engleski

The effectiveness of green bridge Dedin in Gorski kotar (Croatia) for brown bears

The new highway through the wildlife core area in Gorski kotar has a number of viaducts and tunnels and one specifically constructed (100 m wide) green bridge at Dedin near Delnice. We studied the impact of highway on brown bears (Ursus arctos) and other large and medium sized mammal movements to acquire data for future management of the population integrity and gene flow, and in practical situation, for designing the mitigation measures on the newly proposed highway from Karlovac to Split. Since May 1999 we used infrared (IR) sensors for recording crossings over Dedin green bridge. The height of IR beams was set at 40 cm above the ground to permit the smaller animals (up to the size of fox, hare and badger) to cross the bridge unrecorded. Recorder holds in memory up to 1000 beam interruptions with noting the date and time of each record. A total of 9471 crossings have been recorded during 563 different days of active monitors operation. Recalculated to the yearly level (365 days) it gives an estimate of a total of 6096 bridge crossings, or 16.7 per day. Concurrently we noticed 402 animal tracks, 284 of which belonged to animals taller than 40 cm: roe deer 37.0%, red deer 28.2%, wild boar 29.0%, brown bear 9.1%, wolf 1.4, and man 5.3%. A total of 26 brown bear tracks belonged to different size (age) categories: single adult animals, single subadults, females with cubs and females with yearlings. The brown bear share of 9.1% in all recorded tracks permits a calculation that the share in IR recorded crossings is 548 bear bridge crossings per year, or 1.5 per night (24 hours). We conclude that this green bridge, a measure to mitigate the negative effects of the studied highway, served it purpose effectively. Only radio telemetry study of marked animals could reveal the share of individual animals that perhaps avoided the use this bridge to cross the highway. However, as different reproductive categories of bears did cross the bridge we hope that the barrier effect will not have long-term negative effect on bear population. The collected and presented results have already been used in the Environmental Impact Study as arguments to built the similar structures on the highway from Karlovac to Split.

brown bear; Croatia; green bridge; highway; Dedin

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