibernation. Next, we assessed microhabitat selection along five periods of the annual cycle: hibernation, emergence from hibernation, spring, summer and autumn. We then located marked tortoises weekly and classified the plant species observed in each location. Principal component analyses showed that tortoises selected shrubs with trees during hibernation, bramble during summer and herbaceous habitat during the breeding season. All these results can provide guidelines for management programs that set aside areas of habitat critical to conserve viable populations, although it is also important to prevent mortality from forestry works. We therefore tested a new brush cutter head accessory to achieve tortoise-safe undergrowth clearing. To this aim we distributed 52 frozen hybrid tortoises among eight plots of 100 m2, cleared six of these plots with the accessory and two without it, and evaluated the scars of the blade on caparaces. We observed no damage in plots that were cleared with the accessory but scars in most carapaces in the plots cleared without it (with potential mortality ranging from 40% in neonates to 100% in adults). These results outline the importance of supporting habitat management decisions with proper field studies.