1. Understanding animals’ selection of microhabitats is important in both ecology and biodiversity conservation. However, there is no generally accepted methodology for the characterisation of microhabitats, especially for vegetation structure. 2. Here we present a method that objectively characterises vegetation structure by using automated processing of images taken of the vegetation against a whiteboard under standardised conditions. We developed an R script for automatic calculation of four vegetation structure variables derived from raster data stored in the images: leaf area (LA), height of closed vegetation (HCV), maximum height of vegetation (MHC), and foliage height diversity (FHD). 3. We demonstrate the applicability of this method by testing the influence of vegetation structure on the occurrence of three viperid snakes in three grassland ecosystems: Vipera graeca in mountain meadows in Albania, V. renardi in loess steppes in Ukraine and V. ursinii in sand grasslands in Hungary. 4. We found that the variables followed normal distribution and there was minimal correlation between those. Generalized linear mixed models revealed that snake occurrence was positively related to HCV in V. graeca, to LA in V. renardi and to LA and MHC in V. ursinii, and negatively to FHD in V. renardi, and to HCV in V. ursinii. 5. Our results demonstrate that biologically meaningful vegetation structure variables can be derived from automated image processing. Our method minimises the risk of subjectivity in measuring vegetation structure, allows upscaling if neighbouring pixels are combined, and is suitable for comparison of or extrapolation across different grasslands, vegetation types or ecosystems.

Background Understanding predator–prey relationships is fundamental in many areas of ecology and conservation. In reptiles, basking time often increases the risk of predation and one way to minimise this risk is to reduce activity time and to stay within a refuge. However, this implies costs of lost opportunities for foraging, reproduction, and thermoregulation. We aimed to determine the main potential and observed predators of Vipera graeca, to infer predation pressure by estimating the incidence and the body length and sex distribution of predation events based on body injuries, and to assess whether and how the activity of V. graeca individuals is modified by predation pressure. Results We observed n = 12 raptor bird species foraging at the study sites, of which Circaetus gallicus, Falco tinnunculus and Corvus cornix were directly observed as predators of V. graeca. We found injuries and wounds on 12.5% of the studied individuals (n = 319). The occurrence of injuries was significantly positively influenced by the body length of vipers, and was more frequent on females than on males, while the interaction of length and sex showed a significant negative effect. The temporal overlap between predator and viper activity was much greater for the vipers’ potential activity than their realised activity. Vipers showed a temporal shift in their bimodal daily activity pattern as they were active earlier in the morning and later in the afternoon than could be expected based on the thermal conditions. Conclusion The time spent being active on the surface has costs to snakes: predation-related injuries increased in frequency with length, were more frequent in females than in males and occurred in shorter length for males than for females. Our results suggest that vipers do not fully exploit the thermally optimal time window available to them, likely because they shift their activity to periods with fewer avian predators.

Background Understanding predator-prey relationships is fundamental in many areas of ecology and conservation. Basking time often increases the risk of predation and one way to minimise this risk is to reduce activity time and to stay within a refuge. However, this implies costs of lost opportunities for foraging, reproduction, and thermoregulation. We aimed to determine the main potential and actual predators of Vipera graeca, to estimate the incidence and the age and sex distribution of predation events based on body injuries to infer predation pressure, and to assess whether and how the activity of V. graeca individuals is modified by predation pressure. Results We observed n = 12 raptor bird species foraging at the study sites, and we determined Circaetus gallicus, Falco tinnunculus and Corvus cornix as predators of V. graeca. We found injuries and wounds on 12.5% of studied individuals (n = 319). The presence-absence of injuries were significantly positively influenced by estimated age of vipers, and were more frequent on females than on males, while interaction of age and sex showed a significant negative effect. The overlap between the activity of raptors showed significantly smaller overlap with observed viper activity than with potential viper activity. Conclusion The time being active on the surface by the snakes has cost: the incidence of predation-related injuries increased with age, were more frequent in females than in males and they occurred earlier in age for females than for males. The vipers show a shift in the bimodal activity time-frame by being active earlier in the morning and later in the afternoon than could be expected based on thermal conditions suggesting that there is no maximalization to exploit the whole time frame available to reach the preferred body temperature in a cold environment.