Habitat survey of the Skylark (Alauda arvensis L.) and Crested Lark (Galerida cristata L.) in oilseed rape fields of Golestan, Mazandaran and Ardebil provinces

Birds, in particular larks are damaging to oilseed rape leaves (in autumn and winter seasons). In the present research, oilseed rape fields were visited after growing leaves in line transects along their longest diagonals in Golestan, Mazandaran and Ardebil (Moghan) provinces and the following factors were registered: land size area (hectare), cultivation of adjacent fields, existence of trees, bird species and their numbers. When detecting a damaged patch (at least 5%−10% of oilseed rape plants had bird damage signs), cardinal and intercardinal directions in the farm, distance to the farm's edge and center, distance (m) to hedge, river/stream/canal and road were noted and the following characteristics were measured in a 1 × 1 m plot: number of oilseed rape plants, number of oilseed rape plants having bird damage signs, and number of lark faeces. According to the results, bird damage rate in 129 damage patches was averaged at 46.43% ± 1.87 that the highest bird damage rate was found in Golestan province (52.82% ± 2.39). According to statistical analyses, bird damage rate was significantly different among these three regions, damage rate of different bird species in Golestan and Mazandaran provinces, presence of trees around the farm in Golestan and Moghan, position of bird damage patch (P 0.05). According to the results obtained, in order to reduce bird damage rate, it is recommended to: sowing oilseed rape in early autumn and before the arrival of migrating Eurasian Skylarks, cultivation of oilseed rape and wheat farms very close together, and cultivation of oilseed rape near roads.